MCAT Biology

Question 1

If a viral antigen were to bind to the receptors on the surface of a B lymphocyte, which of the following immune responses would NOT occur?

Answer 1

Secretion of toxins by the B lymphocyte that destroy nearby virus-infected cells (NATURAL KILLER / CYTOTOXIC T CELLS NOT B LYMPH)

Question 2

Which of the following gel electrophoresis diagrams obtained from DNA sequencing analysis represents this sequence?

Answer 2

Look for 5’ end on diagram and look for the same sequence from 5’ end to 3’ end (ALL DIAGRAMS)

Question 3

A scientist sequences the genomes of several species and analyzes their evolutionary relationships to a single common ancestor. The percentage of similarity between the genome of each species to the genome of this ancestor is calculated and shown in the table below. Which species diverged from the common ancestor first?
Species A = 95%
Species B = 88%
Species C = 35%
Species D = 22%

Answer 3

Species D as it has the least similarity to the common ancestor, which means that this species had more time to undergo genetic mutations as well as genetic drift. These two phenomena result in a differing genome as time progresses.

Question 4

Camels inhabit water-deficient environments and exhibit an evolutionary adaptation that allows them to absorb more water than their ancestors that dwelled in water-rich environments. The diagram below shows the structure of two nephron types present in the kidneys of camels and other mammals. How would the number of cortical nephrons differ from the number of juxtamedullary nephrons in camels and their ancestors?

Answer 4

Higher number of juxtamedullary and lower number of cortical nephrons. The deep loops in juxtamedullary allow for increased water absorption, which camels need when water is scarce.

Question 5

Which of the following diagrams shows the structure of the cloned (cldnk) gene after digestion with (EcoRI) and (Xhol)?

Answer 5

Check to see which the restriction enzymes are cutting. Look for palindromes and overhands (sticky ends). Check the DNA sequence of each gene and figure out what the final product should look like.

Question 6

What is the size of the pSKII plasmid after it is digested by EcoRI and Xhol and the cldnk gene is inserted?

Answer 6

Look for overall base pairs for plasmid, how many between each gene being inserted and how many for cldnk. In this instance plasmid equals 2958 plus 915 for cldnk and MINUS the removed genes, at 32 base pairs (EcoRI and Xhol). This equals 3841 bp.

Question 7

What observation could have led researchers to conclude that cldnk is expressed in oligodendrocytes?

Answer 7

An RNA probe that was complimentary to cldnk mRNA hybridized in cells that express plp1a. (TO DETERMINE WHETHER A CELL EXPRESSES A SPECIFIC GENE, TISSUES MAY BE INCUBATED WITH A LABELLED RNA STRAND THAT IS COMPLIMENTARY TO THE mRNA OF INTEREST.)

Question 8

Microarrays are chips that contain hundreds of microscopic wells, each of which can detect a distinct nucleic acid. Prior to exposure to cDNA, the wells if the microarray described in the passage most likely contained…?

Answer 8

Single-stranded DNA corresponding to the sense strand of zebrafish genes. (BECAUSE mRNA HAS THE SAME SEQUENCE AS THE SENSE STRAND OF GENOMIC DNA, cDNA WILL HAVE THE SAME SEQUENCE AS THE ANTISENSE STRAND. ACCORDINGLY, cDNA HYBRIDIZES WITH SINGLE-STRANDED DNA THAT CORRESPONDS TO THE SENSE STRAND OF GENOMIC DNA

Question 9

Which experiment could confirm that the cldnk gene product is required for myelination?

Answer 9

Compare myelin formation in wild-type zebrafish to that in zebrafish with cldnk knocked out. (A GENE’S BIOLOGICAL FUNCTION CAN BE INFERRED BY COMPARING THE DIFFERENCES IN ORGANISMS WITH THE GENE KNOCKED OUT TO WILD-TYPE ORGANISMS.)

Question 10

How would expression of cloned cldnk differ from expression of the endogenous gene?

Answer 10

Expression of the cloned gene does not involve splicing whereas expression of the endogenous gene does. (RNA POLYMERASE TRANSCRIBES BOTH EXONS AND INTRONS TO FORM PRE-mRNA. DURING RNA PROCESSING, INTRONS ARE REMOVED BY SPLICING TO YIELD MATURE mRNA. cDNA IS GENERATED FROM MATURE mRNA AND DOES NOT CONTAIN INTRONS, SO IT IS NOT SPLICED DURING EXPRESSION.)

Question 11

The genetic code is said to be degenerate because there are 64 different codons, but translation produces only 20 unique amino acids. The degeneracy of the genetic code is due to which mechanism?

A) Exclusion of protein coding regions from mature mRNA
B) Errors during tRNA charging
C) Ambiguity of the tRNA for the amino acid
D) Nontraditional base pairing of anticodon with the third base of the codon

Answer 11

D.

The genetic code is considered “degenerate” because more than one codon can code for the same amino acid. This occurs because the third position of the mRNA codon and tRNA anticodon can undergo nontraditional base pairing, allowing a single tRNA molecule to bind to different codons.

Question 12

Stenosis is the abnormal narrowing of a tubular structure in the body, such as a blood vessel. Stenosis of the afferent arterioles in the kidney would be expected to:

A) Decrease the glomerular filtration rate
B) Increase blood flow to the glomeruli
C) Decrease resistance in the afferent arterioles
D) Increase output of urine

Answer 12

A

The volume of fluid filtered through the kidney per unit time is known as the glomerular filtration rate (GFR), which can be modulated by controlling blood flow through the glomerulus. Higher hydrostatic (blood) pressure in the glomerulus increases GFR, and lower pressure decreases GFR.

Question 13

Which of the following helps maintain the resting membrane potential of a neuron?

I. Passive transport
II. Adenosine triphosphate
III. Membrane selective permeability

A) II only
B) III only
C) I and III only
D) I, II, and III

Answer 13

D

The presence of protein channels in the cell membrane allows passive transport of certain ions down their electrochemical gradient. This selective membrane permeability is responsible for generating the resting membrane potential in nerve and muscle cells. Active transport pumps help maintain the concentration gradient and are critical for maintaining the resting membrane potential.

Question 14

Which statement most accurately describes the role of T tubules in skeletal muscle cells?

A) T tubules bind acetylcholine at the neuromuscular junction to generate a depolarizing stimulus.
B) Depolarizing current reaches the sarcoplasmic reticulum by traveling down T tubules
C) Muscle contraction is driven by the sliding of T tubules across one another in the sarcomere.
D) T tubules sequester Ca2+ out of the cytosol to prevent prolonged muscle contraction

Answer 14

B

For a skeletal muscle cell to contract, Ca2+ must be released into the cytosol from the sarcoplasmic reticulum (SR). Ca2+ release is induced when a depolarizing current (action potential) runs along the sarcolemma and travels down the T tubules. This current causes the nearby SR to open its Ca2+ channels, allowing Ca2+ ions to flow into the cytosol and induce the sarcomeric actin-myosin interactions required for muscle contraction.

Question 15

The relationship of delta P to cardiac output (CO) and vascular resistance (VR) is given by:

Change(P) = CO x VR

Given this, which of the following physiological changes would cause increased VR within vessels of the circulatory system? (Note: Assume all other physiological factors remain constant.)

A) Increased vasodilation of arteries
B) Heightened activity of the SA node
C) Reduced ventricular filling prior to contraction
D) Decreased arterial blood pressure

Answer 15

C

Rearrange to get changeP/CO = VR
Any increase in P, OR decrease in CO will ultimately INCREASE VR.

Question 16

The attending physician orders an electrocardiogram (ECG) to measure the electrical activity of the patient’s heart. The results of the ECG of a healthy individual at rest (A) and the ECG of the patient at rest (B) are shown below. THERE ARE 2 BEATS ON DIAGRAM (A) AND 4 BEATS ON DIAGRAM (B)

Which of the following conclusions regarding the patient’s cardiac function is best supported by these results?

A) Atrial contraction occurs less frequently than in the healthy individual
B) APs are fired less frequently from AV nodal cells in the patient than in the healthy individual
C) Ventricular depolarization occurs for a longer time period in the patient than in the healthy individual
D) Influx of positive ions into SA nodal cells occurs more rapidly in the patient than in the healthy individual

Answer 16

D

Heart rate is regulated by the activity of specialized clusters of self-depolarizing cells known as SA and AV nodes. APs are initiated in the SA node and travel through the atria, stimulating atrial contraction. These APs then reach the AV node and, after a brief delay, are relayed to ventricular cells, stimulating ventricular contraction.

Question 17

As shown below, CO2 reacts with water in the blood to form H2CO3, a weak acid that can reversibly dissociate to form HCO3- and a free H+ ion.
CO2 + H2O <> H2CO3 <> HCO3- + H+

The patient is noted to have decreased pulmonary gas exchange. Given this, which of the following is most likely to occur in the patient’s blood if this condition is left untreated?

A) More H2CO3 will be produced and blood pH will decrease
B) Less H2CO3 will be produced and blood pH will increase
C) More H+ ions will be present and blood pH will increase
D) Less H+ ions will be present and blood pH will decrease

Answer 17

A

Pulmonary gas exchange facilitates the removal of CO2 from the blood. The amount of circulating CO2 affects blood pH by shifting equilibrium of the bicarbonate buffer system. Impaired gas exchange in the lungs will decrease blood O2 levels and increase blood CO2 levels, causing respiratory acidosis as H+ concentration increases.

Question 18

A 63-year-old male patient collapsed while exercising and was hospitalized. The patient presented with an elevated heart rate, low systemic blood pressure, and abnormally low blood oxygen levels. In addition, x-rays revealed excess fluid in his lungs.

Given the information in the passage, the excess fluid in the patient’s lungs is most likely caused by which of the following at the pulmonary sites of gas exchange?

A) Increased protein concentration in the blood flowing through pulmonary capillaries
B) Decreased osmotic pressure in the interstitial fluid surrounding the pulmonary capillaries
C) Increased hydrostatic pressure within pulmonary capillaries
D) Decreased volume of blood flowing through the pulmonary capillaries

Answer 18

C

Blood flowing through capillaries exerts hydrostatic (blood) pressure on the vessel walls that forces some fluid from the vessel into the interstitial space. If this pressure is higher than reabsorption rates from lymph and capillaries, fluid will build up.

Question 19

The cell cycle of Trypanosoma brucei differs from that of higher eukaryotes. For example, the chromatin does not condense during mitosis, and the nuclear envelop remains intact. In addition, the nucleus divides before cell division, and the cell divides along the longitudinal axis.

T. brucei cells and higher eukaryotes are similar since they both undergo:

I. Interphase
II. Prophase
III. Cytokinesis

A) I only
B) I and II only
C) I and III only
D) I, II, and III

Answer 19

C

The cell cycle consists of interphase (G1, S, and G2) and mitotic (M) phase. In M phase, chromosomes are segregated into two nuclei. During the first phase of M phase (prophase), chromatin condenses into chromosomes and the nuclear envelop disintegrates, allowing the cell to progress into the remaining phases of M phase (meta, ana and telophase). Cytokinesis, or the division of the cell membrane, then yields two daughter cells.

Question 20

A culture of T. brucei was arrested in S phase of the cell cycle by overnight incubation with the reversible inhibitor hydroxyurea. The cells were then washed, and their progression through the cell cycle was monitored by flow cytometry and microscopy.

Why were T. brucei cells incubated with hydroxyurea overnight and washed afterward?

A) To ensure that most cells were in the same phase of the cell cycle at each time point measured
B) To determine how inhibition of DNA synthesis the progression of the cell cycle
C) To limit the size of the T. brucei cells prior to their entrance into mitosis
D) To promote synthesis of the proteins needed for entry into mitosis

Answer 20

A

A random population of cells will likely contain some cells in each phase of the cell cycle. Study of their progress through the cell cycle requires that these cells first be brought to the same phase of the cell cycle (synchronized). These synchronized cells can then be monitored when they are released and progress through the cycle together.

Question 21

A subset of the T. brucei culture was first exposed to the drug VX-680, which arrests cells upon completion of metaphase.

Based on the passage, VX-680 most likely inhibits:

A) Synthesis of transcription factors
B) Replication of the cell’s genome
C) Chromosome alignment on the metaphase plate
D) Migration of sister chromatids to opposite poles of the cell

Answer 21

D

Mitosis typically consists of four phases: Prophase, in which the nuclear envelope disintegrates and chromatin condenses; metaphase, in which chromosomes align on the metaphase plate; anaphase, in which sister chromatids migrate toward opposite poles of the cell; and telophase, in which nuclear envelopes reform and chromatin reverts to its uncondensed form.

Question 22

Marine teleosts (bony fish) live in an aquatic environment where there is a higher external concentration of salt and a lower concentration of water relative to the internal concentrations. Owing to these conditions, salt ions tend to diffuse into the teleost through its skin, whereas water molecules within the organism osmotically traverse the opposite path.

Scientists also study freshwater teleosts, which live in an environment where there is more water and less salt outside their bodies than inside. Osmoregulation in freshwater teleosts would most likely serve to combat their natural tendency to:

A) Lose water and salt
B) Absorb water and salt
C) Absorb salt and loss water
D) Lose salt and absorb water

Answer 22

D

In the absence of external energy input, molecules in solution diffuse from areas of high concentration to low concentration. Osmoregulation provides the energy needed to reverse this process and maintain constant salt and water concentrations within an organism.

Question 23

An eel was transported into seawater that had been treated with the volume marker phenol red. After 20 hours, the eel’s gut contained 2.3mL of fluid but showed a phenol red concentration equivalent to 12.3mL of ingested seawater. Researchers found that the eel lost 2.3g of weight due to urine output.

Which of the following conclusions about the eel can be made based on the experiment in the passage? (Note: Water density is 1g/mL.)

A) The eel absorbed 12.3mL of water through the gut
B) The eel drank 10mL of water
C) The eel lost 7.7mL of water
D) The eel excreted 4.6mL of water renally

Answer 23

C

Intestinal fluid ingestion, weight loss as water, and renal and extrarenal mechanisms of fluid excretion must be taken into account when calculating an organism’s fluid volume.

Question 24

Teleosts with either glomerular kidneys or aglomerular kidneys that are purely tubular have served as experimental subjects for the study of marine teleost osmoregulation. Analyzing the ionic [Na+, Cl-, Mg2+, SO4(-2)] concentration of intestinal fluids, urine, and plasma in each species led to the discovery that the renal tubule of the goosefish has both excretory and reabsorptive functions.

Based on the passage, to confirm that the inorganic composition of marine teleost urine is independent of glomerular function, researchers would most likely have to discover:

A) Higher urinary concentrations of Mg2+ and SO4(-2) in the eel than in the goosefish
B) Higher urinary concentration of Cl- and Na+ in the eel than in the goosefish
C) Equally high urinary concentrations of Mg2+ and SO4(-2) in the eel and the goosefish
D) Equally high urinary concentrations of Cl- and Na+ in the eel and the goosefish

Answer 24

C

To claim that a particular function is independent of an anatomical structure, researchers must show similar function-related findings in organisms with and without the anatomical structure of interest.

Question 25

Norepinephrine and epinephrine are water-soluble compounds, and their actual secretion into the bloodstream is stimulated by acetylcholine (ACh)-mediated signaling in the sympathetic component of the autonomic nervous system. Administration of a drug caused increased secretion of norepinephrine and epinephrine by the adrenal medulla. This most probably occurs because the drug: A) Increases secretion of ACTH B) Inhibits production of TH and AADC C) Mimics the activity of sympathetic neurons D) Activates enzymes that mediate the breakdown of tyrosine derivatives

Answer 25

C The autonomic nervous system is divided into the parasympathetic and sympathetic divisions, which are generally antagonistic in function. Although most tissues are innervated by both sympathetic and parasympathetic motor fibers, the adrenal medulla is unique in that it is only innervated by the sympathetic nervous system and thus the drug must mimic the activity.

Question 26

The adrenal medulla is a collection of irregularly shaped cells located in the interior portion of each adrenal gland. In response to changing serum levels of corticosteroid hormones, medullary cells synthesize and secrete the catecholamines norepinephrine and epinephrine. Hormones secreted by the adrenal medulla most likely influence energy metabolism by: A) Inhibiting proteins that mediate glycogen synthesis B) Activating their cytosolic receptors in target cells C) Reducing the activity of enzymes that catalyze fat hydrolysis D) Increasing the activity of proteins that inhibit gluconeogenesis

Answer 26

A Energy metabolism refers to the processes by which the body manages cellular energy stores. The adrenal gland increases the body-wide level of free cellular energy sources by releasing glucocorticoids, norepinephrine, and epinephrine. Short term response, that needs glucose / energy.

Question 27

For individuals who exhibit insufficient hormone production by the adrenal cortex, ACTH is sometimes administered as a treatment option. Clinicians have reported that most patients fail to respond to this treatment with ACTH. The most likely reason for this outcome is that non-responsive patients: A) Release insufficient amounts of ACTH from the pituitary gland B) Continuously overexpress the genes for DBH and PNMT C) Exhibit impaired cholesterol synthesis in the smooth endoplasmic reticulum of adrenocortical cells D) Express an overactive ACTH receptor on cells responsive to cortisol

Answer 27

C ACTH is released by the anterior pituitary and acts on the adrenal cortex to promote the synthesis and secretion of cortisol, a steroid hormone produced from cholesterol. However, the actual synthesis of this steroid hormone depends on the production of cholesterol by smooth E. reticulum proteins, not ACTH. Consequently, defective SER proteins may compromise cortisol synthesis within the adrenal cortex regardless of ACTH stimulation.

Question 28

A woman with low serum cortisol due to partial adrenal dysfunction is treated with high doses of a synthetic cortisol analogue. According to the negative feedback loop that synthesizes and inhibits cortisol production, treatment with a cortisol analogue will likely cause this patient’s serum level of endogenous cortisol to: A) Increase only B) Decrease only C) Remain the same D) Increase at first, but then decrease over time

Answer 28

B The analogue will be able to mimic the effect of cortisol by binding hypothalamic and pituitary cortisol receptors. This interaction will increase negative feedback and reduce the synthesis and secretion of natural cortisol by the adrenal glands.

Question 29

Skeletal muscle samples of adult mice were surgically harvested, washed, and stripped of connective tissues. Next, the isolated muscle samples were placed in a 150-mL oxygen-infused, electrolyte-rich bath containing glucose and Ca2+ ions that were able to enter the muscle fibers and enable maximal contractile force. Why was Ca2+ added to the oxygen-infused, electrolyte-rich bath? To allow Ca2+ to: A) Be sequestered inside the sarcoplasmic reticulum of the muscle fibers B) Enter the mitochondria to promote sufficient ATP production by muscle fibers C) Increase the affinity of muscle fiber myoglobin for oxygen D) Facilitate the binding of ACh to its receptor on the muscle fiber

Answer 29

A The sarcoplasmic reticulum (SR) is a muscle fiber organelle that tightly regulates intracellular calcium (Ca2+) concentration. The release of calcium from the SR promotes muscle fiber contraction whereas the transport of calcium into the SR promotes and maintains muscle relaxation. Since the muscle was isolated, not pre synaptic junction is available for Ca2+ ions, thus collects in SR.

Question 30

In humans, skeletal muscles are innervated by the somatic nervous system and function to mediate: A) Blood pressure regulation B) Heart contraction C) Propulsion of food contents along the digestive tract D) Movement of the jaw during chewing

Answer 30

D The somatic and autonomic nervous systems are the two branches of the peripheral nervous system. Voluntary activities occur through the contraction of skeletal muscle, which is mediated by the somatic nervous system. Autonomic activities are mediated by subconscious and not under voluntary control.

Question 31

A mutant muscle is found to exhibit normal musculoskeletal function following the administration of anti-nAChR (anti acetylcholine receptor protein) antibodies. Compared to a wild-type mouse, this mutant mouse is most likely to show which of the following changes at the neuromuscular junction? A) Decreased ACh degradation within the synapse B) Reduced expression of nAChR by skeletal muscle fibers C) Decreased reuptake of ACh degradation byproducts into the presynaptic neuron D) Reduced release of ACh from the presynaptic vesicles

Answer 31

A Acetylcholine (ACh) degradation within the neuromuscular junction is one process by which muscle fiber contraction is terminated. However, decreased ACh degradation would allow more ACh molecules to remain in the synapse and prolong stimulation to nAChR and subsequent muscle contraction.

Question 32

In the combined population of 15 X chromosomes and 5 Y chromosomes, which of the following alleles, if any, would be most susceptible to loss due to random chance alone? A) An allele on the Y chromosome B) An allele on the X chromosome C) An allele on either the X or Y chromosome D) Allele loss due to random chance alone would only occur in non-sex chromosome

Answer 32

A Genetic drift refers to random genetic changes in allele frequency that are due to chance events (not natural selection). Low-frequency alleles have an increased probability of being lost by genetic drift compared to those present at higher frequencies.

Question 33

If researchers were to artificially express the SRY gene in WT,XX female rabbit embryos, then these rabbits would most likely develop: A) Male characteristics, because Sp1 expression would increase and induce testis development B) Male characteristics, because expression of SRY would induce testis development C) Female characteristics, because the ratio of X and Y chromosomes dictates the sex in mammalian organisms D) Female characteristics, because X chromosome inactivation in WT,XX females is not affected by SRY expression

Answer 33

B Mammalian sex is determined by the expression of the SRY gene on the Y chromosome. In males (XY), SRY expression induces the development of male sexual characteristics. In females (XX), the lack of SRY expression leads to the development of female sexual characteristics.

Question 34

A gene expression assay shows that the SRY gene is expressed in male embryos during the early stages of development. Which of the following best describes the DNA methylation pattern exhibited by the SRY gene in embryonic gonadal cells compared to embryonic cardiac cells. A) The SRY gene will have higher levels of methylation in embryonic gonadal cells B) The SRY gene will have lower levels of methylation in embryonic gonadal cells C) The SRY gene will have similar levels of methylation in both cell types D) The comparison cannot be performed as cardiac cells do not carry the SRY gene

Answer 34

B The SRY gene is crucial for male sex determination, meaning it is most likely highly expressed in cells important to male sexual development (gonadal cells). The SRY gene in gonadal cells will likely exhibit higher expression than the SRY gene in cardiac cells.

Question 35

Transferrin circulating in the blood consists of 679 amino acids, but it is composed of 698 amino acids when it is post-translationally extracted from liver cells, the primary site of transferrin synthesis. Given this information, researchers would most likely be able to extract and isolate the shorter transferrin peptide from: A) Lymph B) The liquid portion of blood C) All cellular elements of blood D) The nucleus of a liver cell

Answer 35

B Plasma is the liquid portion of blood, and is made up of water, electrolytes, gases, hormones, nutrients, metabolic waste, and proteins. Although derived from blood, lymph is not a component of blood. Once secreted from liver cells, the shortened transferrin enters circulation and is incorporated into the plasma.

Question 36

Iron-bound Tf, known as holotransferrin (holoTf), binds TfR to form a complex that is brought into the developing erythrocyte in an endosome. Iron buildup in the liver can lead to scarfing and loss of liver function. If the change in holoTf excretion rate were to cause this form of liver damage, the rate at which holoTf is filtered from the glomerular capillaries must be: A) Decreased due to increased Na+ reabsorption in the nephron B) Decreased due to decreased hydrostatic pressure within the glomerulus C) Increased due to increased urinary output from the kidney D) Increased due to increased hydrostatic pressure within the glomerulus

Answer 36

B The glomerular filtration rate (GFR) is the rate at which fluid is filtered out of the glomerular capillaries (glomerulus) and into Bowman’s capsule. Decreased GFR in the kidney will lead to increased retention of iron-bound Tf (holoTf) in the blood, which may contribute to iron buildup in the liver and subsequent organ damage.

Question 37

Individuals with beta-thalassemia are at risk for developing an enlarged spleen. The resulting impairment of spleen function in these individuals would NOT affect: A) Immune responses against viral or bacterial infection B) Regulation of blood glucose concentration C) Removal of aged red blood cells from the circulation D) Storage of red blood cells

Answer 37

B Spleen functions: - Filters aged/damaged RBCs - Reservoir for blood - Immune response (B cell activation site, housing macrophages) Not responsible for blood glucose concentrations

Question 38

ApoTf and TfR were analyzed by SDS-PAGE under nonreducing and reducing conditions. Based on the gels shown, which conclusion is LEAST likely to be true? (Gel 1 shows ApoTf at 40 kDa and TfR at 80. Gel 2 shows ApoTf at 40 and TfR at 40 with a thicker band) A) Gel 1 represents the nonreducing SDS-PAGE gel B) ApoTf has a smaller molecular weight than TfR C) ApoTf and TfR were assigned a net negative charge D) TfR is a monomeric protein lacking disulfide bridges

Answer 38

D Comparing the results of reducing and nonreducing SDS-PAGE, both techniques that separate proteins based on molecular weight, can be useful in determining whether disulfide bonds contribute to the tertiary structure of a protein. Although TfR does not split into multiple bands, it does migrate to different positions within the gels depending on the experimental condition.

Question 39

Human sperm and oocytes are substantially different in all of the following aspects EXCEPT: A) Cell volume B) Maturation stage at birth C) The contribution of chromosomes to a zygote D) The rate at which they are produced

Answer 39

C Egg and sperm cells are haploid cells that contribute an equal number of chromosomes to a zygote during fertilization. All other choices are significantly different for both cells.

Question 40

Which of the following would likely cause an embryo to implant in a location other than the uterine lining? A) Reduced number of fallopian cilia B) Surge in luteinizing hormone prior to ovulation C) Incomplete gastrulation D) Lack of follicle rupture from the ovary

Answer 40

A After fertilization, fallopian cilia help propel the fertilized oocyte toward the uterus for implantation. An inadequate number of cilia in the fallopian tube can cause implantation of the fertilized egg outside the uterus. LH and follicle rupture are needed for implantation, while gastrulation is post-implantation.

Question 41

A student adds 5 bacterial cells to a test tube containing fresh medium and incubates it for 3 hours at 37*C. If the bacterial population shows an initial lag phase of 20 minutes followed by a doubling time of 40 minutes, what is the approximate number of bacterial cells present at the end of the incubation period? (Note: Assume unrestricted growth during incubation.) A) 20 cells B) 40 cells C) 80 cells D) 160 cells

Answer 41

C Binary fission is the process by which a unicellular organism divides into two identical daughter cells. The generation time refers to the time in which a bacterial population doubles. When a single cell divides by binary fission, the number of cells that result is calculated by multiplying the original number of bacterial cells by 2^n, where n equals the number of generations.

Question 42

Assume a single celled organism was discovered in water above 100*C. On closer inspection, it is determined that this organism was previously classified under the Archaea domain. Given this information, this organism most likely has: A) A peptidoglycan layer in its cell wall B) A circular chromosome C) Telomeres D) An endoplasmic reticulum

Answer 42

B Prokaryotes are unicellular organisms that can be further classified into the domains of Archaea or Bacteria. Organisms in these domains lack a nucleus and membrane-bound organelles but have circular chromosomes and are able to reproduce asexually through binary fission. However, bacteria (not Archaea) have peptidoglycan in their cell wall as a distinguishing feature.

Question 43

A scientist proposed that ectopic endometrial cells contain extra copies of the VEGF gene. Given this information, which of the following techniques can be used to analyze VEGF gene count? I. DNA sequencing II. Northern blot III. Southern blot A) I only B) II only C) I and III only D) II and III only

Answer 43

C DNA sequencing and Southern blotting are DNA assays that may be used to assess the relative quantity of genes between tissue types. Northern blotting is an RNA assay used to assess gene expression in different tissues.

Question 44

Progesterone concentration is generally lowest in the proliferation phase and highest in the secretory phase of the menstrual cycle. The investigators conclude that VEGF concentrations within peritoneal fluid may be inversely correlated with serum levels of progesterone. Does the data support this conclusion? (Figure just shows VEGF concentration pf normal and endometriosis affected women; only difference is that VEGF concentrations are significantly higher in proliferative phase of endometriosis affected women. Both secretory phases are equal is both women.) A) No, peritoneal VEGF concentration is lowest during the secretory phase of the menstrual cycle B) No, serum levels of progesterone are consistently elevated in women with endometriosis C) Yes, peritoneal VEGF concentration is highest during the proliferative phase of the menstrual cycle D) Yes, women with endometriosis have consistently elevated peritoneal VEGF concentration

Answer 44

C Changes in the serum levels of estrogen and progesterone cause the physiological changes associated with the menstrual cycle, the female reproductive cycle that repeats every 24-36 days. Interpretation of the figure will show that progesterone is inversely correlated to VEGF concentrations “in general”.

Question 45

Surgical removal of the ovaries is one treatment for endometriosis. Complete removal of the ovaries would most likely result in which of the following? A) Significant increase in bone mass B) Degeneration of breast tissue C) Severe immune system impairment D) Increased frequency of menstruation

Answer 45

B The ovaries are female reproductive organs that contain oocytes and secrete female sex hormones (estrogen, progesterone). These hormones influence female reproductive function, and are directly responsible for the development and maintenance of female sex characteristics.

Question 46

Infertility in patients with endometriosis can result from ectopic endometrial tissue deposits in all of the following structures EXCEPT: A) The urethra B) The vaginal canal C) The fallopian tubes D) The ovaries

Answer 46

A The female reproductive tract consists of the ovaries, fallopian tubes, uterus, cervix and vagina. Each of these tissues performa specialized functions that enable pregnancy and delivery. The urethra is part of the urinary tract, not reproductive.

Question 47

The mechanism by which endometrial tissue successfully implants outside the uterine cavity is though to be dependent on signaling molecules that promote the formation of blood vessels locally. One of these signaling molecules is vascular endothelial growth factor (VEGF), a protein that is normally synthesized and secreted by various tissues in response to reduced oxygen levels. VEGF signaling also leads to the dilation of existing blood vessels. One function pf vasodilation is to: A) Increase body temperature in cold environments B) Increase blood flow to the intestines following a meal C) Decrease blood flow to the kidneys during dehydration D) Maintain blood pressure following an episode of fluid loss

Answer 47

B Vasodilation (blood vessel widening) decreases blood pressure and increases flow to the tissues supplied by that blood vessel. Vasoconstriction (blood vessel narrowing) increases blood pressure and decreases blood flow to the tissues supplied by that blood vessel.

Question 48

Which step(s) of the viral life cycle would most likely occur in lytic phages? I. Injection of viral genetic material into the bacterial host II. Integration of viral DNA into the bacterial genome III. Degradation of the host genome A) I only B) III only C) I and II only D) I and III only

Answer 48

D Bacteriophages use the host cell’s machinery and resources to replicate their genome and synthesize viral proteins to form new virions. Phages with a lytic life cycle replicate rapidly and release progeny via lysis of the host cell. In contrast, phages with a lysogenic life cycle integrate their genome with the host genome and replicate as the cell divides.

Question 49

A subset of aggressive cancers has a relatively high growth rate, leading to the formation of large tumors. An effective drug against fast-growing tumors would most likely NOT target which stage of the cell cycle? A) Go B) G2 C) G2 / Mitosis checkpoint D) G1 / S-Phase checkpoint

Answer 49

A Most cells in the human body are arrested in Go. However, cellular transition into G1 prepares a cell for division and DNA synthesis (S phase). In the G2 phase, DNA is checked for errors and the cell ensures that sufficient organelles and cytoplasm are available for cell division. Subsequently, the cell divides in the M phase via mitosis and cytokinesis. Compounds that inhibit cell division typically target the cell cycle in phases G1 to M.

Question 50

In a neuron, mitochondrial biogenesis is believed to occur primarily in the cell body, but mitochondria are often positioned at the presynaptic terminal, a distal site with high metabolic demand. Given this information, which molecular mechanism is most likely responsible for mitochondrial transport from the cell body to the presynaptic terminal? A) Kinesin motors transport mitochondria along microtubules B) Kinesin motors transport mitochondria along microfilaments C) Dynein motors transport mitochondria along microfilaments D) Dynein motors transport mitochondria along microtubules

Answer 50

A The intracellular scaffolding of a eukaryotic cell is composed of three families of protein filaments: Microfilaments, intermediate filaments, and microtubules. Intracellular transport of cargo (organelles, vesicles) is mediated primarily by two microtubular motor proteins (kinesin and dynein). Kinesin mediates anterograde transport (away from the nucleus) whereas dynein mediates retrograde transport (toward the nucleus).

Question 51

Impaired release of which of the following neurotransmitters would directly result in the paralysis of skeletal muscle? A) Norepinephrine B) Epinephrine C) Glutamate D) Acetylcholine

Answer 51

D At the neuromuscular junction, acetylcholine is released via exocytosis from presynaptic motor neurons. Acetylcholine binds to receptor on the motor end plate, triggering muscle contraction. Disruption of this process causes skeletal muscle paralysis.

Question 52

Which of the following cellular processes would most likely lead to increased diversity in a population of organisms? A) DNA replication during S phase of the cell cycle B) Synapsis involving two homologous chromosomes C) Alternative splicing of gene transcripts D) Cell division via mitosis

Answer 52

B In eukaryotes, genetic recombination via crossover events (exchange of DNA segments between homologous chromosomes). Synapsis or the joining of homologous chromosomes into tetrads occurs during prophase I of meiosis and is required for crossing over to occur. Crossovers increase genetic diversity by mixing maternal and paternal alleles into a single chromosome that is then inherited by the offspring. Alternative splicing will result is protein diversity, not genetic.

Question 53

A drug that blocks the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary would most likely: A) Decrease secretion of cortisol from the adrenal cortex B) Decrease secretion of thyroid-stimulating hormone from the anterior pituitary C) Increase secretion of oxytocin from the posterior pituitary D) Increase secretion of calcitonin from the thyroid

Answer 53

A Corticosteroids (glucocorticoids and mineralocorticoids) are steroid hormones released by the adrenal cortex. The release of cortisol from the adrenal cortex is mediated by the secretion of adrenocorticotropic hormone (ACTH) from the anterior pituitary.

Question 54

One function of endothelial cells is to: A) Contract to increase blood pressure B) Line the inside of the gastrointestinal tract C) Form clots at sites of vascular damage D) Line the inside of blood vessels

Answer 54

D Endothelial cells are a specialized type of epithelial cell that line the inside of blood vessels and lymph vessels specifically. The endothelium is a single-cell layer that makes up the innermost surface of the cardiovascular system (heart and blood vessels). The endothelium promotes blood fluidity and functions as a selective barrier between the blood and surrounding tissues.

Question 55

Functional telomerase consists of a protein subunit called telomerase reverse transcriptase (TERT) and a noncoding RNA subunit called telomerase RNA (TR). In healthy somatic cells, TERT transcription is generally downregulated by the absence of the oncogene c-Myc and the presence of the tumor suppressor protein WT1; in cancerous somatic cells, increased telomerase activity is associated with tumorigenesis (WT1 is frequently absent and c-Myc is usually increased in expression). WT1 and c-Myc most likely alter TERT transcription levels by doing which of the following at the TERT gene promoter? A) Inhibiting and facilitating RNA polymerase binding, respectively B) Inhibiting and facilitating DNA polymerase binding, respectively C) Facilitating and inhibiting RNA polymerase binding, respectively D) Facilitating and inhibiting DNA polymerase binding, respectively

Answer 55

A DNA polymerase is involved in replication, NOT transcription. Transcription factors can upregulate or downregulate transcription by influencing the ability of RNA polymerase to bind to a promoter. Transcription factors that increase transcription are called activators and facilitate RNA polymerase binding whereas those that decrease transcription are called repressors and inhibit binding.

Question 56

Considering that healthy somatic cells typically transcribe the telomerase reverse transcriptase (TERT) gene only at low levels, where in the chromosome of these cells is the gene most likely found? A) In a relatively open, uncoiled portion of the chromosome B) In the portion of the chromosome that binds the kinetochore C) In a portion of the chromosome that associates with ribosomes D) In a portion of the chromosome that is tightly wound around histones

Answer 56

D Chromatin can be broadly classified as heterochromatin and euchromatin. Heterochromatin consists of DNA tightly coiled around histones and is not readily transcribed by RNA polymerase. Euchromatin is more loosely associated with histones and is more easily transcribed.

Question 57

Cells thats must be able to divide indefinitely (stem cells and germ cells) express an enzyme known as telomerase. Functional telomerase consists of a protein subunit called telomerase reverse transcriptase (TERT) and a noncoding RNA subunit called telomerase RNA (TR). Using a portion of TR as a template, telomerase extends telomeres by continuously adding the sequence 5’-TTAGGG-3’ to the ends of chromosomes. Based on the sequence that telomerase adds to the ends of chromosomes, the template portion of TR most likely contains which of the following sequences? A) 5’-UUAGGG-3’ B) 3’-AAUCCC-5’ C) 5’-CCCTAA-3’ D) 3’-CCCUAA-5’

Answer 57

B New nucleotide strands are synthesized using complementary strands as templates, with the two strands aligned antiparallel to each other (the 5’ end of one strand aligns with the 3’ end of the other). The DNA, guanine (G) always pairs with cytosine (C), and adenosine (A) always pairs with thymine (T). In RNA, the only difference is that uracil (U) is present instead of thymine.

Question 58

In humans, conditions such as hypertension, liver disease, and Alzheimer disease have been associated with the decreased telomere length and resulting senescence that occur as part of the normal aging process. The telomerase reverse transcriptase (TERT) gene consists of 16 exons and 15 introns that can be spliced into more than 20 different isoforms in humans. Only one isoform (the active isoform) is known to extend telomeres. However, the i2 isoform has been hypothesized to downregulate residual TERT activity in somatic cells. If the role of the i2 isoform of the TERT gene proposed is correct, individuals who express the i2 isoform in somatic cells would be expected to have a decreased risk of: A) Hypertension B) Cancer development C) Alzheimer disease D) Liver disease

Answer 58

B DNA is initially transcribed as precursor mRNA (pre-mRNA), consisting of introns and exons. The pre-mRNA can then be spliced into one of several possible isoforms, each containing multiple exons, and some containing portions of introns. Many inactive isoforms are believed to help regulate the activity of active isoforms. Therefore, i2-mediated downregulation of telomerase activity in somatic cells would be expected to reduce the risk of cancer development.

Question 59

Some eukaryotic organisms have multiple telomerase reverse transcriptase (TERT) genes with high sequence similarity that are expressed at different times in the organism’s life cycle. These genes could have arisen by: A) Alternate splicing B) Conjugation C) Gene duplication D) Transformation

Answer 59

C Genes with high sequence identity are evolutionarily related, having a common origin. They generally arise by gene duplication and, over time, may mutate and fulfill distinct roles within an organism.

Question 60

During a parasitic infection, which of the following would most likely be responsible for phagocytosis of organisms and the release of histamine, respectively? A) Basophils, macrophages B) Natural killer cells, T-cells C) Macrophages, basophils D) T-cells, natural killer cells

Answer 60

C Macrophages are one of the cells responsible for phagocytosis, the process of engulfing solid particles (bacteria) designated for destruction into phagocytic vesicles called phagosomes. In contrast, basophils function to release chemical mediators such as histamine that stimulate an inflammatory response.

Question 61

Which of the following cell-cell junctions would help skin cells withstand mechanical stress by directly anchoring the intermediate filaments of adjacent cells? I. Desmosomes II. Gap junctions III. Tight junctions A) I only B) II only C) I and III only D) II and III only

Answer 61

A Desmosomes, gap junctions, and tight junctions are cell-cell junctions that provide tissue with mechanical strength, cytoplasmic continuity, and watertight seals, respectively.

Question 62

Cirrhosis of the liver is characterized by hepatic cell death, tissue scarring, and altered liver functions. All of the following would be disrupted by cirrhosis of the liver EXCEPT: A) The production of ketone bodies B) The metabolism of most drugs C) The oncotic pressure within capillaries D) The secretion of digestive proteolytic enzymes.

Answer 62

D Digestive proteolytic enzymes that hydrolyze polypeptides, are synthesized and secreted from the pancreas, stomach and small intestine. The liver has various functions, including storage of glycogen, regulation of blood glucose levels, detoxification of drugs, synthesis and secretion of bile, production of serum proteins (albumin, clotting factors), and synthesis of ketone bodies.

Question 63

Compared with blood in the pulmonary veins, blood in the pulmonary arteries has higher concentrations of: I. O2 II. H+ III. CO2 A) I and II only B) I and III only C) II and III only D) I, II, and III

Answer 63

C Within the pulmonary circuit, the pulmonary arteries carry CO2-rich, O2-poor blood from the heart to the lungs, where CO2 is exchanged for O2. The pulmonary veins then carry CO2-poor, O2-rich blood from the lungs to the heart, which then pumps the oxygenated blood to all body tissues.

Question 64

AAV2 binds to transmembrane proteins on the cell surface. The cell membrane invaginates and forms a vesicle in response to AAV2 binding. The vesicle matures to an early endosome. The endosome rides along a microtubule track toward the nucleus. The endosome lumen is acidified as it matures to a late endosome. AAV2 proteins undergo a conformational change in response to the acidic environment and form pores in the endomsomal membrane, allowing AAV2 to escape. AAV2 enters the nucleus, where it uncoats and transduces the cell. AAV2 entry into cells could best be blocked by a drug that inhibits which of the following mechanisms? A) Fusion of viral and cell membranes upon receptor binding B) Formation of membrane extensions that engulf external particles C) Inward budding of the cell in response to receptor binding D) Constitutive invagination of the cell membrane to take up extracellular liquid

Answer 64

C Cells take up their surrounding environment via endocytosis, which includes mechanisms of phagocytosis, pinocytosis, and receptor-mediated endocytosis. Many viruses use receptor-mediated endocytosis to enter cells. Enveloped viruses can also enter cells by fusing their membrane with the membrane of the cell. These are encased in a capsid and it directly fused to the cell membrane and released into the cytosol.

Question 65

Which of the following is true concerning the proteins to which AAV2 binds in Step 1? (Step 1: AAV2 binds to transmembrane proteins on the cell surface.) A) They localize primarily in low-cholesterol environments known as lipid rafts B) They are held statically in place by cytoskeletal component C) They are able to interact only with the phospholipids on the outer leaflet of the cell membrane D) They can migrate laterally through the phospholipid-rich environment of the cell membrane

Answer 65

D Cell membranes are composed largely of phospholipids, which act as a fluid that allows other membrane components such as transmembrane proteins, glycoproteins, cholesterol, and glycolipids to migrate through this environment laterally. Accordingly, the structure of the animal cell membrane is known as the fluid mosaic model. Transmembrane proteins span the width of the membrane and thus must be able to migrate laterally.

