Practice Test 38 - AP Biology

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

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1. A student compares two beakers containing cells with an internal solute concentration of 0.30 M. In beaker 1, the external solution is 0.30 M nonpenetrating solute; in beaker 2, the external solution is 0.15 M nonpenetrating solute. Water crosses the membrane, solute does not. Which outcome is most likely for the cells in beaker 2?
2. Two rocky intertidal sites are surveyed at low tide. Site 1 has 9 invertebrate species and 6 algal species; most species occur in moderate numbers. Site 2 has 9 invertebrate species and 6 algal species, but 90% of all individuals are a single barnacle species and a single alga. Total individuals counted are equal. Which statement best describes the biodiversity pattern between sites?
3. A lizard population shows variation in toe-pad width, a heritable trait. After frequent storms, vegetation becomes smoother and less textured. Lizards with wider toe pads cling better and produce more offspring than lizards with narrower pads. Which outcome is most likely in the population after several generations in the smoother habitat?
4. In a diploid cell with $2n=6$, homologous chromosome pairs align at the metaphase plate during meiosis I. In one observed cell, all three maternal homologs face the same pole while all three paternal homologs face the opposite pole. The cell completes meiosis I and then meiosis II normally, with sister chromatids separating in meiosis II. Which outcome is most likely for the chromosome sets in the four gametes produced from this single cell?
5. A student analyzes an unknown biomolecule that contains long hydrocarbon chains and very few oxygen atoms. The molecule includes a glycerol region connected to three fatty acid chains through covalent bonds formed when hydroxyl groups react with carboxyl groups, releasing water. The resulting structure does not consist of a repeating monomer sequence, yet it is grouped with other molecules that are largely nonpolar and interact weakly with water. Which statement best explains why this molecule is not considered a polymer?
6. In a double-stranded DNA region, one strand reads 5′-AGCT-3′. Which complementary strand sequence best explains accurate information retention during replication?
7. Two signaling molecules, A and B, are added separately to the same cells. Molecule A triggers a response only when added outside intact cells. Molecule B triggers a response only when microinjected into the cytosol. Neither molecule crosses the plasma membrane on its own. Which of the following best explains these observations?
8. Two nucleic acid strands are compared. Strand M contains deoxyribose sugars and uses thymine as a pyrimidine base; Strand N contains ribose sugars and uses uracil instead of thymine. Both strands have negatively charged phosphate groups in their backbones. A solution is treated with an enzyme that recognizes and binds uracil-containing nucleic acids through base-specific interactions, without requiring strand pairing. Which molecule is most likely to be bound by the enzyme under these conditions, and why?
9. Two monosaccharides are isomers with the same molecular formula. In one, the hydroxyl group on carbon 4 points to the right in a Fischer projection; in the other, it points to the left. A lectin protein on a cell surface binds strongly to only the first monosaccharide when it is part of a larger oligosaccharide. Which statement best explains the specificity at the molecular level?
10. In skeletal muscle cells, calcium ions (Ca2+) are stored at high concentration inside the sarcoplasmic reticulum (SR), while cytosolic Ca2+ remains low at rest. During contraction, Ca2+ is released from the SR into the cytosol, where it binds proteins that initiate contraction; afterward, pumps return Ca2+ to the SR. If SR membranes become leaky, cytosolic Ca2+ stays elevated and contraction becomes difficult to regulate. Which feature best explains how compartmentalization enables control of this cellular function?
11. In a meiosis lab, students analyze a cell with two homologous chromosome pairs. Pair 1 carries alleles L and l; pair 2 carries alleles Q and q. No crossing over occurs. The students note that the orientation of each tetrad at metaphase I is random, so either homolog of each pair can face either pole. After meiosis II, gametes differ by which intact homologs they received. Which process best explains why gametes can be LQ, Lq, lQ, or lq?
12. A lake was surveyed at two depths. Shallow water contained 16 zooplankton species with relatively even abundances. Deep water contained 16 species, but two species comprised 90% of individuals. Sampling volume and methods were identical. Which inference is best supported about biodiversity across depths?
13. Two cells have equal volume; one is a flattened disk and one is a sphere. The disk shape mainly improves...
14. In chloroplasts, the light reactions occur on thylakoid membranes. Electron transport moves protons from the stroma into the thylakoid lumen, increasing proton concentration inside the lumen relative to the stroma. ATP synthase in the thylakoid membrane uses proton flow back to the stroma to produce ATP. If thylakoid membranes are damaged so protons leak freely, light absorption can still occur but ATP production decreases. Which feature best explains how compartmentalization supports this process?
15. A researcher compares two storage lipids: triglyceride X has three fatty acid tails with no C=C double bonds, and triglyceride Y has three tails each containing one cis C=C double bond. Both molecules consist of a glycerol backbone ester-linked to three fatty acids, making them largely nonpolar and insoluble in water. Cis double bonds introduce bends that reduce how tightly hydrocarbon chains pack together, while saturated chains remain straight and pack closely via van der Waals interactions. At room temperature, samples of X and Y are observed for physical state. Which statement best predicts the observed difference based on molecular structure?
16. A receptor tyrosine kinase cannot dimerize after ligand binding. What is the immediate result?
17. A bacterial population in a nutrient broth was sampled every 30 minutes. Counts were 1,000 cells/mL at 0 min, 2,000 at 30 min, 4,000 at 60 min, and 8,000 at 90 min. The broth was continuously mixed and temperature was constant. No antibiotics were present, and nutrients were not yet depleted during this interval. Which pattern best illustrates the population growth during the first 90 minutes?
18. Mendel's law of segregation is a direct consequence of which process in meiosis?
19. A cell contains two sets of enzymes that act on the same molecule: one set modifies it and the other reverses the modification. The modifying enzymes are concentrated in a membrane-bounded region near the cell cortex, while the reversing enzymes are concentrated around the nucleus. When membrane boundaries are disrupted, the modified form becomes uniformly low throughout the cell. Which feature best explains the effect of losing compartmentalization?
20. A researcher compares two membrane vesicles. Vesicle 1 contains many phospholipids with unsaturated fatty acid tails; Vesicle 2 contains mostly saturated fatty acid tails. At the same temperature, Vesicle 1 allows small nonpolar molecules to diffuse across slightly faster. Which outcome is most likely explained by the tail composition difference?

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