Most people think we just breathe in oxygen and breathe out carbon dioxide. Not true. Most of the air we breathe in (78%) is nitrogen and we just breathe it all out again. It does nothing for us, but it is useful for some plants.

We only breathe in 21 % oxygen. We don’t use all of this up because we breathe out 16 % oxygen.

We breathe in a tiny % of carbon dioxide (0.03 %), but what we breathe out (4%) is over a hundred times bigger.