Question 66

Prior to reaching their final destination in the plasma membrane, the AAV2-binding proteins on the cell surface passed through all of the following cellular compartment EXCEPT: A) The endoplasmic reticulum B) The Golgi apparatus C) A peroxisome D) A secretory vesicle

Answer 66

C The secretory pathway involves the processing of proteins as they go through the endoplasmic reticulum and the Golgi apparatus. After processing in the Golgi, proteins destined for the cell membrane are packed into secretory vesicles, which fuse with the plasma membrane. Other organelles, such as the nucleus, mitochondria, and peroxisomes, are not involved in the secretory pathway, and most of their proteins are translated in the cytosol.

Question 67

As it matures, the endosomal lumen becomes acidified relative to the cytosol. Protons from the cytosol most likely enter the endosomal lumen by which of the following processes? A) Simple diffusion B) Facilitated diffusion C) Passive transport D) Active transport

Answer 67

D Molecules can cross biological membranes by active or passive transport. Active transport involves a molecule moving against its concentration gradient and requires energy input (ATP). In contrast, passive transport involves molecules diffusing down their concentration gradient and requires no external energy. Passive transport can be divided into simple diffusion, in which molecules cross membranes directly, and facilitated diffusion, in which molecules must go through protein channels.

Question 68

Because it can transduce human cells, including quiescent (nondividing) cells, without causing disease, AAV2 is attractive as gene therapy vector. In quiescent cells, early endosomes containing AAV2 would most likely move toward: A) Ribosomes B) Centrioles C) Cilia D) Centromeres

Answer 68

B The cytoskeleton consists of actin filaments (microfilaments), intermediate filaments, and microtubules. Microtubules are involved in intracellular transport. The microtubules involved in the process originate near the nucleus on organelles called centrioles and radiate out toward the plasma membrane.

Question 69

What is the fate of the virus particles that fail to escape the acidified endosome in Step 6? (Step 6: AAV2 proteins undergo a conformational change in response to the acidic environment and form pores in the endosomal membrane, allowing AAV2 to escape.) A) Degradation in the lysosome B) Repackaging in the Golgi followed by exocytosis C) Reprocessing in the endoplasmic reticulum D) Destruction by a proteasome

Answer 69

A After internalization of extracellular materials into vesicles, the vesicles containing these materials become endosomes, which then mature from an early stage to a late stage, ultimately becoming lysosomes. Endocytic cargo that does not enter alternative pathways (entry into the secretory pathway) and fails to escape from endosomes will end up in the lysosome to be degraded.

Question 70

In bone tissue, RANK is expressed by precursors of mature osteoclasts, also known as osteoclast progenitor cells (OPCs). RANKL is expressed by osteoblasts adjacent to OPCs, and the binding of RANKL to RANK in these neighboring cells causes downstream effects through recruitment of TRAF6, an intracellular protein. The cells that are most important for the differentiation of OPCs are cells that promote: A) Calcium transfer from bone tissue into the blood stream B) Calcium transfer from the bloodstream into bone tissue C) Acid production in bone tissue D) Proteolytic enzyme production in bone tissue

Answer 70

B Bone remodeling is a continuous process in which osteoclasts (bone-resorbing cells) break down old bone and osteoblasts (bone-depositing cells) secrete new bone matrix. This process functions to maintain the strength and integrity of bone over time. Osteoblasts promote the precipitation of calcium and phosphate from the bloodstream and their transfer and incorporation into the bone matrix. In contrast, osteoclasts secrete acids that break down the mineral components of bone, releasing calcium and phosphate into the bloodstream. Because RANKL is expressed by bone-depositing osteoblasts, osteoclasts that promote the breakdown of bone are NOT most important in promoting OPC differentiation.

Question 71

A group of scientists hypothesized that elevated RANKL signaling contributes to the decrease in bone density associated with osteoporosis. To confirm their hypothesis, they collected bone tissue samples from patients with the disease and compared them to healthy controls. RANKL is expressed by osteoblasts (bone-depositing) and RANK is expressed by osteoclasts (bone-resorption). Given this information, all of the following experimental observations would support their hypothesis EXCEPT: A) Higher c-Fos expression in patient samples than in control samples B) More RANK/TRAF6 association in patient samples than in control samples C) Increased RANKL/RANK binding in patient samples than in control samples D) Higher expression of RANK in patient samples than in control samples

Answer 71

D Decreased activity of osteoblasts (bone-depositing cells) or increased activity of osteoclasts (bone-resorbing cells) can lead to reduced bone mass and density.

Question 72

A student isolates the cellular components of OPCs in wild-type (WT) mice and in mutant (MT) mice exhibiting a single base substitution that causes reduced osteoclastic activity. Western blot analysis is then performed to test for NF-kB and c-Fos expression in the cytoplasm and nucleus of OPCs isolated from these mice. The results of this analysis are shown below. (Only differences are c-Fos has a smaller band in the nucleus of MT and NF-kB has no band in the nucleus of the WT) A) MT mice have a mutation that disables the ability of NF-kB to localize to the nucleus B) MT mice have a mutation that prevents c-Fos from interacting with NF-kB C) MT mice have a mutation in the DNA binding region of NF-kB D) MT mice have a mutation that prevents the transcription of c-Fos in OPCs

Answer 72

A Transcription factors have nucleus localization sequences that facilitate their entry into the nucleus, where they regulate the expression of target genes. Because NF-kB requires an intact nuclear localization sequence to enter the nucleus and increase c-Fos expression, a mutation in the NF-kB nuclear localization sequence of MT mice would best explain these results.

Question 73

Cathepsin K is a proteolytic enzyme secreted by osteoclasts. In a clinical trial, patients with osteoporosis due to increased RANK-RANKL signaling are divided into an untreated group (saline placebo administered) and a treated group (cathepsin K inhibitor administered). Given the information, bone density after the trial will most likely be: A) Increased in the untreated group compared to the treated group B) Decreased in the untreated group compared to the treated group C) Nearly the same in both groups D) Nearly the same in both groups initially, but then would increase in the untreated group compared to the treated group

Answer 73

B During bone resorption, osteoclasts release proteolytic enzymes that break down the organic bone matrix. In osteoporosis patients, overactivity of osteoclasts and increased release of enzymes can lead to decreased bone density across time.

Question 74

The information in the passage suggests that increased activity of RANK is most likely due to signaling hormones involving which of the following hormones? A) Parathyroid hormone B) Calcitonin C) Growth hormone D) Glucagon

Answer 74

A To regulate calcium homeostasis, parathyroid hormone (PTH) and calcitonin act antagonistically to each other. PTH is secreted in response to low blood calcium levels and stimulates bone resorption by osteoclasts, causing an increase in blood calcium. In contrast, calcitonin is secreted in response to high blood calcium levels and decreases osteoclast activity, ultimately decreasing blood calcium.

Question 75

The diagram above represents the immature gamete of a male fly that is heterozygous for Ena. If the gamete undergoes meiotic division and Ena alleles do not undergo recombination, during which phase of meiosis will the wild-type Ena alleles be pulled to opposite poles of the cell? A) Metaphase I B) Anaphase I C) Metaphase II D) Anaphase II

Answer 75

D Gamete formation requires cellular division by meiosis I and meiosis II, in which homologous chromosomes and sister chromatids, respectively, are separated. In the absence if recombination, maternal and paternal alleles are separated from each other during anaphase I, and identical alleles on sister chromatids are separated from each other during anaphase II.

Question 76

The genes Abl, Enabled (Ena), and receptor protein tyrosine phosphatase (PTP) are involved in axonal guidance during neuronal development and are all believed to operate in the same pathway. Of the genes tested, which are autosomal? I. Ena II. Abl III. PTP A) II only B) I and III only C) II and III only D) I, II, and III

Answer 76

D Genetic traits may be autosomal or sex-linked (X chromosome). Because males have only one X chromosome, sex-linked recessive traits tend to be present at greater rates in males than in females, whereas autosomal traits are present in the same proportions in both.

Question 77

Which evidence from Table 1 suggests that PTP and Abl are located close together on the chromosome? (Table 1 shows low amounts of recombinant flies in both recombinations and a large number of parental flies) A) The two recombinant genotypes occur with similar frequencies B) Only a small percentage of the progeny are recombinant C) Recombination did not occur in male gametes D) The F1 generation has a high recombination frequency

Answer 77

B Homologous chromosomes can exchange genetic material by recombining. Genes that are located close together on a chromosome have a lower probability of being separated by recombination than those that are far apart. Fewer progeny from a cross will have recombinant genotypes than will have parental genotypes.

Question 78

Axonal guidance is the process through which axons reach their proper targets in the brain. Researchers hypothesize that the wild-type PTP gene product mediates proper axonal guidance by inactivating the Abl gene product. Which experimental observation would best support this hypothesis? A) Suppression of Abl increases the severity of abnormal axonal guidance in PTP mutants B) Overexpression of Abl reduces the severity of abnormal axonal guidance in PTP mutants C) Suppression of Abl reduces the severity of abnormal axonal guidance in PTP mutants D) Overexpression of Abl restores normal axonal guidance in PTP mutants

Answer 78

C Upstream gene products in a biological pathway act on downstream gene products. Failure of an upstream product to act can be compensated for by alterations to downstream targets that mimic the affect of the upstream product. In effect, suppression of Abl activity carries out the same function that active PTP does and therefore should lead to the same outcome.

Question 79

The gustatory-salivary reflex can be modulated (dampened or enhanced) by input higher centers in the central nervous system. Ultimately, ACh released from postganglionic neurons acts on the muscarinic acetylcholine receptors on the secretory cells of the salivary gland to stimulate salivation. To modulate the salivary response, descending pathways from the brain would most likely synapse onto which part of the reflex arc? A) The taste receptor B) The salivary gland C) The preganglionic neuron D) The postganglionic neuron

Answer 79

C A reflex is an involuntary response to a stimulus that does not require input from the brain. Reflexes are mediated by reflex arcs, neuronal pathways that include a sensory neuron, an efferent neuron, and possibly an interneuron. Based on the gustatory-reflex arc, the cell bodies of both the interneuron and the preganglionic neuron lie within the spine. Therefore, descending input could act on either of these two neurons to alter the gustatory-salivary reflex.

Question 80

The gustatory-salivary reflex, the secretion of saliva from the salivary glands in response to gustation (taste), is primarily mediated by the parasympathetic division of the nervous system. The gustatory-salivary reflex pathway is part of which of the following branches of the nervous system? I. Peripheral II. Somatic III. Autonomic A) I and II only B) I and III only C) III only D) I, II, and III

Answer 80

B The nervous system can be divided into two major branches, the central and peripheral nervous systems. The peripheral nervous system can be further divided into the sensory (afferent) and motor (efferent) divisions, with the motor division being composed of the somatic and autonomic nervous systems. Furthermore, the autonomic nervous system is divided in the parasympathetic and sympathetic branches.

Question 81

In the gustatory-salivary reflex, activation of taste receptors in the tongue sends impulses to the superior and inferior salivatory nuclei in the brainstem. Ultimately, acetylcholine released from postganglionic neurons acts on the muscarinic acetylcholine receptors (mAChRs) on the secretory cells of the salivary gland to stimulate salivation. The drug cevimeline hydrochloride is a cholinergic agonist. Administration of cevimeline hydrochloride would be expected to cause: A) Increased salivation due to stimulation of mAChRs B) increased salivation due to inhibition of mAChRs C) Decreased salivation due to stimulation of mAChRs D) Decreased salivation due to inhibition of mAChRs

Answer 81

A Agonists are ligands that activate the receptors they interact with and induce downstream effects. Mimics the effect of acetylcholine on the mAChRs. Antagonists are ligands that inhibit the receptors they interact with and block downstream effects.

Question 82

During periods of stress, many individuals experience dry mouth caused by decreased salivation. Which of the following functions would also be expected to decrease during periods of stress? A) Gluconeogensis B) Cardiac contraction C) Dilation of pupils D) Digestive peristalsis

Answer 82

D The parasympathetic and sympathetic divisions of the nervous system are broadly antagonistic in their effects. The parasympathetic division promotes digestion and other tasks related to an organism’s long-term needs (rest and digest). Alternatively, the sympathetic divisions enables the organism to meet more immediate needs (fight or flight).

Question 83

In the gustatory-salivary reflex, activation of taste receptors in the tongue sends impulses to the superior and inferior salivatory nuclei in the brainstem. Which of the following neurons correspond to the gustatory-salivary reflex’s afferent and efferent components, respectively? A) Sensory neuron, preganglionic neuron B) Preganglionic neuron, sensory neuron C) Interneuron, postganglionic neuron D) Postganglionic neuron, interneuron

Answer 83

A Afferent signals approach the central nervous system. Efferent signals exit the central nervous system. The preganglionic fibers, which transmit impulses away from the spinal cord, make up the efferent component of the reflex arc.

Question 84

The graph below shows the firing rate of preganglionic neurons within the rat gustatory-salivary reflex arc when the lateral hypothalamic area (LHA) is electrically stimulated at various time intervals before the tongue is stimulated. The results are compared to the preganglionic firing rate following tongue-only stimulation, which was used a baseline that represented 100% activity. (The graph simply shows a descending trend from an interval of 50 to 250 and the chart reducing from 140% to 90%, respectively.) A) LHA signaling has no effect on the magnitude of salivation of the reflex B) LHA signaling increases the magnitude of salivation of the reflex C) LHA signaling decreases the magnitude of salivation of the reflex D) There is not enough data to determine the effect of LHA signaling on the reflex

Answer 84

B Input from higher areas in the central nervous system can modulate the activity of reflexes by either strengthening or weakening the magnitude of the response.

Question 85

Assume L410 is an acquired mutation that occurs only in hepatocytes of adults who were exposed to a certain mutagen. A woman with the L410 mutation has a child with an unaffected man. What is the probability that this child has the L410 mutation? A) 0.00 B) 0.25 C) 0.75 D) 1.00

Answer 85

A Mutations that occur in the reproductive cells of parents are called germline mutations. These mutations can be passed on from parent to offspring, and result in the offspring carrying the mutation in all of its cells. Parental somatic mutations, which occur in non-sex cell lineages during an organisms’ lifetime, are not inherited by the offspring.

Question 86

Excess post-exercise oxygen consumption is the extra amount of oxygen consumed after the completion of exercise and before respiration returns to resting levels. This extra oxygen is used to restore muscle fibers to their pre-exercise state by doing all of the following EXCEPT: A) Replenishing the ATP stores within the muscle fiber B) Facilitating calcium release from the sarcoplasmic reticulum in the muscle fiber C) Restocking the myoglobin stores within the muscle fiber D) Supplying the ATP used to replenish glycogen stores in the muscle fiber

Answer 86

B Oxygen intake remains elevated after exercise due to the increased demand in muscle cells for oxygen to replenish ATP, creatine phosphate, and glycogen stores and restock myoglobin with oxygen. The amount of additional oxygen consumed is called the excess post-exercise oxygen consumption, or oxygen debt. During rest or relaxation, calcium is sequestered into, not released from, the sarcoplasmic reticulum.

Question 87

Which of the following is generally true about the path of blood flow through the heart? A) The right ventricle contracts to propel blood to all body tissues except the lungs B) The left ventricle pumps blood into the left atrium C) The aorta receives blood from the left ventricle D) The right atrium receives blood from the pulmonary veins

Answer 87

C The right heart receives deoxygenated blood from the body and pumps it out toward the lungs. The left heart receives oxygenated blood from the lungs and pumps it out toward the rest of the body. Atria receive blood; ventricles release blood. The first vessel to receive blood on the way out of the heart is the aorta.

Question 88

A woman carries an X-linked recessive allele for a disorder characterized by muscle degeneration but does not express this condition. If she has multiple offspring with an unaffected man, how many of the woman’s children are expected to exhibit this degenerative disorder? A) All B) Half C) None D) One-quarter

Answer 88

D For the cross between a female carrier of an X-linked recessive trait and an unaffected man, only male children will express the trait. The probability of a child having the trait is given by P(child inherits affected X-chromosome from mother) x P(child is male) = 0.5 x 0.5 = 0.25. Therefore, 25% of all offspring will express the trait.

Question 89

Neural tube defects (NTDs) arise from abnormalities in the development of the neural tube and can range from mild to severe, depending on which portion of the tube is affected. Spina bifida, a form of NTD, is divided into three categories. The most serious sub-classification of spina bifida is myelomeningocele, which occurs when the lower spine fails to close, which leaves the spinal cord and nerve roots in the lower back damaged and exposed. Neural crest cells migrate away from the neural tube to give rise to most of the peripheral nervous system. Given this information, would neural crest cells be involved in the pathology of myelomeningocele? A) Yes; neural crest cells secrete signals that directly inhibit neural tube closure B) Yes; neural crest cells fail to differentiate into the posterior spinal cord C) No; neural crest cells continue to differentiate into glial cells of the brain D) No; neural crest cells continue to act normally as temporary migratory cells that give rise to other cell types

Answer 89

D Cell migration in embryogenesis is the movement of cells into their final positions within the embryo. The migratory action of neural crest cells during neurulation (the formation of the nervous system) gives rise to many peripheral nervous system structures. In contrast, the central nervous system is derived from the neural tube. Myelomeningocele is an issue of the spinal cord (neural tube) and not peripheral nerves (neural crest cells).

Question 90

The germ layer that gives rise to the notochord also gives rise to which of the following cell types? A) Alveolar cells B) Osteocytes C) Melanocytes D) Islet beta cells

Answer 90

B The three primary germ layers (endoderm, mesoderm, ectoderm) form during gastrulation. Each gives rise to particular cell types in specific organ systems. Alveolar and islet beta cells are derived from the endoderm, while melanocytes are from the ectoderm. Osteocytes are mesoderm.

Question 91

Assume that neural stem cells are considered to be multipotent. Which of the following best describes the classification of stem cells? A) They are able to differentiate into all fetal structures but not placental structures B) They are able to differentiate into both placental and fetal structures C) They are able to differentiate into specialized cell types of a particular tissue D) They are able to differentiate in the zygote but not in the adult organism

Answer 91

C Totipotent stem cells are the least specialized cells and can give rise to both placental and fetal cells. Pluripotent stem cells can give rise to only fetal cells (all cell lineages from the three germ layers). Multipotent cells are able to differentiate only into the specialized cells of certain tissues and are also found in adults.

Question 92

Undifferentiated gastrula cells presumed to give rise to neural tissue were transplanted from a donor frog embryo onto an undifferentiated gastrula area of a host frog embryo. The transplantation region in the host was presumed to give rise to epidermal tissue. Both host and donor embryos were allowed to develop following the transplant, and gave rise to two normal embryos. What was the purpose of this experiment? A) To determine which cells in the gastrula ultimately give rise to epidermal tissue B) To determine if cell specialization is influenced by communication between cells C) To determine how developmental fates of cell are determined during blastula formation D) To determine whether cell differentiation could be reversed based on embryonic location

Answer 92

B Cell fate is influenced by inductive signaling between cells in the early embryo. In inductive signaling, an inducer (the signaling cell) releases chemical signals that act on competent neighboring cells by regulating the expression of specific genes required for cell determination. The researchers wanted to determine whether the prospective donor neural cells would continue to develop independently into nervous tissue or if they would assume a different tissue type or cell fate due to communication with surrounding cells.

Question 93

In vertebrates, researchers found that the concentration pattern of the signaling proteins Sonic Hedgehog (Shh) and Bone Morphogenic Protein (BMP) defined by specific regions of expression for various genes involved in neural tube development. The results of their investigation are shown in the graph provided. (Shh increases from 10% to 100% and BMP from 90% to 5%; these trends progress from Dorsal to Ventral on the graph) A) Shh influences the expression of genes necessary for cell division B) Shh diffuses along a concentration gradient to signal cell differentiation C) Shh signals for development of the ventral neural tube only D) Shh acts as a receptor for BMP in the developing neural tube

Answer 93

B Morphogens are signaling molecules that influence cell differentiation in the embryo. They are released by signaling cells and diffuse outward to alter gene expression in competent cells in a concentration-dependent manner.

Question 94

Neural tube defects (NTDs) are thought to be caused in part by folate deficiency. Folate plays a critical role in normal cell division and growth as it is a necessary coenzyme for DNA synthesis and methylation. It has been hypothesized that folate decreases NTD risk by ameliorating oxidative stress, thereby reducing damage to developing cells in the embryo. Compared to newborns without NTDs, a newborn diagnosed with myelomeningocele would most likely have exhibited which of the following during gestation? A) Lower frequency of cell damage at critical developmental periods B) Lower cellular concentrations of free radicals C) Higher levels of antioxidant enzymes D) Higher incidence of apoptosis

Answer 94

D Apoptosis (programmed cell death) is crucial for normal embryonic patterning and development. Oxidative stress occurs when the body is unable to detoxify naturally generated reactive oxygen species, which then cause considerable cell damage upon accumulation. This damage can result in abnormal apoptosis and congenital malformations.

Question 95

The N-terminal domain of angiopoietin-like 4 induces a conformational change in the enzyme lipoprotein lipase (LPL), forcing the LPL homodimer to dissociate into two inactive 225-residue monomers. A scientist studying the sequence of the homodimer of LPL would most likely expect that: A) 675 mRNA nucleotides must be translated to form a fully functional 50-kDa LPL protein B) 1,350 mRNA nucleotides must be translated to form a fully functional 50-kDa LPL protein C) 675 mRNA nucleotides must be translated to form a fully functional 25-kDa LPL protein D) 1,350 mRNA nucleotides must be translated to form a fully functional 25-kDa LPL protein

Answer 95

B The total number of nucleotides in an mRNA molecule can be calculated by multiplying the number of amino acids in the protein by the number of nucleotides (three) in a codon. The approximate molecular weight of a protein can be obtained by multiplying the number of amino acids in the protein by the average molecular weight of an amino acid (110 Da). Codon (3 nucleotides) = 1 amino acid 1 amino acid = 110 Da 225-residue = 225 amino acids x two inactive monomers = 450 AAs 450 x 3 (codon) = 1,350 total nucleotides in the protein 450 AAs x 110 Da per amino acid = 49,500 Da = 49.5 kDa or 50 kDa

Question 96

Based on the p-values in figure 2, ANGPTL4 mutations were found to decrease coronary artery disease (CAD) risk by significantly altering which of the following? (P values: LDL = 0.06, HDL = 0.087 and Triglycerides = 0.023) I. LDL cholesterol levels II. HDL cholesterol levels III. Triglyceride levels A) I only B) III only C) I and II only D) II and III only

Answer 96

B The p-value is the probability of observing a result due to chance alone, assuming that the null hypothesis is true. A value of p being greater than or equal to 0.05 is generally considered statistically significant whereas a value of p being less than 0.05 is not considered statistically significant.

Question 97

Glucocorticoid deficiency disrupts the negative feedback loop linking the brain to the adrenal gland, leading to hyperplasia (increased cell proliferation) of adrenal tissue. Glucocorticoid deficiency is known to impair healing of superficial wounds, memory formation, and other physiological phenomena. This deficiency most likely leads to these wide-ranging effects because: A) Glucose is the primary energy source in many of the body’s tissues B) Receptors for glucocorticoid hormones are expressed in diverse tissue types C) Glucocorticoids modulate thyroid hormone release by the thyroid gland D) Hyperplasia of adrenal tissue in CAH causes damage to several nearby organs

Answer 97

B In glucocorticoid deficiency, an insufficient amount of glucocorticoid hormones in the blood leads to diminished binding of these hormones to their receptors. This condition would compromise the normal function of the various cells that express glucocorticoid receptors. Any cell type that expresses a hormone receptor will respond to serum levels of the hormone, and will have reduced functionality if the serum levels of the hormone decrease (deficiency).

Question 98

The neuroendocrine signaling cascade that induces adrenal hyperplasia involves coordinated activity among which organs? A) Hypothalamus, parathyroid glands, adrenal glands B) Hypothalamus, pituitary gland, adrenal glands C) Liver, pituitary gland, adrenal glands D) Pituitary gland, parathyroid glands, adrenal glands

Answer 98

B The hypothalamus is a brain structure that regulates numerous endocrine functions through its association with the pituitary gland. Together, the hypothalamus and pituitary gland regulate the synthesis and secretion of hormones that influence metabolism, reproduction, and other important functions. Hypothalamus releases corticotrophin-releasing hormone (CRH) which stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH) into the blood stream. ACTH then acts on the adrenal glands to promote synthesis and secretion of glucocorticoids (neuroendocrine signaling cascade).

Question 99

Patient with congenital adrenal hyperplasia (CAH) exhibit hypoglycemia due to numerous endocrine abnormalities. In healthy individuals, hypoglycemia will trigger an increase in the serum level of: I. Insulin II. Epinephrine III. Glucagon A) I only B) II only C) I and III only D) II and III only

Answer 99

D Glucose is a key energy source for many tissue in the human body. The serum level of glucose is tightly regulated through the actions of the hormones insulin, glucagon, epinephrine, norepinephrine, and the glucocorticoids. Insulin decreases blood glucose concentration by promoting the cellular uptake and storage of glucose; insulin levels will go down as blood glucose goes down.

Question 100

Normally, 21-hydroxylase catalyzes chemical reactions involved in the synthesis of aldosterone and cortisol, the principal mineralocorticoid and glucocorticoid hormones, respectively. As a results, patients with 21-hydroxylase deficiency (congenital adrenal hyperplasia) exhibit diminished serum levels of aldosterone and cortisol. What changes in blood volume and serum sodium content would be expected as a result of using synthetic hormones to replenish aldosterone in congenital adrenal hyerplasia (CAH) patients? A) Increased blood volume and increased serum sodium content B) Increased blood volume and decreased serum sodium content C) Decreased blood volume and increased serum sodium content D) Decreased blood volume and decreased serum sodium content

Answer 100

A Patients with congenital adrenal hyperplasia (CAH) exhibit deficient synthesis and secretion of aldosterone. After administering synthetic aldosterone, increased sodium and water reabsorption by the kidneys will result in increased blood volume and increased serum sodium content.

Question 101

More than 90% of congenital adrenal hyperplasia (CAH) diagnoses are associated with a deficiency of 21-hydroxylase, an enzyme encoded by the CYP21A2 gene on chromosome 6. Given that the fusion of male and female gametes results in fertilization, which statement best explains how unequal crossing over during gametogenesis can lead to 21-hydroxylase deficiency in the fertilized embryo? One of the parental gametes: A) Contained an extra copy of chromosome 6 B) Contained no copies of chromosome 6 C) Underwent an event in which the CYP21A2 gene was duplicated D) Underwent an event in which the CYP21A2 gene was deleted

Answer 101

D Crossing over is a form of genetic recombination involving the exchange of genetic material between non-sister chromatids of homologous chromosomes. Unequal crossing over can result in offspring that lack important genes. If unequal crossing over involving chromosome 6 occurs, it may result in a daughter cell that contains a chromosome lacking CYP21A2, which would contribute to the development of 21-hydroxylass deficiency in offspring (not increasing it).

Question 102

Which statement best describes the characteristics of hormones secreted from the pituitary gland? A) Hormones secreted from the posterior pituitary are synthesized in the hypothalamus B) Hormones secreted from the posterior pituitary act on other endocrine glands C) Hormones secreted from the anterior pituitary only act directly on nonendocrine tissues D) Hormones secreted from the anterior pituitary are released by depolarization of the nerve terminals

Answer 102

B The synthesis and secretion of hormones from the anterior pituitary is regulated by the release of neurohormones into the blood from neurons located in the hypothalamus. In contrast, posterior pituitary hormones are synthesized in hypothalamic neurons and undergo anterograde axonal transport to the posterior pituitary. The secretion of stored posterior pituitary hormones from the axon terminals is mediated by depolarization of the nerve terminals.

Question 103

Human cardiac muscle differs from skeletal muscles because it: A) Appears striated B) Requires acetylcholine to contract C) Contained intercalated discs D) Contains cells with multiple nuclei

Answer 103

C Muscle tissue can classified as cardiac, skeletal, or smooth. Cardiac muscle is striated and under involuntary control. Skeletal muscle is striated and under voluntary control, and smooth muscle is not striated and under involuntary control. Cardiac muscle is unique in that each cell is connected to adjacent cells via intercalated discs, which are regions of cell contact that contain both desmosomes (to prevent cells from separating during contraction) and gap junctions (to facilitate direct ion exchange for synchronized contraction).

Question 104

During muscle contraction, the power stroke is the pivoting motion of the myosin head that pulls the actin filament inward to shorten the sarcomere. Given this, which of the following events immediately precedes the power stroke? A) The binding of ATP to the myosin heads B) The hydrolysis of myosin-bound ATP to ADP and Pi C) The release of ADP and Pi from the myosin head D) The binding of Ca2+ to tropomyosin

Answer 104

C When ATP bound to a myosin head hydrolyzes, the myosin head shifts back and attaches to the actin filament. Dissociation of ADP and Pi leads to a power stroke, which shortens the sarcomere. A new ATP molecule binds to the myosin head, causing it to dissociate from the actin filament. The action of many myosin heads cycling through this process leads to muscle contraction.

Question 105

A scientist claims that endurance training is an exercise method that can improve physical performance by inducing changes in type 1 skeletal muscle fibers that allow the fiber to perform aerobic respiration more efficiently to generate ATP. Given this, which of the following adaptations is most likely to occur in type 1 fibers in response to endurance training? I. Mitochondrial density of the muscle fibers increases II. Capillary supply around the muscle fiber increases III. Myoglobin concentration per muscle fiber increases A) I only B) I and II only C) III only D) I, II, and III

Answer 105

D Skeletal muscle fibers can be classified as type 1 (slow oxidative), 2A (fast oxidative-glycolytic), or 2X (fast glycolytic). The speed of contraction (slow or fast) is determined by the catalytic speed of the myosin ATPase and the activity of the fiber’s associated motor neuron. Oxidative fibers are fatigue resistant and synthesize ATP through aerobic respiration (oxygen-requiring pathways). Glycolytic fibers are easily fatigable and generate ATP through anaerobic glycolysis (in absence of oxygen).

Question 106

It is believed that around 12,000 years ago, Namibian cheetahs experienced an environmental catastrophe that drastically reduced their population. The small number of surviving cheetahs began mating with one another, which led to severe inbreeding depression. The cheetahs that survived the environmental catastrophe that occurred 12,000 years ago are at a greater risk of extinction because of: A) Naturally selected changes in allele frequencies B) Random changes in allele frequencies C) Changes in allele frequencies due to migration D) Changes in allele frequencies due to random mating

Answer 106

B Genetic drift is a mechanism of evolution; however, unlike natural selection, the variations in allele frequencies occur randomly by chance. Because smaller populations have a smaller gene pool, the random (good or bad) variations due to genetic drift cannot be buffered. The smaller the population, the less likely it will have the ability to negate any adverse impact that random changes in allele frequency which may lead to extinction.

Question 107

Assume that a subgroup of Namibian cheetahs exclusively hunt prey that weigh more than 100 kg. The individuals that make up this subgroup possess larger claws and teeth compared to average Namibian cheetahs and retain the ability to naturally mate with them. These morphological and behavioral changes reflect: A) The selection of average over extreme phenotypes B) How extreme characteristics are favored over average ones C) Diversification of characteristics to better fill an ecological niche D) A new species

Answer 107

C Adaptive radiation is the process of diversifying characteristics (claw and teeth size) to better fill an ecological niche. Adaptive radiation can eventually lead to speciation if the subgroup continues to diverge and loses the ability to interbreed with individuals from the original species.

Question 108

Researchers concluded that captive cheetahs have reduced fitness because of their increased susceptibility to diseases. They reached this conclusion based on results of two separate graphs, one in which it showed that for Liver, GI and Kidney disease, captive cheetahs were more affected overall than wild cheetahs. The second graph showed a significant increase in the amount of cortisol in the feces of captive cheetahs. What can best explain the decreased fitness of captive cheetahs? A) Increased MHC diversity B) Decreased MHC diversity C) Increased environmental stress D) Decreased environmental stress

Answer 108

C MHC are cell surface receptors in vertebrates that present foreign molecules in order to elicit an immune response. MHC variations are evolutionarily important to an organism’s fitness because they influence the organism’s ability to combat a variety of infections and diseases. It can be concluded that other factors besides genetics determine the fitness of captive male cheetahs. The decreased fitness can be attributed to increased cortisol levels in captive cheetah fecal matter. Cortisol is a marker for increased environmental stress.

Question 109

It is believed that around 12,000 years ago, Namibian cheetahs experienced an environmental catastrophe that drastically reduced their population. The small number of surviving cheetahs began mating with one another, which led to severe inbreeding depression. Over time, the offspring of subsequent generations exhibited decreased fitness, reduced fecundity (number of offspring), and sustained a loss of major histocompatibility complex (MHC) allele diversity. If wild Namibian cheetahs continue breeding as described in the passage, what is most likely to occur to their population size in the long term? A) Increased population size with equal sex ratio B) A sharp increase followed by a slight decrease in population size C) Elimination of the Namibian cheetah species D) Stable population size consisting of mostly females

Answer 109

C Inbreeding depression is characterized by decreased genetic diversity, reduced fecundity, and decreased fitness. As genetic diversity decreases within a population, the frequency of homozygous deleterious recessive-genes increases within that population. Consequently, inbred populations have an increased probability of becoming extinct.

Question 110

Compared to the blood flowing into the left ventricle, the blood flowing into the right ventricle: A) Has a higher oxygen concentration B) Has a higher pH C) Is passing through a cardiac chamber with thinner walls D) Is passing through a cardiac chamber that contracts to produce higher pressure

Answer 110

C The right ventricle has thinner walls than the left ventricle because it needs to pump blood at a lower pressure to reach only the lungs. In contrast, the thicker walls of the left ventricle allow it to pump blood at a higher pressure to reach all other tissues in the body.

Question 111

The DNA telomeres can be most accurately described as: A) Noncoding and highly repetitive B) Single-stranded and self-complementing C) Able to encode multiple unique proteins D) Easily cleaved by restriction enzymes

Answer 111

A Telomeres are highly repetitive stretches of DNA at the ends of a chromosome. They are shortened by each round of DNA replication, and protect the rest of the chromosome from degradation. Because of this, telomeres do not encode any gene products; if they did, the information for those products would be lost upon replication and could harm the cell.

Question 112

In neurons, action potential propagation occurs along the axon. The analogous structure in skeletal muscle fibers that enables action potential propagation is the: A) Actin filament B) Transverse (T) tubule C) Motor endplate D) Myelin sheath

Answer 112

B Electrical depolarization caused by action potential propagation leads to the contraction of skeletal muscle fibers. As extensions of the plasma membrane that penetrate deep into muscle fibers, transverse (T) tubules are specialized muscle fiber structures that facilitate action potential propagation throughout individual muscle fibers.

Question 113

Researchers are studying a single-celled pathogen. Which experimental method would be LEAST effective for determining whether the pathogen is prokaryotic or eukaryotic? A) Analyzing the cells for the number of origins of replication B) Exposing the pathogen to a fluorescent antimitochondrial antibody C) Testing the pathogen for ribosome size D) Assessing the pathogen for the presence of pyruvate in the cytoplasm

Answer 113

D Eukaryotic cells contain membrane-bound organelles and linear genomes with multiple origins of replication. In contrast, prokaryotic cells lack membrane-bound organelles and have circular genomes with a single origin of replication. However, both cells have ribosomes (80S in eukaryotes and 70S in prokaryotes) and can perform glycolysis. Glycolysis is a process that occurs in the cytoplasm of both cells types and results in the synthesis of pyruvate. Thus, the presence of pyruvate is not an effective method to distinguish between prokaryotes and eukaryotes.

Question 114

Viral genomes (RNA and DNA) are enclosed by a protein shell known as the capsid. Some viruses, known as enveloped viruses, have an additional phospholipid bilayer that fully envelops the capsid. Viruses that lack this outermost phospholipid covering are labeled non-enveloped. Fluorescent antibodies, designed to bind the capsid proteins of the five hepatitis viruses, were added to separate wells containing each type of virus. The fluorescence assay that was performed detected only bound antibodies in media with HAV or HEV. Based on the information, which of the following viruses does NOT have an outer phospholipid bilayer? A) HBV B) HCV C) HAV D) HDV

Answer 114

C All viruses contain a protective protein coat known as the capsid. Viruses that contain only a capsid as an outer layer are known as non-enveloped or naked viruses, and are able to survive in harsh conditions. Viruses with a phospholipid bilayer surrounding the viral capsid are referred to as enveloped viruses; these are more susceptible to changes in environmental conditions. Because the antibodies were able to bind directly to the capsid proteins of both viruses, it can be determined that both HAV and HEV are non-enveloped viruses.

Question 115

An example of an infectious disease is viral hepatitis (inflammation of the liver), which can be caused by any one of five distinct hepatitis viruses (A-E) that infect hepatocytes (liver cells). HAV, HCV, AND HEV contain positive-sense, single-stranded RNA (+ssRNA) as genetic material. In contrast, HBV has a partially double-stranded circular DNA genome. HDV is unique because it has a negative-sense, single-stranded RNA (-ssRNA) genome. Researchers perform an experiment in which they infect wild-type mice with either HBV or HEV and subsequently treat them with a drug that inhibits their cellular RNA polymerase activity. Based on this information, administering this drug to mice infected with either HBV or HEV would result in: I. Decreased viral load in HBV-infected mice II. Decreased viral load in HEV-infected mice III. Reduced number of viral fragments displayed by antigen-presenting cells in HBV-infected mice A) I and II only B) I and III only C) II and III only D) I, II, and III only

Answer 115

B Most double-stranded DNA viruses utilize host machinery and resources to transcribe positive-sense mRNA from viral DNA. Positive-sense ssRNA viruses (except retroviruses) replicate their genomes by encoding their own viral RNA-dependent RNA polymerase. The administered compounds inhibit only the host’s DNA-dependent RNA polymerase activity. The viral polymerase translated from the HEV genome will continue to replicate its viral genome by creating a complementary negative-sense mRNA intermediate.

Question 116

An individual with hepatitis is suspected to have been exposed to either a bacterial strain of Bartonella henselae (0.5 micrometers) or HCV (0.055 micrometers). Healthy hepatocytes and hepatocytes infected with serum from the affected patient were grown on chamber slides separated by double membranes. (Diagram shows membrane between chambers 1 and 2 as well as 2 and 3. Membrane between 1 and 2 has a pore size of 4 micrometers and the other membrane has a pore size of 0.2 micrometers). A cellular morphology similar to infected hepatocytes was observed in both chambers 2 and 3 after a 6 hour incubation time. Using a light microscope, can investigators observe the agent that caused the patient’s hepatitis in chamber 3? A) Yes, because it was caused by HCV B) Yes, because it was caused by B. henselae C) No, because it was caused by HCV D) No, because it was caused by B. henselae

Answer 116

C A light microscope has a resolution of 200 nm (0.2 micrometers); consequently, investigators can use it only to observe cells larger than 0.2 micrometers. For viruses such as HCV, which are 100 times smaller than bacteria and 1,000 times smaller than eukaryotic cells, visual observations require greater resolution. As a result of the 0.2 micrometer pore size leading into chamber 3 and the low resolution of the instrument, investigators will be unable to observe the causative agent of the hepatitis visually using a light microscope

Question 117

Physicians researching a global hepatitis outbreak discover a new strain of hepatitis (HXV) by analyzing chromosomal DNA of patient’s liver cells. They found that HXV has a +ssRNA genome and replicates through DNA intermediates. What characteristic best describes the new hepatitis virus? A) It integrates its retroviral +ssRNA into the host genome B) It has reverse transcriptase function C) It synthesizes a complementary strand D) It translates its own proteins

Answer 117

B The newly discovered hepatitis strain, HXV, was identified while analyzing chromosomal DNA of liver (host) cells. This indicates that the virus is a retrovirus because it integrated with the host genome (DNA). Retroviruses are unique in that they are enveloped and carry two identical +ssRNA molecules. RNA viruses such as HXV must convert their genomes (+ssRNA) into double-stranded DNA (dsDNA) using reverse transcriptase (RNA-dependent DNA polymerase activity) before integration into the host genome can occur.

Question 118

Assume bacteria are infected with a vector containing hepatitis B (HBV) genetic material. This vector has been shown to introduce its genomic content into bacterial cells without fully gaining entry into the bacterial cytoplasm. Based on this information, the vector is most likely a: A)Prion B) Bacterium C) Viroid D) Bacteriophage

Answer 118

D Bacteriophages are viruses that exclusively infect bacterial cells. They contain tail fibers that allow them to recognize and attach to the cell membrane, and a tail sheath that injects the viral genome into the bacterium. Viroids and prions are considered subviral particles because they are smaller in size and complexity compared to viruses.

Question 119

A student analyzing actively dividing cells under the microscope finds that each daughter cell contains half the number of chromosomes as the parent cell. Given this, these cells most likely contain all of the following EXCEPT: A) Peroxisomes B) Nuclear pore proteins C) Single-stranded genomic material D) Microtubules

Answer 119

C Eukaryotic cells can be distinguished by their unique characteristics. For example, they have a genome with multiple linear chromosomes (double-stranded DNA), they use meiosis as one mechanism of cell division (sexual reproduction), and they have membrane-bound organelles. Half the number of chromosomes in the parent cell = 1n or meiosis. Single-stranded found in certain viruses

Question 120

Plasmodium falciparum is a protozoan parasite known to cause malaria, an illness characterized by fever, chills, and flu-like symptoms. Which of the following is the most likely reason why P. falciparum would be classified as a eukaryotic organism? A) It is able to reproduce sexually B) It has a mechanism for intron splicing C) It has a cell wall D) It has a cell membrane

Answer 120

B Protozoa are single-celled eukaryotic organisms, and therefore possess all of the unique characteristics of eukaryotic cells, including a mechanism for splicing introns from mRNA in the nucleus. Eukaryotic and prokaryotic cells are similar in that both have mechanisms of sexual reproduction and are enclosed by a plasma membrane. In addition, all prokaryotes and some eukaryotes have cell walls.

