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Practice Test 56 - AP Biology

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

  1. A biologist monitored a fish population in an isolated lake with no fishing. Population size increased from 800 to 1,600 to 3,200 to 6,400 fish over four consecutive years. Water chemistry, shoreline habitat, and lake area remained constant, and no new species were introduced. Which pattern best illustrates the fish population's growth during the four-year period?
  2. A student compares gene expression in a ciliated epithelial cell and a cardiac muscle cell from the same organism. Genome sequencing indicates the cells share the same DNA. The epithelial cell contains abundant mRNA for a dynein motor protein, while the cardiac cell contains abundant mRNA for a contractile protein; each cell type shows low levels of the other transcript. Which explanation best accounts for the observed differences?
  3. Researchers isolate an organelle from a eukaryotic cell and find it has two membranes. Sequencing reveals a small circular genome whose genes are most similar to genes from alpha-proteobacteria. The organelle's ribosomes resemble bacterial ribosomes, and the organelle divides independently by fission. The organelle is not continuous with the endoplasmic reticulum. Which explanation best accounts for the origin of this organelle?
  4. In a fenced prairie reserve, a rabbit population was counted each spring. Counts rose from 120 to 240 to 410 to 520 rabbits over four years, then remained between 500–540 for the next six years despite similar rainfall. No predators were introduced, and the fence prevented immigration and emigration. Vegetation surveys showed increasing grazing damage as rabbit density increased. Which explanation best accounts for the population pattern over time?
  5. A researcher sequences a gene encoding a membrane channel. In the coding strand, the normal DNA triplet at codon 120 is 5'-TAC-3', which is transcribed to mRNA 5'-UAC-3' and translated as tyrosine. In one cell line, codon 120 is changed to 5'-TAA-3', producing mRNA 5'-UAA-3'. The rest of the gene sequence is unchanged. Translation initiates normally at the start codon, and the channel's C-terminal region is required for insertion into the membrane. Which outcome is most likely from this mutation?
  6. A student uses a plasmid carrying GFP under a promoter that is active only when a specific transcription factor binds an enhancer sequence. Cells are transfected with the plasmid and then divided into two treatments: Treatment 1 receives a small molecule that activates the transcription factor; Treatment 2 receives solvent only. After 24 hours, many cells in Treatment 1 fluoresce green, while few cells in Treatment 2 fluoresce. Which explanation best accounts for the difference?
  7. A student measures catalase activity by recording O2_2 produced from H2_2O2_2 in 2 minutes at pH 7.0. At 25°C the reaction produces 18 mL O2_2, while at 60°C it produces 2 mL O2_2 using the same enzyme concentration and substrate amount. Which explanation best accounts for the reduced activity at 60°C? Consider that catalase is a protein whose active site depends on hydrogen bonds and other weak interactions to maintain shape. No inhibitors are added, and substrate concentration is not limiting in either condition.
  8. A cell is in late G1 with normal chromosome structure (each chromosome is a single chromatid). The cell passes the G1 checkpoint and then enters S phase, where DNA replication occurs. After S phase ends, the cell proceeds into G2 without entering mitosis. Which change in chromosome structure is most likely present in G2 compared with late G1?
  9. A pond has two consumer levels above algae. Algae store 20,000 kJ as new biomass, insect larvae store 2,000 kJ, and fish store 100 kJ over the same time period. Which conclusion is best supported about the fish level relative to the algae level?
  10. A lizard population includes individuals that differ genetically in sprint speed. During a period of increased predation, faster lizards are less likely to be captured and produce more offspring. After several generations, the mean sprint speed of hatchlings increases compared with the original population. Which statement best explains how variation contributed to evolution in this population?
  11. Ultraviolet (UV) radiation was likely more intense on early Earth due to limited atmospheric ozone. In a study, researchers exposed a mixture of simple carbon- and nitrogen-containing molecules in water to UV light. After exposure, they detected increased concentrations of nucleobase-like compounds compared with a dark control kept at the same temperature. Which conclusion is best supported by these results about abiotic synthesis?
  12. In a bacterial cell, a mutation alters the DNA sequence of a promoter region upstream of a gene, reducing the match to the consensus −10 and −35 elements. The coding region of the gene is unchanged. When total RNA is measured, the amount of RNA corresponding to that gene is substantially lower than in wild-type cells. Which explanation best accounts for the reduced RNA level at the molecular level?
  13. In cultured liver cells, hormone H binds a membrane GPCR and activates a G protein. The Gα subunit exchanges GDP for GTP and stimulates adenylyl cyclase, increasing cAMP. cAMP binds protein kinase A (PKA), causing release of catalytic subunits that phosphorylate enzyme X, increasing its activity. A phosphodiesterase (PDE) hydrolyzes cAMP to AMP, limiting signal duration. In an experiment, adding H increases enzyme X activity 5-fold; adding H plus a PDE inhibitor increases enzyme X activity 12-fold. Which change would most likely explain the larger response when PDE is inhibited?
  14. A DNA region contains the template sequence 3′–T A C G G A–5′ on one strand at a replication fork. DNA polymerase synthesizes the complementary strand by adding nucleotides to the 3′ end, producing a new strand in the 5′→3′ direction. A student isolates the newly synthesized complementary segment corresponding to this template. Which sequence is most likely found in the new DNA strand?
  15. A eukaryotic gene contains an intron with the sequence 5′-GU...AG-3′ at its ends. A point mutation changes the intron's 3′ end from AG to AA, without altering nearby exon sequences. After transcription, nuclear RNA analysis shows accumulation of a longer RNA that still contains the intron sequence, while other introns in the transcript are removed normally. Transcription rates are unchanged. Which explanation best accounts for the accumulation of the longer RNA?
  16. A set of taxa (L, M, N, O) was scored for derived characters relative to an outgroup. Character A is present in all four taxa. Character B is present in M, N, and O. Character C is present in N and O. Character D is present only in N. Assume each character evolved once and was not lost. Which inference about relatedness is best supported?
  17. A cell is heterozygous for alleles D and d on one homologous chromosome pair. During prophase I, a crossover occurs near the end of the chromosome, but the D/d locus lies far from the crossover site. After meiosis, the student finds that all gametes still carry either D or d, with no new allele at that locus, even though crossing over occurred elsewhere on the chromosome. Which statement best explains the chromosomal-level reason no new allele forms at the D/d locus?
  18. In a snail population, shell thickness varies and is heritable: allele T produces thicker shells than allele t. A crab predator is introduced and more easily crushes thin-shelled snails, reducing their reproductive output. Crab predation remains high for many generations. Which outcome is most likely in the population?
  19. In a eukaryotic cell, calcium ions (Ca2+) are stored at higher concentration inside the smooth ER than in the cytosol. When ER membranes are damaged, cytosolic Ca2+ rises and several cytosolic enzymes change activity rapidly. Which feature best explains how compartmentalization contributes to regulation in this scenario?
  20. A lipid bilayer membrane contains a hydrophobic interior. Solutes that are nonpolar dissolve into the bilayer and diffuse across more readily than polar solutes. Consider two molecules with similar size: benzene (nonpolar aromatic hydrocarbon) and phenol (benzene with a hydroxyl group, making it more polar). Neither is charged in this comparison. No membrane proteins are present. Which molecule would most likely cross the bilayer faster by simple diffusion?

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