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Practice Test 7 - AP Biology

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

  1. The fossil record provides strong evidence for evolution. Which aspect of the fossil record best supports the concept that evolution is a continuous, ongoing process rather than an event that occurred only in the distant past?
  2. A person enters a cold room; within minutes, skin blood vessels constrict and shivering begins. Which response mechanism best explains these changes?
  3. In an experiment, cells are grown for one generation in medium containing a heavy nitrogen isotope so that newly synthesized DNA strands incorporate the heavy isotope. The cells are then shifted to light nitrogen medium and allowed to complete exactly one round of DNA replication. DNA molecules are separated by density. The results show a single band at an intermediate density. The student recalls that replication uses each parental strand as a template and that complementary base pairing determines the sequence of the new strand. Which explanation best accounts for the intermediate-density band after one round in light medium?
  4. A scientist isolates mitochondria and measures the pH in the intermembrane space and matrix. The intermembrane space is more acidic than the matrix. Which structure best explains how this pH difference is maintained during respiration?
  5. A membrane receptor activates JAK kinase, which phosphorylates a cytosolic protein STAT. Phosphorylated STAT (STAT-P) forms dimers in the cytosol within 1 minute. A phosphatase dephosphorylates STAT-P, returning STAT to monomers. When the phosphatase is inhibited, STAT remains phosphorylated longer and dimer levels stay high. Which change would most likely decrease STAT dimer levels without altering receptor activation?
  6. In an epithelial cell, intracellular glucose is 20 mM while extracellular glucose is 2 mM. A cotransporter moves glucose into the cell only when Na+ is present outside at high concentration (140 mM outside, 10 mM inside). When ATP is depleted, the Na+ gradient dissipates and glucose uptake stops, even though the cotransporter protein remains intact. Which mechanism best explains glucose uptake when ATP is available?
  7. Cells are exposed to ligand V, and within 12 seconds a fluorescent reporter shows increased diacylglycerol (DAG) at the inner leaflet of the plasma membrane. When a drug blocks cleavage of PIP2_2, ligand binding still occurs but DAG does not increase. Which of the following best explains the earliest biochemical event producing DAG?
  8. A chemist synthesizes a nucleic acid analog in which the phosphate group is replaced with an uncharged linkage, while the bases and sugars remain unchanged. Compared with normal DNA, the analog shows reduced attraction to positively charged proteins. Which feature best explains this change?
  9. A cell population is synchronized in metaphase. The spindle-assembly checkpoint prevents anaphase when kinetochores are unattached by generating a signal that inhibits the anaphase-promoting complex/cyclosome (APC/C), an E3 ligase that targets securin for degradation. When securin is degraded, separase becomes active and cleaves cohesin, allowing sister chromatids to separate. A drug is added that stabilizes kinetochore–microtubule attachments, reducing checkpoint signaling, but does not affect cohesin directly. Which change would most likely prevent premature anaphase in the presence of the drug?
  10. In a tropical rainforest, a vine grows on tree trunks to reach sunlight. Measurements show that trees with heavy vine loads have reduced leaf area and slower growth compared with nearby trees without vines. The vine's growth rate is higher on trees than on the forest floor. The vine does not penetrate tree tissues, but it shades the tree's leaves and adds weight to branches. Which interaction best describes the relationship between the vine and the tree?
  11. A coastal marsh has measured annual energy stored as new biomass: cordgrass 20,000 kJ/m2^2/yr, snails 2,000 kJ/m2^2/yr, crabs 200 kJ/m2^2/yr. These values represent energy available to the next trophic level. Which conclusion is best supported about energy flow through this food chain?
  12. A toxin blocks ATP production in cells. Shortly after, an ATP-dependent proton pump in the plasma membrane stops moving H+^+ out of the cytosol, even though the H+^+ concentration is higher outside than inside. When ATP is restored, the pump resumes transporting H+^+ outward. Which mechanism best explains H+^+ movement by this pump when ATP is present?
  13. A coastal marsh is partially drained for development, reducing flooded area by 40%. Over the next year, sediment trapped by marsh plants decreases and water turbidity in nearby channels increases. Which explanation best accounts for the increased turbidity?
  14. A membrane-associated enzyme is assayed in solutions containing different detergent concentrations while keeping pH, temperature, and substrate constant. With 0% detergent, activity is 18 units; with 1% detergent, activity is 3 units. Detergents can insert into hydrophobic regions of proteins and disrupt hydrophobic interactions that help maintain tertiary structure and the shape of the active site. The enzyme amount added is the same in both trials. Which outcome is most likely at 1% detergent?
  15. Two separate populations of the same fish species live in similar lakes with no migration between them. Both populations are large. At a neutral microsatellite locus, allele MM starts at frequency 0.50 in each lake. After 40 generations, lake 1 has M=0.12M=0.12 and lake 2 has M=0.87M=0.87, with no consistent fitness differences among genotypes detected. Which factor most likely explains the divergence in allele frequency between lakes?
  16. A researcher examines a cell in prophase I and observes synapsis: each chromosome is tightly paired with its homolog along much of its length, forming tetrads. Which event is most directly enabled by synapsis at this stage of meiosis?
  17. In a prairie flower population, stalk height varies. Grazers preferentially eat the tallest plants, while very short plants are shaded and set fewer seeds. Plants of intermediate height produce the most seeds. After several generations, extreme heights become less common and the mean height changes little. Which pattern best illustrates the selection acting on stalk height?
  18. A scientist places cells in a solution containing 100 mM solute T; cytosolic T is 10 mM. Cells express a transporter specific for T. When the transporter is inhibited, intracellular T remains low. When the inhibitor is removed, T increases until near 100 mM, with no detectable ATP consumption. Which explanation best accounts for the increase in intracellular T after inhibitor removal?
  19. A ligand binds a receptor and rapidly increases intracellular cAMP. When cells are treated with a drug that inhibits phosphodiesterase (PDE), the peak cAMP level is higher and returns to baseline more slowly. Ligand binding to the receptor is unchanged. Which of the following best explains the early effect of PDE inhibition on the signaling pathway?
  20. A freshwater fish population contains heritable variation in tolerance to low dissolved oxygen, influenced by alleles O (higher tolerance) and o (lower tolerance). During summer, algal blooms repeatedly reduce dissolved oxygen for several weeks, and fish with lower tolerance die at higher rates before spawning. Survivors reproduce within the same lake, and offspring oxygen tolerance resembles parental genotypes. Migration into the lake is rare. Which outcome is most likely after several bloom seasons?

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