Question 121

Researchers analyzing gene expression in connective tissue samples are likely to obtain gene expression profiles for all of the following tissues EXCEPT: A) Bone tissue B) Blood tissue C) Adipose tissue D) Muscle tissue

Answer 121

D The body consists of four types of tissue: epithelial (skin, lining of hollow organs and digestive tract), muscle (skeletal, cardiac and smooth), connective (bone, blood, adipose, tendons/ligament and cartilage), and nervous tissue (brain, spinal cord and nerves). Connective tissue provides protection and support for organs.

Question 122

A pathogen identified in a patient’s blood sample is found to lack a phospholipid bilayer. Therefore, any medications used to treat the disease caused by this pathogen would most likely be classified as: A) Anti-protozoan drugs B) Anti-fungal drugs C) Anti-viral drugs D) Anti-bacteria drugs

Answer 122

C Viruses posses DNA or RNA genomes surrounded by a protein capsid and are unable to reproduce outside of a host. Viruses can also be classified as either enveloped (have a phospholipid bilayer as the cell membrane) or non-enveloped (no phospholipid bilayer). In contrast, all prokaryotic and eukaryotic cells are enclosed by a phospholipid bilayer.

Question 123

Excretion of glucose in the urine (glycosuria) occurs when the glomerular filtration rate (GFR) exceeds the transport maximum of glucose (Tm). First, researchers measured the participants’ fasting serum glucose levels (average ~80 mg/dL) and then began a continuous intravenous infusion of a glucose solution. The rate of glucose infusion was adjusted such that blood glucose concentration steadily rose to 300mg/dL. The experiment was later repeated in the same patients following canagliflozin administration (100 mg, once a day for seven days). The critical concentration of plasma glucose necessary to induce glycosuria is termed the renal threshold of glucose. Compared to untreated T2DM patients, the renal threshold of glucose in T2DM patients treated with canagliflozin is: A) Higher by approximately 75 mg/dL B) Higher by approximately 175 mg/dL C) Lower by approximately 115 mg/dL D) Lower by approximately 300 mg/dL

Answer 123

C Urine glucose excretion is a crude definition for glycosuria. The provided graph (not shown) depicted a graph that showed Canagliflozin began excreting glucose from the urine around 75 mg/dL and the untreated patients were at 200 mg/dL. A threshold is a set of values that must be surpassed for a particular event to take place.

Question 124

Researchers hypothesized that administration of canagliflozin reduces blood pressure in patients with diabetes by increasing urine output and reducing total blood volume. A decrease in which of the following would also result in lowered blood pressure? I. Activation of the renin-angiotensin system II. Production of aldosterone III. Secretion of antidiuretic hormone A) II only B) III only C) I and III only D) I, II, and III

Answer 124

D Hormones such as angiotensin II, aldosterone, and antidiuretic hormone (ADH; vasopressin) regulate blood pressure by modulating the kidney’s reabsorption of water and salts. The renin-angiotensin system (RAS) ultimately raises blood pressure by including both the release of aldosterone from the adrenal cortex and the constriction of arterioles. Aldosterone acts on the distal tubules and collecting ducts to promote reabsorption of Na+ and the secretion of K+. ADH promotes water reabsorption by increasing permeability of the distal tubule and collecting ducts to water. ADH induces vasoconstriction and narrowing of the blood vessels.

Question 125

Urinary retention in patients with poorly controlled diabetes mellitus is most likely the result of nerve damage impairing smooth muscle contraction in which of the following structures? A) Bladder B) Urethral sphincters C) Kidney D) Ureter

Answer 125

A Urination is controlled by musculature lining the urinary tract. Nerve damage that impairs the contraction if the detrusor muscle of the bladder would impair emptying of the bladder and lead to urinary retention. During urine collection, the detrusor muscle is relaxed; the internal and external urethral sphincters are contracted to prevent urine flow down the urethra.

Question 126

Canagliflozin is a sodium-glucose linked transporter (SGLTs) inhibitor, used for the treatment of diabetes mellitus. SGLTs are secondary active transport proteins located in the apical membrane of the proximal tubular cells in the kidney. Their activity determines the transport maximum of glucose Tm, the maximum rate at which the kidneys can reabsorb glucose. Administration of canagliflozin most directly increases urinary output by increasing the: A) Osmotic pressure of the tubular filtrate B) Osmotic pressure of the peritubular capillaries C) Hydrostatic pressure of the renal artery D) Hydrostatic pressure of Bowman’s space

Answer 126

A SGLTs transport glucose out of the proximal tubule so it can be returned to circulation through the peritubular capillaries. Administration of a SGLT inhibitor prevents glucose reabsorption, increasing solute concentration within the tubule and consequently increasing the osmotic pressure of the tubular filtrate. As a result, water is drawn back into the renal tubule, increasing urine output. The kidneys regulate blood osmolarity, and in turn blood pressure, by selectively modulating the reabsorption and secretion of water and solutes.

Question 127

Sodium-glucose linked transporters (SGLTs) transport glucose against its concentration gradient across the luminal membrane of the proximal tubule. The energy to drive this form of glucose transport is most likely directly provided by: A) An electrochemical Na+ gradient B) An action potential C) ATP hydrolysis D) Simple diffusion of Na+ ions

Answer 127

A SGLTs are secondary active transport proteins. This means that they utilize the energy released by the movement of Na+ along its concentration gradient to move glucose against its concentration gradient. The movement of Na+ along its concentration gradient enables glucose reabsorption. Primary active transport utilizes the energy from ATP hydrolysis to move a substance against its concentration gradient. Secondary utilizes the energy released by passive transport of another molecule.

Question 128

In individuals with glycosuria, glucose that is not reabsorbed in the proximal tubule next flows into which of the following nephron structures? A) The distal tubule B) The collecting duct C) The loop of Henle D) Bowman’s capsule

Answer 128

C Fluid that is filtered by the kidney first enters the Bowman’s capsule before passing into a long tubule, where water and solutes are selectively reabsorbed. Wastes and metabolites are excreted as urine. The segments are in the order of proximal tubule, the loop of Henle, distal tubule and finally the collecting duct.

Question 129

Parathyroid hormone (PTH) is an important regulator of calcium and phosphate homeostasis. Specifically, PTH functions to increase plasma calcium concentration and reduce plasma phosphate levels. Secondary hyperparathyroidism is a condition characterised by excessive PTH release in response to depressed serum calcium or elevated serum phosphate levels. Which of the following is a potential complication of secondary hyperparathyroidism? A) Decreased bone mineralization B) Decreased osteoclast activity C) Increased osteoblast activity D) Increased corticol bone mass

Answer 129

A The net effect of parathyroid hormone (PTH) activity is to increase serum calcium and decrease serum phosphate concentration. PTH secretion from the parathyroid gland is triggered by decreased plasma calcium. PTH indirectly stimulates osteoclast activation, promoting bone breakdown and the release of ionic calcium into the blood. PTH ultimately triggers osteoclast activity, which results in decreased bone mineralized as osteoclasts resorb bone material.

Question 130

Parathyroid hormone (PTH) functions to increase plasma calcium concentration and reduce plasma phosphate levels. Secondary hyperparathyroidism is a condition characterized by excessive PTH release in response to depressed serum calcium or elevated serum phosphate levels. Secondary hyperthyroidism may result from: I. Increased intestinal calcium absorption II. Impaired renal phosphate reabsorption III. Deficient renal calcitriol synthesis A) I only B) III only C) I and II only D) I, II, and III

Answer 130

B PTH increases the activity of the enzyme that catalyzes the final step in the conversion of inactive circulating vitamin D into the active form, calcitriol. Increased intestinal absorption of calcium will raise blood calcium levels, which will serve as a negative feedback signal to end PTH secretion. If phosphate cannot be properly reabsorbed in the kidney, it will be excreted in urine, and free calcium ions in the blood will increase.

Question 131

Parathyroid hormone (PTH) is an important regulator of calcium and phosphate homeostasis. Specifically, PTH functions to increase plasma calcium concentration and reduce plasma phosphate levels. Researchers treated mice with regular intraperitoneal infusions of CaCl2 to cause a sustained increase in serum calcium levels. The hormone that was released as a result of this condition was monitored using a hormone-specific radiolabeled antibody. In the tested animals, what organ would most likely show increased binding of radiolabeled antibody? A) Thymus B) Pancreas C) Bone marrow D) Thyroid

Answer 131

D In response to increased plasma calcium concentration, the peptide hormone calcitonin is secreted by the thyroid glands. Calcitonin mainly acts to reduce plasma calcium by decreasing osteoclast activity (bone resorption) and increasing renal excretion of calcium.

Question 132

Osteoarthritis (OA) is a disorder marked by the deterioration of articular (hyaline) cartilage, the connective tissue lining the ends of bones at most movable joints. The progressive breakdown of articular cartilage ultimately results in complete exposure of the corticol portion of the underlying subchondral bone with narrowing of the joint space. Repeated and abnormal joint stress can also cause the development of osteophytes, or bony growths, that form on the subchondral bone. OA commonly affects large, weight-bearing joints of the lower extremities such as the knee and hip. Based on the passage, which of the following would occur in a patient with OA involving the knees? A) Deterioration of the yellow bone marrow in affect bones B) Deposition of excess bone on the epiphysis of affected long bones C) Reduction of hematopoiesis in the red marrow of affected bones D) Degeneration of compact bone at the diaphysis of affected long bones

Answer 132

B The structure of a long bone includes the epiphysis (rounded ends covered by articular cartilage), the diaphysis (shaft containing the medullary cavity filled with yellow bone marrow), and the metaphysis (where the diaphysis and epiphysis meet).

Question 133

Osteoarthritis (OA) is a disorder marked by the deterioration of articular (hyaline) cartilage, the connective tissue lining the ends of bones at most movable joints. Osteoporosis, a disease marked by decreased bone density and mass, is similar to OA in that it is a degenerative bone disorder correlated with old age. Which two skeletal system functions would OA and osteoporosis impair, respectively? A) Mobility and structural support B) Mobility and leukocyte production C) Calcium storage and structural support D) Calcium storage and leukocyte production

Answer 133

A The skeletal system facilitates mobility, provides the body with structural support, is the site of hematopoiesis, protects the body’s internal organs, and serves to store fat, calcium, and phosphate. No research suggests that osteoporosis affects the red bone marrow’s ability to production red and white (leukocytes) blood cells.

Question 134

Osteoarthritis (OA) is a disorder marked by the deterioration of articular (hyaline) cartilage, the connective tissue lining the ends of bones at most movable joints. Microscopic examination of tissue samples obtained from the type of bone that becomes exposed to advanced OA is most likely to reveal all of the following EXCEPT: A) Volkmann canals connecting haversian canals B) Mature chondrocytes C) Canaliculi D) Osteocytes situated within lacunae

Answer 134

B Compact bone is organized into concentric rings of bone matrix called lamellae. The entire unit of concentrically arranged lamellae surrounding a central haversian canal is known as an osteon, or haversian system. Within each osteon, lacunae (spaces containing osteocytes) connect to one another via microscopic channels called canaliculi, which allow osteocyte waste exchange and nutrient delivery. Chondrocytes make up the cellular component of cartilage, not bone.

Question 135

Which of the following statements is NOT true about hyaline cartilage? A) It lacks innervation B) It gives rise to bone through endochondral ossification C) It serves as an attachment that holds bones to muscle D) It is avascular and receives nutrients from surrounding fluids

Answer 135

C Cartilage is a firm but flexible connective tissue that lacks blood veseels and nerves. Chondrocytes (cartilage cells) secrete chondrin, which is specialized extracellular matrix that makes up cartilage. The most common type of cartilage is hyaline cartilage, which plays a role in bone development and lines the ends of articulating bones. Tendons, specifically, tautly anchor muscle to bone, not hyaline cartilage.

Question 136

Which organ synthesizes a compound that facilitates the mechanical digestion of lipids? A) Pancreas B) Salivary glands C) Gallbladder D) Liver

Answer 136

D Bile is synthesized in the liver, stored in the gallbladder, and released into the duodenum to aid lipid digestion. Bile salts, a key component of bile, mechanically digest lipid globules by physically breaking them down into smaller droplets in a process known as emulsification. Subsequently, pancreatic lipase chemically digests emulsified lipids.

Question 137

Nonsteroidal anti-inflammatory drugs (NSAIDs) are weakly acidic compounds that normally pass through the acidic environment of the stomach in a nonionized form until they reach the small intestine, where they become ionized in the less acidic lumen. Ionized NSAIDs are more soluble and therefore dissolve faster. (Ionized NSAIDs just have a H+ removed from the OH group). Would NSAID solubility in the gastric pouch of postoperative RYGB patients be higher than normal? A) No, because RYGB decreases the pH of gastric juice B) No, because RYGB increases the pH of gastric juice C) Yes, because RYGB increases the pH of gastric juice D) Yes, because RYGB decreases the pH of gastric juice

Answer 137

C The acidic pH of the stomach is maintained by gastric juice, which is primarily composed of hydrochloric acid (HCL). This acidic environment is required for protein digestion and to kill harmful bacteria. When gastric juice mixed with food (chyme) enters the duodenum, it is neutralized by bicarbonate ions (from the pancreas) and bile (released from storage in the gallbladder). The small gastric pouch surgically created contains less parietal cells and consequently, the amount of HCL secreted by these cells is reduced. Parietal cells are found strictly in the stomach and less cells means high pH; more soluble is less acidic environments.

Question 138

Roux-en-Y gastric bypass (RYGB) is a highly effective weight loss interventional surgery that facilitates massive and immediate weight loss. The stomach is divided into a small pouch and reverted to bypass everything from the gastric pouch to the upper duodenum; filling into the lower duodenum directly from the gastric pouch. In RYGB patients, ingested food will NOT pass through the: A) Cardiac sphincter B) Intestinal villi C) Pyloric sphincter D) Cecum

Answer 138

C At certain sections along the gastrointestinal tract, sphincters, or rings of muscle, divide the tract into segments with distinct functions. Ingested food passes from the esophagus into the stomach through the cardiac sphincter, and from the stomach into the duodenum through the pyloric sphincter. If reverted from the cardiac sphincter to the lower duodenum, then the only structure not passed through is the pyloric sphincter.

Question 139

Roux-en-Y gastric bypass (RYGB) is a interventional procedure designed to facilitate massive and immediate weight loss by diverting the alimentary canal; by passing stomach to upper duodenum. Researchers have found that transplanting gut microbiota of obese postoperative RYGB mice inti nonoperated, obese mice lacking gut flora may reproduce the therapeutic effects of RYGB in transplant-recipient mice. Obese mice underwent either RYGB or sham (placebo) surgery, and two weeks post-surgery, their fecal matter was transplanted into the guts of nonoperated, obese mice lacking gut flora (germ-free recipients). The body weight of RYGB flora recipients (RYGB-R) and sham surgery flora recipients (SHAM-R) was measure for 3 weeks postcolonization. Which graphic shows the expected results of this experiment? A) RYGB-R decreases in % body weight, SHAM-R stays level B) RYGB-R increases in % body weight, SHAM-R stays level C) RYGB-R stays level, SHAM-R decreases in % body weight D) RYGB-R stays level, SHAM-R increases in % body weight

Answer 139

A Research suggests that restructuring the composition of gut flora can influence body weight. The human gut generally contains nonpathogenic bacterial flora that symbiotically cohabit with enterocytes. These microorganisms produce vitamins (vitamin K, necessary for clotting) and aid with nutrient and drug metabolism.

Question 140

Roux-en-Y gastric bypass (RYGB) is a surgical procedure designed to restructure the alimentary canal and promote massive, immediate weight low. The new tract bypasses the stomach to upper duodenum; anything in between these areas are not visited when bypassed through the new alimentary limb. All of the following are secreted by cells in the alimentary limb of RYGB patients EXCEPT: A) Pepsinogen B) Trypsinogen C) Gastrin D) Mucus

Answer 140

B The pancreas generally secretes proteolytic enzymes, like trypsinogen, into the pancreatic duct, which empties into the duodenum to aid in the digestion of chyme in the lumen. In RYGB patients, pancreatic trypsinogen is released into the biliopancreatic limb, NOT the alimentary limb. The cells in the stomach secrete the following: gastrin (from G cells) signals parietal cells to secrete HCl (from parietal cells); pepsinogen (from chief cells) cleaves polypeptides when activated by HCl; and mucus (from mucous cells) and bicarbonate (from epithelial cells) protect the stomach lining against autodigestion by gastric juice.

Question 141

A staple leak is an unanticipated opening of surgical staples at an incision. In RYGB, a staple line leak at the junction of the biliopancreatic limb and the alimentary limb would cause gastrointestinal tract contents to enter: A) The perineum B) The peritoneum C) The peritoneal cavity D) The pleural cavity

Answer 141

C The peritoneum is composed of two membranes that line the abdomen: the parietal layer, which lines the abdominal wall, and the visceral layer, which cover the abdominal organs. The peritoneal cavity is a potential space between the parietal and visceral layers of the peritoneum. Perineum is the space between the anus and scrotum (or vulva). The pleural cavity is a fluid-filled space between the membranes of the lungs and would not be affected by leaking GI tract contents.

Question 142

All of the following findings in sperm would cause lower fertilization rates in IVF EXCEPT: A) Defects in microtubule structure B) Mitochondrial deficiency C) Cytoplasmic reduction D) Misfolded acrosomal enzymes

Answer 142

C A human sperm cell is composed of a head (contains the acrosome and nucleus), a midpiece (contains mitochondria that generate the ATP required for flagellum-driven sperm motility), and a tail (ie, the flagellum necessary for motility through a fluid environment). Fully developed sperm generally have little to nonexistent cytoplasm; therefore, reporting that the cytoplasm is reduced in sperm used for IVF would be a normal finding that is unlikely to impact fertilization rate.

Question 143

If a man and a woman are having difficulty conceiving a child and decide to undergo ICSI treatment using their own gametes, which of the following represents the proper development pathway of the sperm cell selected to fertilize the egg during this procedure? A) Spermatogonium, spermatocyte, spermatid, spermatozoon B) Spermatogonium, spermatid, spermatozoon, spermatocyte C) Spermatocyte, spermatogonium, spermatozoon, spermatid D) Spermatocyte, spermatid, spermatozoon, spermatogonium

Answer 143

A Spermatogenesis is process in which male gametes (sperm) are produced and occurs in the seminiferous tubules of the testes. Spermatogonia undergo meiotic division and become spermatocytes, which then become spermatids when meiosis is completed. Spermatids then mature into spermatozoa (mature sperm) through a series of morphological changes.

Question 144

The North American flying squirrel and the Draco lizard of Southeast Asia both evolved a membrane between their limbs that allows them to glide between trees in their habitats. Given that the species are distantly related, which of the following patterns of evolution would explain the development of this anatomical structure in both organisms? I. Parallel evolution II. Divergent evolution III. Convergent evolution A) I only B) II only C) III only D) I and II only

Answer 144

C Convergent evolution leads to similar characteristics in distantly related species that are exposed to similar environmental pressures. Parallel evolution also leads to similar characteristics but occurs in species with a more recent common ancestor. Divergent evolution leads to unique characteristics on somewhat closely related species that face contrasting environmental pressures.

Question 145

Given that a species diverged from its ancestor 80 million years ago, which of the following graphs most likely illustrates the pattern of mutation accumulation in the genome of the species over time? A) Graph depicts negative linear slope B) Graph depicts horizontal linear line C) Graph depicts positive linear slope D) Graph depicts positive, then negative linear slopes

Answer 145

C Most genetic mutations are neutral and accumulate at a fairly constant rate across organisms over evolutionary time. The overall number of mutations in a species will therefore increase linearly across time. By analyzing the rate of neutral mutations in the genome, this “molecular clock” of evolution can be used to measure evolutionary time and estimate the evolutionary relationships between species.

Question 146

The diagram below shows the results of a northern blot analysis that tested for the expression of four peptide hormones in two endocrine tissue. Tissue A: Insulin = yes, Growth hormone = no, Glucagon = yes, Luteinizing = no Tissue B: Insulin = no, Growth hormone = yes, Glucagon = no, Luteinizing = yes A. Pituitary gland and pancreas, respectively B) Pancreas and pituitary gland, respectively C) Adrenal glands and hypothalamus, respectively D) Hypothalamus and adrenal glands, respectively

Answer 146

B Endocrine glands modulate physiological activity via the secretion of hormones. For example, the pancreas secretes insulin and glucagon to regulate blood glucose levels. In contrast, the anterior lobe of the pituitary gland secretes multiple hormones that regulate several processes, including metabolism and reproductive function.

Question 147

As the two anatomical divisions of the adrenal gland, the adrenal cortex and adrenal medulla share a common feature in that both: A) Synthesize steroid hormones B) Release signaling molecules into lymph vessels C) Regulate the synthesis of red blood cells D) Secrete hormones that alter blood pressure

Answer 147

D Each adrenal gland is composed of two anatomically distinct regions: the adrenal medulla and the adrenal cortex. Both regions secrete hormones that regulate blood pressure and allow the body to respond to stressors. Aldosterone, secreted from the adrenal cortex, stimulates Na+ reabsorption in the kidneys (increased water intake and increased blood pressure). Norepinephrine and epinephrine work under extreme stress and promote rapid information processing by maximizing blood flow to organs essential for survival (secreted by adrenal medulla).

Question 148

The sequence below is a portion of exon 7 of SMN1 of mRNA transcript. 5’ - UCAAGUGAUUCUCCU - 3’ Which of the following represents the corresponding DNA coding strand sequence for this particular transcript? A) 5’ - AGGAGAATCACTTGA - 3’ B) 5’ - TCCTCTTAGTGAACT - 3’ C) 5’ - AGTTCACTAAGAGGA - 3’ D) 5’ - TCAAGTGATTCTCCT - 3’

Answer 148

D In transcription, RNA polymerase reads the noncoding DNA strand to produce a complementary mRNA transcript (with uracil replacing thymine). The sequence of the mRNA transcript is identical to the sequence of the coding DNA (again, with uracil rather than thymine).

Question 149

What steps are required to produce a mature FL-SMN transcript? I. Excision of noncoding sequences between the 3’ and 5’ untranslated regions in pre-mRNA II. Addition of multiple adenine nucleotides to the 3’ end of SMN1 pre-mRNA III. Removal of the 7-methylguanosine cap from mature mRNA IV. DNA polymerase binding to the SMN1 gene A) I and II only B) III and IV only C) I, II, and IV only D) I, II, III, and IV

Answer 149

A Transcription is the process of synthesizing RNA from template DNA and begins with RNA polymerase II binding to the gene promoter region. RNA polymerase II reads the DNA strand in a 3’ to 5’ direction to generate a 5’ to 3’ pre-mRNA molecule. The pre-mRNA transcript undergoes 5’ capping (7-methylguanosine), the addition of a 3’ poly-A tail, and excision of noncoding regions (introns) to be converted into mature mRNA.

Question 150

Valproic acid (VA) is a histone deacetylase inhibitor that has been investigated for SMA therapy. Valproic acid most likely improves motor neuron survival by: A) Increasing SMN2 expression by making DNA more accesible B) Increasing SMN2 expression by removing acetyl groups from histones C) Decreasing SMN2 expression by modifying CpG sites in DNA D) Decreasing SMN2 expression by inducing heterochromatin formation

Answer 150

A Heterochromatin, or tightly packed chromatin, is composed of deactylated histones (due to histone deactylase activity) and is transcriptionally repressed. In contrast, euchromatin or relaxed chromatin is highly acetylated (due to histone acetylase activity) and transcriptionally active.

Question 151

One function of catecholamines released by the adrenal glands during times of stress is to: A) Stimulate secretion of melatonin by the pineal gland B) Increase dilation of bronchioles in the lungs C) Inhibit glucose reabsorption by the kidneys D) Promote the release of digestive enzymes

Answer 151

B During the stress response, catecholamines secreted from the adrenal medulla act to promote the “fight-or-flight” response. Some effects of catecholamines include redirected blood flow to maximize the delivery of oxygen and other nutrients to organs essential for immediate survival (brain, lungs, skeletal muscle), increased heart rate, and dilated airways.

Question 152

The bones of humans and other vertebrates are alike in that they: A) Consist solely of living tissue B) Develop from the embryonic ectoderm C) Form a rigid outer covering that protects the soft tissue inside the organism D) Form an internal support structure that serves as a scaffold for soft tissues

Answer 152

D The vertebrate endoskeleton is composed of both bone and cartilage and provides an internal scaffold that facilitates mobility while protecting and supporting internal organs. In contrast to vertebrates, many invertebrate animals possess an external skeleton (exoskeleton), which is a rigid outer covering that serves to protect the soft tissues underneath.

Question 153

Which of the following experimental techniques can be used to detect the genetic material of a novel virus that injected its genome into a host Escherichia coli cell. Which was then translated into proteins and assembled within the cell itself. A) Southern blot B) DNA sequencing C) Northern blot D) Gene cloning

Answer 153

C Northern blotting is a technique used to detect and measure the concentration of a specific RNA sequence in a cell or tissue sample. Southern blot is used to detect and measure the concentration of DNA in a cell. DNA sequencing is used to determine the specific nucleotide order of a DNA molecule, not viral RNA genomes. Gene cloning is used to generate many copies of a previously identified gene of interest, not good for detection of anything.

Question 154

In an isolated population of mice, 10,000 mice are randomly sampled every 10 generations and their coat colors are recorded for a scientific study. The data for 100 generations of mice are shown in the graph below. (White coat mice decrease in number to almost 0, while black coat mice increase from almost 0 to 9,000) Which of the following conclusions about the black and white mice in this population is best supported by the graph? A) A population bottleneck caused the loss of white mice from the population but did not affect black mice B) A mating event among white mice produced black mice that went on to have higher reproductive success than white mice C) An environmental change resulted in natural selection for black mice but against white mice D) A speciation event caused the lineage of white mice to split into a new species of black mice and decrease in frequency over time

Answer 154

C In natural selection, beneficial traits that improve fitness are more likely to be passed to subsequent generations than less favorable traits. Beneficial traits should become more common with each generation, allowing the species to adapt to its environment.

Question 155

To investigate how heteroplasmy influences disease manifestation, researchers analyzed an A to G substitution at nucleotide 3243 in the tRNA(leu) gene of mitochondrial DNA (mtDNA). Which of the following would be true regarding the inheritance of the A3243G mutation, the known site of heteroplasmy discrepancies? A) Assume daughters of an affected father are affected B) Only offspring of affected mothers are affected C) All affected males have asymptomatic carrier mothers D) Affected offspring must have two copies of the defective gene

Answer 155

B Mitochondria have their own genome, known as mitochondrial DNA, which is inherited in a maternal fashion (no paternal contribution). Mitochondria within sperm are not transferred into the ovum during fertilization; therefore, males never pass on their mitochondria.

Question 156

Which of the following cell types would be LEAST sensitive to mitochondrial dysfunction due to mtDNA mutation? A) Hepatocytes B) Neurons C) Myocytes D) Erythrocytes

Answer 156

D Erythrocytes are biconcave, disc-shaped cells containing hemoglobin, the carrier protein that delivers oxygen to body tissues. Erythrocytes contain no mitochondria as they expel their organelles during the maturation process in the bone marrow. As a result, mitochondrial mutations do not affect erythrocytes.

Question 157

The image below shows a population of unicellular organisms. In each organism, the shaded mitochondria express a deleterious mutant allele of a mitochondrial gene, and the nonshaded mitochondria express wild-type allele of that same gene. (Diagram shows 4 cells becoming two, 2 of the 4 original have few deleterious alleles. The 2 in the second generation are highly deleterious). Which of the following events most likely occurred between Generation 1 and Generation 2? A) Meiosis B) Population bottleneck C) Natural selection D) New mutation

Answer 157

B Natural selection is the tendency for alleles that make an organism better suited for survival and reproduction to be passed along to the next generation. Bottleneck events reduce genetic diversity and change the allele frequencies of a population in a random way.

Question 158

A standard PCR and PAGE gel electrophoresis was conducted to examine the blood samples of subjects with the 3243 region of the tRNA(leu) mutation. The PCR products were treated with the restriction enzyme Apal and visualized on the PAGE gel. Based on this information, which of the following reagents was most likely used during PCR? A) Free ribonucleoside triphosphate B) RNA polymerase C) A template sequence containing deoxyribonucleotides D) Primer pairs with minimal GC content

Answer 158

C Polymerase chain reaction (PCR) is a thermal cycling technique used to amplify DNA fragments. PCR reagents include a source DNA template, GC-rich primer pairs, a thermostable DNA polymerase, and a buffer solution with positively charged ions.

Question 159

A physician determines that a patient has injured a connective tissue structure connecting two bones within the knee joint. Given this finding, the likely basis of the injury is damage to: A) Skeletal muscle B) Adipose tissue C) A tendon D) A ligament

Answer 159

D Joints are structures of the musculoskeletal system where bones articulate (interact) and can range in mobility from freely moveable to immovable. Within moveable joints, strong connective tissue structures called tendons attach muscle to bone whereas ligaments attach bone to bone.

Question 160

During a nutrition study, a participant consumes five times the physician-recommended amount of food but is unable to sufficiently absorb nutrients. Given this information, this participant would be LEAST likely to exhibit which of the following conditions? A) Loss in diversity of bacteria that produce fatty acids in the large intestine B) Decreased surface area in the small intestine C) Heightened production of serum antibodies against intestinal proteins D) Increased activity of nutrient transporter proteins in the small intestine

Answer 160

D Nutrient absorption in the gastrointestinal tract is affected by the diversity of intestinal bacteria (gut flora), the surface area of the small intestine, and the functions of intestinal proteins (digestive enzymes, nutrient transporters, structural proteins). Intestinal nutrient transporters facilitate nutrient absorption from the intestinal tract into the body. Therefore, increased nutrient transporter activity would increase (not decrease) nutrient absorption.

Question 161

Researchers are studying the last two phases of mitosis, anaphase and telophase, in actively dividing cancer cells. Different fluorescent probes are used to label various cellular components in these cells. Under the microscope, fluorescently labeled DNA appears blue, the nuclear envelope appears green, and the mitotic spindle appears red. Given this, green fluorescence would be most intense during: A) Anaphase only B) Telophase only C) Both anaphase and telophase D) Neither anaphase nor telophase

Answer 161

B Mitosis in eukaryotic cells includes four distinct phases: prophase, metaphase, anaphase, and telophase. The nuclear envelope breaks down during prophase, allowing both metaphase and anaphase to occur in the cytoplasm. During telophase, the nuclear envelope reforms around the chromosomes prior to cytokinesis, the cytoplasmic division of the parental cell into two identical daughter cells.

Question 162

A physician measures the arterial blood pressure of a patient while she is resting and again while she is running on a treadmill. The results of these blood pressure tests are given in the table below. Resting 128/80 Running 155/73 Given this data, was arterial blood pressure during heart contraction higher while the patient was resting or while she was running? A) Resting, because her diastolic blood pressure was higher when at rest B) Resting, because her systolic blood pressure was higher when at rest C) Running, because her systolic blood pressure was higher while running D) Running, because her diastolic blood pressure was higher while running

Answer 162

C Arterial blood pressure is highest when the heart contracts (during systole) and lowest when the heart relaxes (diastole). When measuring blood pressure (mm Hg), the higher systolic blood pressure is recorded over the lower diastolic blood pressure.

Question 163

Which of the following DNA mutations would always lead to truncated PC1 if observed in the coding strand of the PKD1 gene shown below? 5’ ...TGGTGCAACATTGCCTAG... 3’ A) Substitution of the second nucleotide for a thymine nucleotide B) Deletion of the guanine nucleotide in the fifth position C) Addition of three cytosine nucleotides after the third nucleotide D) Insertion of an adenine nucleotide after the second nucleotide

Answer 163

D Various types of DNA mutations can alter the protein product of a gene. Truncated proteins result from nonsense mutations and frameshift mutations with a downstream stop codon (UAA, UAG, UGA) in the new reading frame.

Question 164

A woman whose father is heterozygous for an ADPKD-causing (Autosomal dominant polycystic kidney disease) mutation in PKD1 and whose mother is unaffected has a child with a man with no family history of ADPKD. What is the percent chance that their first child will have ADPKD? (Note: Assume the woman’s ADPKD status is unknown.) A) 0% B) 25% C) 50% D) 100%

Answer 164

B In autosomal dominant inheritance, transmission of only one copy of a dominant allele is necessary to produce the phenotype. A heterozygous parent has a 50% chance of transmitting the mutation to their offspring. P(child with ADPKD) = P(mother inherited 1 allele from her father) x P(mother passes this 1 allele to this child) P(child with ADPKD) = (0.5)(0.5) = 0.25, or 25%

Question 165

Approximately 85% of ADPKD cases are caused by mutations in the PKD1 gene, which codes for the protein polycystin-1 (PC1). The remaining 15% of cases are caused by mutations in the PKD2 gene, which codes for the protein polycystin-2 (PC2). The PC2 protein functions as a mechanically activated calcium (Ca2+) channel in ciliated renal epithelial cells. Which set of amino acids would most likely be found in the pore of the channel formed by PC2? (Assume the amino acids are at a physiological pH.) A) D and E B) R and K C) V and L D) S and T

Answer 165

A PC2 forms a mechanically activated Ca2+ channel. For positively charged Ca2+ to pass, the inside of the pore must be lined by amino acid residues that are negatively charged at physiological pH. Aspartate (D) and glutamate (E) are the only amino acids that fit this criterion. Arginine (R) and lysine (K) are both positively charged. The carbon-hydrogen side chains of valine (V) and leucine (L) are nonpolar and are unable to attract positively charged Ca2+. Serine (S) and threonine (T) are uncharged and polar. Although they could weakly attract Ca2+ via ion-dipole forces, aspartate (D) and glutamate (E) would bind Ca2+ more effectively.

Question 166

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common heterogeneous disorders, with a reported incidence of 1 in 1,000 people. The primary pathology is the development of numerous fluid-filled renal cysts that ultimately expand and severely impair kidney function. In advanced ADPKD, all of the following components of physiological homeostasis would be disrupted EXCEPT: A) Blood nitrogen levels B) Blood pH C) Leukocyte production D) Erythropoietin production

Answer 166

C The kidney’s primary function is to maintain the salt and water balance of the blood. They also play a key role in regulating multiple aspects of physiological homeostasis (blood pressure, waste removal, osmolarity, blood pH, erythrocyte production).

Question 167

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common heterogeneous disorders, with a reported incidence of 1 in 1,000 people. By age 60, approximately 50% of patients with ADPKD progress to end-stage renal disease (ESRD) and kidney failure. Based on this information, is the mutated PKD1 allele, which codes for the protein polycystin-1 (PC1), likely to be eradicated from the gene pool by natural selection? A) Yes, because the disease phenotype is masked by heterozygous genotypes B) Yes, because inclusive fitness is improved for individuals under the age of 50 C) No, because the mutated allele is preserved by directional selection D) No, because the disease phenotype does not emerge until after child-bearing age

Answer 167

D Deleterious dominant alleles can remain in the gene pool if the organism’s fitness remains unaffected, even when the deleterious alleles reduce survival after the reproductive years. Deleterious recessive alleles evade elimination by natural selection through phenotypic masking in heterozygotes.

Question 168

Eukaryotic organelles such as mitochondria and chloroplasts are believed to be relics of formerly free-living prokaryotes. The transition from hypoxic (low O2) to an oxic atmosphere (21% O2) is said to have enabled primitive eukaryotic anaerobes to engulf ancient aerobic prokaryotes and consequently acquire the ability to produce energy through oxidative phosphorylation. On integration into the host genome, mitchondria-derived genes became indistinguishable from the original nuclear genes. Based on this information, which of the following best explains how mitochondrial genes differed from eukaryotic genes prior to gene transfer? Mitochondrial genes were: A) Interspersed with noncoding sequences B) Located on chromosomes without telomeres C) Present on a single-stranded DNA genome D) Associated with histones

Answer 168

B In the nucleoid region of prokaryotic cells, double-stranded DNA is condensed into a circular chromosome that has no telomeres or associated histones. By contrast, eukaryotic cells package their histone-wrapped, double-stranded DNA into linear chromosomes with ends capped by telomeres to prevent DNA from unraveling.

Question 169

Researchers have alternatively proposed that after a prolonged period of symbiosis, there is a possibility of gene transfer from eukaryotes to prokaryotes. This hypothesis was initially supported when copper/zinc (Cu/Zn) superoxide dismutase (SOD), a metalloprotein confined to the cytosol of eukaryotic cells, was found in Photobacterium leioghnathi. Which observation would NOT support the hypothesis of gene transfer from eukaryotes to prokaryotes described in the passage? A) Discovering no difference between the gene sequences of the P. leiognathi and pony fish SODs B) Discovering P. leiognathi and ponyfish SODs have a similar amino acid sequence in their noncatalytic domains C) Discovering Cu/Zn SODs in other free-living bacterial species with no known eukaryotic symbiotic hosts D) Discovering Cu/Zn SODs in other free-living bacterial species with known eukaryotic symbiotic hosts

Answer 169

C The endosymbiotic theory explains how primitive eukaryotic anaerobes engulfed ancient aerobic prokaryotes, and consequently acquired the ability to produce energy through oxidative phosphorylation. The discovery of Cu/Zn in free-living bacteria with no known eukaryotic symbiont hosts would argue against the hypothesis.

Question 170

A hypothesis was initially supported when copper/zinc (Cu/Zn) superoxide dismutase (SOD), a metalloprotein confined to the cytosol of eukaryotic cells, was found in Photobacterium leiognathi, a free-living bacterium. SOD mRNA in P. leiognathi encodes a signal sequence that directw the transport of the SOD protein for secretion. This signal sequence will direct SOD proteins to which strucure in P. leiognathi? A) Smooth endoplasmic reticulum B) Plasma membrane C) Mitchondrial outer membrane D) Golgi body

Answer 170

B Prokaryotic cells lack membrane-bound organelles and utilize specialized channels in the plasma membrane to secrete proteins. In contrast, eukaryotic cells contain membrane-bound organelles (nucleus, Golgi body, mitochondria); the rough endoplasmic reticulum and Golgi body are involved in eukaryotic protein secretion.

Question 171

Ponyfish cells containing P. leiognathi (a free-living bacterium) symbionts were exposed to a spindle fiber toxin that inhibits microtubule polymerization. Given this information, which of the following would most likely results as a consequence of toxin exposure? A) P. leiognathi daughter cells with multiple copies of the Cu/Zn SOD gene B) Ponyfish daughter cells containing the same number copy number of the Cu/Zn SOD gene C) Delayed separation of P. leiognathi cells during binary fission D) Nondisjunction in somatic ponyfish cells undergoing nuclear division

Answer 171

D Most eukaryotic cells (except germ cells) undergo cell division via mitosis. In contrast, prokaryotic cells duplicate via binary fission, a simple form of reproduction that does not involve the separation of chromosomes by spindle fibers. Nondisjunction in mitosis or meiosis can occur when sister chromatids fail to separate properly during anaphase. Ponyfish cells exposed to a spindle fiber toxin would exhibit nondisjunction during mitosis as spindle fibers are necessary to separate sister chromatids.

Question 172

Investigators used a ribosome profiling technique to measure the level of SOD protein synthesis in P. leiognathi and ponyfish cells during radioactive oxygen species (ROS) accumulation. P. leiognathi cells were found to contain greater numbers of ribosome/SOD mRNA complexes than ponyfish cells. What is the best explanation for this result? A) P. leiognathi SOD mRNA is capable of being bound by more than one ribosome B) P. leiognathi SOD mRNA has a greater affinity for ribosomes than ponyfish mRNA C) mRNA transcribed from the ponyfish SOD gene undergoes immediate degradation D) mRNA transcribed from the bacterial SOD gene is being transcribed simultaneously

Answer 172

D Prokaryotic cells have no nucleus; therefore, transcription and translation occur simultaneously in the cytoplasm (translation begins before the mRNA is fully transcribed). By contrast, in eukaryotic cells transcription and post-transcriptional modifications occur in the nucleus, but translation occurs in the cytoplasm.

Question 173

In anaerobic environments, P. leiognathi can produce energy by using an inorganic final electron acceptor other than oxygen in the electron transport chain. Under anaerobic conditions, which of the following is NOT active in ponyfish cells but active in P. leiognathi? A) Glycolysis B) Gluconeogenesis C) Fermentation D) ATP synthase

Answer 173

D The Krebs cycle and the electron transport chain are only active in the presence of a final electron acceptor, such as oxygen (aerobic respiration) or inorganic ions (anaerobic respiration). Although ATP synthase does not directly need O2 to generate ATP, the formation of the proton gradient by which it functions is oxygen-dependent in ponyfish cells but not in P. leiognathi. Consequently, under anaerobic conditions, ATP synthase is not active in ponyfish cells but active in P. leiognathi.

Question 174

A neuron is exposed to a compound that prevents the passage of Na+ channels. Which of the following graphs best represents the local membrane potential charge of this neuron upon injection of positive current that allows the membrane to reach the threshold value? (Note: The solid line represents the action potential after normal stimulation; the dashed line represents the action potential after exposure to the compound.) Answers are graphs* A) No relative change B) Once reaching threshold, does not continue depolarization. Back to resting potential C) Resting membrane potential is higher than normal, depolarization normal D) Once depolarization occurs, graphs tapers off at high resting membrane potential. Does not go back to under threshold levels

Answer 174

B An action potential is fired in an all-or-nothing manner based on the cell’s membrane potential. If the threshold is reached, voltage-gated ion channels open and the membrane rapidly depolarizes. The resting membrane potential is restored by the Na+/K+ pump.

Question 175

Biologist 1 developed a neural staining technique that involved older animal’s myelinated axons. Biologist 2 modified the first biologist’s study by using the brain tissue of younger animals, rather than older more myelinated brain tissue samples. Compared to the axons investigated by Biologist 2, the axons studied by Biologist 1 most likely had: A) Faster decay of the propagating electrical signal B) Axonal membranes that were more exposed to the extracellular space C) Slower rates of action potential conduction D) Voltage-gated ion channels clustered only at specific locations

Answer 175

D The myelin sheath increases the speed of action potential (AP) propagation by acting as an electrical insulator that prevents dissipation of charge across the membrane. APs in myelinated axons travel via saltatory conduction. Due to the lack of myelination, the axons studied by Biologist 2 were fully exposed to extracellular space, were more susceptible to rapid weakening of the electrical signal, and conducted APs at a slower rate.

