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Practice Test 40 - AP Biology

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

  1. Five insect species (P–T) were assessed for derived traits. Trait 1 is present in Q, R, S, and T. Trait 2 is present in R, S, and T. Trait 3 is present only in S and T. Trait 4 is present only in T. Traits evolved once and were retained. Which pair shares the most recent common ancestor?
  2. In a coastal ecosystem, primary producers store 30,000 kJ as new biomass. Two pathways occur: grazers store 3,000 kJ, and detritivores store 6,000 kJ from dead organic matter. Predators that eat grazers store 240 kJ, and predators that eat detritivores store 360 kJ. Which conclusion is best supported about energy flow through these pathways?
  3. Lactase activity is tested at two temperatures using equal enzyme and lactose concentrations. At 25°C, glucose production is 12 μmol/min; at 55°C, glucose production is 2 μmol/min. Lactase is a globular protein stabilized by hydrogen bonds and hydrophobic interactions that help maintain the active site's shape. Increasing temperature increases molecular motion and can disrupt these noncovalent interactions, changing tertiary structure. The assay pH and salinity are constant. Which explanation best accounts for the lower rate at 55°C?
  4. A cell contains a pump that moves 3 Na+^+ out and 2 K+^+ in per cycle. When ATP is present, intracellular Na+^+ remains low despite higher extracellular Na+^+. When ATP is depleted, Na+^+ accumulates inside and K+^+ declines. The pump binds ATP during each transport cycle. Which mechanism best explains the ion movements mediated by this pump?
  5. In a rabbit population, ear length varies and is heritable: allele L produces longer ears than allele l. During unusually hot summers, rabbits with longer ears dissipate heat more effectively and have higher survival to reproduction. Hot summers become common for many decades. Which outcome is most likely in the population?
  6. A researcher loads cells with a fluorescent glucose analog that cannot cross membranes without a transporter. Fluorescence accumulates inside a specific organelle that contains enzymes using the analog, while cytosolic fluorescence remains low. When the organelle membrane transporter is inhibited, organelle fluorescence decreases and cytosolic fluorescence increases. Which feature best explains how compartmentalization affects metabolism in this setup?
  7. In two insect lineages, researchers found the same transposable element inserted at the same genomic location within a noncoding region. A third insect lineage lacks the element and shows an uninterrupted sequence at that site. The flanking DNA sequences align among all three lineages, indicating the same locus was compared. Insertions of transposable elements at identical positions are rare events. Which inference is best supported by this evidence?
  8. A pure phospholipid bilayer is exposed to equal concentrations of acetic acid (60 Da) in its uncharged form (CH3_3COOH) and its charged form (CH3_3COO−^-). No proteins are present. Which statement best predicts permeability across the bilayer?
  9. In a eukaryotic cell, a gene contains three exons separated by two introns. RNA polymerase II produces a primary transcript that includes all five regions in the same order as the DNA. The transcript is then processed in the nucleus by adding a 5′ cap and a 3′ poly(A) tail, and by spliceosome-mediated removal of introns at conserved splice sites. After processing, an RNA sample is treated with a probe that hybridizes only to intron 2 sequence; no hybridization signal is detected, while an exon 2 probe produces a strong signal. Which explanation best accounts for the missing intron 2 signal in the processed RNA?
  10. On an isolated lake, two populations of the same fish species occupy different habitats: open water and near-shore vegetation. Over 2,000 generations, the open-water population evolves a streamlined body and longer pectoral fins, while the near-shore population evolves deeper bodies and shorter fins. Genetic markers show reduced gene flow between habitats compared with the past, but both populations remain in the same lake. Which conclusion is best supported by these observations?
  11. A researcher observes that some animal cells contain numerous peroxisomes. When peroxisome function is inhibited, hydrogen peroxide levels rise and damage membranes. Which feature best explains how peroxisomes normally limit this damage?
  12. In a signaling assay, ligand L activates receptor R, which activates kinase K1, then K2, then K3, yielding a 20× increase in phosphorylated substrate S compared with baseline. When K2 is partially inhibited, phosphorylated S drops to near baseline even though K1 phosphorylation remains high. Which statement best accounts for the large decrease in phosphorylated S?
  13. A double-stranded DNA helix maintains a nearly constant diameter along its length. Which structural feature best explains this uniform diameter?
  14. A mutation changes one base pair in a DNA double helix from G–C to A–T at a specific position. The sugar-phosphate backbone remains intact, and the helix maintains antiparallel strands with bases paired in the interior. The change alters the number of hydrogen bonds holding the strands together at that site. Which molecular-level effect is most directly caused by this base-pair substitution?
  15. A researcher compares two artificial vesicles. Vesicle 1 contains a phospholipid bilayer with many unsaturated fatty acid tails and several embedded channel proteins. Vesicle 2 contains a bilayer with mostly saturated tails and the same number of channel proteins. Both vesicles are placed in identical solutions containing small nonpolar molecules. The phospholipid heads are hydrophilic and face the aqueous environment, while the hydrophobic tails form the membrane interior. Embedded proteins provide specific pathways for certain solutes. Which feature best explains a higher rate of nonpolar molecule diffusion into Vesicle 1?
  16. A cladistic analysis of five reptile species uses derived characters: Character 1 (temporal fenestra) is present in B, C, D, and E; Character 2 (diapsid skull) is present in C, D, and E; Character 3 (feather-like filaments) is present in D and E only. Species A lacks all three characters. Each character evolved once and was retained. Which pair shares the most recent common ancestor?
  17. A toxin covalently modifies the G subunit of a heterotrimeric G protein, preventing GTP hydrolysis but not affecting GTP binding. In cells where a GPCR normally activates adenylyl cyclase transiently, toxin-treated cells show prolonged cAMP elevation after a brief ligand pulse. Which explanation best accounts for the prolonged cAMP signal?
  18. In a eukaryotic cell, digestive enzymes are enclosed in lysosomes whose lumen is more acidic than the cytosol (about pH 5 vs pH 7). When the lysosomal membrane is experimentally made leaky, the cell shows reduced breakdown of ingested macromolecules and increased damage to cytosolic proteins. These observations occur without changing the total amount of enzyme present. Which feature best explains how compartmentalization affects the efficiency and control of digestion in this cell?
  19. Two populations of the same annual plant species grew in adjacent fields with similar soil type and rainfall. Field A had 50 plants per square meter, and Field B had 200 plants per square meter after germination. At the end of the season, plants in Field B produced fewer seeds per plant and were shorter, while Field A plants produced more seeds per plant and were taller. No herbicide drift or flooding occurred. Which factor most likely caused reduced seed production in Field B through density dependence?
  20. Two amino acids differ only at one position: one has a side chain ending in a sulfhydryl group (–SH) containing S, and the other has a side chain lacking sulfur. In an oxidizing environment, proteins containing many –SH groups become more resistant to unfolding when exposed to heat. At the molecular level, two nearby –SH groups can form a covalent bond between their sulfur atoms, creating a cross-link within or between polypeptide chains. Which statement best describes how the presence of S can increase protein stability?

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