Practice Test 78 - AP Biology

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

A cell is experimentally prevented from completing cytokinesis after meiosis I, but it proceeds through meiosis II. Homologs separate in meiosis I and sister chromatids separate in meiosis II. Which outcome is most likely for the nuclei produced at the end of meiosis II?
A cell is observed at the G2 checkpoint with 4C DNA content. DNA replication is complete, but one chromosome is not fully decatenated, and sister chromatids remain physically intertwined along a region. The cell delays entry into mitosis while chromosomes remain uncondensed and the nuclear envelope stays intact. After the issue is resolved, the cell enters mitosis and proceeds normally. Which outcome is most likely if the cell had entered mitosis without this G2 delay?
Genetically identical bacteria were grown in either lactose-containing medium or glucose-containing medium. In lactose medium, cells produced high levels of beta-galactosidase enzyme; in glucose medium, enzyme levels were low. DNA sequencing of the beta-galactosidase gene was identical in both groups. Which explanation best accounts for the difference in enzyme levels?
In a grassland, coat color in a rabbit population is controlled by alleles that produce light, medium, or dark fur. After a wildfire, the ground becomes uniformly dark for several decades. Over 12 generations, field surveys show that dark-fur rabbits produce more surviving offspring than medium-fur rabbits, and medium-fur rabbits produce more surviving offspring than light-fur rabbits. During the same period, the frequency of the dark-fur allele increases from 0.22 to 0.71, while the light-fur allele decreases from 0.41 to 0.08. No evidence suggests migration into the population. Which selection pattern best fits these population-level changes?
In a phylogenetic study, researchers compared a 900–base-pair region of a developmental gene in five vertebrates. The frog and salamander sequences differ at 18 sites, the lizard and mouse differ at 21 sites, and the frog and lizard differ at 79 sites. The salamander and lizard differ at 82 sites, and the mouse differs from the frog at 85 sites and from the salamander at 87 sites. All sequences align without gaps, indicating the same gene region is present in each lineage. Which inference is best supported by the sequence differences?
A eukaryotic gene is transcribed into a primary RNA transcript containing exons and introns. A point mutation changes the 5′ splice site of one intron from GU to AU in the RNA sequence produced. The amount of primary transcript synthesized is unchanged compared with wild type. When processed RNA is analyzed, a longer RNA species accumulates that retains the mutated intron sequence. Which explanation best accounts for the accumulation of the longer RNA species?
A father has a recessive phenotype; his daughter has the dominant phenotype. What must be true of the mother?
A cell has 5 mM glucose outside and 0.5 mM glucose inside. Glucose uptake increases when a specific membrane protein is expressed. As external glucose rises beyond 20 mM, glucose uptake rate reaches a maximum and no longer increases. Blocking ATP production does not change uptake rate. Which mechanism best explains glucose entry into the cell?
A steroid-like ligand cannot cross the plasma membrane and instead binds a cell-surface receptor R. Binding activates an intracellular enzyme that produces IP $_3$ from a membrane lipid. IP $_3$ diffuses to the endoplasmic reticulum (ER) and opens IP $_3$ -gated Ca $^{2+}$ channels, increasing cytosolic Ca $^{2+}$ . Elevated Ca $^{2+}$ activates a cytosolic protease Q by binding to an inhibitory subunit that dissociates. When ER Ca $^{2+}$ stores are depleted experimentally, ligand binding still increases IP $_3$ levels but Q activity does not increase. Which step is most directly disrupted by ER Ca $^{2+}$ depletion?
At the spindle checkpoint, a kinetochore-associated complex generates an inhibitor that binds APC/C and prevents ubiquitination of securin. When all chromosomes are properly attached, inhibitor production stops and APC/C becomes active. A mutation causes continuous inhibitor production even after all kinetochores are attached and under tension. Which outcome is most likely in mutant cells?
A student observes that some cells have many short, hairlike projections on their surface that beat in coordinated waves. When these projections stop moving, fluid transport across the tissue slows. Which structure best explains the fluid movement?
Five lineages (A–E) were scored for derived traits (1 = present, 0 = absent). Trait 1 is present in all five. Trait 2: A0 B1 C1 D1 E1. Trait 3: A0 B0 C1 D1 E1. Trait 4: A0 B0 C0 D1 E1. Trait 5: A0 B0 C0 D0 E1. Assume each trait evolved once and was not lost. Based on shared derived traits, infer the closest relationship. Which pair shares the most recent common ancestor?
In an aqueous environment, two monosaccharides differ only in the orientation of the hydroxyl group on carbon 4: Sugar R has the –OH on the right in a Fischer projection, while Sugar S has it on the left (an epimer). A membrane receptor binds strongly to R but weakly to S. No other chemical groups differ between the sugars. Which feature best explains the receptor's binding specificity?
A scientist alters a membrane by removing most transmembrane proteins while leaving the phospholipid bilayer intact. The bilayer has hydrophilic heads facing outward and a hydrophobic interior formed by fatty acid tails. After removal, the scientist measures transport rates of CO2 (small, nonpolar) and Ca2+ (charged). CO2 transport changes little, but Ca2+ transport decreases sharply. Which feature best explains the different effects on CO2 versus Ca2+ movement?
In immune cells, cytokine C binds a receptor that lacks intrinsic kinase activity but is associated with a cytosolic kinase J. Ligand binding causes receptor dimerization, bringing two J molecules together so they phosphorylate each other and then phosphorylate the receptor tails. A latent cytosolic protein S binds the phosphotyrosines and becomes phosphorylated by J; phosphorylated S rapidly forms dimers and activates a cytosolic enzyme by direct binding. A small molecule is added that prevents receptor dimerization but does not block cytokine binding. Which step is most directly disrupted by the small molecule?
In an ocean upwelling region, phytoplankton store 500 g C/m²/year as new biomass, zooplankton store 60 g C/m²/year, and anchovies store 6 g C/m²/year. Assuming carbon stored in new biomass tracks energy stored, which trophic transfer is more efficient?
Two populations of birds were separated on different islands for 8,000 years. When storms later allow occasional migration between islands, hybrids are produced but have reduced fertility compared with offspring from within-island matings. Over subsequent generations, observations show fewer hybrid pairings as birds increasingly choose mates with local song patterns. Genetic data show continued divergence despite some contact. Which process most directly explains the decrease in hybridization after secondary contact?
A student observes two cells in the same environment. Cell LL has many microvilli that increase plasma membrane surface area without substantially changing cell volume; Cell MM lacks microvilli. Both rely on diffusion for uptake of a solute used at the same rate per unit volume. Cell LL shows higher solute uptake per unit volume than Cell MM. Which explanation best accounts for Cell LL's higher uptake per unit volume?
In a population of mice, coat pattern is determined by alleles $E$ and $e$ . A sample shows genotype frequencies: $EE=0.25$ , $Ee=0.50$ , and $ee=0.25$ . The population is large, mates randomly, and is isolated from other populations. However, a lab assay detects that new $e$ alleles arise from $E$ alleles at a measurable rate each generation. Which Hardy-Weinberg condition is violated, best explaining why equilibrium will not be maintained over time?
What is the probability that an offspring will be homozygous, either homozygous dominant or homozygous recessive?

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