Which process primarily happens in the lungs during gas exchange?

The process that primarily happens in the lungs during gas exchange is diffusion. This occurs when oxygen from the air in the alveoli (tiny air sacs in the lungs) moves into the bloodstream, while carbon dioxide, which is a waste product produced by the body's cells, moves from the blood into the alveoli to be exhaled.

Diffusion is a key process in gas exchange because it relies on the concentration gradient; oxygen is in higher concentration in the alveoli compared to the blood, prompting it to move into the blood. Conversely, carbon dioxide is in higher concentration in the blood than in the alveoli, causing it to diffuse out into the alveoli. This movement continues until equilibrium is reached, facilitating efficient gas exchange that is essential for respiration and maintaining the body's metabolic processes.

The other processes listed, such as osmosis, filtration, and evaporation, are not primarily related to gas exchange in the lungs. Osmosis pertains to the movement of water across semi-permeable membranes, filtration involves the separation of solids from fluids, and evaporation refers to the transition of a substance from liquid to gas. Therefore, diffusion is the accurate description of how gases are exchanged in the lungs.