Question 176

Which of the following synaptic events is most likely to contribute to the generation of an action potential in a postsynaptic neuron? A) The presynaptic neuron releases large quantities of gamma-aminobutyric acid (GABA) B) Postsynaptic neurotransmitter-gated ion channels that pass both Na+ and Ca2+ ions open C) Neurotransmitter reuptake into the presynaptic cell and surrounding glia is inhibited D) Neurotransmitter binding activates G-protein coupled receptors on the postsynaptic membrane

Answer 176

B Although trends in neurotransmitter function exist, the postsynaptic response is ultimately determined by the type of receptor activated. Receptors may be either ligand-gated ion channels or G-protein-coupled receptors. In chemical synapses, when an action potential (AP) reaches the axon terminal of the presynaptic neuron, the terminal membrane depolarizes and causes voltage-gated Ca2+ channels to open. Extracellular Ca2+ ions flow down their electrochemical gradient into the axon terminal and stimulate neurotransmitter-containing synaptic vesicles to fuse with the presynaptic membrane and release their contents into the synaptic cleft by exocytosis.

Question 177

A single diploid cell containing 46 chromosomes underwent meiosis and produced four daughter cells, two with 22 chromosomes and two with 24 chromosomes. An error in which of the following stages of meiosis would most likely explain this result? A) Metaphase II B) Prophase II C) Telophase I D) Anaphase I

Answer 177

D During meiosis, chromosomal nondisjunction occurs when homologous chromosomes (in meiosis I) or sister chromatids (in meiosis II) fail to separate to opposite poles of the cell during anaphase, leading to extra chromosomes in some daughter cells and missing chromosomes in others.

Question 178

A gene regulating tail length in bobtail cats has a genetic variation at a single locus, where organisms can have an allele that produces long tails (L) or an allele that produces long short tails (l). A male cat homozygous for short tail length (ll) was mated with a female cat homozygous for long tail length (LL). The tail lengths of the parents and offspring were recorded. Father is short, mother is long All offspring are a variation between mom and dad tail length. (None are longer or short than the parents) A scientist concludes that the alleles regulating tail length in these cats exhibit incomplete dominance. Do the data support this conclusion? A) No, because all offspring have longer tails than the father’s B) No, because all offspring inherited both types of alleles for tail length C) Yes, because the tail lengths of some offspring are longer than the tail lengths of other offspring D) Yes, because the offspring have tail lengths longer than the father’s but short than the mother’s

Answer 178

D Incomplete dominance between alleles results in the expression of phenotypes in heterozygous offspring that are intermediate to the phenotypes of homozygous parents. Long tail mother mixed with short tail father will results in medium tail in the offspring when dealing with incomplete dominance.

Question 179

Renal studies in mice have revealed that a mutation in various sodium transporters causes impaired active transport of NaCl from the filtrate within the Loop of Henle to the medulla. If mice with wild-type sodium transporters were compared to mice with the mutated sodium transporters, the mutant mice would likely exhibit all of the following EXCEPT: A) Decreased saltiness of the medulla B) Decreased urine output C) Decreased renal water reabsorption D) Decreased blood pressure

Answer 179

B In the loop of Henle, active transport of NaCl from filtrate in the ascending limb maintains the saltiness of the renal medulla, facilitating passive water reabsorption from filtrate on the descending limb and collecting duct. Compared to wild-type mice, mice with mutated sodium transporters would exhibit a decrease in both medullary salt concentration and water reabsorption, a decrease in blood pressure, and an increase in urine output.

Question 180

Certain turtle species exhibit embryonic expression of an enzyme that converts male sex hormones to female sex hormones. The enzyme expression level determines whether a developing embryo will be male or female. Scientists hypothesize that expression of this enzyme depends on incubation temperature during development. To test this, they incubated 30 turtle eggs at 26*C and 30 eggs at 30*C and recorded the sex of each turtle after hatching. Graph depicts high amount of male turtles and low female at 26*C and high amount of female turtles, low males at 30*C Given this, the expression level of this enzyme in developing turtles is most likely: A) High at 26*C and low at 30*C B) Low at 26*C and high at 30*C C) High at both 26*C and 30*C D) Low at both 26*C and 30*C

Answer 180

B In general, the expression of genes produces proteins, and the properties and activities of these proteins lead to the expression of certain traits (phenotypes) in organisms. However, in a gene-environment interaction, certain environmental conditions (temperature, diet, oxygen level) can influence gene expression or protein activity and alter an organism’s phenotype.

Question 181

Skin grafts are used for partial-thickness burns, which damage the epidermis and dermis, and for full-thickness burns, which damage the epidermis, dermis, and hypodermis. Superficial burns injure only epidermal tissue and heal without skin grafts. A skin graft candidate with full-thickness burns on approximately 50% of the total BSA is at risk for all of the following EXCEPT: A) Extensive fluid loss B) Bacterial infection C) Increased sensitivity to touch D) Vitamin D deficiency

Answer 181

C The skin functions as a physical barrier to prevent the loss of fluid from the body while simultaneously blocking the entry of pathogens or harmful chemicals. The skin also contains receptors that gather and respond to sensory information from the surrounding environment. Ultraviolet radiation that strikes the skin induces the synthesis of a vitamin D precursor. This type of burn involves injury to the epidermal and dermal sensory receptors, resulting in impaired touch sensation.

Question 182

Heat acclimation (HA) is the process by which the body increases heat tolerance through adaptive changes in the sympathetic control of skin heat dissipation. It can be induced in healthy individuals by repeated exercise at elevated ambient temperature and humidity. A group of researchers tested whether skin graft recipients could also undergo HA. What physiological change occurs in the skin of control (healthy) subjects during HA exercise? A) Enhanced contraction of arteriole smooth muscle B) Enhanced relaxation of arteriole smooth muscle C) Enhanced contraction of arrector pili muscles due to parasympathetic activation D) Enhanced contraction of arrector pili muscles due to sympathetic activation

Answer 182

B One major function of the skin is thermoregulation. Body temperature can be increased by vasoconstriction of skin arterioles, shivering, and (in hairer animals) piloerection, hair standing upright. Body temperature can be decreased by vasodilation of skin arterioles and sweating.

Question 183

Given that scar tissue forms when collagen-producing cells replace normal tissue after an injury, all of the following processes would be impaired in the area of scarred skin that forms over a partial-thickness burn EXCEPT: A) Resistance to ultraviolet radiation B) Insulation C) Hair growth D) Salt excretion

Answer 183

B Skin has many functions: The subcutaneous layer is composed of adipose cells that insulate the body, epidermal melanocytes prevent UV radiation from damaging the DNA of cells, hair is a keratinized derivative of skin that helps protect the body from external injury, and dermal sweat glands secrete swear onto the skin surface to regulate body temperature. Based on the question, a partial-thickness burn does not affect the subcutaneous layer, so insulation is not affected.

Question 184

Which of the following skin functions will most likely be impaired in tissue with superficial burns? I. Keratinocyte maturation II. Immune surveillance III. Shock absorption A) I and II only B) I and III only C) II and III only D) I, II, and III

Answer 184

A The skin is divided into the epidermis (outermost layer), dermis (middle layer), and hypodermis (innermost layer). The epidermis acts a physical barrier that separates the organism from the external environment. The dermis contains blood vessels, immune cells, sensory receptors, sweat and oil glands, and hair follicles. The hypodermis is composed of insulating and shock-absorbing adipose tissue. Since the burn is only superficial, shock absorption will not be affected.

Question 185

Bacteria are removed from lymph and blood in the: A) Spleen and bone marrow, respectively B) Lymph nodes and spleen, respectively C) Bone marrow and lymph nodes, respectively D) Lymph vessels and thymus, respectively

Answer 185

B In the lymph nodes, white blood cells remove and mount immune responses against pathogens from the lymph, whereas in the spleen, white blood cells remove pathogens and damaged or old red blood cells from the blood.

Question 186

A physician finds that a patient experiences excessive bleeding after sustaining a cut on the arm. The excessive bleeding is LEAST likely to be caused by: A) Reduced liver function B) High numbers of macrophages near the cut C) Reduced proliferation of platelets D) High levels of serum antibodies against clotting factors

Answer 186

B Platelets and specialized proteins (clotting factors) work synergistically in response to blood vessel damage, binding to the damaged portion of the vessel and forming a blockage that prevents blood loss. Although macrophages may destroy pathogens entering the body through the cut, they would not inhibit clot formation and cause excessive bleeding that was observed in the patient.

Question 187

A patient found to have an abnormally low number of helper T cells in her blood contracts a bacterial infection. During the infection, which of the following is most likely NOT affected by the patient’s low count of helper T cells? A) Expression of major histocompatibility complex proteins that present bacterial antigens on the membrane of infected host cells B) Proliferation of B lymphocytes in response to the bacterial infection C) Levels of circulating antibodies against the invading bacterium D) Activation of apoptosis-inducing cytotoxic T cells

Answer 187

A Helper T cells bind foreign antigens presented by other immune cells and release signaling molecules than enhance immune responses, such as cytotoxic T cell activation and antibody production by lymphocytes. Some of the lymphocytes also secrete antibodies and increase levels in circulation.

Question 188

Which of the following mRNA strands contains the longest open reading frame? A) 5’ - CCACGAUGCGUUGAGCGC - 3’ B) 5’ - CAAUGGUAAAGUCUUAGU - 3’ C) 5’ - GACGAUGUAACUUGCACU - 3’ D) 5’ - AGAAUGGUAUCCUGAGCC - 3’

Answer 188

B An open reading frame (ORF) is a set of codons within a strand of mRNA that can be translated by a ribosome. An ORF begins with a start codon (AUG) and ends with a atop codon (UAA, UAG, or UGA). The start and stop codons must be in the same reading frame.

Question 189

Type 1 diabetes mellitus (T1DM) differs from T2DM in that affected patients stop producing insulin at a young age. Which of the following is most likely impaired in T1DM? I. Exocrine function of pancreatic beta cells II. Endocrine function of pancreatic beta cells III. Exocrine function of pancreatic alpha cells IV. Endocrine function of pancreatic alpha cells A) I only B) II only C) I and II only D) III and IV only

Answer 189

B In the setting of high blood glucose, beta cells release insulin to promote glucose uptake from the blood and inhibit alpha cell function. In contrast, when blood sugar levels are low, alpha cells produce glucagon to promote glucose release into the bloodstream and inhibit beta cell function. Cells with endocrine (pancreas) function secrete hormones into the bloodstream to cause an effect in a different part of the body.

Question 190

Intraperitoneal injection of insulin would cause the peptide hormone to enter the bloodstream and exert its effect on target cells by: A) Acting as a second messenger B) Diffusing through the plasma membrane C) Binding an extracellular from a carrier protein D) Disassociating from a carrier protein

Answer 190

C Peptide hormones are amino-acid based, water-soluble molecules that travel freely through the bloodstream and act as first messengers by binding to an extracellular receptor on the target cell membrane, which leads to activation of intracellular second messengers.

Question 191

During the interval between 30 and 60 minutes in the graph, which of the following will be observed in WT mice? (Graph shows a decrease of glucose levels as time progresses from 30 minutes to 60 minutes after injection of glucose) A) Increased glucagon release B) Increased plasma amino acids C) Increased hepatic glycogen stores D) Increased hepatic gluconeogenesis

Answer 191

C In the setting of high blood glucose, insulin is released in response and functions to decrease blood glucose levels. In contrast, glucagon is released from pancreatic alpha cells in response to increase glucose levels. Insulin decreases blood glucose in the 30-60 minute interval by promoting glucose uptake by the liver for glycogen synthesis, which increases hepatic glycogen stores.

Question 192

Recently fed leptin-deficient mice (obese) show deficient binding of glucagon to its G protein-coupled receptor, which most likely leads to: A) Decreased cAMP to ATP conversion B) Upregulated adenylate cyclase activity C) Increased exchange of GDP to GTP D) Reduced protein kinase A activity

Answer 192

D In the G protein-regulated cAMP signaling pathway, a ligand binds the transmembrane G protein-coupled receptor and activates the GDP-bound alpha subunit of the G protein by replacing GDP with GTP. The activated G alpha subunit activates the enzyme adenylyl cyclase, which catalyzes the conversion of ATP into cAMP. Elevated cAMP leads to the activation of protein kinase A and subsequent signaling effects. Deficient binding of glucagon to its G protein-coupled receptor would decrease adenylate cyclase activity, which would result in reduced conversion of ATP to cAMP, not cAMP to ATP.

Question 193

Researchers aimed to cause obesity-induced insulin resistance in wild-type (WT) mice and Alb Tg mice, which express hepatic miR-26a (has been implicated in prevention of obesity-induced insulin resistance) at levels three-fold greater than WT. WT mice and Alb Tg mice were fed either a standard healthy diet (SHD) or a high-fat diet (HFD) for 14 weeks. The researchers hypothesize that miR-26a overexpression can rescue obesity-induced insulin resistance. Which experimental result would NOT support their hypothesis? A) Alb Tg mice fed a HFD had the same levels of random and fasting insulin as WT mice fed a SHD B) Alb Tg mice fed a HFD had the same levels of random and fasting glucose as WT mice fed a SHD C) WT mice fed a HFD had higher insulin sensitivity than Alb Tg mice fed a HFD D) WT mice fed a HFD had lower glucose tolerance than Alb Tg mice fed a HFD

Answer 193

C An organism is considered insulin sensitive if only a minimal amount of insulin is needed to induce an appropriate reduction in glucose levels. In contrast, insulin-resistant organisms need substantially more insulin to take up the same amount of glucose.

Question 194

One of the study subjects with a BMI of 56 kg/m^2 is discovered to have a similar pathology to the ob/ob mouse. Like ob/ob mice, affected individuals exhibit normal weight at birth but become severely obese afterward and have undetectable levels of leptin in the serum. What is the best explanation of serum leptin in this condition? A) Leptin cannot bind its receptor in the hypothalamus B) Leptin cannot bind its receptor in the thyroid gland C) Leptin cannot be secreted from gastric cells D) Leptin cannot be secreted from adipocytes

Answer 194

D In an energy-rich state (after a meal), leptin is released by white adipocytes to trigger appetite suppression via the hypothalamus. In contrast, in an energy-poor state, ghrelin is released by stomach gastric cells to trigger hunger and food-seeking behavior via the hypothalamus.

Question 195

COPD refers to a spectrum of disorders and can be a result of emphysema, the irreversible destruction of pulmonary tissue. The breakdown of elastic proteins in the lungs results in a loss of pulmonary resiliency and chronic lung hyperventilation. According to this information, which of the following changes would be expected in a patient with signs of emphysema? A) Narrowing of the trachea B) Less efficient gas exchange C) Weakened diaphragm muscle D) Overstretched pharyngeal tissues

Answer 195

B The alveoli are highly efficient at gas exchange due to their structure and extensive surface area. The destruction of alveolar walls in emphysematous lungs is expected to decrease the lungs’ ability to perform respiratory gas exchange.

Question 196

Lung diseases can be diagnosed and monitored using spirometry. A spirometer measures the flow rate and volume of inhaled and exhaled air. In one pulmonary test, a patient is asked to exhale forcibly and completely into a spirometer after maximum inhalation. This is to test forced expiratory volume in one second (FEV1) and forced vital capacity (FVC), the total amount of air exhaled in a single breath. If presented with a graph, which would be expected to pair with a patient with asmtha? A) FEV1 lower than normal patient, without reaching same maximum breath exhaled B) FEV1 lower than normal patient, but reaches same maximum breath exhaled C) FEV1 reaches height slightly faster than normal patient, and roughly same maximum breath exhaled D) FEV1 reaches height much faster than normal patient, has exact same maximum breath exhaled

Answer 196

A The narrowing of respiratory airways in asthma increases resistance to airflow, which would decrease the volumetric rate of forcibly exhaled air (FEV1 decreases). The narrow airways also trap air in the lungs, decreasing the total volume of air that can be exhaled (FVC decreases). Less air can be exhaled in asthma due to air trapping in the lungs.

