NCERT Exemplar Class 9 Science Chapter 14 Natural Resources

NCERT Exemplar Class 9 Science Chapter 14 Natural Resources are part of NCERT Exemplar Class 9 Science. Here we have given NCERT Exemplar Class 9 Science Solutions Chapter 14 Natural Resources.

NCERT Exemplar Class 9 Science Solutions Chapter 14 Natural Resources

Multiple Choice  Questions

Question 1.
The atmosphere of the earth is heated by radiations which are mainly
(a) radiated by the sun
(b) re-radiated by land
(c) re-radiated by water
(d) re-radiated by land and water.
Solution:
(d) Heating of air occurs due to re-radiation of solar radiations by land and water bodies. In fact, when the solar radiations fall on the earth, some are absorbed and majority of these are reflected back or re-radiated by land and water bodies. These reflected or re-radiated solar radiations heat up the atmosphere.

Question 2.
If there were no atmosphere around the earth, the temperature of the earth will
(a) increase
(b) go on decreasing
(c) increase during day and decrease during night
(d) be unaffected.
Solution:
(c) Atmosphere acts as a temperature buffer. It prevents the sudden increase in temperature during day light hours. Further during night it slows down the escape of heat into the outer space thereby preventing excessive cooling during night. Due to this reason the average temperature of earth remains fairly steady. If there were no atmosphere around the earth then the temperature of earth will become very high during day and very low during night.

Question 3.
What would happen, if all the oxygen present in the environment is converted to ozone?
(a) We will be protected more.
(b) It will become poisonous and kill living forms.
(c) Ozone is not stable, hence it will be toxic.
(d) It will help harmful sun radiations to reach earth and damage many life forms.
Solution:
Oxygen is found in atmosphere in two forms, i.e., as diatomic molecule (O₂) and as ozone (O₃). Ozone exists as thick blanket called ozone shield or ozonosphere in the stratosphere. Unlike diatomic oxygen, ozone is poisonous. When inhaled, ozone can damage the lungs, and cause other respiratory diseases like asthma etc. Ozone is a weak mutagen and produces various chromosomal abnormalities. So, if all oxygen present in the environment gets converted into ozone, then air will becofhe toxic and kill all living forms.

Question 4.
One of the following factors does not lead to soil formation in nature.
(a) The sun
(b) Water
(c) Wind
(d) Polythene bags
Solution:
(d) Temperature variations due to radiations from the sun, rain water and wind are major biotic factors that influence the formation of soil from rocks. Polythene bags do not participate in the formation of soil. They are non-biodegradable substances which do not undergo decomposition or weathering. These are considered as pollutants that deteriorate the quality of soil.

Question 5.
The two forms of oxygen found in the atmosphere are
(a) water and ozone
(b) water and oxygen
(c) ozone and oxygen
(d) water and carbon dioxide.
Solution:
(c) Oxygen is found in atmosphere in two forms, as diatomic molecule (O₂) and as triatomic ozone (O₃). Normally elemental oxygen is found in the form of a diatomic molecule in the atmosphere. Ozone is not stable near the earth’s surface and is present 18¬50 km above in the atmosphere (stratosphere) as thick blanket called ozonosphere or ozone shield.

Question 6.
The process of nitrogen-fixation by bacteria does not take place in the presence of
(a) molecular form of hydrogen
(b) elemental form of oxygen
(c) water
(d) elemental form of nitrogen.
Solution:
(b) Nitrogen fixation is the conversion of inert atmosphere nitrogen or dinitrogen (N2) into utilisable compounds of nitrate, ammonia, amino acids. Various bacteria like Rhizobium and Azotobacter convert the atmospheric nitrogen into water soluble nitrates. Nitrogenase enzyme is prime requirement for biological nitrogen fixation. This enzyme is vulnerable to oxygen and gets destroyed in its presence. It is due to this reason, that most of nitrogen fixing bacteria live in anaerobic conditions or sequester oxygen with the proteins like leghaemoglobin.

Question 7.
Rainfall patterns depend on
(a) the underground water table
(b) the number of water bodies in an area
(c) the density pattern of human population in an area
(d) the prevailing season in an area.
Solution:
(b) Patterns of rainfall of an area or region are determined by a number of factors such as availability of water vapours, areas of low pressures, prevailing wind patterns, condensation of water vapours and direction of mountains in the path of winds. Since the number of water bodies in area affects the availability of water vapours, they will considerably affect the rainfall pattern of a particular area.

Question 8.
Among the given options, which one is not correct for the use of large amount of fertilisers and pesticides?
(a) They are eco-friendly.
(b) They turn the fields barren after some time.
(c) They adversally affect* the useful component from the soil.
(d) They destroy the soil fertility.
Solution:
(a) Fertilisers and pesticides are not eco¬friendly, in fact they are considered as a source of air, water and soil pollution. Excessive use of fertilisers can turn the soil acidic or alkaline and affects the fertility of soil. Prolonged use of fertilisers can destroy soil fertility by killing the microorganisms that form humus. The soil may become unable to sustain plant life and ultimately become barren.

