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Solutions To Text Questions, 1. Crop Production and Management, Think, Page No. 8, Rice and soya bean are kharif crops because they depend on monsoon rain for, their growth. Thus, they are not grown in winter season., Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 10, 1. (a), 2. (c), 3. (a), 4. (a), 5. (d), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 15, 1. (b), 2. (c), 3. (b), 4. (b), 5. (b), , SECTION A, CLASS RESPONSE, A. Oral questions:, 1. The use of manure or fertilisers to enhance the fertility of the soil is, called manuring., 2. The supply of water to the crop plants at regular intervals through, sources other than rain is called irrigation., 3. Rice, maize, soya bean, groundnut, cotton, B. Science quiz:, 1. Kharif crop, 2. Preparation of soil (ploughing and levelling), 3. Rhizobium bacteria, WORKSHEET, A. Tick (3) the correct options:, 1. (a), 2. (b), 3. (a), 4. (c), B. Circle the odd ones. Give reasons for your choice:, 1. Wheat plant → It is a rabi crop, whereas others are kharif crops., 2. Pesticides, → These are used to kill pests, whereas others are, practices used in preparation of soil., 3. Green manure → It is a manure, whereas others are fertilisers., C. Fill in the blanks:, 1. rabi crops, 2. wooden plank/iron leveller 3. irrigation, , SECTION B, A., B., , 14, , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (c), 2. (b), 3. (b), Very Short Answer Questions:, 1. (i) Broadcasting/By traditional tool (ii) By seed drill/transplantation, 2. (i) Drip system, (ii) Sprinkler system, Teacher’s Resource Pack SCIENCE-8

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3. Preparation of soil → Selection and sowing of seeds → Replenishment, of nutrients in the soil → Irrigation → Crop protection → Harvesting, 4. Wheat, mustard, gram, pea, linseed, C. Short Answer Type-I Questions:, 1. The various tools which are needed during agricultural practices are, called agricultural implements., 2. Pulses are alternated with crops like wheat and rice to replenish the soil, with nitrogen., 3. (i) nature of crop plants, (ii) nature of soil of the crop, , (iii) season when the crop grows, 4. The supply of water to the crop plants at regular intervals through, sources other than rain is called irrigation., The two methods of irrigation are—, (i) Drip irrigation, (ii) Sprinkler irrigation, 5. Leguminous plants have Rhizobium bacteria present in their root, nodules. These bacteria convert atmospheric nitrogen into simpler, nitrogen compounds (nitrates) which are easily absorbed by the plants., This helps in replenishment of soil with nitrogen., 6. The deeply sown seeds will not grow because they will not get proper, sunlight and air for germination., D. Short Answer Type-II Questions:, 1. Fertilisers are human-made chemical substances which are rich in one, or more nutrients like nitrogen, phosphorus and potassium. These are, produced in factories., Urea, superphosphate, nitrophosphate, ammonium sulphate and, potash are examples of fertilisers., 2. It is important to sow seeds at the correct distance from each other, because at appropriate distance they get sufficient space, sunlight,, nutrients and water to grow., 3. (a) Drip irrigation is a water-economical method because it allows water, to fall drop by drop just at the position of roots. Water is not wasted, at all. This system also saves loss of water due to evaporation., (b) Irrigation is necessary for plants because water is one of the, most vital substance that supports life. Rainfall is one of the main, sources of water for crops. Since rainfall (monsoon) is not always, dependable, it is essential that farmers should also have other, ways of supplying water to the crop fields., 4. (a) The process of cutting and gathering of crop after its maturation is, called harvesting. Farmers celebrate Baisakhi to express their joy, and pleasure for getting the product of their hard work and labour., , , (b) Togetherness and unity, , Teacher’s Resource Pack SCIENCE-8, , 15

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E., , 5. Sandy soil needs more frequent irrigation due to its poor water-retaining, capacity, whereas clayey soil needs less frequent irrigation due to its, good water-retaining capacity., Long Answer Questions:, 1. (a) Manure is an organic compound (rich in nutrients) obtained by the, decomposition of plant and animal wastes by microbes., (b) Advantages of fertilisers:, (i) Fertilisers are soluble in water and thus, are easily absorbed, by the plants and increase the crop yield., (ii) They are nutrient-specific. thus, they provide particular, nutrients to the soil., Disadvantages of fertilisers:, (i) Fertilisers are non-biodegradable and thus, cause water and, soil pollution., (ii) Excessive use of fertilisers badly affects the fertility of soil., (iii) When fertilizers are washed away due to rainfall and reach, the water bodies they cause water pollution., 2. (a) The weed-killing chemicals are called weedicides., (b) 2, 4-D (i.e. 2, 4-dichlorophenoxy acetic acid), butachlor, dalapon, (c) The harmful effects of weeds in the crop field are as follows:, (i) Weeds consume a great amount of nutrients, water, sunlight, and space which is for crop plants., (ii) The weeds harbour pests (harmful insects that destroy crops)., Crop pests spread various crop diseases., (iii) Some weeds produce toxic substances that may be poisonous, for animals and human beings., 3. (a) Differences between manure and fertilisers, S.No., , 16, , Parameters, , Manure, , Fertilisers, , (i), , Nature, , It is a natural organic These are, substance., inorganic salts., , (ii), , Preparation It is prepared, in fields by the, decomposition, of animal wastes,, human wastes and, plant residues., , These are, prepared in, factories., , (iii), , Humus, , These do not add, any humus to the, soil., , It provides a lot of, humus to the soil., , Teacher’s Resource Pack SCIENCE-8

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F., , G., , (iv), , Amount of, nutrients, present, , It contains less, amount of essential, plant nutrients., , (v), (vi), , Cost, Examples, , It is not expensive., Sunn hemp or, Sesbania, , These are rich in, plant nutrients, like nitrogen,, phosphorus and, potassium., These are costly., Urea and potash, , (b) Advantages of using manure:, (i) It enhances the water-holding capacity of the soil., (ii) It makes the soil porous and increases aeration., (iii) It increases the number of soil-friendly microbes., (iv) It improves the soil texture and fertility of the soil., (v) It is cost effective, since it can be prepared from organic, wastes naturally., (vi) It is eco-friendly, biodegradable, organic in nature and does, not cause soil or water pollution. , (vii) It adds humus to the soil., HOTS (Higher Order Thinking Skills) Questions:, 1. The farmers level the field before sowing–, (i) to crush the big pieces of soil called crumbs, (ii) to prevent soil erosion, (iii) for uniform distribution of water and manure, 2. Biofertilisers are biodegradable, organic in nature, do not spoil the soil, composition nor do they accumulate into the food chain. Thus, they are, preferred over chemical fertilisers., 3. During ploughing, the land is pressed lightly and not tightly:, • to maintain the space between the soil particles, • to maintain the porous nature of the soil, • to enable exchange of gases, • to maintain the water-holding capacity of the soil, Application Based Questions:, 1. I would advise the use of biological methods for control of weeds because, chemical weedicides are non biodegradable and accumulate in the soil., They are harmful for the soil texture and kill the soil microorganisms. , They also make the crop produce poisonous., 2. Use of manure should always be preferred over fertilisers because unlike, fertilisers, manure is organic and biodegradable. It does not accumulate, in the soil, does not cause water or soil pollution and improves the, texture of the soil., , Teacher’s Resource Pack SCIENCE-8, , 17

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Think And Answer, Tick (3) the correct options:, 1. (c), 2. (d), CROSSWORD PUZZLE, , Across Down, 1. KHARIF, 5. IRRIGATION, 2. MANURING, 3. PLOUGHING, 4. PISCICULTURE, , 2. Microorganisms : Friend and Foe, Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 29, 1. (a), 2. (c), 3. (b), 4. (d), 5. (b), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 33, 1. (c), 2. (d), 3. (a), 4. (c), 5. (a), , SECTION A, CLASS RESPONSE, A. Oral questions:, 1. The toxic substances which are produced by microorganisms, make the, food poisonous and cause serious illness. This is called food poisoning., 2. Polio, influenza, common cold, dengue, chickenpox, measles, smallpox, 3. Chlorella, B. Science quiz:, 1. Bacteriophage, 2. Penicillin, Penicillium notatum, 3. Tuberculosis /common cold/ pneumonia, WORKSHEET, A. Tick (3) the correct options:, 1. (d), 2. (a), 3. (c), 4. (b), B. Fill in the blanks:, 1. immunity , 2. nitrogenous compounds, 3. Salmonella/Staphylococci/Clostridium. 4. preservative, C. State whether the following statements are true (T) or false (F):, 1. F, 2. T, 3. T, 4. T, , SECTION B, A., , 18, , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (b), 2. (c), 3. (a), Teacher’s Resource Pack SCIENCE-8

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B., , C., , D., , Very Short Answer Questions:, 1. Streptomycin, tetracycline, chloromycetin, 2. Common cold, chickenpox, tuberculosis, 3. Salt, sugar, 4. Common cold, tuberculosis, pneumonia, 5. The ability of one’s body to resist a disease is called immunity., Short Answer Type-I Questions:, 1. Pasteurisation is a process for preservation of milk. In this process, milk, is heated at about 70 °C for 15 to 30 seconds to kill the bacteria present, in it and then cooling it quickly to 10 °C to prevent the remaining, bacteria from growing., 2. Viruses are different from other organisms because:, They have the characteristics of both living and non-living things. Viruses, are acellular, i.e., they do not have any of the substances present in a, cell. They only contain a small nuclear material wrapped in a protein, coat. They cannot grow and reproduce on their own. This indicates that, they are non-living. When they enter a living cell, they reproduce using, the energy of the living cell. Thus, they are said to be a connecting link, between living and non-living things., 3. The process of breakdown of sugar into alcohol and carbon dioxide by, the action of microbes like yeast is called fermentation. Louis Pasteur, discovered the process of fermentation., Short Answer Type-II Questions:, 1. Lactobacillus bacteria help to make curd from milk. Curd is formed, when a protein called casein, present in milk, clumps together to form, a solidified mass. Casein coagulation takes place only when the milk is, acidic. A spoonful of curd contains bacteria Lactobacillus which promote, the formation of curd from milk., , , 2. Leguminous plants contain Rhizobium bacteria in their root nodules, which absorb nitrogen from the atmosphere and convert it into nitrates., When roots are decomposed, these nitrates mix with the soil and, increase the soil fertility., 3. (a) Common cold, influenza, mumps, measles, chickenpox, small pox, (b) Typhoid, Cholera, tuberculosis, anthrax, tetanus, (c) Malaria, sleeping sickness, amoebic dysentery, 4. (a) Bacteria and fungi, Teacher’s Resource Pack SCIENCE-8, , 19

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(b) (i), ,  y walking and cycling to near distances and reducing the use, B, of fossil fuels,, (ii) By planting more and more trees, E. Long Answer Questions:, 1. (i) Preservation by common salt: For ages, people have preserved, fish and meat by salting. Meat and fish are covered with dry, common salt. Salting draws out water (moisture) from the food,, thus, prevents microbial growth and reproduction. Salting is also, used to preserve amla, raw mangoes, tamarind, etc., (ii) Chemical method: Food can be preserved by using certain chemical, substances which can check the growth of microorganisms. Such, chemical substances are called food preservatives. Most chemical, preservatives remove oxygen from the food items. This helps in, preventing microbial growth. Sodium benzoate, citric acid and, potassium metabisulphite are common food preservatives. , Advantages of food preservation are—, (i) It decreases wastage of food by avoiding spoilage., (ii) It increases the storage period of food materials., (iii) Nutritional value of the food is retained for a longer period., (iv) It ensures the food availability at distant places and during the off, season., 2., , , 20, , Teacher’s Resource Pack SCIENCE-8

