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Practice Test 93 - AP Biology

20 questions. Answer them in any order, then submit to see your score and every explanation.

  1. In a lab, a eukaryotic cell is observed with extensive rough endoplasmic reticulum and many ribosomes attached to its surface. Vesicles frequently bud from this membrane network and move toward the cell's periphery. The cell releases large amounts of a water-soluble protein into the surrounding medium. No unusual changes are seen in mitochondria or chloroplasts. Which feature best explains how the cell produces proteins for secretion in high quantities?
  2. Two cube-shaped cells have the same membrane composition and live in identical solutions containing glucose. Cell X has side length 5 μm5\,\mu m and cell Y has side length 15 μm15\,\mu m. Both cells use facilitated diffusion through membrane transport proteins to import glucose, and both metabolize glucose throughout the cytoplasm at similar rates per unit volume. After 10 minutes, cell Y shows a larger decrease in cytoplasmic glucose concentration than cell X. Which explanation best accounts for the observed difference?
  3. An enzyme from a freshwater fish is placed in buffers with different NaCl concentrations while substrate concentration is held constant. In 0.1 M NaCl, the reaction rate is 20 units; in 1.0 M NaCl, the rate is 7 units. The enzyme's tertiary structure is maintained partly by ionic interactions among charged side chains. Increasing salt concentration can shield charges, weakening electrostatic attractions that help stabilize the active site's shape. The temperature and pH are unchanged. Which condition would most likely explain the decreased activity at 1.0 M NaCl?
  4. A researcher adds Ligand M to cells and detects rapid activation of a cytosolic kinase only when the receptor's intracellular tail contains phosphorylatable serines. A modified receptor binds M normally but has all serines in the tail replaced with alanines, and kinase activation is not observed. Which of the following best explains the loss of early signaling?
  5. In a neuron, acetylcholine (ACh) binding to a postsynaptic receptor produces an immediate inward current measurable by patch clamp. The response occurs even when intracellular GTP is depleted, but it is abolished by a competitive ACh-binding antagonist. No change in cAMP is detected during the first 30 seconds. Which of the following best explains the receptor type and early transduction event?
  6. In snapdragons, flower color shows incomplete dominance: allele R produces red pigment and allele r produces no pigment. RR plants have red flowers, rr plants have white flowers, and Rr plants have pink flowers. A gardener crosses two pink-flowered plants (Rr × Rr) and grows 200 offspring under the same conditions. Which outcome best predicts the flower-color phenotypes among the offspring?
  7. Two epithelial cell samples are compared. Sample 1 has many membrane proteins with attached carbohydrate chains projecting into the extracellular space, forming a dense surface coat. Sample 2 has far fewer of these carbohydrate-bearing proteins, but similar phospholipid composition. When mixed, cells from Sample 1 clump together more strongly than cells from Sample 2. Which feature best explains the increased cell-to-cell adhesion in Sample 1?
  8. Two populations of frogs occupy adjacent wetlands with no physical barrier between them. Population 1 males call at 800 Hz and females preferentially approach 800 Hz calls; population 2 males call at 1200 Hz and females preferentially approach 1200 Hz calls. When researchers move adults from both populations into the same wetland, males continue their typical calls and females rarely approach males from the other population. Genetic analyses show reduced gene flow and increasing divergence between populations. Which isolating mechanism most directly reduces interbreeding between the frog populations?
  9. In a coastal snail population, shell color is controlled by two alleles. Before 2000, light shells (LL or Ll) were 70% of adults and dark shells (ll) were 30%. After a decade of increased predation by visually hunting crabs, marked-recapture data show light-shelled adults produced an average of 1.1 surviving offspring each, while dark-shelled adults produced 2.0. By 2010, the frequency of allele l increased from 0.40 to 0.62 across the population. Which pattern best illustrates the type of selection acting on shell color?
