Oxygen Cycle

Oxygen is another essential element for living organisms. It is present in large quantities (20.95% v/v) in the atmosphere and is also seen in bound state in water and as oxides and carbonates in rocks.

Dissolved oxygen in water is the source of oxygen for aquatic organisms.

Oxygen in the Ozone layer (O₃) of the outer stratosphere of the atmosphere protects life from ionizing short wave radiations (ultraviolet radiations).

Reservoir of oxygen is the atmosphere (21% of air). Oxygen also occurs in combined state as carbon dioxide and water.

Oxygen Utilisation

a) Oxygen in the atmosphere is in a state of 'dynamic equilibrium'. Plants and animals take in oxygen for respiration.

b) During respiration, oxidation of carbohydrates and other fuels form carbon dioxide and water. Thus, during respiration oxygen enters the living world in free state and is released in combined state.

c) Oxygen is also used in combustion of wood, oxides of nitrogen etc.

d) Oxygen (in combined state) is utilised by plants as carbon dioxide and water during photosynthesis.

e) Microbial oxidation produce varieties of oxides utilising atmospheric oxygen.

Oxygen Production

1) Oxygen is mainly produced during photolysis of water in the light phase of photosynthesis during which molecular oxygen is released into the atmosphere for reuse in respiration.

2) Oxygen is made available to the environment in combination with carbon in the form of carbon dioxide (by decay of dead organic matter) and with hydrogen as water.

Significance of Oxygen

Oxygen is the element, which is essential for the life survival system i.e., respiration.

Molecular oxygen (O₂) combines with atomic oxygen (O) to produce ozone (O₃) layer in the atmosphere, which screens off most of the ultraviolet rays entering the earth's atmosphere from outer space.