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Nitrification: Ammonium salt in the soil is converted first into nitrites by, Nitrosomonas bacteria. The nitrites are then converted into nitrates by, Nitrobacter bacteria. The nitrates, so formed in the soil, can once again, be absorbed by the plants. This process is called nitrification., Denitrification: Some of the nitrates are absorbed by plants. Rest of the, nitrates in the soil are converted by Pseudomonas bacteria into nitrogen, gas which escapes into the atmosphere. The conversion of nitrates into, free nitrogen gas by denitrifying bacteria is called denitrification., 3. (a) Boiling – Heating effect, (b) Canning – Air-free packing/vaccum packing, (c) Freezing – Low temperature treatment, (d) Dehydration – Removal of moisture, 4. (a) A small dose of dead and weakened disease-causing microbes used, to stimulate immune response in the body is called vaccine., (b) When a vaccine is introduced in the body of a healthy person, it, acts like an antigen. The body of the person produces antibodies, against these introduced microbes. These antibodies remain in the, body and protect the person against any future infections of the, same microbe., (c) The children are vaccinated to protect them from several diseases., F. HOTS (Higher Order Thinking Skills) Questions:, 1. The curd sets faster in summers because in summers, the weather is hot, and the bacteria that forms curd is more active in summer., 2. The person who suffers from chickenpox once, gets immunised naturally, for the disease. The antibodies formed earlier immunise the person, against any future attack by the microbe causing chickenpox., 3. We should always wash our hands before handling food items because, our hands may have germs that can infect the food items. The intake of, these infected food items may cause various diseases., G. Practical Skill Based Questions:, , To observe the increase in the volume of dough during the fermentation of, sugar present in dough by yeast cells, Things needed: Half kg flour, sugar and yeast powder, warm water, Method:, 1. Take flour (atta or maida), add two tablespoons of sugar and mix with, warm water., 2. Add a tablespoon of yeast powder and knead it to make a soft dough., 3. Put the soft dough in a container and leave it at a warm place for 2-3, hours or more., Observation: You observe that there is an increase in the volume of the, dough. The dough rises and looks fluffy., Teacher’s Resource Pack SCIENCE-8, , 21

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Conclusion: Yeast breaks sugar to produce carbon dioxide gas which increases, the volume of dough., Think And Answer, Tick (3) the correct options:, 1. (a), 2. (d), , 3. Synthetic Fibres and Plastics, Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 44, 1. (c), 2. (c), 3. (a), 4. (a), 5. (d), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 49, 1. (b), 2. (c), 3. (c), 4. (c), 5. (d), , SECTION A, , CLASS RESPONSE, A. Oral questions:, 1. (a) Jute, cotton, silk, wool, (b) Terylene, rayon, nylon, polyester, 2. Terylene, dacron, terene, 3. Thermosetting plastics, B. Science quiz:, 1. Polymerisation, 2. Rayon, 3. Bakelite, WORKSHEET, A. Tick (3) the correct options:, 1. (b), 2. (b), 3. (c), 4. (c), B. Circle the odd ones. Give reasons for your choice:, 1. Nylon → It is a synthetic fibre, whereas others are natural fibres., 2. PVC, → It is a thermoplastic, whereas others are thermosetting, plastics., C. Fill in the blanks:, 1. amide, 2. drip-dry property, 3. soft, 4. water pollution, , SECTION B, A., B., , 22, , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (d), 2. (b), 3. (d), Very Short Answer Questions: , 1. Rayon, 2. Amide molecule, 3. Polythene and PVC, 4. Raincoats, PVC pipes/soles of shoes and sandals/handbags., 5. (a) glucose, (b) amide, Teacher’s Resource Pack SCIENCE-8

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C., , D., , Short Answer Type-I Questions:, 1. Fibres obtained through different chemical processes in the industries, are human-made or synthetic fibres., 2. Plastics are polymers made up of a very large number of small molecules, joined end to end to form long chains. These are synthetic materials, which on being heated become soft and can be moulded into desired, shapes and then again hardened to provide durable articles., (i) Plastics (PVC) are used for making water pipes, bathroom curtains,, raincoats., (ii) Plastics (bakelite) are used for making electrical switches and plugs,, insulated wires., 3. Due to high tensile strength of the nylon fibres, these are used for, making bristles of toothbrushes., 4. (a) Nylon, (b) We learn that we can do anything by having strong will power and, determination. We should not be scared of anything and should, make constant efforts to achieve our goal. We should always help, others in overcoming their fears., Short Answer Type-II Questions:, 1. (i) Plastics (PVC) are used for making water pipes, bathroom curtains,, raincoats., (ii) Plastics (bakelite) are used for making electrical switches and plugs,, insulated wires., 2. Refuse, Reduce, Reuse, Recycle and Recover is called the 5-R principle., It helps to reduce pollution and keep the environment clean., 3., , S., No., , Parameters, , Thermosetting, plastics, , Thermoplastics, , (i), , Nature, , A plastic which once, moulded into a, particular shape does, not become soft on, heating and cannot be, moulded a second time, , (ii), , Effect of, heat, , They do not become soft They become soft on, on heating., heating., , (iii) Toughness, , A plastic which can, be melted repeatedly, by heating, hardened, on cooling and can be, moulded again and, again into different, shapes, , They are more tough and They are lesser tough, rigid., as compared to, thermosetting plastics., , Teacher’s Resource Pack SCIENCE-8, , 23

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(iv) Effect of high They are more resistant They are less resistant, temperature to high temperatures., to high temperatures., (v), , Recycle, , They cannot be recycled. They can be recycled., , Examples, , Bakelite, melamine,, formica, , Polythene, PVC, , 4. We wear cotton clothes in summers because cotton absorbs sweat, released by the sweat glands in body in hot and humid weather and, makes us feel comfortable., 5. Saucepan handles, electric plugs and switches are made of thermosetting, plastics because they are more tough and rigid and are poor conductors, of heat and electricity., E. Long Answer Questions:, 1. (a) High tensile strength: Synthetic fibres are very strong and can hold, large weight without breaking., (b) Low water absorption: Synthetic fibres absorb very little amount, of water. So, they dry quickly and this property is called drip-dry, property., (c) Abrasion-resistant: Most of the synthetic fibres have wear and tear, resistance. So, the clothes made by these fibres are long lasting or, durable., (d) Less expensive: Synthetic fibres are less expensive and more, affordable., (e) Lightweight: Most synthetic fibres are quite lightweight. Natural, fibres are comparatively heavy., 2. (i) Plastics do not get completely burnt and produce toxic gases that, cause air pollution., (ii) When plastics are dumped in water, they cause water pollution., (iii) Most of the plastics dumped in land fills, pollute land., (iv) Polybags, carelessly thrown here and there, choke the drains and, the sewer lines., (v) Plastic is dangerous for animals especially cows, the plastic, materials choke the respiratory system or the digestive system, this, can lead to their death., 3. (a) Cooking pans have plastic handles because plastic is a poor, conductor of heat., (b) Burning of plastics produces toxic gases and smoke which cause air, pollution., (c) Nylon is used for making climbing ropes because nylon has a high, tensile strength., , 24, , Teacher’s Resource Pack SCIENCE-8

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(d) Refrigerators have a plastic foam core because plastic is a poor, conductor of heat., (e) Electric wires have a plastic covering because plastic is a poor, conductor of electricity., (f) Bakelite is used for making electrical switches because bakelite is, poor conductor of electricity., F. HOTS (Higher Order Thinking Skills) Questions:, 1. Acrylic fibres are made up of synthetic polymers so they are not attacked, by insects or moths, whereas natural fibres have carbohydrates and are, attacked by insects and moths., 2. Use of synthetic fibres reduces the loss of forests because synthetic, fibres are formed of chemicals, whereas natural fibres are obtained, from plants which need to be cut., G. Application Based Questions:, 1. Nylon fibre is used for making fishing nets because it has high tensile, strength and is waterproof., 2. I would choose the steel tiffin box so as to reduce the use of plastic, since, plastic is a non-biodegradable substance and affects the environment, adversely., Think And Answer, Tick (3) the correct options:, 1. (c), 2. (a), , 4. Materials: Metals and Non-metals, Think, Page No. 58, Silver is not used for making electric wires because it is a very costly metal., Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 58, 1. (a), 2. (c), 3. (c), 4. (a), 5. (d), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 65, 1. (a), 2. (c), 3. (a), 4. (a), 5. (d), , SECTION A, CLASS RESPONSE, A. Oral questions:, 1. (a) Gold, silver, copper, tin, iron , (b) Mercury, 2. Rust is basic in nature., B. Science quiz:, 1. Bismuth, tungsten, 2. When magnesium is added to the copper sulphate solution, the bluecoloured copper sulphate solution changes to a colourless solution., Teacher’s Resource Pack SCIENCE-8, , 25

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3. Copper, 4. Gold, WORKSHEET, A. Tick (3) the correct options:, 1. (c), 2. (c), 3. (c), 4. (a), B. Circle the odd ones. Give reasons for your choice:, 1. Sodium → It can easily be cut with knife, whereas others are hard, metals., 2. Bismuth → It is a poor conductor of heat, whereas others are good, conductors of heat., 3. Iodine → It is a lustrous non-metal, whereas others are non-lustrous, non-metals., C. Fill in the blanks:, 1. ductility, 2. bismuth/tungsten, 3. Diamond, 4. Graphite, , SECTION B, A., B., , C., , D., , 26, , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (c), 2. (a), 3. (a), Very Short Answer Questions:, 1. The copper vessel on reacting slowly with carbon dioxide and water of, air loses its shine on being exposed to moist air for a long time., 2. When an iron object is left in damp air (or water) for a considerable, time, it gets covered with a reddish-brown flaky substance called rust., This is called rusting of iron., 3. Acidic oxides, Short Answer Type-I Questions:, 1. (a) Magnesium reacts with dilute hydrochloric acid to form magnesium, chloride and hydrogen gas., (b) Aluminium reacts with dilute hydrochloric acid to form aluminium, chloride and hydrogen gas., 2. Objects made of silver become black with the passage of time due to, the formation of a thin silver sulphide layer on their surface by the, action of hydrogen sulphide present in the air., 3. Arrangement of metals in a vertical column in the order of their, decreasing reactivities is called reactivity series of metals., Short Answer Type-II Questions:, 1. (a) Electric wires are made of copper because it is ductile and a good, conductor of electricity., Teacher’s Resource Pack SCIENCE-8

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(b) Gold and silver are used for making jewellery because they are, lustrous, highly malleable and ductile., (c) Graphite is a good conductor of electricity, that is why, it is used for, making electrodes in electric cells., 2. (a), , 4Na, , +, , sodium , (metal), , , , (b), , , , , , (c), , , , 3. (a), , 2Zn, , +, , zinc , (metal), , 2Mg, , +, , magnesium , (metal), , C, , +, , carbon , (non-metal), , (b), , , , , (c), , P4, , +, , S, , +, , phosphorus , (non-metal), sulphur, (non-metal), , O2, , at room, →, temperature, , O2, , →, , 2Na2O, , oxygen , (from air), , sodium oxide, , strong heating, , 2ZnO, , oxygen , (from air), , burns with a, , zinc oxide, , →, O2   dazzling, white light., , oxygen , (from air), , O2, , →, , 5O2, , →, , O2, , →, , oxygen , (from air), oxygen , (from air), oxygen, (from air), , 2MgO, , magnesium oxide, , CO2, , carbon dioxide, , 2P2O5, , phosphorus pentaoxide, , SO2, , sulphur dioxide, , 4. (a) Sonority, , (b) Care and concern for the poor and needy; spreading happiness and, love with simple gestures., 5. Chlorine, 6. Carbon and sulphur will form acidic oxides because these two are nonmetals., E. Long Answer Questions:, 1. (i) Metals are solid at room temperature, except mercury which is, liquid at room temperature., (ii) Metals are malleable, i.e., they can be beaten into thin sheets., (iii) Metals are ductile, i.e., they can be drawn into thin wires., (iv) Metals are lustrous., (v) Metals are hard., (vi) All metals are good conductors of electricity., (vii) Metals have high tensile strength., 2. (a) Wires cannot be drawn from wood because it is non-ductile and, also, an insulator., (b) Oxygen is not brittle because it is a gas., Teacher’s Resource Pack SCIENCE-8, , 27

