Practice Test 90 - AP Biology

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

Start practice test

1. In a developing embryo, a researcher samples two differentiated cell types: a motor neuron and a cartilage cell. Sequencing confirms both contain the same genomic region that includes a neurofilament gene and a collagen gene. Motor neurons show high neurofilament mRNA, while cartilage cells show high collagen mRNA. No differences in DNA sequence are detected at these genes. Which explanation best accounts for the observed gene expression differences?
2. A phospholipid bilayer without proteins is exposed to equal concentrations of ATP (507 Da, highly charged) and cortisol (≈362 Da, largely nonpolar). Which molecule would most likely diffuse across the bilayer more rapidly?
3. A researcher places a freshwater protist cell (internal solute concentration 0.12 M) into a 0.12 M solution and observes no net volume change. The cell is then placed into a 0.06 M solution. The membrane is permeable to water but not to the solute. Which outcome is most likely for the cell's volume in the 0.06 M solution?
4. A logging operation fragments a continuous forest into small patches separated by roads and clearings. Over two years, the total forest edge length increases and interior humidity declines. Which ecosystem-level change is most likely in the forest patches?
5. In rabbits, the allele for spotted coat (S) is completely dominant to solid coat (s). A spotted rabbit is crossed with a solid rabbit (ss). The spotted parent's genotype is unknown. The first 12 offspring include 6 spotted and 6 solid. Assume this reflects the expected Mendelian ratio for a single gene. Which is the most likely genotype of the spotted parent?
6. A HWE population with $p=q=0.5$ starts complete selfing. Next generation:
7. In a bird population, beak depth varies and is heritable. A drought reduces small, soft seeds, leaving mostly large, hard seeds. Birds with deeper beaks crack hard seeds more effectively and produce more offspring than birds with shallow beaks. Which outcome is most likely after several generations of drought conditions?
8. Genetically identical rabbit kits are fed the same diet but are housed either at 10°C or 25°C for 5 weeks. Kits at 10°C develop thicker fur and show increased expression of keratin genes in hair follicle cells; sequencing shows no differences in keratin gene DNA. When 10°C kits are moved to 25°C, newly grown fur is thinner. Which explanation best accounts for the difference in fur thickness?
9. A protein sequence comparison among species R, S, T, and U shows the following numbers of amino acid differences: R–S:0, R–T:3, R–U:7; S–T:3, S–U:7; T–U:6. Assume the sequences are orthologous and that fewer differences indicate a more recent common ancestor. Which inference about relatedness is best supported?
10. Genetically identical seedlings of a grass species were grown for 10 days with either normal soil moisture or drought conditions. Drought-grown seedlings had fewer open stomata per leaf surface area at midday and showed lower rates of water loss. DNA sequencing of a stomata-regulating gene was identical in both groups. When drought-grown seedlings were rewatered for several days, the proportion of open stomata at midday increased. Which explanation best accounts for the stomatal differences under drought versus normal moisture?
11. A membrane is permeable to urea only when a urea channel is open. Urea is 20 mM outside the cell and 2 mM inside. When the channel opens, urea enters until the concentrations become equal, and the movement is unchanged by ATP depletion. Which mechanism best explains urea entry when the channel is open?
12. A student compares two triglycerides. Molecule 1 has three fatty acid tails with no C=C double bonds (fully saturated). Molecule 2 has two tails that each contain one cis C=C double bond, introducing a bend in each tail. Both molecules contain only C, H, and O, and both have ester linkages between glycerol and fatty acids. When cooled to room temperature, Molecule 1 is more likely to be solid than Molecule 2. Which molecular feature best explains this difference in physical state?
13. A freshwater fish species occupies a single lake. Over time, some individuals feed mostly in open water and others feed near the shoreline. Genetic sampling shows two clusters of allele frequencies within the same lake, and tagging reveals that adults from the two clusters rarely enter the other habitat. During the spawning season, open-water fish spawn in deeper water while shoreline fish spawn in shallow, vegetated areas; fertilization occurs externally, and eggs develop normally when mixed in the lab. No geographic barrier separates the habitats, but gene flow between clusters is low. Which process most directly led to reduced gene flow between the two populations?
14. A student compares two similarly shaped cells that differ only in size. Both cells use diffusion across the plasma membrane for O2 uptake, and both have the same O2 consumption rate per unit volume. When cell diameter doubles, the time required for O2 to reach a given internal concentration increases. Which explanation best accounts for the increased time?
15. In a coastal marsh, an invasive crab reduces snail density by 80% within one year. Snails previously grazed algae on plant stems. Which ecosystem response is most likely after the invasion?
16. An unknown macromolecule is made by linking many monomers through dehydration reactions. Each monomer contains a phosphate group that can form covalent bonds and a nitrogen-containing base that varies among monomers. The polymer forms a backbone with repeating phosphate-sugar units. Which statement best describes the bond formed during polymerization and the monomer type involved?
17. A lab compares two prebiotic mixtures exposed to UV light: Mixture 1 contains water, $\mathrm{CH_4}$, $\mathrm{NH_3}$, and $\mathrm{H_2}$; Mixture 2 contains water, $\mathrm{CO_2}$, $\mathrm{N_2}$, and $\mathrm{O_2}$. After exposure, Mixture 1 contains more diverse organic molecules than Mixture 2. Which conclusion is best supported about how atmospheric composition could affect abiotic synthesis?
18. In a large population of insects, a gene has alleles $C$ and $c$ with allele frequencies $p=0.70$ and $q=0.30$. The population is isolated and mates randomly, and no selection or mutation is detected at this locus. Under these conditions, what is the expected frequency of heterozygotes ($Cc$) in the next generation?
19. A cube-shaped cell with side length $L$ relies on diffusion across its plasma membrane for waste removal. Waste production rate is proportional to cell volume, and removal rate is proportional to membrane surface area. Which explanation best accounts for why waste can accumulate more in cells with larger $L$ under identical conditions?
20. A plasma membrane is a phospholipid bilayer with embedded proteins. Some proteins act as carriers that bind a specific solute and change shape to move it across the membrane. In a test, a polar amino acid is transported into cells faster when its carrier protein is present, even though the amino acid concentration is equal on both sides of the membrane. The bilayer's hydrophobic interior remains unchanged. Which feature best explains the increased amino acid movement when the carrier is present?

Practice tests