Gas exchange occurs in which of the following tissues?

Gas exchange primarily occurs in the capillaries due to their unique structure and function within the circulatory system. Capillaries are the smallest blood vessels and have walls that are only one cell thick, allowing for efficient diffusion of gases such as oxygen and carbon dioxide between the blood and surrounding tissues.

In the capillary network, oxygen from the blood diffuses into the tissues while carbon dioxide, a waste product of metabolism, diffuses from the tissues into the blood. This process is facilitated by the large surface area and extensive branching of capillaries, which enhance the ability of the blood to pick up oxygen and release carbon dioxide.

While veins and arteries play crucial roles in transporting blood throughout the body, they do not engage in gas exchange themselves. Veins return deoxygenated blood to the heart, and arteries carry oxygen-rich blood away from the heart to the tissues. The skin can also participate in gas exchange in certain organisms (like amphibians), but in humans, it is primarily the capillaries within the lungs and body tissues where gas exchange occurs effectively. Therefore, capillaries are the correct choice for the site of gas exchange.