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(c) Sulphur cannot be used for making pipes because it is a non-metal, and is brittle., (d) Diamond is used for making jewellery because it sparkles., (e) Sodium is a very reactive metal, i.e., it can catch fire on reacting, with air, that is why, it is stored in kerosene oil., 3. Physical properties:, (i) Copper is malleable., (ii) Copper is ductile., (iii) Copper is a good conductor of heat and electricity., , Chemical properties:, (i) Copper shows displacement reaction., i.e., Fe +, CuSO4, →, Cu, +, FeSO4, iron, , copper sulphate, , copper, , iron sulphate, , (here, more reactive metal (Fe) displaces less reactive metal (Cu), from CuSO4 solution), , (ii) Copper reacts with oxygen to form basic oxides., i.e., 4Cu +, O2, → 2Cu2O, , copper , oxygen copper oxide , (basic in nature), , F., , HOTS (Higher Order Thinking Skills) Questions:, 1. We cannot store lemon pickle in an aluminium container because lemon, contains acid and aluminium being a highly reactive metal, reacts even, with the mild acids and forms poisonous salts., 2. Utensils made of pyrex glass can be used for heating because pyrex, glass has high melting point and is heat-resistant so it does not break on, heating. No, glass is not a metal., 3. Gallium is a metal which has a very low melting point, so as soon as it is, kept on palm it absorbs the body heat and starts melting., 4. Magnesium being a reactive metal, reacts vigorously with hot water and, forms magnesium oxide and hydrogen gas which makes it float on the, water., , Mg +, H2O, →, MgO, +, H2, magnesium, , , boiling water, or steam , , magnesium, oxide , , hydrogen, gas., , G., , Practical Skill Based question:, When we add a piece of aluminium to a freshly prepared solution of sodium, hydroxide, we observe tiny bubbles of hydrogen gas in the solution. On, bringing a burning matchstick near the mouth of test tube, the gas catches, fire and burns with a pop sound., Think And Answer, Tick (3) the correct options:, 1. (c), 2. (d), , 28, , Teacher’s Resource Pack SCIENCE-8

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5. Coal and Petroleum, Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 78, 1. (b), 2. (a), 3. (a), 4. (c), 5. (c), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 80, 81, 1. (d), 2. (b), 3. (b), 4. (d), 5. (c), , SECTION A, CLASS RESPONSE, A. Oral questions:, 1. The materials which are present in nature and are useful to us to meet, our basic needs are called natural resources., 2. Fossil fuels have limited availability so, they should be conserved., 3. Petroleum gas, petrol, kerosene, diesel, lubricating oil, paraffin wax,, bitumen and fuel oil, B. Science quiz:, 1. Special grade kerosene oil, 2. LPG/coal/ kerosene, 3. CNG, WORKSHEET, A. Tick (3) the correct options:, 1. (c), 2. (c), 3. (b), 4. (c), B. Circle the odd ones. Give reasons for your choice:, 1. Coke, → It is obtained from destructive distillation of coal, whereas, others are constituents of petroleum., 2. Coal tar → It is obtained from destructive distillation of coal, whereas, others are constituents of petroleum., 3. Sunlight → It is an inexhaustible natural resource, whereas others are, exhaustible natural resources., C. Fill in the blanks:, 1. destructive distillation, 2. Bitumen, 3. Petroleum, 4. Compressed Natural Gas, , SECTION B, A., B., , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (c), 2. (c), 3. (d), Very Short Answer Questions:, 1. In India, coal is mainly found in Bihar, Jharkhand, West Bengal, Odisha, and Madhya Pradesh., , Teacher’s Resource Pack SCIENCE-8, , 29

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2., 3., 4., 5., C., , D., , 30, , Petrol and kerosene/LPG/Diesel/fuel oil/lubricating oil/Bitumen, Krishna-Godavari delta, Petroleum, Coke is used as a reducing agent in extraction of metals from their ores., It is also used to heat furnaces in iron and steel industry., Short Answer Type-I Questions:, 1. Resources which are present in unlimited quantity in nature and are, not likely to be exhausted by human activities are called inexhaustible, natural resources. For example, sunlight and air/water/rainfall/clay/, sand., 2. (a) Diesel is used as a fuel–for heavy vehicles like buses, trucks, ships,, tractors, railway engines, etc, and to run water pumps to produce, electricity on small scale., (b) Bitumen is used for–making road surfaces, paints, damp proof, foundation of buildings, coating the underside of electric poles to, prevent rusting., 3. Useful substances obtained from petroleum and natural gas are called, petrochemicals. They are used in the manufacture of synthetic fibres,, polythene, synthetic rubber, etc., 4. The process of separating the various constituents or useful fractions of, petroleum is known as refining of petroleum., Short Answer Type-II Questions:, 1. Coal is used, (i) in railway engines to produce steam that helps to run the engines., (ii) as a fuel to cook food in chulhas., (iii) in thermal power plants to produce electricity., (iv) in many industries to produce organic compounds., (v) in industries to obtain coke, coal tar, ammoniacal liquor and coal gas., 2. Fuels like coal, petroleum and natural gas are all formed from the dead, remains of plants and animals buried under the earth millions of years, ago. These are known as fossil fuels. Burning of fossil fuels produces, gases like carbon dioxide, carbon monoxide, sulphur dioxide and smoke, which cause air pollution., 3. Petroleum is called ‘black gold’ because of its great commercial, importance., 4. (a) I would suggest him to buy a CNG model because CNG is a cleaner, fuel. Petrol causes air pollution., (b) We learn to be environment friendly in all our actions by opting a, CNG model., Teacher’s Resource Pack SCIENCE-8

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E., , Long Answer Questions:, 1. (a) When coal is strongly heated in closed retorts in the absence of, air to get some useful products, the process is called destructive, distillation of coal., (b) The products obtained by the destructive distillation of coal are, coke, coal tar, ammoniacal liquor and coal gas., 2. (a) Coal is formed by carbonisation, i.e., the slow chemical process, of the conversion of the dead vegetation (remains of dead plants), into coal, under the influence of high temperature and pressure,, for million of years., (b) Methods for conservation of fossil fuels are:, (i) By reducing the use of fossil fuels, (ii) By using renewable sources of energy like-hydroenergy, wind, and solar energy, (iii) By using fuel-efficient machines, 3. (a) CNG is preferred over petrol and diesel because it is a cleaner fuel., It produces only carbon dioxide and water. No ash is produced on, burning of CNG. Another great advantage of CNG is that it can be, supplied directly from the gas wells to the houses and factories, through a network of pipelines., (b) We should switch off the engines at traffic lights because this helps, in conservation of fuels. This prevents the unnecessary combustion, of fuels., 4., , 5., , S., Inexhaustible natural, Parameters, No., resources, , Exhaustible natural, resources, , (i), , Availability, , Inexhaustible natural Exhaustible natural, resources are present resources are present in, in unlimited quantity limited quantity in nature., in nature., , (ii), , Effects of, human, activities, , Inexhaustible natural, resources are not, likely to be exhausted, by human activities., , S., Parameters, No., (i), , Availability, , Renewable resources, Renewable resources, are available in, unlimited quantity, if, managed properly., , Teacher’s Resource Pack SCIENCE-8, , Exhaustible natural, resources are likely to be, exhausted by uncontrolled, human activities., Non-renewable, resources, Non-renewable, resources are available, in limited quantity., , 31

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(ii), , Effects of, human, activities, , Renewable resources, are not likely to be, exhausted by human, activities, but excessive, and unwise use by, humans may exhaust, them. Eg. soil, forest,, wildlife, , Non-renewable, resources are likely, to be exhausted by, uncontrolled human, activities. Once used,, they are lost forever. Eg., coal, petroleum, natural, gas, , F., , HOTS (Higher Order Thinking Skills) Questions:, 1. Coal gas cannot be used as a cooking fuel inspite the fact that coal, gas has a high calorific value. This is because, coal gas is produced by, destructive distillation of coal and coal is an exhaustible fossil fuel which, takes millions of years to be formed., 2. Petroleum floats on water because it has less density than water, i.e., it, is lighter than water., 3. Different types of coal have different composition due to variation in, the carbon content. Carbon content varies with the extent of, carbonisation., For example, anthracite is the best variety of coal and has 90% carbon. It, is formed by compression of bituminous coal. Peat coal has more water, and less than 60% carbon as it is the first step of coal formation. So, the, extent of carbonisation increases with increase in pressure., 4. Formation of coal and petroleum takes place under very high temperature, and pressure conditions for millions of years. These conditions cannot, be provided or created in the laboratory. So, we cannot prepare coal, and petroleum in the laboratory., 5. The methods to reduce LPG consumption at home are as follows:, , (a) Use pressure cooker for cooking., (b) Use efficient, smokeless chulhas at homes where kerosene, coal or, wood is used for cooking., (c) Always cook the food covered., (d) Use solar cooker, solar water heater and solar water pump, i.e.,, solar energy., , 6. Combustion and Flame, Think, Page No. 91, Petrol has very low ignition temperature than kerosene, therefore it catches fire, fastly., Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 89, 90, 1. (c), 2. (a), 3. (c), 4. (c), 5. (c), , 32, , Teacher’s Resource Pack SCIENCE-8

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Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 96, 1. (a), 2. (d), 3. (d), 4. (c), 5. (c), , SECTION A, CLASS RESPONSE, A. Oral questions: , 1. (a) LPG, kerosene, coal, (b) Petrol, CNG, Diesel, (c) Coal, coke, CNG, 2. From air, 3. A flame is a region where combustion or burning of a fuel (in its gaseous, form) takes place to produce heat and light., 4. Suspended Particulate Matter, B. Science quiz:, 1. Carbon monoxide (CO), 2. Petrol, 3. Ignition temperature, 4. Carboxyhaemoglobin, WORKSHEET, A. Tick (3) the correct options:, 1. (d), 2. (c), 3. (b), 4. (d), B. Circle the odd ones. Give reasons for your choice:, 1. Coal, → It is a solid fuel, whereas others are liquid fuels., 2. Oxygen → It helps in combustion and respiration, whereas others, are air pollutants., 3. Glass, → It is not a combustible substance, whereas others are, combustible substances., C. Fill in the blanks:, 1. Global warming, 2. acid rain, 3. outermost , 4. Saponin, , SECTION B, A., B., , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (b), 2. (b), 3. (a), Very Short Answer Questions:, 1. Calorific value, 2. Wood and coal/coke/charcoal/paraffin wax, 3. The heating up of the earth’s atmosphere due to the trapping up of Sun, rays or infrared radiations by greenhouse gases, like carbon dioxide in, the atmosphere, causes greenhouse effect., , Teacher’s Resource Pack SCIENCE-8, , 33

