What is the function of alveoli in the lungs?

The function of alveoli in the lungs is to provide a large surface area for gas exchange. Alveoli are tiny air sacs located at the end of the bronchial tubes where the actual exchange of gases occurs. Their structure—numerous small, balloon-like shapes—greatly increases the surface area available for oxygen to diffuse into the blood and for carbon dioxide to diffuse out of the blood. This extensive surface area, combined with the thin walls of the alveoli, facilitates efficient gas exchange, ensuring that the body receives the oxygen it needs while removing carbon dioxide effectively.

The other choices focus on different functions that do not accurately describe the role of alveoli. Alveoli do not produce carbon dioxide; instead, they help in its removal from the bloodstream. They also do not filter blood, as filtering is a function associated with the kidneys. Lastly, while alveoli play a vital role in transporting oxygen indirectly through gas exchange, they themselves do not perform the transport process; that function is primarily part of the circulatory system, which carries oxygen from the lungs to the rest of the body.