MCAT Biology Question 76: Answer and Explanation

Home > MCAT Test > MCAT biology practice tests

Test Information

Use your browser's back button to return to your test results.
Do more MCAT biology practice tests.

Question: 76

1. All of the following facilitate gas exchange in the lungs EXCEPT:

A. thin alveolar walls.
B. multiple subdivisions of the respiratory tree.
C. differences in the partial pressures of O₂ and CO₂.
D. active transporters in alveolar cells.

Correct Answer: D

Explanation:

Gas exchange in the lungs relies on passive diffusion of oxygen and carbon dioxide. This is accomplished easily because there is always a difference in the partial pressures of these two gases and because the subdivision of the respiratory tree creates a large surface area of interaction between the alveoli and the circulatory system. In addition, the thin alveolar walls allow for fast diffusion and gas exchange. Therefore, choices (A), (B), and (C) can be eliminated. Choice (D) is the correct answer because active transport is not used in the gas exchange process in the lungs.

Previous Next