Note of Natural Resources

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Page 193

Ques 1.How is our atmosphere different from the atmospheres on Venus and Mars?

Ans. Earth·s atmosphere is different from those of Venus and Mars. This difference lies essentially intheir compositions. Earth·s atmosphere is a mixture of nitrogen (79%), oxygen (20%), and a smallfraction of carbon dioxide, water vapour and other gases. This makes the existence of life possible on

Earth. However, the atmospheres on Venus and Mars mainly consist of carbon dioxide. The amount ofcarbon dioxide on these planets can range from 95% to 97%.

Ques 2. How does the atmosphere act as a blanket?Ans. The atmosphere acts as a blanket by performing the following functions:(a) It keeps the average temperature of the Earth fairly constant during day time and even during the

course of whole year.(b) It prevents a sudden increase in the temperature during day time.(c) It slows down the escape of heat from the surface of the Earth into outer space during night time.

Ques 3. What causes winds?

Ans. An uneven heating of the Earth·s surface causes winds. On being heated, air becomes lighter andrises up. As a result, a region of low pressure is created. Then, air from a high pressure region moves toa low pressure region, causing wind.

Ques 4. How are clouds formed?Ans. During day time, on being heated, a large amount of water evaporates from various water bodies

and goes into the air. A part of this water vapour also reaches the atmosphere through biologicalactivities such as transpiration and respiration. This causes the air in the atmosphere to heat up. Whenthis heated air rises, it expands and cools, which results in the condensation of water vapour formingwater droplets. The presence of dust and other suspended particles in air also facilitates the process of

condensation. The formation of water droplets leads to the formation of clouds.Ques 5. List any three human activities that you think would lead to air pollution.

Ans. The following three human activities would lead to air pollution:(i) Burning of fossil fuels such as coal and petroleum.

(ii) Industrialization.(iii) Deforestation.

Page 194

Ques 1. Why do organisms need water?

Ans. Organisms need water for the following reasons:(i) All cellular processes need water as a medium. Usually, the reactions that take place in our body orwithin the cells occur between substances that are dissolved in water.(ii) Since most of the substances are transported in a dissolved form, water is necessary.

Ques 2. What is the major source of fresh water in the city/town/village where you live?

Ans. River is a major source of fresh water.Ques 3. Do you know of any activity which may be polluting this water source?

Ans. The discharge of waste water from homes, industries, hospitals, etc. into the river pollutes thisfresh water source.

Page 196Ques 1. How is soil formed?

Ans. Soil is formed by breaking down of rocks at or near the surface of the Earth through various

physical, chemical, and biological processes by various factors such as the sun, water, wind, and living



organisms.

(i) Sun- During day time, the rocks are heated. This causes the rocks to expand. During nighttime, these rocks cool down and contract. Since all parts of the rock do not undergo expansionand contraction at the same rate, this causes the formation of cracks in these rocks. Thesecracks lead to the breaking up of huge rocks into smaller pieces.

(ii) Water- Water catalyses the process of formation of soil in two ways.(a) Water goes into the cracks and crevices formed in the rocks. When this water freezes, its

volume increases. As a result, the size of the cracks also increases. This helps in theweathering of rocks.

(b) Running water wears away hard rocks over long periods of time. Water moving in fast

speed carries big and small particles of rock downstream. These rocks rub against eachother, resulting in breaking down of rocks. These smaller particles are carried away byrunning water and deposited down its path.

(iii) Wind- Strong winds carry away rocks, which causes rubbing of rocks. This results in the

breaking down of rocks into smaller and smaller particles.(iv) Living organisms- Some living organisms like lichens help in the formation of soil. Lichens also

grow on rocks. During their growth, lichens release certain substances, which cause the rock

surface to powder down forming a thin layer of soil. On this thin layer of soil, some smallplants like moss also grow. They further cause the breaking down of the rock particles.

Ques 2. What is soil erosion?Ans. The blowing away or washing away of land surface by wind or water is known as soil erosion.Ques 3. What are the methods of preventing or reducing soil erosion?

Ans. The methods of preventing or reducing soil erosion are:

(i) Prevention of deforestation(ii) Plantation of trees

Page 201

Ques 1. What are the different states in which water is found during the water cycle?Ans. During the water cycle, water is found in solid state (snow, ice, etc.), liquid state (ground water,river water, etc.), and gaseous state (water vapour).Ques 2. Name two biologically important compounds that contain both oxygen and nitrogen.

Ans. Two biologically important compounds that contain both oxygen and nitrogen are:

(i) Amino acids(ii) Deoxyribonucleicacid (DNA) and Ribonucleicacid (RNA)

Ques 3. List any three human activities which would lead to an increase in the carbon dioxidecontent of air.

Ans.

(i) Burning of fuels in various processes like heating, cooking, transportation, and industry.(ii) Human induced forest fires(iii) The process of deforestation includes the cutting down of trees. This decreases the uptake of

carbon dioxide for photosynthesis. Eventually, the content of carbon dioxide increases.

