Practice Test 98 - AP Biology

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

Two lipid hormones are compared. Molecule S is a steroid with four fused carbon rings and a small number of polar functional groups. Molecule P is a short peptide with many polar amino acid side chains. In an experiment, each molecule is added to a suspension of intact cells; S rapidly enters cells, while P remains outside unless a membrane protein is present. Which feature best explains S entering cells without a transport protein?
A population of annual plants in a field was monitored after a wildfire. In year 1, 200 plants were counted. In year 2, 220 were counted. In year 3, 240 were counted. In year 4, 260 were counted. Rainfall and temperature were similar each year, and no major herbivore outbreaks occurred. Which description best fits the pattern of change in population size over these four years?
Researchers measure photosynthesis in chloroplasts while varying light intensity with CO2 held constant and abundant. At low light, ATP and NADPH production increase with light intensity. At higher light, ATP and NADPH production become sufficient to support maximal carbon fixation, and further increases in light do not increase sugar production. No photodamage occurs. Which outcome is most likely when light intensity increases beyond the point where carbon fixation has plateaued?
Genetically identical yeast cells are grown at 30°C or shifted to 40°C for 30 minutes. Cells at 40°C show increased production of heat-shock proteins and higher levels of heat-shock gene mRNA; sequencing reveals no DNA differences. When cells return to 30°C, heat-shock mRNA levels decline. Which explanation best accounts for the temperature-dependent change in protein production?
A bacterial gene includes the coding DNA sequence 5′-ATG AAA GGC TCT-3′, translated as Met–Lys–Gly–Ser. A mutation inserts one nucleotide (C) after the first three bases, changing the sequence to 5′-ATG CAAA GGC TCT-3′ at the start of the coding region. Assume translation begins at the same AUG and continues until a stop codon is reached. Which outcome is most likely for the amino acid sequence downstream of the insertion?
In a population of 500 prairie grasses, allele H has frequency 0.50. A prolonged drought reduces the population to 40 plants that produce most of the seeds for recolonization. In the next generation of 500 plants, allele H frequency is 0.57. Measurements show no consistent differences in seed production among genotypes at this locus during the drought, and no seeds arrive from outside populations. Which process is most likely responsible for the allele-frequency shift?
Plant cells exposed to signaling molecule S show an increase in cytosolic IP $_3$ within 20 seconds. S binds to a receptor at the plasma membrane. When a phospholipase C (PLC) inhibitor is added, S still binds the receptor, but IP $_3$ does not increase. Total PLC protein levels remain unchanged during the assay. Which of the following best explains the earliest transduction event after receptor binding?
Two identical mitochondrial preparations are supplied with the same amount of NADH and oxygen. Preparation 1 has an intact inner membrane; preparation 2 has a leaky inner membrane that allows protons to pass freely. Preparation 2 consumes oxygen at a higher rate but produces less ATP. Which explanation best accounts for the lower ATP yield in preparation 2?
Which of the following outcomes is most consistent with the principles of Mendelian genetics and probability?
A cell is placed in a solution containing 20 mM glucose, while cytosolic glucose is 2 mM. Glucose crosses the membrane only through a specific carrier protein. When ATP production is blocked, glucose uptake continues at the same initial rate, but adding a carrier inhibitor stops uptake. No vesicles form, and the carrier shows saturation at high external glucose. Which mechanism best explains glucose entry into the cell?
A receptor activates kinase K, which phosphorylates two targets: (1) enzyme E to increase its activity and (2) inhibitor I, which then binds K and reduces K activity. In wild-type cells, E phosphorylation peaks then declines within 3 minutes after ligand addition. In cells lacking I, E phosphorylation remains elevated longer. Which statement best describes the role of I in this pathway?
The plasma membrane is a phospholipid bilayer with embedded proteins. The bilayer's hydrophobic interior limits diffusion of polar solutes, while specific transport proteins can facilitate passage. A researcher inserts additional cholesterol molecules between phospholipid tails in a membrane at moderate temperature. The membrane becomes less fluid and shows reduced diffusion of a small nonpolar solute, with no change in transport protein number. Which feature best explains the reduced diffusion of the nonpolar solute?
Cells are placed in a medium with high extracellular K $^+$ and low intracellular K $^+$ . K $^+$ enters only when a specific K $^+$ channel is open, and net influx stops as intracellular K $^+$ rises. No ATP is required for K $^+$ entry, and K $^+$ can move out if the gradient reverses. Which mechanism best explains K $^+$ entry under these conditions?
In heart muscle cells, ligand Z binds a membrane receptor and causes a rapid decrease in cytosolic cAMP. When cells are treated with pertussis toxin, which prevents certain G proteins from interacting with receptors, Z still binds but cAMP levels no longer decrease. Which of the following best explains the earliest intracellular event normally triggered by Z binding?
A triglyceride consists of glycerol ester-linked to three fatty acids and is largely nonpolar. A phospholipid consists of glycerol linked to two fatty acids and a phosphate-containing head group that is polar. In water, triglycerides form separate droplets, while phospholipids can form stable bilayers. Which structural difference best explains these contrasting behaviors in water?
A population of bacteria contains two variants of a membrane protein: variant X and variant Y. Before antibiotic use, 10% of cells carry variant Y. A hospital begins using an antibiotic that targets the membrane protein; after 3 months, 65% of sampled bacteria carry variant Y. The total number of bacteria sampled each month is similar, and sequencing shows no new variants appeared during the period. Which statement best explains the change in variant frequencies in the population?
In an experiment on protocell growth, fatty-acid vesicles containing RNA were supplied with additional fatty acids. These vesicles increased in surface area and volume and divided more frequently under gentle agitation than vesicles lacking RNA, which grew more slowly under the same conditions. No proteins were present. Which inference is best supported about early life origins?
An enzyme U catalyzes S → P. A mutation replaces one amino acid in the active site, and the mutant enzyme binds substrate more weakly but shows the same maximum rate at very high substrate concentration as the original enzyme. Enzyme concentration is the same in both assays. Which change is most consistent with the mutant enzyme's kinetic behavior?
A population of 60 flowering plants is isolated in a roadside patch. Allele G begins at frequency 0.55. Over four generations, allele G fluctuates unpredictably (0.55 → 0.42 → 0.58 → 0.47) with no measured differences in seed set among genotypes and no immigration. The population size remains near 60 each generation. Which factor most directly explains the pattern of allele-frequency change?
In an agricultural region, widespread use of a broad-spectrum insecticide reduces many insect populations in nearby hedgerows and fields. Within a season, insect-eating bats and swallows are observed less frequently, and fewer nests successfully fledge young. Crop plants show increased aphid outbreaks later in the season, despite continued insecticide use. No unusual weather occurs that year. Which explanation best accounts for the increased aphid outbreaks?

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