3. In plants the conservation of water promotes
(A) photorespiration.
(B) photosynthesis.
(C) the opening of stomata.
(D) the light reactions.
(E) a shift to photosynthesis.

49. Why is it important to explain the origin of RNA in the search for the origin of life? (A) Its complexity demands a theory (B) RNA is found in ancient glass shards (C) RNA is the energy source for primordial life forms. (D) RNA is more structurally complicated than DNA

50. How do the top scientists in the search for the origin of life feel about the discovery described in the article? (A) Everyone thinks this is true (B) Everyone thinks this is false (C) Some scientists are doubtful (D) Some scientists are scared

1. Organelles other than the nucleus that contain DNA include (A) ribosomes. (B) chloroplasts. (C) mitochondria. (D) B and C only (E) A, B, and C

2. In the fractionation of homogenized cells using centrifugation, the primary factor that determines whether a specific cellular component ends up in the supernatant or the pellet is (A) the percentage of carbohydrates in the component. (B) the number of enzymes in the fraction. (C) the presence or absence of lipids in the component. (D) the size and weight of the component. (E) the relative solubility of the component.

4. Which of the following statements is a correct distinction between cyclic and noncyclic electron flow? (A) Only noncyclic electron flow produces ATP. (B) In addition to ATP, cyclic electron flow also produces NADPH. (C) Chemiosmosis is unique to noncyclic electron flow. (D) Only cyclic electron flow can operate in the absence of photosystem II. (E) Only cyclic electron flow utilizes light at 700 nm.

5. A drug designed to inhibit the response of cells to testosterone would almost certainly result in which of the following? (A) an increase in receptor tyrosine kinase activity (B) a decrease in transcriptional activity of certain genes (C) an increase in cytosolic calcium concentration (D) a decrease in G-protein activity (E) lower cytoplasmic levels of cAMP

複選題6. Chemical signal pathways (A) operate in animals, but not in plants. (B) use hydrophilic molecules to activate enzymes. (C) often involve the binding of signal molecules to a protein on the surface of a target cell. (D) are absent in bacteria, but are plentiful in yeast. (E) involve the release of hormones into the blood.

7. Which of the following are primarily responsible for cytokinesis in plant cells? (A) cyclin-dependent kinases (B) Golgi-derived vesicles (C) centrioles and basal bodies (D) kinetochores (E) actin and myosin

8. Vinblastine is a standard chemotherapeutic drug used to treat cancer. Because it interferes with the assembly of microtubules, its effectiveness must be related to (A) myosin denaturation and inhibition of cleavage furrow formation. (B) disruption of mitotic spindle formation. (C) inhibition of DNA synthesis. (D) inhibition of regulatory protein phosphorylation. (E) suppression of cyclin production.

9. Because they accumulate in the body, excess ingestion of which of the following can have toxic effects? (A) calcium and phosphorus. (B) fat-soluble vitamins. (C) sugars. (D) water-soluble vitamins. (E) proteins