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Practice Test 77 - AP Biology

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

  1. A cell with 2n=142n=14 completes meiosis I normally. During meiosis II, nondisjunction occurs in one of the two cells when sister chromatids of a single chromosome fail to separate at anaphase II. Which set of gametes is most likely produced from the original cell?
  2. Genetically identical yeast cells are grown in either glucose-rich medium or lactose-rich medium. In lactose medium, cells produce high levels of β-galactosidase enzyme; in glucose medium, β-galactosidase levels are low. Sequencing confirms the same DNA sequence in both groups. Which explanation best accounts for the enzyme differences between conditions?
  3. A student measures the initial rate of an enzyme-catalyzed reaction at six substrate concentrations while keeping the amount of enzyme, temperature, and pH constant. No inhibitors are present. At substrate concentrations of 0.5, 1, 2, 5, 10, and 20 mM, the initial rates are 33, 50, 67, 83, 91, and 95 µmol/min, respectively. Which explanation best accounts for the leveling off of the initial rate at the highest substrate concentrations?
  4. A cell has genotype Hh on one homologous pair and Jj on a different homologous pair. A lab observes two meioses from the same individual with no crossing over. In meiosis X, the H-bearing homolog and the J-bearing homolog move toward the same pole at anaphase I. In meiosis Y, the H-bearing homolog and the j-bearing homolog move toward the same pole at anaphase I. After meiosis II, gametes reflect these different whole-chromosome combinations. Which process best explains the difference between meiosis X and meiosis Y?
  5. A researcher compares two cell lines. In both, DNA replication occurs in S phase, producing sister chromatids and 4C DNA content in G2. In cell line 1, all chromosomes attach to spindle microtubules from opposite poles and align at the metaphase plate before anaphase. In cell line 2, one chromosome remains unattached at metaphase. The spindle checkpoint is functional in both lines. Which difference in mitotic progression is most likely between the two lines?
  6. In neurons, voltage-gated channels and ion pumps in the plasma membrane maintain high Na+ concentration outside the cell and high K+ concentration inside. This separation creates an electrochemical gradient used to generate rapid changes in membrane potential. If the membrane is punctured so ions diffuse freely, the gradients dissipate and action potentials cannot be produced. Which conclusion is best supported about compartmentalization at the cell boundary?
  7. In a human cell, a gene's coding region includes the DNA codon 5′-TGG-3′, which is transcribed to mRNA 5′-UGG-3′ and translated as tryptophan. A point mutation changes the coding DNA codon to 5′-TGA-3′, producing mRNA 5′-UGA-3′ at that position. UGA is a stop codon recognized by release factors. No alternative splicing occurs. Which outcome is most likely for the translated polypeptide?
  8. A wetland was sampled at its edge and center. The edge community had 13 amphibian species with moderate evenness. The center had 13 amphibian species but two species accounted for 85% of individuals. Total individuals counted were similar. Which conclusion is best supported about biodiversity patterns within the wetland?
  9. A flowering plant population contains two alleles affecting flowering time: allele E (earlier) and allele L (later). A shift in climate causes the peak abundance of pollinators to occur earlier in the season. Over 12 generations, the frequency of E increases from 0.35 to 0.67. Which statement best explains how genetic variation influenced this evolutionary response?
  10. A transport protein spans a membrane using several α-helices enriched in nonpolar amino acids facing the lipid tails. Its primary structure positions leucine and isoleucine on the helix exterior, stabilizing the protein's tertiary structure within the bilayer. A mutation replaces multiple exterior leucines with lysines, adding positively charged R groups while the polypeptide length remains unchanged. Cells expressing the mutant protein show much less of the protein embedded in the membrane and reduced transport activity. Which statement best describes the molecular cause of the reduced transport?
  11. In an experiment, isolated chloroplasts are placed in darkness with high ADP + Pi and NADP+^+. No ATP or NADPH is produced until light is provided. Which explanation best accounts for the lack of ATP production in the dark?
  12. In a coastal plant population, salt tolerance is influenced by two alleles at a locus: S (higher tolerance) and s (lower tolerance). A storm permanently increases soil salinity. Over 15 generations, allele frequency changes from S = 0.40 to S = 0.71. Plants are sessile, and pollination occurs locally. Which statement best explains the role of preexisting genetic variation in the population's evolutionary response to increased salinity?
  13. A cell with 2n=82n=8 forms tetrads during prophase I. At metaphase I, each tetrad aligns with either homolog facing either pole, and then homologous chromosomes separate in anaphase I while sister chromatids remain attached. Which explanation best accounts for why the two cells produced after meiosis I can differ in which homologs they contain?
  14. In a drought-response gene tree, unrelated desert birds cluster together. Why?
  15. In a desert lizard population, sprint speed is a heritable quantitative trait. Lizards with intermediate speeds (around 2.5 m/s) produce an average of 14 surviving offspring, while very slow (below 1.5 m/s) and very fast (above 3.5 m/s) individuals each average 6 surviving offspring. This pattern is consistent across 8 generations, and the population size remains large with no migration detected. Over generations, the variance in sprint speed decreases, and the mean stays near 2.5 m/s. Which pattern best illustrates the selection acting on sprint speed?
  16. In an early Earth simulation, researchers exposed a mixture of simple gases and water to ultraviolet (UV) light. Organic molecules accumulated, but many broke down when UV exposure continued. When the same setup included dissolved mineral particles that absorbed UV, the net amount of organic molecules remaining after the same time period was higher. Which conclusion is best supported by the evidence?
  17. A neuron's membrane contains ligand-gated ion channels permeable to Na+. Extracellular Na+ is 145 mM and intracellular Na+ is 12 mM. When a neurotransmitter binds, Na+ influx increases rapidly even when ATP synthesis is blocked, and the influx stops if the channel protein is chemically cross-linked closed. Which explanation best accounts for the Na+ influx observed after neurotransmitter binding?
  18. During S phase, helicase separates the two parental DNA strands, and DNA polymerase adds nucleotides only to a 3′ end using complementary base pairing (A–T, C–G). A cell is exposed to a chemical that prevents DNA polymerase from proofreading mismatched bases but does not affect base-pairing rules or strand separation. Which outcome is most likely after one round of replication?
  19. A population of somatic cells is synchronized in G1 with 2C DNA content. Cells are then given nucleotides and allowed to proceed. After S phase, each chromosome consists of two sister chromatids, and total DNA content becomes 4C. A researcher adds a chemical that blocks the G2 checkpoint's ability to delay entry into mitosis when DNA replication is incomplete. In treated cells, some replication forks remain unfinished at the time the cells begin M phase. Chromosomes still condense, and the nuclear envelope breaks down. Which outcome is most likely in the treated cells during mitosis?
  20. A student compares liver cells and pancreatic beta cells from the same mouse. Genomic DNA analysis indicates identical coding sequences for the insulin gene in both cell types. When nuclei are stained for acetylated histones near the insulin gene promoter, strong staining is observed in beta cells but weak staining in liver cells. Correspondingly, insulin mRNA is abundant in beta cells but nearly undetectable in liver cells. Which explanation best accounts for these observations at the cellular level?

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