Biology (NTSE/Olympiad)  

6. Natural Resources

The Health of Lift - Air

The Health of Lift - Air
Air is a mixture of gases which is odourless, tasteless & invisible. Air also holds water vapour & dust particles.
Atmosphere :
The envelop of air that surrounds the earth is called Atmosphere.
Role of atmosphere in climate control :
Air is a bad conductor of heat. It act as a protective blanket for the living organisms to exist in the following way -
Atmosphere prevent the sudden increase in temperature during the day hours. During night it slow down the escape of heat into the outer space. Thereby preventing excessive cooling during night.
The ozone shield of atmosphere absorb most of the harmful UV radiations coming from the sun. The excessive heat & sun rays are reffected back into the outer space by dust particles.
Movement of Air :
Heating of air occur due to reradiation of solar radiations by the land & water bodies. In fact, when the solar radiation fall on the earth, some are absorbed & majority of these are reflected back or reradiated by the land & water bodies. These solar radiations heat up the atmosphere from below. As a result, convection currents are set up in the air. But since the land gets heated faster than the water, the air over land also gets heated faster than the air over water bodies. Hot air on land rises upwards thereby producing an area of the low air pressure. Air from region of high pressure will move towards this region of low pressure producing breez or wind.
Rain :
The air carrying water vapour also get heated. This hot air rises up in the atmosphere carrying water vapour with it. As the air rises. it expands & cool. This cooling cause the water vapour to condense in the form of tiny droplets. Suspended particles of dust & other materials act as nuclei to facilitate the process of condensation of water around them. A collection of tiny droplets of water appear in the form of ‘clouds’. These droplets of water slowly grown bigger by the condensation of more water droplets.
When the droplets have grown big & heavy they fall down in the form of ‘rain’.


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