Ques 4. What is the green house effect?

Ans. Some gases like carbon dioxide, methane, nitrous oxide prevent the escape of heat from theEarth·s surface by trapping it. This increases the average temperature of the Earth. This is called thegreen house effect. An increase in the content of such gases would lead to a situation of global warming.

Ques 5. What are the two forms of oxygen found in the atmosphere?



Ans. The two forms of oxygen found in the atmosphere are:

(i) Diatomic molecular form with chemical formula O2.(ii) Triatomic molecular form with chemical formula O3 known as ozone.

Exercise

Ques 1. Why is the atmosphere essential for life?

Ans. The atmosphere is essential for life because it maintains an appropriate climate for the sustenance

of life by carrying out the following activities.(i) Atmosphere keeps the average temperature of the Earth fairly constant during day time.(ii) It prevents a sudden increase in temperature during day time.

(iii) It also slows down the escape of heat from the surface of the Earth into outer space duringnight time.

Ques 2. Why is water essential for life?

Ans. Water is essential for life because of the following reasons:

(i) Most biological reactions occur when substances are dissolved in water. Thus, all cellularprocesses need water as a medium to take place.

(ii) Transportation of biological substances needs water as a medium.

Ques 3. How are living organisms dependent on the soil? Are organisms that live in water totallyindependent of soil as a resource?

Ans. Almost all living organisms are dependent on soil. Some depend directly, while some dependindirectly.Plants need soil for getting support as well as nutrients to prepare their food. On the other hand,organisms depend on plants for food and other substances that are essential for life. Herbivores depend

directly upon plants, and carnivores depend upon animals, which in turn depend upon plants for food. Thismakes them depend on soil indirectly.Organisms that live in water are not totally independent of soil as a resource. These organisms dependon aquatic plants for food and other substances. These aquatic plants in turn require minerals for their

sustenance. These minerals are carried to water bodies from soil by rivers, rain water, etc. Without thesupply of minerals from the soil to the water bodies, it is impossible to imagine aquatic life.

Ques 4. You have seen weather reports on television and in newspapers. How do you think we are

able to predict the weather?

Ans. The meteorological department of the government collects data on the elements of weather suchas maximum and minimum temperatures, maximum and minimum humidity, rainfall, wind speed, etc. Theyare able to study these elements using various instruments. The maximum and minimum temperature of aday is measured by a thermometer known as the maximumíminimum thermometer. Rain fall is measured

by an instrument known as the rain gauge. Wind speed is measured by anemometers. There are various

instruments used to measure humidity.Ques 5. We know that many human activities lead to increasing levels of pollution of the air, water

bodies and soil. Do you think that isolating these activities to specific and limited are as would

help in reducing pollution?

Ans. Yes. Isolating human activities to specific areas would help in reducing levels of pollution. Forexample, setting up of industries in isolated regions will control pollution to some extent. The pollutioncaused by these industries will not contaminate water resources, agriculture land, fertile land, etc.Ques 6. Write a note on how forests influence the quality of our air, soil and water resources.

Ans. Forests influence the quality of our air, soil, and water resources in various ways. Some of them



are:

(i) Forests balance the percentages of carbon dioxide and oxygen in the atmosphere. Theincreasing amount of carbon dioxide caused by human activities is balanced by a larger intakeof carbon dioxide by plants during the process of photosynthesis. Simultaneously, a largeamount of oxygen is released.

(ii) Forests prevent soil erosion. Roots of plants bind the soil tightly in a way that the surface ofthe soil cannot be eroded away by wind, water, etc.

(iii) Forests help in the replenishment of water resources. During the process of transpiration, ahuge amount of water vapour goes into the air and condenses to form clouds. These cloudscause rain fall that recharge water bodies.

Extra questionsQues 1.Excess of which gas has present in air leads to green house effect?

Ans. Carbon dioxide.

Ques 2. What causes ozone layer depletion?

Ans. CFC·s and halogen gases.Ques 3. Name two sources that release CO into air.

Ans. Incomplete combustion of diesel and petrol in the engines of motor cars and other vehicles.Ques 4. Define ground water.

Ans. The water steeping ground during rainfalls is available as underground water resource, is calledground water.Ques 5. Which one gas is responsible for green house effect?

Ans. Carbon dioxide.

Ques 6. Name the part of the atmosphere where ozone layer is found.

Ans. Stratosphere.Ques 7. What are the sources of alternative energy to replace fossil fuel?

Ans. Solar energy and nuclear power etc.

Ques 8. Name the group of compounds responsible for ozone layer depletion.Ans. Chloro fluro carbons.Ques 9. Name two gases given out by burning of fossil fuels, which dissolves in rain water to form

acid rain.

Ans. Sulphur dioxide (SO2) and Nitrogen dioxide (NO2).

Ques 10. What is humus?

