Importance of oxygen in air
    Oxygen is required for various process :
    (i) Combustion : The process of burning of fuel in air with release of energy in the form of heat and light.
    (ii) Respiration : a form of combustion in which oxygen reacts with food to release energy.
    (iii) Rusting : the corrosion of iron when exposed to air (oxygen) and moisture (water).

Importance of Carbon dioxide in Air
Carbon dioxide plays a vital role in living beings through Photosynthesis.
Photosynthesis : The process by which plants make their own food (glucose) using carbon dioxide and water in the presence of sunlight and chlorophyll, and release oxygen.

Note : Aquatic plants use carbon dioxide dissolved in water for photosynthesis.

Importance of water vapour in air

    The amount of water vapor present in air is called humidity. In absence of water vapor
    •    plant leaves become dry and crumble
    •    animals can get dehydrated
    Excess water vapor can cause discomfort, heat becomes severe even though the temperatures are not very high.

How Does Oxygen Become Available to Animals and Plants Living in Water and Soil?

In Plants:

Plants have tiny pores called stomata, found on the underside of a leaf.

Air containing carbon dioxide and oxygen enters the plant through these openings where it gets used in photosynthesis and respiration.

In Animals:

All animals need to respire, be it a cockroach, a fish, or an elephant. It is just that they use different organs and mechanisms for respiration.

In Aquatic Animals and Plants:

Most aquatic animals like fish, tadpoles, crabs, and shrimp have special organs for respiration called gills. Gills help to take in oxygen and give out carbon dioxide. Some aquatic animals like dolphins and whales come to the surface of the water regularly to take in air, since they breathe with the help of the lungs. Aquatic plants like Hydrilla also breathe in oxygen dissolved in water through their stomata.

In Amphibians:

Amphibians like frogs, newts, and salamanders need breathing systems for both air and water. Crocodiles and alligators swim through the water with part of their snout above the water surface to breathe easily through nostrils.

In Birds:

Birds have an efficient respiratory system as they need high levels of oxygen during flight. Birds have a pair of lungs with air sacs that remain open all the time so that air can easily pass through them.

In Mammals:

Most mammals breathe with the help of lungs. They take in oxygen and give out carbon dioxide.

Balance of Oxygen in the Atmosphere

It is common knowledge that humans and animals can’t survive without plants because they produce oxygen via photosynthesis. The balance of oxygen in the environment is thus maintained through the respiratory processes of plants and animals.

The importance of Air

Air has a number of uses:

  • The air which is in motion is known as wind. The wind is important for the rotation of windmills which help in drawing water from tube wells.
  • They also help in running flour mills.
  • Windmills are also used to produce electricity.
  • Insects and birds are only able to fly because of the presence of air
  • Boats, yachts, aeroplanes and parachutes also need air to sail and glide
  • Air has a very important role to play in the water cycle as well.

Figure 5 A windmill in action

  • It also helps in distributing the pollen and seeds from flowers of various plants.

Figure 6 Air helps birds and insects fly