Practice Test 12 - AP Biology

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

A beetle species lives on two host plants that grow intermingled in the same region. Adults typically mate on the host plant where they feed. Genetic analysis shows that beetles collected from host plant A differ in allele frequencies from beetles collected from host plant B, and mark-recapture studies show limited movement between host plants. When beetles from different hosts are placed together with both plants available, most matings occur on the beetles' original host plant, and hybrid offspring are viable and fertile. Which process most directly initiated divergence between the two populations?
In a bird population, beak depth varies and is heritable. During a drought, only large, hard seeds remain abundant. Birds with deeper beaks crack these seeds more efficiently and leave more surviving offspring. After four breeding seasons, the distribution of beak depth shifts toward deeper beaks. Which statement best explains how variation affected evolution in this population?
A researcher studies two polysaccharides made of glucose. Polymer M has β-1,4 linkages, producing straight chains that align closely. Polymer N has α-1,4 linkages, producing coiled helices. When both polymers are placed in the same volume of water, polymer N disperses more readily, while polymer M forms insoluble fibers. Which feature best explains polymer M's lower solubility compared with polymer N?
A fish population shows heritable variation in body coloration controlled by alleles G (green) and S (silver). In a lake that becomes covered by dense green algae, predatory birds capture silver fish more often than green fish, reducing silver fish reproductive output. If algae cover persists, which outcome is most likely over generations?
A researcher tracks phosphorylation of a mitotic substrate that is targeted by cyclin B–CDK1. In control cells, substrate phosphorylation rises at prophase and falls at mitotic exit. When an APC/C inhibitor is added, cyclin B persists. The substrate remains highly phosphorylated longer than in controls. Which change best explains the sustained phosphorylation signal?
A DNA fragment is treated with a nuclease that specifically hydrolyzes phosphodiester bonds only when the sugar has a free 2'-OH group. The fragment is double-stranded and contains standard deoxyribose sugars. In a separate tube, an RNA fragment of similar length is treated with the same nuclease. The nuclease does not cut hydrogen bonds or base-stacking interactions; it targets the backbone linkage when the required functional group is present. Which statement best describes the expected outcome of the nuclease treatment?
In a prebiotic chemistry trial, a mixture of simple gases and water was exposed to energy and produced organic monomers. When researchers later added purified RNA nucleotides, no RNA polymers formed unless wet–dry cycles were included. Which conclusion is best supported by this combined evidence?
A meadow food web includes grasses (producers), rabbits (primary consumers), and hawks (secondary consumers). Researchers estimated that rabbits store 600 kJ/m $^2$ /yr as new biomass and hawks store 30 kJ/m $^2$ /yr as new biomass in the same area. Assume hawks feed mainly on rabbits. Which conclusion is best supported about energy transfer from rabbits to hawks?
Genetically identical cuttings from one coleus plant were grown for 3 weeks under either high light (full sun) or low light (shade). Leaves from shade-grown plants were larger and thinner, while sun-grown plants were smaller and thicker. DNA sequencing of a chloroplast gene from both groups showed identical nucleotide sequences. The difference in leaf traits disappeared after moving both groups to the same light condition for 2 weeks. Which explanation best accounts for the leaf differences observed under different light conditions?
Two spherical cells are placed in a solution with a constant concentration of a small, nonpolar molecule that crosses membranes by simple diffusion. Cell A has radius $4\,\mu m$ and cell B has radius $12\,\mu m$ . Both initially lack the molecule inside and both have similar cytoplasmic viscosity. After the same short time interval, the concentration increase inside cell B is smaller than inside cell A. Which explanation best accounts for this result?
Clonal yeast cells were grown in either high-salt medium or normal medium for 24 hours. In high salt, cells produced more of a membrane transporter protein and survived better, but sequencing showed no DNA differences between groups. Which explanation best accounts for the increased transporter protein in high-salt conditions?
A student models transport with agar "cells" containing phenolphthalein in basic solution. Two cubes are used: Cube 1 has side length 1 cm; Cube 2 has side length 2 cm. Both are placed in the same acidic solution. After 10 minutes, Cube 1 is fully colorless, but Cube 2 remains pink in the center. Which explanation best accounts for the persistent pink region in Cube 2?
In mitochondria, the electron transport chain (ETC) is embedded in the inner membrane and pumps H+ from the matrix to the intermembrane space. ATP synthase uses the resulting H+ gradient to produce ATP. In an experiment, the inner membrane becomes permeable to H+, allowing protons to flow back without passing through ATP synthase. Oxygen consumption continues, but ATP production drops sharply. Which feature best explains why compartmentalization is required for efficient ATP production?
A diploid meiotic cell with $2n=6$ experiences nondisjunction in anaphase I for one homologous pair: both homologs move to the same pole, while the other two pairs segregate normally. The cell completes meiosis I and meiosis II. Which outcome is most likely for chromosome number among the four resulting gametes?
Two identical enzyme samples are placed in 0.10 M NaCl and 1.0 M NaCl at the same pH and temperature. The high-salt sample shows a slower initial rate. Which explanation best accounts for the slower rate in 1.0 M NaCl?
A student measures enzyme activity in vitro at different pH values and finds the enzyme works best at pH 4.5. In living cells, the enzyme is found inside a membrane-bound compartment that is acidic relative to the cytosol. If the compartment membrane is removed, the enzyme remains present but activity in the cell decreases. Which feature best explains how compartmentalization affects this enzyme's cellular activity?
A student places identical cells (internal solute concentration 0.20 M) into a solution of 0.05 M solute. The membrane is permeable to water but not to the solute. After 8 minutes, the average cell volume increases. Which outcome is most likely if the same cells are instead placed into a 0.80 M solute solution?
A student models two cube-shaped cells with identical membrane composition and permeability to ions. Cell P has side length 2 µm; Cell Q has side length 6 µm. Both generate the same amount of metabolic waste ions per unit cytoplasmic volume, and waste exits by diffusion across the plasma membrane. In the same external solution, Cell Q reaches a higher internal waste ion concentration than Cell P. Which explanation best accounts for the higher waste concentration in Cell Q?
A student compares the nitrogenous bases in DNA and RNA. In DNA, adenine pairs with thymine; in RNA, adenine pairs with uracil. Both pairings use hydrogen bonds between specific functional groups on the bases. Which statement best explains why uracil can replace thymine in RNA base pairing with adenine?
Rabbit coat color is controlled by multiple alleles at one locus: C (full color) > c^ch (chinchilla) > $c^h$ (Himalayan) > c (albino). A rabbit with genotype c^chc is crossed with an albino rabbit (cc). Assuming simple dominance in this allele series, which phenotype distribution among offspring is expected?

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