Practice Test 28 - AP Biology

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

In a plant root cell, the central vacuole occupies most of the cell volume and is bounded by a selectively permeable membrane. When the cell is placed in a dilute solution, water moves into the vacuole and the plasma membrane is pressed against the cell wall. Which outcome is most likely explained by the vacuole's large size and membrane properties?
A cell maintains a higher concentration of H $^+$ inside an organelle than in the cytosol using a membrane protein in the organelle membrane. When ATP is depleted, the H $^+$ gradient dissipates over time. The protein binds ATP and transports H $^+$ from cytosol into the organelle lumen against the concentration gradient. Which mechanism best explains H $^+$ movement into the organelle?
In an experiment, isolated chloroplasts are illuminated while the thylakoid membrane remains intact. A researcher adds an ionophore that allows H+ to cross the thylakoid membrane freely, without blocking electron transfer through photosystems. Which outcome is most likely for ATP and NADPH production during illumination?
In a chicken population, breeders choose only birds with the largest combs to reproduce each year. Comb size is associated with alleles G (larger) and g (smaller). Initially, both phenotypes are common. After several years, small-comb birds are rare. Which explanation best accounts for the observed shift in comb-size distribution?
A student compares two nucleotides: one contains ribose with a 2' hydroxyl group, and the other contains deoxyribose lacking the 2' hydroxyl. Both nucleotides can be incorporated into polymers via phosphodiester bonds. In an alkaline solution, hydroxyl groups can participate in reactions that promote cleavage of nearby phosphodiester bonds. The student predicts one polymer will be more prone to strand breakage under these conditions. Which polymer is expected to be less stable in alkaline solution, and why?
Initial reaction rates are measured at multiple substrate concentrations for an enzyme with and without Inhibitor Z. With Z present, the maximum rate observed at very high substrate concentration is lower than without Z, and increasing substrate does not restore the original maximum. Enzyme concentration, pH, and temperature are constant. Which explanation best accounts for Inhibitor Z's effect?
A cell-free system contains actin filaments and myosin heads with bound ADP. When ATP is added, myosin detaches from actin; when ATP is then hydrolyzed to ADP and Pi, myosin binds actin and can perform a power stroke as Pi is released. If ATP is replaced with a nonhydrolyzable ATP analog, myosin detaches but repeated power strokes do not occur. The system contains no membranes, ion gradients, or electron carriers. This scenario examines how ATP hydrolysis energy is coupled to mechanical work at the molecular level.
In rabbits, long ears (L) are completely dominant to short ears (l). A breeder crosses a homozygous dominant rabbit (LL) with a heterozygous rabbit (Ll). Each offspring inherits one allele from each parent, and the gene shows complete dominance. Which proportion of offspring is expected to be heterozygous (Ll)?
In a large snail population, allele K has frequency 0.05. A nearby population with allele K frequency 0.05 sends no migrants, and survival does not differ among genotypes. However, a chemical mutagen increases the mutation rate from allele k to K for one year. In the following generation, allele K rises slightly to 0.051, then remains near that value afterward. Which factor most directly explains the small increase in allele K frequency?
In a cell entering meiosis with $2n=4$ , each chromosome replicates to form sister chromatids. During anaphase I, homologous chromosomes separate to opposite poles while sister chromatids remain joined. The cell completes telophase I and cytokinesis, forming two cells. Which description best accounts for the chromosome composition in each daughter cell after meiosis I?
A student digests two DNA samples with the same restriction enzyme and runs them on an agarose gel. Sample X yields three bands; sample Y yields two bands. The student knows both samples are linear DNA fragments of the same total length before digestion. The restriction enzyme recognizes a specific 6-bp sequence and cuts both strands at each recognition site. Which conclusion best accounts for the different band numbers between samples X and Y?
In an in vitro translation system, all amino acids and ribosomes are present, but one specific tRNA species is missing. The mRNA includes a codon that normally pairs with the missing tRNA's anticodon. During elongation, the ribosome requires a charged tRNA to base-pair with each codon in the A site before forming the next peptide bond and translocating. No alternative tRNA can pair with that codon. Which outcome is most likely when the ribosome reaches that codon?
A population of flowering plants shows heritable variation in nectar volume: high-nectar and low-nectar. In a region where a pollinator species becomes more abundant, plants with higher nectar volume receive more visits and set more seeds than low-nectar plants. Both nectar types still occur among seedlings. Which outcome is most likely over generations in this region?
A membrane contains phospholipids and several types of embedded proteins. A toxin binds to and blocks a specific transmembrane channel protein that normally allows K+ to move down its concentration gradient. After toxin exposure, K+ movement across the membrane decreases sharply, while diffusion of O2 remains unchanged. The phospholipid bilayer is intact. Which feature best explains why O2 diffusion is unaffected by the blocked channel?
A researcher compares two cell types that are similar in internal composition and membrane permeability. Cell M has a radius of 4 µm; Cell N has a radius of 12 µm. Both import amino acids by facilitated diffusion through membrane transport proteins present at the same density (proteins per µm²). Amino acid use occurs at the same rate per unit volume. Cell N shows a lower steady internal amino acid concentration than Cell M in the same medium. Which explanation best accounts for Cell N's lower amino acid concentration?
A rabbit hears a sudden loud noise; its heart rate and breathing rate increase within seconds. Which response best explains these changes?
A lab uses Sanger sequencing to determine a DNA segment. During DNA synthesis, normal dNTPs and small amounts of fluorescently labeled ddNTPs are present. Incorporation of a ddNTP prevents addition of further nucleotides to that strand. The resulting fragments are separated by capillary electrophoresis, and a detector records fluorescence to infer the terminal base of each fragment. Which statement best explains why many fragment lengths are produced in a single reaction?
The inheritance pattern of this condition is most likely which of the following?
Six species (A–F) are described by derived traits that evolved once: Trait X is present in B–F; Trait Y is present in D–F; Trait Z is present only in E and F. Species A lacks all three traits. Based on shared derived traits, which inference about relatedness is best supported?
A bacterial population contains two heritable variants: one produces an enzyme that breaks down antibiotic X, and the other does not. When antibiotic X is added to the culture, most non-enzyme bacteria die, but some enzyme-producing bacteria survive and reproduce. After several days, the culture is dominated by enzyme-producing bacteria. Which statement best explains how variation affected evolution in this population?

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