Practice Test 80 - AP Biology

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

Two genes, G and H, are far apart on the same chromosome. A diploid cell has homologs arranged GH on one homolog and gh on the other. During meiosis, crossing over occurs at random positions along the length of the chromosome. Because the genes are far apart, a crossover is likely to occur between them in some meioses, producing recombinant chromatids. Which statement best accounts for why some gametes contain Gh or gH?
In a eukaryotic cell, the cytosol contains enzymes that build a polymer from monomers, while a separate vesicle contains enzymes that rapidly hydrolyze the same polymer back into monomers. When vesicle membranes are disrupted, polymer levels decrease even though total enzyme amounts remain constant. Which feature best explains how compartmentalization helps regulate polymer levels?
A bird population in a city park was estimated annually. The park's area and tree cover remained constant. The population was 90 birds in year 1, 95 in year 2, and 92 in year 3. In year 4, a nearby construction project removed nesting sites outside the park, and the park population rose to 140 in year 5 and 155 in year 6. Which explanation best accounts for the increase after year 4?
A mutation replaces a guanine with adenine in one DNA strand, creating an A–C pair after replication. Which feature best explains why this mismatch alters helix stability locally?
In a lab model, two lipid samples are compared: Sample 1 is a triglyceride with three long, mostly nonpolar hydrocarbon chains ester-linked to glycerol; Sample 2 is a phospholipid with two hydrocarbon tails and a phosphate-containing, charged head group. When each sample is added separately to water and gently mixed, one sample forms stable bilayers while the other forms separate oil droplets. Which feature best explains why Sample 2 forms bilayers in water?
In a lab model of early cells, a population of membrane-bound vesicles forms when the plasma membrane repeatedly infolds and pinches off. Microscopy shows that the new internal sacs remain continuous with the plasma membrane in many cells, and their membrane lipids match the plasma membrane lipid composition. No internal compartment contains its own DNA. Over time, some vesicles become densely packed near the cell's genetic material, creating a double-membrane boundary around it that is still connected to the outer membrane at a few points. Which explanation best accounts for the origin of these internal membranes?
A eukaryotic pre-mRNA is synthesized normally and contains a short exon flanked by two introns. In one condition, a splicing regulatory protein binds to an exonic splicing silencer sequence within the short exon. In control cells lacking the regulatory protein, the exon is included in the mature mRNA. In the experimental condition, the mature mRNA is missing that exon, while the surrounding exons are joined. Which explanation best accounts for exon skipping in the experimental condition?
A huge skeletal muscle fiber has many nuclei. This mainly helps by...
A bird population has allele B at frequency $p=0.20$ and allele b at frequency $q=0.80$ . The population meets Hardy-Weinberg conditions. Which value is expected for the frequency of heterozygotes (Bb)?
In an experimental evolution study using simple lipid-bilayer cells, internal membrane sheets appear after many generations. Fluorescent labeling shows the internal membranes share the same membrane proteins as the plasma membrane, and time-lapse imaging captures the plasma membrane folding inward and separating into enclosed sacs. The sacs do not contain DNA or ribosomes, but they increase the surface area available for membrane-associated reactions. Which evidence best supports plasma membrane infolding as the mechanism generating these internal compartments?
A student observes two adjacent plant cells. In the first pair, small fluorescent molecules injected into one cell appear in the neighboring cell within seconds. In a second pair, the molecules remain confined to the injected cell. Plant cells can be connected by plasmodesmata, membrane-lined channels that pass through the cell wall and connect cytoplasm between cells. Which feature best explains the rapid movement of molecules between the first pair of cells?
In a meiotic cell, a homologous pair is oriented so that both homologs attach to spindle fibers from the same pole at metaphase I. Which outcome is most likely after meiosis I completes for that homologous pair?
A bacterial operon contains genes A–C transcribed from one promoter. A regulatory protein binds an operator between the promoter and gene A, preventing transcription. When amino acid Q is scarce, a small molecule accumulates and binds the regulatory protein, causing it to release the operator. In Q-scarce conditions, a mutation is introduced that changes the operator DNA sequence so the regulatory protein binds it tightly even when the small molecule is present. Which outcome is most likely in Q-scarce conditions?
In a bird population, beak depth varies and is heritable, influenced by alleles D (deeper beak) and d (shallower beak). A shift in available seeds occurs: most remaining seeds are large and hard, and birds with shallower beaks crack them less efficiently and produce fewer offspring. Birds with deeper beaks more often obtain enough food to reproduce. The population continues to interbreed in the same region, with minimal immigration. Which outcome is most likely after several generations?
A cold snap kills most mangrove seedlings at the northern edge of a mangrove-saltmarsh transition zone. Over the next year, saltmarsh grasses expand into areas previously occupied by mangrove seedlings. Which ecosystem effect is most likely along the shoreline?
A paleontologist compares limb bones in four vertebrate lineages. Fossils of early tetrapods (about 360 million years old) show a forelimb with one proximal bone, two distal bones, several wrist bones, and digits. Modern frogs, lizards, bats, and whales also have forelimbs with the same bone arrangement, although the bones differ in relative size and function (jumping, running, flying, swimming). No evidence suggests these lineages acquired the limb pattern through interbreeding. Which conclusion is best supported by the shared forelimb bone pattern across these lineages?
A cladogram is described in words: The root splits into lineage P and a second lineage. That second lineage splits into Q and a third lineage. The third lineage splits into R and S. No other branching occurs. All taxa are extant tips. Using this branching order, determine relatedness among the lineages. Which inference about most recent common ancestry is best supported?
A researcher measures initial rate of an enzyme-catalyzed reaction at 25°C and pH 7.0 while increasing substrate concentration from 0.1 to 10 mM at a fixed enzyme concentration. The rate increases rapidly at low substrate concentrations but approaches a maximum value and changes little beyond 5 mM substrate. No inhibitor is present and the enzyme remains folded throughout the assay. Which explanation best accounts for the rate plateau at high substrate concentration?
A population of fish was introduced into a new, isolated lake. Estimates were: Week 1 = 100, Week 2 = 150, Week 3 = 225, Week 4 = 340, Week 5 = 510. No fishing occurred, and the lake had abundant plankton during these weeks. Which pattern best illustrates the fish population growth over Weeks 1–5?
In a desert ecosystem, annual energy stored as new biomass is estimated as follows: shrubs (producers) 5,000 kJ/m $^2$ /yr, herbivorous insects 250 kJ/m $^2$ /yr, lizards 25 kJ/m $^2$ /yr. Assume energy stored as new biomass represents energy passed to the next trophic level. Which conclusion is best supported about trophic efficiency in this ecosystem?

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