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Practice Test 15 - AP Biology

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

  1. In a large bacterial population, a new allele RR that confers antibiotic resistance arises once by mutation. After antibiotic treatment begins, the frequency of RR increases from 0.001 to 0.35 in 30 generations. The mutation rate is low and unchanged, and population size remains very large. Which process is most likely responsible for the rapid increase in RR frequency?
  2. In rabbits, a dominant allele (R) produces round ears and a recessive allele (r) produces pointed ears. Two rabbits with round ears are crossed. Each parent could be RR or Rr. If one offspring is born with pointed ears (rr), the parents' genotypes can be inferred using Mendelian inheritance. Which parental genotypes are consistent with producing a pointed-eared offspring?
  3. Two populations of frogs live in adjacent valleys with similar climate. During the breeding season, males in valley 1 produce a call with a dominant frequency near 1.2 kHz, while males in valley 2 produce a call near 2.0 kHz. Females show strong preference for local calls in playback experiments, and field surveys find few mixed pairs even where the valleys meet. Genetic data indicate reduced gene flow and increasing divergence between the populations. Which prezygotic barrier most directly contributes to reproductive isolation here?
  4. An organism has the genotype AaBbAaBb, where the genes for traits A and B are located on different chromosomes. Which of the following represents all possible combinations of alleles in the gametes produced by this organism?
  5. A structural carbohydrate in plant cell walls consists of unbranched chains of glucose where each monomer is linked by ββ(1;4) glycosidic bonds. These bonds orient adjacent glucose units in alternating directions, allowing many chains to lie parallel and form extensive hydrogen bonds between hydroxyl groups on neighboring chains. Bundles of these chains form microfibrils with high tensile strength and limited solubility. Which statement best describes how the bond type contributes to this material property?
  6. In a population of 800 snails, genotype counts are 320 GG, 160 Gg, and 320 gg. The population is large, and there is no mutation, migration, or selection at this locus. Which conclusion is best supported about Hardy-Weinberg equilibrium in this generation?
  7. In endothelial cells, nitric oxide (NO) diffuses into the cytosol and binds soluble guanylyl cyclase (sGC), increasing cGMP. cGMP activates protein kinase G (PKG), which phosphorylates myosin light-chain phosphatase, increasing its activity and reducing myosin phosphorylation, relaxing the cell. A cGMP phosphodiesterase (PDE) converts cGMP to GMP. When PDE is overexpressed, NO produces a smaller relaxation response despite normal sGC activation. Which change would most likely restore relaxation in PDE-overexpressing cells?
  8. In a plant cell assay, peptide P binds a membrane receptor kinase and triggers phosphorylation of a cytosolic relay protein K. Phosphorylated K activates an NADPH oxidase in the plasma membrane, producing reactive oxygen species (ROS). ROS oxidize cysteines on a nearby protein phosphatase (PP), decreasing PP activity. PP normally dephosphorylates K, limiting signal duration. When P is added, K phosphorylation rises quickly and then plateaus. A mutant line expresses PP that cannot be oxidized by ROS but retains normal catalytic activity. Compared with wild-type cells, what is most likely in the mutant after P addition?
  9. An mRNA contains the sequence 5′-AUG GAA CUA UAG-3′, where UAG is a stop codon. A researcher introduces a modified tRNA whose anticodon base-pairs with UAG and is charged with an amino acid. In normal cells, release factors bind stop codons and promote polypeptide release. Assume the modified tRNA competes successfully with the release factor at UAG. Which outcome is most likely for translation of this mRNA?
  10. A researcher studies the restriction point in late G1, where sustained CDK signaling is required to commit a cell to DNA synthesis. In the experiment, cyclin is present and binds CDK, but a competitive inhibitor occupies the CDK active site, preventing phosphorylation of downstream targets. The inhibitor does not affect cyclin binding or CDK abundance. Cells remain in G1 despite adequate nutrients. Which change would most likely allow the cells to enter S phase while the inhibitor is present?
