Breathing!

So, I get that your body needs oxygen. But why?

Also, I know that there are other elements (nitrogen is one I think...) in the air that we take in, do we need those?

Oh man, I sooo learned this back in high school in AP Bio... let's see if I can remember...

Gah! I can't. I had to look it up.

The hemoglobin in the blood stream is made to absorb oxygen which is picked up in the lungs, and through the blood stream it is carried to all the cells, where oxygen is required in the process of controlled burning of nutrients inside the cell which supplies us with energy.

Therefore, oxygen is necessary.

The body only extracts oxygen from the air, that we breathe.
It is taken into the lungs, where it is filtered by the alveoli and then absorbed into the blood capillaries in lung tissue. Where the oxygen fuses with the hemoglobin in your blood.

Woop

Cooool. Thanks!

But what about all the other stuff in the air? Like Nitrogen. Do we use that stuff?

My advice is to Google "respiratory system." You'll get more information than you know what to do with.

No, we only need the oxygen. We don't use any of the nitrogen, and we actually breathe out more carbon dioxide than we breathe in.