Practice Test 47 - AP Biology

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

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1. A researcher compares ATP to a similar nucleotide that has only one phosphate group. ATP contains three phosphate groups, each with P bonded to multiple oxygens that carry partial or full negative charges. When ATP binds to a protein active site, positively charged amino acid side chains often stabilize the phosphate region through electrostatic attraction. The single-phosphate nucleotide shows weaker binding to the same site under identical conditions. Which feature best explains ATP's stronger interaction with a positively charged binding pocket?
2. A population of ground beetles lived on a continuous prairie. After a highway and wide gravel median were built, beetles on opposite sides rarely crossed. Ten years later, allele frequencies at multiple loci differ between sides. In lab trials, beetles from the same side mate readily, but cross-side pairings show frequent courtship failure even when placed together. No differences in survival are detected when larvae from both sides are raised under identical conditions. Which process most directly led to the observed divergence and reduced mating between the two populations?
3. Two membranes have identical phospholipid composition, but differ in cholesterol content. Cholesterol fits among phospholipid tails and can restrict their movement at moderate temperatures. Small nonpolar molecules cross the bilayer mainly by simple diffusion through the hydrophobic core, while polar solutes require transport proteins. In an assay at 25°C, Membrane A has high cholesterol and Membrane B has low cholesterol. Which feature best explains a lower diffusion rate of nonpolar molecules across Membrane A?
4. In two related fish lineages, researchers find a shared pseudogene: a nonfunctional copy of a vision gene containing the same 7-base deletion at the same position in the DNA sequence. A third, more distantly related fish lineage has a functional version of the gene without the deletion. The pseudogene is not expressed in either of the two lineages. Which conclusion is best supported by this pattern?
5. During metaphase, unattached kinetochores generate a signal that inhibits the anaphase-promoting complex/cyclosome (APC/C), an E3 ligase that tags securin for destruction. When securin is removed, separase cleaves cohesin, allowing sister chromatids to separate. In a mutant cell line, kinetochores fail to send the inhibitory signal even when microtubules are not attached. APC/C becomes active prematurely. Which result is most likely in the mutant cells?
6. A eukaryotic microbe contains an organelle surrounded by four membranes. The innermost compartment contains circular DNA and bacterial-like ribosomes. Between the inner two membranes is a small compartment with remnants of a membrane system, but it contains no DNA. The organelle divides by fission. These features are consistent across individuals and are not connected to the host's endomembrane system. Which explanation best accounts for the origin of this multi-membraned organelle?
7. A beetle population includes heritable variation in enzyme activity: allele H produces a heat-stable enzyme, while allele h produces a heat-sensitive enzyme. After a regional heat wave each summer, beetles with heat-sensitive enzymes survive to reproduce at lower rates. If heat waves continue for many generations, which outcome is most likely in the population?
8. During S phase, a eukaryotic replication fork opens as helicase separates the two parental strands. Each parental strand serves as a template, and DNA polymerase adds nucleotides only to a free 3′ end, forming phosphodiester bonds as complementary base pairs (A–T, G–C) align. One strand is synthesized continuously in the same direction as fork movement, while the other is synthesized in short segments that are later joined. A researcher briefly inhibits the enzyme that seals nicks between adjacent DNA segments, then removes the inhibitor and allows replication to finish. Which outcome is most likely in the newly synthesized DNA?
9. A phospholipid contains a glycerol backbone (C, H, O), two fatty acid tails (mostly C and H), and a phosphate-containing head group (P and O). In an aqueous solution, phospholipids spontaneously arrange so that the phosphate heads contact water while the fatty acid tails cluster together. The phosphate group's negative charge and polar bonds create strong interactions with water, while the long hydrocarbon tails interact mainly through weak dispersion forces and avoid water. Which statement best describes the molecular basis for phospholipid self-assembly in water?
10. A student compares two cells at different points in the cell cycle. Cell X has uncondensed chromatin, one centrosome, and a DNA content designated 2C. Cell Y has duplicated centrosomes, condensed chromosomes, and a DNA content designated 4C. Cell Y has not yet separated sister chromatids. Both cells are diploid and are not undergoing meiosis. Based on these observations, Cell Y is most likely in late G2 or early M phase. Which statement best predicts what must occur before Cell Y can enter anaphase?