Question 197

``` The regulation of respiratory rate is normally most sensitive to: Partial pressure = P A) P O2 in the blood B) P CO2 in the blood C) P O2 in the alveoli D) P CO2 in the alveoli ```

Answer 197

B The regulation of respiratory rate primarily depends on the pH of the blood as measured by central and peripheral chemoreceptors. These receptors directly detect the [H+] in the blood, which is dependent on the partial pressure of CO2 in the blood through the bicarbonate buffer system. (CO2 + H2O H2CO3 HCO3- + H+)

Question 198

During an asthma attack, temporary bronchoconstriction would have what effect on blood pH, and what would be the expected homeostatic response? A) Respiratory acidosis and an increased respiratory rate B) Respiratory acidosis and a decreased respiratory rate C) Respiratory alkalosis and an increased respiratory rate D) Respiratory alkalosis and a decreased respiratory rate

Answer 198

A Respiratory gas exchange functions to remove CO2 from the blood, and CO2 levels affect the pH of the blood by shifting the equilibrium of the bicarbonate buffer system. A decrease in gas exchange will cause respiratory acidosis, and the body will attempt to restore normal blood pH by increasing the respiratory rate. (CO2 + H2O H2CO3 HCO3- + H+)

Question 199

The inflation of the lungs in normal inspiration involves: I. Contraction of the diaphragm II. Reduction of intrapleural pressure III. Elevation of the rib cage A) I and II only B) I and III only C) II and III only D) I, II, and III

Answer 199

D The intrapleural space is the thin space between the lungs and the thoracic wall. The contraction of the diaphragm and the elevation of the rib cage decreases the pressure in the intrapleural space, causing the lungs to expand. Negative pressure breathing refers to the reduction of intrapleural pressure during inspiration.

Question 200

Primary ciliary dyskinesia (PCD), a rare disease that impairs the normal function of cilia, is often misdiagnosed as atypical asthma because wheezing is observed in both illnesses. Unlike asthma, PCD would cause the inability to: A) Balance respiratory thermoregulation B) Cough or sneeze C) Remove inhaled particulates D) Speak in lower pitches

Answer 200

C In the upper respiratory tract, mucus-producing cells and ciliated cells work together to trap and remove potentially pathogenic bodies. Therefore, dysfunctional cilia would decrease the respiratory system’s ability to remove inhaled particulates.

Question 201

If using antibodies to test for Rheumatoid arthritis (RA) what would they most likely contain? A) Two heavy chains that differ in amino acid sequence B) Two light chains that differ in amino acid sequence C) A variable region that binds only one type of antigen D) A constant region that binds only one type of antigen

Answer 201

C Antibodies are synthesized and secreted by effector B cells, which are part of the adaptive immune system. Each antibody consists of two identical light chains, two identical heavy chains, a variable region that interacts with a specific antigen, and a constant region that interacts with the cells (phagocytes) and proteins of the body to facilitate antigen destruction.

Question 202

Rheumatoid Arthritis (RA) is an autoimmune disease that causes chronic synovial (joint) inflammation. RA immunopathogenesis involves LFA-1, a surface receptor found on leukocytes that is composed of an alpha-chain (CD11a) and beta-chain (CD18). Using this information, cells containing the LFA-1 complex on their cell membranes most likely originate in which of the following tissues? A) Spleen B) Thymus C) Bone marrow D) Lymph nodes

Answer 202

C Hematopoietic (lymphocytes/white blood cells) stem cells originate in the bone marrow and differentiate into myeloid or lymphoid progenitor cells. Lymphoid progenitor cells go on to become T cells, B cells, or NK cells whereas myeloid progenitor cells differentiate into erythrocytes, megakaryocytes, neutrophils, basophils, eosinophils, monocytes, or mast cells.

Question 203

A self-directed antibody known as rheumatoid factor (RF) has been found to be involved in RA-mediated inflammation. RF is an antibody that targets a patient’s own IgG antibodies, which results in the formation of immune complexes that induce an inflammatory response. High concentrations of self-antibodies such as RF are NOT typically found in the human body because: A) RF functions as a complement protein B) B cells and T cells against self-antigens are destroyed C) Antigen-presenting cells cannot present self-antigens D) T-cell receptor recombination cannot produce self-identifying receptors

Answer 203

B Autoimmunity disorders occur due to the immune system’s failure to identify and destroy immune cells that recognize self-antigens. Self-reactive B cells and T cells are normally eliminated in the bone marrow and thymus, respectively.

Question 204

Following digestion in the small intestine, certain lipids are absorbed by intestinal epithelial cells and packaged into large droplets. These lipid droplets are released from intestinal epithelial cells and transported into the lymphatic system to ultimately drain into a large vein near the heart. Which series shows the order in which these lipid droplets are transported from the intestine to the bloodstream? A) Lymph capillaries -> interstitial fluid -> lymph vessels -> lymph duct -> vein B) Interstitial fluid -> lymph vessels -> lymph duct -> lymph capillaries -> vein C) Interstitial fluid -> lymph capillaries -> lymph vessels -> lymph duct -> vein D) Lymph capillaries -> interstitial fluid -> lymph duct -> lymph vessels -> vein

Answer 204

C The lymphatic system collects protein-containing fluid leaked from blood capillaries and transports it back to the bloodstream. In addition, large lipid droplets absorbed by the small intestine are also transported to the bloodstream via lymph vessels. Fluid is collected by lymph capillaries, flows into larger lymph vessels, and is transported into lymph ducts that drain into veins near the heart.

Question 205

The processes of spermatogenesis and oogenesis in humans are similar in that they both: A) Begin at puberty B) Involve cells that undergo more than one round of cell division C) Result in daughter cells of unequal size compared with the parent cell D) Occur throughout the life-span of the organism

Answer 205

B Both spermatogenesis and oogenesis involve cells that undergo meiosis I and II. However, oogenesis in females begins in the female embryo and ends at menopause, whereas spermatogenesis in males does not begin until puberty and continues throughout a male’s life.

Question 206

In an assay, researchers assessed activity levels of an oxidative enzyme present on the inner mitochondrial membrane of skeletal muscle fibers. Enzyme activity was visualized by reacting the product of the enzymatic reaction with a dark-colored salt, which resulted in dark-colored staining of the muscle fibers. Assay results in two different microscopic cross sections of muscle fibers are; fiber 1 has minimal staining if any, and fiber 2 has nearly cell space colored dark. Give these results, muscle fibers in cross section 1 most likely: A) Utilized more oxygen than muscle fibers in cross section 2 B) Relied on anaerobic respiration less than muscle fibers in cross section 2 C) Contained lower oxygen-storage proteins than muscle fibers in cross section 2 D) Had a more extensive network of surrounding blood vessels than muscle fibers in cross section 2

Answer 206

C Oxidative muscle fibers use aerobic respiration for ATP synthesis, requiring large amounts of oxygen supplied by high levels of myoglobin and extensive capillary networks. In contrast, nonoxidative fibers generate ATP through anaerobic glycolysis and require less oxygen than oxidative fibers.

Question 207

A neurotransmitter released from one neuron causes an influx of negatively charged ions into the cytosol of an adjacent neuron. In the adjacent neuron, the influx of these ions would most likely: A) Depolarize the cell membrane and promote initiation of an action potential B) Hyperpolarize the cell membrane and promote initiation of an action potential C) Depolarize the cell membrane and inhibit initiation of an action potential D) Hyperpolarize the cell membrane and inhibit initiation of an action potential

Answer 207

D At inhibitory synapses, pre-synaptic neurons release neurotransmitters that cause either an influx of negative ions into the post-synaptic neuron or an efflux of positive ions out of the post-synaptic neuron. This causes hyperpolarization of the membrane potential and inhibits action potential initiation in the post-synaptic neuron.

Question 208

E. coli K-12, a normal bacterial strain of the human microbiota, is able to cause disease by inducing enterocyte lesions after it is grown in media with EHEC-bacteria that contain the F factor plasmid. What process most likely granted virulence to E. coli K-12? A) Transformation B) Transduction C) Conjugation D) Transfection

Answer 208

C Conjugation is the transfer of genetic information from one bacterial cell to another via direct contact facilitated by the sex pilus. The sex pilus is encoded by genes contained in the F factor plasmid.

Question 209

EHEC is classified as a bacilli bacterium. Given this information, this type of classification is most likely based on the bacterium’s: A) Habitat B) Oxygen dependence C) Morphology D) Virulence

Answer 209

C Bacteria can be classified by morphology, or shape. In morphological classification, three basic shapes are used to classify bacteria: rod-shaped (bacilli), spherical-shaped (cocci), and spiral (spirilli).

Question 210

Which proteins identified in a western blot chart would have the shortest amino acid sequence and the greatest concentration in WT cells, respectively?

Answer 210

Western blot involves protein separation by gel electrophoresis, transfer onto a blotting membrane, and detection with protein-specific antibodies. Proteins with low molecular weight migrate farthest, and protein concentration is generally proportional to band intensity.

Question 211

Which of the following is most likely to be found within the cell membrane of intestinal epithelial cells? A) Peptidoglycan B) Cholesterol C) Cytoskeletal filaments D) Cellulose

Answer 211

B The plasma membrane is a fluid lipid bilayer that contains a diverse array of proteins scattered throughout. Certain cell types have a cell wall surrounding their plasma membrane; however, animal cells do not have a cell wall. The primary component of bacterial cell walls is peptidoglycan.

Question 212

Alzheimer disease (AD) is a progressive condition affecting memory and cognition that can be pathologically characterized by the presence of neurofibrillary tangles (NFTs). NFTs, aggregates of hyperphosphorylated tau proteins that have dissociated from microtubules, are believed to contribute to neuronal degradation and subsequent AD symptoms. While analyzing potential therapeutic strategies for AD, researchers would most likely pursue which of the following approaches? A) Phosphatase upregulation B) Kinase upregulation C) Isomerase downregulation D) Synthase downregulation

Answer 212

A Phosphorylation and dephosphorylation are post-translational modifications that alter the function or activity of proteins by changing their conformation. Kinases catalyze the transfer of phosphate groups from ATP or GTP to proteins, and phosphatases catalyze the removal of phosphate groups via hydrolysis. Excessive tau phosphorylation by kinases leads to the formation of NFTs, so upregulation of phosphatase would cause increased removal of phosphate groups as a therapeutic approach.

Question 213

The cytotoxic protein X.23A induces conformational changes in the large ribosomal subunit, reducing its catalytic activity. Treating neuronal Alzheimer disease (AD) mice cells that overexpress tau protein with X.23A would most likely interfere with the binding of the: A) 70S ribosomes to the nucleus B) 80S ribosomes to the rough endoplasmic reticulum C) 50S ribosomal subunit to the smooth endoplasmic reticulum D) 40S ribosomal subunit to the Golgi body

Answer 213

B Ribosomes translate mRNA sequences into proteins in eukaryotes (80S ribosomes: 60S large subunit and 40S small subunit) and prokaryotes (70S ribosomes: 50S large subunit and 30S small subunit). The ribosome-mRNA complex translocates to the rough endoplasmic reticulum to synthesize secretory, lysosomal, or integral membrane proteins. Due to X.23A treatment, 60S subunit activity will be impaired, reducing both the assembly of a functional 80S ribosome-tau mRNA complex and its binding to the ER.

Question 214

Assume gene expression of tau v1 and v2 are synchronized in AD mice cells, and tau mRNA levels are analyzed. Of the following, which technique would researchers use to identify the tau mRNA isoform with the longer half-life in the cytoplasm of AD mice cells? A) RT-PCR at a single time point B) Western blot at a single time point C) RT-PCR at varying time points D) Western blot at varying time points

Answer 214

C Researchers can assess the half-life of mRNA isoforms by converting mRNA to cDNA via RT-PCR at varying time points, allowing for comparison of isoform concentrations. The isoform with greater cDNA concentration at the final time point has the longer half-life. The number of amplified copies (concentration) of tau v1 cDNA can be compared with that of tau v2 cDNA by performing RT-PCR at varying time points.

Question 215

The translation of tau mRNA would most likely involve: I. An enzyme with the ability to hydrolyze peptide bonds II. tRNA molecules carrying amino acids corresponding to codons on the mRNA molecule III. A ribosomal complex capable of reading the target mRNA in a 3’ to 5’ direction A) I only B) II only C) I and II only D) I and III only

Answer 215

B Eukaryotic translation involves 3 steps: Initiation: The small 40S ribosomal subunit binds the 5’ cap, an initiator transfer RNA (tRNA) is recruited to the start codon, and the large 60S subunit binds the initiator tRNA. Elongation: The ribosome continues to elongate the polypeptide chain by reading each mRNA codon in a 5’ to 3’ direction. Termination: A stop codon is read, and release factors induce translation complex dissociation.

Question 216

To test a hypothesis, wild type (WT) S. typhimurium cells were transformed with plasmids encoding components of the lac operon. Each plasmid also contained genes for the lac repressor (lacl), which can inhibit lac operon transcription in the absence of lactose; the cAMP receptor protein (crp), which induces lac expression in low glucose; and a chloramphenicol resistance gene (cat). Which of the following genes would be the most advantageous for lac+ S. typhimurium bacteria in glucose-rich media. A) cat B) lacl C) lacZ D) crp

Answer 216

B The lacl gene codes for the lac repressor and prevents transcription of the lac genes. When sufficient glucose is available, the repressor helps conserve ATP by inhibiting expression of unnecessary genes. When glucose is depleted and lactose is available, lac genes are again expressed to make use of available energy sources.

Question 217

Which of the following conclusions regarding virulence of lac+ S. typhimurium is most accurate? (Lac+ appears to have less flagellum production than lacZ+,lacY+, and lacA+) A) It cannot detect the presence of epithelial cells B) It lacks the type III secretion proteins needed for invasion C) It infects epithelial cells without using type III secretion proteins D) It sense epithelial cells but cannot move toward them

Answer 217

D Bacteria respond to chemical stimuli in the extracellular environment by moving away from or toward increasing concentrations of signal molecules. This movement, known as chemotaxis, allows bacteria to adjust the direction of their movement toward target cells and is an important part of infection. Impairing the ability to detect or respond to chemical signals can reduce virulence.

Question 218

The reduced virulence of lac+ S. typhimurium has been correlated with an inability to generate the torque that turns the flagellum. Which structure in the flagellum is most likely being affected by the lac gene? A) Hook B) Filament C) Basal body D) Cell membrane

Answer 218

C Bacterial flagella are composed of a basal body, a hook, and a hollow filament filled with flagellin. The hook connects the filament to the basal body, and the basal body serves as the motor that generates motion.

Question 219

Overexpression of the miR-17~92 gene cluster occurs in many human cancers involving c-Myc, a gene coding for a transcription factor that regulates expression of proteins such as p21, an inhibitor of cell cycle progression. miR-17~92 encodes six distinct microRNAs (miRNAs). When expressed, the most likely function of the products generated by miR-17~92 gene cluster is to: A) Assist with the primary enzymatic functions of the ribosome B) Facilitate the processing of pre-mRNA in the cell nucleus C) Interfere with gene expression by binding transcripts with complementary nucleotide sequences D) Prevent small nuclear ribonucleoproteins from forming a large RNA-protein complex

Answer 219

C MicroRNAs (miRNAs), an example of noncoding RNA, silence gene expression at the translational level. miRNAs bind complementary sequences on target messengers RNA (mRNA) molecules, consequently inhibiting expression of the target mRNA by either blocking its translation or marking it for degradation.

Question 220

To asses the relative contribution of each miRNA to the oncogenic ability of the miR-17~92 cluster, A/A cell lines were transduced with an empty vector or with miR-17~92 mutant allele constructs that were engineered to lack expression of miRNA from at least one of the four families of miR (17, 18, 19 and 92). As described, verification that the transduced cells expressed the desired miRNA was an essential experimental step to ensure that: A) Lack of expression of one or more miRNA encoded by the miR-17~92 cluster did not affect the rate of apoptosis in tested cells B) Transduction of tested cells with mutant miR-17~92 alleles did not induce the development of B-cell lymphoma C) Deletion of one or more miRNA encoded by the miR-17~92 cluster did not affect expression of the remaining miRNAs encoded by the constructs D) Expression of one or more mutant miR-17~92 alleles did not provide the transduced cells with a selective growth advantage

Answer 220

C Positive controls are often employed to ascertain test validity and allow researchers to correctly interpret scientific data. This kind of experimental setup can verify that the dependent variable to be studied is present or that the treatment (independent variable) meant to manipulate the dependent variable functions properly. To reliably draw such conclusions, it was necessary to first ensure that deletion of one or more miRNAs encoded by the miR-17~92 cluster did not affect expression/processing of the remaining miRNAs encoded by the mutant constructs.

Question 221

Healthy subjects show a shallow increase in oxygen-carrying capacity at 0-20 mm Hg, but a sharp increase at 20-50 mm Hg. Which statements explains this effects? I. Oxygen binding induces a change from the R state to the T-state II. The affinity of hemoglobin for oxygen increase with O2 pressure III. Hemoglobin exhibits positive binding cooperativity IV. Hemoglobin exhibits negative binding cooperativity A) I and IV B) II and III C) I, II, and III D) I, II and IV

Answer 221

B Hemoglobins affinity for oxygen increases as successive oxygen molecules bind to individual subunits and change neighboring subunits from a tense (T) to a relaxed (R) state. Positive cooperativity between binding sites in proteins and enzymes is indicated by the sigmoidal (S) shape of kinetic graphs.

Question 222

The effect of anaerobic exercise on the oxygen saturation curve in healthy patients is shown in the graph (Curve is slightly less steep as compared to at rest. Takes slightly more time for the saturation % to go up). Which of the following is involved in the change in the oxygen dissociation curve? A) CO2 production decreases in contracting muscle B) Exercise reduces the PO2 of oxygen in muscles C) Hemoglobin binds oxygen tightly during exercise D) Lactic acid production increases during exercise

Answer 222

D Acidic byproducts of glycolysis produced during exercise cause a right shift in the hemoglobin oxygen dissociation curve. This phenomenon, known as the Bohr effect, provides muscles with a means to receive more oxygen from the blood during activity.

Question 223

Upregulation of which enzyme could improve oxygen release into the tissues of cirrhotic patients? A) Phosphoglycerate kinase B) Glyceraldehyde-3-phosphate dehydrogenase C) Bisphosphoglycerate mutasw D) Phosphoglycerate mutasw

Answer 223

C Bisphosphoglycerate mutase converts 1,3-bisphosphoglycerate into 2,3-bisphosphoglycerate, which allosterically regulates hemoglobin. It decreases oxygen affinity by stabilizing the deoxyhemoglobin conformation. Increasing concentrations of 2,3-bisphosphoglycerate produce a right shift in the oxyhemoglobin dissociation curve and favor oxygen delivery to tissues.

Question 224

Hyperventilation leads to oxygen dissociation curves similar to those seen in patients with cirrhosis when at rest. Based on this information, what physiological change in cirrhotic patients most likely decreases the level of oxygen delivery to tissues? (Graph shows Cirrhotic patients increase oxygen saturation quickly and earlier than healthy patients) A) Low carbonic acid and CO2 in the blood B) Increased excretion of bicarbonate by kidneys C) Higher PO2 in the lungs of cirrhotic patients D) Lower affinity of hemoglobin for oxygen in tissues

Answer 224

A A left shift in the oxyhemoglobin dissociation curve signifies an increase in the affinity of hemoglobin for oxygen. This affinity is inversely related to CO2 and H+ concentrations. A left shift in the ODC therefore often indicates lower CO2 and/or acid levels in the blood.

Question 225

A patient treated for cirrhosis was given vitamin B6 to stimulate red blood cell production. To counteract the potential negative side effects of this treatment, extract of ginkgo biloba was also administered. What is the most likely role the ginkgo biloba extract in this scenario? A) It stimulates hemoglobin synthesis B) It increases hemoglobin’s oxygen affinity C) It neutralizes reactive oxygen species D) It inhibits blood acidification

Answer 225

C Oxidative stress, caused by reactive oxygen species, can cause hemolysis. Compounds that remove reactive oxygen species can relieve the adverse effects of oxidative stress. Ginkgo biloba is an antioxidant.

Question 226

Individuals with glucose-6-phosphate dehydrogenase (G6PDH) deficiencies are more susceptible to oxidative stress than others. If a patient with cirrhosis also suffered from G6PDH deficiency, which vitamin could cause the most severe reduction in that patient’s hematocrit? A) Vitamin B1 B) Vitamin B3 C) Vitamin B6 D) Vitamin B12

Answer 226

D Hematocrit, measured as a percentage of the total blood volume, indicates the number of red blood cells in a blood sample. Hemolysis induced by oxidative stress can reduce hematocrit.

Question 227

Scientists studying evolution in yeast found that a certain species underwent a reduction in chromosome number with no loss of coding information. Given this, which of the following mechanisms best explains how the reduction in chromosome number may have occurred? I. End-to-end fusion of two chromosomes followed by inactivation of one centromere on the newly formed chromosome II. Breakage of a chromosome at the centromere and fusion of the two resulting chromosomal portions to the ends of other chromosomes III. Transfer of a DNA sequence from one chromosomal arm to a different chromosomal arm A) I only B) II only C) I and II only D) I and III only

Answer 227

C Eukaryotic chromosomes have both protein-coding DNA and distinct noncoding regions. Noncoding regions include the centromere (facilitates spindle fiber attachment during cell division) and telomeres (protect chromosomal ends from degradation). Because they are noncoding regions, protein coding function will not be affected.

Question 228

Several techniques have been developed to treat blood disorders caused by genetic mutations. Which of the following methods would be most effective in the treatment of a patient homozygous for a deleterious mutation in a gene coding for a subunit of hemoglobin? A) Replacement of the mutant gene with a functional copy in red blood cells B) Treatment with a drug that increases red blood cell production C) Introduction and activation of a functional hemoglobin gene in bone marrow stem cells D) Single blood transfusion from a patient homozygous for the wild-type hemoglobin gene

Answer 228

C Gene therapy is a technique in which a functional copy of a gene is introduced (via retroviral vectors) into the cells of a patient with a mutation in that gene. Because RBCs are produced from stem cells in the bone marrow, the most effective treatment for this patient would be gene therapy to introduce and activate a functional hemoglobin gene in bone marrow stem cells.

Question 229

A specific recessive X-linked mutation prevents the formation of sweat glands within the skin. Individuals heterozygous for this mutation exhibit mosaic phenotype, with some patches of skin lacking sweat glands and other patches containing a normal distribution of sweat glands. Which of the following statements best explains the genetic mechanism underlying this mosaic phenotype in heterozygous individuals? A) Expression of Y chromosome genes masks expression of the mutant gene B) Genes on paternally inherited X chromosomes are silenced C) All mutant genes on the X chromosome are not expressed D) One X chromosome is inactivated at random in embryonic cells during developement

Answer 229

D The inheritance and expression of sex-linked genes (located on either the X or Y chromosome) differ between males and females. Depending on which X chromosome is inactivated, some embryonic cells will contain an active copy of the wild-type chromosome and some will contain an active copy of the X chromosome with the mutation.

Question 230

Hyperbaric oxygen may be used as a treatment for certain types of bacterial infections. In this therapy, the patient is placed in a chamber in which the partial pressure of oxygen is significantly increased, increasing the partial pressure of oxygen in the patient’s tissues. This treatment is most likely used for infections with: A) Obligate aerobic bacteria B) Facultative anaerobic bacteria C) Aerotolerant anaerobic bacteria D) Obligate anaerobic bacteria

Answer 230

D Obligate anaerobes cannot survive in the presence of oxygen and would likely be killed by such a therapy, treating the infection. The other types of bacteria listed can all survive in the presence of oxygen, so infections involving these bacteria would likely not be treated using this therapy.

Question 231

Which of the following does NOT describe connective tissue cells? A) They account for most cells in muscles, bones, and tendons B) They secrete substances to form the extracellular matrix C) In organs, they tend to form the stroma D) In organs, they provide support for epithelial cells

Answer 231

A While bones and tendons are composed predominantly of connective tissue cells, muscle tissue is considered a different tissue type. Other examples of connective tissue include cartilage, ligaments, adipose tissue, and blood. Connective tissue often secretes substances to form the extracellular matrix, such as collagen and elastin. In organs, connective tissue often forms the support structure for epithelial cells, called the stroma.

Question 232

Which of the following types of nucleic acid could form the genome of a virus? I. Single-stranded RNA II. Double-stranded DNA III. Single-stranded DNA A) I only B) II only C) I and II only D) I, II, and III

Answer 232

D In a virus, the nucleic acid can be either DNA or RNA and (in both cases) can be single or double-stranded. Therefore, all of the types of nucleic acids listed could be used for a viral genome.

Question 233

Which of the following activities occurs in the Golgi apparatus? A) Synthesis of proteins B) Modification and distribution of proteins C) Breakdown of lipids and carbohydrates D) Production of ATP

Answer 233

B The Golgi apparatus consists of a stack of membrane enclosed sacs. It receives vesicles and their contents from the endoplasmic reticulum, modifies them (through glycosylation, phosphorylation, and other mechanisms), repackages them into vesicles, and distributes them to appropriate locations in the cell. Protein synthesis occurs in ribosomes and rough endoplasmic reticulum. Lipid and carbohydrate breakdown takes places in the peroxisomes and cytoplasm. ATP production in the mitochondria.

Question 234

Mitochondrial DNA is: I. Circular II. Self-replicating III. Single-stranded A) I only B) II only C) I and II only D) I, II, and III

Answer 234

C Mitochondria are thought to have evolved from an anaerobic prokaryote engulfing an aerobic prokaryote and establishing a symbiotic relationship; therefore, mitochondrial DNA, or mDNA, is likely to be similar to bacterial DNA. Both mDNA and bacterial DNA are organized into a single circular chromosome of double-stranded DNA that can replicate during binary fission.

Question 235

Which of the following is NOT a function of the smooth endoplasmic reticulum? A) Lipid synthesis B) Poison detoxification C) Protein synthesis D) Transport of proteins.

Answer 235

C The smooth endoplasmic reticulum is involved in the transport of materials throughout the cell, in lipid synthesis, and in the detoxification of drugs and poisons. Proteins from the rough ER can cross into smooth ER, where they are secreted into cytoplasmic vesicles and transported to the Golgi apparatus. However, protein synthesis is not a function of the smooth ER, but rather of the free ribosomes or the ribosomes associated with the rough ER.

Question 236

What is the main function of the nucleolus? A) Ribosomal RNA synthesis B) DNA replication C) Cell division D) Chromosome assembly

Answer 236

A The nucleolus (not to be confused with the nucleus) is a dense structure within the nucleus where ribosomal RNA (rRNA) is synthesized.

Question 237

Which of the following organelles is surrounded by a single membrane? A) Lysosomes B) Mitochondria C) Nuclei D) Ribosomes

Answer 237

A Lysosomes are vesicular organelles that digest material using hydrolytic enzymes. They are surrounded by a single membrane. Both mitochondria and nuclei are surrounded by double membranes. Ribosomes must not be surrounded by membranes because they are found not only in eukaryotes but also in prokaryotes, which lack any membrane-bound organelles.

Question 238

Which of the following is NOT a difference that would allow one to distinguish a prokaryotic and a eukaryotic cell? A) Ribosomal subunit weight B) Presence of a nucleus C) Presence of a membrane on the outside surface of the cell D) Presence of membrane-bound organelles

Answer 238

C Some of the main differences between prokaryotes and eukaryotes are that prokaryotes do not have a nucleus, while eukaryotes do; prokaryotes have ribosomal subunits of 30S and 50S, while eukaryotes have subunits consisting of 40S and 60S. Prokaryotes do not have membrane-bound organelles, whereas eukaryotes do. The presence of a membrane on the outer surface of the cell could not distinguish between the two because both gram-negative bacteria and animal cells share this feature.

Question 239

A patient presents to the emergency room with an asthma attack. The patient has been hyperventilating for the past hour and has a blood pH of 7.52. The patient is given treatment and does not appear to respond, but a subsequent blood pH reading is 7.41. Why might this normal blood pH NOT be a reassuring sign? A) The patient’s kidneys may have compensated for the alkalemia B) The normal blood pH reading is likely inaccurate C) The patient may be descending into respiratory failure D) The patient’s blood should ideally become acidemic for some time to compensate for the alkalemia

Answer 239

C When a patient with an asthma attack does not respond to treatment and has been hyperventilating for over an hour, he or she may become fatigued and may not be able to maintain hyperventilation. In this case, the patient begins to decrease his or her breathing rate and is not receiving adequate oxygen. By extension, carbon dioxide is trapped in the blood, and the pH begins to drop. Despite the fact that this pH is normal at the moment, this patient is crashing and may start demonstrating acidemia in the near future. While the kidneys should compensate for alkalemia, this is a slow process and would not normalize the blood pH within an hour; further, adequate compensation by the kidneys would actually be a reassuring sign. After treatment, the patient should return to a normal blood pH with adequate ventilation and would not be expected to overcompensate by becoming acidemic.

Question 240

Suppose that in a mammalian species, the allele for black hair (B) is dominant to the allele for brown hair (b), and the allele for curly hair (C) is dominant to the allele for straight hair (c). When an organism of unknown genotype is crossed against one with straight, brown hair, the phenotypic ratio is as follows: 25% curly black hair 25% straight black hair 25% curly brown hair 25% straight brown hair What is the genotype of the unknown parent? A) BbCC B) bbCc C) Bbcc D) BbCc

Answer 240

D In this dihybrid problem, a doubly recessive individual is crossed with an individual of unknown genotype; this is known as a test cross. The straight and brown-haired organism has the genotype bbcc and can thus only produce gametes carrying bc. Looking at F1 offspring, there is a 1:1:1:1 phenotypic ratio. The fact that both the dominant and recessive traits are present in the offspring means that the unknown parental genotype must contain both dominant and recessive alleles for each trait. The unknown parental genotype must therefore be BbCc.

Question 241

Which of the following does NOT contain tubulin? A) Cilia B) Flagella C) Microfilaments D) Centrioles

Answer 241

C Tubulin is the primary protein in microtubules, which are responsible for the structure and movement of cilia and flagella. Centrioles organize microtubules into the mitotic spindle. Microfilaments are NOT composed of tubulin, but rather actin.

Question 242

Herpes simplex virus (HSV) enters the human body and remains dormant in the nervous system until it produces an outbreak after exposure to heat, radiation, or other stimuli. Which of the following statements correctly describes HSV? A) While it remains dormant in the nervous system, the virus is in its lytic cycle B) During an outbreak, the virus is in the lysogenic cycle C) Herpes simplex virus adds its genetic information to the genetic information of the cell D) The herpes simplex virus contains a tail sheath and tail fibers

Answer 242

C Viruses can exist in either the lytic or lysogenic cycle; they may even switch between them. During the lytic cycle, the virus's DNA takes control of the host cell's genetic machinery, manufacturing numerous progeny. In the end, the host cell bursts (lyses) and release new virions, each capable of infecting other cells. In the lysogenic cycle, DNA is added to the host cell's genome, where it can remain dormant for days or years. Either spontaneously or as a result of environmental circumstances, the provirus can reactivate and enter a lytic cycle. Tail sheaths and fibers describes bacteriophages (viruses infecting bacteria, not humans).

Question 243

Resistance to antibiotics is a well-recognized medical problem. Which mechanism(s) can account for a bacterium's ability to increase its genetic variability and thus adapt itself to resist different antibiotics? I. Binary fission II. Conjugation III. Transduction A) I and II only B) I and III only C) II and III only D) I, II, and III

Answer 243

C Bacterial cells reproduce by binary fission, an asexual process in which the progeny is identical to the parent. Therefore, binary fission does not increase genetic variability. Conjugation can be described as sexual mating in bacteria; it is the transfer of genetic material between two bacteria that are temporarily joined. Transduction occurs when fragments of the bacterial chromosome accidentally become packaged into a viral progeny produced during a viral infection and are introduced into another bacterium by the viral vector.

Question 244

A bacterial cell is noted to be resistant to penicillin. The bacterium is transferred to a colony that lacks the fertility factor, and the rest of the colony does not become resistant to penicillin. However, the penicillin-resistant cell has also started to exhibit other phenotypic characteristics, including secretion of a novel protein. Which of the following methods of bacterial recombination is NOT likely to account for this change? A) Conjugation B) Transformation C) Transduction D) Infection with a bacteriophage

Answer 244

A A bacterial cell that does not rapidly cause a phenotypic change in the rest of the colony is likely not F+, meaning that this cell is not able to form a sex pilus for conjugation. The expression of new phenotypic characteristics indicate that this bacterium may have acquired genetic material from the environment through transformation, or transduction (during bacteriophage infections).

Question 245

In Alzheimer's disease, a protein called the amyloid precursor protein (APP) is cleaved to form a protein called Beta-amyloid. This protein has a Beta-pleated sheet structure and precipitates to form plaques in the brain. This mechanism of disease is most similar to which of the following pathogens? A) Bacteria B) Viruses C) Prions D) Viroids

Answer 245

C Prions are infectious proteins that cause misfolding of other proteins. Prions generally cause a shift toward Beta-pleated sheet conformations, causing decreased solubility and increased resistance to degradation. This ultimately leads to disease.

Question 246

After infection of a cell, a viral particle must transport itself to the nucleus in order to produce viral proteins. What is the likely genomic content of the virus? A) Double-stranded DNA B) Double-stranded RNA C) Positive-sense RNA D) Negative-sense RNA

Answer 246

A A virus that requires transport to the nucleus in order to produce viral proteins likely requires use of nuclear RNA polymerase in order to create mRNA that can be translated to protein. Therefore, only DNA viruses need to be transported to the nucleus to produce viral proteins.

Question 247

Which of the following is the correct sequence of the development of a mature sperm cell? A) Spermatid -> spermatocyte -> spermatogonium -> 2* spermatocyte -> spermatozoan B) Spermatogonium -> 1* spermatocyte -> 2* spermatocyte -> spermatid -> spermatozoan C) Spermatozoan -> 1* spermatocyte -> 2* spermatocyte -> spermatogonium -> spermatid D) Spermatogonium -> 1* spermatocyte -> 2* spermatocyte -> spermatozoan - > spermatid

Answer 247

B Diploid cells called spermatogonia differentiate into primary spermatocytes, which undergo the first meiotic division to yield two haploid secondary spermatocytes. These undergo a second meiotic division to become immature spermatids. The spermatids then undergo a series of changes leading to the production of mature sperm, or spermatozoa.

Question 248

Which of the following correctly pairs the stage of development of an egg cell with the relevant point in a woman's life cycle? A) From birth to menarche --- prophase II B) At ovulation --- metaphase I C) At ovulation --- metaphase II D) At fertilization --- prophase II

Answer 248

C From the time of birth until shortly before ovulation, all egg cells are arrested at the prophase stage of meiosis I. These cells are referred to as primary oocytes. At ovulation, the egg cell has completed meiosis I and is now arrested in metaphase II as a haploid cell called a secondary oocyte. When a sperm penetrates the outer layers of the secondary oocyte, it completes meiosis II to become a mature ovum.

Question 249

Some studies suggest that in patients with Alzheimer's disease, there is a defect in the way the spindle apparatus attaches to the kinetochore fibers. At which stage of mitotic division would one first expect to be able to visualize this problem? A) Prophase B) Metaphase C) Anaphase D) Telophase

Answer 249

A The spindle apparatus first interacts with the kinetochore fibers near the end of prophase. While the spindle apparatus aligns the chromosomes at the equatorial plate during metaphase, the initial connection of the microtubule to the kinetochore occurs in prophase.

Question 250

A researcher wishes to incorporate a radiolabeled deoxyadenine into the genome of one of the two daughter cells that would arise as a result of mitosis. What is the latest stage of cellular development during which the radiolabeled deoxyadenine could be added to achieve this result? A) G1 B) G2 C) M D) S

Answer 250

D To ensure that the labeled deoxyadenine will be incorporated into the DNA of one of the daughter cells, we have to insert the nucleotide before DNA replication has been completed. Because replication occurs during S stage, we could introduce the deoxyadenine during G1 or S stage. Because G1 precedes S, the latest point at which the deoxyadenine could be added is the S stage.

Question 251

Certain ovarian tumors called granulosa cell tumors are known to produce excessive levels of estrogen. A physician who diagnoses a granulosa cell tumor should look for a secondary cancer in which of the following parts of the reproductive tract? A) Fallopian tube B) Cervix C) Endometrium D) Uterus

Answer 251

C Estrogen is known to cause growth of the endometrial lining during the follicular phase of the menstrual cycle, and its levels stay high during the luteal phase to promote vascularization and glandularization of this tissue. Excessive levels of estrogen may provide a strong enough signal for cell growth to promote tumor formation or even cancer. The other tissues listed require estrogen for development, but are not strongly dependent on estrogen for growth.

Question 252

Upon ovulation, the oocyte is released into the: A) Fallopian tube B) Follicle C) Abdominal cavity D) Uterus

Answer 252

C This subtle point about ovulation is missed by most students and remains hard to believe until the organs are examined in anatomy class in medical school. The ruptured ovarian follicle releases an oocyte into the abdominal cavity, close to the entrance of the fallopian tube. With the aid of beating cilia, the oocyte is drawn into the fallopian tube, through which it travels until it reaches the uterus. If it is fertilized in the fallopian tube, it will implant in the uterine wall. If fertilization does not occur, it will be expelled along with the uterine lining during menstruation.

Question 253

Cancer cells are cells in which mitosis occurs continuously, without regard to quality or quantity of cells produced, For this reason, most chemotherapies attack rapidly dividing cells. At which point(s) in the cell cycle would chemotherapy effectively prevent cancer cell division? I. S stage II. Prohpase III. Metaphase A) I only B) I and II only C) II and III only D) I, II, and III

Answer 253

D The question is asking us to determine at which points in the cell cycle we can prevent or at least lower the number of cells undergoing mitosis. One idea would be to prevent DNA synthesis during the S stage of the cell cycle. Without the DNA being replicated, two viable daughter cells could not be formed. Other ideas would be preventing the mitotic cycle from forming altogether in prophase by preventing spindle apparatus formation, preventing the nuclear membrane from dissolving, or interfering with other processes during this phase. Similarly, a treatment that would act on cells in the metaphase stage of the cycle would also interfere with the mitotic cycle. Therefore, any of the three solutions presented would be a viable option.

Question 254

Which of the following INCORRECTLY pairs a structure of the male reproductive system with a feature of the structure? A) Seminal vesicles -- produce alkaline fructose-containing secretions B) Epididymis -- surrounded by muscle to raise and lower the testes C) Vas deferens -- tube connecting the epididymis to the ejaculatory duct D) Cowper's gland -- produce a fluid to clear traces of urine in the urethra

Answer 254

B The epididymis is the site of sperm maturation at the posterior side of the testes. In the epididymis, sperm gain mobility and are stored until ejaculation. It is the vas deferens (ductus deferens) that is surrounded by muscle that raises and lowers the testes to maintain a constant temperature suitable for sperm production, not the epididymis.

Question 255

What is the last point in the meiotic cycle in which the cell has a diploid number of chromosomes? A) During interphase B) During telophase I C) During interkinesis D) During telophase II

Answer 255

B The first meiotic division (reductional division) pulls homologous chromosomes to opposite poles of the cell during anaphase I. Near the end of telophase I, cytokinesis occurs, resulting in two haploid (n) daughter cells. Thus, during interkinesis and anaphase II, the daughter cells are already haploid. The cell is diploid during interphase, but remains diploid up until the end of telophase I.

Question 256

Which of the following does NOT likely contribute to genetic variability? A) Random fertilization of an egg by a sperm B) Random segregation of homologous chromosomes C) Crossing over between homologous chromosomes during meiosis D) Replication of DNA during S stage

Answer 256

D The random fertilization of an egg by a sperm, the random segregation of homologous chromosomes during anaphase I, and crossing over between homologous chromosomes during prophase I all contribute to genetic variability during sexual reproduction because they result in novel combination of genetic material. S stage, should NOT cause increased genetic variability; the DNA should be copied precisely, without error, meaning that both strands of DNA should be identical.

Question 257

Which of the following statements correctly identifies a key difference between mitosis and meiosis? A) In metaphase of mitosis, replicated chromosomes line up in single file; in metaphase II of meiosis, replicated chromosomes line up on opposite sides of the metaphase plate. B) During anaphase of mitosis, homologous chromosomes separate; during anaphase of meiosis I, sister chromatids separate. C) At the end of telophase in mitosis, the daughter cells are identical to each other; at the end of meiosis I, the daughter cells are identical to the parent cell. D) During metaphase of mitosis, centromeres are present directly on the metaphase plate; during metaphase of meiosis I, there are no centromeres on the metaphase plate.

Answer 257

D The key differences between mitosis and meiosis primarily appear during meiosis I. Of note, synapsis and crossing over occurs during prophase I, and homologous chromosomes are separated during meiosis I (rather than sister chromatids, as in mitosis). While the location of the centromeres relative to the metaphase plate may seem trivial, it is representative of the fact that homologous chromosomes line up on opposite sides of the equatorial plate in meiosis, in contrast to the positioning of each chromosome directly upon the metaphase plate in mitosis.

Question 258

Which of the following is true regarding prophase? A) The chromosomes separate and move to opposite poles of the cell. B) The spindle apparatus disappears C) The chromosomes uncoil D) The nucleoli disappear

Answer 258

D In prophase, the chromatin condenses into chromosomes, the spindle apparatus forms, and the nucleoli and nuclear membrane disappear. (A) describes anaphase, while (B) and (C) describe telophase.

Question 259

An individual who is phenotypically female is found to have only one copy of a disease-carrying recessive allele on the X chromosome, yet she demonstrates all of the classic symptoms of the disease. Geneticists determine she has a genotype that likely arose from nondisjunction in one of her parents. What is the likely genotype of this individual? A) 46, XX (46 chromosomes, with XX for sex chromosomes) B) 46, XY C) 45, X D) 47, XXY

Answer 259

C Nondisjunction refers to the incorrect segregation of homologous chromosomes during anaphase I, or of sister chromatids during anaphase II. In either case, one daughter cell ends up with two copies of related genetic material, while the other receives zero. An individual who has only one recessive disease-carrying allele, and yet still expresses the disease, likely does not have a dominant allele for the given trait. This is seen in males, who are hemizygous for many X-linked genes, and can also be seen in women with Turner syndrome (45, X), who have one X chromosome.

Question 260

During which phase of the menstrual cycle does progesterone concentration peak? A) Follicular phase B) Ovulation C) Luteal phase D) Menses

Answer 260

C Progesterone peaks during the luteal phase, as it supports the endometrium for potential implantation of a blastula. Progesterone levels are relatively low during the follicular phase and ovulation. Withdrawal of progesterone actually causes menses.

Question 261

Which of the following would NOT be seen during pregnancy? A) High levels of hCG in the first trimester B) High levels of progesterone throughout the pregnancy C) Low levels of FSH in the first trimester D) High levels of GnRH throughout the pregnancy

Answer 261

D During the first trimester of pregnancy, the corpus luteum is preserved by human chorionic gonadotropin (hCG); hence, progesterone secretion by the corpus luteum is maintained during the first trimester. During the second trimester, hCG levels decline, but progesterone levels rise because the hormone is now secreted by the placenta itself. High levels of progesterone and estrogen inhibit GnRH secretion, thus preventing FSH and LH secretion and the onset of a new menstrual cycle.

Question 262

Which the following developmental stages has the greatest nuclear-to-cytoplasmic ratio? A) Eight-cell embryo B) Morula C) Blastula D) Zygote

Answer 262

C During the series of rapid mitotic divisions known as cleavage, the number of cells increases dramatically but the overall volume of the embryo does not change. In fact, the volume of the embryo does not significantly increase until after the blastula has already implanted. Therefore, a high ratio of nuclear to cytoplasmic material will be found at the stage with the greatest number of cells during early development. From the given choices, the stage with the greatest number of cells is the blastula. This is further supported by the fact that the cells are displaced from the center by the blastocoel.

Question 263

Which of the following associations of a primary germ layer and an adult organ is correct? A) Endoderm -- Cardiac muscle B) Endoderm -- Lens of the eye C) Ectoderm -- Fingernails D) Mesoderm -- Lining of the digestive tract

Answer 263

C The ectoderm gives rise to the integument (the epidermis, hair, nails, and the epithelia of the nose, mouth, and anal canal), the lens of the eye, and the nervous system (including the adrenal medulla). The endoderm gives rise to the epithelial lining of the digestive and respiratory tracts and parts of the liver, pancreas, thyroid, and bladder. Finally, the mesoderm gives rise to the musculoskeletal system, the circulatory system, the excretory system, the gonads, and the adrenal cortex.

Question 264

From which of the following layers does the notochord form? A) Ectoderm B) Mesoderm C) Endoderm D) Archenteron

Answer 264

B A rod of mesodermal cells called the notochord develops along the longitudinal axis just under the dorsal layer of the ectoderm. Through inductive effects from the notochord, the overlying ectoderm starts bending inward and forms a groove on the dorsal surface of the embryo. The dorsal ectoderm will eventually pinch off and develop into the spinal cord and brain. While the neural tube forms from ectoderm, the notochord itself is mesodermal.

Question 265

The influence of a specific group of cells on the differentiation of another group of cells is called: A) Competence B) Senescence C) Determination D) Induction

Answer 265

D The eyes are formed through reciprocal induction between the brain and the ectoderm. Competence refers to the ability of a cell to respond to a given inducer, but not the influence of the group of organizing cells. Senescence is a term for biological aging. Determination may be the result of induction, but this term does not refer to the general concept of the effect of one group of cells on the differentiation of another group of cells.

Question 266

Which of the following is likely to be found in maternal blood during pregnancy? A) Immunoglobulins produced by the fetus B) Fetal hemoglobin released from fetal red blood cells C) Progesterone produced by placental cells D) Carbon dioxide exhaled from fetal lungs

Answer 266

C During pregnancy, the placenta produces estrogen and progesterone to maintain the endometrium. These hormones are necessary for proper gestation of the fetus and should be measurable in maternal blood because they act on maternal organs. Prior to birth, the fetus is immunologically naive and does not yet produce immunoglobulins. Fetal hemoglobin is a large protein and, thus, cannot easily cross the placenta as well as red blood cells themselves. Carbon dioxide from fetal metabolism can be found in maternal blood, but the fetal lungs are nonfunctional prior to birth as the fetus is suspended in amniotic fluid. Carbon dioxide is transferred across the placenta directly from the fetal bloodstream.

Question 267

A cell releases a substance that diffuses through the environment, resulting in differentiation of a nearby cell. This is an example of what type of cell-cell communication? A) Autocrine B) Juxtacrine C) Paracrine D) Endocrine

Answer 267

C Because the cell is acting on a nearby cell and the molecule spreads by diffusion, this is an example of paracrine signaling. Autocrine signaling occurs when a molecule secreted by a cell acts on the same cell. Juxtacrine signaling occurs between adjacent cells, but the signal does not spread by diffusion. In endocrine signaling, a molecule is secreted that travels via the bloodstream to a distant target.

Question 268

A cancer cell is removed from a patient and cultured. The cells in this culture seem to be able to divide indefinitely with no cellular senescence. Which protein is likely activated in these cells that accounts for this characteristic? A) Epidermal growth factor B) Sonic hedgehog C) Transforming growth factor beta D) Telomerase

Answer 268

D Cells that are able to divide indefinitely with no senescence are not exhibiting normal cell behavior. Normally, somatic cells divide a limited number of times until telomeres become too short to be effective protectors of genomic material. When this occurs, cells stop dividing. However, in this case, the cells have continued to divide indefinitely. It is likely that the enzyme telomerase has been activated, which allows for synthesis of telomeres to counteract shortening during DNA replication.

Question 269

A tumor is removed from a patient and when investigated by pathologists, appears to contain tissue resembling placenta, hair, thyroid tissue, and cardiac muscle. What was the likely potency of the cells from which the tumor originated? A) Nonpotent B) Multipotent C) Pluripotent D) Totipotent

Answer 269

D This question stem describes a tumor composed of multiple types of embryonic tissues as well as tissues derived from all three germ layers. Because this tumor contains placental tissue, the tumor must have originated from a cell that was able to produce those types of tissues. Cells capable of producing placental tissue as well as ectoderm, mesoderm, and endoderm are, by definition, totipotent.

Question 270

Which of the following is FALSE with regard to adult stem cells? A) They retain inherent pluripotency if harvested from selected organs. B) They are less controversial than embryonic stem cells. C) They require treatment with various transcription factors. D) There is a reduced risk of rejection if the patient's own stem cells are used.

Answer 270

A Embryonic stem cells are controversial because they require the destruction of an embryo to harvest. Adult stem cells are significantly less controversial, but require treatment with various transcription factors in order to increase the level of potency. Rejection is a concern when foreign cells are introduced into an individual; using one's own stem cells should remove this risk. Adult stem cells are not naturally pluripotent, unless pluripotency has been introduced by strategic use of transcription factors.

Question 271

A child is born with an imperforate anus, in which the anal canal fails to form correctly and the rectum is not connected to the outside world. This pathology is most likely accounted for by a failure of: A) Cell differentiation B) Cell determination C) Apoptosis D) Neurulation

Answer 271

C During development, programmed cell death occurs in multiple locations in order to ensure development of the correct adult structures. One of the places in which this occurs is between fingers and toes; another is in the digestive tract, where a central lumen is formed. If apoptosis does not occur correctly in the digestive tract, an imperforate anus could result. Failure of determination or differentiation would likely result in the absence of anorectal structures altogether. Failure of neurulation would lead to the absence of a nervous system and would not be compatible with life.

