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Practice Test 72 - AP Biology

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

  1. A team modeled hydrothermal vent conditions by mixing H2\mathrm{H_2}-rich fluid with CO2\mathrm{CO_2}-rich fluid across a thin mineral barrier, creating a stable pH gradient. When simple carbon compounds were added, analysis detected increased amounts of reduced organic molecules on the alkaline side compared with a setup lacking the pH gradient. The mineral barrier was the same in both setups. Which conclusion is best supported by these results about possible energy sources for early metabolism?
  2. A scientist tracks movement of lactose into cells with a lactose-specific permease. When lactose is 15 mM outside and 1 mM inside, lactose enters rapidly in the dark and in the presence of ATP synthase inhibitors. When outside lactose is lowered to 1 mM, net transport becomes zero. Which explanation best accounts for these observations?
  3. A ligand binds a receptor and triggers rapid activation of a cytosolic kinase. When the receptor is artificially clustered using antibodies (without ligand), kinase activation is still observed. Antibody treatment does not permeabilize the membrane. Which of the following best explains how receptor clustering can initiate early signaling in this system?
  4. A cell is placed in a solution containing a small, nonpolar molecule. The molecule rapidly enters the cell without any change in ATP levels and without saturation even at higher external concentrations. The plasma membrane consists of a phospholipid bilayer with a hydrophobic interior and embedded proteins. Which feature best explains the molecule's rapid entry into the cell?
  5. A huge spherical cell has an unusually low SA:V yet exchanges wastes rapidly. Which feature best explains this?
  6. In fruit flies, red eyes (R) are completely dominant to sepia eyes (r). A red-eyed fly is crossed with a sepia-eyed fly (rr). All 120 offspring have red eyes. Assume one gene controls eye color and the sample is large enough to reflect expected outcomes. Which genotype is most likely for the red-eyed parent?
  7. A paleontologist finds a series of fossils from sediment layers of increasing age. Younger fossils show a mammal with a single jawbone and three small middle-ear bones. Older fossils show similar skulls but with two small bones attached to the jaw joint that gradually appear smaller and more ear-associated in intermediate layers. The fossils occur in a continuous stratigraphic sequence at one site. Which inference is best supported by this pattern?
  8. A bacterial population contains two genotypes: one carries an antibiotic-resistance plasmid, and one does not. Before antibiotic exposure, resistant cells are 2% of the population. After treatment, the population rebounds and 85% of cells carry the plasmid. Which statement best explains how variation influenced the population's evolution?
  9. During a sudden drop from 25∘25^\circC to 10∘10^\circC, a lizard's activity decreases and it moves into sunlight within minutes. Which response best explains this change?
  10. A herd of deer lives in a protected reserve. Over five years, the deer population increases from 200 to 600 individuals. During the same period, the average body mass of adult deer decreases, and the proportion of fawns surviving their first winter drops from 70% to 35%. The number of wolves in the reserve remains constant, and winter temperatures are similar each year. Which factor most likely contributes to the observed decline in fawn survival as deer density increases?
  11. During translation, a tRNA must bind a specific codon on an mRNA through base pairing between the codon and an anticodon region on the tRNA. The codon is written 5'→3' on the mRNA, and the anticodon nucleotides align antiparallel to it. Hydrogen bonding follows standard RNA base-pairing rules. Which feature best explains how the tRNA recognizes the correct mRNA codon at the molecular level?
  12. A coral reef experiences repeated heatwaves that cause frequent coral bleaching. Over several years, live coral cover declines while turf algae cover increases. Fish surveys show a decline in coral-dependent species and an increase in herbivorous fish that graze algae. Structural complexity of the reef decreases as branching corals become rare. Storms of similar intensity occur as in previous decades. Which consequence is most likely for the reef ecosystem as coral cover remains low?
  13. A researcher uses microscopy to identify mitotic stages. In one cell, chromosomes are condensed and scattered, the nuclear envelope is no longer visible, and spindle microtubules are attaching to kinetochores, but chromosomes are not yet aligned at the metaphase plate. DNA replication has already occurred earlier in the cycle. The researcher classifies the cell as prometaphase. Which event is most likely to occur next if progression continues normally?
  14. A lipid sample contains molecules with one polar phosphate head and two nonpolar fatty acid tails. The head group carries partial charges and can interact with water through ion-dipole interactions and hydrogen bonding, while the tails consist of long hydrocarbon chains that interact mainly through van der Waals forces. When placed in water, the molecules arrange so that tails are shielded from water and heads contact water. Which feature best explains why these molecules form a bilayer rather than a single-layer sphere of tails only?
  15. In a species with 2n=42n=4, homologous chromosomes separate during anaphase I. During anaphase II, sister chromatids separate when centromeres divide. A student examines a cell in anaphase II and counts four chromatids moving toward each pole. Which outcome is most likely for the chromosome number in each gamete produced from this meiosis?
  16. Scientists observe a eukaryotic cell type with an extensive internal membrane network. Electron microscopy shows the network is continuous with the outer nuclear envelope and includes flattened sacs and tubules. Newly synthesized membrane proteins inserted into the plasma membrane are first detected in this internal network, then later at the cell surface. None of these internal membranes contain DNA or ribosomes distinct from the cytosol. Which mechanism best accounts for how this internal membrane system could have originated?
  17. In an in vitro transcription system using purified eukaryotic RNA polymerase II, a DNA template with a promoter and transcription start site produces RNA transcripts of the expected length. However, when nuclear extract is added, the RNA molecules recovered contain an additional structure at the 5′ end: a guanine nucleotide linked by a 5′–5′ triphosphate bridge and methylated. This guanine is not complementary to the DNA template at the +1 position. Which explanation best accounts for the origin of the modified 5′ structure?
  18. A cell synthesizes a triacylglycerol by joining one glycerol molecule to three fatty acids. Each linkage forms when a hydroxyl group on glycerol reacts with a carboxyl group on a fatty acid, releasing water and creating an ester bond. Although assembled by dehydration, the product is not a polymer of repeating monomers. Which classification best matches this molecule based on its subunits and bonding?
  19. A mitotic kinase phosphorylates a kinetochore protein, increasing its ability to recruit spindle checkpoint components when attachment is absent. Once microtubules attach, the kinetochore protein is dephosphorylated, reducing checkpoint signaling. A mutation mimics constant phosphorylation of the kinetochore protein. Which effect is most likely in cells with the phosphomimetic mutation?
  20. In a DNA double helix, one strand has the sequence 5′-A T G C C A-3′. A second strand is synthesized using complementary base pairing and antiparallel orientation. Which statement best describes the sequence and direction of the new strand?

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