Question

We breathe out carbon dioxide......

But where did this come from.....

Answer 1

we don't only breath out carbon dioxide but we also breath it in but carbon dioxide is released by the cell while making energy which with blood reaches the lungs and we breath it out

Answer 2

its is the cellualar waste... it does not come from anywhere it is present in the air whn we take it in....just whn we exhale the content of oxygen becomes less....
we dont exhale carbon dioxide.....we just exhale oxygen less air