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Practice Test 61 - AP Biology

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

  1. A large rabbit population has allele frequencies p(F)=0.5p(F)=0.5 and q(f)=0.5q(f)=0.5 for a gene that affects how efficiently the kidneys conserve water. During a severe drought, researchers found that FFFF and FfFf rabbits survived and produced offspring at similar rates, and both groups survived and produced more offspring than ffff rabbits. The population remained large, mating remained random, no rabbits entered or left the population, and no new mutations at this gene were detected. In the next generation, p=0.6p=0.6. Which evolutionary mechanism is most directly supported by these data?
  2. A river changes course and isolates two populations of the same small mammal on opposite banks. After 800 generations, allele frequencies differ between banks. When researchers bring individuals together in an enclosure, mating occurs and fertilization happens, but most embryos fail to develop to birth. The few offspring that are born are healthy but produce very few viable gametes. Which reproductive isolating mechanism most directly limits gene flow between the populations?
  3. A gene's promoter contains a TATA box sequence on the coding strand: 5'-TATAAA-3' located 30 bases upstream of the transcription start site. In a mutant, the TATA box is changed to 5'-TATGAA-3'. The coding region of the gene is unchanged. The protein product is normally synthesized in large amounts when the gene is transcribed. Which outcome is most likely from this mutation?
  4. A researcher supplies chloroplasts with abundant CO2 but removes ADP and inorganic phosphate from the stroma while keeping light intensity constant. Electron transport through the thylakoid membrane initially proceeds, creating an H+ gradient. Which outcome is most likely after a short time?
  5. A peptide ligand binds a membrane receptor that opens a Ca2+^{2+} channel, raising cytosolic Ca2+^{2+}. Ca2+^{2+} binds calmodulin (CaM), and the Ca2+^{2+}–CaM complex activates kinase M. Kinase M phosphorylates protein P, increasing P activity. A Ca2+^{2+}-ATPase pump returns cytosolic Ca2+^{2+} to baseline within 30 seconds after ligand removal. In cells treated with a Ca2+^{2+}-ATPase inhibitor, cytosolic Ca2+^{2+} remains elevated and P activity stays high even when ligand is washed out. Which change would most likely restore rapid termination of P activation in the inhibited cells?
  6. A student compares two groups of cells entering mitosis. In Group 1, all chromosomes attach to spindle microtubules from opposite poles, and sister chromatids separate normally. In Group 2, one chromosome's kinetochore fails to attach, but the cell still begins anaphase. In Group 2, sister chromatids of the unattached chromosome do not segregate to opposite poles. Which outcome is most likely in the daughter cells from Group 2?
  7. Researchers sequence a 900-base-pair region of a mitochondrial gene from three island bird populations (X, Y, Z) and a mainland population (M). They find that X and Y differ by 6 bases, X and Z differ by 42 bases, and Y and Z differ by 45 bases. Each island population is geographically isolated, and all populations have similar diets and body sizes. Which conclusion is best supported by the molecular differences among these populations?
  8. Two solutes are compared for diffusion through a protein-free phospholipid bilayer: solute P (propane, 44 Da, nonpolar) and solute Q (serine, 105 Da, polar with a zwitterionic charge). Which solute would most likely cross the membrane faster?
  9. In bacteria, gene R is transcribed from a promoter that requires an activator bound upstream to help recruit RNA polymerase. Under low oxygen, the activator binds DNA and transcription increases. A point mutation occurs in the activator's DNA-binding domain so it cannot bind the upstream site, but the promoter sequence is unchanged. Which result is most likely under low oxygen?
  10. A lab compares two cube-shaped cells with identical membrane permeability. Cell A is a cube with side length 10 µm; Cell B is a cube with side length 20 µm. Both are placed in a solution containing a small, nonpolar dye that crosses the membrane by simple diffusion. After the same exposure time, a smaller fraction of Cell B's interior is stained. Which explanation best accounts for the smaller stained fraction in Cell B?
  11. A cell is placed in a solution with equal solute concentration inside and outside (isotonic). The membrane contains aquaporins and is impermeable to the solute. Over time, the cell's volume remains constant, and ATP depletion has no effect on water movement rates. Which statement best describes net water movement across the membrane?
  12. 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?
  13. A membrane receptor activates two parallel pathways after ligand binding. Pathway 1: G protein activates adenylyl cyclase, increasing cAMP and activating PKA, which phosphorylates substrate S1. Pathway 2: the same receptor activates PLC, producing IP3_3 and raising cytosolic Ca2+^{2+}, activating kinase CaK, which phosphorylates substrate S2. A selective adenylyl cyclase inhibitor blocks S1 phosphorylation but does not change S2 phosphorylation. Which statement best explains the inhibitor's specificity?
  14. Replication accuracy depends on correct base pairing and repair of mismatches that escape initial nucleotide selection. After replication, some cells use mismatch repair to identify the newly synthesized strand by transient discontinuities and then replace the incorrect nucleotide. A toxin prevents mismatch repair proteins from binding DNA but does not affect replication speed. Which change is most likely observed over several cell divisions?
  15. In yeast cells, pheromone P binds a GPCR that activates a heterotrimeric G protein. The released Gβγ subunit activates a MAP kinase cascade (M1→M2→M3) through sequential phosphorylation. Activated M3 phosphorylates a cytosolic target protein X, changing its activity within minutes. A specific phosphatase removes phosphate groups from M3, decreasing M3 activity and limiting phosphorylation of X. When the phosphatase is overexpressed, pheromone P produces less phosphorylated X. Which manipulation would most likely increase phosphorylated X levels in cells overexpressing the phosphatase?
  16. In a eukaryotic cell, glycolysis occurs in the cytosol while a different pathway that consumes pyruvate occurs inside mitochondria. A mutation in a mitochondrial pyruvate transporter reduces pyruvate entry into mitochondria, causing cytosolic pyruvate to accumulate. Which feature best explains how compartmentalization contributes to regulating pyruvate use in this cell?
  17. A flowering plant species has a wide range. In the eastern region, flowers are tubular and are visited mostly by hummingbirds; in the western region, flowers are open and are visited mostly by bees. Both regions flower at the same time, and wind can disperse seeds between regions. In a common garden, plants retain their region-typical flower shapes, and pollinators preferentially visit the matching flower type, reducing cross-pollination. Which process most directly reduces gene flow and can promote speciation between the regions?
  18. In a plant guard cell, a peptide ligand binds a receptor kinase that activates a cytosolic kinase (K1). K1 activates an anion channel, causing membrane depolarization and opening voltage-gated Ca2+^{2+} channels. Ca2+^{2+} activates a Ca2+^{2+}-dependent kinase (K2) that phosphorylates K1 on an activation loop, increasing K1 catalytic activity. With constant ligand, K1 activity increases gradually over time rather than reaching a fixed level quickly. Which outcome best supports that the pathway includes positive feedback?
  19. An animal cell with internal solute concentration 0.15 M is placed into a solution containing 0.25 M nonpenetrating solute. Water can cross the membrane. After several minutes, the cell appears crenated (shriveled). Which outcome is most likely for net water movement?
  20. A cell has genotype Tt for a gene on chromosome 3 and Uu for a gene on chromosome 7. A lab observes that two gametes from the same meiotic event can differ because one receives the paternal homolog of chromosome 3 and the maternal homolog of chromosome 7, while the other receives the maternal homolog of chromosome 3 and the paternal homolog of chromosome 7. No crossing over is detected. Which meiotic mechanism best accounts for these different combinations of whole chromosomes in gametes?

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