What gas supports life by being essential for respiration in the human body?

Oxygen is essential for respiration in the human body because it is the primary gas that is utilized by cells to produce energy through the process of aerobic respiration. When we inhale, oxygen enters the lungs, diffuses into the bloodstream, and is transported to cells throughout the body, where it is used to help convert glucose and other nutrients into adenosine triphosphate (ATP)—the energy currency of the cell. This process also produces carbon dioxide as a byproduct, which the body then expels through exhalation.

While nitrogen is abundant in the atmosphere and plays a role in various biological processes, it does not directly support life in terms of respiration. Similarly, hydrogen and carbon dioxide have their own roles in biological and physiological functions, but they are not utilized in the same fundamental way that oxygen is vital for sustaining life through respiration. Therefore, oxygen is uniquely indispensable for life as we know it.