Final answer:
The alveoli are the structures capable of gas exchange in the lungs. They are part of the respiratory zone and are where oxygen and carbon dioxide are exchanged between the lungs and the blood.
Step-by-step explanation:
The structure that can undergo gas exchange is the alveoli. The alveoli are thin-walled structures that are in direct contact with the capillaries, allowing oxygen to diffuse into the blood and carbon dioxide to diffuse out of the blood to be exhaled. The respiratory zone, which includes the alveoli, begins where the terminal bronchioles join a respiratory bronchiole, leading to an alveolar duct and opening into a cluster of alveoli that facilitate this gas exchange.
The main bronchus, trachea, and terminal bronchioles are part of the conducting zone of the respiratory system, which merely transports air to the regions of gas exchange but does not participate in the exchange itself. Gas exchange does not occur in the bronchi or bronchioles. The structure and function of the respiratory and circulatory systems are closely related to optimize the diffusion of gases.