Question 9.
The nitrogen molecules present in air can be
converted into nitrates and nitrites by
(a) a biological process of nitrogen fixing bacteria present in soil
(b) a biological process of carbon fixing factor present in soil
(c) any of the industries manufacturing nitrogenous compounds
(d) the plants used as cereal crops in field.
Solution:
(a) Nitrogen molecules present in the air cannot be used as such by plants and animals and must be converted into biologically 5 acceptable forms. A number of symbiotic and free living bacteria e.g., Rhizobium, Azotobacter etc. convert nitrogen into ammonia. Most of the ammonium compounds are oxidised by nitrite bacteria (Nitrosomonas and Nitrosococcus) to soluble nitrities, which are further oxidised by nitrate bacteria (Nitrobacter and Nitrocystis) to soluble nitrates.

Question 10.
One of the following processes is not a step involved in the water-cycle operating in ‘ nature.
(a) Evaporation
(b) Transpiration
(c) Precipitation
(d) Photosynthesis
Solution:
(d) The movement of water through ‘ living and non-living components of the biosphere or any other ecosystem is called water cycle. Evaporation, transpiration and precipitation are involved in the cycling of water.
Photosynthesis is an anabolic process in which glucose is synthesised using simple inorganic substances like CO₂ and H₂O as raw materials in the presence of light and chlorophyll and with the release of oxygen as a by-product. No water molecules are released into atmosphere in this process. In fact water molecules are used up and fixed into carbohydrates. So,  photosynthesis is not involved in cycling of water.

Question 11.
The term “water-pollution” can be defined in several ways. Which of the following statements does not give the correct definition?
(a) The addition of undesirable substances to water-bodies
(b) The removal of desirable substances from water-bodies
(c) A change in pressure of the water bodies (d) A change in temperature of the water bodies
Solution:
(c) Water pollution can be defined an undesirable change in the physical, biological or chemical qualities of water that adversely affects the aquatic life and makes water unfit for use. Water pollution is caused due to addition of undesirable substances (pollutants) to the water bodies. Polluted water may be devoid of certain desirable substances like oxygen, essential nutrients, optimum pH etc. Thermal pollution, i.e., change in temperature of water bodies can adversely effect the aquatic organisms and cause their death.

Question 12.
Which of the following is not a greenhouse gas?
(a) Methane
(b) Carbon dioxide
(c) Carbon monoxide
(d) Ammonia
Solution:
(d) The gases which are transparent to solar radiation but retain and partially reflect back long wave heat radiations are called greenhouse gases. Greenhouse gases are essential for keeping the earth warm and hospitable. Gases like carbon dioxide (CO₂), methane (CH4), chlorofluorocarbons (CFCs), nitrous oxide (N₂0), carbon monoxide (CO), etc. are considered greenhouse gases. Ammonia is not a greenhouse gas and serves as precursor of food and building block of medicines.

Question 13.
Which step is not involved in the carbon- cycle?
(a) Photosynthesis
(b) Transpiration
(c) Respiration
(d) Burning of fossil fuels
Solution:
(b) The movement of carbon through living and non-living components of biosphere is called carbon cycle. The carbon is present in the form- of CO₂ in the air. The CO₂ in the atmosphere act as a reservoir, from which COz is taken up and returned to by living organisms and non-living components. Photosynthesis, respiration and burning of fossil fuels are important steps involved in carbon-cycle.
CO₂ from air is taken up by green plants and fixed into carbohydrate molecules by process called photosynthesis. These organic compounds (Carbohydrate molecules) are used up by animals to obtain energy.
Animals utilise these carbohydrate molecules to obtain energy and release CO₂ in the atmospheric reservoir. Burning of fossil fuels (hydrocarbons) also releases CO₂ in the atmosphere.
Transpiration on the other hand is loss of water molecules from leaves and is not involved in carbon-cycle.

Question 14.
‘Ozone-hole’ means
(a) a large sized hole in the ozone layer
(b) thinning of the ozone layer
(c) small holes scattered in the ozone layer
(d) thickening of ozone in the ozone layer.
Solution:
(b) Ozone layer, comprising high concentration of ozone about 18-50 km above in the atmosphere is called ozone blanket. Production and release of high levels of ozone depleting substance (ODS) particularly chlorofluorocarbons have resulted in thinning of ozone layer over a restricted area. Such an area is termed ozone hole.
Ozone hole was first discovered over Antarctica in 1985. Amount of atmospheric ozone is measured by Dobson spectrometer and is expressed in Dobson units (DU).