  11. A lab compares two cell types from the same individual and finds that a specific microRNA is abundant in cell type Q but rare in cell type R. Both cell types contain similar amounts of mRNA transcribed from Gene W, yet Gene W protein levels are low in Q and high in R. The DNA sequence of Gene W is identical in both cell types. Which explanation best accounts for the difference in Gene W protein levels?
  12. A scientist prepares a cDNA library from pancreatic cells by isolating mRNA and using reverse transcriptase to synthesize DNA copies. The resulting cDNAs are cloned into plasmids and transformed into bacteria, creating many bacterial colonies. The researcher later screens the colonies to find clones containing the insulin cDNA. Compared with a genomic DNA library made from the same organism, which feature would be expected in the insulin clone from the cDNA library?
  13. A cell imports phosphate (Pi) using a cotransporter that moves Pi into the cell only when H+^+ also moves in. Pi accumulates inside the cell above its extracellular concentration. When the H+^+ gradient is dissipated, Pi uptake stops even though ATP is present in the cytosol. Which mechanism best explains Pi uptake?
  14. A disaccharide is formed by linking one glucose and one fructose through a glycosidic bond that uses both anomeric carbons. In solution, the disaccharide does not open to expose a free aldehyde or ketone group. In a lab assay, this sugar fails to reduce Cu2+^{2+} to Cu+^{+}, unlike maltose. Which statement best describes the structural reason for the negative test result?
  15. Three ponds are sampled for zooplankton. Pond A has 4 species with 25 individuals each. Pond B has 8 species with 12–13 individuals each. Pond C has 8 species, but one species has 70 individuals and the remaining 7 species share 30 individuals. Each pond sample totals 100 individuals. Which pond has the highest biodiversity based on richness and evenness together?
  16. A river fish species occupies both upstream and downstream habitats with no physical barrier between them. Upstream water is clear and fast; downstream water is turbid and slow. Over many generations, females upstream mate mostly with males showing bright flank coloration, while females downstream mate mostly with males showing dull coloration that is less visible in turbid water. Mark-recapture studies show fish move between regions, but genetic data reveal strong allele-frequency differences at loci linked to coloration and mate preference, with fewer mixed-genotype offspring than expected under random mating. Which mechanism most directly explains divergence despite ongoing gene flow?
  17. A phospholipid bilayer lacking proteins is exposed to equal concentrations of iodine (I2_2, 254 Da, nonpolar) and lysine (146 Da, charged at neutral pH). Which molecule would most likely cross the membrane more readily by simple diffusion?
  18. A researcher isolates nuclei from eukaryotic cells and measures RNA lengths from a single gene. The primary transcript averages 2,400 nucleotides and contains one intron of 900 nucleotides flanked by two exons. After RNA processing, the most abundant RNA from this gene averages 1,500 nucleotides and contains the same exon sequences as the primary transcript. No changes are detected in the DNA sequence of the gene. Which explanation best accounts for the 900-nucleotide decrease in RNA length after processing?
  19. A sealed artificial phospholipid bilayer separates two solutions. Five solutes are added separately at equal concentration: O2_2 (32 Da, nonpolar), ethanol (46 Da, polar uncharged), glucose (180 Da, polar uncharged), Na+^+ (23 Da, charged), and a 12–amino acid peptide (~1300 Da, polar). No transport proteins are present. Which solute would most likely cross the bilayer fastest by simple diffusion?
  20. A vesicle preparation contains membranes with an ion transporter that moves Ca2+\text{Ca}^{2+} from the cytosolic side to the lumen. When the luminal Ca2+\text{Ca}^{2+} concentration is already higher than the cytosolic Ca2+\text{Ca}^{2+} concentration, net Ca2+\text{Ca}^{2+} movement into the lumen still occurs if ATP is present. If ATP is removed, net movement stops even though the concentration gradient remains the same. Adding a channel blocker has no effect, but adding an inhibitor that binds the transporter's ATP-binding site stops transport. Which process is most likely occurring?

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