Question

The partial pressure of oxygen in the alveoli of the lungs is

• A. less than that of carbon dioxide
• B. equal to that in the blood
• C. more than that in the blood
• D. less than that in the blood

Answer 1

The correct option is C more than that in the blood

The partial pressure of oxygen in alveoli of lungs is 104 mm Hg, which is more than that of blood (95 mm Hg) in the blood capillaries of lung alveoli. This difference allows passive diffusion of $O_2$ from air filled in the lungs to the blood vessels of lung alveoli.

Alveoli are the site of gaseous exchange and have a higher partial pressure of oxygen than that of blood. Blood is rich in carbon dioxide at cell and tissue levels due to cellular respiration. The higher partial pressure of oxygen in alveoli allow diffusion of oxygen into the blood.