Question Bank in Science Class-IX (Term-II) 14 NATURAL RESOURCES CONCEPTS 1. The gifts of nature like air, water, soil, minerals, coal, petroleum, animals and plants are called natural resources. 2. Natural resources are broadly classified into inexhaustible natural resources and exhaustible natural resources. 3. Ever-increasing population along with industrialisation and consequent urbanisation have compelled human beings to over-exploit these natural resources. 4. The natural resources which are present in the nature in unlimited quantity and which normally cannot be exhausted by human activities are called inexhaustible natural resources, e.g. air, water, solar energy, etc. 5. The natural resources which can degrade in quantity and quality due to human activities are called exhaustible natural resources. e.g. soil, forest, minerals, coal, etc. 6. Air is a mixture of nitrogen (78%), oxygen (21%), carbon dioxide, ammonia, ozone, noble gases and moisture. 7. The envelope of air that surrounds the earth is called atmosphere. 8. Water is the prime natural resource, basic human need and precious national asset. 9. The ground water and surface water available to us come from the rainfall and snow which is a continuous process through hydrological cycle. 10. Depending on the annual rainfall, India has been divided into four regions wet zone, intermediate zone, semi-arid zone and arid zone. 11. Soil is the upper crust of earth. 12. The six major soil types found in India are (i) alluvial soil, (ii) black soil, (iii) red soil, (iv) mountain soil, (v) desert soil and (vi) laterite soil. 13. Coal, petroleum, iron, aluminium, copper, silver and gold are among the important natural resources. 14. Chief sources of energy are coal, petroleum, natural gas, hydel power, solar, wind and nuclear power. 15. Energy resources can be classified into two main categories non renewable/ conventional resources of energy and renewable/non-conventional resources of energy. 16. The pollution-free sources of energy like solar radiation, wind power, biomass and nuclear power are renewable energy resources. 17. Hydel power is the next biggest source of energy after thermal power. 18. Researchers are being involved to develop new non-conventional energy sources/devices. 19. The term flora is used for plants and fauna for animal species it includes all types of plants and animals living in a natural habitat. 20. Our forest cover is estimated to be 63.591 million hectare sq. km that comes to be approximately 1/5th of the total geographical area of the country. 1
21. The movement of air from one region to another region causes winds. 22. The circulation of water in the form of water vapour, clouds, rain and snow forms the water cycle. 23. Major sources of air pollution are burning of fossil fuels (coal and petroleum products), automobiles, thermal power plants and industries. 24. Burning of fossil fuels like coal and petroleum releases oxides of nitrogen and sulphur which are responsible for acid rain. 25. Air containing suspended particles of unburnt carbon and other particles released by the burning of fossil fuels is called smog. 26. Lichens are known as indicator of pollution because they are sensitive to the level of sulphur dioxide in air. 27. The level below the soil surface where the rocks are saturated with water is known as the zone of saturation and the upper level of the zone of saturation is called water table. 28. The increase in concentration of harmful, non biodegradable chemical substances in the body of living organisms throughout the trophic levels of a food chain is called biological magnification. 29. The excessive growth of phytoplankton in water bodies because of discharge of sewage and detergents in it brings about a reduction in dissolved oxygen which affects other aquatic organisms. This is called eutrophication. 30. Conversion of rocks into soil by physical or biological means is called weathering. 31. A fertile soil which contains a mixture of all the different sized particles is called loam or loamy soil. 32. Strip-cropping means planting of crops in rows or strips to check flow of water and soil pollution. 33. A cyclic flow of nutrients between non-living environment and living organisms is called biogeochemical cycle. 34. Rise in the earth s temperature because of increase in the concentration of carbon dioxide in the atmosphere is known as green house effect. 35. The process of converting atmospheric nitrogen into nitrates with the help of a few symbiotic bacteria which live in the root nodules of leguminous plants and nitrites is called nitrogen fixation. 36. Ammonification is conversion of complex organic compounds like proteins into ammonia (NH 3 ). 37. Nitrification is conversion of ammonia into nitrites and nitrates. 38. Denitrification is conversion of nitrate salts present in the soil and water to free nitrogen gas. 39. Ozone layer surrounds the earth, at height of 25-30 km from the earth s surface. It protects earth from ultraviolet light. 40. Chlorofluorocarbons (CFCs) are mainly responsible for the depletion of ozone layer. Nitrogen monoxide (NO) and some other gases also deplete the ozone layer. 2
I. SUMMATIVE ASSESSMENT NCERT QUESTIONS WITH THEIR ANSWERS SECTION A : IN-TEXT QUESTIONS Page 193 Q.1. How is our atmosphere different from the atmosphere on Venus and Mars? Ans. On Venus and Mars the major component of atmosphere is carbon dioxide which constitutes up to 95-97% of the atmosphere. While on earth carbon dioxide constitutes only a small fraction of the atmospheric gases i.e., it constitutes only 0.03% of atmospheric gases. The main gases on earth are nitrogen (78.08%) and oxygen (20.95%). Presence of oxygen in high concentration makes it easy to breathe for living organisms. And this difference in the concentration of oxygen and carbon dioxide differentiates atmosphere on earth from that on Venus and Mars. Q.2. How does the atmosphere act as a blanket? Ans. Being a bad conductor of heat, the atmosphere keeps the average temperature of the earth fairly constant during the day, even during the course of the whole year. Further, during the night, it slows down the escape of heat into outer space. In this way, it maintains the