Exam #4 Flashcards
Which of the following is the source of energy for the synthesis of small organic molecules that predated the earliest forms of life?
A. anaerobic respiration B. photosynthesis in algae C. decomposition by fungi D. lightning E. geothermal vents
D. lightning
This question is based on Miller-Urey’s experiment on the chemical origins of life. Several nonorganic molecules (excluding oxygen) were enclosed in a flask and allowed to react with firing electrodes to replicate lightning. There was a significant amount of lightning on primitive Earth, which we believe helped give the “spark” of life. Choices [A], [B], and [C] can be eliminated because they refer to processes by living organisms, and the question asks for the source of energy before life. Geothermal vents are a plausible distractor, but ultimately the source of energy is believed to be lightning, which was replicated in Miller-Urey’s experiment.
Why are chromosomes not visible during interphase?
A. They uncoil to allow replication and transcription
B. They condense into separate small packets of genes
C. Unexpressed genes are degraded to allow the cell to specialize
D. They reform the nuclear envelope
E. They migrate to the cytoplasm to be translated into proteins
A. They uncoil to allow replication and transcription
A cell goes through several phases in the cell cycle. These stages include G1, S, G2, and M phases. Each of these phases has a checkpoint to ensure everything is working properly. The deregulation of the cell cycle leads to cancer.
The G1, S and G2 phases are collectively known as interphase. During this period, the cell grows (G1 and G2 phases, G for “grow”) and replicates its DNA in the S phase (S for synthesis). The M phase stands for mitosis, where the cell spends the least amount of its time.
During mitosis, the chromosomes condense to separate both copies of the DNA to each daughter cell. However, the DNA is so tightly coiled that enzymes cannot transcribe the DNA. During interphase, the DNA uncoils to allow enzymes to transcribe and replicate the DNA.
The second law of thermodynamics can explain which of the following statements?
A. Some of the energy transferred in a cell is lost as heat.
B. The ultimate source of all energy comes from the Sun.
C. Saprophytes recycle unusable energy such as heat.
D. Isolated systems tend to decrease in entropy.
E. Energy can be created through photosynthesis.
A. Some of the energy transferred in a cell is lost as heat.
The second law of thermodynamics states that the entropy in a system always increases. Entropy is a measure of disorder in a system. Anytime we transfer between two types of energy or use energy, we do not have 100% efficiency. This is because a lot of the energy will be lost as heat due to the second law of thermodynamics. Note that the energy is not destroyed, it is simply transformed into a different unusable state. The first law of thermodynamics states that energy cannot be created nor destroyed.
In centrifugation, which factor determines if a cellular component ends up in the pellet or supernatant?
A. size and weight B. ATP production C. polarity D. solubility E. electric charge
A. size and weight
A centrifuge separates a homogenized solution into a precipitate, or a pellet, which is a solid mass at the bottom of the tube, and the supernatant, which is a solution of everything else in the original solution. Centrifugation separates cellular components based on their size and weight. This is why the nucleus pellets from a lysate first – it is the largest and heaviest organelle. Next, mitochondria are pelleted, and then microsomes (vesicles of the ER), and finally ribosomes. Small soluble proteins remain in the supernatant after ribosomes are pelleted.
During cell division, which of the following stages are most similar?
A. Mitotic prophase and meiosis metaphase I
B. Mitotic telophase and meiosis telophase I
C. Mitotic anaphase and meiosis anaphase I
D. Mitotic metaphase and meiosis metaphase II
E. Mitotic metaphase and meiosis metaphase I
D. Mitotic metaphase and meiosis metaphase II
During mitotic metaphase, all of the chromosomes (each with two chromatids) line up on the metaphase plate in the cell. During metaphase II in meiosis, half of the chromosomes (each with two chromatids) also line up on the metaphase plate. Metaphase II is more similar to mitotic metaphase because metaphase II only consists of chromosomes with 2 chromatids each, while metaphase I consists of homologous chromosomes (or tetrads, with 4 chromatids).
During which step can nondisjunction occur in mitosis?
