What is the primary function of the alveoli in the respiratory system?

The primary function of the alveoli in the respiratory system is to facilitate gas exchange. Alveoli are tiny, balloon-like structures located at the end of the bronchioles in the lungs. Their structural design, featuring thin walls and a large surface area, is specifically adapted to maximize the efficiency of oxygen and carbon dioxide exchange. When air enters the lungs, oxygen diffuses from the alveoli into the bloodstream, while carbon dioxide diffuses from the blood into the alveoli to be exhaled. This critical process ensures that oxygen is delivered to the body’s cells for metabolic processes, while waste gases like carbon dioxide are removed.

In contrast, the other functions suggested by the remaining choices do play a role in the respiratory system but are not the primary function of the alveoli. For instance, while moistening, warming, and filtering air are important for preparing it before it reaches the alveoli, these processes are primarily managed by other parts of the respiratory tract, such as the nasal passages and bronchi. Therefore, the alveoli’s main role is strictly focused on gas exchange, making option B the most accurate answer.