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C., , Short Answer Type-I Questions:, 1. Substances which can burn easily in air to produce heat and light are, called combustible substances. For example, wooden stick, paper, cloth,, dry leaves., 2. A chemical process in which a substance reacts with oxygen (of air) to, give off heat and light (which may or may not be produced) is called, combustion. Burning of magnesium and charcoal are examples of, combustion, since, both give heat and light on burning., 3. When a combustible substance burns on its own without the help of, any external heat, it is called spontaneous combustion., Examples : fire in coal mines, forest fires, burning of white phosphorus., 4. Water can be boiled in a paper cup without burning it because the heat, supplied to the paper cup is transferred to water by conduction. The, water takes away the heat and does not allow the paper cup to reach its, ignition temperature. Hence, the paper cup does not burn., 5. Incomplete combustion produces carbon monoxide which is a very, poisonous gas. Carbon monoxide forms carboxyhaemoglobin when it, combines with haemoglobin of our blood. This decreases the oxygencarrying capacity of the blood. This causes suffocation and in extreme, conditions leads to death. Thus, incomplete combustion is harmful to, human beings., D. Short Answer Type-II Questions:, 1. Characteristics of an ideal fuel:, , (i) It should be cheap and easily available., (ii) It should burn smoothly., (iii) It should not produce any harmful and irritating or toxic fumes, during burning., (iv) It should have a proper ignition temperature., (v) It should not leave any residue after burning., (vi) It should be easy to handle, safe to transport and convenient to, store., (vii) It should have high calorific value., 2. The three conditions necessary for burning of a substance are—, (i) presence of a combustible substance, , (ii) presence of oxygen, (iii) attainment of ignition temperature of the combustible substance, 3. The middle zone of a candle flame is luminous because there is not, enough air for complete combustion of wax vapour. The incomplete, burning of wax vapour produces carbon particles and CO. The unburnt, carbon particles become hot and emit yellow light and makes the, middle zone luminous., , 34, , Teacher’s Resource Pack SCIENCE-8

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E., , 4. (a) Nitika used fire extinguisher and not water because water being, heavier than oil settles down at the bottom and the oil floats over, this water and continues to burn. Thus, we cannot extinguish fire, caused by kerosene oil with water., (b) In this act, Nitika shows her presence of mind, awareness and that, we should always help our neighbours., Long Answer Questions:, 1. Water is not used to put off fire caused by burning of petrol because, water being heavier than petrol, settles down at the bottom. The petrol, floats over this water and continues to burn., Water is not used for extinguishing fire in electrical appliances because, it is a good conductor of electricity. When water is poured over burning, electrical appliances, it causes electric shocks to the people involved in, firefighting., 2. Differences between the three zones of a candle flame, S., No., , Parameters, , Innermost, Zone, , Middle, Zone, , Outer, Zone, , (i), , Availability, of oxygen (or, air), , Not much air Not enough air Plenty of air is, or oxygen is is available., available., available., , (ii), , Combustion, , No, combustion, takes place., , Partial, (incomplete), combustion, takes place., , Complete, combustion, takes, place., , (iii) Hotness, , It is the least It is, hot region of moderately, the candle, hot., flame., , It is very hot,, i.e, it is the, hottest zone, of the flame., , (iv) Luminous, (light-giving), , It is dark (or, black)., , It is luminous, zone., , It is a nonluminous, zone. , , (v), , Nil, , Unburnt, carbon, particles (in, the form, of smoke, and soot), with carbon, monoxide, , It produces, carbon, dioxide and, water vapour., , By-products, formed, , Teacher’s Resource Pack SCIENCE-8, , 35

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(vi) Zone around, the candle., , Appears, black, contains, unburnt wax, vapour., , Emits yellow, light contains, partially burnt, wax vapour, , Emits blue, flame. Wax, vapour burns, completely., , 3. Combustible substances support combustion and burn easily in, the presence of air or oxygen to produce heat and light, while noncombustible substances do not support combustion and do not burn in, presence of oxygen., Examples (a) Combustible substances are-cloth, wooden stick, dry, leaves, paper, etc., (b) Non-combustible substances are iron nail, glass,, stone piece, steel spoon, etc., 4. (a) Fuels are classified on the basis of physical state in which they, occur. So, fuels are classified as follows:, (i) Solid fuels, (ii) Liquid fuels, (iii) Gaseous fuels, (b) The increase in the concentration of carbon dioxide in the, atmosphere increases the rate of greenhouse effect. This leads to, increase in the average temperature of the earth. This leads to a, condition called global warming., F. HOTS (Higher Order Thinking Skills) Questions:, 1. Water cannot be used to put off fire in petrol pumps because petrol, being lighter than water will float on the surface of water and due to, the supply of oxygen, will continue burning. Available arrangements for, extinguishing fire at petrol pumps are sand bags and fire extinguishers., 2. Bursting of crackers causes burning of phosphorus, sulphur and, magnesium. These substances when burn, produce, (i) harmful gases causing air pollution., (ii) certain oxides which combine with water present in air, forming, acids in the atmosphere, causing acid rain., G. Practical Skill Based Questions:, (a) Dry leaves, (b) A piece of paper, Dry leaves and a piece of paper have low ignition temperature because, there is no moisture content in them, whereas the other two things, i.e,, green leaves and a piece of wood have moisture content which increases, their ignition temperature., Think And Answer, Tick (3) the correct options:, 1. (b), 2. (c), , 36, , Teacher’s Resource Pack SCIENCE-8

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7. Conservation of Plants and Animals, Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 106, 1. (d), 2. (b), 3. (a), 4. (c), 5. (b), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 109, 1. (d), 2. (a), 3. (d), 4. (c), 5. (c), , SECTION A, CLASS RESPONSE, A. Oral questions:, 1. The diverse variety of plants and animals, along with the microorganisms, living in a particular region is called biodiversity., 2. In a wildlife sanctuary, any human activity that disturbs the wild animals, and their habitats, is not allowed. Some activities, like harvesting of, timber and collection of minor forest products, are allowed as they do, not interfere with the well being of the animals., 3. The International Union for Conservation of Nature (IUCN) is now, known as the World Conservation Union (WCU)., B. Science quiz:, 1. Satpura forest reserve, 2. Conservation, 3. IUCN (now WCU), WORKSHEET, A. Tick (3) the correct options:, 1. (b), 2. (c), 3. (c), 4. (b), B. Circle the odd ones. Give reasons for your choice:, 1. Camel → It lives in deserts, whereas others live in forests., 2. Deer → It is a vulnerable species, whereas others are endangered, species., C. Fill in the blanks:, 1. poaching , 2. Protected areas, 3. National parks, 4. Kaziranga National Park, , SECTION B, A., B., , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (d), 2. (a), 3. (a), Very Short Answer Questions:, 1. Eucalyptus, water hyacinth, 2. Dinosaurs are extinct., 3. Deforestation, , Teacher’s Resource Pack SCIENCE-8, , 37

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C., , Short Answer Type-I Questions:, 1. Deforestation increases the level of carbon dioxide in the air and, disturbs the natural balance of gases in the atmosphere. Increased, concentration of CO2 may lead to global warming which disturbs the, water cycle and reduces rainfall, causes drought and leads to melting of, glaciers., 2. The species listed in the Red list are under the categories of extinct,, critically endangered, vulnerable, endangered, extinct in the wild, near, threatened, least concern, data deficient and not evaluated., 3. A species refers to a group of organism (plants or animals) that have, common characteristics and can interbreed themselves., 4. Planting a large number of trees on a deforested area is called, reforestation., 5. In a wildlife sanctuary, protection and suitable living conditions are, provided to the animals in their natural habitat. Animals live freely in, their natural habitats, whereas in a zoo, natural environment is not, given to the animals and they are kept in cages., D. Short Answer Type-II Questions:, 1. Animals are hunted for their skin, fur, tusks, claws, meat and other body, parts. There is a great demand for rhino horns, tiger bones, elephant, tusks and fur of several animals., 2. National park is a large area that is protected and maintained by the, government to preserve wildlife where activities like grazing and, cultivation of crops are not allowed. Only tourism is permitted. The, popular national parks of India are—, (i) Jim Corbett National Park (ii) Gir National Park, (iii) Kaziranga National park, (iv) Kanha National Park, (v) Sariska National Park., 3. The book which keeps a record of all endangered animals, plants and, other species is called Red Data Book., Advantage of maintaining Red Data Book are—, (i) It provides useful information on the status of various species., , (ii) It tries to create awareness about the endangered species., 4. Deforestation has taken place due to the following reasons:, • To build homes, factories, roads and dams for the increasing, human population, • To obtain wood as fuel and for making furniture and paper, • To obtain more agricultural land for cultivation of crops for the, growing population, • For mining of minerals such as coal, petroleum and ores, , 38, , Teacher’s Resource Pack SCIENCE-8

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E., , 5. Seasonal movement of birds and other animals in large numbers from, one place to another to overcome unfavourable conditions and returning, back to their original habitats when conditions become favourable is, called migration. Arctic tern and Siberian Crane are migratory birds., 6. (a) Animals are hunted for trading their skin, fur, tusks, claws, meat,, horns and other body parts., (b) Due to illegal hunting, many animals in the world are under threat, and on the verge of extinction., (c) Presence of mind, concern and care for animals and our, environment., Long Answer Questions:, 1. A multi-purpose protected area which is developed to conserve, biodiversity and also to educate, train and create awareness about, environmental aspects and eco-friendly living is called a biosphere, reserve. The three main biosphere reserves in India are—, (i) Nanda Devi Biosphere Reserve, (ii) Gulf of Mannar Biosphere Reserve, (iii) Sunderban Biosphere Reserve, 2. (a) The diverse variety of plants and animals, along with the, microorganisms living in a particular region is called biodiversity., Biodiversity is important for us because every component of it, plays an important role in nature. In other words, it maintains the, environment around us. We are economically dependent upon, biodiversity. We get variety of food items, cloth items, wood, oil,, medicines from various plants. We get food, leather and milk from, animals., (b) We should conserve biodiversity to prevent the endangered species, from becoming extinct and to maintain the ecological balance in, nature., 3. The clearing of forests over a wide area is called deforestation. The, consequences of deforestation are –, (i) It causes soil erosion and makes the soil infertile. Due to gradual, erosion of fertile topsoil, the land gets converted into a desert. This, is called desertification., (ii) It causes global warming which disturbs the water cycle, reduces, the rainfall and causes drought and melting of glaciers., (iii) It decreases the water-holding capacity of the soil and can cause, floods., (iv) Forests are natural habitat of many species of animals. Cutting, down trees destroys the homes of these species which poses a, threat for their survival., , Teacher’s Resource Pack SCIENCE-8, , 39

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F., , HOTS (Higher Order Thinking Skills) Questions:, 1. Introducing a new species of a plant into a habitat threatens the survival, of the native species of that habitat because it increases the struggle of, native species for existence by competing with the availability of food, and space., 2. If lions are totally killed in a forest, then herbivores (like, deer) will keep, on increasing in population. This will cause overgrazing, leading to the, loss of producers. Altogether, this will disturb the food chain of that, ecosystem., 3. Recycling of paper conserves the forests by reducing the need for, overproduction of paper and hence, prevents the cutting down of trees., Think And Answer, Tick (3) the correct options:, 1. (d), 2. (d), 3. (a), , 8. Cell—Structure and Functions, Think, Page No. 120, If nucleus is not present in the cell, the cell will die because nucleus controls all, the activities of the cell and other cell organelles., Multiple Choice Questions (MCQs). Tick (3) the correct options:, , Page No. 117, 118, 1. (d), 2. (c), 3. (b), 4. (c), 5. (b), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 122, 1. (c), 2. (d), 3. (c), 4. (a), 5. (a), , SECTION A, CLASS RESPONSE, A. Oral questions: , 1. Cell division is necessary for the growth and multiplication of cells., 2. Robert Hooke, 3. Amoeba and WBCs, B. Science quiz:, 1. Chloroplast contains a green pigment called chlorophyll., 2. Plastids, cell wall, 3. Cytoplasm, WORKSHEET, A. Tick (3) the correct options:, 1. (a), 2. (a), 3. (b), 4. (d), B. Fill in the blanks:, 1. Robert Hooke, 2. organ, 3. cell membrane, 4. prokaryotes, , 40, , Teacher’s Resource Pack SCIENCE-8

