Anatomy and Physiology II Practice Test

The exchange of gases in the respiratory system primarily occurs through diffusion, which is a passive process. In this context, oxygen and carbon dioxide move across the alveolar and capillary membranes based on their concentration gradients. Oxygen diffuses from areas of higher concentration (the alveoli) to areas of lower concentration (the blood in the capillaries), while carbon dioxide moves in the opposite direction, from the blood where it is in higher concentration to the alveoli where it is lower in concentration. This movement does not require energy input from the body, thus reinforcing that it is a passive process.

In contrast, an active process would involve energy expenditure, usually via ATP, to move substances against their concentration gradient, which does not occur during typical gas exchange in the lungs. Therefore, the nature of gas exchange being a passive process is fundamental to understanding how respiration efficiently operates without direct energy use.