Ans. Remains of dead decomposing of organisms mixed with soil.Ques 11. Name two leguminous plant and two non-leguminous plants which can fix nitrogen.Ans. Leguminous plants: Pea, Bean.

Non-Leguminous plants: Alnus, Ginkgo.

Ques 12. What are the main natural resources?Ans. Water, air, soil (land), energy, minerals and organisms.Ques 13. Give a few examples of non-renewable resources.

Ans. Petroleum, minerals and coal.

Ques 14. Define non-renewable resources.

Ans. The resources which cannot be renewed e.g. exhaustible.Ques 15. Give the main cause of salinity.

Ans. Accumulation of soluble salt above or below the soil.

Ques 16. List the three different kinds of soil.



Ans. Sandy, clayey and loamy.

Ques 17. Define a natural resource.

Ans. Natural resource is found in reserve in nature. Natural resources are components of atmosphere,hydroshpher and lithosphere e.g. energy, air, soil, water, land etc.Ques 18. Why do plants die in water-logged area?

Ans. The roots get rotten in water-logged area.Ques 19. What source of energy can easily replace the use of wood in villages?

Ans. Biogas.Ques 20. Give reasons why respiration is called slow combustion.

Ans. Respiration is called slow combustion because in the respiration process food materials are burned

slowly and at a lower temperature to produce the products of ordinary combustion like CO2 water andenergy.Ques 21. Differentiate between renewable and non-renewable resources.

Ans.(i) Renewable: They are replenished e.g. water, soil, plants, animals.

(ii) Non-renewable: They are replenished e.g. underground water, fossil, fuels, coal, petroleum. Ques 22. What is biological fixation of nitrogen?

Ans.The process of converting atmospheric nitrogen into proteins and other nitrogenous organic

compounds by the action of certain bacteria and algae is called biological fixation of nitrogen.Ques 23. Name any two non-renewable resources.

Ans. (i) Coal (ii) Petroleum.Ques 24. What are various kinds of natural resources?

Ans. (i) Inexhaustible, and (ii) Exhaustible natural resources.Ques 25. What do you understand by ¶Silviculture·?

Ans. Silviculture is the growing of crops in the fields. It is also called as agriculture.Ques 26. Give two ill effects of soil erosion.

Ans. Leaching and reduction in soil fertility.Ques 27. Mention any two causes of air pollution?

Ans. (i) Over population, (ii) Deforestation.Ques 28. What are the biodegradable wastes?

Ans. Biodegradable waste materials are those waste materials which can be broken down into simple,non-poisonous substances by the action of microorganisms.

Ques 29. Expand SPM.

Ans. SPM: Solid Particulate Matter.Ques 30. What is soil erosion?

Ans. The soil erosion is a process in which various elements accumulated in a place and some where, arewashed away by any of the abiotic factors.

Ques 31. Name two main abiotic factors that affect human development.

Ans. Air and Water.Ques 32. Writes two natural sourced of air pollution.

Ans. Forest fir, ash from smoking volcanoes, dust storm and decay of organic matters are the naturalsources of air pollution.

Ques 33. What is meant by abiotic environment?

Ans. Abiotic means non-living or without life.Ques 34. Define pollutants.

Ans. Pollutants are ´those agent or substances that cause changes in the substanceµ.

Ques 35. Define pollution.



Ans. Pollution is defined ´as the undesirable change in physical, chemical and biological characteristics

of our air, water and landµ.Ques 36. Mention any two sources of air pollution.

Ans. (i) Natural sources e.g.,Volcanoes. (ii) Man-made sources e.g., motor vehicles.Ques 37. Define air pollution.

Ans. An undesirable change in the physical, chemical and biological characteristics of air is known as airpollution.

Ques 38. Arrange the following steps in order of their sequence of occurrence in nitrogen cyclestarting from nitrogen gas:

Ammonification, Denitrification, Nitrification, Nitrogen fixation.

Ans. Nitrogen fixation Ammonification, Nitrification, Denitrification.Ques 39. Name any two environmental problems caused by the various activities of human beings.Ans. Soil erosion and global warming.

Ques 40. Arrange the following in the sequence they appear in oxygen cycle:

Photosynthesis, water and CO2, Cellular respiration, Atmospheric oxygen.

Ans. Atmospheric oxygen, cellular respiration, water and CO2, photosynthesis.Ques 41. Name some aquatic weeds which are regarded as pollutants.

Ans. Eichhornia and some algae.Ques 42. What are the nature·s cleansing agent?

Ans. Natural cleansing agents are ³microorganisms, bacteria, algae.Ques 43. Give one cause of water pollution.

Ans. Industrial wastes like oils, grease, phenols, salts etc.Ques 44. Name two main abiotic factors, which affect human environment.

Ans. ¶Air and water· are the abiotic factors which affect human environment.Ques 45. Name two Green House Gases.

Ans. Carbon dioxide (CO2) and methane (CH4).Ques 46. Write full form of CFC·s.

Ans. CFC·s = Chloro Fluoro Carbons.Ques 47. How is ozone layer useful to us?

