Oxygen Cycle

Almost all living things need oxygen.  They use this oxygen during the process of creating energy in living cells.  




Just as water moves from the sky to the earth and back in the hydrologic cycle, oxygen is also cycled through the environment.  Plants mark the beginning of the oxygen cycle.  Plants are able to use the energy of sunlight to convert carbon dioxide and water into carbohydrates and oxygen in a process called photosynthesis.
 

 

Animals form the other half of the oxygen cycle.  We breathe in oxygen which we use to break carbohydrates down into energy in a process called respiration.