What function do the alveoli serve in the respiratory system?

The alveoli play a crucial role in the respiratory system as the sites of gas exchange. These tiny, balloon-like structures are located at the end of the bronchioles and provide a vast surface area for oxygen and carbon dioxide to be exchanged between the air we inhale and the blood in the surrounding capillaries.

When fresh air enters the lungs, it reaches the alveoli where oxygen diffuses through the thin alveolar walls and into the bloodstream. Simultaneously, carbon dioxide, which is a waste product of cellular metabolism, moves from the blood into the alveoli to be exhaled. This exchange is essential for maintaining the body's respiratory needs and overall metabolic function.

In contrast to the correct answer, the other choices do not accurately describe the function of the alveoli. Hemoglobin production occurs in red blood cells, not in the alveoli. The transportation of oxygen throughout the body is primarily the function of the circulatory system, where hemoglobin in red blood cells carries oxygen from the lungs to various tissues. Filtration of incoming air is mainly performed by the nasal passages and the upper respiratory tract, which help trap dust, microbes, and other particles before they reach the alveoli.