Ans. Ozone layer is helpful to us. It protects us from the harmful radiations. This layer does notallow harmful ultraviolet rays of sunlight to pass through it. So it is due to ozone layer in theatmosphere that the harmful U.V. rays coming from the sun do not reach us on the earth and

we are saved from their bad effects.Ques 48. (i) Why do eukaryotic cells and many prokaryotic cells need oxygen?

(ii) What does this result in?Ans. (i) They need oxygen to break down glucose molecules and get energy for their activities.

(ii) This results in the production of carbon dioxide.

Ques 49. State two effects of depletion of ozone layer in the atmosphere.Ans. Two effects of depletion of ozone layer are:

(i) UV rays coming to earth surface any cancer, cataract and inflammatory diseases.(ii) It may change the gene structure in animals and plants.

Ques 50. (i) What is top soil?

(ii) Why is the quality of top soil important?Ans. (i) The top most layer of the soil that contains humus and living organisms in addition to thesoil particles is called the top soil.

(ii) The quality of the top soil is an important factor that decides bio-diversity in that area.



Ques 51. Give your viewpoint about the conservation of natural resources.

Ans. Conservation of natural resources: The conservation of air, water, animals, plants, soil resourcesshould be according to the rules and regulations laid down by the government. They should be usedrationally. Alternative sources of energy should be used. Management of our forests and wild life isessential.

Ques 52. What is global warming?

Ans. According to some ecologists Green House Effect will lead to global warming. In about next 50

years the temperature of the earth will rise by 2°C - 5°C due to which there will be an increase of waterlevel by five metres. The water will enter to the low lying areas. With the result of that, many prominentcities will be merged in the sea.

Ques 53. Explain how ozone layer acts as our saviour.

Ans. Ozone layer acts as our saviour. It is situated in the upper part of the atmosphere. It acts asthe saviour as it absorbs the ultraviolet rays which are harmful to all animals and plants. Theserays come out from the sun. It causes cancer in the animal body. It is also responsible for the

genetic disorder.Ques 54. What are aerosol spray propellants? What damages do they cause?

Ans. Aerosal spray propellants: These are the chemical such as fluorocarbons and chlorofluorocarbons

These chemicals react with the ozone layer gas and decompose it.Ozone layer is the only source which absorbs ultra-violet rays coming out from the sum. These

rays are the responsible cause for producing skin cancer in human beings and other animals too.These rays are also responsible for many genetic disorders in all the living beings.

Ques 55. Distinguish between lithosphere and atmosphere.

Ans. Lithosphere and Atmosphere: The lithosphere is the solid portion of the earth. The lithosphere

is a sphere of solid material about 6400 km. in radius.The atmosphere is the sea of air which surrounds the earth. It has no distinct boundary. Asthe gravitational contraction and radioactive decay resulted in that generation, gases werereleased from their compounds. These were retained as atmosphere around them due to

sufficient gravity.Ques 56. Give the meaning of biogeochemical cycle.

Ans. Biogeochemical Cycle:The cyclic flow of nutrients between abiotic environment e.g., soil, air, waterand the biotic organisms is called the biogeochemical cycle.Ques 57. What is the contribution of photosynthesis in carbon cycle?

Ans. Contribution of Photosynthesis in Carbon Cycle: Carbon enters the plants during the process ofphotosynthesis to make food. O2 is given out in this process. During respiration O2and carbohydrates areconsumed and water and CO2 are formed. CO2 goes back to atmosphere. Plant food is eaten byherbivores and then herbivores are eaten up by carnivores.

Ques 58. Define point source of water pollution.

Ans. Point source of water pollution includes factories, power plants, underground coal mines and oil wellPoint source of water pollution is that of which are situated near water and its products pollute thewater.Ques 59. Mention some factors responsible for ecological imbalance.

Ans. (i) Deforestation,(ii) Mining of various elements and fossil fuels.(iii) Urbanisation and industrialization.

Ques 60. How does development affect the environment?



Ans. Man has to plant more plants. Green grassy patches have to be interspersed between concrete

buildings. Plants help in balancing the gases in the environment.Ques 61. How does smoke pollute air?

Ans. Cigarette and bidi smoking exit toxic substances like CO and nicotine. They pollute the air.Burning of fuels also release CO2 and CO2.

Ques 62. Describe the various pollutants in the atmosphere.

Ans. Various pollutants in the atmosphere are forest fires, ash from smoking, volcanoes, dust storm and

decay or organic matters, pollen grains floating in air are also a natural source.Man-made sources: Population explosion, deforestation, urbanization and industrialisation. Manreleases several pollutants through various activities like carbon monoxide, carbon dioxide, sulphur

dioxide, hydrocarbons, oxides of nitrogen, lead, arsenic, asbestos, radioactive matter and dust.Ques 63. How does water get polluted?Ans. Water gets polluted by mixing pollutants. These pollutants are ³ Domestic wastes, industrial

wastes, agricultural wastes, atomic explosion, oil spills, clay-pesticides, acids, base etc.

