The figure below shows a model generated from a study of interactions in a Serengeti ecosystem. This figure describes hypothesized relationships between a parasite that causes disease in wildebeest, rinderpest, and other important components of the ecosystem. Thick arrows represent dominant effects, and “grass” is in a dotted circle because that variable was not directly measured in the study.
Which of the following can most reasonably be predicted based on this figure?
A: Increasing the amount of rinderpest would decrease the amount of grass.
B: Increased fire would lead to higher tree and elephant populations.
C: Increasing the amount of rinderpest could indirectly lower tree numbers.
D: Increased human populations have a net positive effect on the elephant population.
C: Increased rinderpest prevalence would lower wildebeest populations, increasing the amount of grass (because wildebeests feed on the grass) and providing more mate-rial to start and spread fires, thereby decreasing the number of trees. Choice (C) is thus correct. Choice A is incorrect because more rinderpest means fewer wildebeests, which in turn leads to more grass. Choice B is incorrect because fire reduces the tree population. Choice D is incorrect because the figure suggests that humans have only an adverse effect on the elephant population.
Human red blood cells lack mitochondria. Which of the following correctly explains the primary pathway that red blood cells use to produce energy?
A: Red blood cells generate ATP and NADH via aerobic respiration.
B: Red blood cells generate ATP and NADH via anaerobic fermentation.
C: Red blood cells metabolize glucose via glycolysis followed by carbon dioxide and ethanol production to produce ATP.
D: Red blood cells produce ATP via glycolysis followed by lactic acid production.
D: Lacking mitochondria, red blood cells predominantly produce energy by anaerobic respiration. Thus, red blood cells produce ATP via glycolysis followed by lactic acid fermentation. The correct answer is (D). Choice A is incorrect because aerobic cellular respiration occurs in mitochondria, which red blood cells lack. Choice B is incorrect because the products of anaerobic fermentation are ATP and NAD+ (glycolysis produces ATP and NADH, and fermentation regenerates NAD+). Choice C is incorrect because human red blood cells undergo lactic acid fermentation, not alcohol fermentation.
D: In the light-dependent reactions of photosynthesis, light energy splits water, releasing oxygen, and NADPH and ATP are produced. In the light-independent reactions of photosynthesis, carbon dioxide is reduced by NADPH and ATP to make glucose. Thus, the correct answer is (D). Choices A and B are incorrect because photosynthesis consumes water and carbon dioxide and produces oxygen and glucose (6CO2+ 6H2O → C6H12O6+ 6O2). Choice C is incorrect because the light-dependent and light-independent reactions are switched: light-dependent reactions produce NADPH and ATP for light-independent reactions.
Luteinizing hormone (LH) and follicle stimulating hormone (FSH) are released by the pituitary gland during menstruation. The pituitary hormones influence the production of hormones in the ovaries, including estrogen and progesterone. A biotechnology company is testing an ovulation kit to plan pregnancy. The window of fertilization is restricted by the viability of the ovule, which is fertile up to 12 hours after ovulation.
According to the diagram, which hormone would be the most effective target for the ovulation kit to measure?
A: FSH, because it peaks early enough to “catch” the ovule
B: LH, because it displays a single peak just before ovulation
C: Estrogen, because it is produced by mature follicles, which indicate that an egg is ready for release
D: Progesterone, because it promotes readiness of the uterus for implantation of an embryo
B: LH spikes immediately before ovulation, but otherwise remains at consistently low levels. Thus, it is the most effective target for determining ovulation. Choice (B) is correct. Choice A is incorrect because FSH peaks twice, once early in the cycle and once prior to ovulation, so it would be a less reliable marker of ovulation than LH. Choice C is incorrect because estrogen peaks twice, once before and once after ovulation, making it an unreliable indicator. Choice D is incorrect because the progesterone peak only appears well after ovulation.
Which of the following conclusions can most reasonably be drawn if a host cell’s function has been impaired following a viral infection?
A: The host cell will lyse or undergo apoptosis regardless of the severity of damage.
B: The host cell will lyse or undergo apoptosis if the severity of damage exceeds the cell’s ability to repair itself.
C: The host cell will only lyse.
D: The host cell will only undergo apoptosis.
B: If a cell loses its ability to function and cannot be repaired, then it could lyse (burst open) or undergo apoptosis (programmed cellular death). Whether it does either depends on the severity of the damage to the cell. Choice (B) is thus correct. Choice A is incorrect because the cell will remain intact if it is capable of repairing the damage. Choices C and D are incorrect because they only present one of the two viable options for a damaged cell.
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