Question

Gaseous $\left(O_2\text{and}C{O}_2\right)$ exchange between alveoli and blood, and blood and tissues takes place by

• A. Simple diffusion
• B. Active transport
• C. Facilitated diffusion
• D. All of the above

Answer 1

The correct option is A Simple diffusion

• When diffusion of substances takes place due to a pressure gradient without any use of a carrier or energy requirement it is called simple diffusion.
• Diffusion of gases occurs from a region of their higher partial pressure to a region of their lower partial pressure. The alveolar air has high $p{O}_2$ compared to the $p{O}_2$ in the blood.
• Thus oxygen diffuses from alveoli to blood.
  In the tissues, the $pC{O}_2$ is more than in the oxygenated blood, thus diffusion of carbon dioxide takes place from tissue to blood.
• Hence, option A is correct.