1- NATURAL RESOURCES – AIR, WATER AND LAND
Q. 1. Fill in the blanks :
Ans.
(1) The layer of ozone gas absorbs ultraviolet rays that come from the sun to
the earth.
(2) Of
the total water available on the earth, fresh water forms 0.3 per cent.
(3)
Both abiotic and biotic constituents are present in the soil.
Q. 2. Write whether the following
statements are true or false:
Ans. (1)
Land and soil are the same thing.
False
(2) The
water in a lake is called ground water. False
(3) It
takes about 1000 years to form 25 cm thick layer of soil. False
(4) Radon is used in decorative lights. False
Q. 3. Name the following: (Note : Answers are
given directly.)
(1)
Constituents of the biosphere : Animals and plants. (2) Biotic constituents of
soil : Microbes, insects, rodents like rats and mice. (3) Fossil fuel : Petrol,
diesel, kerosene. (4) Inert gases in air : Argon, Helium, Neon, Krypton, Xenon.
(5) Gases that are harmful to the ozone layer : Chlorofluorocarbons, Carbon
tetrachloride.
Q. 4. Match the following:
Ans (1) Carbon dioxide - Plants and food production
(2) Oxygen - Combustion
(3) Water vapour – Rain
(4) Microbes - Generation of soil
Q. 5. Why is it said that.?
(1) The ozone layer is a protective shell of
the earth.
Ans.
Ultraviolet rays of the sun are very harmful for the living organisms present
on the earth. The ozone layer present at the high altitude around the earth,
absorbs these harmful radiations. The life on the earth is thus protected.
Therefore, the ozone layer is called a protective shell of the earth.
(2)
Water is life.
Ans.
Living organisms cannot survive without water. The blood of the animals and sap
of the plants also have high proportion of water. Therefore, water is said to
be life
(3) Sea
water is useful even though it is not potable.
Ans.
(1) There are many aquatic organisms in the marine waters (water of the seas
and oceans), of some of these are edible varieties such as fish, crab, prawn,
bivalves, oysters, lobsters, etc.
(2)
Fishery is an important occupation of coastal people which is entirely
dependent on seas.
(3)
Salt, iodine and some other minerals are obtained from the sea water.
(4)
The valuable jewels such as corals and pearls are obtained from some of the
marine animals.
(5)
Transport of goods and cargo is done via sea routes.
(6)
Due to evaporation of sea water, the water cycle remains operative. Monsoon
rains, weather patterns and cycle of seasons all are possible due to oceans.
(7) In
some countries. potable and usable water is obtained from sea water through a
process called desalination. All these facts explain to us that though sea
water is salty, it is useful.
Q. 6. Answer the following questions:
(1)
Explain with the help of a diagram how soil is formed.
Ans. (1) Soil is formed by the natural process. (2) Heat, cold and the rainwater cause weathering of the bedrock. (3) This weathering process forms stones, sand and soil from the original rock,
(4) This supplies the abiotic components of the soil. (5) Microbes. worms. insects and rodents
further adds to the process of soil formation. (6) The roots of big trees that grow on land also are weathering agents. All these factors cause soil formation in a very slow and continuous way.
(2) Why is there a shortage of water even
though it occupies about 71% of the earth's surface ?
Ans.(1)
Though 71% of the earth's surface is covered with the water, most of this water
is not usable and potable. (2) 97% of this water is salty water of the sea.
This water cannot be used for agriculture or for drinking cooking, etc. (3)
Some fresh water is in frozen state. (4) Due to tremendous increase in the
population the demand for water is also rising. (5) Due to global warming there
are droughts and this results in lack of water. (6) Due to all these reasons
there is always a water shortage even though the 71% of earth's surface is
occupied by water.
(3) What are the various constituents of air ?
Write their uses.
Ans. I.
Different constituents of the air : (1) Gases such as nitrogen, oxygen,
carbon dioxide, nitrogen dioxide, sulphur dioxide. (2) Inert gases such as
argon, helium, neon, krypton and xenon. (3) Other inclusions such as water
vapour, smoke, fog, smog, soot, etc.
II. Uses
of the constituents of air :
(1)
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.
(2)
Oxygen : Oxygen is essential for respiration and also for combustion of all the
substances
(3)
Carbon dioxide : Plants need carbon dioxide to perform photosynthesis. It is
also used in fire extinguishers.
(4)
Argon : Argon is used in the electric bulbs.
(5)
Helium : Helium is used for obtaining low temperature and also for generating
lift in airships.
(6)
Neon : Neon is used in decorative lights used for advertisements and also for
street lighting
(7)
Krypton : Krypton is used in fluorescent tubes.
(8) Xenon
: Xenon is used in flash photography,
(4) Why
are air, water and land considered to be valuable natural resources?
Ans.
Air. water and land are the factors essential for sustaining living world on
the earth. All the essential things required for the survival are obtained
through air, water or land. Since by fulfilling the needs of living organisms,
they help in survival of all living organisms, therefore, air. water and land
are considered to be valuable natural resources.
Q. 7. What will happen if.
(1) Microbes in the soil get destroyed.
Ans. The decomposition process in the
soil is done by the microbes. The weathering of rocks is also done to some
extent by the microbes. If all the microbes in the soil are destroyed the
processes of decomposition and weathering would not take place. The humus will
not be formed. Due to lack of decomposition process, the dead and decaying
matter will remain scattered everywhere on the earth
. (2) The number of vehicles and
factories in your surroundings increases
Ans. In vehicles as well as factories there is
continuous combustion process occurring Particularly in vehicles there is
incomplete combustion of the fossil fuels releasing many air polluting gases in
the atmosphere. Polluting gases like carbon dioxide, carbon monoxide, sulphur
dioxide, nitrogen dioxide. etc. will cause dangerous and harmful effects on the
surrounding environment and human beings. Industries will also throw toxic
gases and effluents into the surrounding. If the number of vehicles and
factories in our surroundings increases then it will be hazardous for the environment
and health of the entire living world.
(3) The total supply of potable water is
finished.
Ans. If the total supply of potable
water is finished, the living world will also come to an end.
