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 drive oxygen into the bloodstream and remove carbon dioxide from it. This process occurs primarily in the lungs, where inhaled oxygen passes through the alveoli and into the blood, while carbon dioxide is expelled from the blood and then exhaled. This gas exchange is crucial for maintaining the body's metabolism and overall cellular function, as oxygen is essential for energy production in cells, and the removal of carbon dioxide is necessary to prevent toxic buildup.

The other functions mentioned, such as digesting food, circulating blood, and regulating body temperature, are associated with different bodily systems. The digestive system is responsible for processing food, the circulatory system handles blood circulation, and thermoregulation is primarily managed by the integumentary system, among other mechanisms. Thus, the choice correctly identifies the specific role of the respiratory system in the context of overall bodily functions.