What is the primary function of the process known as internal respiration?

Internal respiration refers specifically to the process of gas exchange that occurs at the cellular level, where oxygen is delivered from the blood to the cells and carbon dioxide, a metabolic waste product, is returned to the blood from the cells. This process primarily happens in the capillaries surrounding the tissues throughout the body, allowing for the exchange of gases between the systemic capillaries and the individual cells.

In contrast, other options do not align with the definition of internal respiration. Gas exchange between cells and atmospheric air pertains to external respiration, which involves the lungs and the environment. The breakdown of glucose is related to cellular metabolism but is not directly tied to the concept of respiration. Lastly, the exchange of gases in the lungs also characterizes external respiration, focusing on the transfer of gases between the atmosphere and the bloodstream. Hence, the primary function of internal respiration is accurately represented in the correct answer, emphasizing the exchange between the systemic capillaries and the cells.