Ques 64. What are the two types of sources of air pollution? Differentiate between them.

Ans. Sources of Air Pollution are(i) Natural sources, and (ii) Man-made sources

Natural Sources of Air Pollution Man-made sources of Air-Pollution1. They emit from natural sources.

2. They are pollen grains floating inatmosphere, forest fires, dust storms, ashfrom volcanic eruptions and death anddecay of the matter

1. They are not natural but are created by

man·s activities.2. They are deforestation, industrialization,population explosion, urbanization, burning of

fossil fuels, human activities release

CO, CO2, SO2 ,NO2, hydrocarbons, lead,Asbestos, dust, marble dust, stonedust, Arsenic etc.

Ques 65. Describe the ill-effect of acid rain.Ans. 1. Damages crop plants and trees in forests.

2. Corrodes buildings, statues and monuments of marble.3. Makes the soil acidic.

Ques 66. How will you prevent soil erosion?

Ans. 1. Planting more trees and sowing grasses?2. Terracing on the sloping fields. This slows down the speed of the flowing water.

3. Grazing of Cattles in forests should be discouraged because it damages the vegetation aswell as exposes the soil to atmosphere. It causes soil erosion.Ques 67. What are pesticides? Give a few examples.

Ans. Pesticides: These are those chemical compounds which are used in the fields to kill the agriculturapests. D.D.T (Dichloro Diphenyl Trichloroethane), B.H.C. (Benzene Hexachloride), Inorganic pesticideslike sulphur, Copper, Arsenic etc.Ques 68. What is meant by water cycle? How are nutrients from land made available to marine

organisms by this cycle?

Ans. Water cycle: The whole process is which water evaporates and falls on the land as rain and later

flows back into the sea via rivers is known as the water cycle.Water can dissolve many substances when it passes through rocks. In this way the rivers take nutrientsfrom land to sea.



Ques 69. State in brief the role of photosynthesis and respiration in carbon cycle in nature.

Ans. During photosynthesis, plants release free oxygen in the atmosphere for the respiration. Animalstakes up oxygen for oxidation of food and return back the CO2 to the atmosphere. Thus, there is anaddition of CO2 to atmosphere by respiration of plants and animals.Ques 70. Explain with a labeled diagram, how cycling of carbon takes place in nature?

Ans. Cycling of Carbon. The carbon enters the living system through plants. The plants pick up carbondioxide from the atmosphere and prepare their food by the process of photosynthesis with the help of

sunlight. The carbon in the form of carbohydrates is transferred as food to the animals.Ques 71. What is ozone layer? What is its importance?

Ans. Some part of oxygen is convertesd into ozone. This ozone is accumulated in the upper part of

atmosphere and forms a layer known as ozone layer. It is very important as it absorbs ultra-violet rayscoming out from the sun which are responsible for skin cancer and genetic disorders.Ques 72. Explain nitrogen cycle in nature only by a figure.

Ans. From book

Ques 73. Write a note on ozone layer in atmosphere.

Ans. Ozone Layer: Stratosphere contains small amounts of ozone (O3). Ozone absorbs some of theultraviolet radiation of the sun. Ultra Violet rays are responsible for diseases like cataract,

inflammatory diseases and cancer.

Ques 74. What is environmental pollution? Name three non-biodegradable pollutants that are

harmful to human beings.

Ans. Environmental pollution means ´the pollution of air, water and soilµ.Environmental pollution: It is the undesirable change in physical, chemical and biological

characteristics or air, land and water.Pollution can be natural or man-made. These non-biodegradable pollutants are: Insecticides,

pesticides, DDT, mercury, lead arsenic, aluminium, plastics, radioactive wastes etc.Ques 75. How can you make a balance between environment and development?

Ans. Balance between environment and development: To maintain a balance between environmentand development, it is necessary to strike for sustainable development to meet the need of presentgeneration without foreclosing the options for future generation. To achieve this, one has to considerdifferent aspects of development. Sustainability and biological diversity are interrelated. If humanbeings have to survive, they have to live in harmony with nature. More plants have to be planted.

Ques 76. What is acid rain? Mention two adverse effects of acid rain.

OrHow is acid rain formed? Mention any one of its harmful effects other than the corrosion

of monuments?



Ans. Acid Rain: There are many non-metallic oxides like sulphur dioxide (SO2), sulphur trioxide (SO3),

oxides of nitrogen (NO2, NO) etc. in the atmosphere which are produced as the by-products in theindustries.When it rains, these gases are mixed with the rainy water and become acids. Such rain is called acid

rain. This acid rain, when falls on a marble building, reacts with marble and produces carbon

dioxide and the calcium salts thus the building damaged. It has adverse effect on agriculture. The soilbecomes acidic. There is decline in forest and agricultural productivity.

