Air is a mixture of all gases.... our lungs breathe in exclusively the oxygen..how this wonder happens?
We breathe in all the elements that are found in air, but our lungs only actually process and use the oxygen
The hemoglobin in our blood stream is designed to attach to oxygen molecules. Although other molecules, such as carbon monoxide, can attach themselves as well.
Plants take in Carbon dioxide and breathe out oxygen for humans to take in while we breathe out carbon dioxide for the plants. That is just one of the wonders of God
Both nitrogen and oxygen will dissolve in blood, but hemoglobin will actively bind to oxygen so our blood preferentially extracts oxygen from the air we breathe in.