temperature on the earth and acts as a blanket. Q.3. What causes winds? Ans. Wind is caused by the movement of air from one region to another region. During the day the air above the land gets heated faster and starts rising, therefore, a region of low pressure is created below and air above the sea moves into this area of low pressure. Thus, movement of air from land to upper region of atmosphere and from sea to the land causes wind. Q.4. How are clouds formed? Ans. When water bodies like ocean, sea, etc., get heated during the day, a large amount of water evaporates and goes into the air. The wind carries the water vapour to various places. When this vapour reaches a certain height, it cools and in turn changes to tiny droplets of water or snow. An enormous collection of these tiny droplets appears in the form of clouds. Q.5. List any three human activities that you think would lead to air pollution. Ans. Human activities which are responsible for adding more pollutants in the air are : 1. Excessive use of fossil fuels i.e., coal and petroleum. Because burning of these fossil fuels adds carbon particles to the atmosphere which causes smog. It produces huge amount of carbon monoxide and carbon dioxide as well. 2. Use of chlorofluorocarbons (CFCs) in refrigeration is responsible for depletion of ozone layer. 3. Establishment of a number of industries which release carbon monoxide, sulphur dioxide, oxides of nitrogen, hydrocarbons, heavy metals, etc. All these are responsible for deterioration of air quality. Page 194 Q.1. Why do organisms need water? Ans. Water is the most essential component of life. It is essential for the sustenance of life. 3
Water makes up about 70 percent of body weight and plays a vital role in the metabolic reactions taking place within the body. It acts as a universal solvent, thus providing a medium for many chemical reactions to take place. It also acts as a medium for transporting substances from one part of the body to the other in a dissolved form. Water is unique as its density is similar to that of protoplasm. Water is also required for many other purposes like drinking, cooking, cleaning, crop irrigation, generation of hydro-electricity, industrial needs, etc. Q.2. What are the major sources of freshwater in the city/town/village where you live? Ans. Freshwater is present as ground water and surface water. In our city, we get freshwater from rivers, lakes as well as underground reservoirs made by the engineers. Q.3. Do you know of any activity which may be polluting this water source? Ans. Water used for industrial purposes is discharged into the rivers, lakes, etc. after being used in production processes. This water may contain acid, alkalies, toxic substances, etc. Freshwater bodies are also the sites for the disposal of sewage and other domestic wastes. All these activities pollute the water sources. Page 196 Q.1. How is soil formed? Ans. Soil is formed from parent rock material over millions of years by a process called weathering. In this process, rocks at or near the surface of the earth are broken down into small particles due to physical factors such as sun, wind, rain, etc., and it is called physical weathering. The small particles of rocks are then converted into fine particles of soil by the help of plants, animals, and micro-organisms, this is called biological weathering. Q.2. What is soil erosion? Ans. Soil erosion is washing away of the top soil with flowing water or wind. If all the soil gets washed away, the rocks underneath are exposed. This results in the loss of a valuable resource, the topsoil which contains humus and living organisms and it is the most fertile soil. Q.3. What are the methods of preventing or reducing soil erosion? Ans. Following methods will be effective in the prevention of soil erosion 1. Afforestation is tree plantation, which should be undertaken in areas where plants/trees are already cut and additional areas should also be brought under plantation. 2. Crop rotation is cultivation of different crops in succession on the same area of land over a period of time. It maintains the fertility of the soil and the water-holding capacity of the soil. In this way it prevents soil erosion. 3. Strip-cropping is the planting of crops in rows or strips to check flow of water. It is a common practice on the sloping areas in hills, this reduces the steepness of the slopes and checks soil erosion. Page 201 Q.1. What are the different states in which water is found during the water cycle? Ans. Water is found in three different states during the water cycle. These are : 1. Liquid (in the form of rain). 4
2. Solid (in the form of snow). 3. Gaseous (in the form of water vapour). Q.2. Name two biologically important compounds that contain both oxygen and nitrogen. Ans. Nitrites (NO 2 ) and nitrates (NO 3 ) are two compounds which contain both oxygen and nitrogen. These are biologically important because plants can absorb nitrogen only in the form of nitrates (NO 3 ) and nitrites (NO 2 ). Q.3. List any three human activities which would lead to an increase in the carbon dioxide content of air. Ans. Human activities which are responsible for adding carbon dioxide to the atmosphere are : 1. Respiration : Both plants and animals release carbon dioxide to the atmosphere as a product of respiration. 2. Decomposition : Decomposition of organic wastes and dead bodies by decomposer releases carbon dioxide to the atmosphere. 