Practice Test 29 - AP Biology

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

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1. A population of flowering plants shows heritable variation in flowering time controlled by alleles F (early) and f (late). A new mowing schedule cuts the field in mid-season each year, removing many late-flowering plants before they set seed, while early-flowering plants often produce seeds before mowing. Plants cross-pollinate within the same field, and offspring flowering time resembles parental genotypes. Other environmental factors remain similar across years. Which outcome is most likely over time?
2. In a diploid cell, DNA replication finishes in S phase, producing sister chromatids for each chromosome. During mitosis, a toxin weakens kinetochore–microtubule attachments, so several chromosomes attach to only one spindle pole (no bipolar attachment). The spindle checkpoint is experimentally disabled, and the cell proceeds from metaphase into anaphase. Cytokinesis completes. No additional DNA replication occurs during mitosis. Which outcome is most likely in the resulting daughter cells?
3. Genetically identical fruit fly larvae were split into two incubators. One incubator was maintained at $18^\circ\text{C}$ and the other at $29^\circ\text{C}$. Adults from the warmer incubator developed shorter wing veins than adults from the cooler incubator. Sequencing of a wing-patterning gene revealed no differences between groups. Which explanation best accounts for the temperature-associated wing phenotype variation?
4. Lactose is a disaccharide composed of glucose and galactose linked by a β-1,4 glycosidic bond. Sucrose is a disaccharide composed of glucose and fructose linked by an α-1,β-2 glycosidic bond that joins both anomeric carbons. In aqueous solution, some disaccharides can open into a linear form that has a free anomeric carbon, allowing the sugar to act as a reducing sugar. Which statement best describes the consequence of sucrose's glycosidic bond arrangement?
5. Biologists examined forelimb skeletons from a bat, whale, cat, and lizard. Each forelimb contains a humerus, radius, ulna, carpals, metacarpals, and phalanges arranged in the same relative order, though their sizes and shapes differ among lineages. The forelimbs perform different functions (flight, swimming, running, and walking). Which inference is best supported by the shared bone arrangement across these vertebrate lineages?
6. Two heterozygotes have two children. What is the probability the children have the same phenotype?
7. A plant population was surveyed in two plots of equal area. Plot 1 had 20 plants and produced 100 seeds total in one season; Plot 2 had 80 plants and produced 160 seeds total. All seeds had similar germination rates, and no migration occurred between plots. Which statement best describes the density-dependent effect suggested by the data?
8. A mutant plant has chloroplasts with normal photosystems and electron carriers, but its thylakoid membrane is unusually permeable to H+. Light absorption and electron flow still occur, and water can be oxidized. Which effect is most likely on the products of the light reactions compared with wild type?
9. A researcher studies diffusion of a small molecule into two similarly shaped cells. Cell 1 is smaller and reaches equilibrium with the external concentration faster than Cell 2. Membrane permeability is the same, and both start with zero internal molecule. Which explanation best accounts for Cell 1 reaching equilibrium faster?
10. A scientist adds ligand G to cells and observes rapid receptor dimerization at the plasma membrane using fluorescence. Shortly after dimerization, receptor phosphorylation increases. When a drug prevents dimerization, ligand binding still occurs but phosphorylation is greatly reduced. Which of the following best explains why dimerization is important early in this signaling pathway?
11. A cell-surface glycoprotein has a short oligosaccharide attached that contains several monosaccharides with different orientations of hydroxyl groups (stereoisomers). A second glycoprotein has the same monosaccharide types but in a different sequence and linkage pattern. A lectin protein binds strongly to the first glycoprotein but not the second. Which feature best explains the binding specificity at the molecular level?
12. A population of ground-nesting birds occupies two islands with similar vegetation. On Island X, nests are spaced far apart and only 5% are destroyed by predators. On Island Y, nests are clustered and 35% are destroyed. Predator abundance is similar on both islands, but predators locate nests by searching areas with frequent bird activity. Over several seasons, nest clustering varies with bird density, increasing when more birds breed on the island. Which statement best identifies a density-dependent effect on the bird population?
13. A researcher compares two nucleic acid duplexes in the same salt concentration: Duplex 1 is 30 bp with 70% G≡C pairs; Duplex 2 is 30 bp with 30% G≡C pairs. Both have identical sugar-phosphate backbones and are heated at the same rate. G≡C base pairs form three hydrogen bonds, while A=T base pairs form two hydrogen bonds. Base stacking interactions also increase with higher G≡C content because of stronger pi-pi interactions among adjacent bases. No proteins are present. Which statement best describes the expected difference in strand separation behavior between the duplexes as temperature increases?
14. A gene's promoter contains a consensus TATA box sequence that helps recruit transcription factors and RNA polymerase II. A mutation changes the TATA box from TATAAA to TATGAA, without altering the coding region. In cells with this mutated promoter, the mRNA produced from the gene is measured and found to be substantially lower than in cells with the normal promoter. Which outcome is most likely for the protein encoded by this gene in mutated cells?
15. In humans, hemoglobin alleles $H^A$ and $H^S$ are codominant; $H^A H^A$ individuals have normal hemoglobin, $H^S H^S$ individuals have sickle-cell disease, and $H^A H^S$ individuals have both hemoglobin types. Two heterozygous parents ($$H^A$ $H^S$ $H^A H^S$) have a child. Which outcome best predicts the child's hemoglobin type?
16. On a rocky shore, two barnacle species occupy overlapping zones. In plots where Species A is removed, Species B expands into the area previously occupied by Species A, while survival of Species B remains unchanged in areas where Species A was never present. Wave exposure and substrate type are similar across plots. Which interaction best explains Species B's expansion after Species A is removed?
17. In plant guard cells, signal molecule M binds a receptor that activates a cytosolic protein kinase (PK1). PK1 phosphorylates and activates an anion channel, leading to anion efflux and membrane depolarization. Depolarization opens a voltage-gated K$^+$ efflux channel, decreasing intracellular K$^+$ and causing water to leave the cell by osmosis, reducing turgor. A protein phosphatase (PP) dephosphorylates the anion channel, reducing its open probability and limiting depolarization. Inhibiting PP increases anion efflux after M addition. Which change would most likely counteract the effect of PP inhibition on anion efflux?
18. A cell is placed in a solution containing a fluorescent dye that is too large and polar to cross the lipid bilayer. After 5 minutes, the dye is detected inside membrane-bound vesicles in the cytoplasm, not freely in the cytosol. The process is inhibited when ATP levels drop. No specific membrane transporter for the dye is present. Which mechanism best explains how the dye enters the cell?
19. A unicellular eukaryote contains green organelles that carry out photosynthesis. Each organelle has a double membrane, contains circular DNA, and divides by a process resembling binary fission. The organelle's ribosomes are similar in size to bacterial ribosomes. Which explanation best accounts for the origin of these photosynthetic organelles?
20. A frog population has heritable variation in skin peptide composition: allele P produces peptides that inhibit a fungal pathogen, while allele p produces peptides with weaker inhibition. During repeated fungal outbreaks, frogs with weaker inhibition have lower survival to reproduction. If outbreaks continue for many generations, which outcome is most likely?

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