Misc. #2

Question 1

Erwin Chargaff investigated the nucleotide composition of DNA . He analyzed DNA from various organisms and measured the relative amounts of adenine ( A ), guanine ( G ), cytosine ( C ), and thymine ( T ) present in the DNA of each organism. Table 1 contains a selected data set of his results.

Which of the following statements best explains the data set?

Answer 1

Since the %A and the %T are approximately the same in each sample, adenine and thymine molecules must pair up in a double-stranded DNA molecule.

Question 2

Antibiotics can be used to kill the specific pathogenic bacterium, Mycobacterium tuberculosis, that causes tuberculosis. The appearance of antibiotic-resistant strains has made it more difficult to cure M. tuberculosis infections. These antibiotic-resistant bacteria survive and pass on the genes to their offspring, making the resistant phenotype more common in the population.

DNA analysis indicates that the genes for antibiotic resistance are not normally present in bacterial chromosomal DNA.

Which of the following statements best explains how the genes for antibiotic resistance can be transmitted between bacteria without the exchange of bacterial chromosomal DNA?

Answer 2

The genes for antibiotic resistance are located on a plasmid that can be passed to neighboring bacteria.

Question 3

Which of the following statements best explains the structure and importance of plasmids to prokaryotes?

Answer 3

Plasmids are circular, double-stranded DNA molecules that provide genes that may aid in survival of the prokaryotic cell.

Question 4

Which of the following statements best describes how organisms such as rabbits obtain the carbon necessary for building biological molecules?

Answer 4

Rabbits eat plants and break down plant molecules to obtain carbon and other atoms that they rearrange into new carbon-containing molecules.

Question 5

The figure shows a model of the exchange of matter between the organisms that live together in an aquarium. The model includes matter exchange between plants, fish, and bacteria. The bacteria are represented as rod-shaped organisms living in the gravel at the bottom of the aquarium.

Which of the following statements best describes how molecules released by the fish become nutrients for the plants?

Answer 5

The ammonia molecules released by the fish are converted by the bacteria to nitrates, which are used by the plants to make proteins and nucleic acids.

Question 6

Students conducted a controlled experiment to investigate whether sawdust provides enough nutrients to support plant growth. The students separated ten nearly identical sunflower seedlings into two groups. They grew the seedlings in the first group in potting soil and the seedlings in the second group in sawdust composed mostly of cellulose. After twenty days, the students recorded observations about the seedlings in each group. The students’ observations are presented in the table.

The observed differences between the groups most likely resulted from differences in the ability of the seedlings to produce which of the following monomers?

Answer 6

Answer C
Correct. Sawdust will not provide sufficient amounts of nitrogen and phosphorus, resulting in the seedlings having a reduced ability to produce both of the monomers shown (amino acids and nucleotides).

Question 7

Which of the following statements best predicts the effect of increasing the concentration of substrate (ethyl alcohol), while keeping the concentration of the inhibitor (methyl alcohol) constant?

Answer 7

Competitive inhibition will decrease because the proportion of the active sites occupied by substrate will increase.

Question 8

The enzyme peroxidase is found in many organisms. It catalyzes the breakdown of hydrogen peroxide into water and oxygen gas. The rate of peroxidase activity at different pH values was assessed by students in the lab. The students’ results are shown in graph 1.

If the experiment is repeated at pH 11, the observed activity level of the enzyme will most likely be

Answer 8

lower than the level at pH 9

Question 9

Protein digestion in humans is primarily carried out by three enzymes. Pepsin is found in the stomach (pH2), where it aids in the breakdown of large proteins into smaller peptides, while trypsin and chymotrypsin are found in the small intestine (pH8), where they aid in the further breakdown of the proteins into amino acids and dipeptides that can be absorbed into the bloodstream. Graph 1 shows the effect of pH on the activity levels of the three enzymes.

Which of the following best predicts how the structure and function of pepsin will change as it enters the small intestine?

Answer 9

Pepsin will change in shape because of the basic environment of the small intestine; therefore, its enzymatic activity will decrease.

Question 10

Amylase is a protein that catalyzes the conversion of starch to simple sugars. Amylase activity in an aqueous solution can be measured by using iodine as a starch indicator. A solution containing iodine and starch will have a dark-blue color, whereas a solution containing iodine but no starch will have a light-brown color. The color change of an iodine solution from dark blue to light brown can be used to measure the rate at which starch is converted to simple sugars.

Which of the following statements best justifies the inclusion of test tube V as a control in the experiment?

