A tree breathes through its leaves using chlorophyll, the substance that makes leaves green. Chlorophyll absorbs the carbon dioxide in the air and uses it alongside water to break down minerals absorbed through the tree's roots. The leaves then release water vapor and oxygen.
The process a tree uses to breathe is called photosynthesis. Photosynthesis is the process that converts energy from light sources into organic chemical energies such as sugar. The leaves absorb the light energy and use it to convert carbon dioxide and water minerals into oxygen and carbohydrates. The oxygen releases into the atmosphere, where it benefits all life on the planet.
Respiration, the opposite of photosynthesis, is another part of the breathing process. It occurs constantly in the tree's cells. Respiration uses up stored oxygen and releases carbon dioxide, energy and water into the atmosphere. While trees do not technically breathe, respiration is comparable to inhaling air into the lungs, and photosynthesis is comparable to exhaling. Even though respiration does not directly benefit the environment, trees still absorb far more harmful carbon dioxide than they release, thanks to the process of photosynthesis. A medium-sized tree releases the same amount of air required for a human being to breathe.