So how do they do it? Trees convert carbon dioxide into oxygen through a process called photosynthesis. Photosythesis means “to put together with light.” The light is sunlight, shining on the tree, and the pieces being put together are carbon dioxide and water. When a tree has these three ingredients it uses the energy from the sunlight to combine the carbon from the carbon dioxide with the water to make a carbohydrate, or more simply, a sugar. The sugar is food for the tree, just as people eat sugar and carbohydrates. When the tree makes the carbohydrate, there is extra oxygen from the water, which luckily for us gets released into the air, giving us the oxygen we breathe.