- A Active transport across alveolar walls
- B Facilitated transport using carrier proteins
- C Bulk flow driven by blood pressure
- D Simple diffusion along a pressure gradient
Correct answer: D. Simple diffusion along a pressure gradient
Explanation: Gases move across the alveolar-capillary membrane by simple diffusion, driven by differences in their partial pressures on either side.
Concept context
The mechanics of breathing, lung volumes, gas transport in blood, the Bohr effect, and respiratory regulation.