Ques 77. Explain how the ozone layer in atmosphere protects us from the harmful radiations.Ans. Ozone occurs only in minute traces in the atmosphere and has a peak concentration around 25 kmabove the surface of the earth. This layer of zone does not allow harmful ultraviolet rays of sunlight

to pass through it. So, it is due to the ozone layer in the atmosphere that the harmful ultravioletradiations coming from the sun do not reach us on the earth and we are saved from their badeffects. The ultraviolet radiations destroy the organic molecules necessary for life.

Ques 78. Mention the main causes of soil erosion.

Ans. Causes of Soil Erosion: Soil erosion occurs when the soil is removed faster than it is formed.

There are various process by which soil is removed but the cause is usually the removal of treesand other vegetation that hold the soil together and in place. Some causes are:

(a) Deforestation. It is the removal of trees and other vegetation which hold the soiltogether. When vegetation is removed, the soil surface is loosened and removed by running water

and wind etc. Rain water that could have been absorbed by the soil, rapidly runs off thesurface, carrying soil with it.

(b) Overgrazing of land by animals. It results in removal of grass over a large area makingit easy for wind and running water to remove the soil. Hillsides have become barren because of

overgrazing by goats. The hooves of cattle compact the soil. It leads to desertification.

Ques 79. What are the biogeochemical cycles? Explain the pathways of any one.

Ans. Biogeochemical Cycles of Materials: The circulation of chemical nutrients like carbon, oxygen,nitrogen, phosphorus, sulphur and water etc. through the biological and physical world (or biosphere) is

known as biogeochemical cycles. Mineral cycles are also biogeochemical cycles. They may be gaseous.Important Bio-geochemical Cycles in Biosphere: Carbon cycle, nitrogen cycle and oxygen cycle etc.The energy transfer in the biosphere is unidirectional whereas the transfer of mineral nutrients in thebiosphere is C yclic.Ques 80. What are biogeochemical cycles? Name any two bio-geochemical cycles. In what ways

does cycling of nutrients differ from the flow of energy in the biosphere?

Ans. The circulation of chemical nutrients like carbon, oxygen, nitrogen, phosphorus, sulphur and wateretc. through the biological and physical world (or biosphere) is known as bio-geochemical cycles.Important biogeochemical cycles in biosphere. Carbon cycle, nitrogen cycle and oxygen cycle etc.

Ques 81. Draw schematic diagram to show carbon cycle in nature.

Ans. From book Ques 82. (a) What is smog?

(b) Write two harmful effects of smog.

Ans. (a) The combination of smoke particles with the tiny droplets of fog is called smog.

Smoke + Fog Smog(b) Harmful effects of smog:(i) It decreases the visibility and cause hindrance to air and road traffic.(ii) It causes diseases such as bronchitis, asthma, and heart problems.



Ques 83. A deforested land has been reforested. Give the scientific term for the above process.

Describe any four changes which will occur in the water cycle if the area.

Ans. The term given for reforestation is afforestation.Changes in the water cycle:1. Sub-soil water level will increase.

2. The rainfall would increases in that area.3. The rivers would not flood easily.

4. The water in ponds, lake, would be sufficient for the use of animals.Ques 84. Distinguish between nitrogen and carbon cycles.

Ans. Distinguish between Nitrogen and Carbon cycles.

Nitrogen cycles Carbon cycles

1. It is completed by bacteria. So it iscomplicated cycle.2. Nitrogen (78.6%) is produced byvarious organisms.3. Nitrogen may be used by someprokaryotes only. e. g. Blue green

algae.4. Fixation is both bio-logical and

physical.

There is no need of bacteria in carboncycle.

Carbon dioxide (0.032%) is producedby the same organisms.

CO2is used directly by all theproducers.

Fixation is biological.

Ques 85. (a) At what height ozone layer is present? In which sphere of atmosphere, ozone layerexists?

(b) Name the group of chemical compounds which adversely affect ozone layer.

(c) How does the ozone layer protect us from harmful effects in the environment?

Ans. (a) Ozone layer is present at a height of 15 km to 60 km. Ozone layer exists in stratosphere.(b) Chlorofluoro carbons (CFC) and fluro carbon.

(c) Ozone layer absorbs the harmful ultraviolet (UV) radiation of sun light.Ques 86. State the natural factors affecting the soil erosion.

Ans. Natural Factors Affecting Soil Erosion:

1. Water Erosion: The drops of rain during the rainfall breakdown the soil particles anddisperse these particles. Thus the loosened soil is transported downhill by the run offwater. Drought causes depletion of vegetation. The rain drops hit the soil easily.

Ques 87. How is gaseous nitrogen fixed by the plants? What is its significance?

Ans. Nitrogen Fixation by Plants and its Significance: Some microbes e.g. Rhizobium convertsatmospheric N2 into nitrogenous compounds. Dead organisms and proteins are changed into NH3 (ammonia). Urea (in urine) is converted into NH3 and then to NO-2 and NO-3 into the soil.

