Answer the questions put against each of the following constituents of air:

(a) Nitrogen : Explain its significance for plants and animals.

(b) Oxygen : What is the percentage proportion of oxygen in air? Why is oxygen called active air?

(c) Carbon dioxide : "Although carbon dioxide plays no role in respiration, all life would come to an end if there is no carbon dioxide in air." Support this statement with relevant facts.

(d) Water vapour : Explain its role in modifying the earth's climate.

(a) Nitrogen provides a vital nutrient protein to all living beings i.e. plants and animals essential for their growth and development. Plants convert nitrogen into proteins while human beings and animals get it from plants.

(b) Oxygen constitute about 21% of air by volume. Oxygen is called active air because it supports combustion and life.

(c) "Although carbon dioxide plays no role in respiration, all life would come to an end if there is no carbon dioxide in air." This statement is justified by following two facts:

1. Carbon dioxide is essential for photosynthesis process as green plants required it to prepare food and all other animals including human beings depends upon plants for food.
2. It minimizes heat loss by radiation by reflecting heat back to earth's surface particularly at night thus balances the temperature of earth.

(d) The presence of water vapour in air causes rain. At low temperatures water vapour condenses to form snow, sleet, mist, frost, hail, dew, fog, etc. In this way water vapour plays an important role in modifying earth's climate.