AP Biology Practice Questions, Examples, and FRQ Samples

A cell is placed in a solution with a higher solute concentration than the cell's cytoplasm. What will most likely happen to the cell?

• AWater will move into the cell and it will swell.
• BWater will move out of the cell and it will shrink.
• CSolutes will move into the cell by active transport.
• DThe cell volume will stay constant because the membrane is impermeable.

An enzyme's activity increases as temperature rises from 10°C to 37°C and then drops sharply above 45°C. Which statement best explains the drop?

• ASubstrate molecules stop colliding with the enzyme above 45°C.
• BThe enzyme becomes a competitive inhibitor of itself at high temperatures.
• CHeat disrupts hydrogen bonds and changes the enzyme's three-dimensional shape, reducing active-site binding.
• DThe enzyme forms more substrate-enzyme complexes than it can release.

A student measures oxygen production from an aquatic plant at increasing light intensities. Oxygen output rises steeply at first, then plateaus at high intensity.

Which factor most likely limits the rate of photosynthesis at the plateau?

• AAvailability of light-independent-reaction substrates such as CO₂.
• BThe number of photons striking the leaves.
• CWater availability inside the plant.
• DThe amount of chlorophyll in the stroma.

A scientist adds a chemical that makes the inner mitochondrial membrane freely permeable to protons (H⁺). What is the most direct effect on the cell?

• AGlycolysis stops because pyruvate cannot enter the mitochondrion.
• BATP synthesis by ATP synthase decreases because the proton gradient collapses.
• CThe Krebs cycle runs faster to compensate for lost ATP.
• DOxygen stops being consumed because the electron transport chain halts.

In pea plants, purple flowers (P) are dominant over white (p). A heterozygous purple plant is crossed with a white plant. What fraction of offspring are expected to have white flowers?

• A0
• B1/4
• C1/2
• D3/4

A point mutation changes a single base in the middle of a gene's coding sequence, but the resulting protein is unchanged. Which type of mutation is this most likely to be?

• AA frameshift mutation.
• BA silent mutation due to the redundancy of the genetic code.
• CA nonsense mutation that creates a stop codon.
• DA missense mutation that substitutes a chemically similar amino acid.

In a large, randomly mating population at Hardy-Weinberg equilibrium, 16% of individuals express a recessive phenotype. What fraction of the population is heterozygous?

• A0.16
• B0.24
• C0.36
• D0.48

Antibiotic use in a hospital rises sharply over a decade. Over the same period, the proportion of a bacterial species that carries a resistance gene increases from 3% to 62%.

Which statement best explains the change in the bacterial population?

• AIndividual bacteria mutated in response to the antibiotic so they could survive.
• BThe antibiotic acted as a selective pressure, favoring the reproduction of resistant bacteria that already existed.
• CResistance was acquired by the hospital environment and transferred to the bacteria.
• DThe bacterial population size decreased, which raised the frequency of all traits equally.

A population of deer on an island grows rapidly until it approaches the island's carrying capacity. What most likely happens next?

• AThe birth rate continues to exceed the death rate indefinitely.
• BDensity-dependent factors such as food limitation and disease slow population growth.
• CThe population immediately goes extinct.
• DCarrying capacity rises to match the new population size.

A student wants to test whether caffeine increases the heart rate of Daphnia (water fleas). She observes five Daphnia in caffeine solution and five in pond water and records heart rates once.

Which single change would most improve the validity of her experiment?

• AUsing a larger, standardized sample size and repeating measurements at multiple caffeine concentrations.
• BIncreasing the caffeine concentration tenfold to make the effect larger.
• CUsing only Daphnia that happened to have visible heartbeats in the first trial.
• DCombining all the Daphnia into one beaker so conditions are identical.