What is respiration?

Respiration is best described as the exchange of oxygen and carbon dioxide. This process occurs in two primary locations within the body: the lungs and the cells. In the lungs, oxygen is inhaled and exchanged for carbon dioxide, which is then exhaled. This exchange is crucial for maintaining the body's oxygen supply and removing carbon dioxide, a waste product of cellular metabolism.

Furthermore, respiration encompasses both external respiration, which involves the lungs, and internal respiration, which occurs at the cellular level. During internal respiration, cells utilize oxygen to produce energy and release carbon dioxide as a byproduct, thus reinforcing the importance of the oxygen-carbon dioxide exchange.

In contrast, while the physical act of breathing is a component of this process, it does not capture the entire scope of respiration. Loading oxygen onto hemoglobin is a specific step within respiration, and cellular metabolism refers to biochemical processes that occur within cells, which are separate from the gas exchange process. Thus, option C encompasses the full definition of respiration, focusing on the essential exchange of gases crucial for sustaining life.