Humans exhale carbon dioxide (CO2) after breathing in oxygen. During the process of respiration, oxygen is utilized by the cells in the body for metabolic functions, producing energy. As a byproduct of this process, carbon dioxide is generated. The circulatory system transports this CO2 back to the lungs, where it is expelled from the body during exhalation. This gas exchange is crucial for maintaining the body's pH balance and overall respiratory health. Understanding the mechanics of breathing is important for recognizing how our bodies utilize air efficiently.