These nitrates are absorbed by the producers or plants. Denitrifying bacteria convertnitrates of soil into free oxygen which is released into atmosphere.

Ques 88. Describe the carbon cycle in detail.

Ans. The Carbon Cycle: Carbon forms an important constituent of organic compounds present in allliving beings as the carbohydrates, fats, proteins and nucleic acids etc. It also occurs in variousforms in atmosphere, seas and carbonate rocks. The plants utilize atmospheric CO2 to make

carbohydrates, proteins and fats. These are then consumed by all living beings. Carbon travelsthrough various living beings (producers-consumers) as food in Successive trophic levels of

food chains. It returns to atmosphere by decomposers. Carbon dioxide is also released by all



living beings during the process of respiration, by burning of materials and the combustion of

fuels. Volcanic eruptions release CO2 into atmosphere. So, there is a complete cycling of

carbon Fixation is biological in environment by different living and non-living beings.Ques 89. Show oxygen and CO2 cycle to show their relation.

Ans. From book page number 199, 200

Ques 90. What role do organisms play in (i) Water cycle, (ii) Oxygen cycle, (iii) Nitrogen cycle?

Ans. (i) Water Cycle: The water cycle makes the fresh water available to the organisms. Water

evaporates from the surface of living organisms. Water evaporated forms water vapours in theair. At low temperatures these vapours condense into droplets. These droplets fall as rain andsnow. Thus water returns to the earth.

(ii) Oxygen Cycle: Organisms ² both plants, animals and even the decomposers use oxygenavailable in the atmosphere for respiration. The by-product of this process, CO2 is released intothe atmosphere. Thus the percentage of oxygen in air is nearly constant.

(iii) Nitrogen Cycle: On the death of living beings (animals or plants), the nitrogenous compounds

of their body pass into the soil or water. The excreta of animals also pass on to the soil andwater. The organic nitrogenous compounds are broken down by some bacteria to form ammonia.Some nitrifying bacteria present in the soil oxide ammonium ions first into nitrites and then to

nitrates. Nitrogenous compounds present in the soil are also being constantly decomposed by theaction of denitrifying bacteria.

Ques 91. What is the significance of a balanced environment?Ans. The significance of a Balanced Environment. It includes the flow of energy and cycle of

matters. It is supported by different living beings by acting as the producers (plants) andconsumers like animals.

Three components of biotic environment are plants, animals and microorganisms, they are

closely interlinked to each other. The plants are the producer of world. They prepare andprovide food as well as oxygen (life sustaining gas) for all the living organisms of the earth.Animals are consumers. They depend on the plants for their survival. The microbes, the

decomposers are minute animals and plants. The provide help in different ways in thesustainance of our environment.

Ques 92. Write a note on the importance of water cycle in the environment.

Ans. Importance of Water Cycle in the Environment: The water is an essential component of theenvironment. The survival of all living organisms depends on water. Ocean is the biggest

store house of water. The water on evaporation forms clouds. After condensation clouds falldown in the form of rain. The rain passes through rivers. The river water goes again inocean. This circulation of water in this manner is called as the water cycle. It is alsoaccomplished through living beings like absorption by roots of plants and transpiration of

water by leaves of plants as well as drinking by animals. Water plays an essential role in

the formation of soil.Ques 93. Define nitrogen fixation. Name a few bacteria involved in it.

Ans. Nitrogen Fixation: It is defined ´as the fixing of free atmospheric nitrogen into the nitrates bythe bacteriaµ.

Thus Nitrogen Fixation and Organisms Involved in it:

Various organisms Role/Function in Nitrogen Cycle





Ans. ¶Green House Effect·: It means the increasing of temperature in the atmosphere. It is caused by

(i) burning of fossil fuel like coal, oil, CNG, LPG, Diesel etc. by volcanic activity. The green housegases are carbon dioxide and oxides of nitrogen, CFC, methane etc. These gases act as thecovering glass which increases due to the combustion of fuel, deforestation and agriculturalactivity. These gases increase the atmospheric temperature which cause melting of glaciers and

ice caps and with the result of that water level in the oceans submerge several islands anddevelop different rain patterns and increased desertification. The phenomenon is called as

Green House Effect.The concentration of carbon dioxide is increasing day by day in the atmosphere. It about 1890

it was about 275 ppm. In the year 2003, it is about 350 ppm. And by the year 2040, it will

become 450 ppm.

Ques 98. Name the various air pollutants, their main sources and harmful effect on animals, plants

and human beings.

Ans. Table: Air Pollutants, Sources and their Effect:

Air

Pollutants

Sources Harmful effects

1. SO2 and H2O

«««««««««««««««

2. NO and NO2

Sulphide containing ores and

combustion of coal and petroleum(fossil fuels).

«««««««««««««««««««««««.

Power generators, Exhausts from

the automobiles and N2 fertilizersand explosives, forest fires,lightning

In plants, there is loss of

chlorophyll (chlorosis) andnecrosis (death of cells), growthis stunted. In human there is

bronchitis, eye, irritation, cough,headache and reduced lungcapacity (emphysema)««««««««««««««.

