what plants do for us

     We need the plants, and it could be that they need us. People and other mammals breathe in the air, use the oxygen, and breathe out carbon dioxide. Plants "breathe in" carbon dioxide and breathe out oxygen. This is usually called "plant respiration"--the same thing it is called in people, although plants do not have lungs, and don't breathe the way we do. In a world with no plants at all, we might use up all the oxygen, and we wouldn't be able to breathe.