Question 272

Following a myocardial infarction, the heart often heals by the creation of a scar by fibroblasts. This is an example of: A) Complete regeneration B) Incomplete regeneration C) Competency D) Multipotency

Answer 272

B After an injury, healing occurs by some sort of regenerative process. In humans, some tissues, such as the liver, are capable of regenerating tissue with much the same function and structure as the original tissue. However, the heart is not capable of this sort of regeneration, often forming a fibrous scar in an area of injury. This is an example of incomplete regeneration, in which newly formed tissues are not identical in structure or function to the tissues that have been injured or lost.

Question 273

Neurofibromatosis type I, or von Recklinghausen's disease, is a disorder that causes formation of tumors in multiple nervous system structures as well as the skin. While all cells carry the same mutation on chromosome 17, selective transcription of the genome appears to cause the most significant tumorigenesis in which of the following primary germ tissue layers? A) Ectoderm B) Mesoderm C) Endoderm D) Notochord

Answer 273

A Here, the mutation affects the skin and nervous system, both of which are derived from ectoderm. The other germ tissue layers do not lead to skin or nervous system formation. The notochord is not actually a primary germ tissue layer, and thus cannot be an answer to the question.

Question 274

Which of the following shows the correct order of early development milestones during embryogenesis? A) Blastula -> gastrula -> morula B) Morula -> gastrula -> blastula C) Morula -> blastula -> gastrula D) Gastrula -> blastula -> morula

Answer 274

C After the first cell divisions occur, the embryo consists of a solid ball of cells known as a morula. Then a hollow center forms, creating a blastula. Finally, as the cells begin to differentiate into the three germ layers, the embryo is considered a gastrula.

Question 275

A pregnant woman is accidentally given a single dose of a teratogenic drug late in the third trimester. The baby is born three days later. Which of the following is the most likely outcome? A) Complete failure of organ development and death of the fetus B) Partial failure of organ development with survival of the fetus C) Serious disfigurement of the fetus D) Respiratory distress at birth, but no long-term effects

Answer 275

D It is important to remember that organogenesis occurs during the first trimester. The last structure to become fully functional is the lungs. Because the organs were already largely formed prior to the administration of the teratogenic drug, it is likely that there was no major effects on the development of most organs as a result of exposure to the teratogen. However, because lung tissues are so sensitive and because they mature so late, it is likely that the infant may have some respiratory distress at birth.

Question 276

Which of the following statements regarding fetal circulation is FALSE? A) In the umbilical cord, there are more arteries than veins. B) The foramen ovale is the only shunt that connects two chambers of the heart. C) Blood flow in the ductus arteriosus is from the aorta to the pulmonary artery. D) The ductus venosus is the only shunt that bypasses the liver

Answer 276

C Blood flow in the ductus arteriosus is from the pulmonary artery to the aorta. The direction of flow is determined by the pressure differential between the right side of the heart (and pulmonary circulation) and the left side of the heart (and system circulation). Unlike in adults, the right side of the heart is at a higher pressure during prenatal life than the left side, so blood will shunt from the pulmonary circulation to the systemic circulation through both the foramen ovale and ductus arteriosus.

Question 277

Resting membrane potential depends on: I. Differential distribution of ions across the axon membrane II. The opening of voltage-gated calcium channels III. Active transport of ions across the membrane A) I only B) I and II only C) I and III only D) II and III only

Answer 277

C The polarization of the neuron at rest is the result of an uneven distribution of ions between the inside and outside of the cell. This difference is achieved through the active pumping of ions into and out of the neuron (using NA+/K+ ATPase). Voltage-gated calcium channels are important in the nerve terminal, where the influx of calcium triggers the fusion of vesicles containing neurotransmitter with the membrane, but not in maintaining resting membrane potential.

Question 278

All of the following are associated with the myelin sheath EXCEPT: A) Faster conduction of nerve impulses B) Nodes of Ranvier forming gaps along the axon C) Increased magnitude of the potential difference during an action potential D) Saltatory conduction of action potential

Answer 278

C Myelin is the white lipid-containing material surrounding the axons of many neurons in the central and peripheral nervous systems. It is arranged on the axon discontinuously; the gaps between the segments of myelin are called Nodes of Ranvier. Myelin increases the conduction velocity by insulating segments of the axon so that the membrane is permeable to ions only at the Nodes of Ranvier. The action potential jumps from node to node, a process known as saltatory conduction. Action potentials are often described as being "all-or-nothing"; the magnitude of the potential difference of an action potential is fixed, regardless of the intensity of the stimulus. Thus, myelin does not affect the magnitude of the potential difference in an action potential.

Question 279

Which of the following is true with regard to the action potential? A) All hyperpolarized stimuli will be carried to the axon terminal without a decrease in size. B) The size of the action potential is proportional to the size of the stimuli that produced it. C) Increasing the intensity of the depolarization increases the size of the stimuli. D) Once an action potential is triggered, an impulse of a given magnitude and speed is produced.

Answer 279

D The action potential is often described as an "all-or-nothing" response. This means that, whenever the threshold membrane potential is reached, an action potential with a consistent size and duration is produced. Neuronal information is coded by the frequency and number of action potentials, not the size of the action potential. Hyperpolarization (inhibitory) signals are not transmitted to the nerve terminal.

Question 280

Which of the following correctly describes a difference between nerve and tracts? A) Nerves are seen in the central nervous system and tracts are seen in the peripheral nervous system. B) Nerve cells have cell bodies in nuclei; tracts have cell bodies in ganglia. C) Nerves may carry more than one type of information; tracts can only carry one type of information. D) Nerves contain only one neuron; tracts contain many neurons.

Answer 280

C Nerves are collections of neurons in the peripheral nervous system and may contain multiple types of information (sensor or motor); they contain cell bodies in ganglia. Tracts are collections of neurons in the central nervous system and contain only one type of information; they contain cell bodies in nuclei.

Question 281

Which of the following accurately describes sensory neurons? A) Sensory neurons are afferent and enter the spinal cord on the dorsal side. B) Sensory neurons are efferent and enter the spinal cord on the dorsal side. C) Sensory neurons are afferent and enter the spinal cord on the ventral side. D) Sensory neurons are efferent and enter the spinal cord on the ventral side.

Answer 281

A Sensory neurons are considered afferent (carrying signals from the periphery to the central nervous system) and enter the spinal cord on the dorsal side. Motor neurons are considered efferent (carrying signals from the central nervous system to the periphery) and exit the spinal cord on the ventral side.

Question 282

When a sensory neuron receives a stimulus that brings it to threshold, it will do all of the following EXCEPT: A) Become depolarized B) Transduce the stimulus to an action potential C) Inhibit the spread of the action potential to other sensory neurons D) Cause the release of neurotransmitters onto cells in the central nervous system

Answer 282

C When a sensory neuron receives a signal that is strong enough to bring it to threshold, one can assume that the receptor becomes depolarized, allowing it to transduce the stimulus to an action potential. The action potential will then be carried by sensory neurons to the central nervous system, where the cell will release neurotransmitters. If a receptor is stimulated, it will promote the spread of the action potential to postsynaptic sensory neurons in the spinal cord, which can send the signal toward the brain.

Question 283

When the potential across the axon membrane is more negative than the normal resting potential, the neuron is said to be in a state of: A) Depolarization B) Hyperpolarization C) Repolarization D) Polarization

Answer 283

B When the potential across the axon membrane is more negative than the normal resting potential, the neuron is referred to as hyperpolarized. Hyperpolarization occurs right after an action potential and is caused by excess potassium exiting the neuron.

Question 284

Which of the following statements concerning the somatic division of the peripheral nervous system is INCORRECT? A) Its pathways innervate skeletal muscle B) Its pathways are usually voluntary C) Some of its pathways are referred to as reflex arcs D) Its pathways always involve more than two neurons

Answer 284

D The somatic division of the peripheral nervous system innervates skeletal muscles and is responsible for voluntary movement. Some of the pathways in this part of the nervous system are reflex arcs, which are reflexive responses to certain stimuli that involve only a sensory and a motor neuron. These neurons synapse in the spinal cord and do not require signaling from the brain. The pathways of the somatic division can involve two, three, or more neurons, depending on the type of signal.

Question 285

Which of the following is a function of the parasympathetic nervous system? A) Increasing blood sugar during periods of stress B) Dilating the pupils to enhance vision C) Increasing oxygen delivery to muscles D) Decreasing heart rate and blood pressure

Answer 285

D The parasympathetic nervous system governs the "rest-and-digest" response. The parasympathetic nervous system slows the heart rate, decreases blood pressure, promotes blood flow to the GI tract, and constricts the pupils, among other functions. The sympathetic nervous system governs the "fight-or-flight" response, including increased heart rate and blood pressure, decreased blood flow to the digestive tract, and increased blood flow to the muscles.

Question 286

Which of the following neurotransmitters is used in the ganglia of both the sympathetic and parasympathetic nervous system? A) Acetylcholine B) Dopamine C) Norepinephrine D) Serotonin

Answer 286

A Acetylcholine is the neurotransmitter released by the preganglionic neuron in both the sympathetic and parasympathetic nervous systems. The postganglionic neuron in the sympathetic nervous system usually releases norepinephrine, while the postganglionic neuron in the parasympathetic nervous system releases acetylcholine.

Question 287

In which neural structure are ribosomes primarily located? A) Dendrites B) Soma C) Axon Hillock D) Axon

Answer 287

B Neurons contain very specialized structures, including dendrites, axons, and the axon hillock. However, neurons are still cells and must carry out cellular functions including protein synthesis. The cell body or soma contains the nucleus, endoplasmic reticulum, and ribosomes.

Question 288

An autoimmune disease attacks the voltage-gated calcium channels in the synaptic terminal of an excitatory neuron. What is a likely symptom of this condition? A) Spastic paralysis (inability to relax the muscles) B) Flaccid paralysis (inability to contract the muscles) C) Inability to reuptake neurotransmitters once released D) Retrograde flow of action potentials

Answer 288

A When the nerve terminal depolarizes, voltage-gated calcium channels open, allowing for influx of calcium. This influx of calcium triggers fusion of synaptic vesicles containing neurotransmitters with the membrane of the neuron at the nerve terminal. This allows for exocytosis of the neurotransmitters into the synapse. If a disease blocked the influx of calcium, there would be not release of neurotransmitters. A lack of neurotransmitters means that the neuron cannot send excitatory signals. Thus, any symptoms resulting from this disease would be due to an inability of neurons to transmit excitatory signals to the muscle. If neurons cannot communicate, flaccid paralysis may be one of the results.

Question 289

A neuron only fires an action potential if multiple presynaptic cells release neurotransmitter onto the dendrites of the neuron. This is an example of: A) Saltatory conduction B) Summation C) A feedback loop D) Inhibitory transmission

Answer 289

B Some neurons require multiple instances of excitatory transmission to be brought to threshold. These excitatory signals may be close to each other in time (temporal) or in space (spatial); either way, this pattern of excitation is termed summation.

Question 290

A disease results in the death of Schwann cells. Which portion of the nervous system is NOT likely to be affected? A) Central nervous system B) Somatic nervous system C) Autonomic nervous system D) Parasympathetic nervous system

Answer 290

A Schwann cells are responsible for myelination of cells in the peripheral nervous system. Thus, the central nervous system is unlikely to be affected. The peripheral nervous system includes the somatic nervous system and the autonomic nervous system. The autonomic nervous system is composed of both the parasympathetic and sympathetic nervous systems.

Question 291

A surgeon accidentally clips a dorsal root ganglion during a spinal surgery. What is a likely consequence of this error? I. Loss of motor function at that level II. Loss of sensation at that level III. Loss of cognitive function A) I only B) II only C) I and II only D) I, II, and III

Answer 291

B The dorsal root ganglion contains cell bodies of sensory neurons only. If a dorsal root ganglion is disrupted at a certain level, there will be loss of sensation at that level.

Question 292

Which of the following associations between a hormone and its category is INCORRECT? A) Aldosterone - mineralocorticoid B) Testosterone - cortical sex hormone C) ADH - mineralocorticoid D) Cortisone - glucocorticoid

Answer 292

C Unlike the other hormones, ADH is not secreted by the adrenal cortex and is therefore not a -corticoid. Rather, ADH is a peptide hormone produced by the hypothalamus and released by the posterior pituitary that promotes water reabsorption.

Question 293

Which of the following hormones directly stimulates a target tissue that is NOT an endocrine organ? A) ACTH B) TSH C) LH D) GH

Answer 293

D A hormone that directly stimulates a non-endocrine target tissue is referred to as a direct hormone. Glancing at the answer choices, we notice that all of the hormones are secreted by the anterior pituitary gland. The direct hormones secreted by the anterior pituitary are prolactin, endorphins, and growth hormone (GH). The tropic hormones of the anterior pituitary including follicle-stimulating hormone (FSH), luteinizing hormone (LH), adrenocorticotropic hormone (ACTH), and thyroid-stimulating hormone (TSH).

Question 294

Increased synthetic activity of the parathyroid glands would lead to: A) An increase in renal calcium reabsorption B) A decrease in the rate of bone resorption C) A decrease in basal metabolic rate D) A decrease in blood glucose concentration

Answer 294

A The parathyroid glands secrete parathyroid hormone (PTH), a hormone that functions to increase blood calcium levels. An increase in synthetic activity of the parathyroid glands would lead to an increase in PTH and, therefore, an increase in blood calcium levels through three mechanisms: increased calcium reabsorption in the kidneys (decreased excretion), increased bone resorption, and increased absorption of calcium from the gut (via activation of vitamin D).

Question 295

Which of the following statements concerning growth hormone is NOT true? A) Overproduction of growth hormone in adults results in acromegaly. B) It promotes growth of bone and muscle. C) It is produced by the hypothalamus but secreted by the pituitary. D) A childhood deficiency in growth hormone results in dwarfism.

Answer 295

C Growth hormone is a direct hormone secreted by the anterior pituitary. Among its many functions, GH promotes growth of bone and muscle. An overproduction of growth hormone in children results in gigantism, whereas in adults it results in acromegaly (enlargement of the small bones in the extremities and of certain facial bones, such as the jaw). On the other hand, a childhood deficiency of growth hormone results in dwarfism. GH is synthesized and secreted in the anterior pituitary; the hypothalamus synthesizes antidiuretic hormone and oxytocin, not GH.

Question 296

Iodine deficiency may result in: A) Galactorrhea B) Cretinism C) Gigantism D) Hyperthyroidism

Answer 296

B Inflammation of the thyroid or iodine deficiency can cause hypothyroidism, in which the thyroid hormones are under-secreted or not secreted at all. Hypothyroidism in newborn infants causes cretinism, which is categorized by poor neurological and physical development (including mental retardation, short stature, and coarse facial features). While iodine deficiency can result in a swelling of the thyroid gland (called a goiter), which can also be seen in causes of hyperthyroidism, iodine deficiency does not cause hyperthyroidism. Galactorrhea is associated with prolactin; gigantism is associated with growth hormone.

Question 297

A patient has a very high TSH level. Which of the following would NOT cause a high TSH level? A) Autoimmune destruction of thyroid cells that produce T3 and T4. B) A tumor in the hypothalamus that secretes high levels of TRH. C) High levels of T4 from thyroid replacement medications. D) Cancerous growth of parafollicular cells in the thyroid, destroying other types in the organ.

Answer 297

C The hypothalamic-pituitary-thyroid axis includes the secretion of thyroid-releasing hormone (TRH) from the hypothalamus triggering the secretion of thyroid-stimulating hormone (TSH) from the anterior pituitary, which stimulates the secretion of triiodothyronine (T3) and thyroxine (T4) from the thyroid. Overproduction of TRH would promote overproduction of TSH. Destruction of the follicular cells that produce T3 and T4 would remove negative feedback, allowing TSH levels to rise. High levels of T4 would cause too much negative feedback and lower TSH levels.

Question 298

Which of the following hormones is NOT derived from cholesterol? A) Aldosterone B) Estrogen C) Oxytocin D) Progesterone

Answer 298

C Steroid hormones are derived from cholesterol. Many of their names end with -one, -ol, or -oid, and they include the hormones of the adrenal cortex and gonads. Aldosterone is a mineralocorticoid from the adrenal cortex, while estrogen and progesterone are sex hormones from the ovaries. Oxytocin is a peptide hormone and is thus not derived from cholesterol. Peptide and amino acid-derivative hormones often end with -in or -ine.

Question 299

Which of the following is true regarding pancreatic somatostatin? A) Its secretion is increased by low blood glucose. B) It is always inhibitory C) It is regulated by cortisol levels. D) It stimulates insulin and glucagon secretion.

Answer 299

B Pancreatic somatostatin secretion is increased by high blood glucose or amino acid levels, leading to decreased insulin and glucagon secretion. Somatostatin is thus always an inhibitory hormone. The stimuli for somatostatin release include high blood glucose or amino acids, as well as high levels of certain gastrointestinal hormones, but not cortisol.

Question 300

Destruction of Beta-cells in the pancreas would cause: A) Glucagon secretion to stop and an increase in blood glucose concentration B) Glucagon secretion to stop and a decrease in blood glucose concentration C) Insulin secretion to stop and an increase in blood glucose concentration D) Insulin secretion to stop and a decrease in blood glucose concentration

Answer 300

C Beta-cells are responsible for insulin production. The function of insulin is to lower blood glucose levels by promoting the influx of glucose into cells and by stimulating anabolic processes, such as glycogenesis or fat and protein synthesis. Thus, destruction of Beta-cells would result in a cessation of insulin production, which would lead to hyperglycemia, or high blood glucose concentration.

Question 301

Which of the following is FALSE regarding aldosterone regulation? A) Renin converts the plasma protein angiotensinogen to angiotensin I. B) Angiotensin II stimulates the adrenal cortex to secrete aldosterone. C) Angiotensin I is converted to angiotensin II by angiotensin-converting enzyme. D) A decrease in blood oxygen concentrations stimulates renin production.

Answer 301

D The stimulus for renin production is low blood pressure, which causes the juxtaglomerular cells of the kidney to produce renin, an enzyme that converts the plasma protein angiotensinogen to angiotensin I. Angiotensin I is then converted to angiotensin II by an enzyme in the lungs; angiotensin II then stimulates the adrenal cortex to secrete aldosterone. Aldosterone helps to restore blood volume by increasing sodium reabsorption in the kidney, leading to an increase in water reabsorption. This removes the initial stimulus for renin production. A decrease in blood oxygen concentration describes the stimulus for erythropoietin secretion.

Question 302

A scientist discovers a new hormone that is relatively large in size and triggers the conversion of ATP to cAMP. Which of the following best describes the type of hormone that was discovered? A) Amino acid-derivative hormone B) Peptide hormone C) Steroid hormone D) Tropic hormone

Answer 302

B The newly discovered hormone functions as a first messenger, stimulating the conversion of ATP to cAMP; cAMP functions as a second messenger, triggering a signaling cascade in the cell. Hormones that act via second messengers and are relatively large in size (short peptides or complex polypeptides) are peptide hormones. This hormone could be a tropic hormone, but it is also entirely possible for it to be a direct hormone.

Question 303

A patient presents with muscle weakness, slow movement, and calcium deposits in his tissues. A blood test reveals very low calcium levels in the blood. Administration of which of the following would be an appropriate treatment for the blood test findings? A) Calcitonin B) Parathyroid hormone C) Aldosterone D) Thymosin

Answer 303

B Regardless of the cause, the low levels of calcium in the blood require treatment. While other therapies are more frequently used to treat hypocalcemia (low blood calcium levels), such as calcium gluconate or calcium chloride, administration of parathyroid hormone would also raise blood calcium concentration. Calcitonin would be a poor choice in this case, as this hormone lowers blood calcium concentrations. Aldosterone and thymosin play no role in calcium homeostasis.

Question 304

Oxytocin and antidiuretic hormone are: A) Peptide hormones produced and released by the pituitary. B) Steroid hormones produced and released by the pituitary. C) Peptide hormones produced by the hypothalamus and released by the pituitary. D) Steroid hormones produced by the hypothalamus and released by the pituitary.

Answer 304

C Both oxytocin and vasopressin (another name for antidiuretic hormone) end with the suffix -in; this should hint that they are peptide or amino acid-derivative hormones. These two hormones are both synthesized by the hypothalamus, but released by the posterior pituitary. Remember that the posterior pituitary does not actually synthesize any hormones itself; rather, it contains the axons that originate in cells in the hypothalamus and is the site of release for these hormones.

Question 305

Excessive levels of dopamine in the brain are associated with psychosis. Accordingly, many antipsychotic medications block dopamine receptors. Which of the following effects may be seen in an individual taking antipsychotics? A) Increased secretion of growth hormone B) Decreased secretion of growth hormone C) Increased secretion of prolactin D) Decreased secretion of prolactin

Answer 305

C Dopamine is used in a number of neurological systems; most relevant to the endocrine system is the fact that dopamine secretion prevents prolactin release. Thus, an individual taking medications that block dopamine receptors would lose this inhibition on prolactin release and have elevated prolactin levels.

Question 306

All of the following facilitate gas exchange in the lungs EXCEPT: A) Thin alveolar walls B) Multiple divisions of the respiratory tree C) Differences in the partial pressures of O2 and CO2 D) Active transporters in alveolar cells.

Answer 306

D Gas exchange in the lungs relies on passive diffusion of oxygen and carbon dioxide. This is accomplished easily because there is always a difference in the partial pressures of these two gases and because the subdivision of the respiratory tree creates a large surface area of interaction between the alveoli and the circulatory system. In addition, the thin alveolar walls allow for fast diffusion and gas exchange. Active transport is not used in the gas exchange process in the lungs.

Question 307

Which of the following associations correctly pairs a stage of respiration with the muscle actions occurring during that stage? A) Inhalation - diaphragm relaxes B) Inhalation - internal intercostal muscles contract C) Exhalation - diaphragm contracts D) Exhalation - external intercostal muscles relax

Answer 307

D The muscles involved in ventilation are the diaphragm, which separates the thoracic cavity from the abdominal cavity, and the intercostal muscles. During inhalation, the diaphragm contracts and flattens, while the external intercostal muscles contract, pulling the rib cage up and out. These actions cause an overall increase in the volume of the thoracic cavity. During exhalation, both the diaphragm and the external intercostals relax, causing a decrease in the volume of the thoracic cavity because of the recoil of the tissues. In forced exhalation, the internal intercostals and abdominal muscles may contract to force out air.

Question 308

Total lung capacity is equal to the vital capacity plus: A) Tidal volume B) Expiratory reserve volume C) Residual volume D) Inspiratory reserve volume

Answer 308

C Total lung capacity is equal to the vital capacity (the maximum volume of air that can be forcibly inhaled and exhaled from the lungs) plus the residual volume (the air that always remains in the lungs, preventing the alveoli from collapsing).

Question 309

The intrapleural pressure is necessarily lower than the atmospheric pressure during: A) Inhalation, because the expansion of the chest cavity causes compression of the intrapleural space. B) Inhalation, because the expansion of the chest cavity causes expansion of the intrapleural space. C) Exhalation, because the compression of the chest cavity causes compression of the intrapleural space. D) Exhalation, because the compression of the chest cavity causes expansion of the intrapleural space.

Answer 309

B During inhalation, the chest cavity expands, causing expansion of the intrapleural space. According to Boyle's law, an increase in volume at a constant temperature is accompanied by a decrease in pressure. When the intrapleural pressure (and, by extension, the alveolar pressure) is less than atmospheric pressure, air enters the lungs. During exhalation, these pressure gradients reverse: thus, during exhalation, intrapleural pressure is higher than atmospheric pressure; not lower.

Question 310

A patient presents to the emergency room with a stab would to the left side of the chest. On a chest x-ray, blood is noted to be collecting in the chest cavity, causing collapse of both lobes of the left lung. The blood is most likely located between: A) The parietal pleura and the chest wall. B) The parietal pleura and the visceral pleura. C) The visceral pleura and the lung. D) The alveolar walls and the lung surface.

Answer 310

B The intrapleural space, bounded by the parietal and visceral pleurae, is a potential space. As such, it is normally collapsed and contains a small amount of fluid. However, introduction of fluid or air into the intrapleural space can fill the space, causing collapse of the lung.

Question 311

The intrapleural pressure is necessarily lower than the atmospheric pressure during: A) Inhalation, because the expansion of the chest cavity causes compression of the intrapleural space. B) Inhalation, because the expansion of the chest cavity causes expansion of the intrapleural space. C) Exhalation, because the compression of the chest cavity causes compression of the intrapleural space. D) Exhalation, because the compression of the chest cavity causes expansion of the intrapleural space.

Answer 311

B During inhalation, the chest cavity expands, causing expansion of the intrapleural space. According to Boyle's law, an increase in volume at a constant temperature is accompanied by a decrease in pressure. When the intrapleural pressure (and, by extension, the alveolar pressure) is less than atmospheric pressure, air enters the lungs. During exhalation, these pressure gradients reverse: thus, during exhalation, intrapleural pressure is higher than atmospheric pressure; not lower.

Question 312

Which of the following is a correct sequence of passageways through which air travels during inhalation? A) Pharynx -> trachea -> bronchioles -> bronchi -> alveoli B) Pharynx -> trachea -> larynx -> bronchi -> alveoli C) Larynx -> pharynx -> trachea -> bronchi -> alveoli D) Pharynx -> larynx -> trachea -> bronchi -> alveoli

Answer 312

D Air enters the respiratory tract through the external nares (nostrils) and travels through the nasal cavities. It then passes through the pharynx and into the larynx. Ingested food also passes through the pharynx on its way to the esophagus; to ensure that food does not accidentally enter the larynx, the epiglottis covers the larynx during swallowing. After the larynx, air goes to the trachea, which eventually divides into two bronchi, one for each lung. The bronchi branch into smaller bronchioles, which terminate in clusters of alveoli.

Question 313

Idiopathic pulmonary fibrosis (IPF) is a disease in which scar tissue forms in the alveolar walls, making the lung tissue significantly more stiff. Which of the following findings would be detected through spirometry in a patient with IPF? I. Decreased total lung capacity II. Decreased inspiratory reserve volume III. Increased residual volume A) I only B) II only C) I and II only D) I, II, and III

Answer 313

B In a patient with IPF, the increased stiffness of the lungs would likely decrease both the total lung capacity and inspiratory reserve volume. However, spirometry cannot measure the total lung capacity accurately because it cannot determine the residual volume - the volume of air left in the lungs when an individual has maximally exhaled. Because the residual volume makes up a portion of the total lung capacity (total lung capacity = vital capacity + residual volume), a spirometer cannot be used to determine the total lung capacity. Increased stiffness of the lungs would be expected to decrease the residual volume, not increase it.

Question 314

Studies have indicated that premature babies are often deficient in lysozyme. What is a possible consequence of this deficiency? A) Respiratory distress and alveolar collapse shortly after birth B) Increased susceptibility to certain infections C) Inability to humidify air as it passes through the nasal cavity D) Slowing of the respiratory rate in response to acidemia

Answer 314

B Lysozyme is an enzyme present in the nasal cavity, saliva, and tears that degrades peptidoglycan, preventing infection by gram-positive bacteria. Thus, premature infants who lack lysozyme are more likely to suffer from infections with these organisms.

Question 315

Some forms of pneumonia cause an excess of fluids such as mucus or pus to build up within the entire lobe of the lung. How will this affect the diffusion of gases within the affected area? A) Carbon dioxide can diffuse out, but oxygen will not be able to enter the blood. B) Oxygen can diffuse into the blood, but carbon dioxide cannot diffuse out. C) No change in diffusion will occur. D) No diffusion will occur in the affected area.

Answer 315

D If an area of the lung becomes filled with mucus and inflammatory cells, the area will not be able to participate in gas exchange. Because no air will enter or leave the area, the concentration gradient will not longer exist, and neither oxygen nor carbon dioxide will be able to diffuse across the alveolar wall.

Question 316

Some people with anxiety disorders respond to stress by hyperventilating. It is recommended that these people breath into a paper bag and then rebreathe this air. Why is this treatment appropriate? A) Hyperventilation causes an increase in blood carbon dioxide, and breathing the air in the bag helps to readjust blood levels of carbon dioxide. B) Hyperventilation causes a decrease in blood carbon dioxide, and breathing the air in the bag helps to readjust blood levels of carbon dioxide. C) Hyperventilation causes an increase in blood oxygen, and breathing the air in the bag helps to readjust blood levels of oxygen. D) Hyperventilation causes an decrease in blood oxygen, and breathing the air in the bag helps to readjust blood levels of oxygen.

Answer 316

B When people hyperventilate, their respiratory rate increases. When the respiratory rate increases, more carbon dioxide is blown off. This causes a shift to the left in the bicarbonate buffer equation, and the blood becomes more alkaline. Breathing into the bag allows some of this carbon dioxide to be returned to the blood stream in order to maintain the proper pH.

Question 317

A patient presents to the emergency room with an asthma attack. The patient has been hyperventilating for the past hour and has a blood pH of 7.52. The patient is given treatment and does not appear to respond, but a subsequent blood pH reading is 7.41. Why might this normal blood pH NOT be a reassuring sign? A) The patient's kidneys may have compensated for the alkalemia. B) The normal blood pH reading is likely inaccurate. C) The patient may be descending into respiratory failure. D) The patient's blood should ideally become acidemic for some time to compensate for the alkalemia.

Answer 317

C When a patient with an asthma attack does not respond to treatment and has been hyperventilating for over an hour, he or she may become fatigued and may not be able to maintain hyperventilation. In this case, the patient begins to decrease his or her breathing rate and is not receiving adequate oxygen. By extension, carbon dioxide is trapped in the blood, and the pH begins to drop. Despite the fact that this pH is normal at the moment, this patient is crashing and may start demonstrating acidemia in the near future. While the kidneys should compensate for alkalemia, this is a slow process and would not normalize the blood pH within an hour; further, adequate compensation by the kidneys would actually be a reassuring sign.

Question 318

Premature infants with respiratory distress are often placed on ventilators. Often, the ventilators are set to provide positive end-expiratory pressure. Why might this setting be useful for a premature infant? A) Premature infants lack surfactant. B) Premature infants lack lysozyme. C) Premature infants cannot thermoregulate. D) Premature infants are unable to control pH.

Answer 318

A Premature infants often require ventilation using positive end-respiratory pressures. At the end of respiration, the ventilator will provide a higher pressure than normal, which forces extra air into the alveoli. This pressure must be used to prevent alveolar collapse; surfactant serves the same purpose by reducing surface tension. Providing extra air at the end of respiration would be beneficial to a premature infant that was lacking surfactant.

Question 319

In emphysema, the alveolar walls are destroyed, decreasing the recoil of the lung tissue. Which of the following changes may be seen in a patient with emphysema? A) Increased residual volume B) Decreased total lung capacity C) Increased blood concentration of oxygen D) Decreased blood concentration of carbon dioxide

Answer 319

A The intrinsic elastic properties of the lung are important during exhalation as the passive recoil of lung tissue helps decrease lung volume. With decreased recoil, the patient will have difficulty exhaling completely, increasing the residual volume. The total lung capacity would be expected to increase in this case because there would be less recoil opposing inhalation.

Question 320

In emphysema, the alveolar walls are destroyed, decreasing the recoil of the lung tissue. Which of the following changes may be seen in a patient with emphysema? A) Increased residual volume B) Decreased total lung capacity C) Increased blood concentration of oxygen D) Decreased blood concentration of carbon dioxide

Answer 320

A The intrinsic elastic properties of the lung are important during exhalation as the passive recoil of lung tissue helps decrease lung volume. With decreased recoil, the patient will have difficulty exhaling completely, increasing the residual volume. The total lung capacity would be expected to increase in this case because there would be less recoil opposing inhalation.

Question 321

Which of the following is NOT a difference that would allow one to distinguish a prokaryotic and a eukaryotic cell? A) Ribosomal sub-unit weight B) Presence of a nucleus C) Presence of a membrane on the outside surface of the cell D) Presence of membrane-bound organelles

Answer 321

C The main differences between prokaryotes and eukaryotes include: prokaryotes do not have a nucleus, while eukaryotes do; prokaryotes have ribosomal subunits of 30S and 50S, while eukaryotes have ribosomal subunits of 40S and 60S; and prokaryotes do not have membrane-bound organelles, whereas eukaryotes do. The presence of a membrane on the outer surface of the cell could not distinguish a prokaryotic cell from a eukaryotic one because both gram-negative bacteria and animal cells share this feature.

Question 322

Vitamins are essential nutrients and cannot be synthesized by the body. That is why they need to be consumed in diet. Vitamins are either water-soluble or lipid-soluble, with the later accumulating in stored fat. Water-soluble vitamins are excreted through the urine. Which vitamin is involved in clotting? ``` A) Vitamin A B) Vitamin D C) Vitamin E D) Vitamin K E) None of the above ```

Answer 322

D Vitamin A is important in vision, growth and development, and immune function. Vitamin D can be consumed or formed from a UV-driven reaction in the skin. In the liver and kidney, vitamin D is then converted to calcitriol, which in turn increases calcium and phosphate uptake in the intestines. This ultimately promotes bone production. Vitamin E characterizes a group of closely related lipids. These are called tocopherols and tocotrienols. Tocopherols are antioxidants. Vitamin K is crucial to posttranslational modifications required to form prothrombin, which is an important clotting factor in the blood.

Question 323

Which of the following is a FALSE statement regarding erythrocytes? A) Erythrocytes contain hemoglobin. B) Erythrocytes are anaerobic. C) The nuclei of erythrocytes are located in the middle of the biconcave disc. D) Erythrocytes are phagocytized in the spleen and liver after a certain period of time.

Answer 323

C Erythrocytes, or red blood cells, are produced in the red bone marrow and circulate in the blood for about 120 days, after which they are phagocytized in the spleen and the liver. Red blood cells have a disk-like shape and lose their membranous organelles (nuclei) during maturation. Erythrocytes are filled with hemoglobin; their lack of mitochondria makes their metabolism solely anaerobic.

Question 324

Which of the following is the correct sequence of a cardiac impulse? A) SA node -> AV node -> Purkinje fibers -> bundle of His -> ventricles B) AV node -> bundle of His -> Purkinje fibers -> ventricles -> atria C) SA node -> atria -> AV node -> bundle of His -> Purkinje fibers -> ventricles D) SA node -> AV node -> atria -> bundle of His -> Purkinje fibers -> ventricles

Answer 324

C An ordinary cardiac contraction originates in, and is regulated by, the sinoatrial (SA) node. The impulse travels through both atria, stimulating them to contract simultaneously. The impulse then arrives at the atrioventricular (AV) node, which momentarily slow conduction, allowing for completion of atrial contraction and ventricular filling. The impulse is then carried by the bundle of His and its branches through the Purkinje fibers in the walls of both ventricles, generating a contraction.

Question 325

Hemoglobin's affinity for O2: A) Increases in exercising muscle tissue B) Decreases as blood PaCO2 decreases C) Decreases as blood pH decreases D) Is higher in maternal blood than in fetal blood

Answer 325

C According to the Bohr effect, decreasing the pH in the blood decreases hemoglobin's affinity for O2. The affinity is generally lowered in exercising muscle to facilitate unloading of oxygen to tissues. A decrease in the PaCO2 would cause a decrease in [H+] or increased pH - which increases hemoglobin's affinity for O2. Fetal hemoglobin has a higher affinity than adult blood.

Question 326

Which of the following correctly traces the circulatory pathway? A) Superior vena cava -> right atrium -> right ventricle -> pulmonary artery -> lungs -> pulmonary veins -> left atrium -> left ventricle -> aorta B) Superior vena cava -> left atrium -> left ventricle -> pulmonary artery -> lungs -> pulmonary veins -> right atrium -> right ventricle -> aorta C) Aorta -> right atrium -> right ventricle -> pulmonary artery -> lungs -> pulmonary veins -> left atrium -> left ventricle -> superior vena cava D) Superior vena cava -> right atrium -> right ventricle -> pulmonary veins -> lungs -> pulmonary artery -> left atrium -> left ventricle -> aorta

Answer 326

A Blood drains from the superior and inferior venae cavae into the right atrium. It passes through the tricuspid valve and into the right ventricle, and then through the pulmonary valve into the pulmonary artery, which leads to the lungs. Oxygenated blood returns to the left atrium via the pulmonary veins. It flows through the mitral valve into the left ventricle. From the left ventricle, it is pumped through the aortic valve into the aorta for distribution throughout the body.

Question 327

At the venous end of a capillary bed, the osmotic pressure: A) is greater than the hydrostatic pressure B) results in a net outflow of fluid C) is significantly higher than the osmotic pressure at the arterial end D) causes proteins to enter the interstitium

Answer 327

A The exchange of fluid is greatly influenced by the differences in the hydrostatic and osmotic pressure of blood and tissues. The osmotic (oncotic) pressure remains relatively constant; however, the hydrostatic pressure at the arterial end is greater than the hydrostatic pressure at the venous end. As a result, fluid moves out of the capillaries at the arterial end and back in at the venous end. Fluid is reabsorbed at the venous end because the osmotic pressure exceeds the hydrostatic pressure. Proteins should not cross the capillary wall under normal circumstances.

Question 328

A patient's chart reveals that he has a cardiac output of 7500 mL per minute and stroke volume of 50mL. What is his pulse in beats per minute? A) 50 B) 100 C) 150 D) 400

Answer 328

C Cardiac output = heart rate x stroke volume. Thus, HR = CO/SV or 7500/50 = 150 beats per minute. This is actually pathologically fast; the normal range is 60-100 beats at rest.

Question 329

An unconscious patient is rushed into the emergency room and needs an immediate blood transfusion. Because there is no time to check her medical history or the determine the blood type, which type of blood should she receive? A) AB+ B) AB- C) O+ D) O-

Answer 329

D Without knowing a patient's blood type, the only type of transfusion that we can safely give is O-. People with O- blood are considered universal donors because their blood cells contain no surface antigens. Therefore, O- blood can be given to anyone without potentially life-threatening consequences from ABO or Rh incompatibility.

Question 330

Which of the following is true regarding arteries and veins? A) Arteries are thin-walled, muscular, and elastic, whereas veins are thick-walled and inelastic. B) Arteries always conduct oxygenated blood, whereas veins always carry deoxygenated blood. C) The blood pressure in the aorta is always higher than the pressure in the superior vena cava D) Arteries facilitate blood transport by using skeletal muscle contractions, whereas veins make use of the pumping of the heart to push blood.

Answer 330

C The pressure in the aorta usually ranges between 120 and 80 mmHg, depending on whether the heart is in systole or diastole, whereas the pressure of the superior vena cava is near zero. Arteries are thick-walled and veins are thin. Pulmonary and umbilical veins carry oxygenated blood (not deoxygenated). Arteries snap back because of their elastic walls and use the heart to pump blood, veins use skeletal muscles to return blood to the heart.

Question 331

At any given time, there is more blood in the venous system than the arterial system. Which of the following feature of veins allows for this? A) Relative lack of smooth muscle in the wall B) Presence of valves C) Proximity of veins to lymphatic vessels D) Thin endothelial lining

Answer 331

A The relative lack of smooth muscle in venous walls allows stretching to store most of the blood in the body. Valves in the vein allow for one-way flow of blood toward the heart, not stretching. Both arteries and veins are close to the lymphatic vessels, which has no bearing on their relative difference in volume. Both arteries and veins have a single-cell endothelial lining.

Question 332

Which of the following is involved in the body's primary blood-buffering mechanism? A) Fluid intake B) Absorption of nutrients in the gastrointestinal system C) Carbon dioxide produced from metabolism D) Hormones released by the kidney

Answer 332

C Carbon dioxide is a byproduct of metabolism in cells that later combines with water to form bicarbonate in a reaction catalyzed by carbonic anhydrase. This system is blood plasma's most important buffer system. Food and fluid absorption are not significant sources of buffering. While the kidney can be involved in acid-base balance, it carries out this function through its filtration, secretion, and reabsorption mechanisms, not through hormone release.

Question 333

Due to kidney disease, a person is losing albumin into the urine. What effect is this likely to have within the capillaries? A) Increased oncotic pressure B) Increased hydrostatic pressure C) Decreased oncotic pressure D) Decreased hydrostatic pressure

Answer 333

C In circulation, plasma proteins play an important role in generating osmotic (oncotic) pressure. This allows water that is displaced at the arterial end of a capillary bed by hydrostatic pressure to be reabsorbed at the venule end. Loss of these plasma proteins would cause a decrease in the plasma osmotic (oncotic) pressure.

Question 334

The tricuspid valve prevents backflow of blood from the: A) Left ventricle into the left atrium B) Aorta into the left ventricle C) Pulmonary artery into the right ventricle D) Right ventricle into the right atrium

Answer 334

D The atrioventricular valves are located between the atria and the ventricles on both sides of the heart. Their role is to prevent backflow of blood into the atria. The valve on the right side of the heart has three cusps and is called the tricuspid valve. It prevents backflow of blood from the right ventricle into the right atrium.

Question 335

The world record for the longest-held breath is 22 minutes and 0 seconds. If a sample were taken from this individual during the last minute of breath-holding, which of the following might be observed? A) Increased hemoglobin affinity for oxygen B) Decreased PaCO2 C) Increased hematocrit D) Decreased pH

Answer 335

D Holding one's breath for a prolonged period would result in a drop in oxygenation and an increase in PaCO2. This increased carbon dioxide would associate with water to form carbonic acid, which would dissociate into a proton and a bicarbonate anion. Further, the low oxygen saturation would essentially lead to anaerobic metabolism in some tissues, causing an increase in lactic acid. This would all lead to a decreased pH.

Question 336

A person has a heart attack that primarily affects the wall between the two ventricles. Which portion of the electrical conduction system is most likely affected? A) AV node B) SA node C) Bundle of His D) Left ventricular muscle

Answer 336

C The cardiac conduction system starts at the SA node, which is located near the top of the right atrium, and continues down to the AV node, which is located between the two AV valves. The bundle of His is located within the wall between the ventricles, and is likely to be affected if the wall between the ventricles has been damaged by a heart attack. This may affect the left ventricle, but the left ventricular muscle itself is not part of the cardiac conduction system.

Question 337

Which vascular structure creates the most resistance to blood flow? A) Aorta B) Arterioles C) Capillaries D) Veins

Answer 337

B The greatest amount of resistance is provided by the arterioles. Arterioles are highly muscular and have the ability to contract and dilate in order to regulate blood pressure.

Question 338

Which of the following associations correctly matches a gastric cell with a compound it secretes? A) G-cells - HCl B) Chief cells - pepsinogen C) Parietal cells - alkaline mucus D) Mucous cells - intrinsic factor

Answer 338

B Chief cells secrete pepsinogen, a protease secreted as a zymogen that is activated by the acidic environment of the stomach. G-cells secrete gastrin, parietal cells secrete hydrochloric acid and intrinsic factor, and mucous cells secrete alkaline mucus.

Question 339

Which of the following associations correctly matches a gastric cell with a compound it secretes? A) G-cells - HCl B) Chief cells - pepsinogen C) Parietal cells - alkaline mucus D) Mucous cells - intrinsic factor

Answer 339

B Chief cells secrete pepsinogen, a protease secreted as a zymogen that is activated by the acidic environment of the stomach. G-cells secrete gastrin, parietal cells secrete hydrochloric acid and intrinsic factor, and mucous cells secrete alkaline mucus.

Question 340

In an experiment, enteropeptidase secretion was blocked. As a direct result, levels of all of the following active enzymes would likely be affected EXCEPT: A) Trypsin B) Aminopeptidase C) Chymotrypsin D) Carboxypeptidase A

Answer 340

B Aminopeptidase is a brush-border peptidase secreted by the cells lining the duodenum; it does not require enteropeptidase for activation. Both trypsinogen and procarboxypeptidases A and B are activated by enteropeptidase. Once activated, trypsin can activate chymotrypsinogen; if trypsinogen cannot be activated, then chymotrypsinogen will not be activated either.

Question 341

Which of the following INCORRECTLY pairs a digestive enzyme with its function? A) Trypsin - hydrolyzes specific peptide bonds B) Lactase - hydrolyzes lactose to glucose and galactose C) Pancreatic amylase - hydrolyzes starch to maltose D) Lipase - emulsifies fats

Answer 341

D Lipase is involved in the digestion of fats, but its function is not to emulsify fats - this is the job of bile. Rather, lipase chemically digests fats in the duodenum, allowing them to be brought into duodenal cells and packaged into chylomicrons.

Question 342

Which of the following correctly lists two organs in which proteins are digested? A) Mouth and stomach B) Stomach and large intestine C) Stomach and small intestine D) Small intestine and large intestine

Answer 342

C Protein digestion begins in the stomach, where pepsin (secreted as pepsinogen) hydrolyzes specific peptide bonds. Protein digestion continues in the small intestine as trypsin (secreted as trypsinogen), chymotrypsin (secreted as chymotrypsinogen), carboxypeptidases A and B (secreted as procarboxypetidases A and B), aminopeptidase and dipeptidases hydrolyze specific parts of the peptide. No protein digestion occurs in the mouth or large intestine.

Question 343

Which of the following choices INCORRECTLY pairs a digestive enzyme with its site of secretion? A) Sucrase - salivary glands B) Carboxypeptidase - pancreas C) Trypsin - pancreas D) Lactase - duodenum

Answer 343

A Sucrase is a brush-border enzyme found on duodenal cells and is not secreted by the salivary glands. This enzyme hydrolyzes sucrose (a disaccharide) to form glucose and fructose (monosaccharides).

Question 344

A two-week-old male infant is brought to the emergency room. His mother reports that he has been unable to keep any milk down; shortly after he nurses, he has sudden projectile vomiting. During examination, an olive-shaped mass can be felt in his upper abdomen. It is determined that there is a constriction in the digestive system that prevents food from reaching the small intestine from the stomach. Which structure is most likely the site of the problem? A) Cardiac sphincter B) Pyloric sphincter C) Ileocecal valve D) Internal anal sphincter

Answer 344

B Identify the structure that lies between the stomach and the small intestine. This is the pyloric sphincter; the question gives a classic example of pyloric stenosis, in which the pyloric sphincter is thickened and cannot relax to permit chyme through. The cardiac sphincter lies between the esophagus and the stomach. The ileocecal valve lies between the ileus of the small intestine and the cecum of the large intestine. The internal anal sphincter lies at the end of the rectum.

Question 345

Many medications have anticholinergic side effects, which block the activity of parasympathetic neurons throughout the body. Older individuals may be on many such medications simultaneously, exacerbating the side effects. Which of the following would NOT be expected in an individual taking the medications with anticholinergic activity? A) Dry mouth B) Diarrhea C) Slow gastric emptying D) Decreased gastric acid production

Answer 345

B The parasympathetic nervous system has many roles in the digestive system. It promotes motility of the gut tube and secretion from glands. Therefore, blocking the parasympathetic nervous system would likely result in dry mouth (from reduced secretion of saliva), slow gastric emptying (from decreased peristalsis), and decreased gastric acid production (from reduced HCl secretion from the parietal cells in the gastric glands). We would expect constipation in such an individual, not diarrhea: slowed motility through the colon would lead to increased water reabsorption, making the feces too firm and causing constipation.

Question 346

2 graphs showed a relationship of pH (x-axis) and enzyme function (y-axis). The first graph shows enzyme function high in the 2-3 pH range and very little as it increases above 3. The second graph shows enzyme function is high in the 8.5-9 pH range but very little above and below this range. Which of the following choices correctly identifies to the two enzymes that could be in these environments, respectively? A) Chymotrypsin, pepsin B) Pepsin, carboxypeptidase B C) Lactase, aminopeptidase D) Enteropeptidase, amylase

Answer 346

The first graph shows maximal enzyme activity at a very acidic pH, implying this is an enzyme acting in the stomach. The second graph shows maximal activity around 8.5 pH, implying that this is an enzyme acting in the duodenum. Pepsin and carboxypeptidase B are the only enzymes that correctly match as stomach and duodenum enzymes, respectively.

Question 347

Which of the following would NOT likely lead to elevated levels of bilirubin in the blood? A) Cholangiocarcinoma, a cancer of the bile ducts that can ultimately lead to full occlusion of the duct lumen B) Autoimmune hemolytic anemia, a disease in which the red blood cells are attacked by antibodies and are lysed C) Menetrier's disease, in which rugae thicken and overlying glands lose secretory ability D) Acetaminophen (Tylenol) overdose, in which the accumulation of toxic metabolites can cause rapid liver failure

Answer 347

