Question

What is the source of oxygen?

Answer 1

Hint: Oxygen is one of the most abundant element present in the body of a living organism. It is important for the oxidation of food both in plants and animals and to release energy. It is present in a substantial amount in the atmosphere as well as present in water.

Complete answer:
Oxygen is the second abundant element that is present in the atmosphere. The atmosphere contains around 21% of the oxygen. The major sources of oxygen for the living organisms are-
Water- Maximum amount of oxygen is supplied by the water. The water is made up of two components hydrogen and oxygen. The water contains hydrogen: oxygen in the ratio of 2:1. This oxygen is utilised by the plants through the photolysis of the water. The photolysis of water provides oxygen to plants for carrying out their physiological process. The flora and fauna present in the water utilise the dissolved oxygen for their living.
Through plants- The plants are one of the chief sources of oxygen. The plants carry out photosynthesis in which they take in carbon dioxide from the air and liberate oxygen. This oxygen is liberated freely into the atmosphere which unlike nitrogen can be easily utilised by living beings.
The decomposers decompose the organic matter which along with carbon and nitrogen contains oxygen. This oxygen is left as the by-product in the lithosphere. All these sources help in stabilising a constant oxygen supply irrespective of utilisation.

Note: The circulation of the oxygen within the lithosphere, hydrosphere and biosphere is known as the oxygen cycle. The organisms which utilise oxygen for respiration are known as aerobic organisms. Oxygen along with respiration is important for combustion.