Plants need air to breathe. They give off oxygen and take in carbon dioxide - which is a very useful trick since people need the oxygen to breathe too. Of course, when plants live in the open air, the oxygen they expel simply joins the other gasses and elements - they have a "zen moment" with the atmosphere, if you know what I mean! In exchange for the relief of getting rid of that oxygen, plants take in carbon dioxide and that's plentiful because animals and other breathing things expel or exhale that carbon dioxide. But, what if a plant can't give and take these things in constant fresh supply? Put the plant in a plastic bag, and watch what happens!
