Question 1:
Fill in the blanks.
(a) The layer of ozone gas absorbs ………… rays that come from the sun to the earth.
(b) Of the total water available on the earth, fresh water forms ...... percent.
(c) Both ...…. and ……... constituents are present in the soil.
ANSWER:
(a) The layer of ozone gas absorbs UV 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.
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Question 2:
Why is it said that – ?
(a) The ozone layer is a protective shell of the earth.
(b) Water is life.
(c) Seawater is useful even though it is not potable.
ANSWER:
b. Water is one of the most precious resource which we have on earth. All the biochemical processes which occur in plants and animals, our surroundings etc. require water to function. It is required for the existence of life on earth as it is an essential component of all the biological processes. We cannot imagine our lives without the presence of water.
c. 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.
- 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.
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Question 3:
What will happen if –
(a) Microbes in the soil get destroyed.
(b) The number of vehicles and factories in your surroundings increases.
(c) The total supply of potable water is finished.
ANSWER:
a. 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.
b. 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. 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 owuld hamper their developemnt process and their survival.
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Question 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 |
ANSWER:
| 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 |
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Question 5:
Name the following.
(a) Constituents of the biosphere
(b) Biotic constituents of soil
(c) Fossil fuel
(d) Inert gases in air
(e) Gases that are harmful to the ozone layer
ANSWER:
(a) Constituents of the biosphere- hydrosphere and atmosphere
(b) Biotic constituents of soil- microorganisms and insects
(c) Fossil fuel- coal and petroleum
(d) Inert gases in air- oxygen and nitrogen
(e) Gases that are harmful to the ozone layer- carbon tetrachloride
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Question 6:
True or false?
(a) Land and soil are the same thing.
(b) The water in a lake is called ground water.
(c) It takes about 1000 years to form a 25 cm thick layer of soil.
(d) Radon is used in decorative lights.
ANSWER:
(a) Land and soil are the same thing.- False
(b) The water in a lake is called ground water.- Flase
(c) It takes about 1000 years to form a 25 cm thick layer of soil.-False
(d) Radon is used in decorative lights.- False
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Question 7:
Answer in your own words.
(a) Explain with the help of a diagram how soil is formed.
(b) Why is there a shortage of water even though it occupies about 71% of the earth’s surface?
(c) What are the various constituents of air? Write their uses.
(d) Why are air, water and land considered to be valuable natural resources?
ANSWER:
a. 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.
b. 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.
Constituents of air | Uses |
| 1. Nitrogen | Required in building proteins. Useful in production of ammonia. 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. |
| 8. Xenon | Used in flash photography. |
d. 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:
- 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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