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Practice Test 17 - AP Biology

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

  1. In a thylakoid membrane preparation, a researcher shines light and measures pH in the thylakoid lumen and stroma. Under illumination, the lumen becomes more acidic than the stroma due to H+ movement associated with electron transport. If the researcher blocks ATP synthase so H+ cannot pass through it, which change is most likely during continued illumination?
  2. A dominant plant is testcrossed. If it is heterozygous, what is the probability that all 6 offspring are dominant?
  3. A student compares two spherical cells in the same solution. Cell CC has radius 2 µm; Cell DD has radius 6 µm. Both rely on diffusion across the plasma membrane for uptake of a small ion, and both use the ion at the same rate per unit volume. The student measures ion influx per unit cytoplasmic volume and finds it is lower in Cell DD. Which explanation best accounts for the lower influx per unit volume in Cell DD?
  4. In a greenhouse experiment, researchers grow the same species of annual plant in identical pots with the same soil and water schedule. Pot Group 1 contains 2 seedlings per pot, and Pot Group 2 contains 20 seedlings per pot. After 5 weeks, Group 1 plants average 18 cm tall with 90% survival, while Group 2 plants average 6 cm tall with 40% survival. Light intensity and temperature are constant across groups. Which factor is most likely responsible for the lower survival in Group 2?
  5. A lab group places identical cells (cytosol 0.20 M nonpenetrating solute) into three solutions: I = 0.10 M, II = 0.20 M, III = 0.35 M. Membranes are permeable to water but not solute, and each solution's concentration stays constant. The group records whether cells swell, shrink, or stay the same after 5 minutes. Which result is most likely for cells in Solution III?
  6. A single cell increases its diameter while maintaining the same density of membrane transporters per µm² and the same internal metabolic demand per µm³. Nutrients enter across the plasma membrane by transport proteins. As diameter increases, the cell begins to show lower internal nutrient concentration under the same external conditions. Which explanation best accounts for the decreased nutrient availability in the larger cell?
  7. This change in the green anole population serves as an example of continuing evolution primarily because it shows that...
  8. An amoeba moves across a surface by extending a bulge of cytoplasm in one direction, then pulling the rest of the cell forward. In the leading edge, actin filaments rapidly assemble near the plasma membrane. Which feature best explains how actin assembly supports this type of movement?
  9. A prokaryotic gene H is controlled by attenuation. The leader region of the mRNA contains codons for tryptophan and can form either a terminator hairpin that stops transcription or an antiterminator that allows transcription to continue. When tryptophan is abundant, ribosomes translate the leader quickly, favoring terminator formation and lowering downstream transcription. When tryptophan is scarce, ribosomes stall at the Trp codons, favoring antiterminator formation and increasing transcription. Which change would most likely decrease transcription of gene H during tryptophan scarcity?
  10. In a large population of insects, wing color is controlled by alleles G and g. Researchers estimate allele frequencies as p(G)=0.10p(G)=0.10 and q(g)=0.90q(g)=0.90. Assuming Hardy-Weinberg conditions are met, expected genotype frequencies are p2p^2 for GG, 2pq2pq for Gg, and q2q^2 for gg. The population is well mixed, and no migration is detected. Mutation is negligible over the time scale considered. Under Hardy-Weinberg equilibrium, what is the expected frequency of heterozygotes (Gg)?
  11. A membrane carrier transports solute Q. When extracellular Q is 60 mM and intracellular Q is 6 mM, net influx occurs. Adding a molecule structurally similar to Q reduces influx, but ATP levels remain constant and no ATP is consumed by the carrier. Which explanation best accounts for reduced influx after adding the similar molecule?
  12. A cell contains an mRNA with the codon sequence 5′-AUG UUC GGA UAA-3′. A mutation deletes one nucleotide within the second codon, shifting the reading frame so that all downstream nucleotides are regrouped into different codons. Translation still begins at AUG, and the ribosome continues codon-by-codon until a stop codon appears in the new reading frame. No genetic code table is needed to answer: only that codon grouping determines which tRNAs bind. Which outcome is most likely after the deletion?
  13. A cell membrane contains a channel that allows Ca2+ to pass when open. Extracellular Ca2+ is 2 mM and cytosolic Ca2+ is 10−410^{-4} mM. Opening the channel produces Ca2+ influx even when ATP is depleted. Which explanation best accounts for Ca2+ influx under ATP-depleted conditions?
  14. Plant cells with an internal solute concentration of 0.25 M are transferred to Solution Y containing 0.40 M sucrose, which does not cross the membrane. Water can cross the membrane. Within minutes, the plasma membrane pulls away from the cell wall in many cells. Which outcome is most likely for net water movement and cell volume?
  15. A student investigates waste removal from cells that produce carbon dioxide (CO2_2) at the same rate per unit volume. CO2_2 leaves the cell by diffusion across the plasma membrane. Two cells have identical membrane permeability, but Cell P has double the linear dimension of Cell Q. After 5 minutes, Cell P has a higher internal CO2_2 concentration than Cell Q. Which explanation best accounts for the higher CO2_2 concentration in Cell P?
  16. A membrane contains a potassium channel that is open under the experimental conditions. Intracellular K+^+ concentration is higher than extracellular K+^+. Net K+^+ efflux is observed and decreases when the channel is blocked, while ATP concentration remains unchanged. When intracellular K+^+ is experimentally lowered below extracellular K+^+, net K+^+ movement becomes inward through the unblocked channel. Which explanation best accounts for the observed direction changes in K+^+ movement?
  17. A researcher treats two cultured human cell types with the same signaling molecule. In response, only one cell type shows increased transcription of Gene X, even though both cell types contain Gene X in their DNA. The researcher confirms both cell types have functional RNA polymerase. Which explanation best accounts for why only one cell type increases Gene X transcription?
  18. Students compare embryos of a lizard, chicken, and mouse at an early developmental stage. In all three, they observe pharyngeal arches and a post-anal tail, even though these structures are modified or reduced later in development. The observations are made at the same stage across species, and no adult traits are discussed. Which inference is best supported by these embryological similarities?
  19. In a species of bird, feather pattern is controlled by a single autosomal gene with two alleles that show incomplete dominance. BB birds are black, WW birds are white, and BW birds are gray. Two black birds mate and produce offspring. Which outcome best predicts the offspring feather colors?
  20. Two forest plots are sampled for breeding birds. Plot X contains 12 species, with 1–3 pairs per species. Plot Y contains 12 species, but one species accounts for 70% of all pairs and the remaining 11 species share 30%. Total bird pairs are the same in both plots. Which explanation best accounts for the difference in biodiversity between the plots?

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