MCAT Biology 3

Question 1

Which of the following best explains why facilitated diffusion does not require ATP?

Accepted Answer

Molecules move down their concentration gradient

Answer

Facilitated diffusion is passive; channel and carrier proteins simply provide a pathway for molecules to move spontaneously down their electrochemical gradient.

Question 2

During the light-dependent reactions of photosynthesis, which molecule directly donates electrons to Photosystem II?

Accepted Answer

Water

Answer

Water is oxidized by the oxygen-evolving complex associated with PSII, providing electrons to replace those excited by light energy and releasing O2 as a byproduct.

Question 3

A frameshift mutation caused by a single nucleotide insertion would have the most severe effect if it occurred at which location?

Accepted Answer

Near the 5' end of the coding sequence

Answer

A frameshift near the 5' end alters the reading frame for nearly the entire protein, causing the most extensive change in amino acid sequence.

Question 4

Which of the following hormones acts via a G-protein coupled receptor to increase intracellular cAMP?

Accepted Answer

Epinephrine

Answer

Epinephrine binds β-adrenergic receptors (GPCRs) that activate adenylyl cyclase through Gs proteins, increasing intracellular cAMP levels.

Question 5

In an experiment, researchers block the sodium-potassium ATPase in a neuron. Which immediate effect would be observed?

Accepted Answer

Gradual depolarization of the resting membrane potential

Answer

Without Na+/K+-ATPase, Na+ accumulates inside the cell while K+ decreases, gradually reducing the resting membrane potential toward zero (depolarization).

MCAT - Medical College Admission Test Practice Test

MCAT - Medical College Admission Test Practice Test

MCAT Biology 3