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C., , Match the following:, 1. (d), 2. (a), , 3. (b), , 4. (c), , SECTION B, A., B., , C., , D., , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (c), 2. (c), 3. (b), Very Short Answer Questions:, 1. Microscope, 2. Micron or micrometre (µm), 3. (a) Red Blood Cells (7 µm), (b) Nerve cells (100 cm), Short Answer Type-I Questions:, 1. Staining is a method to colour the colourless and transparent cells, for detailed observation of the cell and its internal structure under a, microscope., 2. (a) Egg cells, (b) Smooth muscle cells, (c) Nerve cells, (d) Red blood cells/corpuscles, 3. The main functions of the cell membrane are—, (a) It is selectively permeable as it allows only selected substances to, pass in and out of a cell., (b) It provides an outer boundary to the cell and protects the cell from, injury., (c) It also separates cells from one another and from the surrounding, medium., 4. Chloroplasts are green plastids that contain chlorophyll (green, pigment) which helps in photosynthesis. Since, only plants perform, photosynthesis, chloroplasts are present only in plants., Short Answer Type-II Questions:, 1. Organisms which are made up of only one cell are called unicellular, organisms, whereas organisms which are made up of many cells are, called multicellular organisms., Examples of unicellular organisms are — Amoeba, Euglena/bacteria/, yeast and Paramecium and of multicellular organisms are insects and, trees, grasses, human beings and animals., 2. The cells which have a well-organised nucleus with a nuclear membrane, are called eukaryotic cells. Examples are Hydra, insects, plants, animals,, fungi and protozoa., 3. (a) Organ system, (b) Teamwork and cooperation, , Teacher’s Resource Pack SCIENCE-8, , 41

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E., , Long Answer Questions:, 1. (a), , (b), , S.No. Parameters, , Animal cell, , Plant cell, , (i), , Size, , Animal cells are, smaller than plant, cells., , Plant cells are, larger in size with, distinct outlines., , (ii), , Cell wall, , Cell wall is absent., , Cell wall is present., , (iii), , Plastids, , Plastids are absent., , Plastids are, present., , (iv), , Vacuoles, , Vacuoles are absent., If present are small., , A large vacuole is, present., It fills most of the, space of cell., , (v), , Golgi, apparatus, , Have well-developed, golgi apparatus that, are present near, nucleus., , Many dictyosomes, are scattered in, the cytoplasm., , (vi), , Centrosome Centrosome is, absent., , Centrosome is, present., , 2. (a) Mitochondria: It provides energy for all the activities of a cell. The, energy is produced by the oxidation of food (respiration). Thus,, these are often called powerhouses of the cell., (b) Cell membrane: It is selectively permeable membrane, i.e., allows, only the entry and exit of selected substances. It also provides an, outer boundary to the cell and separates the cells from one another, and also from the surrounding medium., (c) Vacuole: It stores soluble food, wastes and secretions of cell, dissolved in water as cell sap., , 42, , Teacher’s Resource Pack SCIENCE-8

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(d) Ribosome: It takes part in synthesis of proteins., (e) Nucleus: It controls all the metabolic activities of the cell. It is also, responsible for passing genetic characteristics from parents to the, offspring. , F. HOTS (Higher Order Thinking Skills) Questions:, 1. Plant cells contain cell wall which provides protection against, temperature variations, high wind speeds and moisture. Animal cells, do not have cell wall because they do not face such weather conditions, directly., 2. Plasma membrane is called selectively permeable membrane because it, allows only certain selective substances to pass or exit through it., 3. Chromosomes are called hereditary vehicles because they carry the, unit of inheritance– the genes, from parents to the offspring (from one, generation to another). They are responsible for transferring the traits, from parents to the offspring., G. Application Based Questions:, 1. We can distinguish a plant cell from an animal cell by looking for the, presence of cell wall, a large vacuole and chloroplasts in the plant cell., 2. To observe the detailed structure of onion peel cells, Megha should use, an electron microscope because it helps in observing various internal, parts (organelles) of the cells. The magnification power of an electron, microscope is also quite high (i.e., 1,00,000 to 5,00,000 times)., , 9. Reproduction in Animals, Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 128, 1. (a), 2. (b), 3. (c), 4. (b), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 132, 1. (a), 2. (a), 3. (c), 4. (a), , SECTION A, CLASS RESPONSE, A. Oral questions:, 1. The production of new individuals by their parents is called reproduction., 2. Reproduction is important for the survival of a species on the earth. It, ensures the continuity of life on the earth., 3. Sexual and asexual, B. Science quiz:, 1. Asexual reproduction, 2. In vitro fertilisation, 3. During implantation, the embryo gets embedded in the inner lining of, the uterus., Teacher’s Resource Pack SCIENCE-8, , 43

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WORKSHEET, A. Tick (3) the correct options:, 1. (d), 2. (d), 3. (c), 4. (b), 5. (c), B. Circle the odd ones. Give reasons for your choice:, 1. Mammals, → These are viviparous, whereas others are oviparous, animals., 2. Fallopian tube → It is a part of female reproductive system, whereas, others are parts of male reproductive system., 3. Testes, → These are the part of male reproductive system,, whereas others are parts of female reproductive, system., C. Fill in the blanks:, 1. asexual, 2. ova, 3. external, 4. foetus, D. State whether the following statements are true (T) or false (F):, 1. T, 2. F, 3. F, , SECTION B, A., B., , C., , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (a), 2. (b), 3. (c), Very Short Answer Questions:, 1. (a) Amoeba, Paramecium, yeast, hydra, (b) Frogs, human beings, fishes, cows, dogs, horses, 2. Oestrogen, progesterone, 3. Internal fertilisation, Short Answer Type-I Questions:, 1. The fertilisation which occurs outside the female's body is called, external fertilisation. It takes place in frogs and fishes., 2. The animals that give birth to young ones are called viviparous animals., Humans, Cows, Cats and dogs are viviparous animals., 3., , 44, , S.No., , Sexual reproduction, , Asexual reproduction, , (i), , It produces new animals from, the existing two parents by the, fusion of their gametes., , It produces new animals, without the involvement of, gametes., , (ii), , Formation of zygote takes place. No zygote is formed., Eg. Fishes, frogs, cows, dogs,, Eg. Amoeba, hydra, yeast, horses, human beings, Euglena, paramecium, Teacher’s Resource Pack SCIENCE-8

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D., , Short Answer Type-II Questions:, 1. Fallopian tube (oviduct) is a thin and coiled muscular tube with a, funnel-shaped opening near ovaries. It joins the uterus to the ovary. The, fertilisation of egg (or ovum) by the sperm takes place in the fallopian, tube., Testes produce male gametes called sperms and male sex hormone, called testosterone., 2. The stage of embryo in which all the body parts can be identified is, called foetus. After 8 weeks of development, a human embryo is said to, become foetus. , 3. In binary fission, the parent organism splits or divides to form two new, organisms of the same kind. In binary fission of a fully grown Amoeba,, the nucleus lengthens first and divides into two parts. After that, the, cytoplasm divides into two parts around each nucleus and forms two, daughter cells. In this way, a single parent Amoeba divides to form, daughter Amoebae, which grows to its full size and divides again., , , , E., , Amoeba reproduce by binary fission, 4. (a) Blockage of fallopian tubes, (b) We can adopt the orphans and give them love, care and good, education. There are many children in the world who need love, and care. By giving these children whatever they need, we can set, an excellent example and serve the society. The girls and boys are, equal and we should give equal opportunities to both., Long Answer Questions:, 1. (a), , , , Teacher’s Resource Pack SCIENCE-8, , 45

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(b) (i), , Testes – The function of testes is to produce male gametes, called sperms and the male sex hormone called testosterone., (ii) Vas deferens – It carries sperms to the urethra by the muscular, action of its walls., (iii) Urethra – It carries urine from the bladder as well as semen, (consisting of sperms) from the vas deferens through the penis., (iv) Penis – It injects sperms into the vagina of the female's body., 2. In Hydra (Fig. a), first a small outgrowth called a ‘bud’ grows on the, side of its body (Fig. b). This bud then gradually grows to form a small, Hydra by developing a mouth and tentacles (Fig. c). The tiny daughter, Hydra detaches itself from the body of the parent Hydra (Fig. d). This, tiny Hydra grows to its full size by eating food., , , 3. An adult female frog lays a large number of eggs in water. After some, time, the eggs hatch into small fish-like larvae called tadpoles. Tadpoles, grow larger as they feed on algae and bits of plant materials. The, tadpole grows hindlimbs. After the development of both pairs of limbs,, the young frog crawls on the land. The frog reabsorbs the rest of its tail, and continues to grow until it reaches its adult body size., , , 4. In human beings, fertilisation is internal. Millions of sperms are, introduced into the vagina of a female through penis during mating., The sperms are highly active and motile. They reach the fallopian tubes, through the uterus. One of the sperm fuses with the ovum in a fallopian, tube to form a zygote., , 46, , Teacher’s Resource Pack SCIENCE-8

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F., , HOTS (Higher Order Thinking Skills) Questions:, 1. A woman with blocked fallopian tube can give birth to a baby by, fertilisation of eggs outside the body. The method is called in vitro, fertilisation. In such cases, the doctor collects freshly released eggs and, sperms and keeps them together for a few hours for in vitro fertilisation, to take place. The zygote formed as a result of fertilisation of egg is, placed in the mother's uterus for further development., 2. Humans mostly give birth to a single baby at a time because at the time, of ovulation, usually a single mature egg is released into the oviduct. So,, a single egg is fertilised and thus, a single baby is developed., 3. The larva of frog is not the same as adult frog because the larval stage of, frog (i.e., tadpole) is restricted to water as the egg gets fertilised in water, and hatches into a tadpole. The tadpole, thus, possesses characteristics, of fish like a tail which enables it to survive in water., 4. Inspite of internal fertilisation in hens, they do not give birth to young, ones, rather they lays eggs because hen is an oviparous animal., CROSSWORD PUZZLE, , Across (→) Down (↓), 1. METAMORPHOSIS, 4. TESTES, 2. FOETUS , 5. BUDDING, 3. FERTILISATION, 6. OVIPAROUS, , 7. SEXUAL, , 10. Reaching the Age of Adolescence, Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 142, 1. (c), 2. (d), 3. (d), 4. (c), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 146, 1. (c), 2. (c), 3. (b), 4. (a), 5. (a), , SECTION A, CLASS RESPONSE, A. Oral questions:, 1. The period of life, when the body undergoes changes, leading to, reproductive maturity is called adolescence., 2. 46, B. Science quiz:, 1. Genetic character, 2. Endocrine glands, WORKSHEET, A. Tick (3) the correct options:, 1. (c), 2. (c), 3. (c), 4. (b), Teacher’s Resource Pack SCIENCE-8, , 47

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B., , C., , Circle the odd ones. Give reasons for your choice:, 1. Growth → It is a natural process, whereas others are various stages of, growth in humans., 2. AIDS, → It is a disease, whereas others are drugs., Fill in the blanks:, 1. sperms, 2. Adam's apple, 3. acne and pimples, 4. Pituitary, , SECTION B, A., B., , C., , D., , 48, , Multiple Choice Questions (MCQs) Scientific /Practical skills:, 1. (a), 2. (d), 3. (b), Very Short Answer Questions:, 1. Menarche, 2. (a) Dwarfism, (b) Gigantism, 3. (a) XY , (b) XX, Short Answer Type-I Questions:, 1. (i) Menstrual cycle stops, (ii) Enlargement of breasts, 2. Pituitary gland is located at the base of the brain. It secretes the growth, hormone., 3. Thyroxine hormone controls metamorphosis. It also stimulates the rate, of cellular oxidation of carbohydrates, proteins and fats in humans., 4. The period of life when the body undergoes changes leading to, reproductive maturity is called adolescence., 5. Adolescents often find themselves confused due to changes in levels of, hormones., Short Answer Type-II Questions:, Present height (cm), × 100, 1. Calculation of full height =, % of full height at this, age (given in question), 120, =, × 100, 80, = 150 cm, 2. The first menstrual flow which begins at puberty in women is called, menarche. This marks the beginning of reproductive life of females. The, stoppage of menstrual flow at the age between 45-50 years in females, is called menopause., 3. (a) If the egg (ovum) gets fertilised by a sperm in the fallopian tube, the, fertilised egg begins to divide to form an embryo. The embryo gets, embedded in the lining of the uterus and this results in pregnancy., Teacher’s Resource Pack SCIENCE-8

