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What are the main resources on the earth?

The main resources on the earth are the land, the water and the air.

Lithosphere The outer crust of the Earth.  Hydrosphere. Water covers 75% of the Earth’s surface. It is also found underground.  Atmosphere These comprise the air that covers the whole of the Earth like a blanket.  Biosphere The life-supporting zone of the Earth where the atmosphere, the hydrosphere and the lithosphere interact and make life possible is known as the biosphere.


Mention the main sources of Carbon dioxide?
A break down of glucose molecules to get energy for life activities results in the production of carbon dioxide.

Another process that results in the consumption of oxygen and the concomitant production of carbon dioxide is combustion.

Forest fire also produce carbon dioxide.


How is water vapour formed?

Water vapour is formed due to the heating of water bodies and the activities of living organisms.


What are the factors, which lead to the formation of wind?

The factors which help in the formation of wind are as follows

The air above the land gets heated faster and starts rising. As this air rises, a region of low pressure is created and air over the sea moves into this area of low pressure. The movement of air from one region to the other creates winds.


The rotation of the Earth helps in the formation of wind. The presence of mountain ranges also helps in wind formation and also in changing the direction of wind.


Explain the process in the formation of rain?

When water bodies are heated during the day, a large amount of water evaporates and goes into the air. Some amount of water vapour also gets into the atmosphere because of various biological activities. This air also gets heated. The hot air rises up carrying the water vapour with it. As the air rises, it expands and cools. This cooling causes the water vapour in the air to condense in the form of tiny droplets. This condensation of water is facilitated if some particles could act as the ‘nucleus’ for these drops to form around. Normally dust and other suspended particles in the air perform this function.

Once the water droplets are formed, they grow bigger by the ‘condensation’ of these water droplets. When the drops have grown big and heavy, they fall down in the form of rain.



What is air pollution and what are the causes and effects of for air pollution?

An increase in the content of harmful substances in air is called air pollution.
The various reasons for air pollution and their effects are given below:


The fossil fuels like coal and petroleum contain small amounts of nitrogen and sulphur. When these fuels are burnt, nitrogen and sulphur too are burnt and this produces different oxides of nitrogen and sulphur. These gases also dissolve in rain to give rise to acid rain.

The combustion of fossil fuels also increases the amount of suspended particles in air. These suspended particles could be unburnt carbon particles or substances called hydrocarbons.

Presence of high levels of all these pollutants causes visibility to be lowered, especially in cold weather when water also condenses out of air. This is known as smog and is a visible indication of air pollution. 

A regular breathing of air that contains any of these substances increases  the incidence of allergies, cancer and heart diseases.


Explain the availability and existence of water?

Water occupies a very large area of the Earth’s surface and is also found underground.

(i) Some amount of water exists in the form of water vapour in the atmosphere.

(ii) Most of the water on Earth’s surface is found in seas and oceans and is saline.

(iii) Fresh water is found frozen in the ice caps at the two poles and on snow-covered mountains.

(iv) The underground water and the water in rivers, lakes and ponds are also fresh.


How is water is polluted?

There are various reasons for water pollution:

a. Water dissolves the fertilisers and pesticides that we use on our farms. So some percentage of these substances are washed into the water bodies.


b. Sewage from our towns and cities and the waste from factories are also dumped into rivers or lakes.

c. Specific industries also use water for cooling in various operations and later return this hot water to water-bodies.

d. Another manner in which the temperature of the water in rivers can be affected is when water is released from dams. The water inside the deep reservoir would be colder than the water at the surface, which gets heated by the Sun.


Give the fate water, which reaches the earth?

The water that falls on the land does not immediately flow back into the sea. Some of it seeps into the soil and becomes part of the underground reservoir of fresh-water. Some of this underground water finds its way to the surface through springs. For human requirement we bring it to the surface through wells or tube-wells. Terrestrial animal and plants for various life-processes also use water.


Give the importance of nitrogen?

Nitrogen gas makes up 78% of our atmosphere and nitrogen is also a part of many molecules essential to life like proteins, nucleic acids (DNA and RNA) and some vitamins. Nitrogen is found in other biologically important compounds such as alkaloids and urea too. Nitrogen is thus an essential nutrient for all life-forms and life would be simple if all these life-forms could use the atmospheric nitrogen directly.


What is nitrogen fixing bacteria?

The ‘nitrogen-fixing’ bacteria may be free-living or be associated with some species of dicot plants. Most commonly, the nitrogen-fixing bacteria are found in the roots of legumes (generally the plants which give us pulses) in special structures called root-nodules.


Explain the physical process of fixing atmospheric nitrogen?

The physical process is during lightning, the high temperatures and pressures created in the air convert nitrogen into oxides of nitrogen. These oxides dissolve in water to give nitric and nitrous acids and fall on land along with rain. These are then utilised by various life- forms.


Give the source of carbon-dioxide and state the reason for its increase?

The utilisation of glucose to provide energy to living things involves the process of respiration in which oxygen may or may not be used to convert glucose back into carbon dioxide. This carbon dioxide then goes back into the atmosphere. Another process that adds to the carbon dioxide in the atmosphere is the process of combustion where fuels are burnt to provide energy for various needs like heating, cooking, transportation and industrial processes.

The percentage of carbon dioxide in the atmosphere is said to have doubled since the industrial revolution when human beings started burning fossil fuels on a very large scale.


What is green house effect?

There are some gases, which prevent the escape of heat from the Earth. An increase in the percentage of such gases in the atmosphere would cause the average temperatures to increase worldwide and this is called the greenhouse effect.


Briefly describe the oxygen cycle?

Oxygen from the atmosphere is used up in three processes, namely combustion, respiration and in the formation of oxides of nitrogen. Oxygen is returned to the atmosphere in only one major process, that is, photosynthesis. And this forms the broad outline of the oxygen-cycle in nature.


How is the ozone layer depleted?

Various man-made compounds like CFCs, which are carbon compounds having both fluorine and chlorine that are very stable and not degraded by any biological process were found to persist in the atmosphere. Once they reached the ozone layer, they would react with the ozone molecules. This resulted in a reduction of the ozone layer and it is called ozone layer depletion. Recently they have discovered a hole in the ozone layer above the Antartica.

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