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Practice Test 35 - AP Biology

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

  1. Researchers studied a pseudogene (a nonfunctional copy of a gene) in three carnivore lineages: seals, bears, and wolves. Seals and bears share the same premature stop codon at an identical nucleotide position in the pseudogene, while wolves have a different stop codon at a different position. The surrounding sequences align across all three lineages. Because the pseudogene is nonfunctional, the shared stop codon is unlikely to be maintained by selection. Which inference is best supported by these data?
  2. A plant breeder crosses only the tallest 10% of a sunflower population each generation. Height is influenced by a locus with alleles T (taller) and t (shorter). Initially, the frequency of allele T is 0.40. After five generations of selecting and breeding only the tallest plants, allele T frequency is measured at 0.68. Which explanation best accounts for the change in allele frequency?
  3. A scientist increases CO2_2 concentration around a leaf while keeping light intensity constant. For a short period, sugar production increases while oxygen production changes little. Which explanation best accounts for why oxygen production changes little?
  4. In a species of fish, juvenile coloration can vary with background environment. Genetically identical juveniles were raised in tanks with either dark gravel or light sand. After 2 weeks, fish in dark-gravel tanks showed increased dark pigment in their skin compared with fish in light-sand tanks. Sequencing of a pigment gene showed identical DNA sequences in both groups. When fish were moved to the opposite background, pigment levels shifted over the next week. Which explanation best accounts for the pigment differences between tank backgrounds?
  5. In a desert ecosystem, measured energy stored as new biomass each year was 5,000 kJ in shrubs (producers) and 250 kJ in herbivorous rodents (primary consumers) within the same area. Assume rodents feed mainly on shrubs. Which conclusion is best supported about energy transfer from shrubs to rodents?
  6. A student compares chromatids before and after meiosis in a heterozygous cell with linked genes G and H on the same chromosome. Before meiosis, the homologs are GH and gh. After meiosis, the student finds gametes containing GH, gh, Gh, and gH chromatids. The only step that could have produced chromatids with new combinations of G and H is an exchange between homologous chromatids while they are paired. Which meiotic process generated the Gh and gH chromatids?
  7. A tundra food chain is measured for annual energy stored as new biomass: mosses 8,000 kJ/m2^2/yr, lemmings 400 kJ/m2^2/yr, foxes 40 kJ/m2^2/yr. Assume these values represent energy passed to the next trophic level. Which conclusion is best supported about energy loss between trophic levels?
  8. A student mixes purified phospholipids in water and observes spontaneous formation of spherical structures with an aqueous interior. Each phospholipid has a hydrophilic phosphate head and two hydrophobic fatty acid tails. In water, the heads interact with water molecules while the tails avoid water and associate with other tails. This arrangement creates a barrier that separates an internal water compartment from the external solution. Which statement best describes the molecular interactions that drive formation of these spheres?
  9. In a pathway, ligand L activates receptor R, leading to activation of small GTPase Q. Q-GTP activates enzyme Z, which produces second messenger M. M activates kinase K, which phosphorylates target T. A GTPase-activating protein (GAP) increases GTP hydrolysis on Q, promoting Q-GDP. When GAP is overexpressed, M levels and phosphorylated T are reduced after L stimulation. Which intervention would most likely restore phosphorylated T despite GAP overexpression?
  10. A plant cell has plasmodesmata that form cytoplasmic channels through the cell wall, connecting adjacent cells. In a tissue sample, small fluorescent molecules introduced into one cell are later detected in neighboring cells. Which feature best explains the movement of these molecules between cells?
  11. In late mitosis, APC/C activity promotes the destruction of M-cyclin, lowering Cdk1 activity and allowing dephosphorylation of mitotic substrates. This shift supports nuclear envelope reformation and cytokinesis. A researcher adds a proteasome inhibitor at anaphase onset; APC/C can still tag proteins, but tagged proteins are not degraded. DNA separation begins, but many cells fail to complete cytokinesis and remain highly phosphorylated. Which signaling change best explains the failure to exit mitosis?
  12. A cytosolic enzyme functions as a homodimer; each subunit folds into a tertiary structure, and the two subunits associate through complementary hydrophobic surfaces to form the active enzyme. The active site lies at the interface, requiring correct quaternary structure for catalysis. A chemical is added that disrupts hydrophobic interactions but leaves peptide bonds intact. The enzyme's subunits remain present but separate in solution, and activity drops. Which statement best describes why activity decreases?
  13. In mitosis, high CDK–cyclin activity maintains chromosome condensation and nuclear envelope breakdown. Mitotic exit requires a sharp decrease in CDK signaling, achieved when APC/C targets mitotic cyclin for degradation. A lab adds a compound that partially inhibits APC/C, reducing cyclin degradation, without affecting microtubule dynamics or kinetochore attachment. Cells show prolonged chromosome condensation and delayed nuclear envelope reformation. Which change would most likely counteract the compound's effect and promote mitotic exit?
  14. A scientist introduces a point mutation in the 3′ splice site (AG) of intron 1 in a eukaryotic gene. The 5′ splice site of intron 1 and all splice sites of other introns remain unchanged. When nuclear RNA is analyzed, a new RNA species appears that includes exon 1, intron 1, and exon 2 in a single continuous segment, while downstream introns are still removed normally. Which explanation best accounts for the structure of this new RNA species?
  15. In dogs, a dominant allele (S) produces short hair and the recessive allele (s) produces long hair. A short-haired dog of unknown genotype is crossed with a long-haired dog (ss). Among 8 puppies, 4 are short-haired and 4 are long-haired. Assume a single gene with complete dominance and that this sample reflects expected ratios. Which genotype is most consistent with the short-haired parent?
  16. A desert camel's body temperature rises 7°C during the day. How does this help it?
  17. A pure phospholipid bilayer is exposed to equal concentrations of two 100 Da solutes: solute R is nonpolar; solute S is polar uncharged. No proteins are present. Which explanation best accounts for the expected difference in their permeability?
  18. In early mitosis, high Cdk1 activity promotes spindle formation. The spindle checkpoint prevents APC/C activation until all kinetochores are attached. A researcher artificially activates APC/C in prometaphase using a chemical dimerizer, without changing kinetochore attachment status. APC/C then ubiquitinates securin and M-cyclin. Which outcome is most likely immediately after APC/C activation?
  19. A toxin blocks G-alpha GTPase activity. What result is expected?
  20. A cell begins meiosis with 2n=142n=14 and completes S phase beforehand. During metaphase II, chromosomes align individually at the equator, and in anaphase II sister chromatids separate. Which outcome is most likely regarding chromosome composition in each cell at the start of metaphase II?

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