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Practice Test 95 - AP Biology

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

  1. A secretory cell shows a large stack of flattened membrane sacs with distinct "cis" and "trans" faces. Small vesicles fuse on one side and bud off on the other. Which outcome is most likely associated with this organelle's structure?
  2. A population of field mice shows variation in fur thickness. During 15 unusually cold winters, mice with very thin fur averaged 0.6 surviving offspring, mice with very thick fur averaged 0.7, and mice with intermediate fur thickness averaged 1.8. Over the same period, the population's mean fur thickness changed little, but the proportion of intermediate phenotypes increased and overall variance decreased. Which explanation best accounts for the change in the distribution of fur thickness?
  3. A pond ecosystem reports annual energy stored as new biomass: aquatic plants 6,000 kJ/m2^2/yr, snails 600 kJ/m2^2/yr, sunfish 60 kJ/m2^2/yr. Assume these values represent energy available to the next trophic level. Which statement is best supported regarding energy flow in this pond?
  4. A membrane channel protein spans the lipid bilayer and contains many nonpolar amino acids on its exterior surface where it contacts phospholipid tails. Polar and charged amino acids line the channel interior, allowing selective passage of ions. The protein's primary structure determines where α-helices form, and helix arrangement contributes to the tertiary structure that creates the pore. A mutation replaces several exterior leucines with lysines. Channel protein is still produced but is less abundant in the membrane. Which feature best explains the reduced membrane abundance?
  5. Translation requires that the ribosome maintain a reading frame, grouping nucleotides into codons from the start codon. A wild-type mRNA segment is 5′-AUG AAA CCG UUU GGA UAA-3′. In a mutant, a single nucleotide is inserted immediately after the start codon, producing 5′-AUG UAAA ACC GUU UGG AUAA-3′ when regrouped from the same start site. Assume the ribosome initiates at AUG in both cases and continues until it encounters the first in-frame stop codon. Which outcome is most likely for the mutant compared with the wild type?
  6. A cell performs two metabolic reactions that use the same substrate but produce different products. One reaction occurs in the cytosol and the other occurs inside a membrane-bound organelle with selective transporters for the substrate. When the organelle membrane is disrupted, the products become less predictable and intermediate levels fluctuate widely. Which feature best explains how compartmentalization influences control of these competing reactions?
  7. A cell is modeled as a cube. When side length increases from 2 units to 4 units, the cell's surface area increases from 24 to 96 square units and volume increases from 8 to 64 cubic units. Assume membrane transport rate is proportional to surface area and cellular requirement is proportional to volume. Which explanation best accounts for why the larger cube is more likely to experience transport limitation?
  8. In a lake, a population of zooplankton is exposed to an introduced predatory fish beginning in 2010. A spine-length trait is heritable and influenced by alleles S (long spines) and s (short spines). Researchers estimated allele frequencies from random samples: in 2009, f(S)=0.40f(S)=0.40; in 2012, f(S)=0.55f(S)=0.55; in 2016, f(S)=0.67f(S)=0.67. Long spines reduce predation risk. Which observation best demonstrates continuing evolution in this zooplankton population?
  9. A large insect population has allele KK at frequency 0.55. After a pesticide is introduced, genotype fitness estimates show KKKK has the lowest survival, KkKk is intermediate, and kkkk has the highest survival. Over eight generations, p(K)p(K) decreases to 0.18. No immigration occurs, and the mutation rate is unchanged. Which factor most directly explains the decline in allele KK frequency?
  10. A researcher measures catalase activity by recording oxygen production while keeping enzyme concentration constant. At pH 7.0 the reaction rate is 40 units; at pH 3.0 it is 5 units. The enzyme is returned to pH 7.0 and the rate returns to 38 units. Which explanation best accounts for the low rate at pH 3.0?
  11. A rabbit population in a grassland was monitored monthly. It increased from 50 to 80 to 130 over the first three months. In month 4, a viral disease outbreak occurred; counts then were 70 in month 4 and 60 in month 5. No major changes in predators or food were observed. Which factor most directly explains the population decrease after month 3?
  12. A neuron is experimentally treated with a drug that depolymerizes microtubules. Within hours, vesicles containing neurotransmitter accumulate near the cell body and are less abundant at the axon terminal. The plasma membrane and ion channels at the terminal remain intact, but synaptic transmission decreases. In untreated neurons, vesicles move along long tracks extending from the cell body to the terminal. Which feature best explains the reduced neurotransmitter release after microtubule depolymerization?
  13. A researcher compares two populations of single cells that are geometrically similar. Population 1 has average cell radius 4 µm; Population 2 has average cell radius 12 µm. Both populations have the same membrane transporter density and are exposed to the same external glucose concentration. Glucose uptake per cell increases from Population 1 to Population 2, but glucose uptake per unit cell volume decreases. Which explanation best accounts for the decrease in uptake per unit volume in larger cells?
  14. A researcher surveys two nearby ecosystems of equal area in spring. In a coastal salt marsh, 1,000 individual plants are counted: 980 are cordgrass and 20 are pickleweed (2 species). In an adjacent coastal prairie, 1,000 individual plants are counted: 200 each of five grass and forb species (5 species). Both sites have similar soil moisture and no recent disturbance. Which conclusion is best supported about biodiversity at the community level across the two ecosystems?
  15. A eukaryotic pre-mRNA is synthesized and then processed. When a drug that inhibits RNA polymerase II is added, no new pre-mRNA is produced. However, existing pre-mRNA molecules in the nucleus still become shorter over time and then appear in the cytoplasm with internal sequences removed. The drug does not inhibit enzymes in the nuclear extract responsible for RNA processing. Which explanation best accounts for why mature mRNA still appears after transcription is inhibited?
  16. Two double-stranded DNA fragments of equal length are compared. Fragment 1 has 70% G+C base pairs, while Fragment 2 has 40% G+C base pairs. Both fragments are heated until the strands separate. The temperature at which half of the DNA becomes single-stranded (melting temperature) differs between the fragments due to differences in base-pair interactions. Which feature best explains why Fragment 1 has a higher melting temperature than Fragment 2?
  17. A cell maintains a high intracellular concentration of Ca2+^{2+} compared with the cytosol by pumping Ca2+^{2+} into an organelle lumen. When ATP is added to purified pump-containing membranes, Ca2+^{2+} accumulation inside the vesicles increases. When ATP is replaced with a nonhydrolyzable ATP analog that can bind but not be cleaved, Ca2+^{2+} accumulation does not increase. The pump forms a phosphorylated intermediate only when ATP can be hydrolyzed. Which explanation best accounts for why ATP hydrolysis, not just ATP binding, is required for Ca2+^{2+} transport?
  18. A DNA sample is analyzed and found to contain 20% adenine. Assuming the DNA is double-stranded and follows standard base-pairing rules, which statement best predicts the percentage of guanine in the sample?
  19. In a large insect population, allele S starts at frequency 0.30. A pesticide is applied each season. After five seasons, allele S increases to 0.85. Field data show individuals with genotype SS and Ss are more likely to survive to reproduction than ss individuals in treated areas. No new individuals enter the population during the study. Which process is most likely responsible for the increase in allele S frequency?
  20. In a meadow, flowering plants rely on bees for pollination. A nonnative flowering plant becomes abundant and blooms at the same time as a native plant species. After the nonnative plant increases, bee visits to native flowers decrease, and native seed set declines, even though native flower abundance remains similar. Bee abundance in the meadow does not increase during the bloom period. Which interaction best explains the reduced seed set of the native plant?

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