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E., , (b) If the egg (ovum) does not get fertilised, then the thick and soft, inner lining or wall of the uterus is no longer needed and hence it, breaks, and leads to menstruation., 4. (a) Rohan is probably experiencing the following changes:, • He has started giving more importance to his friends, his peer, group and less importance to his parents/guardians., • He often feels confused, has emotional outbursts, feels sad, or, has strong emotions or moods that change quickly., • He has become more independent and self-conscious ., • He has started feeling the need for acceptance and, understanding., • He is frequently found to be confused between what is ‘right’, and what is ‘wrong’., • He feels insecure while trying to adjust to the changes in the, body and mind., • He feels attracted towards the opposite sex., (b) We learn to be honest, sharing and convey what we feel to our, parents. We should seek their advice whenever we feel confused., We learn to be caring, friendly and supportive from Rohan's father., We should always help and guide our young children as and when, they need us. We should provide them a strong mental support, and the right guidance., Long Answer Questions:, 1. (a) Health of an individual is defined as his/her state of physical, social, and mental well-being. An adolescent should follow a healthy, lifestyle which includes proper nutrition, personal hygiene, physical, exercise and maintaining good habits to be healthy and fit., (b) The conditions necessary for maintaining good reproductive health, during adolescence are –, (i) Having balanced diet, (ii), Personal hygiene, (iii) Physical exercise, (iv) Say 'No' to drugs , 2. All human beings have 23 pairs of chromosomes in the nucleus of, their cells. Out of these 46 chromosomes, 44 are called autosomes, and remaining two are called sex chromosomes. They are represented, as X and Y chromosomes. In females, the cells contain two identical X, chromosomes. So, the sex chromosomes in females are represented by, XX. In males, the cells contain two different chromosomes, X and Y. So,, the sex chromosomes in males are represented as XY., Each gamete contains only one sex chromosome. An egg always contains, X chromosome, whereas a sperm may contain either X or Y chromosome., • If a sperm having X chromosome fertilises the egg, the zygote, would have two X chromosomes. It develops into a female child., , Teacher’s Resource Pack SCIENCE-8, , 49

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•, , If a sperm carrying the Y chromosome fertilises the egg, the zygote, would have one X and one Y chromosome. It develops into a male, child., , , 3. (a) Pituitary gland– It is located at the base of the brain. It controls, the overall development and growth of the body, development of, muscles and bones., (b) Thyroid gland– It is located in the neck region below the larynx. It, stimulates the rate of cellular oxidation of carbohydrates, proteins, and fats., (c) Pancreas– It is located below the stomach. The hormones secreted, from pancreas maintain the blood sugar level., (d) Adrenal gland– It is located on the top of each kidney. It controls, emotions like fear and anger. It also regulates blood pressure and, heartbeat., F. HOTS (Higher Order Thinking Skills) Questions:, 1. An adolescent is short in height because at the time of attaining, adolescence, the growth and development of an individual depends on, , (a) certain hormones, and, (b) proper nutrition., , Probably, there has been an insufficient amount of proteins in his/her, diet and secretion of the growth hormones., 2. Adolescents are advised to take more proteins in diet because proteins, are necessary for growth and development of the body., 3. The pelvic region of girls becomes wider during puberty because a, female attains reproductive growth and maturity during this stage., Think And Answer, Tick (3) the correct options:, 1. (d), 2. (b), 3. (b), , 11. Force and Pressure, Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 155, 1. (d), 2. (c), 3. (c), 4. (a), 5. (a), , 50, , Teacher’s Resource Pack SCIENCE-8

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Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 160, 1. (a), 2. (a), 3. (c), 4. (c), 5. (b), , SECTION A, CLASS RESPONSE, A. Oral questions:, 1. The five effects of force are:, (i) It can cause motion in a stationary object., (ii) It can stop a moving object., (iii) It can change the direction of motion of a moving object., (iv) It can change the speed of a moving object., (v) It can change the shape and size of an object., 2. The force acting along two surfaces in contact which opposes the, motion of one object over the other is called the force of friction or, frictional force., Examples of frictional force:, (i) A moving or rolling ball stops after some time., (ii) A bicycle comes to rest, when we stop pedalling., 3. Force acting on a unit area of an object is known as pressure., Force (F), Pressure (P) =, Area (A), The SI unit of pressure is N/m2 or pascal., B. Science quiz:, 1. Barometer, 2. Force and area, 3. Electrostatic force/gravitational force, WORKSHEET, A. Tick (3) the correct options:, 1. (c), 2. (c), 3. (a), 4. (c), 5. (d), B. Circle the odd ones. Give reasons for your choice:, 1. Muscular force → It is a type of contact force, whereas others are the, types of non-contact forces., 2. Lubricant → It is used to reduce friction, whereas others are, applications of atmospheric pressure., C. Fill in the blanks:, 1. greater pressure, 2. equal, 3. atmospheric pressure, 4. gravitational, Teacher’s Resource Pack SCIENCE-8, , 51

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SECTION B, A., , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (d), 2. (c), 3. (c), B. Very Short Answer Questions:, 1. The resultant force will be the sum of both the forces., 2. N/m2 or pascal, 3. The small pieces of paper get attracted to the plastic comb and stick to, it because of the electrostatic force., C. Short Answer Type-I Questions:, 1. We can feel force of 1 N by placing 100 g weight on our palm., 2. An apple dropped from a height always falls on the earth because of the, force of gravity. This force is due to the attraction between the earth, and the object., 3. The force of attraction exerted by the earth on the objects due to which, the objects fall vertically downwards is called force of gravity., 4. Since, there is no atmosphere outside the earth, so to maintain the, normal atmospheric pressure of their body, astronauts wear specially, designed spacesuits., 5. The pressure is higher at 20 m below the surface of the sea because the, pressure of a liquid increases with depth., D. Short Answer Type-II Questions:, 1. A wide steel belt is provided over the wheels of army tanks so as to, reduce pressure on the ground, otherwise the heavy wheels of tanks, may sink in the ground., 2. (a) The mountaineers suffer nose bleeding at high altitudes because, at high altitudes, the atmospheric pressure is much less than our, blood pressure. Due to this, some of the blood capillaries burst and, blood comes out through the nose of the mountaineers., (b) When we suck air at the upper end of the straw with our mouth,, the pressure of the air inside the straw is reduced. But the pressure, acting on the surface of the fruit juice is equal to the atmospheric, pressure. So, the greater atmospheric pressure acting on the, surface of the fruit juice pushes the fruit juice up into the straw to, our mouth which helps to drink juice with straw., 3. (a) As the cutting edge is sharpened, the area of contact reduces which, increases the pressure over any object and hence, knife cuts the, objects easily., (b) We learn to love, take care and to help our elders, especially, grandparents., , 52, , Teacher’s Resource Pack SCIENCE-8

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E., , Long Answer Questions:, 1. (a) A heavy truck is fitted with six to fourteen tyres because these tyres, increase the area of contact on which their weight acts and hence,, reduce their pressure on the ground., (b) Skiers use long, flat skies to slide over snow because the area of, contact is larger and therefore, lesser is the pressure on the snow,, enabling the skier to slide over the snow without sinking in the, snow., (c) Foundations of high-rise buildings are kept wide, so that they exert, less pressure on the ground and do not sink in due to the extremely, high pressure of the building., 2. (a) A school bag has wide straps made of thick cloth, so that the, weight of the bag may fall over large area of the shoulder of the, child, producing less pressure on the shoulders and making it more, comfortable to carry the heavy school bag., (b) The walls of a dam are made thicker at the bottom because water, pressure increases with depth and a thicker wall can withstand a, greater pressure exerted by the water at greater depths., 3. (a) The pressure exerted by the air due to its own weight is known as, atmospheric pressure., (b) Our body is not crushed by the large pressure exerted by the, atmosphere because the pressure of the blood in the blood vessels, and other fluids present in the body, balances the atmospheric, pressure., (c) Working of a syringe is based on the presence of atmospheric, pressure. When we dip a syringe in a liquid and pull its piston, the, pressure inside the syringe gets reduced. The atmospheric pressure, acting on the surface of the liquid is more in comparison to the air, pressure in the syringe and thus, it pushes the liquid up into the, syringe., F. HOTS (Higher Order Thinking Skills) Questions:, 1. Iron rails of railway tracks are fixed over wide wooden or concrete, sleepers to distribute the load (force) of train over a large area of the, ground, since, pressure decreases on increasing area, hence, it prevents, sinking of railway tracks into the ground., 2. The weight of a person on Jupiter is three times more than that on the, Earth because Jupiter has three times more gravity than that on the, Earth., 3. The water comes out slowly from an upstair’s tap than from a similar, tap downwards because the liquid pressure increases with the depth, and so it flows faster in taps placed down., Teacher’s Resource Pack SCIENCE-8, , 53

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G., , Numericals:, 1. Resultant force = (1000 + 1000)N = 2000 N, Both the horses pull the horse-cart in the same direction, the resultant, force is calculated by adding the force, therefore, resultant force is the, sum of both the forces., 2. Force exerted by team A = (80 + 100 +120) N = 300 N, Force exerted by team B = (85 + 105 + 125) N = 315 N, , ∴ Resultant force = Force exerted by team B – Force exerted by team A, = (315 – 300) N, = 15 N, , ∴ Team B is the winner., 3. Area of contact = 10 m2, Force exerted by solid object on wooden plank = 250 N, Force, ∴ Pressure =, Area, , ∴ Pressure exerted by solid object on the wooden plank, Force exerted by solid object on wooden plank, =, Area of contact, , 250, , ∴=, = 25 Pa, 10, 4. Force exerted by the brick on the ground = 16 N, Area of brick = l × b, = 32 × 10 = 320 cm2 = 0.032 m2, (Q 1 m = 100 cm), Force, ,  Pressure =, Area, , ∴ Pressure exerted by the brick on the ground, Force exerted by the brick on the ground, =, Area of the brick, 500, , = 16 × 1000 = 16000 = 500 N / m2 or Pa, 32, 32, 5. Given,, , , Force, Area, , , , , Pressure =, , , ∴, , Pressure =, , 54, , = 120 N, = 3m2, Force, Area, 120, 3, , = 40 N/m2 or 40 Pa, Teacher’s Resource Pack SCIENCE-8

