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Practice Test 89 - AP Biology

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

  1. Clonal cuttings from one pothos plant were grown for 6 weeks under identical watering and temperature, but different light. Plants in bright light developed smaller leaves with darker green color, while plants in low light developed larger, lighter green leaves. DNA sequencing of a chlorophyll-related gene showed identical sequences in both groups. Which explanation best accounts for the leaf differences observed between the two light conditions?
  2. In corn, tall plants (T) are completely dominant to short plants (t). A tall plant of unknown genotype is crossed with a short plant (tt). The offspring include both tall and short individuals in approximately equal numbers. Assume a single gene controls height. Which genotype most likely describes the tall parent?
  3. A scientist studies a polysaccharide that includes many hydroxyl (–OH) groups exposed on the surface of each chain. When the polymer is placed in water, it dissolves readily and increases solution viscosity. A chemically modified version replaces many hydroxyl groups with hydrogens, reducing polarity without changing chain length. Which outcome is most likely for the modified polymer in water?
  4. Two triglycerides are compared: Lipid X has three saturated fatty acid tails (no C=C double bonds), and Lipid Y has three cis-unsaturated tails (each with at least one C=C double bond). At the same temperature, Lipid X forms a more solid fat, while Lipid Y remains more fluid. Which statement best describes the molecular reason for this difference in physical state?
  5. A mouse population has variation in coat color, and the trait is heritable. After snowfall becomes rare, the ground remains dark for most winters. Owls capture light-colored mice more often than dark-colored mice, reducing reproduction of light-colored mice. Which outcome is most likely over generations as dark winters persist?
  6. A scientist records presence (1) or absence (0) of four derived traits in taxa K, L, M, N: Trait A: K1 L1 M1 N1; Trait B: K0 L1 M1 N1; Trait C: K0 L0 M1 N1; Trait D: K0 L0 M0 N1. Each trait evolved once with no reversals. Using this information to infer branching order, which taxa are most closely related?
  7. In a large population of beetles, color is controlled by two alleles: BB and bb. A random sample of 1,000 beetles shows genotype counts: 360 BBBB, 480 BbBb, and 160 bbbb. Assume mating is random and there is no migration. Which conclusion is best supported about Hardy-Weinberg equilibrium in this population?
  8. A student compares ATP production in two conditions using mitochondria supplied with pyruvate, ADP, and Pi. In condition 1, the inner mitochondrial membrane is intact. In condition 2, the inner membrane is punctured so it cannot maintain a proton gradient. The electron transport chain proteins are still present, and oxygen is available in both conditions. The student measures ATP made inside the mitochondria over a short time interval. Which outcome is most likely when comparing condition 2 to condition 1?
  9. A student compares two dehydration reactions. Reaction 1 links monomers by joining a hydroxyl group on one monomer to a carboxyl group on another, forming an ester bond. Reaction 2 links monomers by joining a hydroxyl group on one sugar to a hydroxyl group on another sugar, forming a glycosidic bond. The products differ in whether they form long chains of repeating units. Which statement best predicts the macromolecule class produced by Reaction 1?
  10. In smooth muscle cells, ligand L binds receptor R and activates PLC, producing IP3_3. IP3_3 triggers Ca2+\mathrm{Ca^{2+}} release from the ER. Ca2+\mathrm{Ca^{2+}} binds a regulatory protein that activates myosin light-chain kinase (MLCK), which phosphorylates myosin and increases contraction. A drug blocks MLCK activity but does not affect Ca2+\mathrm{Ca^{2+}} release. Which outcome is most likely after L addition in the presence of the drug?
  11. A scientist designs an antisense oligonucleotide that binds to the branch point sequence within an intron of a eukaryotic pre-mRNA. After treatment, sequencing of nuclear RNA shows that this intron is frequently retained, while other introns in the same transcript are removed normally. The 5′ cap and poly(A) tail are still detected on the RNA molecules. Which explanation best accounts for the intron retention after treatment?
  12. A lab measures transport of solute U across a membrane using radiolabeled U. With U at 5 mM outside and 0.5 mM inside, net uptake occurs in cells expressing a U-specific carrier. When outside U is 0.5 mM, net uptake is zero, although labeled U still exchanges in both directions. ATP inhibitors do not change results. Which explanation best accounts for zero net uptake at 0.5 mM outside?
  13. A cell contains 1 mM urea inside and is placed in 10 mM urea outside. Urea crosses the membrane slowly without proteins, but when a specific urea channel is inserted, the rate increases greatly. The rate does not require ATP and increases with the urea concentration difference. Which mechanism best explains urea movement when the channel is present?
  14. A cell has genotype JjKk, with J/j on chromosome pair 3 and K/k on chromosome pair 7. The cell undergoes meiosis without crossing over. During metaphase I, the J-bearing homolog of pair 3 aligns toward the same pole as the K-bearing homolog of pair 7 in some cells, but toward the opposite pole in others. After meiosis, different combinations of J and K appear among gametes. Which meiotic event produces these different combinations?
  15. A chemist treats DNA with a reagent that specifically breaks hydrogen bonds but does not cleave covalent bonds. After treatment, the double helix separates into two intact single strands; the sugar-phosphate backbones remain unbroken. Which statement best describes the molecular interaction disrupted by the reagent to cause strand separation?
  16. In a prairie grass population, a locus affecting flowering time has two alleles: E (earlier flowering) and L (later flowering). In year 1, E = 0.50 and L = 0.50. A drought begins, shortening the growing season; in year 8, E = 0.68 and L = 0.32. Plants are wind-pollinated, and no new alleles are detected. Which statement best explains the population-level role of variation in producing the observed evolutionary change?
  17. A student compares mitosis and meiosis in a diploid cell with 2n=62n=6. In meiosis, homologous chromosomes separate in the first division and sister chromatids separate in the second division, producing four cells. In mitosis, sister chromatids separate in a single division, producing two cells. Which outcome is most likely when comparing the chromosome number of the final cells produced by each process?
  18. A cell contains numerous small membrane-bound vesicles with acidic interiors and hydrolytic enzymes. After the cell engulfs a damaged organelle, the organelle is found inside one of these vesicles and is gradually degraded. Which feature best explains the degradation process?
  19. An intestinal epithelial cell has many microvilli, each supported by bundles of actin filaments just beneath the plasma membrane. Compared with a nearby cell lacking microvilli, this cell shows a higher rate of nutrient uptake from the lumen. Which feature best explains the increased uptake?
  20. A student compares two spherical cells with identical membrane composition. Cell A radius = 7 µm; Cell B radius = 14 µm. Both rely on diffusion for potassium ion exchange through open channels at equal density per µm². Under identical external conditions, Cell B shows slower adjustment of internal potassium concentration after a sudden change outside. Which explanation best accounts for Cell B's slower adjustment?

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