The chemical element essential for respiration in humans is oxygen, with the symbol O and atomic number 8. Oxygen is a vital component of the air we breathe, making up about 21% of the Earth's atmosphere. During respiration, humans inhale oxygen, which is transported by red blood cells to cells throughout the body. Oxygen is crucial for cellular respiration, a process that converts glucose into energy, enabling all biochemical functions necessary for survival. Lack of oxygen can lead to serious health issues, as the human body and brain are highly dependent on a constant supply of oxygen to function effectively.