Humans breathe in oxygen to survive. Oxygen is essential for cellular respiration, a process where cells convert glucose and oxygen into energy, carbon dioxide, and water. The air we breathe is composed of about 21% oxygen, which we inhale through our lungs. Once in the bloodstream, oxygen is transported to cells throughout the body to provide the energy needed for various bodily functions. Importantly, the process of respiration also involves exhaling carbon dioxide, a waste product of metabolism. The respiratory system, composed of the lungs, airways, and diaphragm, plays a crucial role in this essential life-sustaining process.