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H., , Application Based Questions:, 1. The two forces acting on the rocket are the force of gravity, which pulls, the rocket towards the ground, and the force of friction due to earth’s, atmosphere, which opposes its motion., 2. Some pulses got stuck into the polythene and did not fall because of the, electrostatic force developed between the two surfaces., I. Practical Skill Based Question:, To show that the pressure increases with depth, Things needed: A plastic bottle, water and an adhesive tape, Method:, 1. Take an empty plastic, least depth,, bottle (1 litre). Make, A, increasing, least pressure, three holes of equal, depth of, jets of water, B, diameters at different, water, greatest depth,, C, heights. Apply adhesive, greatest pressure, tape over all holes., Pressure increases with depth., 2. Now, fill the bottle with, water. Remove the adhesive tape figures., , Observation: You observe that on removing the tape, the water from the, uppermost hole A is found to travel the shortest distance from the base of, the vessel. The water from the hole B goes a little farther away whereas the, water from the lowermost hole C travels the maximum distance., , Discussion: The depth of water near hole A is the least, so the water comes, out from hole A with less pressure and falls near the base of the vessel. The, depth of water near hole B is greater (than A), so the water comes out with, the greater pressure from hole B and falls farther away from the base of the, plastic bottle. The depth of water near hole C is the greatest. So, the water, comes out with the greatest pressure and goes farthest from the container, (plastic bottle)., , Conclusion: The pressure of a liquid increases with depth., , 12. Friction, Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 174, 1. (d), 2. (c), 3. (d), 4. (a), 5. (d), , SECTION A, CLASS RESPONSE, A. Oral questions:, 1. The force acting along the two surfaces in contact which opposes the, motion of one object over the other is called friction., 2. When an object is pulled over another, tiny hills and valleys present, on both the surfaces in contact get entangled with one another. The, Teacher’s Resource Pack SCIENCE-8, , 55

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interlocking of the two surfaces opposes the motion of one object over, another and gives rise to friction., 3. The opposing force that comes into play when one object is actually, rolling over the surface of another object is called rolling friction., Eg. Rolling of a wheel or a log of wood, B. Science quiz:, 1. Limiting friction, 2. Athletes wear spiked shoes to increase friction because spiked shoes, have better grip on the ground and prevent slipping., 3. It is difficult to walk on wet marble floor because friction on the surface, of wet marble is very less as compared to friction on dry marble. , WORKSHEET, A. Tick (3) the correct options:, 1. (a), 2. (c), 3. (c), 4. (d), B. Circle the odd ones. Give reasons for your choice:, 1. Making grooves → This is to increase friction, whereas others are, used to decrease friction., 2. Rolling friction → It is a type of kinetic friction, whereas others are, types of friction., 3. Insect, → It doesn’t have a streamlined body, whereas, others have streamlined body., C. Fill in the blanks:, 1. less, 2. increase, 3. friction, 4. streamlined, , SECTION B, A., B., , C., , 56, , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (c), 2. (b), 3. (a), Very Short Answer Questions:, 1. (i) Nature of surfaces in contact with each other, (ii) Weight of the object, 2. When a wooden block is moved over the surface of a table, it slides. The, opposing force acting here is sliding friction., 3. When a wheel or circular disc rolls on a flat surface, the opposing force, acting here is rolling friction., Short Answer Type-I Questions:, 1. The special shape of a body or an object around which a fluid (liquid or, air) can flow, offering minimum amount of friction is called streamlined, shape., Teacher’s Resource Pack SCIENCE-8

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2. The substances which reduce friction are called lubricants., For example, oil, grease, D. Short Answer Type-II Questions:, 1. The different ways of increasing friction are –, (i) By making the surfaces rough : Friction can be increased by, increasing the roughness of the surfaces in contact. For example,, the surface of the head of a matchstick and the sides of a matchbox, are deliberately made rough to increase the friction to produce, more heat because of which the matchstick lights up easily., (ii) By making grooves : We can increase the friction in case of tyres, of bicycles, cars, buses, etc., by making grooves in them. Due, to greater friction, the tyres get a better grip on the road which, prevents skidding of the vehicles., 2. Rolling friction is less than sliding friction because the area of contact, of the surfaces is reduced when we use round objects (e.g., wheels,, ball bearings, roller bearings, etc.). In case of sliding friction, the area, of contact is greater and offers more friction. So, whenever possible,, sliding friction is replaced by rolling friction., 3. (a) When we apply brakes, the car stops due to the force of friction, between the brakes’ lining and the drum of the wheel., (b) We should try to be punctual by proper time management and, be cautious. We should always care for others. A person's life is, valuable than anything else in this world and we should always try, to save one's life., E. Long Answer Questions:, 1. (a) The bodies of birds are streamlined such that they experience least, amount of friction due to air., (b) When we strike a matchstick against a rough surface, it catches, fire because the force of friction raises the temperature of the, matchstick head to such an extent that the chemicals stored in it, catches fire to produce flame., (c) Grooves are made in tyres to increase friction due to which the, tyres get a better grip on the road. This prevents skidding of the, vehicles., (d) A lubricant reduces friction by forming a thin layer between the, moving surfaces so that they do not directly rub each other. , 2. (a) Ball bearing is a hollow, circular device containing small metal balls, which are fitted around the moving part of a machine (like an axle)., The ball bearing reduces the friction by converting sliding friction, into rolling friction. For example, when the axle of a machine fitted, with ball bearing rotates, then the metal balls also roll and hence,, the friction is reduced., Teacher’s Resource Pack SCIENCE-8, , 57

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(b)   , , metal balls, , axle, , ball, bearing, ,       Ball bearings, , F., , G., , 58, , 3. (a) The magnitude of friction increases with the increase in weight of, an object., (b) Smooth surfaces offer less friction and rough surfaces offer more, friction., (c) Friction increases with the increase in area of surfaces in contact, with each other., HOTS (Higher Order Thinking Skills) Questions:, 1. Oil is a lubricant and is used to reduce friction. On holding the glass, with an oily hand, the force of friction between the two surfaces is, minimised. Due to this, the glass slips from the hand., 2. Friction damages the machines because of—, (i) continuous opposing force acting over the machines., (ii) heat produced due to friction., 3. It is easy to hold an earthen pot than a glass tumbler because earthen, pots have a rough surface which applies force of friction and stops it, from slipping down., 4. When we write on a glass sheet with a piece of chalk, the particles of, chalk are not left behind because glass is a smooth surface which does, not apply frictional force on the surface of chalk., 5. Rough surface of the beach applies greater opposing force (friction) on, boat than water which has smooth surface. That is why, it is difficult to, pull a boat on the beach than on the sea., 6. By dragging the feet along the ground, the frictional force applied to, oppose the moving bicycle is not only on the bicycle but also against the, feet of the cyclist. So, more the opposing force, easier to slow down the, fast moving bicycle., 7. The force of friction produces heat and the walls of the mixer grinder, become hot when run continuously for a few minutes., 8. Gymnasts apply a coarse substance on their hands to increase the, friction between the surface and the hands so that they have a better, grip and do not slip down., Application Based Questions:, 1. Wet marble floor < dry marble floor < newspaper < carpet, 2. Soap reduces the force of friction applied by our hand on the glass, so it, does not stop it from falling down., Teacher’s Resource Pack SCIENCE-8

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H., , Practical Skill Based Question:, There will be more friction when the trolley is loaded. This is because force, of friction depends on weight of the object. More weight, more friction., Think And Answer, Tick (3) the correct options:, 1. (b), 2. (c), , 13. Sound, Think, Page No. 191, To produce a shrill sound, Suraj should tighten the strings of the guitar., Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 183, 1. (b), 2. (a), 3. (a), 4. (d), 5. (c), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 189, 1. (c), 2. (c), 3. (b), 4. (d), 5. (b), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 192, 1. (a), 2. (b), 3. (c), 4. (b), 5. (c), , SECTION A, CLASS RESPONSE:, A. Oral questions:, 1. Sound is a form of energy which produces a sensation of hearing in our, ears., 2. (a) In solids, (b) In gases, 3. Hammer, anvil and stirrup, B. Science quiz:, 1. 20 Hz – 20,000 Hz, 2. Voice box or larynx, 3. Loudness of sound depends upon the amplitude of vibrations., 4. Inaudible sounds having frequency less than 20 Hz are known as, infrasonic vibrations., WORKSHEET, A. Tick (3) the correct options:, 1. (c), 2. (a), 3. (a), 4. (a), B. Circle the odd ones. Give reasons for your choice:, 1. 40 dB , → It is the loudness level of normal conversation,, whereas others are the loudness levels of loud sounds, which cause noise pollution., 2. Loudspeakers → They increase noise pollution, whereas others are, used to decrease noise pollution., 3. Flute, → This is a wind instrument, whereas others are stringed, instruments., Teacher’s Resource Pack SCIENCE-8, , 59

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SECTION B, A., , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (c), 2. (c), 3. (a), B. Very Short Answer Questions:, 1. Flute, shehnai, trumpet, 2. Amplitude is the maximum displacement of the bob from its mean, position on either side., 3. The number of oscillations made by a simple pendulum per second is, called frequency of the pendulum., C. Short Answer Type-I Questions:, 1. Wind instruments are generally made in the form of pipes. When we, blow air into them, the column of air inside vibrates, producing a note, (a sound of particular frequency)., 2. Loudness of sound is directly proportional to the square of amplitude of, the vibration, producing the sound. Loudness ∝ Amplitude2., 3. Cochlea receives the amplified vibrations from the three bones of, middle ear and converts them into nerve impulses and sends to the, brain through auditory nerves., 4. Dolphins and bats can hear the sounds that we cannot hear., 5. (a) By stretching the sheet spread on tabla surface, (b) By varying the lengths of strings of violin, (c) By closing the holes of the flute, 6. The owners of dogs use Galton’s whistles to give signals to their dogs., D. Short Answer Type-II Questions:, 1. Inaudible sounds having frequency more than 20,000 Hz are known as, ultrasonic sounds. Animals like porpoises, dolphins and bats produce, ultrasonic sounds., 2. The pendulum makes 20 oscillations in 4 seconds., , ∴ The pendulum makes oscillations in one second = 5 oscillations, , ∴ The frequency of pendulum = 5 Hz, 3., , 60, , Teacher’s Resource Pack SCIENCE-8

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E., , 4. It is not the correct way of celebration because bursting crackers causes, air pollution and playing loud music causes noise pollution, which, is not good for our health. It disturbs the other people living in the, neighborhood, especially the infants, old and the sick people., Long Answer Questions:, 1. (a) The characteristics of sound are (i) pitch (ii) loudness and (iii) quality., (i) Pitch : Pitch is the characteristic of sound by which we can, distinguish a shrill sound from a grave (hoarse) sound even, though the two sounds have the same loudness., (ii) Loudness : Loudness is the characteristic of sound by which, a loud sound can be distinguished from a faint sound even, though both have the same pitch., (iii) Quality : Quality of the sound is the characteristic that enables, us to distinguish between two sounds of the same pitch and, loudness produced by two different sources., (b) Pitch of a sound depends upon the frequency of vibration., (i) The pitch of the sound produced by an object vibrating with a, low frequency is low and the sound is called a grave sound., (ii) The pitch of the sound produced by an object vibrating with a, high frequency is high and the sound is called shrill sound., Thus, the higher the frequency of the sound, the higher will be its, pitch and vice versa. , 2., , , , 3. (a) Noise from any source that causes disturbance or discomfort of any, kind in the environment is called noise pollution., (b) The three sources of noise pollution are–, (i) loudspeakers, (ii) moving trains and aeroplanes, (iii) bursting crackers, (iv) excessive use of horns, Teacher’s Resource Pack SCIENCE-8, , 61

