Answer:
Breathing – It is the physical process, through which all living organisms, including plants, animals and humans inhale oxygen from the outside environment into the cells of an organism and exhale carbon dioxide back into the atmosphere.
Decomposition: It is one of the natural and most important processes in the oxygen cycle and occurs when an organism dies. The dead animal or plants decay into the ground, and the organic matter along with the carbon, oxygen, water and other components are returned into the soil and air. This process is carried out by the invertebrates, including fungi, bacteria and some insects which are collectively called as the decomposers. The entire process requires oxygen and releases carbon dioxide.
Combustion: It is also one of the most important processes which occur when any of the organic materials, including fossil fuels, plastics and wood, are burned in the presence of oxygen and releases carbon dioxide into the atmosphere.
Rusting: This process also requires oxygen. It is the formation of oxides which is also called oxidation. In this process, metals like iron or alloy rust when they are exposed to moisture and oxygen for an extended period of time and new compounds of oxides are formed by the combination of oxygen with the metal.
Explanation: The Stages
Stage-1: All green plants during the process of photosynthesis, release oxygen back into the atmosphere as a by-product.
Stage-2: All aerobic organisms use free oxygen for respiration.
Stage-3: Animals exhale Carbon dioxide back into the atmosphere which is again used by the plants during photosynthesis. Now oxygen is balanced within the atmosphere.