Question 15.
Ozone-layer is getting depleted because of
(a) excessive use of automobiles
(b) excessive formation of industrial units
(c) excessive use of man-made compounds containing both fluorine and chlorine
(d) excessive deforestation.
Solution:
(c) Ozone-layer is getting depleted due to excessive use and emission of certain chemicals named as ODS (ozone depleting substances). ODS are the substances which react with ozone present in the stratosphere and destroy the same.
The major ODS CFCs (Chlorofluorocarbons) that are synthetic harmful chemicals widely used in refrigerators and air conditioners as coolants, in fire extinguishers, and as propellants. Once released in the air, these harmful chemicals produce ‘active chlorine’ (Cl and CIO) radicals and fluorine in the presence of UV radiations. These radicals, through chain reaction, then destroy the ozone by converting it into oxygen. Due to this, the ozone layer in stratosphere becomes thinner. A single chlorine atom can destroy ‘ one lakh ozone molecules.

Question 16.
Which of the following is a recently originated problem of environment?
(a) Ozone layer depletion
(b) Green house effect
(c) Global warming
(d) All of the above
Solution:
(a) and (c) Due to unrestricted utilisation of natural resources and excessive emission of harmful gaseous pollutants into the environment, the quality of air has been considerably deteriorated. The percentage of carbon dioxide in the atmosphere is said to have doubled since the industrial revolution when human beings started burning fossil fuels on a large scale. Increased amount of gases like CO₂ etc. has resulted in increased greenhouse effect and hence global warming. Release of CFCs and other ozone depleting substances in atmosphere has caused ozone hole which was discovered in 1985 in Antarctica.

Question 17.
When we breathe in air, nitrogen also goes inside along with oxygen. What is the fate of this nitrogen?
(a) It moves along with oxygen into the cells.
(b) It comes out with the CO₂ during exhalation.
(c) It is absorbed only by the nasal cells.
(d) Nitrogen concentration is already more in the cells so it is not at all absorbed.
Solution:
(b) Nitrogen is an inert gas and is not used as such by human body. About 78% of atmospheric air contains nitrogen gas and %age of nitrogen in exhaled air is also 78%. Nitrogen gas is not absorbed by any molecule in human body and is exhaled as such in the environment. Elemental nitrogen which is an essential component of human body, is consumed in other fixed forms like NH₄ ions, amino acids, etc.

Question 18.
Top-soil contains the following.
(a) Humus and living organisms only
(b) Humus and soil particles only
(c) Humus, living organisms and plants
(d) Humus, living organisms and soil particles
Solution:
(c) and (d) Soil profile shows four distinct layers, called horizons. Horizon A is the top soil. It is darker and of a looser texture than underlying layers. Plant and animal matter collects at the surface of this horizon,

Question 19.
Choose the correct sequences.
(a) CO₂ in atmosphere → decomposers → organic carbon in animals → organic carbon in plants
(b) CO₂ in atmosphere → organic carbon in plants → organic carbon in animals → inorganic carbon in soil
(c) Inorganic carbonates in water → organic carbon in plants → organic carbon in animals → scavengers
(d) Organic carbon in animals → decomposers → CO₂ in atmosphere→ organic carbon in plants
Solution:
(b) Carbon is present as a combined state in the atmosphere in the form of carbon dioxide. This C02 from the atmosphere is incorporated into life-forms through the basic process of photosynthesis. This process converts carbon dioxide into glucose molecules (organic carbon in plants). Animals feed on the plants and utilise the glucose molecules to release C02 and energy (organic carbon in animals). The dead plants and animals are then consumed up by decomposers and made available as fossil fuel and humus (inorganic carbon in soil).

Question 20.
Major source of mineral in soil is the
(a) parent rock from which soil is formed
(b) plants
(c) animals
(d) bacteria.
Solution:
(a) Soil is formed by physical, chemical or biological weathering of hard rocks. Rocks contain minerals in one or other forms. The mineral nutrients that are found in a particular soil mainly depend on the type of rock from which the soil was formed.

Question 21.
Total earth’s surface covered by water is
(a) 75%
(b) 60%
(c) 85%
(d) 50%.
Solution:
(a) Water covers approximately 75% of earth’s surface. 97.5% of the water on the planet earth is found in seas and oceans as saline water. Remaining 2.5% of water is present in the form of fresh water. Majority of it (2%) is frozen in the ice-caps at the poles. Remaining 0.6% of total water is available to support terrestrial life.

Question 22.
Biotic component of biosphere is not constituted by
(a) producers
(b) consumers
(c) decomposer
(d) air.
Solution:
(d) Biosphere is global sum of all ecosystems. It can also be termed as zone of life on earth. Biosphere is the global ecological system integrating all living beings and their relationships including their interaction with elements of lithosphere, geosphere, hydrosphere and atmosphere.
Biotic components of biosphere constitute all the living members of an ecosystem i.e. producers, consumers and decomposers. The different biotic components are connected through food.
Abiotic components on the other hand are the non-living chemical and physical part of the ecosystem like air, water, sunlight etc.

