What are the small sacs in the lungs that are responsible for gas exchange?

The small sacs in the lungs that are responsible for gas exchange are the alveoli. These tiny, balloon-like structures at the end of the respiratory tree have thin walls that allow for the efficient transfer of oxygen and carbon dioxide between the air in the alveoli and the blood in the surrounding capillaries.

Alveoli are specifically designed for this purpose; they provide a large surface area relative to their volume, and the moist environment within them facilitates the diffusion of gases. Each lung contains millions of alveoli, maximizing the area available for gas exchange, which is crucial for efficient respiratory function.

In contrast, bronchioles are the small airways that branch from the bronchi and lead to the alveoli but do not participate directly in gas exchange. The pleura refers to the membranes that line the thoracic cavity and cover the lungs themselves, providing a lubricated surface for lung expansion and contraction, but are not directly involved in gas exchange. Lobules refer to the sections of the lung composed of clusters of alveoli but do not themselves facilitate the gas exchange process. Thus, the alveoli are essential for oxygen uptake and carbon dioxide removal, making them the correct answer to this question.