3. Combustion : Burning of fossil fuels, like wood, coal, petrol, gas and kerosene also releases carbon to the atmosphere. Q.4. What is the greenhouse effect? Ans. Greenhouse effect is an atmospheric phenomenon, in which an increase in the percentage of some gases such as carbon dioxide in the atmosphere causes the average temperatures to increase worldwide. Q.5. What are the two forms of oxygen found in the atmosphere? Ans. Elemental oxygen is normally found in the form of a diatomic molecule i.e. (O 2 ). But at the upper layers of atmosphere there is another form of oxygen which is a triatomic molecule of oxygen and it is called ozone (O 3 ). Thus, the two forms of oxygen found in the atmosphere are O 2 and O 3 (ozone). SECTION B : QUESTIONS AT THE END OF CHAPTER Q.1. Why is the atmosphere essential for life? Ans. Atmosphere is essential for life for several reasons. Some of these reasons are : (i) Oxygen, which is required for the survival of every living organism is present in the atmosphere. (ii) Atmosphere works as an insulator, it keeps the average temperature of the earth fairly constant during the day and night by preventing escape of heat into outer space. (iii) Atmosphere also acts as protective blanket for the Earth. It absorbs most of the harmful radiations such as ultraviolet (UV) radiations coming from the Sun. It results in the Earth receiving just the right amount of heat and sun's rays, which helps in the climate control and allows the living organisms to exist. Q.2. Why is water essential for life? Ans. Water is the most essential component of life. It is essential for the sustenance of life. Water makes up about 70 percent of body weight and plays a vital role in the metabolic reactions taking place within the body. It acts as a universal solvent, thus providing a medium for many chemical reactions to take place. 5
It also acts as a medium for transporting substances from one part of the body to the other in a dissolved form. Water is unique as its density is similar to that of protoplasm. Water is also required for many other purposes like drinking, cooking, cleaning, crop irrigation, generation of hydro-electricity, industrial needs, etc. Q.3. How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource? Ans. Man and animal obtain their food from the plants (cereals, vegetables, grass, etc.) growing on the soil. These plants obtain their food from the nutrients found in soil. In addition, soil also contains various micro-organisms which derive their food from the soil. Thus, all living organisms depend on soil for their survival. Soil is essential for all living organisms whether they are aquatic or terrestrial. Soil plays important role in biogeochemical cycle which is a main source of recycling of nutrients from atmosphere to soil and then to water. Aquatic plants obtain their nutrients from the bottom of that water body and these aquatic plants are source of food for the aquatic animals. In this way soil is essential for the aquatic organisms as well. Q.4. You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather? Ans. Weather stations and weather ships around the world make daily measurements of temperatures, rainfall, wind speeds and directions, air pressures and other weather features with various instruments. This information is then sent to local weather forecasting stations. From the information they receive, the Meteorological Department prepares a weather report in which all the weather information is plotted on the maps. Using these maps, weather forecasters predict the weather reasonably accurately which is then transmitted on the radio and television, etc. Q.5. We know that many 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 areas would help in reducing pollution? Ans. Isolation of these activities which are causing pollution of air, water and soil to a specific and limited area can reduce pollution to some extent but even this is not a permanent solution of the problem of pollution, because pollutants released after the decomposition of these wastes will recycle through soil, water and atmosphere. In this way they will come back to the place from where they had been removed. So, there should be a permanent procedure for the removal of pollutants. Q.6. Write a note on how forests influence the quality of our air, soil and water resources. Ans. Forests influence the quality of air, soil and water resources in the following ways 1. Influence of forests on air : Both plants and animals release carbon dioxide to the atmosphere as a product of respiration. Forests take up this carbon dioxide for the manufacture of their food and release oxygen to the atmosphere after photosynthesis. In this way they are helpful in cleaning the air. 6
2. Influence of forests on soil : (a) The deep-rooted plants of the forests are helpful in holding soil particles tightly. In this way forests help in reducing soil erosion. (b) Forests are also a component of biogeochemical cycles, thus help in cycling of nutrients and returning them back to the soil, thus increasing the soil fertility. 3. Influence of forests on water : Forests lose water to the atmosphere through transpiration which is then converted into clouds, water vapours, etc. which are responsible for causing rain. Thus, forests help in increasing the water resources of the earth. ADDITIONAL QUESTIONS (As Per CCE Pattern) A. Very Short Answer Questions (1 Mark) Other Important Questions Q.1. What are the types of natural resources? Ans. Types of natural resources are water, air, soil, minerals, sunlight, plants, animals, coal and petroleum. Q.2. Why plants do not utilise nitrogen directly from atmosphere? Ans. Most of the plants cannot utilise nitrogen directly from the atmosphere. They use nitrogen only when it is converted into nitrates and nitrites by the process nitrogen fixation. Q.3. Name the process in which water vapour changes to a liquid. Ans. Condensation Q.4. Which gas is the chief component of earth s atmosphere? Ans. Nitrogen Q.5. Name the substance that reduces the amount of dissolved oxygen in water. Ans. Excessive growth of phytoplanktons reduces dissolved oxygen level in water. Q.6. Which gas is formed in the layers of earth due to bacterial decomposition in the absence of oxygen? Ans. Ammonia Q.7. Name the rays essential for formation of ozone in atmosphere. Ans. UV rays Q.8. Name the elements present in fossil fuels, which cause air pollution. Ans. Sulphur, carbon and nitrogen. Q.9. In a coastal region, what would be the direction of wind during the day? Ans. In coastal region, direction of wind during day will be towards the land to take place of warm air. Q.10. When clouds cool down, water droplets fall to the land as rain, hail or snow. Name the phenomenon. Ans. Precipitation 7