Question 23.
An increase in carbon dioxide content in the atmosphere would not cause
(a) more heat to be retained by the environment
(b) increase in photosynthesis in plants
(c) global warming
(d) abundance of desert plants.
Solution:
(d) Since carbon dioxide is a green house gas, an increase in its concentration will lead to retention of more heat by the environment. The increased level of carbon dioxide and temperature will increase the rate of photosynthesis in plants. The retention of heat due to increased CO₂ concentration will cause an increase in average global temperature, resulting in global farming. Since increase in CO₂ concentration does not create xerophytic conditions, thus there is no increase in abundance of desert plants.

Question 24.
0xygen is returned to the atmosphere mainly by
(a) burning of fossil fuel
(b) respiration
(c) photosynthesis
(d) fungi.
Solution:
(c) Plants release 02 into the environment by process of photosynthesis, which is anabolic process in which C02 is fixed to form carbohydrates (glucose molecules) and oxygen is returned the atmosphere.

Burning of fossil fuel utilises O2 and releases CO₂ in the atmosphere. Respiration is a catabolic process in which glucose molecules are used up and oxidised to release energy and carbon dioxide. Fungi do not perform photosynthesis and take up 02 from environment for using in respiration process.

Question 25.
Low visibility during cold weather is due to
(a) formation of fossil fuel
(b) unburnt carbon particles or hydrocarbons suspended in air
(c) lack of adequate power supply
(d) none of these.
Solution:
(b) Low visibility during cold weather is due to formation of smog. Combustion of fossil fuels increases the amount of suspended particles in the air. These could be unburnt carbon particles or substances called hydrocarbons. Presence of high levels of all these pollutants causes the visibility to be lowered, especially in cold weather when water also condenses out of air. This is known as smog and is a visible indication of air pollution.

Question 26.
Growth of Lichens on barren rocks is followed by the growth of
(a) moss
(b) ferns
(c) gymnosperms
(d) algae.
Solution:
(a)Lichens are considered to be pioneer inhabitants of a rocky surface. They produce acids like carbonic acids that corrode the rock to form a thin layer of soil. Lichens are succeeded by mosses, which later grow on such surfaces. Rhizoids of mosses penetrate deeper in the rocks and cause the rocks to break up further.

Question 27.
Marked temperature changes in aquatic environment can affect
(a) breeding of animals
(b) more growth of aquatic plants
(c) process of digestion in animals
(d) availability of nutrients.
Solution:
(a), (c) and (d) Temperature of water bodies is raised due to discharge of hot water from thermal plants. These thermal plants use water for cooling in various operations and later return this hot water to water-bodies. A rapid increase in temperature adversely effects the aquatic organisms. A significant halt in the reproduction of marine wildlife can happen due to increase in temperature because reproduction can happen only within certain range of temperature. Excessive temperature can cause release of immature eggs or can prevent the normal development of certain eggs. Enzymes work at specific temperature. Therefore, in aquatic animals the process of digestion will be affected with the increase of temperature of water. This increased temperature will affect the solubility of nutrients in the water as well as aerobic decomposition is replaced by anaerobic fermentation and putrefaction.

Question 28.
Soil erosion can be prevented by
(a) raising forests
(b) deforestation
(c) excessive use of fertiliser
(d) overgrazing by animals.
Solution:
(a) Soil erosion is the removal and transportation of top layer of soil from its original position to another place with the help of strong winds and fast running rain water.
Soil erosion can be prevented by raising forests, as roots of plants have an important role in preventing soil erosion. Roots hold the soil particles and reduce the exposure of soil to air and wind, thereby reducing its displacement.

Question 29.
What happens when rain falls on soil without vegetational cover?
(a) Rain water percolates in soil efficiently
(b) Rain water causes loss of surface soil
(c) Rain water leads to fertility of the soil
(d) Rain water does not cause any change in soil
Solution:
(b) Vegetational cover plays an important role in preventing soil erosion. Roots of the plants hold the soil particles in place. These also plays a role in percolation of water into the deeper layers too. Thus absence of vegetational cover will cause the removal or displacement of upper layer of soil, a process called soil erosion.

Question 30.
Oxygen is harmful for
(a) ferns
(b) nitrogen fixing bacteria
(c) Chara
(d) mango tree,
Solution:
(b): Refer to answer 6

Question 31.
Rivers from land, add minerals to sea water. Discuss how?
Solution:
A large number of salts, minerals and other substances are capable of getting dissolved in water. Flowing water wears away hard rocks. Fast flowing water of river carries various-sized particles of rocks down stream. The soluble minerals present in the rock particles^get dissolved in river water that flows over them. These dissolved minerals are carried along the stream and passed from land to sea.