A. Prophase B. Prometaphase C. Metaphase D. Anaphase E. Telophase
D. Anaphase
Nondisjunction is the failure of one or more chromosome pairs to separate properly during mitotic anaphase, anaphase I, or anaphase II. It most often occurs in embryonic development. The result is two daughter cells with extra or missing chromosomes. If this occurs in meiosis, and the aneuploidic gamete is fertilized, a number of syndromes may result. This is commonly known as trisomy; examples of trisomies include Down’s syndrome (trisomy 21) and Turner syndrome (absence of one X chromosome in females, monosomy X).
Which product(s) is/are common in both glycolysis and the electron transport chain?
I. Oxygen
II. ATP
III. NADH
IV. NAD+
ll. ATP
The products of glycolysis are two pyruvate molecules, NADH, and ATP. The products of the electron transport chain are NAD+, FAD, H2O, and ATP. The only product common to both is ATP, or Choice [B]. Memorize the table below for the reactants and products of the five big cellular respiration pathways. Note: pyruvate is converted into acetyl CoA in a step before the Krebs cycle, releasing 1 NADH and 1 CO2.
All of the following events occur during photosynthesis EXCEPT for one. Which one is the EXCEPTION?
A. Glucose is produced in the stroma
B. The pH inside of the thylakoid is decreased
C. Carbon dioxide is more concentrated in the stroma
D. The inner membrane of the chloroplast absorbs light
E. Photolysis of water provides the source of electrons
D. The inner membrane of the chloroplast absorbs light
The thylakoid membrane contains the chlorophyll molecules that absorb light. The inner membrane does not have a large role in photosynthesis. Most of photosynthesis occurs in the stroma and thylakoid. Water undergoes photolysis inside of the thylakoid to provide electrons for the chlorophyll molecules to excite with photons of light. As the electrons fall through the electron transport chain of the thylakoid membrane, H+ ions flow into the thylakoid (OPPOSITE of mitochondria, where H+ ions flow OUT of the matrix). The flow of H+ ions into the thylakoid decreases the pH because it becomes more acidic. The electrons react with NADP+ to form NADPH. ATP is produced by ATP synthase in the thylakoid membrane. The light dependent reactions generally take place inside of the thylakoid or in the thylakoid membrane.
The LIGHT INDEPENDENT reactions generally take place in the STROMA. CO2 concentrates in the stroma to be fixed into glucose by the Calvin-Benson cycle.
Which organelle is the nucleus attached to?
A. mitochondrion B. endoplasmic reticulum C. nucleolus D. centriole E. Golgi complex
B. endoplasmic reticulum
All of the following are methods plants use to reduce water loss EXCEPT for one. Which one is the EXCEPTION?
A. trichomes and hairs on the leaves B. needle-like leaf structure C. thick waxy cuticles D. reflection of green light E. guard cells in stomata
D. reflection of green light
Plants have evolved many different mechanisms to decrease the amount of water they lose to transpiration. Among them include growing little “hairs” on their leaves to retain more moisture and a thin needle-like leaf structure. Christmas trees and other conifers have needle leaves as an adaptation to growing in a dry environment. Desert plants have thick waxy cuticles as a way to minimize the amount of moisture the plant transpires, and guard cells in the stomata close off the holes in the leaves when activated. The reflection of green light is irrelevant to reducing water loss.
Trichomes (tiny hair-like structures) and hairs on leaves can help prevent water loss by trapping moisture
Guard cells are specialized epidermal cells that control opening and closing of the stomata
Which of the following has a similar function to the cristae of mitochondria?
A. Thylakoid membrane in chloroplast B. Cisternae in Golgi complex C. Nuclear envelope D. Intermembrane space in chloroplast E. Endoplasmic reticulum
A. Thylakoid membrane in chloroplast
The crista of mitochondria houses the electron transport chain (ETC) to create a proton force for ATP synthesis. The thylakoid membrane is the equivalent to this in photosynthesis; this is where the electron transport chain occurs to produce ATP and NADPH in photosynthetic organisms in the light-dependent reactions.