Q.11. Name the organisms found to be very sensitive to the levels of contaminants like sulphur dioxide in the air. Ans. Lichens Q.12. What do you mean by humus? Ans. Humus is an organic matter formed by decomposition of dead organisms. Q.13. Give two examples of exhaustible natural resources. Ans. Exhaustible natural resources : (i) Fossil fuels (ii) Plants and animals. Q.14. Name two atmospheric gases responsible for causing acid rain. Ans. Sulphur dioxide (SO 2 ) and Nitrogen dioxide (NO 2 ). Q.15. How would you define the term atmosphere? Ans. The air that covers the whole of the earth like a blanket is called atmosphere. Q.16. What do you understand by the term Natural resources? Ans. Natural resources are the variety of substances that human beings get from the nature to meet their basic needs. Q.17. What is strip-cropping? Ans. Strip-cropping is the planting of crops in rows or strips to check flow of water. It is practiced in the sloping areas of hills to check soil erosion. Q.18. What portion of our country s geographical area is covered by forest? Ans. According to forest survey of India, the actual forest cover of India is about 19.27% of the geographical area. It corresponds to 63.3 million hectare. Q.19. Name any two examples of inexhaustible natural resources. Ans. Inexhaustible natural resources : (i) Air (ii) Water. Q.20. How much air is required by a normal human being in one day? Ans. A normal human being requires about 250 265 kg of air everyday for various activities. B. Short Answer Questions - I (2 Marks) Previous Years' Questions Q.1. What is soil erosion? List two activities which cause soil erosion. Ans. The loss of soil due to winds or water flow is called soil erosion. Soil erosion is also caused due to some activites of human as- (i) Deforestation (Destroying Forests) (ii) Industrialisation of Croplands. Q.2. What is greenhouse effect? How is it caused? Ans. Greenhouse effect is the progressive warming up of the earth s surface due to the blanketing effect of man-made carbon dioxide in the atmosphere. The greenhouse gases increase the temperature of the earth's surface and lower atmosphere. Q.3. (i) Many Municipal Corporations are trying water harvesting to improve the availability of water. Give reason. (ii) Rain water sometimes contains traces of acid. Why? Explain in brief. 8
Ans. (i) With the increasing population the level of surface water and ground water is decreasing continuously. To maintain the availability of water, water harvesting is an important step. (ii) The air pollution and fumes from automobiles causes acid rain as a result in rain water also found. Q.4. (i) Define the term Smog. (ii) Name two types of diseases caused by regularly breathing the polluted air. Ans. (i) The presence of suspended particles in air during cold season causes the formation of smog. (ii) Regularly breathing the polluted air affects the respiratory system of living beings and causes bronchitis, pneumonia, asthma and lung cancer. Q.5. (i) Why is water so necessary for all living organisms? Mention any two points in support of your answer. (ii) Water is known as A Wonder Liquid. Justify this statement by giving any two reasons. Ans. (i) Water makes up about 70 per cent of body weight and plays a vital role in the metabolic reactions taking place within the body. Water is required for many purposes like drinking, cooking, cleaning, crop irrigation, navigation, generation of hydro-electricity and industrial needs. (ii) Water, as you know, is the most essential component of life. It is essential for the sustenance of life. Life is impossible without water. It acts as a universal solvent, thus providing a medium for reactions to take place. Q.6. What is atmospheric fixation of nitrogen? Ans. Air contains about 78% of nitrogen, which exists in molecular form as N 2. Plants cannot absorb nitrogen in its elemental form. So the process of converting atmospheric nitrogen into nitrates is called nitrogen fixation. The atmospheric nitrogen after nitrogen fixation gets converted into nitrates. Q.7. (a) What is soil erosion? State any one way by which it can be prevented. (b) What is humus? What is the role of earthworms in increasing the quantity of humus? Ans. (a) The removal of soil layer due to climate change or physical processes such as rainfall, wind, etc. is called soil erosion. Afforestation should be undertaken to prevent the soil erosion. (b) Humus is a dark coloured colloidal material that constitutes the organic components of soil. It is formed by the decomposition of plant and animal remains. Earthworms feed on the humus and increase its fertility. Q.8. (a) List two ways by which carbon dioxide is fixed in the environment. (b) Name two diseases caused due to an increased content of pollutants in the air produced due to the burning of fossil fuels. Ans. (a) Carbon dioxide is fixed in environment in two ways : (i) By the process of photosynthesis in plants. (ii) It get dissolve in water in the form of bicarbonates which gives rise to carbonate rocks. 9
(b) Bronchitis and lung cancer. Q.9. The heaps of solid wastes are a menace. Give two reasons. Ans. The heaps of solid wastes are a menace because- (i) The unpleasant smell with harmful gases pollute the air of surrounding areas. (ii) The solid wastes litter in the surrounding areas choking the sewage system. Q.10. How addition of undesirable substances and change in temperature affect the water life. Ans. The undesirable substances in water influence the aquatic life. The poisonous things like pesticides can kill the fish or other water creatures. The algal bloom causes the deficiency in oxygen in the water bodies while the change in temperature will affect breeding and development of young ones of aquatic organism. Q.11. (a) What is the role of atmosphere in climate control? (b) What percentage of nitrogen and oxygen is present in air? Ans. (a) Atmosphere acts as a protective blanket for the Earth. (b) Nitrogen - 78% and oxygen 21% is present in the atmosphere. Q.12. Mention any two human activities which are responsible for water pollution. Ans. (i) Domestic wastes like detergents and sewage. (ii) Agricultural wastes, such as fertilisers and pesticides which are used to increase crop yield. Q.13. (a) Mention the role of ozone layer in the atmosphere. (b) Give reason Lichens do not grow in Delhi whereas they commonly grow in Manali or Darjeeling. Ans. (a) Ozone layer cuts out some of the UV light coming from the sun. UV