Biology STAAR (State of Texas Assessments of Academic Readiness) Practice Test

Alveoli are primarily involved in gas exchange with the bloodstream. These tiny, balloon-like structures are found in the lungs and serve as the primary site where oxygen from the air is transferred into the blood, while carbon dioxide from the blood is expelled into the lungs to be exhaled. This gas exchange process is essential for respiration; it enables the body to obtain the oxygen necessary for cellular metabolism and to eliminate carbon dioxide, a waste product of this metabolism.

The structure of alveoli, with their vast surface area and thin walls, enhances this gas exchange efficiency. They are surrounded by capillaries, which are small blood vessels that facilitate the transfer of gases. This arrangement allows for a very short distance over which diffusion can occur, optimizing the respiratory process.

Other options such as producing hormones, transporting nutrients, or clotting blood do not describe the primary function of alveoli. Hormone production occurs in glands like the pancreas and thyroid, nutrient transport is primarily managed by the digestive and circulatory systems, and blood clotting involves platelets and clotting factors rather than the alveoli.