Which process occurs in the alveoli during respiration?

During respiration, the primary process that occurs in the alveoli is the exchange of oxygen and carbon dioxide, which is essential for gas exchange in the lungs. The alveoli are tiny air sacs where this exchange occurs due to the difference in partial pressures of the gases in the air and the blood.

When fresh oxygen-rich air is inhaled, it travels into the alveoli, where the oxygen diffuses through the alveolar walls into the bloodstream. Simultaneously, carbon dioxide, which is produced by cells during metabolism and carried in the bloodstream, diffuses from the blood into the alveoli to be exhaled. This process ensures that the body receives the oxygen it needs for cellular processes while removing carbon dioxide, a waste product of metabolism.

The other processes mentioned do not occur in the alveoli. For example, filtration of blood takes place in the kidneys, not in the alveoli; dissolution of carbon dioxide might occur in the context of blood chemistry but isn't the primary function of the alveoli; and the absorption of nutrients occurs in the gastrointestinal tract rather than in the lungs. Therefore, the correct answer highlights the crucial role of the alveoli in facilitating vital gas exchange during respiration.