Question 32.
How can we prevent the loss of top soil?
Solution:
The removal and transportation of top layer of soil by certain agents like strong winds and fast running rain water, is called soil erosion. Loss of top layer of soil can be prevented by:

1. Increasing the vegetational cover: Various methods like intensive cropping and planting of xerophytes, prevent the exposure of top soil to wind and rain. Increase in vegetation cover will bind the loose soil and reduce the erosion.
2.  Checking deforestation: The large- scale deforestation leads to soil erosion. Top soil that is bare of vegetation is likely to be removed very quickly. Roots of plants especially trees have a paramount role in preventing soil erosion by holding the soil. Thus excessive cutting of trees should be restricted or reduced in ordepr to save trees, which prevents soil erosion.
3. Preventing overgrazing: Certain pasture lands are being devoid of the grasses due to grazing activities of animals like goat and sheep, etc. Preventing the overgrazing will help to restore the vegetation cover that will prevent the soil erosion.
   (iv) Terrace farming: It is a method of farming followed in hilly areas in which steps are made at the slopes, which allow rain water to move slowly so that the soil is not washed away. It helps to prevent soil erosion.

Question 33.
How is the life of organisms living in water affected when water gets polluted?
Solution:
Life of organisms living in water is adversely affected due to addition of pollutants in water in the following ways :

1. Addition of untreated industrial wastes adds various acids and alkalies to the water bodies that kill various useful microorganisms present in water bodies.
2. Addition of fertilisers and sewage, adds nutrients to the water. This addition of nutrients causes excessive growth of algae, a phenomenon called eutrophication. The death and subsequent decomposition of organic matter, increase the biological oxygen demand, which ultimately reduces the dissolved oxygen which lead to death of aquatic organisms including fishes.
3. Regular discharge of industrial wastes carrying heavy metals in water bodies leads to biomagnification of heavy metals like mercury, cadmium etc. that threatens the life of aquatic organisms.
4. Hot water released from thermal power plants, reduces the dissolved oxygen content and kills various aquatic organisms (fishes, etc.) present in water.

Question 34.
During summer, if you go near the lake, you feel relief from the heat, why?
Solution:
Going or sitting near the water body during summer provides relief from heat. This is because the air coming from water body contains water vapours and is cool. During summers the water body gets heated up due to solar radiations. This heating up of water causes the water vapour to rise upwards and condense. The air laiden with Vater vapour is cooler than the dry air blowing on land. It is this cooler air flowing from water body that provides relief from the heat or high temperature during summer.

Question 35.
In coastal area, wind current moves from the sea towards the land during day; but during night it moves from land to the sea. Discuss the reason.
Solution:
In coastal areas, cool breeze flows regularly from sea towards the land during the day time. However, at night there is a reverse flow of air from land to sea. It is so because during day, the air above land gets heated faster and starts rising, creating a region of low pressure below. The air above sea, is comparatively cool. As a result, the air over the sea moves into this region of low pressure. Thus during the day, the direction of wind is from sea to the land. At night, both the land and the sea start to cool. Since water cools down slower than the land, the air above water is warmer than the air above land. Thus, during night, the direction of wind is from land to the sea.

Question 36.
Following are a few organisms:
(a) Lichen
(b) Mosses
(c) Mango tree
(d) Cactus
Which among the above can grow on stones; and also help in formation of soil? Write the mode of their action for making soil.
Solution:
Lichens and mosses are the first inhabitants or pioneers on a bare rock. They bring about slow weathering of rocks and formation of soil. The lichens live on the rocks and produce acids like carbonic acids. The latter corrode the surface of rocks to form thin layer of soil. Other plants like mosses later grow on such surfaces and causes the further breaking up of rocks. The cracks further become wider and deeper when the roots of short-lived herbs pass into them. This whole process of weathering of rocks involving living organisms is called biological weathering.

Question 37.
Soil formation is done by both abiotic and biotic factors. List the names of these factors by classifying them as abiotic and biotic?
Abiotic factors that cause soil formation include non-living components of environment, which are: sun, water and wind.
Biotic factors that cause soil formation include living organisms, which are: lichens, mosses, herbs, shrubs etc.

Question 38.
All the living organisms are basically made up of C, N, S, P, H and O. How do they enter the living forms? Discuss.
Solution:
All living organisms require some essential elements which include carbon, hydrogen, oxygen, nitrogen, sulphur, phosphorus, etc. The living organisms can get these nutrient elements from lithosphere, hydrosphere and atmosphere, but these elements enter into living forms through plants. Most of these elements first enter plants and become components of their organic material by the processes of photosynthesis, nitrogen fixation, etc. From plants, these elements are further passed on to the other organisms through the food chain.

