why we breathe oxygen and not something like carbon dioxide or nitrogen?

Question

why we breathe oxygen and not something like carbon dioxide or nitrogen?

In: 40

Answer 1

We don’t breathe carbon dioxide because we evolved well after the CO2 was depleted from the environment, so there really isn’t much in the air to work with.

We don’t breathe nitrogen because nitrogen is extremely stable, and you’d have to put in a large amount of energy to get it to do anything that might be useful for biological life.