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Practice Test 19 - AP Biology

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

  1. In a population of field mice, fur color ranges from very light to very dark. After a wildfire blackens the soil, hawks capture more light-colored mice than dark-colored mice. Over five generations, the frequency of an allele associated with darker fur increases from 0.35 to 0.72, and average fur darkness increases. Which pattern best illustrates the selection acting on fur color in this population?
  2. A diploid cell has two homologous pairs: chromosome pair 3 (alleles M/m) and chromosome pair 5 (alleles N/n). No crossing over occurs. In one meiosis, the maternal homolog of chromosome 3 and the paternal homolog of chromosome 5 move to the same pole at anaphase I, while the other homologs move to the opposite pole. After meiosis II, the gametes produced from this cell are all either Mn or mN. Which process best explains why only these two gamete types were produced in this single meiosis?
  3. A comparative anatomy study examines the forelimbs of a mole (digging mammal) and a mole cricket (insect). Both have enlarged, shovel-like front appendages used for digging. However, the mole's limb contains bones arranged as humerus, radius/ulna, carpals, and phalanges, while the mole cricket's appendage is composed of an exoskeletal segment series without bones. Which statement is best supported by these observations?
  4. In a salt marsh, cordgrass produces 15,000 kJ/m2^2/yr of new biomass. Only 1,500 kJ/m2^2/yr becomes new biomass of herbivorous snails, and 150 kJ/m2^2/yr becomes new biomass of crabs that eat snails. Assume each consumer feeds primarily on the level below. Which conclusion is best supported about trophic efficiency across these levels?
  5. Two flowering plant lineages, one in South America and one in Africa, both have tubular red flowers and are pollinated by hummingbird-like birds. However, DNA sequences from multiple nuclear genes place the South American plant closer to a nearby white-flowered lineage than to the African red-flowered lineage. Fossil pollen indicates the two continents have been separated for over 100 million years. Which conclusion is best supported by these data?
  6. A coral reef experiences a prolonged heat wave, and coral cover declines from 40% to 10% in six months. Herbivorous fish abundance remains similar, but macroalgae cover increases markedly. Which outcome is most likely for reef ecosystem stability?
  7. In a plant, red petals (R) are completely dominant to white petals (r), and round seeds (S) are completely dominant to wrinkled seeds (s). A plant heterozygous for both traits (RrSs) is testcrossed with a plant homozygous recessive for both traits (rrss). Assume independent assortment. Which proportion of offspring is expected to have white petals and wrinkled seeds?
  8. A lipid bilayer with no proteins is tested with three solutes at equal concentration: water (18 Da, polar), sucrose (342 Da, polar), and steroid hormone (≈300 Da, largely nonpolar). Which solute would most likely show the greatest permeability through the bilayer?
  9. A red blood cell is moved from a 300 mOsm solution to a 150 mOsm solution. The membrane contains aquaporins that allow rapid water movement but does not allow sucrose to cross. After several minutes, the cell's volume increases. No ATP is required for the volume change. Which outcome is most likely and what transport process best explains it?
  10. A biologist examines two storage molecules. Molecule T is a triglyceride composed of glycerol ester-linked to three long fatty acid chains; Molecule G is glycogen, a highly branched polymer of glucose with many hydroxyl groups. Equal masses of T and G are placed in water. T separates from water, while G dissolves. Which feature best explains why T is insoluble in water compared with G?
  11. A student builds a macromolecule by linking amino acids into a chain. Each linkage forms when the carboxyl group of one amino acid reacts with the amino group of another, releasing a molecule of water. The resulting covalent bond repeats along the backbone, producing a polymer with a specific sequence of monomers. Which statement best describes the bond and process that formed this polymer backbone?
  12. A scientist compares two spherical cells that both rely on diffusion for exchange of a small molecule. The molecule is produced at the same rate per unit volume and exits across the membrane. The scientist halves the radius of the larger cell while keeping membrane properties constant. After the change, internal molecule concentration decreases. Which explanation best accounts for the decrease after reducing cell size?
  13. A pure phospholipid bilayer is exposed to equal concentrations of a fatty acid in its uncharged form (R–COOH) and its deprotonated form (R–COO−^-). The hydrocarbon chain (R) is long and nonpolar. Which form would most likely cross the bilayer more readily?
  14. A eukaryotic gene is transcribed into a primary RNA that includes exons 1–5. Two mature RNA isoforms are detected: Isoform X contains exons 1, 2, 4, and 5; Isoform Y contains exons 1, 3, 4, and 5. Sequencing shows that exon 2 and exon 3 are never present together in the same mature RNA. All introns are removed in both isoforms. Which explanation best accounts for the production of both isoforms from the same primary transcript?
  15. A student compares two single-stranded nucleic acids of similar length. Molecule X contains uracil, and Molecule Y contains thymine. Both have a sugar-phosphate backbone. Which statement best describes a structural inference about Molecule X compared with Molecule Y?
  16. In a flock of chickens, a breeder allows only the 20% with the highest egg production to reproduce each generation. Egg production is influenced by a gene with alleles H (higher production) and h (lower production). After six generations, the proportion of chicks showing high egg production increases from 35% to 70% in the flock. Which outcome is most likely in the flock's gene pool after these generations of artificial selection?
  17. A protist contains a chloroplast-like organelle with two membranes and circular DNA. Sequencing shows several genes in the organelle are most similar to cyanobacterial genes, while other related genes are located in the host nucleus and encode proteins imported into the organelle. The organelle divides independently of the host cell cycle. Which inference best connects these observations to the origin of the organelle?
  18. A signaling molecule binds to a receptor on the cell surface and activates a cytosolic kinase within seconds. When the receptor's transmembrane domain is replaced with a different hydrophobic helix of similar length, ligand binding still occurs, but kinase activation is greatly reduced. The receptor remains localized to the plasma membrane. Which of the following best explains how altering the transmembrane domain could reduce early signal transduction?
  19. In a grassland ecosystem, net primary productivity (NPP) by grasses is measured at 12,000 kJ/m2^2/yr. Energy stored as new biomass in grasshoppers that feed on the grasses is measured at 1,200 kJ/m2^2/yr, and energy stored as new biomass in frogs that feed on the grasshoppers is 120 kJ/m2^2/yr. Assume these values represent energy available to the next trophic level. No additional trophic levels are considered. Which conclusion is best supported about energy transfer between these trophic levels?
  20. The continued use of broad-spectrum insecticides to control mosquito populations that transmit diseases like malaria and dengue fever can have an unintended evolutionary consequence on other, non-target insect species. Which of the following describes the most likely evolutionary impact on these non-target species?

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