Question

Question #768bc

Answer 1

To exchange `CO_2` and `O_2` between the blood stream and the air as efficiently as possible.

Explanation:

If we burn glucose in our cells, which we do a lot, `CO_2` is released. This excess of carbon dioxide is not needed and therefore we have to get rid of it. This is the mean reason why we breath. The concentration `CO_2` triggers us directly to breathe, not the need of oxygen.
The mechanism of oxygen is not directly influencing the frequency of breathing, but indirectly.

To make this exchange as efficient as possible, we have these lungs that have a very big exchange area (50 to 75 `m^2`).