Question

why do we breath oxygen insted of caarbondioxid

Answer 1

Answer:

because oxygen is needed for breaking down of that food from starch into simple food forms which is needed for the cells for their development.

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Answer 2

Answer:    Basically when air fills our alveoli, by the process of diffusion, only oxygen in the air is taken into the blood stream while the other gases along with the waste CO2 is exhaled. So you do breathe in nitrogen, but it is exhaled as it is by the body.

Explanation:

When we exhale, we breathe out less oxygen but more carbon dioxide than we inhale. The carbon we breathe out as carbon dioxide comes from the carbon in the food we eat. ... The glucose molecule is then combined with oxygen in the cells of the body in a chemical reaction called "cellular oxidation".∞∞