  10. Two cell types express the same receptor for ligand Q. In both, Q binds the receptor with equal affinity. In cell type 1, Q rapidly increases cAMP; in cell type 2, Q rapidly increases IP3_3. The receptor's extracellular domain sequence is identical in both cell types. Which of the following best explains the difference in the initial intracellular response?
  11. Two tide pools were sampled for algal species. Pool A contained 5 species with abundances 20, 20, 20, 20, and 20. Pool B contained 5 species with abundances 96, 1, 1, 1, and 1. Total algal individuals counted were 100 in each pool. Which conclusion is best supported about biodiversity?
  12. In a cell, extracellular ATP activates a purinergic receptor that opens a cation channel, allowing Na+^+ influx and depolarization. Depolarization opens voltage-gated K+^+ channels, causing K+^+ efflux that repolarizes the membrane. Repolarization reduces opening of the ATP-gated channel by lowering its driving force for Na+^+ entry. Blocking the K+^+ channels increases the duration of depolarization after ATP addition. Which outcome best illustrates the feedback's role?
  13. In a population of rabbits, a locus has alleles HH and hh. A random sample of 1,000 rabbits shows genotype counts: HH=640HH=640, Hh=320Hh=320, and hh=40hh=40. The population is large, isolated, and no selection or mutation is detected. Which conclusion is best supported about Hardy-Weinberg equilibrium at this locus based on the observed data?
  14. A bacterial population in a closed flask was measured every hour. The population increased from 1,000 cells at hour 0 to 2,000 at hour 1, 4,000 at hour 2, and 8,000 at hour 3. At hour 4 it reached 8,200, and at hour 5 it decreased to 7,900. Dissolved oxygen dropped sharply after hour 3. Which explanation best accounts for the change after hour 3?
  15. A cell in an isotonic solution shows no net change in volume. When a drug blocks aquaporins, water movement across the membrane slows, but the final cell volume remains unchanged. ATP depletion does not alter the direction of water movement. Which mechanism best explains water movement across the membrane in both conditions?
  16. A researcher compares permeability of a pure phospholipid bilayer to different solutes. The bilayer's interior is hydrophobic, so solutes that are nonpolar dissolve into it more easily than polar solutes. Charge greatly reduces permeability because ions remain stabilized by water and are unfavorable in the hydrophobic core. Compare two small solutes: hydrogen sulfide (H2S), which is relatively nonpolar, and sodium ion (Na+), which is charged. No proteins are present. Which solute would most likely cross the bilayer more readily by simple diffusion?
  17. In a herd of 200 cattle, ranchers allow only the 20 bulls with the greatest muscle mass to sire calves each year for 10 years; other bulls are excluded from breeding. Calves are raised similarly regardless of parent. Muscle mass varies continuously, and the trait is heritable. After 10 years, the average muscle mass in the calf population is higher than at the start. Which outcome is most likely in the population's gene pool after this artificial selection?
  18. In a fish population, a gene has alleles A and a that influence tolerance to low oxygen. When a lake becomes eutrophic, low-oxygen events become frequent. Fish with genotype aa have the highest survival and produce more offspring than AA fish. After multiple generations, allele a frequency increases. Which statement best explains the role of variation in this change?
  19. Two human cell lines are observed under a microscope during migration across a culture dish. In line X, actin filaments rapidly assemble at the leading edge, forming broad lamellipodia, and the cell changes shape frequently. In line Y, actin filaments are present but are bundled into stable stress fibers, and the leading edge forms fewer protrusions. When both lines are treated with a compound that prevents actin polymerization, neither line forms lamellipodia and migration slows markedly. Which feature best explains the role of actin in cell migration?
  20. A researcher compares two cube-shaped cells with identical membrane protein density. Cell M has side length 4 units; Cell N has side length 8 units. A waste product leaves the cell by facilitated diffusion through membrane transporters, and the outside concentration is kept near zero. Waste is produced at the same rate per unit cytoplasmic volume in both cells. Which explanation best accounts for why Cell N is more likely to accumulate waste internally?

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