is bad for us and for crops. (b) Lichens do not grow in Delhi because of its very polluted atmosphere (environment). Q.14. How do Sun and wind influence the formation of soil? Ans. (i) The Sun heats up rocks during the day so that they expand. At night, the rocks cool down and contract. This unequal expansion and contraction in different parts of the rock results in the formation of cracks. (ii) Minute rock particles are carried away by the blowing wind and deposited elsewhere. Q.15. List any two consequences of global warming. Ans. (i) Over-use of fossil fuels for domestic, industrial and other purposes. (ii) Increasing fast rate of releasing large volume of carbon dioxide in the air. Q.16. Give the chemical formula of ozone. What is its role in atmosphere? Ans. Ozone - O 3 Ozone protects the Earth from the direct effect of ultraviolet rays which can cause skin cancer, damage the eyes and immune system. Q.17. Name two measures that can be taken to reduce water pollution. Ans. (i) Do not wash the clothes near a water body. (ii) Do not throw the wastes into the river or any other water body. 10
Q.18. Suggest two methods to control air pollution. Ans. (i) By minimum use of fossil fuels. We can replace fossil fuels with solar energy or biogas. (ii) By reducing the deforestation and by planting more and more trees. Q.19. Differentiate between biodegradable and non-biodegradable pollutants. Ans. Biodegradable pollutants Non-biodegradable pollutants (i) These pollutants degrade within a certain time period. (ii) For example-ash, paper, smog, etc. (i) These pollutants do not degrade at all. (ii) For example-lead, silicon, etc. Q.20. (a) Name the process that returns oxygen to the atmosphere. (b) Write the condition responsible for poor visibility in cold weather. Ans. (a) Photosynthesis (b) Smog Q.21. Which symbiotic life forms can grow on stones and help in the formation of soil? Write the mode of their action for making soil from rocks. Ans. Lichens can grow on stones and help in the formation of soil. The water absorbing and retaining power of fungus makes it possible to grow even on rocks and making crevices while extracting minerals as food, finally making loose soil there. Q.22. (a) Why does moon have very cold and very hot temperature variations i.e. from 190 C to 110 C even though it is at the same distance from the Sun as Earth? (b) Why does Mathura refinery pose problem to the Taj Mahal? Ans. (a) Due to the absence of atmosphere (gases) on moon it becomes very hot during day and very cold during night. (b) Environmental pollution is damaging the monument Taj Mahal and discolouring its once translucent white marble. Mathura refinery is a biggest culprit in damaging Taj Mahal. Sulphur dioxide emission from industry have reached levels ten times above the precribed level. Combined with oxygen and moisture, sulphur dioxide settles on the surface of the tomb and corrodes the marble, farming a fungus that experts call as 'marble cancer;' The environmentalists analysed that the refinery is creating high levels of suspended particulate matter, dust and exhaust. These are causing the Taj Mahal to change colour. Q.23. How do forest play an important role in maintaining water cycle. Ans. The roots of plants/ trees bind the soil compactly. It affects the level of ground water at that place. Trees also lower down the temperature of surrounding areas by transpiration. Forests change the water into water vapours which form clouds. Clouds after condensation starts raining. Q.24. Why is atmosphere essential for life? Write two points in support of your answer. Ans. (a) The atmosphere acts as a protective blanket for the Earth. (b) Atmosphere absorbs most of the harmful radiations such as ultraviolet (UV) radiations coming from the Sun. The harmful radiations are absorbed in the upper atmosphere as well as reflected back into the space. 11
Q.25. How are clouds formed? Ans. When water bodies are heated during the day, a large amount of water evaporates into the air. The wind carries the water vapour to various places. When this vapour reaches a certain height, it cools and in turn changes to tiny droplets of water or snow. The enormous collection of these tiny droplets appears to us in the form of clouds. From the clouds the water comes down to the surface of Earth in the form of rain or snow. Q.26. (a) Why do terrestrial forms require freshwater? (b) Mention any two processes involved in water cycle. Ans. (a) The terrestrial forms require water for drinking, bathing, washing clothes, etc. For these purposes only freshwater is fit to used. (b) (i) Evaporation (ii) Condensation Q.27. What is top soil? Mention any two factors that decide which plants will thrive on that soil. Ans. The uppermost layer of soil profile containing humus and other organic nutrients, is called top soil. Two factors which decide the type of plants thrive on that soil are- (i) Presence of organic matter (humus) and nutrients, (ii) Capacity of the soil to retain water and air. Other Important Questions Q.1. How do the rivers from land, add minerals to sea water? Ans. As the rain fall and water or rivers flows over the land, the water dissolves out of the rocks, washes the minerals into stream and finally carries to the sea. These salts stay in the sea because no water flows out of the sea. The rivers are flowing bodies of land and carry soil and dirt also with them. This deposition adds many minerals into the sea water. Q.2. How can we prevent the loss of top soil? Ans. The uppermost layer of soil is very fertile and rich in humus. The main threat to top soil is soil erosion. Soil erosion is loss of soil due to wind or water flow. Loss of top soil can be prevented by stopping soil erosion by following methods : (i) Afforestation (ii) strip cropping (iii) By following crop rotation to maintain the fertility of soil. (iv) Proper drainage and irrigation arrangements. Q.3. Why does the percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere? Ans. The cycling process of all these gases maintains their percentage in the atmosphere at constant level. Constant recycling replenishes the lost gas in the atmosphere and balance is maintained. Q.4. Lichens are called pioneer colonisery of bare rock. How can they help in formation of soil? Ans. A bare rock consists of solid surface or very large boulders and there is no place for rooting plants to colonize. The thalli of lichens can adhere to the surface of rock and absorb moisture from atmosphere. Therefore, these colonize the bare surfaces of rocks first. These lichens produce acids which corrode the rock and their thalli collect wind blown soil particles with them that help in formation of a thin film of soil. When these lichens die their thalli are decomposed to add humus. This promotes soil formation. 12
