What is the site of oxygen and carbon dioxide exchange with the blood?

The respiratory zone is the correct answer because it is specifically designed for the exchange of gases—oxygen and carbon dioxide—between the air and the bloodstream. This zone includes structures such as the alveoli, which are tiny air sacs surrounded by capillaries. It is here that the process of diffusion occurs, allowing oxygen to enter the blood and carbon dioxide to be expelled from the blood into the lungs.

The conducting zone, on the other hand, consists of the airways that serve primarily to transport air to the respiratory zone but do not participate in gas exchange. The diffusion zone, while it reflects the mechanism of gas exchange, is not a commonly used term in respiratory physiology specifically. The alveolar zone could be seen as an aspect of the respiratory zone but is not recognized as the main term for the entire area where exchange happens. Thus, the respiratory zone encompasses all the necessary components for efficient gas exchange.