In which part of the lung do diffusion processes occur for oxygen and carbon dioxide?

Diffusion processes for oxygen and carbon dioxide primarily occur in the alveoli of the lungs. The alveoli are tiny air sacs where the exchange of gases takes place. They have a large surface area and are lined with thin walls consisting of a single layer of cells, which facilitates the rapid diffusion of gases.

In the alveoli, oxygen diffuses from the air inside the sacs into the blood in the surrounding capillaries, while carbon dioxide diffuses from the blood into the alveolar air to be exhaled. This process is driven by differences in partial pressures of the gases, ensuring that oxygen moves into the bloodstream where it is needed and that carbon dioxide, a waste product of metabolism, is expelled from the body.

The other options do not serve the same function in gas exchange. The bronchi are the air passages that lead from the trachea to the lungs but do not participate directly in the diffusion of gases. The trachea is the windpipe that carries air into the bronchi, while the term "lungs" is too broad since the actual gas exchange occurs specifically in the alveoli.