Q.5. Why do people love to fly kites near the seashore? Ans. The movement of air from one region to another region is called wind. On Earth, wind consists of bulk movement of air. It plays major role in recreational activity like kite flying. Sea shores are major windy areas where wind power can be used for kite flying because during day the air above land gets heated faster and starts rising. So the air above the sea moves into this area rapidly. Q.6. Why do lichens not occur in Delhi whereas they commonly grow in Manali or Darjeeling? Ans. Lichens are also called the bio-indicators of the pollution. They are found only in the nonpolluted areas. Lichens are highly susceptible towards sulphur dioxide. A compound in them reacts with sulphur dioxide to form a poisonous chemical that kills the plant itself. This is because lichens grow in areas where sulphur dioxide pollution is very less, e.g., in Manali and Darjeeling. Delhi is highly polluted place where lichens cannot grow and survive. Q.7. Why does water need conservation even though large oceans surround the land masses? Ans. Water conservation is important because we need water for many essential activities. About three-fourth of Earth consists of water, but only 1% of it is freshwater. It is this freshwater which we can utilise for daily use. As water resources are not judiciously used, these are getting depleted. This will lead to the time when there will be no water. If water conservation is carried out seriously, this will help to preserve wildlife water habitats and the need of building dams, etc. It will also help to ensure water availability for future generations. Q.8. Soil is formed by water. If you agree to this statement then give reasons. Ans. Role of water in soil formation : Rocks on earth s surface are not chemically stable and constantly undergo the process of weathering. It is the first step of soil formation. Chemical weathering involves the breakdown of primary minerals in the rock to new minerals that are more stable in the surface environment. Water is the essential agent in chemical weathering. It either reacts directly with the minerals or carry dissolved species which themselves react with the mineral. Q.9. During summer, if you go near the lake, you feel relief from the heat. Why? Ans. During summer, we feel relief from the heat when visit near the lake. The lake breeze forms during daylight in summer months because water does not warm as quickly as the surrounding land surfaces. Air cooled by contact with the cold lake water is denser than that surrounding the lake and thus forms a zone relatively high pressure over the lake. When the sun heats land, the air above it warms becoming less dense. With high pressure over the lake and low pressure over land, the regional pressure gradient pushes cool winds towards the land. This is the lake breeze flow because of which we feel better during summer near the lake. C. Short Answer Questions - II (3 Marks) Previous Years' Questions Q.1. (a) "The flow of energy is unidirectional whereas the biogeochemical transfer is cyclic". Explain why? (b) Justify the statement "The nitrogen cycle is supposed to be an ideal cycle in the biosphere". 13
Ans. (a) The flow of energy is unidirectional from one organism to another in a reduced quantity but decomposition of such animals by decomposers make the cyclic movement of elements (nutrients). All these takes place between the living organisms and their nonliving surroundings. (b) Nitrogen is an important component of amino acids, proteins and nucleic acids which form structural and functional constituents of cell protoplasm. Air contains about 78% of nitrogen, which exists in molecular form as N 2. Water bodies also contain nitrogen. Producers cannot absorb nitrogen in its elemental form. It has to be first converted into nitrates for the use of plants. The process of converting atmospheric nitrogen into nitrates is called nitrogen fixation. The atmospheric nitrogen after nitrogen fixation gets converted into nitrates, which is then absorbed by plants and assimilated into their system. Organic compounds like proteins are formed which are decomposed to ammonia and amino acids by decomposers in the soil. Q.2. List three ways to control soil pollution. Ans. (i) Proper drainage and sewer system in densely populated areas, so that they do not go in open for defaecation. (ii) Less use of chemicals in the form of fertilizers, pesticides, weedicides, etc. (iii)proper disposal of non-degradable waste materials such as plastic carry bags, glass bottles, electronic wastes, etc. Other Important Questions Q.1. 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. Ans. Lichens can grow on stones. These are a close association of a fungus and an alga. Lichens are the pioneer plants on barren rocks and hard rocky soil. Their continuous growth can even disintegrate rocks which helps in soil formation. They do this by secreting some organic acids. The disintegrated rock particles and the decaying of lichen form a fertile layer of soil where other plants particularly mosses can colonise. Q.2. Why does moon have very cool and very hot temperature variations eg. from 190 C to 110 C even though it is at the same distance from the Sun as the Earth is? Ans. Moon does not have any air around it. The air that surrounds our Earth acts as a nice blanket to keep us warm and comfortable. But the moon, since it does not have this blanket, gets much colder than the Earth during night and much hotter than the Earth during day. On the side of moon, that the Sun is shining on, the temperature reaches up to 110 C, i.e., much hotter than boiling. On the dark side of the moon, it gets very cold, i.e., 190 C, much colder than the Earth. Q.3. There is mass mortality of fishes in a pond. What may be the reasons? Ans. The mass mortality of fishes in a pond is a result of eutrophication. Eutrophication is a process by which plant growth increases in a water body like ponds or lakes. The increased growth and overcrowding of plants is due to either natural fertilising agents that are washed off from 14