C Elevated bilirubin implies a blockage to bile flow, increased production of bilirubin (from massive hemoglobin release), or an inability of the liver to produce bile. If the bile duct were occluded, then bile would not be able to flow into the digestive tract and would build up, increasing bilirubin levels in the blood. If many blood cells were lysed, then bilirubin levels would rise in accordance with the increased hemoglobin release. If liver failure occurred, then the liver would be unable to produce bile, and bilirubin would again build up. Menetrier's disease is a pathology of the stomach - the key word being rugae, which are folds in the stomach. Lack of gastric function would have no effect on bilirubin levels.

Question 348

Which of the following correctly pairs the molecule with its primary site of absorption? A) Chylomicrons - lacteals B) Amino acids - large intestine C) Vitamin A and E - stomach D) Cholesterol - ascending colon

Answer 348

A Chylomicrons contain triacylglycerols, cholesteryl esters, and fat-soluble vitamins and are secreted by intestinal cells into lacteals. Amino acid, fat-soluble vitamins (like vitamins A and E), and cholesterol are all absorbed in the small intestine.

Question 349

Starch is hydrolyzed into maltose by enzymes from the: I. Salivary glands II. Brush border III. Pancreas A) I only B) I and III only C) II and III only D) I, II, and III

Answer 349

B Starch is hydrolyzed to maltose by two enzymes: salivary amylase (secreted by salivary glands) in the mouth and pancreatic amylase (secreted by the pancreas) in the duodenum. Brush-border disaccharidases can further break down maltose, but do not break down starch.

Question 350

Which of the following biomolecules does NOT drain into the liver before arriving at the right side of the heart? A) Cholecalciferol (Vitamin D) B) Threonine (an amino acid) C) Fructose (a monosaccharide) D) Pantothenic acid (Vitamin B5)

Answer 350

A While the capillaries from the intestine come together to form the portal vein, which drains to the liver, the lacteals come together to form the thoracic duct, which drains directly into the left subclavian vein. Therefore, fat-soluble compounds do not pass through the liver before reaching the right side of the heart.

Question 351

Which of the following hormones increases feeding behavior? A) Leptin B) Cholecystokinin C) Ghrelin D) Gastrin

Answer 351

C Ghrelin promotes a sensation of hunger, increasing feeding behavior. Both leptin and cholecystokinin promote satiety, decreasing feeding behavior. Gastrin increases acid production and gastric motility, but does not have any significant relationship with feeding behavior.

Question 352

Which of the following biomolecules does NOT drain into the liver before arriving at the right side of the heart? A) Cholecalciferol (Vitamin D) B) Threonine (an amino acid) C) Fructose (a monosaccharide) D) Pantothenic acid (Vitamin B5)

Answer 352

A While the capillaries from the intestine come together to form the portal vein, which drains to the liver, the lacteals come together to form the thoracic duct, which drains directly into the left subclavian vein. Therefore, fat-soluble compounds do not pass through the liver before reaching the right side of the heart.

Question 353

Which of the following hormones increases feeding behavior? A) Leptin B) Cholecystokinin C) Ghrelin D) Gastrin

Answer 353

C Ghrelin promotes a sensation of hunger, increasing feeding behavior. Both leptin and cholecystokinin promote satiety, decreasing feeding behavior. Gastrin increases acid production and gastric motility, but does not have any significant relationship with feeding behavior.

Question 354

Which of the following is likely to be seen in a patient with liver failure? A) High concentrations of urea in the blood B) High concentrations of albumin in the blood C) Low concentrations of ammonia in the blood D) Low concentrations of clotting factors in the blood

Answer 354

D The liver serves many functions, including carrying out metabolic processes (glycogenesis and glycogenolysis, fat storage, and gluconeogenesis), detoxification or activation of medications, and synthesis of bile. Also relevant are the roles of converting ammonia into urea through the urea cycle and synthesis of proteins, including albumin and clotting factors. A patient with liver failure would thus not be able to convert ammonia into urea and would have high concentrations of ammonia and low concentrations of urea in the blood. With decreased synthetic activity, both albumin and clotting factor concentrations would be low.

Question 355

In DiGeorge syndrome, the thymus can be completely absent. The absence of the thymus would leave an individual unable to mount specific defenses against which of the following cell types? A) Viruses B) Bacteria C) Parasites D) Fungi

Answer 355

A T-lymphocytes, which mature in the thymus, are the only specific defense against intracellular pathogens. While some bacteria, fungi, and parasites can live intracellularly, viruses - by definition - must replicate within cells. The absence of T-cells would leave an individual unable to fight viral infections with specific defenses.

Question 356

Which of the following are NOT involved in cell-mediated immunity? A) Memory cells B) Plasma cells C) Cytotoxic cells D) Suppressor cells

Answer 356

B The lymphocytes involved in cell-mediated immunity are the T-lymphocytes, or T-cells. There are four types of T-cells, each playing a different role in cell-mediated immunity; cytotoxic T-cells, helper T-cells, memory T-cells, and suppressor T-cells. Thus, the only cells not involved in cell-mediated immunity are the plasma cells, which are differentiated immunoglobin-secreting B-lymphocytes involved in humoral immunity.

Question 357

The lymphatic system: A) Transports hormones through the body. B) Transports chylomicrons to the circulatory system. C) Causes extravasation of fluid into tissues. D) Is the site of mast cell specialization.

Answer 357

B The main function of the lymphatic system is to collect excess interstitial fluid and return it to the circulatory system, maintaining the balance of body fluids. In addition, the lymphatic system accepts chylomicrons from the small intestine and delivers them to the cardiovascular circulation. Transport of hormones is a function of the cardiovascular system. The lymphatic system absorbs fluid that has been pushed into tissues, but does not cause the extravasation of the fluid. Mast cells reside in (and are activated in) the skin and mucous membranes.

Question 358

Which of the following are involved in antibody production? A) Plasma cells B) Memory cells C) Helper T-cells D) Cytotoxic cells

Answer 358

A Antibodies are produced by plasma cells derived from B-lymphocytes. The other cells are all types of T-lymphocytes, although memory B-cells can also exist. Still, memory B-cells do not produce antibodies; plasma cells do.

Question 359

Which of the following is NOT an example of a nonspecific defense mechanism? A) Skin provides a physical barrier against invasion B) Macrophages engulf and destroy foreign particles C) An inflammatory response is initiated in response to physical damage D) Cytotoxic T-cells destroy cells displaying foreign antigens

Answer 359

D The body employs a number of nonspecific defense mechanisms against foreign invasion. The skin and mucous membranes provide a physical barrier against bacterial invasion. In addition, sweat contains enzymes that attack bacterial cell walls. Certain passages, such as the respiratory tract, are lined with ciliated mucous-coated epithelia, which filter and trap foreign particles. Macrophages engulf and destroy foreign particles. The inflammatory response is initiated in response to physical damage. Cytotoxic T-cells are involved in (specific) cell-mediated immunity.

Question 360

Which of the following is an example of adaptive immunity? A) PRRs recognize that a pathogen is an invasive parasite and eosinophils are recruited to the area. B) Complement is activated, causing osmotic instability in a bacterium. C) Memory B-cells generated through vaccination are activated when their antigen is encountered. D) Dendritic cells sample bacteria within a laceration and travel to the lymph nodes to present the antigen.

Answer 360

C Adaptive immunity involves the activation of B-cells and T-cells specific to the encountered antigen. Pattern recognition receptors, or PRR, recognize patterns common to certain pathogens, but do not identify the specific pathogen. Complement is an example of a blood-borne nonspecific defense against bacteria. Dendritic cells traveling to the lymph nodes are a part of the interaction between the innate and adaptive immune systems, but the dendritic cells themselves are nonspecific.

Question 361

Which of the following is true regarding passive and active immunity? A) Active immunity requires weeks to build, whereas passive immunity is acquired immediately. B) Active immunity is short-lived, whereas passive immunity is long-lived. C) Active immunity may be acquired during pregnancy through the placenta. D) Passive immunity may be acquired through vaccination.

Answer 361

A Active immunity refers to the production of antibodies during an immune response. Active immunity may be conferred on an individual by vaccination, such as when an individual is injected with a weakened, inactive, or modified form of a particular antigen that stimulates the immune system to produce antibodies. Active immunity may require weeks to build. Passive immunity, on the other hand, involves the transfer of antibodies through, for example, breast milk or injection. An example would be during pregnancy, when some maternal antibodies cross the placenta and enter fetal circulation, conferring passive immunity to the fetus. Although passive immunity is acquired immediately, it is very short-lived, lasting only as long as the antibodies circulate in blood.

Question 362

Where are the most self-reactive T-cells eliminated? A) Spleen B) Lymph node C) Bone marrow D) Thymus

Answer 362

D T-cells mature in the thymus, where they are "educated." This education involves the elimination of T-cells with improper binding to MHC-antigen complexes (positive selection) and self-reactive T-cells (negative selection). Thus, self-reactive T-cells are eliminated in the thymus.

Question 363

What is the response of the immune system to downregulation of MHC molecules on somatic cells? A) B-cells are activated and antibodies are released B) T-cells are activated, resulting in a cytotoxic response C) Natural killer cells induce apoptosis of affected cells D) Macrophages engulf the pathogen and display its antigens

Answer 363

C Healthy cells exhibit MHC class I molecules. Natural killer cells monitor the expression of MHC molecules on the surface of cells. Viral infection and cancer often cause a reduction in the expression of MHC class I molecules on the cell surface. Natural killer cells detect a lack of MHC and induce apoptosis in the affected cells.

Question 364

Which of the following correctly indicates the response of CD8+ T-cells when activated? A) Secretion of cytotoxic chemicals B) Causing isotype switching C) Presentation of antigens D) Activation of B-cells

Answer 364

A CD8+ T-cells are largely responsible for the cytotoxic immune response. By releasing toxic chemicals into virally infected cells, CD8+ T-cells are able to kill these cells in an effort to contain viral infections. Isotype switching refers to changes in the isotype of antibody produced, which is not caused by CD8+ cells. Antigens are presented by macrophages, dendritic cells, certain epithelial cells, and some B-cells. B-cells are not activated by cytotoxic T-lymphocytes.

Question 365

Lymphoma is cancer of the cells of lymphoid lineage. These cells often reside within lymph nodes. What type of cell is NOT likely to cause a lymphoma? A) CD8+ T-cells B) B-cells C) Macrophages D) Th1 cells

Answer 365

C Lymphocytes arise from the lymphoid lineage, which includes B-cells and T-cells. Thus, all types of B and T-cells are capable of causing lymphoma. Macrophages, however, are not lymphocytes and are not likely to cause lymphoma.

Question 366

Upon encountering an antigen, only T-cells with a specific T-cell receptor are activated. This is an example of: A) Innate immunity B) A cytotoxic T-cell response C) Humoral immunity D) Clonal selection

Answer 366

D When the adaptive immune system encounters an antigen, only the cells with antibodies or T-cell receptors specific to that antigen are activated. This is known as clonal selection. While a T-cell response may be a cytotoxic response, it could also be the activation of helper T-cells; plus, this does not explain the specificity of the response.

Question 367

Which cell type is a phagocyte that attacks bacterial pathogens in the bloodstream? A) Neutrophils B) Eosinophils C) Basophils D) Dendritic cells

Answer 367

A The only phagocytes that attack bacteria on this list are neutrophils and dendritic cells. Dendritic cells are able to sample and present any type of material, and reside in the skin. Neutrophils, on the other hand, are present in the bloodstream and can attack bacteria present there or in tissues. Eosinophils and basophils are involved in the development of allergies; eosinophils also defend against parasites.

Question 368

What type of immunity is likely to be affected by removal of the spleen? A) Cytotoxic immunity B) Humoral immunity C) Innate immunity D) Passive immunity

Answer 368

B The spleen is a location where B-cells mature and proliferate. Therefore, removal of the spleen is likely to result in a reduction of humoral immunity. In fact, many people receive vaccinations prior to removal of the spleen in order to bolster their immunity.

Question 369

Which of the following is NOT a granulocyte? A) Natural killer cell B) Mast cell C) Eosinophil D) Basophil

Answer 369

A Granulocytes are cells with granules in their cytoplasm. These granules are released in immune responses to attack a pathogen. Granulocytes include neutrophils, basophils, eosinophils, and mast cells. Natural killer cells are agranulocytes, which include lymphocytes (B, T and NK cells) and monocytes/macrophages.

Question 370

Which of the following would most likely be filtered through the glomerulus into Bowman's capsule? A) Erythrocytes B) Monosaccharides C) Platelets D) Proteins

Answer 370

B The glomerulus functions like a sieve; small molecules dissolved in fluid will pass through the glomerulus, including glucose, which is later reabsorbed. Large molecules, such as proteins, and cells, such as erythrocytes and platelets, will not be able to pass through the glomerular filter.

Question 371

In which of the following segments of the nephron is sodium NOT actively transported out of the nephron? A) Proximal convoluted tubule B) Thin portion of the ascending limb of the loop of Henle C) Distal convoluted tubule D) Thick portion of the ascending limb of the loop of Henle

Answer 371

B Sodium is actively transported out of the nephron in the proximal and distal convoluted tubules, where the concentration of sodium outside of the nephron is higher than inside; thus, energy is required to transport the sodium molecules against their concentration gradient. In the inner medulla, however, sodium and other ions (such as chloride) diffuse passively down their concentration gradients at the thin ascending limb of the loop of Henle. The thick ascending limb of the loop of Henle is thick because its cells contain many mitochondria - which produce the ATP needed for active transport of sodium and chloride out of the filtrate.

Question 372

Which region of the kidney has the lowest solute concentration under normal physiological circumstances? A) Cortex B) Outer medulla C) Inner medulla D) Renal pelvis

Answer 372

A The region of the kidney that has the lowest solute concentration is the cortex, where the proximal convoluted tubule and a part of the distal convoluted tubule are found. The solute concentration increases as one descends into the medulla, and concentrated urine can be found in the renal pelvis.

Question 373

Which of the following sequences correctly shows the passage of blood through the vessels of the kidney? A) Renal artery -> afferent arterioles -> glomerulus -> efferent arterioles -> vasa recta -> renal vein B) Afferent arterioles -> renal artery -> glomerulus -> vasa recta -> renal vein -> efferent arterioles C) Glomerulus -> renal artery -> afferent arterioles -> efferent arterioles -> renal vein -> vasa recta D) Renal vein -> efferent arterioles -> glomerulus -> afferent arterioles -> vasa recta -> renal artery

Answer 373

A Blood enters the kidney through the renal artery, which divides into many afferent arterioles that run through the medulla and into the cortex. Each afferent arteriole branches into a convoluted network of capillaries called a glomerulus. Rather than converging directly into a vein, the capillaries converge into an efferent arteriole, which divides into a fine capillary network known as the vasa recta. The vasa recta capillaries envelop the nephron tubule, where they reabsorb various ions, and then converge into the renal vein. The arrangement of tandem capillary beds is known as a portal system.

Question 374

Which of the following statements is FALSE? A) ADH increases water absorption in the kidney. B) Aldosterone indirectly increases water reabsorption in the kidney. C) ADH acts directly on the proximal convoluted tubule. D) Aldosterone stimulates reabsorption of sodium from the collecting duct.

Answer 374

C ADH and aldosterone ultimately act to increase water reabsorption in the kidney; their respective mechanisms of action, however, are different. ADH increases water reabsorption by increasing the permeability of the collecting duct to water, whereas aldosterone stimulates reabsorption of sodium from the distal convoluted tubule and collecting duct. ADH does not act on the proximal convoluted tubule, but rather on the collecting duct.

Question 375

In the nephron, amino acids enter the vasa recta via the process of: A) Filtration B) Secretion C) Excretion D) Reabsorption

Answer 375

D Essential substances, such as glucose, salts, amino acids, and water, are reabsorbed from the filtrate and returned to the blood in the vasa recta. In general, reabsorption refers to the movement of solutes from the filtrate back into the blood.

Question 376

On a very cold day, a man waits for over an hour at the bus stop. Which of the following structures helps his body set and maintain a normal temperature? A) Hypothalamus B) Kidneys C) Posterior pituitary D) Brainstem

Answer 376

A The hypothalamus functions as a thermostat that regulates body temperature. When it's cold outside, nervous stimulation to the blood vessels in the skin is increased, causing the vessels to constrict. This constriction diminishes blood flow to the skin surface and prevents heat loss. Sweat glands are turned off to prevent heat loss through evaporation. Skeletal muscles are stimulated to shiver (rapidly contract), which increases metabolic rate and produces heat. The hypothalamus is also involved in other processes, including the release of endocrine hormones, regulation of appetite, and circadian rhythms.

Question 377

Glucose reabsorption in the nephron occurs in the: A) loop of Henle B) Distal convoluted tubule C) Proximal convoluted tubule D) Collecting duct

Answer 377

C The filtrate enters Bowman's capsule and then flows into the proximal convoluted tubule, where virtually all glucose, amino acids, and other important organic molecules are reabsorbed via active transport.

Question 378

Under normal physiological circumstances, the primary functions of the nephron is to create urine that is: A) hypertonic to the blood B) hypotonic to the blood C) isotonic to the filtrate D) hypotonic to the vasa recta

Answer 378

A The kidneys function to eliminate wastes such as urea, while reabsorbing various important substances such as glucose and amino acids for reuse by the body. Generation of a solute concentration gradient from the cortex to the medulla allows a considerable amount of water to be reabsorbed. Excretion of concentrated urine serves to limit water losses from the body and helps to preserve blood volume. Thus, the primary function of the nephron is to create urine that is hypertonic to the blood. Water should be reabsorbed from the filtrate, so urine should be hypertonic to the filtrate.

Question 379

Diabetic nephropathy is commonly detected by finding protein in the urine of a patient. In such a disease, where is the likely defect in the nephron? A) Glomerulus B) Proximal convoluted tubule C) Loop of Henle D) Collecting duct

Answer 379

A The glomerulus is the most likely location of pathology if large proteins are detected in the urine. This is because large proteins should be able to pass through the filter of the glomerulus in the first place. Once large proteins are in the filtrate, no other nephron structure can reabsorb them. Thus, the only likely source of proteins in the urine is glomerular pathology.

Question 380

A laceration cuts down into a layer of loose connective tissue in the skin. Which layer of the skin is this? A) Stratum corneum B) Stratum lucidum C) Papillary layer D) Reticular layer

Answer 380

C The layer of the skin that is predominantly loose connective tissue is the papillary layer of the dermis. The stratum corneum and stratum lucidum contain dead keratinocytes, while the reticular layer consists of dense connective tissue.

Question 381

When the pH of the blood is high, which substance is likely to be excreted in larger quantities in the urine? A) Urea B) Ammonia C) Hydrogen ions D) Bicarbonate ions

Answer 381

D When the pH of the blood is high, this indicates that the blood is alkalemic. In order to correct the pH of the blood, the kidney will increase the excretion of a base, namely bicarbonate. Excretion of urea would have little effect on the pH. While ammonia is a base, it is quite toxic and is generally converted into urea before excretion. Excretion of hydrogen ions would exacerbate the alkalemia.

Question 382

In which layer of the skin can the stem cells of keratinocytes be found? A) Stratum lucidum B) Stratum granulosum C) Stratum basale D) Stratum corneum

Answer 382

C The stratum basale contains the stem cells that proliferate to form keratinocytes, which then ascend through the other layers of the skin until they are shed from the stratum corneum.

Question 383

A drug is used that prevents the conversion of angiotensin I to angiotensin II. What is a likely effect of this drug? A) Increased sodium reabsorption B) Increased potassium reabsorption C) Increased blood pressure D) Increased blood pH

Answer 383

B Normally, angiotensin II causes secretion of aldosterone from the adrenal cortex. Aldosterone serves to increase reabsorption of sodium, while promoting excretion of potassium and hydrogen ions. Thus, blocking the release of aldosterone should result in decreased reabsorption of sodium, while decreasing excretion of potassium and hydrogen ions. In the absence of aldosterone, less sodium reabsorption will occur, leading to less water reabsorption.

Question 384

Sarin is a potent organophosphate that can be used in chemical warfare. As an inhibitor of acetylcholinesterase, sarin causes excessive build up of acetylcholine in all synapses where it is a neurotransmitter. Which of the following symptoms would most likely be seen in an individual with sarin poisoning? A) Increased urination and increased sweating B) Increased urination and decreased sweating C) Decreased urination and increased sweating D) Decreased urination and decreased sweating

Answer 384

A An excess of acetylcholine will lead to activation of all parasympathetic neurons, preganglionic sympathetic neurons, and the postganglionic sympathetic neurons that innervate sweat glands. Because the parasympathetic nervous system causes contraction of the bladder, one would expect increased urination. The increased activation of sweat glands would lead to increased swelling as well.

Question 385

With which of the following molecules does Ca2+ bind after its release from the sarcoplasmic reticulum to regulate muscle contraction? A) Myosin B) Actin C) Troponin D) Tropomyosin

Answer 385

C Calcium is released from the sarcoplasmic reticulum into the sarcoplasm. It binds the troponin molecules on the thin filaments, causing the strands of tropomyosin to shift, thereby exposing the myosin-binding sites on the thin filaments.

Question 386

Which of the following cells is correctly coupled with its definition? A) Osteoblasts - bone cells involved in the secretion of bone matrix B) Osteoclasts - immature bone cells C) Osteocytes - polynucleated cells actively involved in bone resorption D) Chondrocytes - undifferentiated bone marrow cells

Answer 386

A Osteoblasts are bone cells involved in the secretion of bone matrix. Osteoclasts are large, polynucleated cells involved in bone resorption. Osteocytes are mature bone cells that eventually become surrounded by their matrix; their primary role is bone maintenance. Finally, chondrocytes are cells that secrete chondrin, an elastic matrix that makes up cartilage.

Question 387

An X-ray of the right femur in a child shows that it is shorter than the opposite femur, and below the average length for a child of this age. Which region of the bone is most likely to have caused this abnormality? A) Diaphysis B) Metaphysis C) Epiphysis D) Periosteum

Answer 387

C This question is essentially asking where longitudinal growth occurs in bones. The most likely site of abnormalities in this child's femur is the epiphyseal plate, a disk of cartilaginous cells at the internal border of the epiphysis, because the epiphyseal plate is the site of longitudinal growth. Damage to the epiphysis (with or without metaphysis involvement) can imply damage to the epiphyseal plate.

Question 388

Which of the following INCORRECTLY pairs a type of muscle fiber with a characteristic of that fiber? A) Red fibers - rich in mitochondria B) Red fibers - high levels of myoglobin C) White fibers - fast-twitching D) White fibers - predominantly use aerobic respiration

Answer 388

D Red fibers are slow-twitching fibers that have high levels of myoglobin and many mitochondria. They derive their energy from aerobic respiration and are capable of sustained vigorous activity. White fibers, on the other hand, are fast-twitching fibers and contain lower levels of myoglobin and fewer mitochondria. Because of their composition, they derive more of their energy anaerobically and fatigue more easily.

Question 389

When the knee moves back and forth during walking, what prevents the surfaces of the leg bones from rubbing against each other? A) Articular cartilage B) Epiphysis C) Synovial fluid D) Smooth muscle

Answer 389

A The articular surfaces of the bones are covered with a layer of smooth articular cartilage. The epiphysis is a portion of the bone itself. Synovial fluid lubricates the movement in the joint space, but does not stop the bones from contacting one another; this is the job of articular cartilage. There is no appreciable function for smooth muscle in the joint space.

Question 390

Which type(s) of muscle is/are always multinucleated? I. Cardiac muscle II. Skeletal muscle III. Smooth muscle A) I only B) II only C) III only D) I and II only

Answer 390

B The only type of muscle that is always multinucleated is skeletal muscle. Cardiac muscle may contain one or two centrally located nuclei, so statement I is incorrect. Smooth muscle, on the other hand, always has only one centrally located nucleus.

Question 391

Which type(s) of muscle has/have myogenic activity? I. Cardiac muscle II. Skeletal muscle III. Smooth muscle A) I only B) II only C) III only D) I and III only

Answer 391

D Myogenic activity refers to the ability of a muscle to contract without nervous stimulation, such as in response to other stimuli like stretching. Smooth and cardiac muscle both possess myogenic activity.

Question 392

Red bone marrow is involved in erythrocyte formation. In contrast, yellow bone marrow: A) Is involved in leukocyte formation B) Is responsible for drainage of lymph C) Causes the formation of spicules D) Contains predominantly adipose tissue

Answer 392

D Yellow marrow is largely inactive and is infiltrated by adipose tissue.

Question 393

Which of the following statements regarding the periosteum is INCORRECT? A) The periosteum serves as a site of attachment of bone to muscle B) Cells of the periosteum may differentiate into osteoblasts C) The periosteum is a fibrous sheath that surrounds long bones D) The periosteum secretes fluid into the joint cavity

Answer 393

D The periosteum, a fibrous sheath that surrounds long bones, is the site of attachment to muscle tissue. Some periosteum cells are capable of differentiating into bone-forming cells called osteoblasts. It is the synovium that secretes fluid into the joint cavity (joint space), not the periosteum.

Question 394

Which of the following bones is NOT a part of the appendicular skeleton? A) The triquetrum, one of the carpal bones B) The calcaneus, which forms the heel C) The ischium, one of the fused pelvic bones D) The sternum, or breastbone

Answer 394

D The axial skeleton includes the skull, vertebral column, rib cage, and hyoid bone. The sternum is a point of attachment of the rib cage and is thus a part of the axial, not appendicular skeleton. The limb bones, pectoral girdle, and pelvis are all part of the appendicular skeleton.

Question 395

To facilitate the process of birth, an infant's head is somewhat flexible. This flexibility is due in part to the two fontanelles, which are soft spots of connective tissue in the infant's skull. With time, the fontanelles will close through a process known as: A) Endochondral ossification B) Intramembranous ossification C) Bone resorption D) Longitudinal growth

Answer 395

B Bones form in one of two ways: endochondral ossification and intramembranous ossification. Endochondral ossification is the replacement of cartilage with bone and occurs mostly in long bones. Intramembranous ossification is the formation of bone from undifferentiated connective tissue cells (mesenchyme) and occurs mostly in the skull. Bone resorption is the breakdown of bone, not its formation. Longitudinal growth occurs in long bones and is responsible for increasing height over time, but does not play a role in fontanelle ossification.

Question 396

A young woman presents to the emergency room with a broken hip. She denies any recent history of trauma to the joint. Blood tests reveal a calcium concentration of 11.5 mg/dl (normal: 8.4-10.2). Which tissue is likely responsible for these findings? A) Thyroid B) Cartilage C) Parathyroid D) Smooth muscle

Answer 396

C An unprovoked fracture of the hip is not a normal finding in a young woman. Given that she has a high calcium level, it is likely that she has an increased level of bone resorption that is causing her bones to be more fragile. Parathyroid hormone causes calcium release from bones. If this woman had an overactive parathyroid gland - or even cancer in this gland - then it is likely that calcium could still be resorbed from her bones even though her blood calcium levels are already high.

Question 397

What is the gene order of linked genes M, N, O and P, given the following recombination frequencies? MN: 6% NO: 18% MO: 12% NP: 1% MP: 5% OP 17% A) MOPN B) NPMO C) ONPM D) PNMO

Answer 397

B Because there is a correlation between the frequency of recombination and the distance between genes on a chromosome, if we are given the frequencies, we can determine gene order. Remember that one map unit equals 1 percent recombination frequency. The easiest way to begin is to determine the two genes that are farthest apart; in this case, N and O recombine with a frequency of 18%, so they are 18 map units apart on the chromosome: NP recombine with 1% frequency, and PO recombine with 17% frequency, so P must be between N and O. Finally, MP recombine with 5% frequency, and MO recombine with 12% frequency, so M must be between P and O.

Question 398

Suppose that in a mammalian species, the allele for black hair (B) is dominant to the allele for brown hair (b), and the allele for curly hair (C) is dominant to the allele for straight hair (c). When an organism of unknown genotype is crossed against one with straight, brown hair, the phenotypic ratio is as follows: I. 25% curly black hair II. 25% straight black hair III. 25% curly brown hair IV. 25% straight brown hair What is the genotype of the unknown parent? A) BbCC B) bbCc C) Bbcc D) BbCc

Answer 398

D In this dihybrid problem, a doubly recessive individual is crossed with an individual of unknown genotype; this is known as a test cross. The straight and brown-haired organism has the genotype bbcc and can thus only produce gametes carrying bc. Looking at the F1 offspring, there is a 1:1:1:1 phenotypic ratio. The fact that both the dominant and recessive traits are present in the offspring means that the unknown parental genotype must contain both dominant and recessive alleles for each trait. The unknown parental genotype must therefore be BbCc.

Question 399

If a male with hemophilia (XhY) is crossed with a female carrier of both color blindness and hemophilia (XcXh), what is the probability that a female child will be phenotypically normal? A) 0% B) 25% C) 50% D) 100%

Answer 399

C The female in this example is a carrier of two sex-linked traits; based on her genotype, the affected alleles are found on different X chromosomes. When drawing a Punnett square, we see that 25% of the offspring will be female hemophiliacs (XhXh) and 25% will be female carriers of both alleles (XcXh). The question is asking what percentage of FEMALES will have a normal phenotype, which would be HALF of all females (since those who are carriers for both traits are phenotypically normal). The males are irrelevant to the specifics of the question.

Question 400

If a test cross on a species of plant reveals the appearance of a recessive phenotype in the offspring, what must be true of the phenotypically dominant parent? A) It must be genotypically heterozygous B) It must be genotypically homozygous C) It could be genotypically heterozygous or homozygous D) It must have the same genotype as the test cross control parent

Answer 400

A The control parent in a test cross is always recessive. Therefore, if the test parent is phenotypically dominant, yet can provide a recessive allele (as evidenced by the presence of recessive children), then the parent must have both a dominant and recessive allele. Therefore, this test parent must be heterozygous.

Question 401

Which of the following definitions is FALSE? A) Penetrance - the percentage of individuals in the population carrying the allele who actually express the phenotype associated with it B) Expressivity - the percentage of individuals in the population carrying the allele who do not express the phenotype associated with it C) Incomplete dominance - occurs when the phenotype of the heterozygote is an intermediate of the phenotypes of the homozygotes D) Codominance - occurs when multiple alleles exist for a given gene and more than one of them is dominant

Answer 401

B The definition given here for expressivity is a much better match for defining penetrance (or, really, one minus the penetrance). Expressivity refers to the variable manifestations of a given genotype as different phenotypes; the degree to which various phenotypes are expressed. Everything else is accurate.

Question 402

In a species of plant, a homozygous red flower (RR) is crossed with a homozygous yellow flower (rr). If the F1 generation is self-crossed and the F2 generation has a phenotypic ratio of red:orange:yellow of 1:2:1, which characteristic accounts for these results? A) Codominance B) Incomplete dominance C) Penetrance D) Expressivity

Answer 402

B Some progeny in the second generation are apparently blends of the parental genotypes. The orange color is the result of combined effects of the red and yellow alleles. An allele is incompletely dominant if the phenotype of the heterozygotes is an intermediate of the phenotypes of the homozygotes.

Question 403

Which of the following statements is INCORRECT regarding inheritance of traits according to the modern synthesis model? A) A mutation due to excessive amounts of ultraviolet light occurs in an unfertilized egg; this will affect the child who is born from that egg. B) The muscular strength gained by a weight lifter during his lifetime is inherited by his children. C) A green-feathered bird that survived all of the predators in the forest will pass on the green feather gene to its offspring. D) A flower with a tasty nectar eaten by a butterfly is more likely to pass on its genes through the pollen spread by the butterfly than a flower with less desirable nectar.

Answer 403

B Modern-day theories of inheritance states that the genes that make an organism most fit for its environment will be passed to offspring. C and D both demonstrate that an organism with improved fitness will pass those genes to offspring. Choice A mentions a gamete being exposed to mutagens; a zygote created from this gamete would contain any mutations that were present in the egg and would be affected by them. Acquired characteristics (muscular strength) not encoded in the genome should not be passed to offspring according to the modern synthesis model.

Question 404

Which of the following statements is FALSE based on Darwin's theory of evolution? A) Natural selection is the driving force for evolution. B) Favorable genetic variations become more and more common in individuals throughout their lives. C) Natural selection can drive organisms living in groups to ultimately become distinct species. D) Fitness is measured by reproductive success.

Answer 404

B Darwin's theory of natural selection argues that chance variations between organisms can help certain organisms survive to reproductive age and produce many offspring, transmitting their variations to the next generation. Thus, natural selection would drive the process of evolution forward, enabling the persistence of characteristics that impart an advantage in the environment. In Darwin's theory, fitness is measured in terms of reproductive success. Through natural selection, organisms may be separated into groups depending on environmental pressures, and these groups can eventually separate to the point of becoming distinct species. The theory of natural selection applies to a population of organisms, not to a particular individual. As such, favorable genetic variations become more and more common from generation to generation, not during the lifetime of an individual.

Question 405

Which of the following is NOT a necessary condition for Hardy-Weinberg equilibrium? A) Large population size B) No mutations C) Monogamous mating partners D) No migration into or out of the population

Answer 405

C Hardy-Weinberg equilibrium exists under certain ideal conditions that, when satisfied, allow one to calculate the gene frequencies within a population. The Hardy-Weinberg equation can be applied only under these five conditions: (1) the population is very large; (2) there are no mutations that affect the gene pool; (3) mating between individuals in the population is random; (4) there is no migration of individuals into or out of the population; (5) the genes in the population are all equally successful at being reproduced. Monogamy is not a necessary condition for Hardy-Weinberg equilibrium.

Question 406

As the climate became colder during the Ice Age, a particular species of mammal evolved a thicker layer of fur. What kind of selection occurred in this population? A) Stabilizing selection B) Directional selection C) Disruptive selection D) Speciation selection

Answer 406

B The situation described is an example of directional selection. In directional selection, the phenotypic norm of a particular species shifts toward an extreme to adapt to a selective pressure, such as an increasingly colder environment. Only those individuals with a thicker layer of fur were able to survive during the Ice Age, thus shifting the phenotypic norm.

Question 407

At what point are two populations descended from the same ancestral stock considered to be separate species? A) When they can no longer produce viable, fertile offspring B) When they look significantly different from each other C) When they can interbreed successfully and produce offspring D) When their habitats are separated by a significantly large distance so that they cannot meet

Answer 407

A A species is defined as the largest group of organisms that can interbreed to produce viable, fertile offspring. Therefore, two populations are considered separate species when they can no longer do so.

Question 408

In a nonevolving population, there are two alleles, R and r, which code for the same trait. The frequency of R is 30%. What are the frequencies of all the possible genotypes? A) 49% RR, 42% Rr, 9% rr B) 30% RR, 21% Rr, 49% rr C) 0.09% RR, 0.42% Rr, 0.49% rr D) 9% RR, 42% Rr, 49% rr

Answer 408

D We are told that the frequency of R equals 30%, and as such, p = 0.30. The frequency of the recessive gene is r = 100% - 30% = 70%; thus, q = 0.70. The frequency of the genotypes, according to the Hardy-Weinberg equilibrium, are given by p^2 = RR, 2pq = Rr, and q^2 = rr. Therefore, the frequency of the genotypes are (0.3)^2 = 0.09 = 9% RR, 2 x 0.3 x 0.7 = 0.42 = 42% Rr, and (0.7)^2 = 0.49 = 49% rr.

Question 409

In a particular Hardy-Weinberg population, there are only two eye colors; brown and blue. Of the population, 36% have blue eyes, the recessive trait. What percentage of the population is heterozygous? A) 24% B) 48% C) 60% D) 64%

Answer 409

B We can determine that the percentage of the population with blue (genotype bb) = 36% = 0.36 = q^2; therefore, q = 0.6. Because this is a Hardy-Weinberg population, we can assume that p + q = 1, so p = 1 - 0.6 = 0.4. The frequency of heterozygous brown eyes is therefore 2pq = 2 x 0.4 x 0.6 = 0.48 = 48%.

Question 410

Which of the following was NOT a belief of Darwin's? A) Evolution of species occurs gradually and evenly over time B) There is a struggle for survival among organisms C) Genetic recombination and mutation are the driving forces of evolution D) Those individuals with fitter variations will survive and reproduce

Answer 410

C Darwin's main argument was that natural selection is the driving force for evolution. Darwin did not consider the role of genetic mutation and recombination, which were unknown at that time. These aspects were added to Darwin's theory as part of the modern synthesis model, which was not developed until significantly after Darwin's time.

Question 411

A child is born with a number of unusual phenotypic features and genetic testing is performed. The child is determined to have a partial trisomy 21, with three copies of some segments of DNA from chromosome 21, and partial monosomy 4, with only one copy of some segments of DNA from chromosome 4. Which of the following mutations could have occurred in one of the parental gametes during development to explain both findings? A) Deletion B) Insertion C) Translocation D) Inversion

Answer 411

C This scenario - a deletion of some DNA and a duplication of other DNA - would be consistent with a translocation between chromosomes 4 and 21 during development of can egg or sperm. If part of chromosome 21 was swapped with part of chromosome 4, then a gamete resulting from meiosis in this cell would result in a daughter cell with two copies of some of the DNA from 21 and no copies of some of the DNA from 4. Therefore, after fertilization, there would be partial trisomy 21 and partial monosomy 4. While a deletion or insertion could explain one of the findings, it cannot explain both. An inversion should not lead to partial trisomy or partial monosomy because the DNA is simply reversed.

Question 412

In a small lake, sea urchins graze upon small grasses that grow on the bottom. After the introduction of an exotic sea urchin, the small grasses became over grazed and absent. To solve the problem, a species of otter is introduced into the lake to predate upon the sea urchins, and the balance between the urchins and sea grasses is restored. What would be the appropriate term for the otter that was introduced? A) Tertiary consumer B) Top carnivore C) Keystone predator D) Primary consumer

Answer 412

C The otter would be considered a secondary consumer, the urchins are the primary consumers, and a hypothetical predator of the otter would be a tertiary consumer. Since the otter is responsible for preventing overgrazing of the small grasses by predating on the out of control urchin population, it is termed a keystone predator that exerts a “top-down” effect on the ecosystem.

Question 413

If a gene has two alleles, A and B, and its frequencies are p and q, respectively, which statement holds true (suppose that population gas reach the Hardy-Weinberg equilibrium): A) p^2 + q^2 = 1 B) p + q > 1 C) Frequency of homozygote BB is q^2 D) Frequency of homozygote AA is 2p

Answer 413

C According to the Hardy-Weinberg equation (p+q)^2 = 1, or rather; p^2 + 2pq + q^2 = 1. If we have a gene with two alleles, A and B, and its frequencies are p and q, then we can know that the frequencies of the genotypes are as follows, by plugging into the Hardy-Weinberg equation: Predicted frequency of homozygote AA = p^2 Predicted frequency of homozygote BB = q^2 Predicted frequency of heterozygote AB = 2pq.

Question 414

Nondisjunction results in an uneven distribution of chromosomes during cell replication. If nondisjunction occurs during meiosis I, the homologous chromosomes do not separate. If nondisjunction happens in meiosis II, sister chromatids do not separate. If a cell has a diploid number of six (2N = 6) before meiosis, how many chromosomes will be in each of the four daughter cells if one pair of chromosomes experiences nondisjunction during meiosis I? A) Two cells will have 6 chromosomes, two cells will have none B) Two cells will have 4 chromosomes, two cells will have 2 chromosomes C) Two cells will have 5 chromosomes, two cells will have 1 chromosome D) All four cells will have 3 chromosomes

Answer 414

B For an organism with a diploid number of 6 (2N = 6), each of the 4 meiotic cells will have 3 chromosomes. However, if nondisjunction occurs in meiosis I, one daughter cell will have 4 doubled chromosomes and the other cell will have 2 doubled chromosomes. One pair of the homologous chromosomes did not separate. However, all chromatids will separate in the second division, resulting in four single chromosomes in two of the products and two single chromosomes in the other two products.

Question 415

Which of the following is considered to be the defining characteristic of organisms in the Kingdom Monera? A) Single-celled with no confined storage area for genetic material B) Protein-based infectious particle C) Single-celled using flagella for locomotion D) Single-celled with separation of genetic material from cellular machinery

Answer 415

A Though some organisms in the Kingdom Monera utilize flagella for locomotion, the defining characteristic of organisms in the Kingdom Monera is that they do not house their genetic material in a confined space separate from their cellular machinery. Organisms that do confine their genetic material are eukaryotic organisms, some of which are single celled and some of which have multicellular organization, and are not part of the Monera Kingdom.

Question 416

Once a mammalian zygote has become a blastocyst and implants itself into the uterine wall, it will develop into? A) Gastrula B) Embryoblast C) Trophoblast D) Oocyte

Answer 416

A The oocyte and morula are both precursors to the blastula stage. The embryoblast and the trophoblast are both components of the blastula, but are not the next stage in embryonic development. Once the blastula undergoes gastrulation, it will become a gastrula with three distinct layers of tissue: endoderm, mesoderm, and ectoderm.

Question 417

Pulmonary alveolus (plural form:alveoli) is an integral component of the mammalian respiratory system, which of the following characteristics describes this component? A) Actively transports O2 into the bloodstream B) Allows for gas diffusion to occur and the exchange of CO2 for O2 in the bloodstream C) Hollow cavities at the end of the respiratory tree D) Both B and C

Answer 417

D Alveoli are found in the parenchyma of the lungs at the terminal end of the respiratory tree. Alveoli in the lungs of mammals are the key structure in facilitating the exchange of CO2 and O2 across the alveolar membrane by pumping CO2 rich blood from the body into the oxygen rich alveoli and allowing the exchange to occur through diffusion, not active transport.

Question 418

Blood pressure is a function of cardiac output (heart rate x stroke volume), as well as peripheral resistance (a measure of friction between the blood and the blood vessel walls). Factors that can increase peripheral resistance include: A) Vasoconstriction and low blood viscosity B) Vasoconstriction and high blood viscosity C) Vasodilation and low blood viscosity D) Vasodilation and high blood viscosity

Answer 418

B If peripheral resistance reflects friction between the blood and the walls of the blood vessels, both narrower blood vessels (vasoconstriction) and a thicker, more viscous blood will increase peripheral resistance.

Question 419

Curare is a chemical used in arrow poisons as well as in pharmaceutical compounds. It competes with acetylcholine for receptor sites along the motor end plate. The immediate physiological effects of high doses of curare can include: A) Decreased ability to relax muscles B) Inability to contract muscles and paralysis C) Inability to repolarize muscles D) Abnormal heat production in the affected muscle cells

Answer 419

B If curare competes with acetylcholine along the motor end plate (at the neuromuscular junction), ACh cannot perform its function. ACh normally causes skeletal muscles to depolarize and contract. If the function of ACh is blocked, B is clearly the correct choice. Choices A and C refer to events after depolarization has taken place. Heat production results from contraction, which requires ACh in the first place.

Question 420

In general, each cell synthesizes its own macromolecules and does not receive them previously formed from other cells. For example, muscle cells make their own glycogen, rather than receiving it intact from the: A) Pancreas B) Kidney C) Liver D) Small intestine

Answer 420

C Knowledge about the roles of the liver is required. In addition, it should be understood that the liver first catabolizes its stored glycogen back to glucose. The monosaccharides enter the bloodstream, not the entire insoluble polysaccharide.

Question 421

Which statement is true concerning the sites at which muscles attach to bones? A) The origin of a muscle is never on a bone that forms part of a movable joint B) The insertion of a muscle is usually on the same bone as the body of the muscle C) The same bone can serve as the origin for one muscle and the insertion for a different muscle D) No muscles are attached to bones forming immovable joints

Answer 421

C The origin of a muscle is the end which attaches to a site (bone) that does not move when the muscle contracts. In contrast, the insertion is the end that does move when the muscle contracts. The same bone can serve as the origin (site) for one muscle while serving as the insertion (site) for a different muscle.

Question 422

Which of the following animal pairings demonstrates the principle of convergent evolution? A) The monkey and the human B) The shark and the dolphin C) The alligator and the snake D) The kangaroo and the whale

Answer 422

B Convergent evolution is the process where organisms from different ancestral lineages, grow to look alike and share similar physical characteristics because they live in the same or very similar environments. Whereas divergent evolution is defined as the evolutionary process whereby organisms from the same ancestral lineage differ in appearance. This difference would result because of the different habitats of the organisms. Only the shark and the fish are from different animal lineages and look very similar because they both live in aquatic environments. The other animal pairings all originate from a similar ancestral lineage and have grown to look very different over time because of their terrestrial habitats.

Question 423

Which of the following terms refers to the burden or degree of disease associated with a given illness? A) Morbidity B) Mortality C) Second sickness D) Chronicity

Answer 423

A Morbidity refers to the burden of illness, or the severity or degree of illness. Mortality refers to deaths caused by a given illness. Second sickness is a term used to describe the exacerbation of health outcomes due to social injustice. Chronicity refers to the duration of a disease, not its severity or significance for the patient.

Question 424

A blood cell is placed into a salt-water mixture (70% salt). What is likely to result if the red blood cell’s membrane is permeable to water? A) The cell will burst B) The cell will shrivel C) The cell will degrade D) The cell will shrivel, then expand

Answer 424

B For cells with a selectively permeable membrane, water will move from higher water concentrations to lower water concentrations. In this problem, the salt is too large to cross the membrane, so the salt concentration will remain the same. Since red blood cells have more water than the salt-water mixture, the water in the cell would leave to try to make the two environments isotonic. If water leaves the cell, the cell will eventually shrink.

Question 425

Which membranes separate the interstitial fluid from the blood plasma and the interstitial fluid from the intracellular fluid, respectively? A) The cell surface membrane and the capillary wall B) The capillary wall and the cell surface membrane C) The capillary wall and the cell wall D) The cell wall and the cell surface membrane

Answer 425

B The ISF (interstitial fluid) is the fluid outside the blood vessels while the blood plasma is the fluid within the blood vessels. Thus, the two fluids are separated by the wall of the blood vessels (i.e. the capillary wall). The ICF (intracellular fluid) of the cells bathing in the ISF are separated from their environment by the cell surface membrane, in accordance with answer choice B. You should be aware that human cells, unlike bacteria, do not contain a cell wall.

Question 426

In certain insects, juvenile hormone suppresses metamorphosis from larva to adult. Instead, this hormone allows the young organism to grow in size while remaining in the immature larval stage. Eventually, the juvenile hormone decreases, causing metamorphosis to take place. If the corpora allata, the site of juvenile hormone production and release, is surgically removed an an early larval stage, what is expected to happen? A) A tiny adult will form B) The larva will continue to grow, and metamorphosis will occur at the normal age C) The larva will no longer grow or undergo metamorphosis D) The larva will continue to grow until it looks like a giant, adult-sized larva

Answer 426

A No previous knowledge about insects, hormones, or metamorphosis is required. The ability to logically apply the given information is required. If juvenile hormone inhibits metamorphosis, removal of the hormone should cause metamorphosis to occur earlier.

Question 427

A student is trying to determine the type of membrane transport occurring in a cell. She finds that the molecule to be transported is very large and polar, and when transported across the membrane, no energy is required. Which of the following is the most likely mechanism of transport? A) Active transport B) Simple diffusion C) Facilitated diffusion D) Exocytosis

Answer 427

C We are asked to identify the type of transport that would allow a large, polar molecule to cross the membrane without any energy expenditure. This scenario describes facilitated diffusion, which uses a transport protein (or channel) to facilitate the movement of large, polar molecules across the nonpolar, hydrophobic membrane. Facilitated diffusion, like simple diffusion, does not require energy, which explains why no ATP was consumed during this transport process.

Question 428

Which of the following is true about cholesterol? A) Cholesterol always increases membrane fluidity in cells B) Cholesterol is a steroid precursor C) Cholesterol is a precursor for vitamin A, which is produced in the skin D) Cholesterol interacts only with the hydrophobic tails of phospholipids

Answer 428

B Cholesterol is a steroid precursor that has variable effects on membrane fluidity depending on temperature. It interacts with both the hydrophobic tails and the hydrophilic heads of membrane lipids. It is also the precursor for vitamin D (not vitamin A), which can be produced in the skin in a UV-driven reaction.

Question 429

It is well known that methylation of cytosine residues within CpG dinucleotides represents an important mechanism of gene expression control. Regulation of DNA methylation is crucial in many processes such as differentiation, growth and development. Hypermethylation of the gene promoter causes transcriptional silencing. Aberrant methylation may contribute to the development of a broad range of malignant tumors. Based on the foregoing, which group of genes is prone to methylation in a cancer cell? A) Genes that stimulate angiogenesis B) Genes that stimulate cell growth C) Genes responsible for the promotion of apoptosis D) Oncogenes

Answer 429

