What is the primary function of the respiratory system?

The primary function of the respiratory system is to facilitate the exchange of gases—specifically, to take in oxygen from the air and expel carbon dioxide from the body. This process occurs in the lungs, where oxygen is absorbed into the bloodstream and transported to cells throughout the body. The cells then utilize this oxygen in a process called cellular respiration, which is how they release energy from nutrients. Thus, the respiratory system plays a pivotal role in using air not just for gas exchange but also for enabling energy production at the cellular level.

In contrast, the other options focus on unrelated physiological functions. The function of processing food and eliminating waste pertains to the digestive system, while controlling blood sugar levels is primarily associated with the endocrine system, especially involving hormones like insulin. Supporting bone movement is a function of the muscular and skeletal systems, which work together to enable locomotion and physical activity.