Question 39.
Why does the percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere?
Solution:
The percentage of gases like oxygen, nitrogen and carbon dioxide remains almost constant in the atmosphere. This constant percentage is maintained by their constant flow through nutrient cycles.
Various nutrient cycles likes oxygen cycle, carbon cycle and nitrogen cycle continuously operate in the nature by constant interaction between biotic and abiotic components of the biosphere. This interaction consists of transfer of matter and energy between different components of the biosphere.
The environment acts as a reservoir for these gases and living organisms continuously take up gases from it. These gases are further returned to the environment by various processes like respiration, combustion, decomposition, etc., thereby maintaining a constant percentage. Any major change in percentage of these gases can disrupt the ecosystem and adversely affect the living components of ecosystem.

Question 40.
Why does moon have very cold and very hot temperature variations e.g., from -190°C to 110°C even though it is at the same distance from the sun as the earth is?
Solution:
Atmosphere plays a vitakrole in climate control and acts a temperature buffer. It prevents the sudden increase in temperature during the day light hour and slows down the escape of heat into the outer space during night thereby preventing the excessive cooling during the night. In this way, the average temperature of earth remains fairly steady. Although the moon is at the same distance from the sun as the earth is, but since moon has no atmosphere, so the temperature on the surface of moon shows large variations. Moon gets heated up as sun’s rays fall on its surface and it cools down drastically when sun’s rays are not falling over it.

Question 41.
Why do people love to fly kites near the seashore?
Solution:
In coastal areas, during day time, there is regular flow of cool air from the sea towards the land. During day, the air above the land gets heated fastc and starts rising. This rising of air creates a region of low pressure. The ’ cooler air from the sea constantly moves into this area of low pressure. This continuous movement of air from sea to land creates winds and direction of this wind would be from sea to land. So, flying kites near sea shore is easy and joyful as compared to anywhere else.

Question 42.
Why does Mathqra refinery pose problems to the Taj Mahal?
Solution:
The Mathura oil refinery discharges huge amounts of toxic gases into the i atmosphere. Tones of sulphur dioxide, oxides of nitrogen, hydrocarbons, carbon monoxide and aerosols are released in the atmosphere every day. The oxides of sulphur, carbon and nitrogen combine with water vapour or moisture present in the air to form weak sulphuric, carbonic and nitric acids.

These acids are corrosive to stones, metals, paints and textiles. The gaseous pollutants from the refinery get converted into acids and [ travel towards Agra for most of the time and
cause serious air pollution problem and pose a threat to Taj Mahal. The acids present in rain react with marble (calcium carbonate) of Taj Mahal and corrode it.

Question 43.
Why do not lichens occur in Delhi whereas they commonly grow in Manali or Darjeeling?
Solution:
Lichens are pollution indicators. They are considered as bioindicators of air pollution. They are sensitive to sulphur dioxide and do not grow in areas where air is having high amounts of SO₂.
Delhi has maximum air pollution and high amount of SO₂ in air due to vehicular emission. Manali and Darjeeling on the other hand are not polluted and are green cities, therefore the S02 concentration is comparatively low in these areas. Due to this growth of lichens does not occur in Delhi which is air polluted and has high SO₂ concentration.

Question 44.
Why does water need conservation even though large oceans surround the land masses?
Solution:
Water is one of the basic necessities of life. Availability of water is one of the important factor that decides the sustainability of life in a region. Water occupies a very large area of earth’s surface. 97.5% of the water on planet earth is found in seas and oceans as saline water and unavailable for human consumption because bodies of terrestrial life-forms cannot tolerate high amounts of dissolved salts present in saline water.

Only 2.5% of the total water resources of the world consists of fresh water. Majority of it (about 2%) is found frozen in the ice-caps at the two poles and on snow-covered mountains. Remaining (only about 0.6% of the total) is available to support terrestrial life. Majority (90%) of this fresh water is found underground as ground water and only 10% occurs as surface water. Since limited amount of fresh water is available to us as a renewable source through water cycle and its distribution is also limited, conservation of water is a prime requirement.

Question 45.
There is mass mortality of fishes in a pond. What may be the reasons ?
Solution:
Mass mortality of fish in a pond must have occured due to addition of certain substances that deteriorate the quality of water and render it unfit for sustaining life. Following can be the reasons for death of fish in pond :
(i) Heat: Some thermal plants release hot water directly into water bodies, which
reduces the dissolved oxygen content of water and causes the mortality of living aquatic organisms.
(ii) Radioactive wastes: Certain industries discharge radioactive metals or heavy metals like (Hg) directly into the water body. These toxic metals are then eaten up by fish. Ingestion of such toxic metals disrupts their basic life processes and causes their death.
(iii) Algal bloom: Addition of organic nutrients by increased amount of fertilisers and sewage into water body causes the growth of excessive algae (algal bloom), which further reduces the dissolved oxygen in water body and causes death of various aquatic organisms like fish, etc.

