What best describes the function of alveoli in the lungs?

The function of alveoli in the lungs is best described as facilitating the exchange of oxygen and carbon dioxide. Alveoli are tiny, balloon-like structures located at the ends of the respiratory bronchioles and are essential for the respiratory system's gas exchange process. Their walls are extremely thin and are surrounded by a network of capillaries, which allows for the efficient diffusion of oxygen into the blood and the removal of carbon dioxide from it.

When we inhale, air enters the alveoli, where the oxygen in the air passes through the alveolar wall and enters the bloodstream, binding to hemoglobin in red blood cells. Simultaneously, carbon dioxide, which is a waste product produced by metabolism, moves from the blood into the alveoli to be exhaled. This process is vital for maintaining the body's acid-base balance and supplying tissues with the oxygen they need for cellular respiration.

The other options refer to functions that do not take place in the lungs. Mixing food with digestive enzymes and storing bile pertain to digestive processes, while filtering impurities from the air is a job primarily done by the upper respiratory tract rather than the alveoli themselves.