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Practice Test 25 - AP Biology

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

  1. A mosquito population in a wetland was estimated weekly. For weeks 1–5, the population rose from 2,000 to 2,500 to 3,100 to 3,900 to 4,800. In week 6, a cold snap occurred, and the population dropped to 1,200 in week 7. By week 9, it returned to 4,600 even though food availability and standing water were similar to earlier weeks. Which explanation best accounts for the sharp decline between weeks 5 and 7?
  2. A wetland is surveyed before and after a controlled burn. Before: 11 plant species, with 55% of cover from one cattail species. After: 14 plant species, with the most common species at 18% cover; total plant cover is similar. Surveys use the same transects and timing. Which conclusion is best supported about community biodiversity following the burn?
  3. A cell is experimentally forced to bypass the G1 checkpoint and enter S phase even though it has not grown to its typical size. DNA replication proceeds normally, and the cell reaches G2 with fully replicated chromosomes. The cell then enters mitosis and completes chromosome segregation and cytokinesis. The resulting daughter cells are noticeably smaller than typical daughter cells from untreated divisions, but each contains a complete set of chromosomes. Which outcome is most consistent with bypassing the G1 checkpoint in this scenario?
  4. A chemist identifies an unknown macromolecule as a polymer whose monomers each contain an amino group and a carboxyl group. Adjacent monomers are connected by a covalent bond formed when water is released during linkage formation. Given this monomer chemistry and polymerization reaction, which feature best predicts a general property of the polymer's backbone?
  5. Four species (W, X, Y, Z) were compared using a 12–amino acid protein segment. Species W and X differ at 1 position. Species Y differs from W at 4 positions and from X at 4 positions. Species Z differs from W at 6 positions and from X at 6 positions, and differs from Y at 5 positions. Assume substitutions accumulate at a roughly constant rate in this protein segment and that fewer differences indicate a more recent common ancestor. Which pair of species is most closely related based on the data?
  6. A researcher adds ligand K to cells and measures receptor binding. When extracellular pH is lowered, K still binds the receptor but the response is reduced. The receptor's cytosolic domain is known to change shape depending on membrane conditions. Which of the following best explains the reduced response despite binding?
  7. In a tundra ecosystem, warmer summers deepen the seasonal active layer above permafrost. Measurements show increased soil microbial respiration and higher atmospheric CO2_2 flux from soils. Which consequence is most likely for ecosystem carbon balance?
  8. A polysaccharide used in extracellular matrices contains many monosaccharides with amino groups that are acetylated (–NHCOCH3) and also contains occasional sulfate groups. The polymer attracts water and forms a hydrated, compressible gel. If sulfate groups are removed while the backbone remains intact, the gel becomes less hydrated and less compressible. Which feature best explains the original gel's high water retention?
  9. In an experiment, two polysaccharides are placed in water. Polysaccharide R is composed of glucose monomers linked by αα(1;4) bonds and forms compact helices. Polysaccharide S is composed of glucose monomers linked by ββ(1;4) bonds and forms extended chains that align side-by-side. After mixing, S forms visible insoluble fibers, while R remains dispersed. Which statement best explains the difference in behavior?
  10. In a large grass population, allele T is initially at frequency 0.10. A new fungal pathogen spreads through the habitat. After several generations, allele T frequency rises to 0.60, and plants with genotype TT and Tt have higher seed production than tt plants in pathogen-present plots. No migration occurs between plots, and the population remains large each generation. Which process is most likely responsible for the change in allele frequency?
  11. A researcher measures the rate of RNA breakdown in cells. When RNases are experimentally confined to membrane-bound compartments, cytosolic RNA remains stable longer; when RNases are released into the cytosol, cytosolic RNA levels drop quickly. The total amount of RNase protein is unchanged. Which feature best explains how compartmentalization affects cellular control of RNA stability?
  12. A cell is placed in a solution containing 200 mM glucose outside and 5 mM glucose inside. The membrane is impermeable to glucose unless a specific carrier protein is present. When the carrier is expressed, glucose enters the cell rapidly, and uptake stops if the carrier is inhibited. Cellular ATP levels do not change during uptake, and glucose continues to move until concentrations equalize across the membrane. Which mechanism best explains glucose entry under these conditions?
  13. Chitin is a structural polysaccharide whose monomers contain C, H, O, and N. Each monomer has an acetamide group (–NHCO–) attached to the sugar ring. Cellulose, another structural polysaccharide, contains only C, H, and O and lacks this nitrogen-containing group. Both polymers can form long chains with many –OH groups, but chitin's acetamide groups add additional sites for hydrogen bonding between adjacent chains. In arthropod exoskeletons, chitin forms tough fibers. Which feature best explains how nitrogen contributes to chitin's mechanical strength?
  14. In photoreceptor cells, light activates rhodopsin (a GPCR), which activates transducin (G protein). Transducin activates phosphodiesterase (PDE), which decreases cGMP. Lower cGMP closes cGMP-gated Na+\mathrm{Na^+} channels, hyperpolarizing the cell. A guanylyl cyclase restores cGMP levels, reopening channels. In a mutant with reduced PDE activity, light causes a much smaller hyperpolarization. Which change would most likely increase hyperpolarization in the mutant during light exposure?
  15. A diploid organism has genotype EeFf, with E/e on chromosome 4 and F/f on chromosome 12. No crossing over occurs. A researcher compares two meioses from different cells and finds that one meiosis produced gametes EF and ef, while the other produced gametes Ef and eF. The researcher confirms chromosome number is normal in all gametes. Which meiotic process best explains the difference in gamete combinations between the two meioses?
  16. In a forest study plot, annual net primary production was 20,000 kJ/m2^2/yr. Measurements showed that only 2,000 kJ/m2^2/yr became new biomass of caterpillars that feed on leaves, and 200 kJ/m2^2/yr became new biomass of birds that feed on caterpillars. Which conclusion is best supported about energy flow in this plot?
  17. A population of island finches shows beak-depth variation: 8–14 mm. During a sequence of dry years, small soft seeds become rare while large hard seeds remain common. After 5 generations, the mean beak depth increases from 10.1 mm to 11.6 mm, and the distribution shifts toward deeper beaks. No evidence indicates immigration or a population bottleneck. Which statement best explains how existing variation influenced the evolutionary outcome?
  18. A researcher disrupts microtubules in cultured eukaryotic cells using a drug that prevents tubulin polymerization. After treatment, vesicles containing membrane proteins accumulate near the Golgi apparatus and fewer vesicles reach the cell surface, even though vesicle formation continues. Actin filaments remain intact. Which outcome is most likely caused by the loss of this cytoskeletal structure?
  19. A protein-free phospholipid bilayer is tested with two molecules of similar size: methanol (32 Da, polar uncharged) and oxygen (32 Da, nonpolar). Which molecule would most likely have greater permeability through the bilayer?
  20. Leaf disks are placed in a solution containing dissolved CO2 and exposed to constant light. A compound is added that specifically inhibits the enzyme complex that reduces NADP+ to NADPH at the end of the light reactions. Which change is most likely to occur in the Calvin cycle shortly after inhibition?

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