Question

why do we breathe oxygen and not other gases?

Answer 1

Basically when air fills our alveoli, by the process of diffusion, only oxygenin the air is taken into the blood stream while the other gases along with the waste CO2 is exhaled. So you do breathe in nitrogen, but it is exhaled as it is by the body......

We breathe because oxygen is needed to burn the fuel [sugars and fatty acids] in our cells to produce energy. Oxygen is brought into the lungs via breathing, where it is transported by red blood cells to the entire body to be used to produce energy.

Answer 2

Hope this was helpful