Oxygen is the element essential for human respiration. It is a crucial component of the air we breathe, making up about 21% of Earth's atmosphere. During respiration, oxygen is taken in by the lungs and transported via red blood cells to body tissues, where it is used for the process of cellular respiration. This process converts glucose and oxygen into carbon dioxide, water, and energy (ATP), which is vital for bodily functions. Without adequate oxygen, cells cannot produce the energy needed for survival, leading to significant health issues or even death.