Where does the gas exchange take place in the lungs?

• A. In the bronchi
• B. In the trachea
• C. In the alveoli
• D. In the pleura

Answer: (C)

Gas exchange in the lungs occurs in the alveoli, which are tiny air sacs located at the end of the respiratory tree. The primary function of the alveoli is to provide a large surface area for the exchange of oxygen and carbon dioxide between the air in the lungs and the blood in the capillaries that surround them.

Oxygen from the inhaled air diffuses through the thin walls of the alveoli into the blood, where it binds to hemoglobin in red blood cells for transport throughout the body. Conversely, carbon dioxide, which is a waste product of metabolism, diffuses from the blood into the alveoli to be exhaled.

The design of the alveoli, being numerous and clustered, allows for an extensive surface area—about the size of a tennis court—which enhances the efficiency of gas exchange. This process is vital for maintaining proper oxygen levels in the body and removing carbon dioxide effectively from the bloodstream.

In contrast, other structures within the respiratory system such as the bronchi and trachea do not play a direct role in gas exchange; instead, they serve primarily as passageways for air to move in and out of the lungs. The pleura are membranes surrounding the lungs that help create a protective and lubric