What is the primary function of the respiratory system?

The primary function of the respiratory system is to exchange gases, specifically oxygen and carbon dioxide, between the body and the environment. This process is vital for maintaining cellular respiration, where cells utilize oxygen to produce energy and generate carbon dioxide as a waste product. The respiratory system, comprising organs such as the lungs, trachea, and diaphragm, facilitates the inhalation of oxygen-rich air and the exhalation of carbon dioxide. This gas exchange occurs in the alveoli, tiny air sacs in the lungs where oxygen diffuses into the bloodstream and carbon dioxide is removed.

The other options are functions of different bodily systems. Circulating blood pertains to the cardiovascular system, which is responsible for transporting nutrients, gases, hormones, and waste products throughout the body. Ingesting food is a function of the digestive system, which handles the processing and absorption of nutrients necessary for energy and growth. Synthesizing hormones is primarily a function of the endocrine system, which regulates various physiological processes through hormones.

Thus, the correct answer emphasizes the unique role of the respiratory system in gas exchange, a critical process for sustaining life.