the soil or the runoff of chemical fertilisers applied to agricultural lands. As the overcrowd plants die off, the dead and decaying vegetation depletes the pond s oxygen supply. This in turn leads to the mass scale death of fish in the pond. Q.4. Soil formation is done by both abiotic and biotic factors. List the names of these factors by classifying them as abiotic and biotic? Ans. Soil formation by biotic and abiotic factors : Soil formation occurs due to five important factors. Differences in soil particles within and between regions are a result of the interaction between these factors. (i) Abiotic factors : Rocks (parent material), rain, temperature, slope and elevation, time, etc. (ii) Biotic factors : Vegetation, microbes, soil organisms, animals and human beings. Q.5. All the living organisms are basically made up of C, N, S, P, H and O. How do they enter the living forms? Discuss. Ans. All living organisms are basically made up of carbon, nitrogen, sulphur, phosphorus, hydrogen and oxygen. These chemical elements tend to circulate in the biosphere in a characteristic cyclic path, i.e., from environment to living organisms and back to the environment. These more or less circular paths are called biogeochemical cycles or nutrient cycles. In simple way, these elements are absorbed by the plants from nature and convert them into food. This food passes through different trophic levels of various food chains for utilization by consumers. Finally, the decomposers return the inorganic nutrient to the environment by decomposing the dead bodies and excreta of various consumers. Q.6. Why does the percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere? Ans. Photosynthesis helps to balance oxygen and carbon dioxide in the air. Oxygen gas is produced during photosynthesis which animals breathe in. Animals breathe out CO 2 and the plants need this CO 2 for photosynthesis. So, the levels of CO 2 and O 2 are balanced in the air. Nitrogen gas is also circulated continuously between living and nonliving components of the biosphere. It also enters through the producer level through various processes and get transferred to other trophic levels. Finally, decomposers act on dead bodies of living organisms and the inorganic nitrogen enters the nature again. Q.7. Why are root nodules useful for the plants? Ans. Root nodules are extra lobes of certain plants such as peas and beans in which nitrogen-fixing bacteria are found. Leguminous plants are plants with root nodules. Bacteria in these root nodules convert the atmospheric nitrogen into nitrates which the plants can utilise. The plants use this nitrogen to synthesise proteins and other materials. D. Long Answer Questions (5 Marks) Previous Years' Questions Q.1. Many human activities lead to increasing levels of pollution of air, water bodies and soil. Isolating these activities to specific and limited areas would not help in reducing pollution. Justify this statement giving at least five reasons. 15
Ans. Isolation of these activities which are causing pollution of air, water and soil to a specific and limited area can reduce pollution to some extent but even this is not a permanent solution of the problem of pollution, because (i) Pollutants released after the decomposition of these wastes will recycle through soil, water and atmosphere. In this way they will come back to the place from where they had been removed. (ii) Excessive use of fossil fuels i.e., coal and petroleum. Because burning of these fossil fuels adds carbon particles to the atmosphere which causes smog. It produces huge amount of carbon monoxide and carbon dioxide as well in the areas restricted for such activity. (iii)use of chlorofluorocarbons (CFCs) in refrigeration is responsible for depletion of ozone layer in all the surrounding large area. (iv) Establishment of a number of industries which release carbon monoxide, sulphur dioxide oxides of nitrogen, hydrocarbons, heavy metals, etc. (v) Rain water flows many pollutants alongwith the water from one place to another. So there should be a permanent procedure for the removal of pollutants. Q.2. (i) Describe greenhouse effect. How the presence of greenhouse gases would lead to global warming? Explain. (ii) Draw a neat labelled diagram of water cycle in nature. Ans. (i) Greenhouse effect is an atmospheric phenomenon, in which an increase in the percentage of some gases such as carbon dioxide in the atmosphere causes the average temperatures increase of atmosphere worldwide leading to global warming. (ii) Q.3 (i) With the help of a neat labelled diagram, depict the cycling of carbon in nature. 16
(ii) Mention the two ways in which carbon dioxide is fixed in the environment. Ans. (i) Carbon Cycle In the abiotic environment, carbon is present in four forms: (a) As carbon dioxide in the atmosphere or air (about 0.03 0.04%), (b) As dissolved carbon dioxide or carbonic acid and bicarbonates in water or hydrosphere, (c) As fossil fuels like coal, petroleum and natural gas, and (d) As carbonates and graphite in the rocks. The basic movement of carbon is from the atmosphere. During photosynthesis, plants take in carbon dioxide from the atmosphere to synthesise organic compounds. These organic compounds enter the food chain as food and reach animals in successive trophic levels. (ii) (a) The carbon dioxide is fixed by green plant by the process of photosynthesis. (b) Carbon dioxide get dissolve in water as bicarbonate enter interior of earth ultimately to form carbonate rocks. Q.4. (i) Make neat and labelled sketch of Nitrogen cycle in nature. (ii) Describe in brief the role of Nitrogen fixing bacteria and of lightening in fixing atmospheric nitrogen. 17