Question 46.
Lichens are called pioneer colonisers of bare rock. How can they help in formation of soil?
Solution:
Lichens are called pioneer colonisers of bare rock because they are first to inhabit a rocky surface and help in formation of soil. The lichens grow on the surface of rocks. While growing, they release certain acids that corrode the surface of rocks to form thin layer of soil. This surface is now available for the growth of other plants like mosses, etc. which cause the rock to break up further. The whole process of weathering of rocks involving living organisms is called biological weathering.

Question 47.
“Soil is formed by water.” If you agree to this statement then give reasons.
Solution:
Water causes the physical weathering of rocks and influences the formation of soil in following two ways:
(i) It gets into the cracks of the rocks formed due to uneven heating of different parts of the rocks by the sun. On freezing, the water expands in rock crevices and breaks the rocks.
(ii) Flowing water wears away even hard rocks over long periods of time. Fast flowing water generally carries various-sized particles of rocks downstream. On the way, these moving particles rub against other rocks. The resultant abrasion forms smaller particles. The water takes these particles of rocks and deposits them down its path. In this way, soil is formed in places far away from its parent rock.

Question 48.
Fertile soil has lots of humus Why?
Solution:
Soil is said to be fertile when it is able to sustain plant growth i.e., provide habitat to plants and result in constant yields of high quality. A fertile soil is rich in nutrients necessary for basic plant nutrition including nitrogen, phosphorus and potassium. Fertile soil has adundant humus. Humus is dark- coloured partially decayed organic matter rich in nutrients. It makes the soil porous, thereby increasing its air and water holding capacity. Humus is rich in nutrients that promote plant growth. Being black, it also absorbs heat to warm up the soil.

Question 49.
Why step farming is common in hills?
Solution:
Step farming or terrace farming is practiced in hilly areas in which small fields are formed in the form of steps or terraces for cultivation of crops. This technique reduces the flow of rain water down the slopes of hills. Moreover, eroded soil from upper regions of hills gets deposited in lower terraces. In this way, soil erosion can be checked in hilly regions.

Question 50.
Why are root nodules useful for the plants?
Solution:
Root nodules are present in leguminous plants such as peas and beans. These root nodules contain symbiotic nitrogen fixing bacteria like Rhizobium, etc.
These symbiotic bacteria are very useful for plants as they take up free atmospheric nitrogen which cannot be used as such by plants and animals and needs to be converted into biologically acceptable forms. They convert it into ammonia. Most of the ammonium compounds are oxidised by nitrite bacteria (Nitrosomonas and Nitrosococcus) to soluble nitrities, which are further oxidised by nitrate bacteria (Nitrobacter and Nitrocystis) to soluble nitrates. This process is called biological nitrogen fixation.
These leguminous plants containing root nodules are cultivated by farmers after wheat to replenish the nitrogen in soil as nitrates.

Long Answer Type Questions

Question 51.
How do fossil fuels cause air pollution?
Solution:
Burning of fossil fuels (coal, petroleum and natural gas) in automobiles, industries and thermal power plants is the major cause of air pollution.
(i) Acid rain: The harmful gases i.e., oxides of sulphur and nitrogen, emitted by burning of fossil fuels, react with water in the atmosphere to form H2S04 and HN03 respectively. These acids combine with rainwater and fall in the form of acid rain. Acid rain increases acidity f of soil, thereby decreasing its fertility. It also increases the acidity of water, affecting aquatic life.

(ii) Carbon monoxide poisoning: Incomplete ‘ burning of fossil fuels produces carbon monoxide. It affects the central nervous system. When present in large quantities in air, it can also lead to carbon monoxide ‘ poisoning reduction in the availability of oxygen to body tissues that lead to suffocation and finally death.

(iii) Global warming: Burning of fossil fuels adds large amounts of ‘green house gases’ particularly carbon dioxide, methane andoxides of nitrogen to the atmosphere. These green house gases trap the infra-red radiations reflected by earth. This lead to an increase in earth’s temperature, a phenomenon termed as ! global warming. This global warming further causes the melting of polar ice caps which 1 will eventually rise the sea level and flooding of coastal regions.

(iv) Smog: The burning of fossil fuels also increases the amount of suspended particles ‘ in the air. These suspended particles could be unbumt carbon particles or substances like
hydrocarbons. Their presence in air lowers the visibility of air especially during cold r weather. This is known as smog and causes allergies, heart diseases and cancer.

Question 52.
What are the causes of water pollution? Discuss how you can contribute in reducing water pollution.
Solution:
Water pollution is an undesirable change in the physical, biological or chemical qualities of water (due to addition of foreign organic, inorganic, biological or radioactive substances) that adversely affects the aquatic life and makes water less fit or unfit for use. Some of the main causes of water pollution are:

(i) Sewage: It is filthy matter, that mainly includes organic wastes and is carried in large underground drains called sewers. It is the main water pollutant in towns and cities. It increases nutrient load of water bodies which leads to eutrophication.

