Through what process does oxygen and carbon-dioxide exchange occur between the blood and the air?

Through what process does oxygen and carbon-dioxide exchange occur between the blood and the air?

• A. Osmosis
• B. Diffusion
• C. Chemical reaction
• D. Enzymatic actions

Answer: (B)

Gas exchange occurs by diffusion across the thin alveolar-capillary membrane, driven by partial pressure gradients. Oxygen in the alveolar air is at a higher partial pressure than in the blood, so it diffuses into the blood. Carbon dioxide is at a higher partial pressure in the blood than in the alveolar air, so it diffuses from blood into the air to be exhaled. This movement is passive and does not require energy. Osmosis involves the movement of water, not gases. Chemical reactions would change the substances involved, not simply move them across a membrane. Enzymatic actions are catalysts for reactions, not the mechanism of gas diffusion.

Gas exchange occurs by diffusion across the thin alveolar-capillary membrane, driven by partial pressure gradients. Oxygen in the alveolar air is at a higher partial pressure than in the blood, so it diffuses into the blood. Carbon dioxide is at a higher partial pressure in the blood than in the alveolar air, so it diffuses from blood into the air to be exhaled. This movement is passive and does not require energy. Osmosis involves the movement of water, not gases. Chemical reactions would change the substances involved, not simply move them across a membrane. Enzymatic actions are catalysts for reactions, not the mechanism of gas diffusion.