The carbon-oxygen cycles are actually two independent cycles. However, both these cycles are interconnected as well as interdependent on each other to some extent. There are four processes involved in the completion of the carbon-oxygen cycle. Oxygen-carbon cycle processes are:
Plants undergo photosynthesis that helps them produce energy and food for themselves. During photosynthesis, plants take in carbon dioxide (CO2) and absorb water (H2O) with the help of their roots. The chlorophyll present in the leaves and the energy from the sun, helps convert CO2 and H2O into O2, sugar and water vapor.
Oxygen (O2) is released by the plants as bi-product into the atmosphere.
Just as plants carry out photosynthesis, animals carry out respiration. Respiration occurs when animals take in oxygen from the air along with simple sugars from their food. This helps in release of carbon dioxide, water and energy from the animal body. During cellular respiration, animals require O2 during inhalation. When they exhale the waste product of cellular respiration, they release CO2 into the atmosphere again.
Combustion is a process of burning that occurs naturally in the nature. For example, volcanic eruptions are natural combustion processes where carbon dioxide is released into the atmosphere due to burning.
After the death of any living organism, that is, unicellular or multicellular organism, it is decomposed. This decomposition means insects, fungi and bacteria, together called decomposers, help in breaking down the cellular components of the dead organism into its basic elements. These elements include water, calcium, nitrogen, carbon and oxygen. Thus, decomposers help in release of oxygen and carbon dioxide back into the atmosphere as their metabolic waste products.