Question

we intake oxygen but how can do we expell carbon dioxide

Answer 1

hi
hope this helps
actually it's not that we intake only Oxygen. We intake Oxygen along with carbon dioxide. But in our boat carbon dioxide remains infused while the Oxygen is used. Therefore the unused Carbon dioxide comes out and the Oxygen remains in our body

Answer 2

tress and plants give off carbondioxide when they breath,and when they die and rot.we breath in oxygen and some of this carbondioxide.when we exhale,we breath out less oxygen but more carbondioxide we inhale