Biology Exam 2020

Section I: Multiple-Choice Questions The following are examples of the kinds of multiple-choice questions found on the exam. 1. Insulin is a protein hormone that is secreted in response to elevated blood glucose levels. When insulin binds to its receptors on liver cells, the activated receptors stimulate phosphorylation cascades that cause the translocation of glucose transporters to the plasma membrane. Based on the information provided, which of the following best describes the role of insulin in this liver cell signal transduction pathway? (A) It acts as a ligand. (B) It acts as a receptor. (C) It acts as a secondary messenger. (D) It acts as a protein kinase. 2. Humans have a diploid number (“2n” ) of 46. Which of the following statements best predicts the consequence if meiosis did not occur during gametogenesis? (A) The gametes would get larger from one generation to the next. (B) The chromosome number would double with each generation. (C) (D) The chromosome number would triple with each generation. 3. Mutations in the MYO6 and POU4F3 genes have been associated with a form of hereditary hearing loss in humans. Researchers studying the genes have proposed that POU4F3 encodes a transcription factor that influences the regulation of MYO6. Which of the following questions will best help guide the researchers toward a direct test of their proposal? (A) Have mutations in other genes also been associated with hearing loss? (B) In what types of cells are the mutant forms of the POU4F3 gene expressed? (C) Are mutations in the MYO6 and POU4F3 genes also found in mice? (D) 00762-113-CED-Biology_Exam Information.indd 200 POU4F3 gene affect MYO6 mRNA levels in cells? 2/28/19 8:17 PM Phytoplankton Biomass (mg/m3) Questions 4–7 refer to the following material. 8,000 6,000 4,000 2,000 0 1970 1975 Year 1980 1985 Treated with sucrose Treated with sucrose and phosphate Impermeable Curtain Figure 1. Phytoplankton biomass in two sides of a small lake that is divided by an impermeable curtain In the early 1970s, researchers hypothesized that carbon was the limiting nutrient in many aquatic ecosystems. To test this hypothesis, the researchers divided a small lake in two roughly equal halves with an impermeable curtain that was fastened and sealed to the bedrock of the lake. Beginning in 1971 the researchers treated one side of the lake with sucrose and the other side with both sucrose and phosphate. From 1971 to 1983 the researchers monitored the phytoplankton biomass in both parts of the lake. The results are shown in Figure 1. 4. Which of the following claims is best supported by the data? (A) Carbon was a limiting factor for phytoplankton in the lake. (B) Phosphate was a limiting factor for phytoplankton in the lake. (C) Both carbon and phosphate were limiting factors for phytoplankton in the lake. (D) Neither carbon nor phosphate was a limiting factor for phytoplankton in the lake. 5. The average growth rate of the phytoplankton population from 1971 to 1975 in the side of the lake treated with sucrose and phosphate is closest to which of the following? (A) 125 (mg/m3)/year (B) 1,000 (mg/m3)/year (C) 1,500 (mg/m3)/year (D) 6,000 (mg/m3)/year 00762-113-CED-Biology_Exam Information.indd 201 2/28/19 8:17 PM 6. Which of the following treatments would have been the best control treatment for the experiment? (A) An untreated section of the lake (B) A section of the lake that was treated with phosphate but not sucrose (C) A different lake that was treated with sucrose and phosphate (D) A small pool of the lake water maintained in a controlled laboratory environment 7. Which of the following was most likely a direct consequence of the addition of phosphate to the lake? (A) (B) The amount of biomass in the second trophic level decreased. (C) The amount of energy available to producers in the lake increased. (D) The amount of energy available to consumers in the lake increased. The enzyme trypsin aids in protein digestion in the small intestine. The relative activity of trypsin at different pH values is shown in Figure 1. Relative Activity 8. 0 1 2 3 4 5 6 7 8 9 10 11 12 pH Figure 1. Effect of pH on the activity of trypsin Which of the following statements best explains the activity levels of trypsin shown in Figure 1? (A) The small intestine releases inhibitor molecules that block the activity of trypsin unless it is at its optimum pH. (B) The number of effective collisions between trypsin and its substrate increase at higher pH values. (C) As pH values increase, the substrate concentration decreases, leading to an eventual decline in the rate of the trypsin-catalyzed reaction. (D) At extremely low pH values, trypsin is denatured and cannot function efficiently. 00762-113-CED-Biology_Exam Information.indd 202 2/28/19 8:17 PM Different photosynthetic organisms have different types of chlorophyll molecules. The distribution of chlorophylls in several different groups of organisms is shown in Table 1. A plus sign (+) in the table indicates the presence of a chlorophyll, while a minus sign (−) indicates its absence. Table 1. The distribution of chlorophylls in several groups of organisms Chlorophyll a Chlorophyll b Chlorophyll c Chlorophyll d Flowering plants + + − − Green algae + + − − Brown algae + − + − Red algae + − − + Cyanobacteria + − − − 9. Based on the data, which of the following most likely describes the evolutionary relationship among the organisms? (A) Because brown algae, red algae, and cyanobacteria lack chlorophyll b, they evolved before green algae and flowering plants did. (B) Because green algae and flowering plants contain chloroplasts, they evolved more recently than brown algae, red algae, and cyanobacteria did. (C) Because increasingly complex forms of chlorophyll are found in red algae, brown algae, green algae, and flowering plants, respectively, this reflects the order of their appearance. (D) Because all of the organisms contain chlorophyll a, the organisms share a common ancestor. 