NCA Respiratory Practice Exam

Gas exchange in the alveoli primarily occurs through the process of diffusion. This is the movement of molecules from an area of higher concentration to an area of lower concentration. In the case of the alveoli, oxygen (from the air within the alveoli, where its concentration is high) diffuses into the bloodstream, where its concentration is lower. Simultaneously, carbon dioxide, which is in higher concentration in the blood than in the alveolar air, diffuses from the blood into the alveoli to be exhaled.

This process efficiently facilitates the body's needs for oxygen and the removal of carbon dioxide, which is a metabolic waste product. Understanding that gas exchange is driven by concentration gradients rather than active transport or other mechanisms is crucial for comprehending how respiration works at the cellular level. The other options describing the gas exchange process do not accurately reflect how gases move across the alveolar membrane.