What gas do humans breathe to survive?

Humans breathe oxygen to survive because it is essential for cellular respiration, a process that occurs in the cells to produce energy. During respiration, oxygen is used to metabolize glucose, releasing energy in the form of adenosine triphosphate (ATP), which powers various bodily functions.

Oxygen is transported by the bloodstream to all body tissues, where it is used to generate energy. Additionally, oxygen is crucial for the proper functioning of organs and tissues, allowing for growth, repair, and maintenance of bodily functions.

The other gases listed do not fulfill the same role as oxygen. For instance, nitrogen, while making up a significant portion of the atmosphere, is not directly used by the human body for energy production. Carbon dioxide is a byproduct of respiration; while it is necessary for maintaining the pH balance in the body and facilitating gas exchange, it does not support life like oxygen does. Hydrogen is not a gas that humans breathe; rather, it is found in water and organic compounds, playing roles in biochemical processes but not serving as a primary source of energy.