Answer 10

It will show the color change that occurs in the absence of enzyme activity.

Question 11

A researcher claims that some bacteria contain factors that influence the function of a particular enzyme but other bacteria do not. To test the claim experimentally, the researcher will grow two different bacterial strains in separate liquid cultures and isolate the contents of the cells in each culture. The researcher will add different combinations of cellular contents, substrate, and enzyme to test tubes containing a buffer solution adjusted to the optimal pH of the enzyme and then measure the rate of product formation. The design of the researcher’s experiment is presented in Table 1.

Which of the following statements best justifies the inclusion of test tubes 3 and 7 in the experiment?

Answer 11

They will show whether the isolated cellular contents have enzymatic activity.

Question 12

A researcher designs an experiment to investigate the effect of environmental temperature on the function of an enzyme. For each trial included in the experiment, the researcher will add the enzyme and its substrate to an aqueous buffer solution and then measure the amount of product formed over 20 minutes.

Which of the following must remain the same for all trials of this experiment?

Answer 12

The initial concentration of the substrate

Question 13

Gelatin is a protein that is derived from collagen which is found in the bones, skin, and connective tissue of animals. To investigate the ability of various enzymes to digest gelatin, a group of students set up an assay involving camera film. Camera film contains gelatin and appears black when exposed to light but turns clear as the gelatin gets broken down. The students incubated pieces of exposed camera film in test tubes, each containing one of three different enzyme solutions (trypsin, lipase, or amylase) as indicated in Figure 1. The students recorded the time it took for the enzymes to digest the gelatin in each test tube, turning the film from black to clear.

Which of the following would be the most appropriate control for this experiment?

Answer 13

A test tube containing a piece of exposed camera film submerged in water

Question 14

A researcher claims that different enzymes exhibit maximal function over different pH ranges. To test the claim, the researcher carries out an experiment that includes three different enzymes: pepsin, salivary amylase, and arginase. The results of the experiment are represented in Figure 1.

Which of the following actions will provide the most appropriate negative control for the experiment?

Answer 14

Repeating the experiment with denatured enzymes

Question 15

A researcher claims that increasing the environmental temperature by 10°C will double the rate of an enzyme-catalyzed reaction. To test the claim, the researcher designs an experiment that uses a particular enzyme isolated from plants. The design of the experiment is presented in Table 1. For each test tube in the experiment, the researcher will measure the rate of product formation.

Which of the following statements best helps justify the inclusion of test tube 5 as a control in the experiment?

Answer 15

It will provide a measurement of product formation in the presence of a denatured enzyme.

Question 16

Which of the following statements best helps explain the reaction specificity of an enzyme?

Answer 16

The shape and charge of the substrates are compatible with the active site of the enzyme.

Question 17

The enzyme hexokinase catalyzes the conversion of glucose to glucose-6-phosphate, which is an important step in glycolysis. The reaction involves the transfer of a phosphate group from ATP to glucose.

Either a glucose molecule or a water molecule can fit in the active site of hexokinase. The presence of a water molecule in hexokinase’s active site would result in the hydrolysis of ATP to ADP instead of the conversion of glucose to glucose-6-phosphate.

Which of the following statements best helps explain the reaction specificity of hexokinase?

Answer 17

Glucose has the right shape and charge to cause hexokinase to undergo a structural change needed for catalysis, whereas water does not.

Question 18

The illustration shows the active transport of hydrogen ions through a membrane protein.

Which of the following best predicts the effect of not having ATP available to supply energy to this process?

Answer 18

H+ ions will stop moving through the protein.

Question 19

Which statement best describes the effect on water transport across the cell membrane if the aquaporin in the figure ceases to function?

Answer 19

Water molecules will still be able to move across the cell membrane but at a slower rate.

Question 20

A cell’s membrane potential is maintained by the movement of ions into and out of the cell. A model showing the influence of membrane proteins on the movement of sodium (Na+) and potassium (K+) ions across the plasma membrane is presented in Figure 1.
Based on the model presented in Figure 1, which of the following outcomes will most likely result from a loss of protein x function?

Answer 20

The membrane potential will be disrupted by an increase in K+ concentration inside the cell.

Question 21

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1.

Cyclic AMP phosphodiesterase is an enzyme that catalyzes the conversion of cyclic AMP to a different molecule. Which of the following best predicts the effect of inhibiting cyclic AMP phosphodiesterase in a muscle cell stimulated by epinephrine?

Answer 21

Phosphorylase kinase will remain active because protein kinase A will no longer be deactivated.