Ans. (i) (ii) Certain bacteria and blue-green algae can fix atmospheric nitrogen directly into nitrates. The nitrogen-fixing bacteria can be free-living, like Azotobacter and Clostridium, or symbiotic bacteria (Rhizobium). Rhizobium is found in the root nodules of certain leguminous plants, like peas and beans. Q.5. (a) In coastal area, wind current moves from sea towards the land during day; but during night it moves from land to sea. Discuss the reason. (b) How are CFCs harmful for the environment and living beings? Ans. (a) The movement in the air or wind current are brought about by the following: (i) Evaporation of water takes place when it is heated. (ii) Condensation of water vapours take place at low atmospheric pressure due to cooling. (iii) Heating and cooling rates of water and land are different. Land gets heated faster but cools also soon compared to water. In coastal regions, the land and air near the sea gets heated faster than the sea. The sea water is comparatively cooler, so is the air on sea water. The cool air rushes towards the sea breeze and brings temperature down. At night, both the land and sea water start to cool. Since, the water cools down slower than the land, the air above water would be warmer than the air above land. Hence, the cool air flows towards sea during night to replace the warm air. (b) CFCs are responsible for the depletion of ozone layer. Since ozone layer protect us from UV rays CFCs disturbs the protection from UV rays causing a number of skin diseases like skin cancer. Q.6. (a) What are the forms of oxygen found in the atmosphere? (b) Forests influence the quality of our air, soil and water resources. Justify the statement. 18
Ans. (a) (i) Oxygen is present in dissolved form in water bodies and helps in the survival of aquatic life. (ii) Oxygen is also present in combined forms such as carbon dioxide (CO 2 ) and water (H 2 O). (iii) It is also present in the combined form in the Earth's crust as the oxides of most metals and silicon. (b) Forests influence the quality of air, soil and water resources in the following ways 1. Influence of forests on air : Both plants and animals release carbon dioxide to the atmosphere as a product of respiration. Forests take up this carbon dioxide for the manufacture of their food and release oxygen to the atmosphere after photosynthesis. In this way they are helpful in cleaning the air. Q.7. (a) Mention the two forms of oxygen found in atmosphere. (b) Name the form of oxygen absorbing U.V. rays. (c) Draw flow diagram of Oxygen cycle. Ans. (a) (i) Diatomic oxygen, O 2 (ii) Triatomic oxygen or ozone O 3 (b) Ozone (c) Oxygen Cycle Q.8. (a) What do you understand by ozone layer depletion? (b) What is air pollution? How does air pollution affect animal and plant life? Ans. (a) Depletion of ozone layer means reduction of the thickness of ozone layer due to the excess release of CFCs chlofluorocarbons in the atmosphere. The other factor responsible for ozone destruction is the pollutant nitrogen monoxide (NO). CFCs are very stable and are found to persist in the atmosphere. Once they reach the ozone layer, they with the ozone molecules, resulting in the reduction of the ozone layer. (b) The gases in air are present in a fixed ratio. Air pollution is caused whenever there is any imbalance in the ratio of gases present in air. 19
Harmful effects of air pollution are (i) Air pollution affects the respiratory system of living beings and causes bronchitis, pneumonia, asthma and lung cancer. (ii) Burning of fossil fuels like coal and petroleum releases oxides of nitrogen and sulphur. Not only the inhalation of these gases is dangerous, they also dissolve in rain to produce acid rain. Acid rain destroy the small plants and crops. Q.9. What are the causes of increase in the concentration of carbon dioxide in the atmosphere? How is carbon dioxide converted into organic compounds? Justify with the help of a labelled diagram. Ans. When fossil fuels are burnt they release carbon dioxide in the air. While these fossil fuels are formed very slowly over a period of million of years, they are being used at an increasingly fast rate, releasing large volume of carbon dioxide in the air, far in excess of the nature's capacity to recycle. This has led to a perceptible rise in CO 2 concentration in the atmosphere. During photosynthesis, plants take in CO 2 from the atmosphere to synthesise organic compounds. These organic compounds enter the food chain as food and reach animals in successive trophic levels. For diagram See Q. No. 3, Page 212 Q.10. Why is circulation of water necessary in the environment? Discuss any two human activities which are disturbing the water cycle. Ans. The circulation of water in the form of water vapour, clouds, rain and snow forms a water cycle. Water cannot remain in one state for a long term because it may lead to the disturbance in nature. For example, if the water of sea, rivers, lakes, ponds, etc. remain in solid form (snow) for a long term the animals and the plants living around them will be destroyed. So circulation of water from one state to another is important for the nature. Human activities disturbing the water cycle are (i) Destroying the forests results in evaporation of more and more surface water. It leads to drought. (ii) Global warming is also affecting the water cycle by melting the snow on earth poles. Q.11. How do clouds formed in the sky? Draw the biogeochemical cycle involved in it. What are the different states in which water is found in the water cycle? Ans. When water bodies like ocean, sea, etc., get heated during the day, a large amount of water evaporates and goes into the air. The wind carries the water vapour to various places. When this vapour reaches a certain height, it cools and in turn changes to tiny droplets of water, into snow. An enormous collection of these tiny droplets appears in the form of clouds. For Diagram See Q. No 2 Page 211 Water is found in different stages in a water cycle, such as water (liquid), snow (solid) and water vapours (gas). Q.12. (a) Study the given figure of Nitrogen cycle and mention what do A, B, C, D, E represents. (b) What will happen if step A does not occur? (c) Write the role of N 2 fixing bacteria in the biosphere. (d) Name two biologically important compounds that contains both O 2 and N 2. 20