Which gas do living beings need to breathe?

Living beings require oxygen to breathe because it is essential for the process of cellular respiration, which occurs in the cells of most organisms. During cellular respiration, oxygen is utilized to convert glucose into energy, a process that releases carbon dioxide as a byproduct. This energy is crucial for various biological functions, including growth, reproduction, and maintaining bodily processes.

Although other gases like carbon dioxide, nitrogen, and helium are present in the atmosphere, they do not serve the same fundamental purpose as oxygen in regard to respiration. Carbon dioxide is actually a waste product of respiration that organisms need to expel. Nitrogen, while abundant in the air, is inert and cannot be used by the body for respiration. Helium, being a noble gas, does not participate in any biological processes that involve respiration. Therefore, oxygen is the only gas among those listed that is necessary for living beings to breathe and sustain life.