Practice Test 32 - AP Biology

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

Scientists compare the arrangement of Hox genes in two animal species. Species A and species B each have a cluster of Hox genes in the same order along the chromosome, and several corresponding genes share highly similar DNA sequences. A third species, C, has a Hox cluster with a different gene order and lower sequence similarity to A and B. Which inference is best supported by these observations about ancestry?
A large dam is built on a river, converting a long stretch of flowing water into a reservoir. Downstream of the dam, peak spring floods are greatly reduced and water flow becomes more constant year-round. Over several years, cottonwood seedlings along downstream banks become rare, and the riverbank shifts from mixed forest to more drought-tolerant shrubs and grasses. Bird surveys show fewer insect-eating songbirds that nest in cottonwoods. Which consequence is most likely downstream of the dam?
A small aquatic organism lives in a pond where air temperature drops rapidly after sunset. Water molecules are polar: oxygen carries a partial negative charge and hydrogens carry partial positive charges. When water molecules are close, hydrogen bonds form between the partially positive hydrogen of one molecule and the partially negative oxygen of another. Breaking these hydrogen bonds requires energy input, and forming them releases energy. As the pond cools, many hydrogen bonds remain intact, slowing the decrease in molecular motion compared with a liquid lacking these intermolecular attractions. Which statement best describes how hydrogen bonding affects the pond's temperature change overnight?
In pea plants, purple flowers (P) are completely dominant to white (p). A plant with purple flowers that is heterozygous (Pp) is crossed with a white-flowered plant (pp). Each offspring receives one allele for flower color from each parent. Assuming Mendelian segregation and no linkage to other traits, the offspring phenotypes depend only on whether they inherit at least one P allele. Which proportion of offspring is expected to have white flowers?
In an epithelial sheet, adjacent cells are connected by gap junctions. When cell 1 is injected with a small dye that mimics a second messenger, neighboring cells fluoresce within seconds. When a gap-junction inhibitor is added, fluorescence remains confined to cell 1. Which of the following is the most likely explanation?
A diploid cell with $2n=10$ undergoes meiosis. In anaphase II of one of the two meiosis I products, sister chromatids of a single chromosome fail to separate and both move to the same pole; all other chromatids separate normally. The other meiosis I product completes meiosis II normally. Which outcome is most likely among the four gametes?
A membrane model contains phospholipids with hydrophilic phosphate heads and hydrophobic fatty acid tails. The model is placed in a solution containing a small, nonpolar dye molecule and a similarly sized polar dye molecule. Over time, the nonpolar dye enters the vesicles more readily than the polar dye. Which statement best explains this observation at the molecular level?
A rabbit population varies in fur density due to heritable alleles C (denser coat) and c (less dense coat). Following several unusually cold winters, rabbits with less dense coats experience lower survival before breeding, while rabbits with denser coats more often survive to reproduce. The population remains in the same region with continued interbreeding and little migration. No additional selective pressures are described. Which outcome is most likely after multiple cold winters?
A researcher studies two spherical cells with identical membrane permeability to water. Cell NN has radius 5 µm; Cell OO has radius 15 µm. Both are transferred to a hypertonic solution with the same water potential difference. The rate of volume decrease per unit initial volume is greater in Cell NN than in Cell OO. Which explanation best accounts for the greater fractional volume loss in Cell NN?
On an island, a population of lizards shows two color morphs controlled by alleles G (green) and B (brown). After a wildfire darkened the ground, researchers recorded allele frequencies each breeding season. The frequency of allele B rose from 0.30 in the first season after the fire to 0.67 five seasons later, with similar census sizes each year. Which observation best demonstrates continuing evolution in this lizard population?
In a lab model of early protocells, repeated cycles of membrane growth and division produced inward folds that pinched off into internal vesicles. Enzymes that bind membranes were found concentrated on the inner surfaces of these vesicles, while the outer plasma membrane retained transport proteins. No DNA was detected inside the vesicles, and each vesicle membrane had the same lipid composition as the cell's plasma membrane. Over many cycles, vesicles remained connected to the plasma membrane in some cells, forming continuous internal sheets. Which explanation best accounts for the origin of these internal membranes?
Red blood cells (internal solute concentration 0.30 M) are placed into Solution Z, which contains 0.30 M glucose. The membrane is permeable to water but not to glucose during the experiment. After 5 minutes, the cells appear unchanged in size and shape. Which outcome is most likely for water movement in Solution Z?
A biologist monitors two island seabird colonies of the same species. Colony 1 has 300 nesting pairs; Colony 2 has 3,000 nesting pairs. During the same breeding season, both islands experience similar weather and no major storms. The biologist records that nestling survival is 82% in Colony 1 but 41% in Colony 2. Many more nestlings in Colony 2 show signs of starvation, and adults in Colony 2 make longer foraging trips. Which factor most likely explains the lower nestling survival in Colony 2?
A receptor binds ligand J and activates a kinase cascade. A mutant receptor binds J normally but cannot recruit a cytosolic scaffold protein that organizes signaling proteins near the receptor. In mutant cells, early phosphorylation of the first cytosolic kinase is reduced. Which of the following best explains how scaffold recruitment affects early transduction?
A neuron's axon contains long, parallel microtubules extending from the cell body toward the synaptic terminal. Vesicles containing neurotransmitter are observed moving directionally along these tracks. Which feature best explains the directed movement of vesicles within the axon?
A cell line is synchronized in G2. Entry into mitosis occurs when cyclin B–CDK1 becomes active after removal of an inhibitory phosphate placed on CDK1. In untreated cells, cyclin B–CDK1 activity rises sharply and cells enter mitosis. A drug is added that keeps the inhibitory phosphate on CDK1 even though cyclin B remains bound. Cells remain in G2 with low CDK1 activity. Which change would most likely allow these cells to enter mitosis despite the drug?
Two desert shrublands were sampled for reptile communities. Shrubland P had 8 species with one species at 55% abundance. Shrubland Q had 8 species with each species near 12–13% abundance. Total reptiles counted were equal. Which conclusion is best supported about diversity?
A grassland contains two seed-eating rodent species that forage at night. In experimental enclosures, when species 1 is removed, species 2 increases its use of open ground and consumes more large seeds. When both species are present, species 2 forages mostly under shrubs and consumes mostly small seeds. Predator abundance and vegetation structure are similar across treatments. Which interaction best explains the shift in foraging habitat and diet of species 2?
In a eukaryotic nucleus, an enzyme that adds a 7-methylguanosine cap to the 5′ end of nascent RNA is inactivated. Transcription initiation and elongation still occur, and introns are removed from the primary transcript. When the 5′ ends of the processed RNAs are sequenced, they begin with the first transcribed nucleotide rather than a modified guanine linked by a 5′–5′ triphosphate bond. Which explanation best accounts for this sequencing result?
In a meiocyte, genes R and S are located on the same homologous chromosome pair. One homolog carries RS and the other carries rs. A student observes that most gametes are RS or rs, but a smaller fraction are Rs and rS. The student confirms homologs pair as a tetrad in prophase I and that at least one chiasma forms between the R and S loci in some cells. Which meiotic event best explains why recombinant gametes (Rs and rS) occur less frequently than parental gametes?

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