The splitting of water in the plant provides two electrons to be excited by photons of light in Photosystem II, which will then travel through the ETC to produce some ATP. The pair of electrons can be excited again in Photosystem I, where they can go through the ETC again to produce ATP (cyclic photophosphorylation), or react with NADP+ and H+ from splitting water earlier to form NADPH. NADPH and ATP will be used in the light-independent reactions to reduce CO2 into glucose.
While functionally similar, the key difference between the two is that in CHLOROPLAST, H+ MOVE from inside the thylakoid lumen OUTWARD to the stroma to synthesize ATP, while in mitochondria H+ move from outside the cristae (the intermembrane space) inward to the mitochondrial matrix.
Which of the following classes do sponges belong to?
A. Rotifera B. Cnidaria C. Annelida D. Porifera E. Platyhelminthes
D. Porifera
Porifera are the sponges. You can remember this because sponges are porous and “porifera” sounds similar. They are also classified with the parazoa, meaning even though they are multi-cellular, the cells are not organized and no organs develop.
Rotifera are rotifers, again both names sound very similar. Rotifers are especially cool because they are microscopic animals. They have a pseudocoelom.
Cnidaria include hydrozoans, jellyfish, sea anemones, and corals.
Annelida are segmented worms, such as leeches, earthworms, and polychaete worms.
Platyhelminthes are the flatworms and are known to be acoelomate. Some of the flatworms include planarians (planarians, planar meaning flat) and tapeworms (tape is flat). Tapeworms do not have a complete digestive tract because they just absorb pre-digested food from the stomach of their hosts.
Rotifers are very similar in characteristics to the phylum Nematoda, with the exception of excretory system (Rotifers have protonephridia and flame cells). They are typically found in freshwater environments.
Examples of Cnidaria include hydra, jellyfish, sea anemones, and coral. They are diploblasts with radial symmetry.
Examples of Annelida include earthworms and leeches. They are triploblasts with bilateral symmetry, and have segmented bodies.
Porifera are asymmetrical and have no true tissue organization or specialized body systems. They use intracellular digestion, via AMOEBACYTES
Examples of Platyhelminthes include flatworms and tapeworms. They are triplopblasts with bilateral symmetry, and are ACOELOMATE.
A sample of verotoxin, which destroys blood vessels, is exposed to an earthworm and flatworm. It is found that the earthworm died while the flatworm remains unaffected. Which of the following explains why the flatworm survived?
A. Flatworms lack a circulatory system
B. The earthworm has an open circulatory system
C. The earthworm could not excrete the toxin fast enough
D. Verotoxin cannot penetrate the flatworm
E. Flatworms have a closed circulatory system
A. Flatworms lack a circulatory system
This is an application question regarding the circulatory system of different organisms. Flatworms have no circulatory system. All cells can diffuse with the environment. Oxygen can be absorbed and carbon dioxide can be excreted without the need of a medium, like blood. Thus, they lack blood vessels, and are immune to verotoxin. On the other hand, earthworms are annelids, which have closed circulatory systems and do have blood vessels, which explains why they die when exposed to verotoxin.
Open circulatory systems pump blood into sinuses and bathe all tissues with nutrients and oxygen. Open circulatory systems occur in arthopods (insects) and some mollusks.
***Earthworms have METANEPHRIDIA for excretion.
What is the difference between a liposome and micelles?
Liposome= HOLLOW spheres made of phospholipids
Micelles= SOLID sphere made of phospholipids
Liposomes are spherical vesicles with lipid bilayers believed to be PROTOBIONTS
Sebaceous glands can be found in all of the following areas EXCEPT for one. Which one is the EXCEPTION?
A. Eyelids B. Palms C. Scalp D. Underarms E. Earlobes
B. Palms
Sebaceous glands are tiny glands in the skin that secrete an oil called sebum. They are located in the dermis of the skin and found nearly everywhere in human skin EXCEPT for the palms of the hands and soles of the feet. The body releases this oil to waterproof and protect the skin, but it also is a lipid and reduces friction. It doesn’t make sense to make your hands and feet slippery, so we can infer this must be the correct answer.
***The underarms are also one of the few regions of the body that contain APOCRINE glands, a type of SUDORIFEROUS (sweat) gland with viscous secretions that open to hair follicles.
