The carbon dioxide and oxygen cycles work through processes that convert carbon in the atmosphere into oxygen and transform oxygen back into carbon dioxide. Plants are the main producers of oxygen through a process called photosynthesis. They use carbon dioxide and sunlight to produce energy and release oxygen into the atmosphere.
The oxygen cycle and carbon cycle are closely interconnected. After plants release carbon dioxide into the air, humans and animals take in the oxygen and breathe out carbon dioxide. Plants use the carbon dioxide again, repeating the cycle.
The processes that use oxygen are breathing, decomposing, rusting and combustion. Breathing, or respiration, enables humans and animals to use oxygen when inhaling and transform oxygen into carbon dioxide upon breathing out. Decomposing is another process that uses up oxygen and releases carbon dioxide. Decomposers, such as microbes and fungi, digest waste carbon-based material from animals. They also respire and give off carbon dioxide into the air. Rusting, also called oxidation, involves the use of oxygen when something rusts. In combustion, oxygen, fuel and heat are necessary to create fire.
The major process that produces oxygen is photosynthesis, which is used by plants to produce food and energy. Plants are responsible for creating the majority of oxygen that humans and animals need. Through the oxygen and carbon cycles, the amount of available oxygen and carbon in the atmosphere is balanced.