Practice Test 5 - AP Biology

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

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1. A scientist compares two nucleic acid strands: one contains deoxyribose and thymine, and the other contains ribose and uracil. Both strands have a sugar-phosphate backbone with negatively charged phosphate groups. The charge distribution affects how the molecules interact with positively charged ions and proteins. The negative charges are located on a repeating chemical group that is not part of the nitrogenous bases. Which feature best explains the source of the overall negative charge of nucleic acids?
2. A plant cell has 300 mM solute inside its cytoplasm and is placed in a 100 mM solute solution. The plasma membrane is permeable to water but not to the solute. Over several minutes, the cell's volume increases. No ATP-dependent transporters for water are involved. Which direction of net water movement is expected across the membrane?
3. In a heterozygous cell with alleles J and j on a homologous chromosome pair, the homologs exchange segments during prophase I. After meiosis, two gametes contain chromatids with a mix of maternal and paternal segments, while the other two gametes contain chromatids matching the original parental segments. Which description best explains why only some gametes show mixed segments?
4. A population of rabbits has heritable variation in ear length. Over 18 generations in a habitat with dense shrubs, rabbits with very short ears averaged 0.8 surviving offspring, rabbits with very long ears averaged 0.9, and rabbits with intermediate ears averaged 1.7. After 18 generations, the mean ear length stayed similar, but extreme ear lengths became rarer. Which explanation best accounts for the observed change?
5. A muscle cell is treated with an inhibitor that blocks ATP synthase. Shortly after, the proton gradient across the inner mitochondrial membrane becomes very large and oxygen consumption decreases. Which process is most directly reduced, causing the decrease in oxygen use?
6. A cell's radius increases while the concentration gradient for a small nonpolar molecule remains constant. The molecule crosses the membrane by simple diffusion, and the cell's internal requirement for the molecule scales with cytoplasmic volume. Which explanation best accounts for why the internal concentration is harder to maintain as the cell becomes larger?
7. A student compares the wings of bats and the wings of insects. Both structures enable powered flight, but bat wings contain bones corresponding to a humerus, radius, ulna, and elongated digits, while insect wings are extensions of the exoskeleton and contain no bones. Genetic data place bats within mammals and insects within arthropods. Which inference is best supported by these observations about evolutionary relationships?
8. Enzyme Q catalyzes S → P at constant pH and temperature. With 2.0 µM Q and 5 mM S, the initial rate is 80 µM/min. When 2.0 µM Q and 5 mM S are used plus 1 mM inhibitor I, the initial rate decreases to 40 µM/min. Increasing S to 50 mM in the presence of 1 mM I restores the rate to ~80 µM/min. Which prediction is most consistent with these results?
9. A rabbit population shows heritable variation in fur thickness: thin, medium, and thick. A series of unusually cold winters occurs. Field data show that rabbits with thick fur have higher overwinter survival and contribute more offspring to the next spring's population. After six winters, the average fur thickness in newborn rabbits increases. Which statement best explains how variation influenced evolution in this population?
10. Replication requires unwinding of the double helix and stabilization of exposed single-stranded templates so they do not reanneal. A mutation prevents single-strand binding proteins from attaching to separated DNA, but polymerase function is normal. Which outcome is most likely at the replication fork?
11. On early Earth, the atmosphere likely lacked O2 and contained gases such as CH4, NH3, H2, and water vapor. In a laboratory simulation, researchers circulated these gases through a closed apparatus, applied electrical sparks, and condensed the vapor. After one week, the collection trap contained several amino acids, while an identical setup without sparks produced none. Which conclusion is best supported by these results about the origin of life on Earth?
12. A population of frogs breeds in ponds near a highway. Researchers measure allele frequencies at a locus with alleles N (noise-tolerant call) and n. Over 12 years, the frequency of allele N increases from 0.15 to 0.44, with similar numbers of breeding adults each year and no translocations. Which observation best demonstrates evolution in this frog population?
13. A coral reef and a nearby seagrass meadow were surveyed for reef-associated fishes. The reef had 22 species, but 3 species accounted for 75% of individuals. The seagrass meadow had 16 species, with no species exceeding 15% of individuals. Total fish abundance was similar. Which conclusion is best supported about biodiversity across these ecosystems?
14. An archaeal species is observed under electron microscopy to have extensive internal membrane folds that increase over generations in a stable environment. The folds are continuous with the plasma membrane and share the same membrane proteins, including transporters found at the cell surface. No separate genome is detected inside the folded regions, and the folds do not divide independently of the cell. Which inference best explains how these compartments could have arisen?
15. A lab uses DNA microarrays to compare gene expression between untreated cells and cells exposed to a chemical. mRNA from each sample is converted to cDNA and labeled with different fluorescent dyes, then both are hybridized to an array containing thousands of gene-specific DNA probes. For one gene spot, fluorescence is much stronger for the treated-sample dye than for the untreated-sample dye. Which conclusion is best supported for that gene?
16. A 120–amino acid enzyme has a hydrophobic core stabilized by nonpolar R groups and an active site formed by distant residues brought together in its tertiary structure. A mutation replaces one interior valine with aspartic acid, adding a charged, hydrophilic R group without changing the amino acid sequence length. In vitro, the enzyme's catalytic rate decreases while the amino acid sequence remains otherwise unchanged. Which feature best explains the reduced catalytic activity?
17. Researchers compare a 900-base-pair segment of a nuclear gene in three species: species X, Y, and Z. X and Y differ at 9 nucleotide positions, X and Z differ at 48 positions, and Y and Z differ at 50 positions. No evidence of hybridization among these species is observed. Which inference is best supported by the genetic differences regarding common ancestry among the lineages?
18. A lab compares two similarly shaped cells that both depend on diffusion for nutrient uptake. In Cell A, the linear dimension is increased by a factor of 3 relative to Cell B. Membrane permeability and external nutrient concentration remain constant. Which prediction best describes the effect on nutrient uptake per unit volume in Cell A compared with Cell B?
19. A population of annual plants shows variation in flowering time: some plants flower at 30–35 days, others at 45–50 days. A drought now begins earlier each year, reducing seed set for plants still flowering late. After several generations, the proportion of early-flowering plants increases. Which statement best explains how variation contributed to this evolutionary change?
20. In a vertebrate survey, students note that fish, amphibians, reptiles, birds, and mammals all have a vertebral column formed from repeated bony or cartilaginous segments. In contrast, insects have an exoskeleton and no vertebral column. Molecular analyses group fish, amphibians, reptiles, birds, and mammals within a single clade distinct from insects. Which inference is best supported by the shared vertebral column trait?

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