In plants, there is chlorosis

and dropping of leaves and fruits.Nose and eye irritation,pulmonary oedema is caused in



«««««««««««««««3. CO and CO2

«««««««««««««««

4. Hydrocarbons

«««««««««««««««5. Methyl Icocyanate

(MIC)

««««««««««««««

6. chlofoflurocarbons

(CFCs)

««««««««««««««

7. Lead

««««««««««««««

8. Cement, Coal,

Flyash and Asbestos

dust

««««««««««««««

9. DDT pesticide

««««««««««««««

10. Smog

««««««««««««««

11. Tobacco Smoke

«««««««««««««««

Burning of coal in defective

furnaces, fuels, petrol, dieselengines, gasoline.

«««««««««««««««

Incomplete combustion of fuel,petroleum and refineries.

«««««««««««««««Pesticide Industry

««««««««««««««Jet aeroplanes, spray cans can

refrigerators

««««««««««««««Unburnt petrol

««««««««««««««Mining industry, Power plants andstone crushers

««««««««««««««

Agriculture, Pesticide Spray

««««««««««««««Fog and smoke

««««««««««««««

Activite smoking, passive smoking

man.«««««««««««««««Reduced O2 carrying capacity.

Difficulty in breathing, nausea,headache, poisoning, dizzinessetc.«««««««««««««««

Growth is stunted in plants.There is necrosis and chlorisis offloral buds in plants.««««««««««««««Irritation of mucous membrane

and eye chocking leads to death(e.g., Bhopal gas)««««««««««««««O3 layer depletion, skin cancer in

man

««««««««««««««

Nausea, dizziness, anaemia, liverdamage and kidney damage.««««««««««««««T.B., bronchits, silicosis,emphysema, allergy.

««««««««««««««

Biomagnification, effect onnervous system.

««««««««««««««Poor, visibility leading toaccidents, respiratory disorders,asthma etc.««««««««««««««

Throat cancer, lip cancer, windpipe and lung cancer.

Ques 99. Make a list of microorganisms involved in ¶Nitrogen cycle·.Ans. Table: Microorganisms involved in Nitrogen Cycle.

Name of microorganism Role played in nitrogen cycle

1. (a) Rhizobium bacteria (inrootnodules)

(b) Asotobactor bacteria insoil.

(c) Blue-green algae.

Nitrogen fixationNitrogen fixation(conversion of atmospheric nitrogen gas into nitrogencompounds) Nitrogen fixation.Ammonification.



2. (a) Puterfying bacteria.

(b) Fungi;

3. Nitrifying bacteria(a) Nitrosomonas bacteria.(b) Nitrobacter bacateria.

4. Denitrifying bacteria:Pseudomonas

Ammonofication (Conversion of nitrogen containing proteins ofdead plants and animals into ammonia)Nitrification (Conversation of ammonia into nitrites and then

into nitrates)Convert ammonia into nitrites (NO2

-)Vonvert nitrites into nitrates (NO3

-)Denitrification

(Conversion of nitrates salts into free nitrogen gas).

Ques 100. Explain O2 cycle in detail.

Ans. Oxygen-cycle: O2 is a very abundant element on our Earth. O2 occurs in the elemental form in theatmosphere by 21%. It is mostly in the combined form in the Earth·s crust and in the air in the form ofCO2. In the crust, O2 is found as oxides of most metals and silicon, and also as carbonate, sulphate,nitrate and other minerals. O2 is also an essential component of most biological molecule e.g.,carbohydrates, proteins, nucleic acids and fats lipids.

Oxygen cycle maintains the level of O2 in our atmosphere. Oxygen from the atmosphere is usedup in three processes: (i) combustion, (ii) respiration and (iii) in the formation of oxides of nitrogen.

comes back in the atmosphere in only one major process called the photosynthesis.O2 is necessary to life in respiration. Some forms of life, like bacteria, are poisoned by

elemental oxygen. The process of nitrogen-fixing by bacteria does not occur in the presence of oxygen.Ques 101. What is biosphere? Discuss.Ans. Biosphere: It consists of lithosphere, atmosphere and hydrosphere.

(a) Lithjosphere : solid outer layer of the Earth includes the crust and solid part of the

mantle down to 75 km. The uppermost layer of the Earth·s crust is called soil. Soil provides thenutrients for all organisms.

(b) Hydrosphere : Water available in gaseous, liquid and solid states necessary to carry outchemical reactions. It dissolves and transports nutrients from the soil to the plants.

(c) Atmosphere : Protects organisms from the harmful ultraviolet radiations of the sunlight,helps in food manufacture by green plants, and N2helps in growth.

(d) Biosphere: Life is possible only where the lithosphere, hydrosphere and the atmospherecome in contact. The part of the earth where life exists is known as biosphere.

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Note of Natural Resources