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(a)The layer of ozone gas absorbs UV / ultraviolet rays that come, from the sun to the earth., (b) Of the total water available on the earth, fresh water, forms 0.3 percent., (c) Both biotic and abiotic constituents are present in the soil., , Q. 2. Why is it said that – ?, (a) The ozone layer is a protective shell of the earth., Ans: The ozone layer acts as a protective layer for life on the earth, because it absorbs harmful ultraviolet radiations of the sun. These, radiations, if reach the Earth’s surface, can cause skin cancer., (b) Water is life., Ans: i. Water is one of the most precious resource which we have on, earth., ii. All the biochemical processes which 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 the biological processes., iv)We cannot imagine our lives without the presence of water., ( C ) Seawater is useful even though it is not potable., Ans: Although sea water is not potable, it has various other kinds of, uses which prove its importance:, •, •, , Water from oceans can be used for making hydroelectricity, a form, of renewable source of energy., It can be used as a cheap transport method.
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•, , •, , •, , They can be used for the activities like scuba diving, water sports, etc. which is a means of boosting the tourism and economic growth, of a country., Nuclear power plants require coolants like water to bring down the, temperature of the reactors. For this purpose several gallons of, water is required and this demand is fulfilled by the water from, oceans., They support a variety of flora and fauna which have both, ecological and economical value., , 3. What will happen if –, (a) Microbes in the soil get destroyed., Ans: Soil contains various kinds of microbes like bacteria, fungi, algae,, protozoa etc. All of these microorganisms play an important roles like:, •, , •, , •, , Certain bacteria and blue-green algae have the ability to fix, atmospheric nitrogen. This, in turn, enriches the fertility of soil., Such microorganisms are known as biological nitrogen-fixers., Example − Rhizobium is a symbiotic bacterium which lives in the, root nodules of leguminous plants. Rhizobium fixes atmospheric, nitrogen into nitrogenous compounds., The bacteria and fungi present in soil decompose dead organic, wastes of plants and animals, and convert them into manure. The, manure contributes to the humus content of the soil, thereby, helping in increasing its fertility., Not only these, microorganisms which are found in soil are also a, part of many biogeochemical cycles which would not take place in, their absence., , The above points explain the fact that how important microbes are and if, they are destroyed its effect can be irreversible.
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(b) The number of vehicles and factories in your surroundings, increases., Ans: Vehicles and factories are the major sources of air pollution. If the, number of vehicles and factories increase in our surroundings, it is, obvious that it would result in increased levels of air pollution. Not only, air pollution but they also result in noise pollution. In case, the no. of, industries increase in our surrounding it means, more trees would have, to be cut down to make way for them and thus resulting in damage to the, environment., (c) The total supply of potable water is finished., Ans: If the total supply of potable water is finished then the life on earth, will end. Water is required for the existence of living beings and in its, absence, it would hamper their development process and their survival., , Question 4:, Match the following., ANSWER:, , (1), (2), (3), (4), , Group ‘A’, Carbon, dioxide, Oxygen, Water, vapour, Microbes, , Group ‘B’, Plants and food, (c), production, (d) Combustion, (b) Rain, (a) Generation of soil
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Question 5:, Name the following., (a) Constituents of the biosphere, Ans: Constituents of the biosphere- hydrosphere and atmosphere, (b) Biotic constituents of soil, Ans: Biotic constituents of soil- microorganisms and insects, (c) Fossil fuel, Ans: Fossil fuel- coal and petroleum, (d) Inert gases in air, Ans: Inert gases in air- oxygen and nitrogen, (e) Gases that are harmful to the ozone layer, Ans: Gases that are harmful to the ozone layer- carbon tetrachloride
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Question 6:, (a) Land and soil are the same thing.- False, (b) The water in a lake is called ground water.- False, (c) It takes about 1000 years to form a 25 cm thick layer of soil.-False, (d) Radon is used in decorative lights.- False, , Question 7:, ANSWER:, A., , Explain with the help of a diagram how soil is formed., , Ans: Soil is formed by the process of weathering during which rocks, break down to form soil particles. This breaking down of rock occurs, over a period of millions of years. Weathering can be physical,, chemical, and biological. The bedrock breaks down into pieces due to, the effects of heat, cold, water, wind and rain. Microbes, insects and, rodents also help iin this process. The roots of trees also help in the, process of weathering.
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(b) Why is there a shortage of water even though it occupies about, 71% of the earth’s surface ?, Ans: Although water occupies about 71% of the earth's surface, all of it, is not potable water. Most of the water is available in the form of seas, and oceans which is salty in nature. This saline water has its limitations, and cannot be used for many purposes. Around 2.7% of water exists in, frozen state or as groundwater which is unaccessible. Only 0.3% of, water is available as potable water which is fit for human consumption., , (c) What are the various constituents of air ? Write their uses., Ans:, Constituents of, air, , 1. Nitrogen, , Uses, , Required in building proteins., Useful in production of ammonia.
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Used in airtight packaging of food, products., , 2. Oxygen, , Necessary for respiration and, combustion., , 3. Carbon dioxide, , Used by plants to make their foods., Used in fire extinguishers., , 4. Argon, , Used in electric bulbs., , 5. Heluim, , Used for obtaining low, temperatures., Used for generating lifts in, airships., , 6. Neon, , Used in decorative lights and street, lighting., , 7. Krypton, , Used in fluorescent tubes.
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8. Xenon, , Used in flash photography., , (d) Why are air, water and land considered to be valuable natural, resources ?, Ans: The following points elucidate the fact that air, land and water are, valuable natural resources:, , Importance of air:, •, •, , The importance of air can be understood by the fact that earth, supports life becuase of the present of this air in our surrounding., It is required for various biological functions and biogeochemical, cycles., , Importance of land:, •, •, •, •, , All terrestrial organisms live on land., We use it for the purpose of land farming, building houses, roads, etc., The plants and animals which we use also grow on the land., The minerals which we obtain from deep inside the earth are also, important resources. For example, petrol, coal etc., , Importance of water:
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•, , •, , •, •, , Water plays an important role in various vital processes that are, carried out by our body. All cellular processes take place in water, medium., The availability of water plays an important role in deciding the, number of individuals of each species that will be able to survive, in a particular area, and also the sustainability of life in the region., Fresh water is utilized by humans for consumption., Water is central to the lives of aquatic animals which live in water.
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