Question

The partial pressure gradient for carbon dioxide across the respiratory membrane is ______________ than that for oxygen. The rate of diffusion of carbon dioxide across the respiratory membrane is ______________ than that of oxygen.

A. Less, less
B. More, more
C. Less, more
D. More, less

Answer 1

The partial pressure gradient for carbon dioxide is C. less than that for oxygen, yet carbon dioxide diffuses more rapidly across the respiratory membrane due to its greater solubility.

Step-by-step explanation:

The partial pressure gradient for carbon dioxide across the respiratory membrane is less than that for oxygen. The rate of diffusion of carbon dioxide across the respiratory membrane is more than that of oxygen. Therefore, the correct answer to the student's question is: C. Less, more.

The partial pressure of carbon dioxide in the blood of the capillary is about 45 mm Hg, and in the alveoli, it is about 40 mm Hg. Although this pressure gradient is smaller than the gradient for oxygen, the solubility of carbon dioxide is significantly higher. It is about 20 times more soluble than oxygen in both blood and alveolar fluids. As a result, despite a smaller pressure gradient, carbon dioxide diffuses across the respiratory membrane at a comparatively faster rate.