Practice Test 97 - AP Biology

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

Start practice test

1. A biologist places freshwater paramecia into two solutions for 2 minutes: Solution 1 (distilled water) and Solution 2 (0.5 M sucrose). In Solution 1, cells swell and contractile vacuoles pulse rapidly; in Solution 2, cells shrink and vacuole pulsing slows. Which response best explains how paramecia maintain internal water balance during these short exposures?
2. Scientists examine a lineage of single-celled organisms that lacks mitochondria but contains internal membrane sacs that store ions. These sacs are bounded by a single membrane and are connected to the plasma membrane via narrow tubules. Lipid analysis shows the sacs and plasma membrane share the same sterol composition, and no circular DNA is detected in the sacs. Which evidence best supports plasma membrane infolding as the origin of these sacs?
3. A secretory cell produces a large amount of digestive enzyme that is exported from the cell. Electron micrographs show abundant rough endoplasmic reticulum (RER) with ribosomes attached and an extensive Golgi apparatus with many budding vesicles. When cells are treated with a chemical that disrupts Golgi function, enzyme accumulates in intracellular vesicles and little is detected outside the cell. Which feature best explains the role of the Golgi apparatus in enzyme export?
4. In an experiment, two animal cells are connected by gap junctions. A fluorescent dye that is too large to cross membranes is injected into Cell 1, and fluorescence appears in Cell 2 within minutes. When a gap junction blocker is added, dye remains only in Cell 1. Which of the following best explains the original movement of dye?
5. A ribosome has an A site (acceptor) and P site (peptidyl) that coordinate elongation. In a cell-free system, a drug prevents peptidyl transferase activity, so peptide bonds cannot form between the amino acid in the A site and the growing chain in the P site. Initiation and codon-anticodon pairing still occur, and tRNAs can still enter the A site. Which outcome is most likely during translation in the presence of the drug?
6. The use of herbicides to control weeds in agricultural fields often leads to the evolution of herbicide-resistant weeds. Which of the following is a necessary condition for the continued evolution of this resistance?
7. A population of rabbits includes two alleles at a coat-color locus: W (white) and B (brown). In 2017, snow cover duration decreased due to warmer winters. Researchers sampled the same population each spring: 2016 $f(B)=0.12$, 2018 $f(B)=0.20$, 2020 $f(B)=0.29$, 2022 $f(B)=0.33$. Predators more easily detect white coats on snow-free ground. Which observation best demonstrates continuing evolution in this rabbit population?
8. A weed population grows in farm fields where herbicide Y has been applied annually since 2014. The population carries two alleles at a target-site gene: susceptible (s) and resistant (r). Field surveys using the same sampling method found $f(r)=0.05$ in 2014, $f(r)=0.19$ in 2016, and $f(r)=0.41$ in 2019. Resistant plants survive recommended herbicide doses more often than susceptible plants. Which observation best demonstrates evolution in this weed population?
9. A cell has an internal solute concentration of 0.35 M. It is placed into Solution 1 (0.35 M), and its volume does not change. It is then placed into Solution 2 (0.50 M), and its volume decreases. The membrane is permeable to water but not to the solute. Which inference about Solution 2 is most consistent with the observation?
10. A eukaryotic gene's coding DNA (template strand) includes the triplet 3′-TAC-5′, which is transcribed into mRNA codon 5′-AUG-3′ (start). A point mutation changes the template triplet to 3′-TAT-5′, producing mRNA 5′-AUA-3′ at the same position. Translation initiates at the first AUG encountered by the ribosome during scanning. No other mutations occur, and the next AUG in the mRNA is 60 nucleotides downstream in the same reading frame. Which outcome is most likely for the protein produced from the mutated mRNA?
11. In a grass population, leaf wax thickness varies. After a new fungal pathogen spreads, plants with very thin wax are infected frequently, and plants with very thick wax grow more slowly and produce fewer seeds. Plants with intermediate wax thickness have the highest reproductive success. After twelve generations, the distribution of wax thickness becomes more concentrated around the intermediate value. Which type of selection best explains the observed change?
12. In a bacterial population, some cells carry an allele that produces an enzyme that degrades a specific antibiotic; the allele is heritable and passed during cell division. When the antibiotic is added to the environment, cells with the enzyme survive and divide more than cells lacking it. Which outcome is most likely after many generations under antibiotic exposure?
13. A plant cell is placed in a hypertonic solution. Over several minutes, the plasma membrane pulls away from the cell wall, and the central vacuole becomes smaller. The cell wall remains rigid and maintains the overall shape of the cell, even though the cytoplasm volume decreases. In a second treatment, the same cell is returned to an isotonic solution, and the vacuole increases in volume as water enters. Which feature best explains why the cell wall maintains cell shape during water loss?
14. A cell is in G1 with 2C DNA and passes the G1 checkpoint, entering S phase. The cell completes S phase and enters G2 with 4C DNA. During mitosis, chromosomes align and the spindle checkpoint is satisfied. Immediately after anaphase begins, the cell is experimentally returned to an interphase-like state with a reformed nuclear envelope around both chromosome sets before cytokinesis occurs. The cell now contains two separated chromosome groups in one cytoplasm. Which outcome is most likely regarding DNA content per nucleus in this single cell?
15. This relationship is an example of a coevolutionary arms race, which demonstrates that evolution is an ongoing process because...
16. In pancreatic cells, ligand G binds a GPCR coupled to Gi. Activated Gi inhibits adenylyl cyclase, decreasing cAMP. Lower cAMP reduces PKA activity, leading to decreased phosphorylation of a metabolic enzyme; the enzyme's activity increases when dephosphorylated. A toxin is introduced that prevents Gi from binding GTP, but receptor binding by G is unchanged and phosphodiesterase activity is normal. Cells are exposed to ligand G and enzyme activity is measured within 2 minutes. Which result is most likely in toxin-treated cells compared with untreated cells?
17. A lipid bilayer membrane lacks transport proteins. The hydrophobic core favors diffusion of small, nonpolar molecules. Polar molecules can cross only slowly because they are poorly soluble in the membrane interior, and ions are effectively excluded due to charge and hydration shells. Consider ammonia (NH3), which is small and polar, and neon (Ne), which is small and nonpolar. Both are uncharged in this scenario. Which molecule would most likely diffuse across the membrane faster?
18. A ribosome begins translating an mRNA that normally contains the codons 5′-AUG CCG GAA UGA-3′. In a mutant, the second codon changes from CCG to CCU. Both CCG and CCU are codons that can be matched by tRNAs carrying the same amino acid (proline), because different codons can specify the same amino acid. The start codon AUG still recruits the initiator tRNA, and UGA is still a stop codon recognized by a release factor. Which outcome is most likely for the polypeptide produced from the mutant mRNA?
19. A fossil series documents changes in horse-like mammals across multiple strata. Older fossils show three-toed forelimbs and low-crowned teeth; younger fossils show a single dominant toe and high-crowned teeth with complex enamel folds. The fossils occur in successive layers with intermediate forms present, and pollen data indicate a shift from forest plants to grass-dominated habitats over the same interval. Which conclusion is best supported by the fossil and environmental evidence?
20. Cells are grown in a medium containing either glucose or a fatty acid as the primary fuel source, with oxygen available in both treatments. Both fuels can be oxidized to generate NADH and FADH2, which donate electrons to the electron transport chain, where oxygen acts as the terminal electron acceptor. Oxidation of fatty acids generates a larger number of reduced electron carriers per molecule than oxidation of a single glucose molecule. Which outcome is most likely when cells oxidize fatty acids instead of glucose under these conditions?

Practice tests