Page 5 - 2. Lesson notes- Bio- geo chemical cycles-2

The four main processes that use Atmospheric oxygen are:

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 back
into the soil and air.

Combustion:- 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:- 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.