Question 22

Figure 1 is a proposed model of the feedback system controlling erythrocyte (red blood cell) production.

Air is less dense at very high elevations, so less oxygen is available than in the denser air at sea level. Based on the model in Figure 1, if a person travels from sea level to a high elevation location, which of the following correctly predicts the response to the decreased blood oxygen level?

Answer 22

More erythropoietin will be secreted from the kidneys, increasing production of erythrocytes.

Question 23

The coagulation cascade controls blood clot formation in response to blood vessel injury. Thrombin is an enzyme that plays a key role in regulating the coagulation cascade. A simplified model of thrombin’s role in regulating the coagulation cascade is represented in Figure 1.

Argatroban is a competitive inhibitor of thrombin. Which of the following effects on the coagulation cascade is most likely to result from inhibiting thrombin activity with argatroban?

Answer 23

The rate of fibrin formation will decrease.

Question 24

researcher claims that different metabolic pathways allow bacteria to use different molecules as sources of matter and energy.

Which of the following statements best helps justify the researcher’s claim by providing a relevant example?

Answer 24

E. coli bacteria reproduce in liquid media containing either glucose or galactose.

Question 25

Cyanobacteria contain a variety of pigment molecules, as shown in Table 1. As a result, the color of cyanobacteria cultures can vary significantly based on the relative amount of each pigment produced.

A researcher placed a culture of cyanobacteria under green lights. Within a few weeks, the appearance of the cyanobacteria changed from green to red. The researcher claimed the color change in the culture was the result of an adaptation allowing greater photosynthesis.

Which of the following provides the best reasoning to justify the researcher’s claim?

Answer 25

In green light, more phycoerythrin molecules are produced, allowing more green light to be absorbed, thus increasing photosynthesis.

Question 26

In addition to the pigments commonly associated with photosynthesis, a certain photosynthetic species contains two additional pigment types.

Which of the following best supports the claim that this species is better adapted to environmental changes than other photosynthetic species are?

Answer 26

The additional pigments allow the species containing them to harvest energy from wavelengths of light that the other photosynthetic species cannot use.

Question 27

Figure 1. Formation of a peptide bond

Which of the following best describes the formation of the bond shown in Figure 1 ?

Answer 27

A covalent bond is formed between a carbon atom and a nitrogen atom along with the formation of H2O

Question 28

Figure 1 represents a common process that occurs in organisms.

Figure 1. Structural formula for a common biological reaction

Which of the following is an accurate description of the process shown in Figure 1 ?

Answer 28

The formation of a covalent peptide bond in a dehydration synthesis reaction

Question 29

Polypeptides are continuously being formed and degraded. One of these processes is shown.

Figure 1. Polypeptide reaction

Which statement is the most accurate description of the reaction shown in Figure 1?

Answer 29

It represents a polypeptide chain that is broken down through a hydrolysis reaction.

Question 30

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1.

Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells

Based on Figure 1, which of the following statements best describes the epinephrine signaling pathway?

Answer 30

In involves enzymes activating other enzymes.

Question 31

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1.

Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells

Which of the following statements best describes the role of adenylyl cyclase in the epinephrine signaling pathway?

Answer 31

It accelerates the production of a second messenger.

Question 32

In a certain signal transduction pathway, the binding of an extracellular molecule to a cell-surface protein results in a rapid increase in the concentration of cyclic AMP inside the cell. The cyclic AMP binds to and activates cytosolic enzymes that then activate other enzymes in the cell.

Which of the following statements best describes the role of cyclic AMP in the signal transduction pathway?

Answer 32

It acts as a second messenger that helps relay and amplify the signal within the cell.

Question 33

Based on the information presented, which of the following is the most likely explanation for a buildup of cholesterol molecules in the blood of an animal?

Answer 33

The animal’s body cells are defective in endocytosis.

Question 34

Which of the following statements best explains the processes of passive and active transport?

Answer 34

Passive transport is the net movement of substances down a concentration gradient that does not require metabolic energy. Active transport is the movement of substances up a concentration gradient that requires energy.

Question 35

In an experiment, cells were isolated from an aquatic plant and suspended in pond water, a sucrose sugar solution, or distilled water. All of the cells were then viewed under a microscope. Compared with the cell in the pond water, the cell in the sugar solution appeared shriveled, and the cell in the distilled water appeared inflated. The results of the experiment are represented in Figure 1.

Which of the following statements best explains the observations represented in Figure 1 ?

Answer 35

There was a net movement of water out of the cell suspended in the sugar solution and a net movement of water into the cell suspended in the distilled water.