11. Red blood cells (0.30 M internal nonpenetrating solute) are transferred to a 0.45 M nonpenetrating solute solution. The membrane allows water movement but not solute movement. After several minutes, the cells look crenated (shrunken). Which outcome is most likely during this interval?
12. In a plant, two adjacent cells share plasmodesmata. When a small fluorescent signaling molecule is introduced into Cell A, it appears in Cell B shortly after. When callose deposition blocks plasmodesmata, the molecule remains in Cell A. Which of the following best explains the original movement into Cell B?
13. In a chloroplast, electrons excited by light move through thylakoid membrane carriers, and the released energy is used to pump protons into the thylakoid lumen. ATP synthase uses the gradient as protons move back into the stroma. A student experimentally increases the pH of the thylakoid lumen (making it less acidic) while keeping light intensity constant. Which outcome is most likely for ATP production during illumination?
14. Genetically identical human muscle cells were cultured in vitro. One group received regular electrical stimulation that induced repeated contraction, while the other group was unstimulated. After several days, stimulated cells had higher levels of mitochondrial proteins and greater oxygen consumption. DNA sequencing of a mitochondrial-protein gene showed identical sequences in both groups. When stimulation stopped, mitochondrial protein levels gradually decreased. Which explanation best accounts for the differences between stimulated and unstimulated cells?
15. A cell extract contains molecules composed of glycerol and three long hydrocarbon chains. Each hydrocarbon chain is attached to glycerol by a covalent bond formed when a hydroxyl group on glycerol reacts with a carboxyl group on the hydrocarbon chain, releasing water. The molecules do not consist of repeating monomer units forming long chains like proteins or nucleic acids. Which statement best describes why these molecules are classified as lipids rather than polymers?
16. A cell is followed through the cycle using a fluorescent marker that binds newly synthesized DNA. The marker is absent in G1, becomes incorporated throughout the nucleus during S phase, and remains present through G2 and early mitosis. In one cell, the marker is present, chromosomes condense, and a spindle forms. However, one chromosome's kinetochores attach only to microtubules from the same pole, so the chromosome is not under bipolar tension. The spindle checkpoint detects improper attachment before anaphase. Which outcome is most likely if the checkpoint functions normally?
17. A DNA molecule replicates when helicase separates strands and DNA polymerase adds complementary DNA nucleotides to each template strand. Polymerase adds nucleotides only to the 3′ end, producing new strands in the 5′→3′ direction. Because the two templates are antiparallel, one new strand is synthesized continuously toward the replication fork and the other in short fragments away from the fork that are later joined. A researcher observes many unjoined short DNA fragments accumulating near replication forks. Which explanation best accounts for the accumulation of these fragments?
18. On an island chain, a lizard genus occurs on three islands separated by deep water. Mitochondrial DNA comparisons show Island 1 and Island 2 populations differ by 1.2% sequence divergence, while Island 3 differs from each by about 6.5%. Geological dating indicates Island 3 emerged 4 million years earlier than Islands 1 and 2, which emerged at similar times. No land bridges are known during these periods. Which conclusion is best supported by the biogeographic and molecular evidence?
19. In a bird population, beak depth varies continuously. Over 15 years, rainfall becomes more consistent and seeds are mostly medium hardness each season. Researchers measure beak depth and track reproductive success. Birds with intermediate beak depth consistently leave more surviving offspring than birds with either very shallow or very deep beaks. Across generations, the population mean beak depth changes little, but the proportion of extreme beak depths declines. Which pattern best illustrates the observed selection on beak depth?
20. A membrane-bound cell compartment is modeled as a sphere. Two vesicles have identical membrane permeability to a solute. Vesicle 1 has radius 1 µm; Vesicle 2 has radius 3 µm. A solute is generated inside each vesicle at the same rate per unit internal volume and exits by diffusion across the membrane. Vesicle 2 reaches a higher internal solute concentration. Which explanation best accounts for Vesicle 2's higher concentration?

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