Maharashtra Board Class 6 Science Chapter 1 Natural Resources Air Water and Land PDF Download

Natural Resources – Air, Water And Land

Observe

Observe the picture alongside and answer the questions.

1. Where do we see the birds ?

2. Where is the cow grazing?

3. Locate the trees and the road.

4. Where does the river come from? How does it flow?

5. Where is the aeroplane ?

6. Where are the fish seen?

7. On what is the sailboat floating?

You can see that some things in the picture are in water, some on land, and some in the sky, that is, in the air. Thus, all things on the earth are associated with air, water and land. Air, water and land are called the earth's atmosphere, hydrosphere and lithosphere, respectively. Moreover, different living things occupy these three spheres of the earth. These living things and the parts of the lithosphere, hydrosphere and atmosphere which they occupy are together called the biosphere. These spheres have formed on the earth naturally. We have learnt all this in the previous standards.

The atmosphere is the layer of air that surrounds the earth. The surface of the earth comprises water and land, that is, the hydrosphere and lithosphere. Of these, the hydrosphere occupies a much larger part than the lithosphere. Figure 1.2 shows the proportion of land and water on the earth's surface.

We also look upon these natural components in solid, liquid and gaseous form as resources. In other words, we use them to fulfil our requirements. Let us now study all these three components in detail.

Natural Resources

Air, water and land are the factors important for sustaining the living world on the earth and for fulfilling their basic needs. They are called natural resources.

Teacher's Note

In India, farmers depend on water, soil and air for growing crops. Rain and soil together help farmers grow rice and wheat for our food.

Exam Trick

Remember: Three spheres = three resources. Atmosphere (air) + Hydrosphere (water) + Lithosphere (land) = all we need to live!

Points to Remember

Air, water and land are three natural resources we need to live.
Atmosphere is the air around the earth.
Hydrosphere is all the water on earth.
Lithosphere is all the land and rocks.
Biosphere is where living things live.

Air

The air in the atmosphere around the earth contains nitrogen, oxygen, carbon dioxide, six inert gases, nitrogen dioxide, sulphur dioxide, water vapour and dust particles. The troposphere contains about 80% of the total mass of gases in the air, while this proportion is about 19% in the stratosphere. Further, in the mesosphere and ionosphere, the proportion of the mass of gases goes on decreasing. Gases are not found in the exosphere and beyond.

You can see that air is a mixture of several gases and is the chief constituent of the earth's atmosphere. Besides these gases, air also contains water vapour and dust particles. The amount of the gases in the air is the greatest near the surface and decreases as we go higher and higher from the surface. That is, air becomes rarer at higher altitudes.

The proportions of the constituents of air and some of their uses are given here.

Some Uses Of Gases In Air

Nitrogen – Helps living things to build the necessary proteins. It is useful in the production of ammonia and in airtight packaging of foodstuffs.

Oxygen – Necessary for respiration in living things and for combustion.

Carbon dioxide – Plants use it for producing their food. Used in fire extinguishers.

Argon – Used in electric bulbs.

Helium – Used for obtaining low temperature and also for generating lift in airships.

Neon – Used in decorative lights and for street lighting.

Krypton – Used in fluorescent tubes.

Xenon – Used in flash photography.

Teacher's Note

Air is all around us but we cannot see it. When you ride a bicycle fast, you feel air pushing against your face. This is the air we breathe.

Exam Trick

Remember: Nitrogen is 78%, Oxygen is 21%. Together they make almost 99% of air. The rest is other gases. Think: N (Many) + O (Little) = Air!

Points to Remember

Nitrogen helps plants grow.
Oxygen helps us breathe and helps fire burn.
Carbon dioxide helps plants make food.
Air has water vapour and dust in it.
Air is rarer higher up in the sky.

The living world on the earth is sustained due to the balance between various gases and other constituents of air. The atmosphere is a very important filter. It allows the light and heat of the sun to reach the earth, which is necessary for life. But it prevents the harmful elements from reaching the earth. It is in the atmosphere that fog, clouds, snow and rain are produced.

Air Pollution

All the above pictures show large scale emission of smoke through different agencies. This smoke directly mixes with the atmosphere, disturbing the balance between the constituents of air. This is called air pollution. Harmful gases are given out through combustion of fuels in vehicles and in big industries and also through incomplete combustion of fuels like wood and coal. As a result, air pollution is increasing day by day.

Harmful Substances Released In Air Through Combustion Of Fuels

Nitrogen dioxide

Carbon dioxide

Carbon monoxide

Sulphur dioxide

Soot

Ozone Layer – The Protective Shell

There is a layer of ozone (O\(_3\)) gas in the lower part of stratosphere. Ozone gas is not directly useful for the survival of living things, yet it is very important for living things to have this layer of ozone at a high altitude around the earth. The ultra violet rays coming from the sun are very harmful for living things. The ozone gas absorbs these rays. As a result, life on earth is protected.

The ozone layer is destroyed if chemical gases like carbon tetrachloride or the chlorofluorocarbons used in air conditioners and refrigerators mix with the air.

The 16th of September is celebrated as 'Ozone Protection Day' all over the world to make everyone aware of the importance of ozone.

In metropolitan cities like Mumbai, Pune or Nagpur boards are displayed at places of heavy traffic to show the proportions of the various constituents of the air at that place. Due to these boards, we can see the amount of harmful elements in the air.

Teacher's Note

The ozone layer is like a big shield above the earth. It protects us from the sun's harmful rays just like sunscreen protects our skin.

Exam Trick

Remember: Ozone protects us. Air conditioners and refrigerators destroy ozone. So use them carefully!

Points to Remember

Ozone is a gas high up in the sky.
It blocks harmful rays from the sun.
Air pollution harms the ozone layer.
We must protect the ozone layer.
September 16 is Ozone Protection Day.

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