Which term describes ventilation: movement of air in and out of the lungs?

• A. Diffusion
• B. Perfusion
• C. Ventilation
• D. Eupnea

Answer: (C)

Ventilation means the physical flow of air into and out of the lungs, driven by pressure changes from the respiratory muscles. This is the mechanism that brings in oxygen-rich air and clears carbon dioxide from the alveoli. Diffusion, in contrast, is the transfer of gases across the alveolar–capillary membrane driven by concentration differences. Perfusion refers to the blood flow through the lungs that picks up oxygen and releases CO2. Eupnea describes normal, quiet breathing pattern, not the process of moving air itself. So the term that best fits “movement of air in and out of the lungs” is ventilation.