C Cancerogenesis is an evolutionary process. Cancer cells are under heavy selective pressure and only those cells that possess appropriate genetic characteristics will survive. All changes that result in increased angiogenesis, cell growth and expression of oncogenes favor cancer development. On the other hand, apoptosis (programmed cell death) represents the way in which an organism eliminates potential cancer cells. Silencing the genes responsible for promotion of apoptosis is an essential step in malignant tumor development.

Question 430

Cyanide is a poison that interferes with cytochrome activity. In what part of a human cell does cyanide have its effects? A) Cytosol B) Mitochondria C) Ribosomes D) All of the above

Answer 430

B Cytochromes function as electron transfer agents in many metabolic pathways, especially cellular respiration. Only glycolysis takes place in the cytosol. Both the Krebs cycle and transport chain occur in the mitochondria (ribosomes are the site of protein synthesis).

Question 431

During the fusion stage in human fertilization, which of the following would you NOT expect to occur? A) A fusion of chromosomes from the sperm and oocyte B) Oocyte transfers itself into a mature ovum C) The disintegration of the flagellum and mitochondria of the sperm during the creation of the male pronucleus D) Blending of the pronucleus from the ovum and sperm into one

Answer 431

D The blending or fusing of the pronuclei from the oocyte and the sperm cell does not occur, in that the two do not become one. What does occur is that the protective membranes on both dissolve, allowing for the genetic material to co-mingle. A mitotic spindle is formed and attaches itself to the chromosomes from each pronucleus before the chromosomes are fully dispersed throughout the cytoplasm of the oocyte. Mitosis then takes place creating daughter cells that are genetically identical. You may remember that all of a female’s eggs are arrested at meiosis II. The eggs remain in this stage until sperm fertilizes them.

Question 432

Rigor mortis, a condition in which skeletal muscles temporarily remain in a rigid state of partial contraction due to the absence of ATP, occurs a few hours after death. Which of the following steps is NOT necessary for muscle relaxation? A) Repolarization of the sarcolemma B) The return of calcium to the sarcoplasmic reticulum C) The detachment of the troponin-tropomyosin complex from actin D) The decomposition of acetylcholine by cholinesterase

Answer 432

C Choices A, B, and D are all necessary for a muscle cell to return to its resting state. The troponin-tropomyosin complex must return to its original position on actin (the position it occupied before calcium was released from the sarcoplasmic reticulum). When the complex detaches, muscle contraction occurs.

Question 433

Multicellular organisms are always composed of many small cells rather than fewer large cells. As a cell’s surface area increases by the square of its linear dimension, its volume increases by the cube of its linear dimension. Which statement is true about how cellular functions would be directly affected in a cell that grew too large? A) The rate of membrane transport could not keep up with the needs of the cell B) The distances to be traveled by molecules within the cell would make metabolic functions inefficient C) Both A and B D) Neither A nor B

Answer 433

C A large cell would have an outer surface area that would not be large enough to service the even larger cell volume inside. Similarly, the various organelles and assorted components of the cytoplasm would be too far apart for proper coupling of reactions.

Question 434

What process is described by an animal’s ability to involuntarily contract a skeletal muscle without receiving a direct signal from the brain? A) Depolarization B) Reflex Arc C) Metabolism D) Redirection

Answer 434

B A reflex arc is a nervous system process whereby the stimulus causes a motor movement that is coordinated by the spinal cord and not the brain. Sensory neurons are able to capture the environmental stimuli and send the afferent signal to the spinal cord, which is able to send an efferent (motor) signal directly to the effector, a muscle, which then moves. Plasticity refers to the brain’s ability to repair itself following damage. Metabolism is the general term defining the cell’s use and production of energy. Redirection is not an accurate term and is not used in biology. Depolarization is the process of changing the cell membrane’s to become more positive, commonly observed when in the nervous system with the propagation of an action potential.

Question 435

The high concentration of salt in the interstitial fluid of the medulla is due to a counter-current mechanism in the kidney. This occurs in a site near to where the hypotonic filtrate passes before elimination. This allows the: A) Secretion of excess salts B) Adjustment of filtrate pH C) Filtration of venous blood returning to the heart D) Reabsorption of water

Answer 435

D This question refers to kidney function and osmotic interaction. A hypotonic filtrate has more water than solute and passes through a hypertonic tissue (more solute, less water), so water will move from the filtrate to the tissue.

Question 436

A radioactive element is injected into a patient which preferentially accumulates in parasympathetic ganglia. Where will the signal be the highest? A) Arms B) Brain C) Spinal cord D) Bladder

Answer 436

D The parasympathetic fibers travel mainly through the vagus nerves and the anterior roots of the sacral segments of the spinal cord. They are not as extensively distributed in the body as the sympathetic fibers and their ganglia (= collection of nerve cell bodies outside the CNS, eliminating answer choice B.) are located near or within the visceral organs. From the answer choices provided, the bladder is the only organ innervated by the parasympathetic system. Recall that the parasympathetic system is important in the ‘vegetative responses’ of the body.

Question 437

Genetic drift is the process responsible for: A) Gaining a new allele within large populations B) Gaining a new allele within sufficiently small populations C) Losing an existing allele due to emigration. D) Losing an existing allele due to random sampling

Answer 437

D Genetic drift represents the change in an allele frequency in a population due to random sampling. Influence from genetic drift is particularly important in small populations. The random changes in allele frequencies could result in the elimination of an existing allele from a population.

Question 438

Oxidative phosphorylation is best described as: A) The process in which ATP is formed as electrons are transferred from electron carriers to oxygen B) The process to repay the oxygen debt C) The process in which ATP is formed as pyruvate is converted into acetyl CoA D) The process in which ATP is formed as acetyl CoA is completely oxidized to carbon dioxide

Answer 438

A Oxidative phosphorylation is defined by A; B may be true but it is an inadequate description of oxidative phosphorylation; C describes the intermediate step between glycolysis and the Krebs cycle; D describes the Krebs cycle.

Question 439

Human blood types are most often examined in reference to the ABO gene locus. The IA and IB alleles are both dominant to the i allele. If blood from a type AB individual were donated to three individuals who were, respectively, types A, B and O, which of the recipients blood would agglutinate? A) The recipients with blood types A and B B) The recipient with blood type O C) None of the recipients D) All of the recipients

Answer 439

D The A and B antigens on the red blood cells donated from the Type AB donor will be agglutinated by anti-B in the plasma of the Type A recipient, anti-A (in the Type B recipient), and both anti-A and anti-B (in the Type O recipient). Type AB donors are universal acceptors, but Type O are universal donors.

Question 440

Animal cells are cultured in petri dishes with a nutrient medium containing radioactive adenine and uracil. Which molecules produced by the cells would you anticipate to be radioactively labeled? A) Adenine and uracil in DNA, RNA, and ATP B) Adenine and uracil in DNA and ATP; uracil in RNA C) Adenine in DNA and RNA; uracil in RNA; neither in ATP D) Adenine and DNA, RNA, and ATP; uracil in RNA

Answer 440

D This is an easy question testing your knowledge of nucleic acids and simple biological molecules. Adenine is one of the four nucleotide bases found in DNA and RNA, as well as in the adenosine triphosphate (ATP) molecules found in all cells. Uracil is one of the four nucleotide bases found mostly in RNA.

Question 441

After mitosis, the chromosomes of daughter cells contain: A) Four DNA molecules B) One DNA molecule C) Two DNA molecules D) Four DNA chains

Answer 441

B After mitosis, each daughter cell has the same number of chromosomes, like the mother cell. However, chromosomes of the daughter cell have only one chromatid, i.e. one DNA molecule.

Question 442

In gene therapy, which of these non-viral DNA delivery methods requires endocytosis? A) DNA injection B) Dendrimer delivery C) Magnetofection D) Sonoporation

Answer 442

B DNA injection, electroporation, magnetofection and sonoporation are all examples of physical methods used to deliver DNA non-virally. The use of dendrimers on the other hand is considered a chemical method of DNA delivery, whereby cationic dendrimers are temporarily associated with DNA until endocytosis takes place, where DNA can subsequently be released from the dendrimer.

Question 443

Individuals with Turner’s Syndrome have 45 chromosomes (one sex chromosome is missing in the cells of these “XO” individuals). This usually is caused by meiotic nondisjunction during gametogenesis. Which statement is NOT correct concerning people with this disorder? A) They are genetic females B) They are subject to sex-linked disorders at frequencies similar to those predicted for normal females C) The nondisjunction event could have occured during meiosis in either the male or female parent D) If meiosis occurs in Turner's Syndrome individuals, one daughter cell resulting from the first meiotic divison will have no sex chromosome

Answer 443

B Since normal females have two X-chromosomes, Turner’s Syndrome females do not have the same probabilities of inheriting sex-linked disorders (they actually have the same chances as males).

Question 444

What are two characteristic features of the fungus genus? A) Monophyletic and heterotrophic B) Polyphyletic and heterotrophic C) Paraphyletic and heterotrophic D) Monophyletic and autotrophic

Answer 444

B Fungi are classified as a group based upon common biological traits acquired through convergent evolution, without a common ancestor, and are therefore considered polyphyletic. Unlike plants, fungi cannot make their own food supply. Instead, they obtain nutrition by parasitism, saprobism or symbiosis.

Question 445

A variety of organs with similar functions among the vertebrates are thin, moist, highly vascular, and cover a relatively large surface area. These are necessary characteristics for an efficient: A) Heart B) Blood-brain barrier C) Neuromuscular interface D) Respiratory membrane

Answer 445

D The characteristics described are shared by structures including gills, lungs, and even the skin of frogs (which can serve as an extra respiratory organ underwater).

Question 446

If a muscle cell is stimulated a second time before it has time to relax completely, a stronger contraction results. What is this phenomenon called? A) Tetany B) Partial (incomplete) tetany C) Summation D) Threshold stimulation

Answer 446

C Since the described phenomenon involves only a second contraction, summation is the appropriate answer. If the situation involved multiple stimuli (20-30) in rapid succession, partial tetany would be correct. Tetany occurs when multiple stimuli occur so rapidly that there is no time to relax at all. Threshold refers to the level of stimulation required to initiate any response by the muscle cell.

Question 447

Penicillin exerts its effect on bacterial growth through inhibition of cell-wall synthesis. This antibiotic blocks the last step in the formation of the cell wall. Glycopeptide transpeptidase is a bacterial enzyme that catalyzes the cross-linking reaction between peptidoglycan molecules, which are the main constituents of the cell wall. Penicillin inhibits the enzyme by binding covalently to its active site. The penicillin-enzyme complex cannot react further. This is an example of: A) Irreversible inhibition B) Competitive inhibition C) Noncompetitive inhibition D) Uncompetitive inhibition

Answer 447

A Penicillin covalently binds to the active site of the bacterial enzyme and permanently disables its action. This mode of action is inherent to irreversible inhibitors. Notice this is similar to competitive inhibitors, but competitive inhibitors are reversible and adding more substrate can overcome the competitive inhibitor. Here is an excellent explanation on enzyme mechanics.

Question 448

Which membranes separate the interstitial fluid from the blood plasma and the interstitial fluid from the intracellular fluid, respectively? A) The cell surface membrane and the capillary wall B) The capillary wall and the cell surface membrane C) The capillary wall and the cell wall D) The cell wall and the cell surface membrane

Answer 448

B The ISF (interstitial fluid) is the fluid outside the blood vessels while the blood plasma is the fluid within the blood vessels. Thus, the two fluids are separated by the wall of the blood vessels (i.e. the capillary wall). The ICF (intracellular fluid) of the cells bathing in the ISF are separated from their environment by the cell surface membrane, in accordance with answer choice B. You should be aware that human cells, unlike bacteria, do not contain a cell wall.

Question 449

Thyroid releasing hormone is released from which of the following endocrine glands? A) Pituitary B) Thyroid C) Parathyroid D) Hypothalamus

Answer 449

D The direction of release is as follows: hypothalamus -> (TRH) -> pituitary -> (TSH) -> thyroid.

Question 450

Which of the following is the most accurate statement regarding the theory of Natural Selection? A) Individuals who reproduce in greater numbers are more likely to pass on their genes B) Individuals who have favorable random genetic mutations are not likely pass on their genes C) The environment can only support a finite number of individuals D) Individuals with the most genetic mutations are more likely pass on their genes

Answer 450

C The most accurate statement is C. The statement for A can be true when discussing particular reproductive strategies, however, is not true in all cases. Individuals that are best adapted to their environment will have the greatest chance to pass on their genes, not the ones that produce the most amount of offspring. If an animal produces 1000 offspring and 999 of them die, then the fitness level of that animal is very low, compared to another animal with high fitness that only produces 2 offspring and both live to pass on their genes. Statement B would be correct if it were stated oppositely, since favorable genetic mutations is what creates natural selection. Statement D is not at all accurate regarding the principles of natural selection.

Question 451

How do chylomicrons and VLDLs differ? A) Chylomicrons contain apoproteins, VLDLs do not B) Chylomicrons are synthesized in the intestine, VLDLs are synthesized in the liver C) Chylomicrons transport triacylglycerol, VLDLs transport cholesterol D) VLDLs are another term for chylomicron remnants; they differ in age

Answer 451

B Chylomicrons and VLDLs are very similar. Both contain apolipoproteins and primarily transport triacylglycerol. The only major difference between them is the tissue of origin. Chylomicrons transport dietary triacylglycerol and originate in the small intestine, while VLDLs transport newly synthesized triacylglycerol and originate in the liver.

Question 452

Some vertebrates have developed various renal systems to deal with osmoregulation in their environments. Bony fish that live in seawater drink large amounts of seawater and use cells in gills to pump excess salt out of the body. This is in response to: A) A loss of water by active transport to their hypertonic surroundings. B) A loss of salt to their surroundings. C) An influx of water by osmosis into their tissues. D) A need to maintain their tissues in a hypoosmotic state.

Answer 452

D Different organisms have different needs to maintain their water balance, depending on the environment they live in. Bony fish living in saltwater maintain hypoosmotic body fluids. The hyperosmotic water they live in tends to draw the water out of their body by osmosis. They can obtain water by ingesting ocean water, but this raises their internal osmolarity. They excrete salt, then, to lower their internal osmolarity.

Question 453

Which of the following disorders is a mistake that occurred during meiosis, which resulted in a trisomy of the sex chromosome? A) Kawasaki Disease B) Ketoacidosis C) Down Syndrome D) Klinefelter Syndrome

Answer 453

D Klinefelter syndrome is a result of an extra X chromosome in men. The syndrome is normally not diagnosed until after puberty, and its outward symptoms are mild. Generally, men are diagnosed when they seek treatment for symptoms of other diseases or infertility.

Question 454

Some enzymes experience a decrease in activity proportional to the concentration of their products. This phenomenon could be an example of what process? A) Feedback inhibition B) Non-competitive inhibition C) Allosteric activation D) Both A and B

Answer 454

D Many cellular enzymes exhibit decreasing activity with increasing levels of reaction product. This feedback inhibition help regulate the activity of enzymatic processes. Often this process occurs through non-competitive inhibition. The product of the chemical reaction binds to the enzyme in a location other than the active site, which causes a conformational change in the enzyme and decreases enzymatic activity. Allosteric activation describes a process in which enzymatic activity is increased because of binding of some molecule to a site other than the active site.

Question 455

Which one of the following molecule is amphipathic, with both a hydrophilic and hydrophobic region? A) Starch B) Phospholipids C) Steroids D) Cholesterol

Answer 455

B The cell membrane is composed of a phospholipid bilayer that has a hydrophilic head (where the polar phosphate is attached) and a hydrophobic tail (made up of hydrocarbon chains). Starch is a polysaccharide that is generally hydrophilic and can be dissolved in water. Triglycerides, steroids and cholesterol are all entirely hydrophobic not being able to be dissolved in water. The molecule mentioned in the question is both hydrophilic and hydrophobic, indicative of the phospholipid, therefore only answer option [B] is correct.

Question 456

The cerebellum is the part of the brain that helps coordinate skeletal muscles and helps maintain posture and balance. To perform this complex function, the cerebellum must receive input from: A) The cerebrum and the proprioceptors B) The cerebrum and the inner ear C) The cerebrum, proprioceptors, and the inner ear D) Proprioceptors and the inner ear

Answer 456

C The movement of skeletal muscles is initiated in the cerebrum. Posture and balance are influenced, in part, from sensory signals originating in the joints, tendons, and muscles themselves (proprioception), as well as from the utricle, saccule, and semicircular canals in the inner ear.

Question 457

In general, each cell synthesizes its own macromolecules and does not receive them previously formed from other cells. For example, muscle cells make their own glycogen, rather than receiving it intact from the: A) Pancreas B) Kidney C) Liver D) Small intestine

Answer 457

C Knowledge about the roles of the liver is required. In addition, it should be understood that the liver first catabolizes its stored glycogen back to glucose. The monosaccharides enter the bloodstream, not the entire insoluble polysaccharide.

Question 458

Which of the following statements is NOT true regarding gastrin secretion and function? A) Increased production of HCl by parietal cells stimulates gastrin secretion B) Gastrin stimulates ECL cells to release histamine C) Somatostatin is an inhibitor of gastrin secretion D) Elevated gastric pH stimulates G cells to release gastrin

Answer 458

A Gastrin stimulates parietal cells to release HCl. If A were true, then there would be a positive feedback loop where gastrin is stimulating more HCl production, and HCl is stimulating more gastrin production, causing us to burn a hole through our stomach! Increased production of HCl by parietal cells leads to somatostatin secretion, which inhibits the secretion of gastrin. Lastly, an elevated gastric pH (i.e. low amount of acid) would stimulate the G cells to release more gastrin in an attempt to stimulate the parietal cells to release more HCl to bring the acidity back to normal.

Question 459

Cerebrospinal fluid (CSF) is created by special capillary networks located in the brain. CSF bathes the hollow regions of the brain, spinal cord, and around the central nervous system, within its protective coverings. The areas that the CSF pathway includes are: A) The ventricles, spinal canal, and meninges B) The ventricles, spinal canal, and cranial nerves C) The spinal canal, ventricles, and spinal nerves D) The spinal canal, meninges, and cranial nerves

Answer 459

A The organs of the central nervous system (CNS), the brain and spinal cord, have hollow regions (ventricles and spinal canal, respectively). The CNS also contains the meninges, which consists of three layers of protective covering. The question states that CSF circulates in these areas. Thus A is the correct answer. The spinal nerves and cranial nerves are not part of the CNS, they are part of the peripheral nervous system (with the exception of cranial nerve II, but that’s a little advanced for the MCAT).

Question 460

The process of the breakdown of fatty acid molecules (beta oxidation) in mammalian cells takes place in: A) Mitochondria and peroxisomes B) Mitochondria C) Cytosol D) Smooth endoplasmic reticulum

Answer 460

A Beta oxidation occurs in the peroxisomes in plant and yeast cells. In contrast, this vital reaction takes place in mitochondria and peroxisomes in mammalian cells. Peroxisomes are equipped with the appropriate enzymes that can facilitate the break down of very long fatty acid molecules.

Question 461

Which of the following is/are produced in both glycolysis and the electron transport chain? I. ATP II. NADH III. Oxygen IV. FADH2 A) I only B) I and III C) II and IV D) I, II and III

Answer 461

A ATP is the only product formed in both glycolysis and the ETC. Item II is false: NADH is produced only in glycolysis, and it is used in the ETC. Items III and IV are false: oxygen and FADH2 are not produced in either of these processes.

Question 462

Which of the following accurately describes the complement system? A) Part of the innate immune system comprised of leukocytes from the hematopoietic system B) Part of the innate immune system involving the inflammatory response of vascular tissues C) Part of the innate immune system comprised of plasma proteins synthesized primarily by hepatocytes D) Part of the adaptive immune system that involves Helper T-cells from the hematopoietic system

Answer 462

C The complement system is a clear example of innate immunity, being a form of host defense that is non-specific and does not adapt in response to antigens. However, there is evidence of cross-talk between the complement system and adaptive immunity. Similarly components of the complement system communicate with components of the inflammatory system and hematopoietic system. Nonetheless, complement system components are distinct from leukocytes and the components of the inflammatory system and are primarily synthesized in the liver.

Question 463

The lethal poison cyanide causes death by interfering with cellular respiration. What is cyanide’s mechanism of toxicity? A) Cyanide blocks the passage of electrons from cytochrome oxidase a3 to oxygen B) Cyanide inhibits the binding of ATP to ATP synthase C) Cyanide covalently binds to coenzyme Q (ubiquinone) D) Cyanide breaks down the proton gradient across the inner mitochondrial membrane

Answer 463

A Cyanide blocks the passage of electrons from cytochrome oxidase a3 to oxygen since it has a very high binding affinity for the enzyme. The cell cannot use oxygen so even if the person can breathe, the cells cannot use the oxygen that is delivered to tissues. Oligomycin inhibits the electron transport chain by directly affecting ATP synthase. A class of poisons called uncouplers makes the lipid bilayer permeable to hydrogen ions, which eliminates the electrochemical gradient.

Question 464

Mendel’s second law, the Law of Independent Assortment, states that each trait assigned to offspring is done so without regard to any other trait assigned. In a dihybrid cross of two dogs, one that is black with a short tail and the other that is white with a long tail, the inheritance of one fur color is not dependent upon the inheritance of tail length. Assuming that black fur is dominant and a long tail is dominant and each parent is homozygous for each trait, how many offspring in the F2 generation will be white with a short tail? A) 0 B) 1/16 C) 3/16 D) 9/16

Answer 464

B F1 generation is the heterozygous offspring of the homozygous parents. F2 generation is the offspring of the heterozygous offspring generation F1. The ratio is 9:3, 3:1 in this generation, meaning that only one of the offspring will have black fur and a long tail.

Question 465

Embryonic mesoderm in humans develops into which of the following structures? A) Liver and pancreas B) Brain C) Lining of the respiratory tract D) Skeleton

Answer 465

D The mesoderm develops into muscle and connective tissue which includes blood and bone (skeleton!), as well as circulatory, reproductive and excretory organs. The ectoderm produces the epidermis and the nervous system including the brain. The endoderm will become the epithelial lining of the respiratory tract, and the digestive tract including the glands of the accessory organs (i.e. the liver and pancreas). The stage of the embryo where the 3 primary germ layers first develop is called the ‘gastrula’.

Question 466

Which of the following is NOT considered part of the respiratory system? A) Pharynx B) Bronchus C) Trachea D) Esophagus

Answer 466

D While both the trachea and the esophagus are located in the throat and connected to the oropharynx, the esophagus is part of the digestive system, not the respiratory system.

Question 467

The human kidney can be damaged from a number of causes resulting in a patient’s inability to filter toxins (i.e. urea) from the body which could result in death. Complete kidney failure is usually first treated with dialysis which “cleans” the blood. The “dialyzer” is a glass container that has 3 main components: (1) blood percolating through to be cleaned; (2) a dividing membrane; and (3) the dialysate. The latter is liquid containing chemicals used to draw fluids and toxins out of the bloodstream and supply electrolytes and other chemicals to the bloodstream. All of the following are consistent with the process of dialysis EXCEPT: A) The membrane in the dialyzer separating the dialysate and the blood must be semipermeable B) The concentration of toxins in the dialysate must increase during dialysis C) The concentration of glucose and vital minerals in the dialysate must be similar to that of the patient’s blood D) Excessive minerals and toxins cross the membrane in the dialyzer by osmosis

Answer 467

D On the Surface: Dialysis only refers to the transfer of the solute (diffusion), while the transfer of the solvent is called osmosis. Going Deeper: On average, there is one question regarding diffusion or osmosis on the MCAT. Diffusion is the movement of a molecule across a semi-permeable barrier down its concentration gradient (from a region of high concentration to one of lower concentration). This is the process that must be occurring in the dialyser to remove toxins from the blood (because the dialysate, logically, would have no toxins so the toxins defuse out of the blood into the dialysate). Note that vital substances in the blood should be kept in the blood: options would include having a dialysate with the same concentration of those substances (so they don’t diffuse out of the blood) or by adjusting the permeability of the membrane. Osmosis is the movement of water – specifically water – across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration. So in summary, osmosis deals with how much water passes through the membrane, while dialysis deals with what type of solute (i.e., sodium, protein, glucose) passes through by simple diffusion.

Question 468

DNA is not found in which of the following body cells? A) Lymphocytes B) Erythrocytes C) Hair cells D) All cells in the body contain DNA

Answer 468

B Erythrocytes (or red blood cells) do not contain a nucleus and thus contains no DNA. This is to maximize the amount of O2 an erythrocyte can carry.

Question 469

In the kidney, the distal convoluted tubules of the nephron contain a filtrate in which the sodium concentration is lower than in the surrounding peritubular capillaries. If sodium ions move from filtrate to blood, what process is at work? A) Diffusion B) Osmosis C) Facilitated transport (facilitated diffusion) D) Active transport

Answer 469

D This question requires a basic understanding of membrane transport mechanisms. When a substance moves against a concentration gradient (from low concentration to high), energy is required. Active transport is the only mechanism capable of moving sodium in the direction described.

Question 470

Parathyroid hormone (PTH) is a peptide hormone produced in the parathyroid gland. It plays a major role in increasing blood calcium (Ca) levels, primarily through a negative feedback loop. Which of the following statements best describes how this feedback loop works? A) As Ca levels go up, PTH rises. This lowers Ca levels, leading to a drop in PTH B) As Ca levels go down, PTH drops. This raises Ca levels, leading to a rise in PTH C) As Ca levels go down, PTH rises. This raises Ca levels, leading to a drop in PTH D) None of the above is a negative feedback loop

Answer 470

C Hormone concentration usually changes in the opposite direction of the substance it regulates. When they change in the same direction, a positive feedback mechanism is at work.

Question 471

In high doses, aspirin functions as a mitochondrial uncoupler. How would this affect glycogen stores? A) It causes depletion of glycogen stores B) It has no effect on glycogen stores C) It promotes additional storage of glucose as glycogen D) Its effect on glycogen stores varies from cell to cell

Answer 471

A Uncouplers inhibit ATP synthesis without affecting the electron transport chain. Because the body must burn more fuel to maintain the proton-motive force, glycogen stores will be mobilized to feed into glycolysis, then the TCA, and finally oxidative phosphorylation.

Question 472

The velocity of nerve impulse propagation could be increased by: A) The process of nerve myelination B) Decreasing nerve diameter C) Increasing nerve diameter D) A and C

Answer 472

D During the evolution of living systems, there were two ways the velocity of nerve impulse propagation could be increased. The first way was increasing nerve diameter, while the second way was the formation of the myelin sheath. The latter mechanism is less energetically expensive than the former.

Question 473

Which of the following occurs when the heart is in systole? A) Blood is pumped from the ventricles to the arteries B) Blood is pumped from the veins to the heart C) Blood is collected in both veins and arteries D) Blood is collected in the right atria and right ventricle

Answer 473

A Systole is the state of contraction of the heart muscles. The heart contracts to pump blood out of the ventricles and into the arteries to move the blood to the body. During diastole or when the heart is resting, blood collects in the chambers of the heart. Arteries carry blood away from the heart and veins carry blood back to the heart. During systole, the blood is being pumped away from the heart, thereby the use of arteries is essential. The only answer option that aligns with the correct function of the heart during systole is [A].

Question 474

Color-blindness is a common sex-linked recessive trait in humans. If a woman is color blind, which is the most accurate statement about color-blind individuals in her family line? A) Both of her parents were color blind B) Both of her parents were carriers of color blindness C) Both of her parents, at least one of her mother's parents, and at least one of her father's parents had the gene D) Both of her parents, both of her mother's parents, and at least one of her father's parents had the gene

Answer 474

C If a woman is born color blind (a sex-linked recessive trait: XCXC), she must have a color blind father (XCY) who can donate one recessive X gene and a mother who was at least a carrier (XCXC, or XCX). The father must have received the color blindness allele from his mother. The mother must have had at least one parent with the color blindness allele.

Question 475

Pepsin is a hydrolytic enzyme found in the cell. How does pepsin prevent destroying the cells in the stomach which produce this enzyme? A) The stomach is coated by a substance that halts the effect of hydrolytic enzymes B) Pepsin remains in an inactive state until it is cleaved by HCl C) Enzymes do not destroy cells that are their precursors D) The amount of pepsin in the stomach is so small that it cannot destroy stomach cells

Answer 475

B Pepsin along with many other hydrolytic enzymes are produced in a “zymogen” form which remain inactive during their production. Once they are in the correct conditions, they self cleave and become active. Pepsin is secreted in the inactive form known as pepsinogen, which is cleaved in the acidic conditions of the stomach to form the active protease pepsin.

Question 476

Water and small proteins leak out of capillaries at their arterial ends because hydrostatic pressure (exerted mainly by blood pressure pushing outward against the capillary walls) is greater than colloid osmotic pressure (a fluid-retaining force caused by large solutes in the blood). Most of the fluid returns at the venule end because blood pressure: A) Increases and large solutes decrease B) Decreases and large solutes decrease C) Increases and large solutes stay the same D) Decreases and large solutes stay the same

Answer 476

D The major osmotic blood proteins are too large to leave the capillaries. Thus, colloid osmotic pressure (COP) normally remains the same at both ends of the capillary. However, blood pressure decreases in vessels as distance from the heart increases, resulting in hydrostatic pressure being lower than COP at the venule end.

Question 477

Arrector pili muscles are smooth muscles that cause “goosebumps” by pulling hairs in your skin. What causes the arrector pili muscles to contract? A) Somatic motor neurons B) Autonomic motor neurons C) Exocrine secretions D) Endocrine secretions

Answer 477

B The question directly states that arrector pili muscles are smooth muscles, and are therefore involuntary and under the control of autonomic motor neurons. Smooth muscles include muscles in your circulatory system and intestines that cause peristalsis.

Question 478

In the species of violet Viola granulanica, the allele Y is responsible for pigmentation of the petals and the allele X is responsible for petal shape. The dominant allele Y creates a red pigmentation in the petals, and a homozygous recessive pair of this allele will result in blue petals. The dominant allele X creates pointed petals, and a homozygous recessive pair of this allele will result in rounded petals. If a flower with the alleles YyXX and a flower with the alleles YyXx breed, what percent of the offspring will have blue-pointed petals? A) 0% B) 25% C) 33% D) 50%

Answer 478

B The resulting progeny will have 4 violets with blue-pointed petals out of a total of 16 possible combinations. If we generate a Punnet Square, we can lay out the alleles in the genetic cross. As we can see, there are 16 combinations possible, 12 of which result in red-pointed petals and 4 of which result in blue-pointed petals. There are no combinations featuring rounded petals, because the first flower did not contain any recessive alleles for X, and therefore all the resulting progeny in the cross have pointed petals.

Question 479

If the hormone aldosterone is released in the bloodstream, which of the following is most likely to occur? A) Bile and lipid production will increase B) The amount of glucose in the blood will decrease C) The amount of calcium ions in the blood will decrease D) The amount of salt reabsorbed in the kidneys will increase

Answer 479

D Aldosterone is a hormone released from the adrenal gland. Its presence in the blood helps the kidney’s retain more sodium chloride (NaCl) in the nephrons, thereby desalinating the urine. Glucose regulation is controlled by the pancreas’ release of insulin. Calcium ion levels are controlled by calcitonin and parathyroid hormone. The amount of water retained by the kidneys is controlled by the release of the antidiuretic hormone (ADH) or vasopressin. Aldosterone helps to retain water too, so the amount of water excreted by the body will decrease. Therefore, the correct answer is [D].

Question 480

The basic premise of cladistics is organisms that are closely related share a common evolutionary history. The characteristics that are shared by group members and derived from their ancestors are called: A) Plesiomorphies B) Synapomorphies C) Apomorphies D) Autapomorphies

Answer 480

B Plesiomorphies are characteristics that are original in the organism. While apomorphic means “derived characteristic”, the prefix syn- alters the meaning to “shared derived characteristic.” Using the prefix aut- causes the meaning to change to “self-derived characteristic” implying that it isn’t shared by another group. Homoplasy or homoplastic characteristics are shared among groups, but weren’t derived from an ancestral source.

Question 481

Which of the following is considered the most effective laboratory sterilization technique? A) UV light exposure for 10 minutes B) Boiling at 100 °C C) Spraying of 90% ethanol D) Autoclave

Answer 481

D The autoclave is the laboratory proven method for killing bacteria, fungi, and some viruses. It can reach temperatures of 121 °C and 2.7 atm, and the combined pressure and temperature are enough to kill the majority of existing pathogens. However, the autoclave cannot kill some species that are able to form heavy spores or protein coats, which include some viruses and fungi.

Question 482

Which layer of the epidermis is the characterized by a low rate of mitosis and a high concentration of keratin? A) Stratum basale B) Stratum spinosum C) Stratum corneum D) Stratum lucidum

Answer 482

C If a layer of epidermis has a low rate of mitosis, this indicates that the cells in this layer are not dividing very frequently. Likewise the presence of keratin, signals that the layer of epidermis must have a waterproofing function. The stratum basale is the most mitotic layer and is the bottom layer of the epidermis. As the cells are produced in the stratum basale, older cells are pushed up to the stratum spinosum, which is also high in mitotic activity. Keratin dominates in the stratum corneum, which is the most superficial layer of the epidermis, characterized by dead skin cells that are no longer undergoing mitosis.

Question 483

Which of the following is an example of a naturally occurring catabolic process? A) DNA replication B) Photosynthesis C) Cellular respiration D) Protein synthesis

Answer 483

C In the cell, metabolism is defined as the chemical reactions that occur within the cell to sustain life. Metabolism can further be divided into anabolism (the synthesis of new compounds) and catabolism (breaking down of substances). Answer options A, B and D, are all anabolic processes, that require the use of energy to make new compounds. In cellular respiration, glucose is broken down to produce ATP, therefore this is a catabolic process.

Question 484

Organisms within the Kingdom Plantae have which of the following cellular components? A) Chlorosomes B) Rigid cell membrane C) Vacuole D) Lysosome

Answer 484

C The correct answer is C. Cells within the Kingdom Plantae have chlorophyll containing cells called CHLOROPLASTS, a rigid cell WALL outside of the plasma membrane, and vacuoles that serve to store carbohydrates. Plant cells do not contain lysosomes, as other eukaryotic cells, instead they have peroxisomes for digestion of foreign material.

Question 485

Which of the following is NOT true of the different kinds of RNA in eukaryotes? A) They are single stranded molecules B) They all contain codons C) They may contain guanine and/or uracil D) They all elongate from the 5′ to 3′ direction

Answer 485

B There are 3 types of RNA: (1) ribosomal RNA (rRNA); (2) messenger RNA (mRNA) and (3) transfer RNA (tRNA). RNA is a single-stranded polymer made up of four bases, namely uracil, adenine, guanine and cytosine. Only mRNA can contain a codon, a genetic code consisting of three base pairs that can be translated by the cellular machinery into an amino acid during protein synthesis. RNA elongates elongates from the 5' to 3' direction using a DNA strand with the opposite orientation as a template for transcription.

Question 486

The human placenta is implicated in all of the following EXCEPT one. Which one is the EXCEPTION? A) Transporting urea and carbon dioxide from the fetus to the mother B) Initiating uterine contraction prior to birth C) Synthesizing glycogen to be used as an energy source for the fetus D) Secreting estrogen and progesterone during the gestation period Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning. First name Enter your email

Answer 486

B The placenta is formed from cells of the chorion of the embryo and the maternal endometrium, following implantation of the fertilized egg into the uterus. The placenta has 3 main functions: 1. The transfer of nutrients from the mother to the fetus and the transfer of wastes from the fetus to the mother (answer choice A.); 2. The production of nutrients for energy (answer choice C.), and 3. The production and secretion of hormones such as hCG, estrogen and progesterone (answer choice D.). Note that IgG is the only isotype that can pass through the human placenta. An increase in the hormone oxytocin, produced by the posterior pituitary, is associated with the initiation of uterine contractions.

Question 487

The plasma proteins that bind thyroid hormones are albumin, a prealbumin called thyroxine-binding prealbumin (TBPA), and thyroxine-binding globulin (TBG). The free thyroid hormones in plasma are in equilibrium with the protein-bound thyroid hormones in the tissues. Free thyroid hormones are added to the circulating pool by the thyroid. It is the free thyroid hormones in plasma that are physiologically active (increasing the metabolic rate) and imbalances in these hormones result in thyroid disease. In thyroid storm, a form of hyperthyroidism, the normal body temperature of 37.5 °C may rise to over 40 °C. Parathormone and the thyroid hormone calcitonin work antagonistically to regulate the plasma calcium and phosphate levels. Which of the following is an example of positive feedback? A) A body temperature of 39 °C causes a further increase B) Elevated TSH results in elevated thyroxine C) Calcitonin and parathormone regulate calcium levels D) Increased TBG leads to an increase in TSH

Answer 487

A Endocrine glands are often linked to neural control centers by homeostatic feedback mechanisms. The two types of feedback mechanisms, which happen to be frequent visitors to the real MCAT, are negative feedback and positive feedback. Negative feedback decreases the deviation from the normal value, and is important in maintaining homeostasis and thus controls most endocrine glands. The classic example of negative feedback is the thermostat in your home. As the temperature rises (deviation from the ideal normal value), the thermostat detects the change and triggers the air-conditioning to turn on and cool the house (or, it turns off the heating). Once the temperature reaches its thermostat setting (normal value), the air conditioning turns off. Positive feedback controls self-perpetuating events that can be out of control and do not require continuous adjustment. For example, in positive feedback the original stimulus is promoted rather than negated, thus the deviation from the normal value increases. Unlike negative feedback that maintains hormone levels within narrow ranges, positive feedback is rarely used to maintain homeostatic functions. If calcium decreases, the parathyroid glands sense the decrease and secrete more parathyroid hormone. The parathyroid hormone stimulates calcium release from the bones and increases the calcium uptake into the bloodstream from the collecting tubules in the kidneys. Conversely, if blood calcium increases too much, the parathyroid glands reduce parathyroid hormone production. Both responses are examples of negative feedback because in both cases the effects are negative (opposite) to the stimulus. If your increased body temperature triggers a further increase in body temperature (getting further away from the normal), then this is a classic example of positive feedback.

Question 488

Which of the following terms best describes the process of a cell engulfing solid particles? A) Exocytosis B) Apoptosis C) Pinocytosis D) Phagocytosis

Answer 488

D A cell can bring things into the cell, a process referred to as endocytosis. More specifically, when the cell engulfs liquid this is called pinocytosis or “cell drinking” and when the cell engulfs solids this is called phagocytosis or “cell eating”. Exocytosis is the process by which particles are taken out of the cell and apoptosis is the process of cell death.

Question 489

If you desire to prevent the initial enzymatic breakdown of polysaccharides, where in the body should the release of such enzymes be blocked? A) In the mouth, stomach, pancreas, and small intestine B) In the mouth, stomach, and pancreas C) In the mouth, pancreas, and small intestine D) In the mouth and pancreas

Answer 489

D The initial breakdown of polysaccharides to disaccharides is in the mouth via salivary amylase and pancreatic amylase via the pancreas to the small intestine. We do not block the small intestine since the pancreatic amylase is not produced there, we block the source as the question wanted to know how to block the enzyme.

Question 490

Which of the following is considered to be the defining characteristic of organisms in the Kingdom Monera? A) Single-celled with no confined storage area for genetic material B) Protein-based infectious particle C) Single-celled using flagella for locomotion D) Single-celled with a separation of genetic material from cellular machinery

Answer 490

A Though some organisms in the Kingdom Monera utilize flagella for locomotion, the defining characteristic of organisms in the Kingdom Monera is that they do not house their genetic material in a confined space separate from their cellular machinery. Organisms that do confine their genetic material are eukaryotic organisms, some of which are single celled and some of which have multicellular organization, and are not part of the Monera Kingdom.

Question 491

What will happen if a person with AB-negative blood receives a blood transfusion from someone with O-positive blood? I. Nothing; AB blood is the “universal recipient” and can receive any blood type without eliciting an immune response. II. Nothing; O-positive blood is the “universal donor”, meaning that any blood type can receive it without eliciting an immune response. III. The recipient will experience an immune response against the Rh antigen. IV. The recipient will experience an immune response against the O antigen. A. I only B. I and II only C. III only D. IV only

Answer 491

C This question is a little tricky. A person with AB blood is the universal recipient ONLY if they contain ALL antigens — this includes the Rh antigen (aka if they are “positive”). In other words, a person with AB-negative blood will have antibodies against the Rh antigen (against any “positive” blood type). Additionally, universal donor blood must contain NO antigens, meaning it must not contain A, B or Rh antigens. While O blood is the “universal donor”, this is ONLY true if the blood is negative (void of the Rh antigen). While O-positive blood can be accepted by A-positive, B-positive, and AB-positive, it will trigger an immune response in someone with negative blood, because their blood would contain antibodies against the Rh factor. Thus, because the recipient blood is negative (does not contain Rh antigens), it therefore contains antibodies (and will elicit immune response) against the Rh factor of someone with O-positive blood. This leaves us with answer choice C.

Question 492

Blood pressure is increased when: A) Aldosterone increases water permeability in the collecting ducts of nephrons B) Sympathetic activation decreases the diameter of arterioles systematically C) Parasympathetic innervation increases the flow of blood to digestive organs D) Antidiuretic hormone increases sodium reabsorption in nephrons

Answer 492

B Activation of the sympathetic division of the ANS triggers systemic vasoconstriction (decrease in diameter) in arterioles, leading to an increase in systemic blood pressure. Choices A and D have the functions of the hormones backwards (and thus are wrong): aldosterone increases sodium reabsorption in nephrons and antidiuretic hormone increases water permeability, to learn about other ways to boost your hormones, check out the Men's Journal website. (Note that the two hormones working together would lead to a increase in total body salt and consequently, total body water, followed by an increase in blood pressure.) While it is true that blood flow to digestive organs is increased when the body is under parasympathetic control, this is not due to the direct action of the parasympathetic division on the blood vessels to those organs. The parasympathetic division actually does not innervate the blood vessels at all; the increased blood flow under these conditions is due to the withdrawal of sympathetic stimulation. Even if the parasympathetic division did increase vessel diameter, this would not lead to an increase in blood pressure (choice C is wrong).

Question 493

The semiconservative hypothesis of replication refers to: A) The process of transcription B) The activity of lysogenic viruses C) An aspect of protein formation D) The formation of chromatids

Answer 493

D It should be known that the semiconservative hypothesis refers to the supported model of how DNA replication works. This occurs at the beginning of mitosis or meiosis, when chromatids are synthesized.

Question 494

A cell receives a treatment that inhibits DNA polymerase activity. Which stage of the cell cycle will be most affected? A) Interphase B) Prophase C) Anaphase D) Telophase

Answer 494

A DNA polymerase is the enzyme involved with bringing DNA nucleotides into place during DNA replication. In the cell cycle, this occurs during the S phase of interphase.

Question 495

The placenta is an organ that develops from cells of the chorion and endometrium. Therefore, it is comprised of: A) Maternal tissue B) Embryonic tissue C) Both maternal and embryonic tissues D) It is an independent organ consisting of neither maternal nor embryonic tissues

Answer 495

C The chorion forms from cells of the trophoblast, an embryonic tissue. The endometrium is the inner lining of the uterus, a maternal tissue. Therefore, the placenta consists of tissues derived from both.

Question 496

Point mutations are changes in a single DNA nucleotide base pair. Which point mutations have the highest probability of causing drastic results? A) Substitutions B) Deletions C) Additions and Deletions D) All three have and equal chance of causing drastic results

Answer 496

C Substitutions affect only one codon, and as a result, only one amino acid. Both additions and deletions affect the codons in which they occur, and every codon thereafter (frameshift mutations).

Question 497

Which statement is most true concerning obligate anaerobes? A) These organisms can use oxygen if it is present in their environment B) These organisms cannot use oxygen as their final electron acceptor C) These organisms carry out fermentation for at least 50 percent of their ATP production D) Most of these organisms are vegetative fungi

Answer 497

B Obligate anaerobes require the absence of oxygen to survive.

Question 498

The polio virus can infect and destroy cell bodies location in the anterior horn of the spinal cord. These motor neurons are vital because they stimulate: A) The part of the brain that controls voluntary movement B) Receptors found in freely movable joints C) Skeletal muscles D) Interneurons along circuits leading to the cerebrum

Answer 498

C Motor neurons, by definition, carry impulses from the CNS to the effectors. Only choice C is a plausible answer.

Question 499

Which of the following gives the relative amounts of the smooth and rough endoplasmic reticulum in liver vs. pancreatic cells? A) Rough ER is more abundant in liver cells and smooth ER is more abundant in pancreatic cells B) Smooth ER is more abundant in liver cells and rough ER is more abundant in a pancreatic cells C) Rough ER is more abundant in both cell types D) Smooth ER is more abundant in both cell types

Answer 499

B The most abundant organelle in a liver cell is the smooth ER. The smooth ER is involved in lipid synthesis/modification and in the liver is important for detoxification. The rough ER is the site of protein synthesis for secretory and membrane proteins. Pancreatic cells contain large amounts of rough ER to manage the manufacturing of large amounts of secretory proteins (digestive enzymes).

Question 500

During respiratory ventilation, impulses along the phrenic nerves stimulate the diaphragm, causing it to contract and move downward. When this occurs, which of the following takes place in the thoracic cavity and lungs? A) Volume increases, pressure increases, and air moves out B) Volume decreases, pressure decreases, and air moves out C) Volume increases, pressure decreases, and air moves in D) Volume decreases, pressure increases, and air moves in

Answer 500

C When the diaphragm contracts (moves downward), the volume in the thoracic cavity increases, causing the pressure to decrease. As a result, the air outside the body is under high pressure than the air in the lungs, and air rushes in.

Question 501

Chromosome puffs can be observed along giant polytene chromosomes in the salivary gland cells of insect larvae. They appear to be regions of DNA that uncoil or decondense. The locations of puffs change at different times during larval development in response to hormonal signals. This phenomenon is an example of: A) Gene regulation at the transcriptional level B) A polygenic trait C) Posttranscriptional RNA processing D) Gene expression at the translational level

Answer 501

A If chromosome puffs represent uncoiled or decondensed regions of DNA, this suggests that the DNA sequence has to be “read”, either for DNA replication or protein synthesis. Since the insect larva is undergoing different developmental changes in response to hormones, the synthesis of various proteins needed during each subsequent stage seems more probable. The hormone appears to be “activating” genes along the DNA so that transcription of these DNA sequences can occur.

Question 502

The inflammatory response results from the release of histamine by mast cells or basophils. The redness, heat, pain, and swelling associated with inflammation are due to which physiological effects of histamine? A) Dilation of local blood vessels/ Less fluid leakage from capillaries B) Dilation of local blood vessels/More fluid leakage from capillaries C) Constriction of local blood vessels/Less fluid leakage from capillaries D) Constriction of local blood vessels/More fluid leakage from capillaries

Answer 502

B The symptoms described, i.e. redness and heat, would result from more red, warm blood in the area (dilation of blood vessels). Similarly, swelling and pain would result from additional fluids in the area stimulating pain receptors (more fluid leakage from capillaries).

Question 503

The human body has various ways to protect itself against pathogens, including specific and nonspecific defense mechanisms. The nonspecific defenses do not distinguish one pathogen from another. Which of the following would NOT be considered a component of the nonspecific defenses? A) Macrophages B) Inflammation C) Antibodies D) Interferon

Answer 503

C Phagocytosis by macrophages, inflammation, and interferon are all general, nonspecific responses by the immune system. Each type of antibody, on the other hand, is normally produced in response to a specific antigen (usually associated with a specific invading organism).

Question 504

Which of the following vitamins is absorbed in the stomach, not duodenum, via parietal cell production of a Glycoprotein (GIF)? A) Niacin B) Alpha-Tocopherol C) B12 D) Cholecalciferol

Answer 504

C Vitamin B12 is the only vitamin absorbed by the body prior to transportation through the Pyloric Sphincter into the small intestines.