Solution: The alveoli present in the lungs are small air sacs that allow the fast exchange of gases. The alveolar membrane has a total thickness of less than a millimeter, and the outside surface of the membrane is in close proximity to the blood capillary connection.

A fine basement material distinguishes the endothelial membrane of blood capillaries and the alveolar membrane. The gases can easily diffuse through this thin barrier. The gas-diffusion is aided by higher levels of partial pressure of oxygen () and lower levels of partial pressure of carbon dioxide () in alveolar air that comes close to the blood capillaries. All of these structural advantages seen in alveoli are not found in any other respiratory system structure. As a result, the gas diffusion phenomenon occurs exclusively in the alveolar region and not elsewhere.