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Practice Test 44 - AP Biology

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

  1. Researchers compared an intron sequence from the same nuclear gene in three primates. Humans and chimpanzees share an identical 120-base-pair insertion at the same position in the intron, while gorillas lack the insertion and instead have a different 14-base-pair deletion at that location. The surrounding intron sequence aligns among all three lineages. Because intron changes are typically selectively neutral, shared insertions at identical positions are unlikely to occur independently. Which inference is best supported by these data?
  2. A student examines liver cells and red blood cell precursors from the same person. Both cell types initially contain nuclei and the same genomic DNA. In liver cells, mRNA for albumin is abundant, while in red blood cell precursors, mRNA for beta-globin is abundant. The student confirms that both genes are present in both cell types. Which explanation best accounts for why the two cell types produce different major proteins?
  3. In a beetle species, spotted wings (W) are completely dominant to unspotted wings (w). A cross between two beetles produces offspring with a 1:1 ratio of spotted to unspotted wings. Assume a single gene controls the trait and inheritance is Mendelian. Which parental genotypes most likely produced this ratio?
  4. A population of beetles was reared in identical containers with unlimited food but different starting sizes. Container 1 began with 10 beetles and reached 40 after 2 weeks. Container 2 began with 100 beetles and reached 130 after 2 weeks. Temperature and humidity were the same, and no predators were present. The number of eggs laid per female was similar in both containers, but larvae survival was lower in Container 2. Which explanation best accounts for the different growth outcomes?
  5. Two cell types are exposed to the same hydrophilic ligand H2. Cell type 1 shows rapid cAMP increase; cell type 2 shows no change in cAMP. Fluorescent labeling shows that only cell type 1 has the matching membrane receptor for H2. Which of the following best explains the difference in early cellular response?
  6. A bacterial population uses an autoinducer molecule A that accumulates outside cells as cell density increases. When A is added to low-density cultures, a membrane receptor binds A and within 10 seconds activates a cytosolic protein by transferring a phosphate group to it. If the receptor's extracellular binding site is blocked, no phosphorylation of the cytosolic protein occurs. Which of the following best explains signal reception in this system?
  7. In cultured liver cells, addition of epinephrine causes a rapid increase in cytosolic cAMP within 10 seconds. A membrane-impermeable epinephrine analog produces the same cAMP increase, while epinephrine added to cell-free cytosol has no effect. When cells are pretreated with a compound that blocks ligand binding to a specific plasma membrane protein, epinephrine no longer elevates cAMP. Which of the following best explains how the signal is initially received and transduced?
  8. A receptor activates a kinase cascade at the plasma membrane. In untreated cells, ligand addition increases phosphorylation of Kinase 1 within 10 seconds. When a competitive antagonist binds the receptor's ligand-binding site, Kinase 1 phosphorylation does not increase, even though intracellular ATP levels are unchanged. Which of the following best explains how the antagonist affects signal reception?
  9. A DNA nucleotide contains a sugar (C, H, O), a nitrogenous base (N-containing ring), and a phosphate group (P and O). Along a DNA strand, nucleotides are linked by covalent phosphodiester bonds between the phosphate of one nucleotide and the sugar of the next, producing a sugar-phosphate backbone. The phosphate group has negatively charged oxygens at cellular pH, making the backbone highly polar. In aqueous solution, the bases tend to be oriented toward the interior of the double helix while the backbone remains exposed to water. Which statement best explains the outward orientation of the backbone?
  10. A botanist compares chloroplast DNA sequences from three plant species. Two flowering plant species (R and S) share 99.2% sequence identity across a chloroplast region, while a moss species (T) shares 93.5% identity with R and 93.4% with S. The region is present in all three species. Which inference is best supported by these data about common ancestry?
  11. In an experiment with cultured cells, ligand H binds receptor U and causes a rapid rise in cytosolic Ca2+^{2+}. When extracellular Ca2+^{2+} is removed, the Ca2+^{2+} rise still occurs briefly but then returns to baseline. A drug that blocks IP3_3 receptors on the endoplasmic reticulum eliminates the initial Ca2+^{2+} rise. Ligand H does not cross the plasma membrane. Which of the following best explains the source of the initial Ca2+^{2+} increase after receptor activation?
  12. A student builds a model of double-stranded DNA showing antiparallel strands: one strand runs 5'→3' while the complementary strand runs 3'→5'. Each nucleotide has a sugar with a 3' hydroxyl group and a 5' phosphate group; adjacent nucleotides are connected by phosphodiester bonds between the 3' OH and 5' phosphate. The student then tries to extend one strand by adding a nucleotide to the end. Which feature best explains why nucleotides can be added only to the 3' end of a growing DNA strand?
  13. A freshwater protist is placed in a hypotonic solution and swells repeatedly, but survives by expelling water every few minutes using a contractile vacuole that fills and then rapidly empties into the plasma membrane. The vacuole is surrounded by small vesicles and microtubules that help position it near the cell surface. When microtubules are disrupted, the vacuole still fills but empties less efficiently, and the cell often lyses. Which feature best explains how this structure prevents lysis in hypotonic conditions?
  14. A breeder crosses only corn plants with the highest drought-survival scores to produce seed for the next generation. All plants are grown under the same drought-stress protocol each generation. After five generations, a larger fraction of plants survive the drought treatment than in generation 1. Which outcome is most likely responsible for the increased survival?
  15. In a coastal ecosystem, net primary production is 6,000 kJ/m2^2/yr. Energy stored as new biomass in herbivorous insects is 300 kJ/m2^2/yr, and energy stored as new biomass in insect-eating lizards is 30 kJ/m2^2/yr. Which outcome is most likely if a bird species is added that feeds mainly on lizards, assuming ~10% transfer efficiency continues?
  16. A student places identical animal cells (internal solute concentration 0.30 M) into Solution X (0.10 M nonpenetrating solute). After 5 minutes, which outcome is most likely for the cells? Assume membranes are permeable to water but not the solute, and temperature is constant. Water movement is driven by differences in solute concentration across the plasma membrane. The cells begin at the same volume and have no cell wall. Ignore any active transport and focus only on osmosis. The external solution remains at 0.10 M throughout the observation period.
  17. Five plant species (A–E) were scored for derived traits: Trait 1 (vascular tissue), Trait 2 (seeds), Trait 3 (flowers). Species A: none; B: Trait 1 only; C: Traits 1 and 2; D: Traits 1, 2, and 3; E: Traits 1 and 2. Traits arose once and were retained in descendants. Which inference about most recent common ancestry is best supported?
  18. In a cell with 2n=82n=8, homologous chromosomes pair and form tetrads in prophase I. At metaphase I, each tetrad aligns at the metaphase plate with one homolog facing each pole. If spindle fibers attach so that both sister chromatids of each homolog connect to the same pole during meiosis I, which outcome is most likely at anaphase I?
  19. A phospholipid bilayer contains embedded transport proteins. The hydrophobic tails create a barrier to charged particles, while some proteins form selective pores lined with polar amino acids. A student compares movement of K+ across membranes with and without a functional K+ channel protein. The concentration of K+ is higher outside than inside. Which feature best explains why K+ moves into the cell only when the channel is functional?
  20. Two closely related snail populations live in the same coastal marsh. Population 1 has shells that coil clockwise, and population 2 has shells that coil counterclockwise. When individuals from the two populations attempt to mate, their reproductive openings rarely align, and successful copulation is uncommon. Genetic surveys show limited gene flow and increasing divergence between the populations despite overlapping ranges. Which prezygotic barrier most directly accounts for the reduced interbreeding?

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