Final answer:
The partial pressures of O2, CO2, and H2O change as air courses through the airways in the respiratory system. Oxygen diffuses from the alveoli into the blood while carbon dioxide diffuses from the blood into the alveoli during gas exchange.
Step-by-step explanation:
The partial pressures of O2, CO2, and H2O change as air courses through the airways in the respiratory system. In the alveoli, the amount of carbon dioxide is higher and the amount of oxygen is lower compared to atmospheric air. As a result, during gas exchange in the alveoli, oxygen diffuses from the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli. The change in partial pressure from the alveoli to the capillaries drives the movement of oxygen into the tissues and carbon dioxide into the blood from the tissues.