10. A student used a microscope to observe a wet-mount slide of red onion epidermal cells that were suspended in a 1% NaCl solution. The student then added a 15% NaCL solution to the slide and observed the changes that occurred. The student’s observations are represented in Figure 1. Original Wet-Mount Slide 15% NaCl Figure 1. Student’s observations of onion cells Which of the following most directly explains the changes in the cells? (A) The degradation of DNA in the nuclei of the cells (B) The lysis of chloroplasts in the cells (C) The movement of water from the central vacuoles of the cells into the solution (D) The movement of NaCl from the solution into the cytoplasm of the cells 00762-113-CED-Biology_Exam Information.indd 203 2/28/19 8:17 PM 11. The human TPM1 gene encodes members of the tropomyosin family of cytoskeletal proteins. Which of the following best explains how different proteins can be made in different cell types from the one TPM1 gene? (A) Different introns are selectively converted to exons. (B) Different exons are retained or spliced out of the primary transcript. (C) The GTP cap is selectively added to and activates different exons. (D) Different portions of the primary transcript remain bound to the template DNA. 12. Scientists examined the folded structure of a purified protein resuspended in water and found that amino acids with nonpolar R groups were primarily buried in the middle of the protein, whereas amino acids with polar R groups were primarily on the surface of the protein. Which of the following best explains the location of the amino acids in the folded protein? (A) Polar R groups on the surface of the protein can form ionic bonds with the charged ends of the water molecules. (B) Polar R groups are too bulky to fit in the middle of the protein and are pushed toward the protein’s surface. (C) Nonpolar R groups that cannot form hydrogen bonds with water are pushed into the middle of the protein. (D) Nonpolar R groups from different parts of the protein form covalent bonds with each other to maintain the protein’s structure. 13. The apple maggot fly, Rhagoletis pomonella, is native to North America and originally fed on fruit of the wild hawthorn. Since the mid-1800s, a population of flies has emerged that instead feed on domesticated apples. Apple maggot flies typically mate on or near the fruit of their host plants. Many varieties of apples ripen three to four weeks before the hawthorn fruits do. The different fruit preferences of the two fly populations will most likely have which of the following effects? (A) The flies that eat hawthorn fruit will increase in number, while the flies that eat apples will decrease in number because of the use of insecticides on apple trees. (B) The single fly species will evolve into two distinct species because of the lack of gene flow between the two populations. (C) The ability to survive on a diet of two different fruits will help the flies learn to eat many more types of fruit. (D) The flies that eat hawthorn fruit will lay some of their eggs on the earlierripening apples to minimize competition among the larvae. Platelets are fragments of larger cells and normally circulate in the blood without adhering to blood vessel walls. When the wall of a blood vessel is damaged, collagen fibers in the wall are exposed to the interior of the blood vessel. The exposed fibers and chemicals released from the endothelial cells that line the blood vessel attract platelets, which start to form a plug and release other chemicals (Figure 1). 00762-113-CED-Biology_Exam Information.indd 204 2/28/19 8:17 PM Blood Vessel Walls Interior of Blood Vessel Released Chemicals Smooth Muscle Collagen Layer Endothelial Cells Platelets Damage to Blood Vessel Wall Figure 1. Formation of a platelet plug in a damaged blood vessel wall 14. Which of the following best explains the feedback mechanism illustrated in Figure 1? (A) This is an example of positive feedback, because the few platelets that initially bind attract more platelets to the damaged area. (B) This is an example of positive feedback, because it results from the interactions among collagen, endothelial cells, and platelets. (C) This is an example of negative feedback, because a large clump of platelets can block the blood vessel and prevent blood flow through it. (D) This is an example of negative feedback, because the accumulation of platelets returns the open blood vessel wall to a closed state. 15. It is estimated that oxygen production first evolved in photosynthetic prokaryotes approximately 2.7 billion years ago. The first photosynthetic prokaryotes are presumed to be similar to today’s cyanobacteria. Which of the following best supports the claim that photosynthetic prokaryotes were responsible for the oxygen in Earth’s atmosphere? (A) The light reactions of photosynthesis split carbon dioxide into carbon and oxygen. (B) The light reactions of photosynthesis split water into hydrogen ions and oxygen. (C) The Calvin cycle splits glucose into carbon, hydrogen, and oxygen. (D) The Calvin cycle splits water into hydrogen ions and oxygen. 00762-113-CED-Biology_Exam Information.indd 205 2/28/19 8:17 PM