Practice Test 65 - AP Biology

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

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1. A neuron's axon membrane contains many voltage-gated ion channels concentrated at specific regions. When these channels are blocked, electrical signals travel a much shorter distance. Which feature best explains how channel placement affects signal propagation?
2. DNA polymerase synthesizes DNA by adding nucleotides to the 3′ end, and the two new strands are produced in opposite physical directions because the templates are antiparallel. In a cell, ligase is inhibited so covalent joining of adjacent DNA fragments cannot occur. Which outcome is most likely after replication?
3. A developmental biologist compared early embryo stages of a chicken and a lizard. In both lineages, embryos form a transient pharyngeal-arch pattern and a segmented tail bud, and the same set of regulatory genes is expressed in similar spatial regions during these stages. Later development diverges, producing distinct adult morphologies. The shared embryonic structures and gene-expression pattern appear before major lineage-specific traits form. Which inference is best supported by these observations?
4. A plant cell is examined under a microscope and shows a large central vacuole occupying most of the cell volume. When placed in a mildly hypotonic solution, the vacuole expands and the plasma membrane presses firmly against the cell wall. The cell becomes rigid without bursting. Which feature best explains the functional consequence observed in the plant cell?
5. A rabbit population is introduced to a 10-hectare fenced grassland with abundant food and no predators. Counts each month show 20, 40, 80, 160, and 320 rabbits. Which pattern best illustrates the population's growth over this interval?
6. In a meiosis experiment, a diploid cell contains a homologous chromosome pair with alleles M and m at one locus. Each homolog replicates to form sister chromatids. During prophase I, a crossover occurs between nonsister chromatids at a site near the locus, so one chromatid of the M homolog now carries a small segment from the m homolog, and one chromatid of the m homolog carries the reciprocal segment. After meiosis II, gametes differ in the specific chromatid versions they receive. Which process best explains this chromosomal source of gamete diversity?
7. The results of this cross demonstrate which of the following Mendelian principles?
8. In an experiment, cells are placed in a solution containing a polar sugar analog at a higher concentration outside than inside. Uptake of the sugar analog increases rapidly and then plateaus as external concentration continues to rise. When a membrane protein inhibitor is added, uptake drops to near zero. When cellular ATP is depleted, uptake rate is unchanged. The sugar analog does not cross a pure phospholipid bilayer at a measurable rate. Which mechanism best explains the sugar analog entering the cells under normal conditions?
9. At the same ligand concentration, two cells with the same receptor respond differently. Why?
10. An enzyme's activity is measured at constant pH while temperature rises from 10°C to 35°C, increasing rate from 4 to 22 units. At 45°C the rate decreases to 15 units without changing substrate concentration. Which outcome is most likely as temperature reaches 45°C?
11. A lab compares two animal cell types exposed to a drug that blocks ATP production. In cell type 1, intracellular pH quickly decreases and lysosomes swell. In cell type 2, intracellular pH changes little and lysosomes maintain size. Both cell types contain lysosomes with hydrolytic enzymes that function best at low pH. The main difference is that lysosomal membranes in cell type 2 have fewer proton pumps than those in cell type 1. Which outcome is most likely in cell type 1 after ATP production is blocked?
12. A plant population contains two pigment alleles affecting leaf color: G (green) and P (purple). In a shaded forest understory, birds eat more insects on green leaves than on purple leaves, reducing herbivory on purple plants. Over 12 generations, P increases from 0.22 to 0.47. No new alleles are detected and population size stays large. Which statement best explains how variation in leaf color affected evolution in this population?
13. Two groups of genetically identical zebrafish embryos were raised in identical water conditions except oxygen level. One group developed in normal oxygen, and the other in low oxygen. Low-oxygen embryos showed increased red blood cell production compared with controls. DNA sequencing of an erythropoietin-related gene revealed identical sequences in both groups. Which explanation best accounts for the difference in red blood cell production?
14. A researcher tracks a population of cycling cells and notes that some cells are much smaller than average after cytokinesis. In these small cells, microscopy shows unreplicated chromosomes (one chromatid per chromosome) and a single centrosome. When nutrients are limited, these cells do not begin DNA synthesis, and their DNA content remains constant for several hours. Cells in the same culture that are larger do begin DNA synthesis and later show duplicated chromatids. Which checkpoint behavior best accounts for the small cells failing to enter S phase?
15. A polymer is composed of repeating monomers that each have multiple hydroxyl groups and a carbonyl group. When monomers join, a covalent bond forms with the loss of water, and the resulting polymer can be linear or branched depending on which hydroxyl groups react. This macromolecule class often interacts with water due to many polar groups. Which feature best explains the polymer's ability to form branched structures?
16. In a desert, kangaroo rats and ground squirrels both consume the same seeds. In fenced plots that exclude kangaroo rats but allow ground squirrels, ground squirrel seed consumption increases and seed abundance decreases compared with unfenced plots. Predator access and rainfall are similar across plots. Which interaction best explains the increased seed consumption by ground squirrels in fenced plots?
17. Skin fibroblasts and pancreatic beta cells from the same person are grown in identical media. DNA sequencing confirms the cells have identical alleles for the insulin gene. RT-PCR detects abundant insulin mRNA in beta cells but not in fibroblasts, while a housekeeping gene is expressed in both. Which explanation best accounts for insulin mRNA being present only in beta cells?
18. A cell membrane consists of a phospholipid bilayer with a nonpolar interior. Two solutes are compared at the same temperature and concentration gradient: glycerol (3 carbons, 3 hydroxyl groups; uncharged) and propanone/acetone (3 carbons, one carbonyl group; uncharged). Neither solute has a specific channel or carrier present. Diffusion occurs only by crossing the lipid portion. Solutes that form fewer hydrogen bonds with water and have greater nonpolar surface area tend to partition into the bilayer more easily. Both molecules are similar in size, so differences in polarity dominate their relative permeability.
19. Ligand binding to receptor R activates phospholipase C (PLC), producing DAG in the plasma membrane. DAG recruits and activates protein kinase C (PKC), which phosphorylates cytosolic protein U, increasing U activity. A DAG kinase converts DAG to phosphatidic acid, lowering DAG levels. In cells treated with a DAG kinase inhibitor, ligand addition causes PKC activity to remain elevated for several minutes, while control cells return to baseline within 45 seconds. Which change would most likely mimic the inhibitor's effect without directly targeting DAG kinase?
20. A population of insects includes two heritable color morphs controlled by alleles G (green) and T (tan). In a drought year, grasses dry and become tan. After the drought, the frequency of T rises from 0.30 to 0.62 over several generations, while the population size remains large. Field data show tan individuals leave more offspring than green individuals during drought conditions. Which statement best explains how variation affected evolution in this population?

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