Oxygen is the essential element for breathing in humans. It is a colorless, odorless gas that constitutes approximately 21% of the Earth's atmosphere. Humans and many other organisms rely on oxygen for cellular respiration, a biochemical process that converts glucose and oxygen into energy. This energy is critical for sustaining life, supporting functions such as movement, growth, and metabolism. Oxygen is absorbed through the lungs during inhalation and transported by red blood cells to tissues and organs throughout the body. The importance of oxygen emphasizes the need for a healthy environment and clean air to maintain human health.