(ii)Industrial wastes: The industrial wastes  (including both organic and inorganic chemicals) contain large quantities of harmful chemicals including acids and alkalies that are discharged into water bodies. The industrial wastes sometimes contain radioactive substances like mercury, etc.
(iii) Synthetic soaps and detergents: Water containing soaps and detergents is called gray water. These pollutants are discharged from house and certain factories, and make water unfit for human consumption.

(iv) Fertilisers and pesticides: Fertilisers and pesticides, being excessively used in fields to increase crop production are washed by rainwater into water bodies and pollute them.
(v) Oil spills: Drilling and shipping operations in oceans sometimes cause leakage of petroleum which leads to destruction of flora and fauna of ocean water.

(vi) Heat: Release of hot water from power plants increases the temperature and reduces the dissolved oxygen in water, thus killing the aquatic organisms.

(vii) Unhygienic habits: Bathing of humans and animals, washing clothes, defecation etc. near water bodies is another major cause of water pollution in a country like India. Water pollution can be considerably reduced by taking some steps which are as follows :

• The sewage should not directly discharged into the water body. Treatment of sewage should be done that converts the harmful substances of sewage into harmless ones.
  (ii) Throwing of garbage and domestic wastes in the water body should be prohibited.
  (iii) Dumping of toxic wastes from industries should be prevented by legal restrictions.
  (iv) Trees should be planted near the river banks to check soil erosion which would otherwise cause siltation of water body.
• Use of fertilisers and pesticides should be considerably reduced and farmers should be encouraged to switch to organic harmless manures and other eco-friendly methodologies of farming.

Question 53.
A motor car, with its glass totally dosed, is parked directly under the sun. The inside temperature of the car rises very high. Explain why?
Solution:
When a motor car, with its glasses totally closed is parked directly under the sun, the inside temperature of car rises very high. This is because of the greenhouse effect.
The short wavelength infra-red radiations from sunlight pass through the glasses of the car and heat the interior of the car. Heated inner parts and upholstery of the car emit long wavelength heat radiations. The glass of windows of the car will not allow these long wavelength heat radiations to pass out of the car. Hence, the heat gets trapped inside the car and raises the interior temperature.

Question 54.
Justify”dust is a pollutant”.
Solution:
Air pollutant is any agent or substance whose addition or increase in concentration beyond normal deteriorates the quality of air and affects the heath of living organisms. Pollutant can be a particulate matter or a gaseous substance.
Dust is classified as a particulate matter which is also called as suspendend particulate matter (SPM) because it remains suspended in air for a reasonable period of time. Dust is harmful to humans, plants and animals, and is considered as an important (primary) air pollutant. Some of the harmful effects of dust are:

(a) Dust affects plant growth and health as it clogs stomata and covers the surface of leaf, preventing photosynthesis, respiration etc.
(b) Dust is a major cause of allergic reactions in humans especially bronchial asthma and chronic bronchitis. ,
(c) Dust from various industries like cotton dust, iron mill dust, mine dust, flour mill dust etc. results in various respiratory problems like emphysaema, tuberculosis etc.
(d) Dust also carries heavy toxic metals like Hg, Pb, Cu, etc. which are harmful to both animals and plants.
(e) Sometimes the particulates accumulate in upper layers of atmosphere to form large coloured clouds that hinder passage of solar radiation and lower the temperature of earth’s surface.

Question 55.
Explain the role of the Sun in the formation of soil.
Solution:
The process of formation of soil from rocky earth’s crust is termed as pedogenesis. Over long periods of time, the rocks at or near the surface of earth are broken down by various physical, chemical and biological processes to form fine soil particles.

Temperature variations due to radiation of sun is one of the major factor that influences the formation soil from the rocks. Under the influence of solar radiations, the rocks heat up and expand. At night, these cool down and contract. Since all parts of the rocks do not expand and contract at the same time, cracks appear in the rocks and ultimately the large rocks break up into smaller pieces.

Question 56.
Carbon dioxide is necessary for plants. Why do we consider it as a pollutant?
Solution:
Green plants, through photosynthesis, convert carbon dioxide to glucose in the presence of sunlight, which is a food for plants and further stored in the form of starch. Thus, carbon dioxide is an essential requirement for plants and is being regularly fixed by them.

CO₂ is considered as a pollutant because of its increased concentration since recent years. Due to burning of fossil fuels, deforestation and other human activities, large amounts of CO₂ and other greenhouse gases are added to the atmosphere. These increased greenhouse gases trap the heat reflected by earth. This heats up the atmosphere which further leads to an increase in earth’s average temperature. This phenomenon is called global warming. Some of the harmful effects of global warming are:
(i) Increase in temperature of earth can lead to melting of polar ice caps. This will result in rise in the sea level, due to which coastal regions will be flooded or might even be submerged.
(ii) Increase in temperature of earth due to green house effect will result in changes in weather and precipitation patterns.

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