Chapter 1 – Natural Resources – Air, Water and Land
1. Fill in the blanks.
(a) The layer of ozone gas absorbs _____ rays that come from the sun to the earth.
Ans: ultraviolet
(b) Of the total water available on the earth, fresh water forms _____ percent.
Ans: 0.3
(c) Both _____ and _____ constituents are present in the soil.
Ans: abiotic, biotic
2. Why is it said that – ?
(a) The ozone layer is a protective shell of the earth.
Ans:
(i) Ultraviolet rays of the sun are very harmful for the living organisms present on the earth.
(ii) The ozone layer present at the high altitude around the earth, absorbs these harmful radiations.
(iii) Life on the earth is thus protected.
(iv) Therefore, the ozone layer is called a protective shell of the earth.
(b) Water is life.
Ans:
(i) Water is one of the most precious resources we have on earth.
(ii) All the biochemical processes that occur in plants and animals, our surroundings, etc., require water to function.
(iii) It is required for the existence of life on earth, as it is an essential component of all biological processes.
(iv) We cannot imagine our lives without the presence of water.
(v) Hence, water is life.
(c) Seawater is useful even though it is not potable.
Ans: Although seawater is not potable, it has various other uses that prove its importance.
(i) Water from oceans can be used to make hydroelectricity, a form of renewable energy.
(ii) It can be used as a cheap transport method.
(iii) They can be used for activities like scuba diving, water sports, etc., which is a means of boosting the tourism and economic growth of a country.
(iv) Nuclear power plants require coolants like water to bring down the temperature of the reactors. For this purpose, several gallons of water are required, and this demand is fulfilled by the water from the oceans.
(v) They support a variety of flora and fauna that have both ecological and economic value.
3. What will happen if –
(a) Microbes in the soil get destroyed.
Ans:
(i) The decomposition process in the soil is done by microbes.
(ii) The weathering of rocks is also done to some extent by microbes.
(iii) If all the microbes in the soil were destroyed, the processes of decomposition and weathering would not take place and the humus will not be formed.
(iv) Due to a lack of decomposition processes, the dead and decaying matter will remain scattered everywhere on the earth.
(b) The number of vehicles and factories in your surroundings increases.
Ans:
(i) Vehicles and factories are the major causes of air pollution.
(ii) They release harmful gases like carbon dioxide, carbon monoxide, and sulphur dioxide into the air.
(iii) These pollutants are harmful to the environment and to the people living in the surrounding area.
(iv) Hence, if the number of vehicles and factories in our surroundings increases, air pollution will also increase.
(c) The total supply of potable water is finished.
Ans:
(i) Water plays a very important role in the survival of living organisms.
(ii) All living things are dependent on water.
(iii) A very small quantity of water is potable and can be used for drinking.
(iv) All bodily functions are regulated by water.
(v) Therefore, if the total supply of potable water is exhausted, plants and animals will not survive, and there will be no life on earth.
4. Match the following.
| Group ‘A’ | Group ‘B’ |
|---|---|
(1) Carbon dioxide | (a) Generation of soil |
(2) Oxygen | (b) Rain |
(3) Water vapour | (c) Plants and food production |
(4) Microbes | (d) Combustion |
Ans:
| Group ‘A’ | Group ‘B’ |
|---|---|
(1) Carbon dioxide | (c) Plants and food production |
(2) Oxygen | (d) Combustion |
(3) Water vapour | (b) Rain |
(4) Microbes | (a) Generation of soil |
5. Name the following.
(a) Constituents of the biosphere
Ans: Animals and plants.
(b) Biotic constituents of soil
Ans: Microbes, insects, rodents like rats and mice.
(c) Fossil fuel
Ans: Petrol, diesel, kerosene.
(d) Inert gases in air
Ans: Argon, Helium, Neon, Krypton, Xenon.
(e) Gases that are harmful to the ozone layer
Ans: Chlorofluorocarbons, Carbon tetrachloride.
6. True or false ?
(a) Land and soil are the same thing.
Ans: False
(b) The water in a lake is called groundwater.
Ans: False
(c) It takes about 1000 years to form a 25 cm thick layer of soil.
Ans: False
(d) Radon is used in decorative lights.
Ans: False
7. Answer in your own words.
(a) Explain with the help of a diagram how soil is formed.
Ans:
(i) Soil is formed by a natural process.
(ii) Heat, cold, and rainwater cause weathering of the bedrock.
(iii) This weathering process forms stones, sand, and soil from the original rock.
(iv) This supplies the abiotic components of the soil.
(v) Microbes, worms, insects, and rodents further add to the process of soil formation.
(vi) The roots of big trees that grow on land are also weathering agents.
All these factors cause soil formation in a very slow and continuous way.
(b) Why is there a shortage of water even though it occupies about 71% of the earth’s surface?
Ans:
(i) Though 71% of the earth’s surface is covered with water, most of this water is not usable or potable.
(ii) 97% of this water is salty seawater. This water cannot be used for agriculture, drinking, cooking, etc.
(iii) Some fresh water is in a frozen state.
(iv) Due to the tremendous increase in population, the demand for water is also rising.
(v) Due to global warming, there are droughts, which result in a lack of water.
(vi) Due to all these reasons, there is always a water shortage, even though 71% of the earth’s surface is occupied by water.
(c) What are the various constituents of air? Write their uses.
Ans:
(A) Different constituents of the air:
(i) Gases such as nitrogen, oxygen, carbon dioxide, nitrogen dioxide, sulphur dioxide.
(ii) Inert gases such as argon, helium, neon, krypton and xenon.
(iii) Other inclusions such as water vapour, smoke, fog, smog, soot, etc.
(B) Uses of the constituents of air:
(i) Nitrogen: Nitrogen helps in building up proteins in the living organisms. It is also used in the production of ammonia and also in the airtight packaging of the foodstuffs.
(ii) Oxygen: Oxygen is essential for respiration and also for combustion of all the substances.
(iii) Carbon dioxide: Plants need carbon dioxide to perform photosynthesis. It is also used in fire extinguishers.
(iv) Argon: Argon is used in electric bulbs.
(v) Helium: Helium is used for obtaining low temperature and also for generating lift in airships.
(vi) Neon: Neon is used in decorative lights used for advertisements and also for street lighting.
(d) Why are air, water and land considered to be valuable natural resources?
Ans:
(i) Air, water, and land are the factors essential for sustaining life on earth.
(ii) All the essential things required for survival are obtained through air, water, or land.
(iii) Since they fulfill the needs of living organisms, they help in the survival of all living organisms.
(iv) Therefore, air, water, and land are considered valuable natural resources.