Final answer:
The function of the alveoli is to serve as small air sacs in the lungs where gas exchange occurs. They are essential for absorbing oxygen into the blood and expelling carbon dioxide as a waste gas.
Step-by-step explanation:
The function of the alveoli is a) Small air sacs in the lungs; gas exchange. Alveoli are essential components of the respiratory system located within the lungs. Each alveolus is a small air sac about 200 μm in diameter with elastic walls that are surrounded by a network of capillaries. These structures allow for the efficient exchange of gases—oxygen is absorbed into the blood, and carbon dioxide is released from the blood into the alveoli to be exhaled.
The lungs may contain up to 700 million alveoli, which provide a large surface area for gas exchange. This surface area can be as extensive as half a tennis court in adults, facilitating a significant amount of gas exchange to support bodily functions. The alveoli and the capillaries form a blood-air barrier where gas exchange occurs through simple diffusion, thereby playing a crucial role in oxygenating the blood and removing waste gases.
Alveoli are found at the end of alveolar ducts, housed within sac-like clusters called alveolar sacs. This structural organization of millions of alveoli together provides the lungs with a sponge-like consistency and enables a vastly large area for gas exchange.