What is the mechanism of diffusion in the respiratory system?

The mechanism of diffusion in the respiratory system primarily refers to the process by which gas molecules move from an area of higher concentration to an area of lower concentration. In the context of respiration, this is critical for the exchange of oxygen and carbon dioxide between the alveoli (tiny air sacs in the lungs) and the blood in the capillaries surrounding them.

When fresh air enters the lungs, oxygen levels in the alveoli are higher than those in the blood returning from the body, which has a higher concentration of carbon dioxide due to cellular metabolism. As a result, oxygen diffuses into the blood where it can be transported to tissues, while carbon dioxide diffuses from the blood into the alveoli to be exhaled. This passive transport process does not require energy and is driven solely by the concentration gradients of the gases involved.

The other options involve processes related to breathing or specific physiological mechanisms, but they do not capture the fundamental concept of diffusion itself, which is entirely about the movement based on concentration gradients.