Practice Test 31 - AP Biology

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

A rooted tree is summarized by these nested groups: {A,B,C,D} share ancestor X; within that, {B,C,D} share ancestor Y; within that, {C,D} share ancestor Z. Taxon E is outside {A,B,C,D} and shares only the root ancestor with them. No other splits occur. Based on this structure, answer the relatedness question. Which pair shares the most recent common ancestor?
A forest food web includes plants, deer, and wolves. Over one year, plants add 80,000 MJ of new biomass energy, deer add 6,400 MJ, and wolves add 320 MJ. Which conclusion is best supported regarding the relative energy available to higher trophic levels?
In snapdragons, flower color shows incomplete dominance: allele R produces red pigment, allele r produces no pigment. RR plants are red, rr plants are white, and Rr plants are pink. A pink plant is crossed with a white plant, and 80 offspring are produced. Assuming the trait is autosomal and the parents are true for their phenotypes, predict the expected phenotypic outcomes among the offspring. Which outcome best matches this inheritance pattern?
A phospholipid bilayer with no proteins is tested with three solutes: NH $_3$ (17 Da, uncharged, polar), NH $_4^+$ (18 Da, charged), and N $_2$ (28 Da, nonpolar). All are present at equal concentration. Which solute would most likely cross the bilayer at the highest rate?
A cell is placed in a solution containing 20 mM glucose while the cytosol contains 2 mM glucose. The plasma membrane includes a specific glucose transporter protein. When ATP production is inhibited, glucose still enters the cell until intracellular and extracellular concentrations become similar, and uptake stops when the transporter is blocked by a competitive inhibitor. Which explanation best accounts for glucose movement into the cell under these conditions?
A protein phosphatase inactivates cyclin B–CDK1 targets at mitotic exit by removing phosphates from those targets after cyclin B–CDK1 activity drops. In a mutant, APC/C activation and cyclin B degradation occur normally, but the phosphatase is inactive. Which observation is most likely in the mutant cells after anaphase begins?
In cardiac cells, epinephrine binds a β-adrenergic GPCR, activating Gs and increasing cAMP. cAMP activates PKA, which phosphorylates a Ca2+ channel, increasing Ca2+ influx. Elevated Ca2+ binds a regulatory subunit of an enzyme complex, increasing the complex's catalytic activity. A second protein, arrestin, binds phosphorylated GPCRs and prevents further G protein activation without blocking epinephrine binding. Cells are treated with a kinase inhibitor that prevents GPCR phosphorylation but does not affect PKA. Which effect is most likely during continuous epinephrine exposure?
An enzyme is placed in a solution containing 2 M urea, and its reaction rate decreases rapidly despite constant temperature, pH, and substrate concentration. Which explanation best accounts for the decreased rate in urea?
In cultured liver cells, hormone H binds a G protein–coupled receptor (GPCR) and increases intracellular cAMP within seconds. cAMP binds the regulatory subunits of protein kinase A (PKA), releasing active catalytic subunits that phosphorylate enzyme E, increasing its activity. A phosphodiesterase (PDE) normally hydrolyzes cAMP to AMP, limiting signal duration. In an experiment, cells are treated with H in the presence or absence of a PDE inhibitor. Compared with H alone, H plus the PDE inhibitor results in higher cAMP levels and greater phosphorylation of enzyme E. Which change would most likely reduce phosphorylation of enzyme E in response to H?
A lake was sampled for phytoplankton in spring and late summer. Spring samples contained 20 species with no species exceeding 12% of cells. Late-summer samples contained 20 species, but one species comprised 65% of cells. Total phytoplankton cell counts were similar. Which conclusion is best supported about seasonal biodiversity?
A membrane made only of phospholipids is exposed to equal concentrations of ribose (150 Da, polar uncharged) and benzene (78 Da, nonpolar). No proteins are present. Which molecule would most likely be more permeable through the membrane?
A DNA molecule is described as having two strands that run in opposite directions. Each strand has a 5′ end with a phosphate group and a 3′ end with a hydroxyl group. Base pairing occurs between the strands, and the sugar-phosphate backbones are on the outside of the helix. The orientation of the strands constrains how bases align for hydrogen bonding in the interior of the helix. Which feature best describes the strand arrangement that permits consistent base pairing throughout the DNA double helix?
A ligand binds a receptor on the plasma membrane and triggers opening of an ion channel, causing Na $^+$ influx within milliseconds. When extracellular Na $^+$ is removed and replaced with an impermeant cation, ligand binding still occurs but the membrane potential does not change. The receptor protein sequence includes multiple transmembrane helices typical of ion channels. Which of the following best explains the earliest intracellular response in this system?
A seabird colony size was tracked on an island for 8 years. The number of nesting pairs stayed near 1,200 for Years 1–4, then dropped to 700 in Year 5 and remained between 650–720 through Year 8. In Year 5, a storm destroyed much of the nesting habitat; food availability in surrounding waters did not change. Which explanation best accounts for the new population level after Year 5?
A marine ecologist compares barnacle survival on two stretches of rocky shoreline. In both areas, wave action is similar. On Site A, barnacle density averages 50 per square decimeter and annual survival is 40%. On Site B, density averages 10 per square decimeter and annual survival is 75%. The ecologist observes that a parasitic worm spreads through direct contact between neighboring barnacles. Which factor is most likely density dependent in this system?
A breeder maintains two lines of mice from the same starting population. In Line 1, only the fastest runners (top 10%) are used as parents each generation. In Line 2, breeders choose parents randomly with respect to running speed. Both lines are housed identically. After 15 generations, Line 1 has a higher mean running speed than Line 2. Which statement best accounts for the difference?
A lizard population includes heritable variation in leg length. A new invasive predator is introduced, and lizards that can sprint faster are more likely to survive and reproduce. After several generations, the frequency of alleles associated with longer legs increases. Which statement best explains the connection between variation and evolution in this scenario?
An mRNA is translated by a ribosome moving 5′ to 3′. A student writes that the amino acid sequence should be determined by reading the mRNA 3′ to 5′ because base pairing between codon and anticodon is antiparallel. In translation, each tRNA anticodon pairs antiparallel to an mRNA codon, but the ribosome advances along the mRNA one codon at a time in the 5′ to 3′ direction. Which explanation best accounts for why the student's prediction is incorrect?
Two spherical cells are placed in the same solution containing a permeable solute that diffuses across the membrane. Cell Small has radius 2 µm; Cell Large has radius 6 µm. Both begin with the same internal solute concentration, lower than outside. Over the first minute, the internal concentration rises faster in Cell Small. Which explanation best accounts for the faster rise in Cell Small?
A researcher compares how quickly two liquids evaporate from identical open dishes: water evaporates more slowly than a similar-sized sample of a less hydrogen-bonding liquid. Water molecules are polar, and neighboring molecules form hydrogen bonds through attractions between partially positive hydrogens and partially negative oxygens. For a molecule to enter the gas phase, it must separate from neighboring molecules, which requires overcoming intermolecular attractions. In water, many hydrogen bonds can link nearby molecules, increasing the energy needed for separation. Which statement best explains water's slower evaporation rate at the molecular level?

Practice tests