What is a function of the alveoli in the lungs?

The primary function of the alveoli in the lungs is gas exchange. Alveoli are tiny, sac-like structures at the ends of the bronchioles, which are the smallest air passages in the respiratory system. Their walls are extremely thin and are surrounded by a network of capillaries. When air enters the alveoli, oxygen from the inhaled air diffuses through the alveolar walls and into the blood in the capillaries. At the same time, carbon dioxide from the blood diffuses into the alveoli to be exhaled. This process is essential for respiration, as it allows the body to take in oxygen, which is crucial for cellular functions, while removing carbon dioxide, a metabolic waste product.

The other options describe functions that are not performed by alveoli. For example, they do not provide structural support for the lungs, nor do they produce mucus or transport blood. These roles are carried out by other components of the respiratory and circulatory systems.