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(c) The five measures to reduce noise pollution are –, (i) Automobiles should be fitted with silencers and soft horns., (ii) We should not play radio, television and stereo system too, loudly., (iii) The use of loudspeakers at social and religious functions, should be banned., (iv) Machines should be maintained in a good condition to reduce, industrial noise pollution., (v) We should avoid bursting fireworks that make loud noise., (vi) The airports and noise making factories should be shifted, away from the residential areas., F. HOTS (Higher Order Thinking Skills) Questions:, 1. We cannot talk in space because there is vacuum in the space and sound, cannot travel in vacuum., 2. Vibrations of the ringing alarm clock cannot travel in vacuum so its, ticking sound cannot be heard., 3. It is convenient to put the ears on the track to hear a train approaching, from far away because vibrations travel faster through the solid iron, track than in air and can be heard earlier than in the air., 4. (a) Loudness will become nine times of the original., (b) Loudness will become four times of the original., 5. Tuning fork produces sound of single frequency, whereas a sitar, produces sounds of different frequencies. So, the tuning fork sounds, flat, whereas the sitar sounds shrill., Think And Answer, Tick (3) the correct options:, 1. (d), 2. (a), , 14. Chemical Effects of Electric Current, Multiple Choice Questions (MCQs). Tick (3) the correct options:, Page No. 200, 201, 1. (c), 2. (b), 3. (b), 4. (a), 5. (c), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 205, 1. (b), 2. (c), 3. (a), 4. (c), , SECTION A, CLASS RESPONSE, A. Oral questions:, 1. Materials that allow electricity to flow through them easily are called, conductors. Iron and copper are two conductors., , 62, , Teacher’s Resource Pack SCIENCE-8

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2. A LED means a Light Emitting Diode. It is similar to a bulb but it runs on, a very low voltage., 3. (i) Heating effect, (ii) Magnetic effect    (iii) Chemical effect, B. Science quiz:, 1. Cation, 2. LED and magnetic compass are used as weak electric current detectors, 3. Gold and silver, WORKSHEET, A. Tick (3) the correct options:, 1. (a), 2. (c), 3. (b), 4. (a), B. Circle the odd ones. Give reasons for your choice:, 1. Graphite, → It is a good conductor of electricity, whereas others, are bad conductors of electricity., 2. Distilled water → It is a bad conductor of electricity, whereas others, are good conductors of electricity., 3. Tap water, → It is a good conductor of electricity, whereas others, are bad conductors of electricity., C. Fill in the blanks:, 1. electrolytic, 2. electrolysis, 3. chemical, 4. electroplating, , SECTION B, A., B., , C., , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (b), 2. (a), 3. (a), Very Short Answer Questions:, 1. Lemon juice and tap water, vinegar, dilute hydrochloric acid, 2. Voltameter, 3. The three examples of electrolytes are–, (i) aqueous solution of copper sulphate, (ii) aqueous solution of hydrochloric acid, (iii) aqueous solution of ammonium hydroxide, Short Answer Type-I Questions:, 1. The method of coating the metal's surface of a given article with a, thin layer of superior metal with the help of electric current is called, electroplating. For example, coating of iron with chromium, nickel or, zinc is done to protect it from rusting., 2. When an electric current is passed through an electrolyte, chemical, reactions take place. This is called the chemical effect of electric current., , Teacher’s Resource Pack SCIENCE-8, , 63

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3. No, distilled water does not conduct electricity. We can make it, conductive by adding –, • salts like common salt, copper sulphate, sodium nitrate, zinc, chloride, etc., • acids like dilute hydrochloric acid, nitric acid, sulphuric acid, etc., • bases like sodium hydroxide, ammonium hydroxide, potassium, hydroxide, etc., D. Short Answer Type-II Questions:, 1. Non-electrolytes are chemical compounds which do not conduct, electricity when dissolved in water. Glucose and alcohol are nonelectrolytes., 2. The four applications of electrolysis are–, (i) Extraction of metals from their ores: For example, when an electric, current is passed through molten sodium chloride, sodium is, deposited at the cathode and chlorine gas is evolved at the anode., (ii) Manufacture of chemicals: For example, manufacture of oxygen, gas, chlorine gas, hydrogen gas is done by electrolysis., (iii) Refining of metals (electrolytic refining): For example, many, metals like copper, zinc, tin, silver, gold and nickel are refined by, this method., (iv) Electroplating: The method of coating the metal’s surface of a, given article with a thin layer of superior metal with the help of, electric current is called electroplating. For example, coating of iron, with chromium or nickel or zinc to protect it from rusting., 3. Iron objects are electroplated with chromium to protect them from, rusting. This is because chromium is less reactive metal and does not, corrode easily. Chromium plating is done in many objects such as car, parts, bath taps, kitchen utensils, gas burners, bicycle handles, wheel, rims and many others., 4. (a) The method of coating the metal’s surface of a given article with, a thin layer of superior metal with the help of electric current is, called electroplating., (b) No, it is not right to cheat others and make profit because it is, being dishonest and is a crime. Such things creates an insecurity in, leading a good and honest life in future. Also, we should never be, selfish and take undue advantage of a common men’s belief and, faith in the jewellers., E. Long Answer Questions:, 1. Chemical effects of electric current are used in the following ways:, (a) Extraction of metals from their ores: Electrolysis is used in the, extraction of metals from their ores. For example, when an electric, , 64, , Teacher’s Resource Pack SCIENCE-8

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current is passed through molten sodium chloride, sodium is, deposited at the cathode and chlorine gas is evolved at the anode., Aluminium and potassium are also extracted from their ores by, electrolysis., , (b) Manufacture of chemicals: Electrolysis is used for the manufacture, of chemicals which are used in industries in large quantities., Manufacture of oxygen, chlorine and hydrogen gas is done by, electrolysis., (c) Refining of metals (electrolytic refining): Electrolytic refining, means refining (purification) by electrolysis. It is the most important, and widely used method for refining of metals. Many metals, like, copper, zinc, tin, silver, gold and nickel are refined by this method., (d) Electroplating: The method of coating the metal’s surface of a, given article with a thin layer of superior metal with the help of, electric current is called electroplating., 2. The method of electroplating of copper on an iron strip is as follows:, (a) The object to be, electroplated, i.e., an iron, strip is made cathode, (negative electrode)., , (b) A thin sheet of pure copper, is made anode (positive, electrode)., (c) An acidified solution of, copper sulphate is used as, an electrolyte, taken in an electrolytic tank., When electric current is passed through the acidified copper sulphate, solution, copper from the solution gets deposited on the surface of iron, strip, forming a reddish brown layer of copper metal all over the iron, strip. Thus, electroplating of copper on an iron strip is done., F. HOTS (Higher Order Thinking Skills) Questions:, 1. During heavy downpour, the electrician will be wet and water serves, as a good conductor of electric current. He may be electrocuted if he, carries out electrical repairs in the outdoor areas. Thus, it is dangerous, for his life., 2. Sea water is water containing salts, so it provides ions for electrical, conductivity in comparison to drinking water which lacks salts. Thus,, the bulb glows more in case of sea water., G. Application Based Questions:, 1. On interchanging the connections of the electrodes, the copper ions, previously deposited on the iron strip (previously cathode now anode), will move towards the copper strip (previously anode now cathode)., Teacher’s Resource Pack SCIENCE-8, , 65

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H., , 2. The liquids that contain impurities (which serve as free ions) conduct, electricity, whereas liquids such as distilled water that lack ions do not, conduct electricity., Practical Skill Based Question:, No, distilled water does not conduct electricity. We can make it conducting, by adding –, • salts like common salt, copper sulphate, sodium nitrate and zinc chloride., • acids like dilute hydrochloric acid, nitric acid and sulphuric acid., • bases like sodium hydroxide, ammonium hydroxide and potassium, hydroxide., , 15. Some Natural Phenomena, Think, Page No. 210, No, because in case of wet hair friction is very less so the comb is not electrically, charged due to lack of force and therefore, transfer of charge does not take, place., Think, Page No. 213, When the weather is dry, synthetic fibres get charged. The force of attraction, that acts between the charged particles, opposes their detachment and creates, a crackling sound while taking of sweater., Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 215, 1. (a), 2. (a), 3. (a), 4. (b), 5. (a), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 222, 1. (c), 2. (c), 3. (a), 4. (d), , SECTION A, CLASS RESPONSE, A. Oral questions:, 1. Storms, cyclones, lightning, earthquakes, 2. When ebonite rod is rubbed with the wool, it gets negatively charged., 3. A kite, silk string, iron key, silk ribbon, thin metal wire and Leyden jar, 4. The surface of the earth is not one continuous piece. It is broken into, many large pieces called tectonic plates., B. Science quiz:, 1. Epicentre, 2. Tsunamis , 3. Charged, WORKSHEET, A. Tick (3) the correct options:, 1. (d), 2. (b), 3. (b), 4. (c), , 66, , Teacher’s Resource Pack SCIENCE-8

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B., , C., , Circle the odd ones. Give reasons for your choice:, 1. Pollution → It is not a natural phenomenon, whereas others are, natural phenomena., 2. Ocean, → It is not the layer of earth, whereas others are layers of, the earth., 3. Drought → It is not caused due to earthquakes, whereas others are, consequences of an earthquake., Fill in the blanks:, 1. electric current, 2. thunder, 3. faults, 4. seismic waves, , SECTION B, A., B., , C., , D., , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (b), 2. (a), 3. (b), Very Short Answer Questions:, 1. An object is said to be charged when it acquires electric charges by, rubbing or by any other method from another object., 2. Seismograph, 3. The loud sound produced during lightning is called thunder., 4. A comb rubbed on dry hair attracts pieces of paper because a kind of, force is produced between them, which is called electrostatic force., Short Answer Type-I Questions:, 1. Charging an object by rubbing it with another object is called charging, by friction., 2. An earthquake is a sudden shaking of the earth's crust which lasts, for a very short time. Richter scale is a scale used for describing the, magnitude of an earthquake., 3. The force exerted by a charged object on another charged or uncharged, object is known as electrostatic force., 4. We say that repulsion is a sure test of charge on an object. When the, object being tested is repelled by a charged object, we are sure that the, object under examination is charged and has the same charge as that on, the charged object., Short Answer Type-II Questions:, 1. The three causes of earthquake are –, (i) Movement of the tectonic plates, (ii) Volcanic eruptions, (iii) Dislocation (or faults) of the crust, (iv) Underground nuclear explosion, , Teacher’s Resource Pack SCIENCE-8, , 67

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The three effects of earthquake are –, (i) Human-made structures like buildings, railway tracks, roads,, bridges, dams, etc., get severely damaged in earthquake. People, can get trapped inside the collapsed structures and many may die., (ii) Fire often breaks out following earthquakes which can be caused, by sparking from electrical short circuits., (iii) Groundwater pipes usually rupture, totally disrupting municipal, water supply systems., (iv) Earthquakes can change the course of rivers and cause floods., (v) Tremors in hilly areas and mountains cause landslides., 2. The harmful effects of lightning are –, (i) It can cause fire and shatter buildings, resulting in lot of destruction, and damage to the property., (ii) It can burn trees and also cause forest fires., (iii) It injures or sometimes even kills animals and people instantly., 3. (a) Sameer and Sachin did not take shelter under the tree because, trees provide a good conducting path for lightning., (b) Yes, he did the right thing to save himself and his brother’s life., 4. Precautions to be taken during an earthquake–, (i) Move to an open area immediately., (ii) Move away from buildings, trees, bridges, flyovers or overhead, electric cable lines or any other structures that can collapse., (iii) While travelling in a car or bus do not come out. Drive slowly to an, open area., E. Long Answer Questions:, 1. (a) An electroscope is an instrument used for detecting electrical, charge and its nature on an object., , (b) See Fig. (a), (c) Uses of a gold-leaf electroscope are:, (i) Detection of electrical charge, (ii) To identify the nature of, charge, 2. (a) A cloud has the negative charges, concentrated at the base and, positive charges concentrated at, its upper region. When a charged, cloud passes over a tall building or, a tall tree, it induces an opposite, charge on them. The negative, charges at the base of the clouds, , 68, , Teacher’s Resource Pack SCIENCE-8

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F., , G., , pull the positive charges induced on the tall buildings upwards at, a tremendous speed. As soon as the negative and positive charges, connect, a continuous path is formed from the cloud to the tall, building or a tree on the ground., The large amount of negative charges accumulated in the clouds, rushes down this path, giving rise to an electric discharge in the, form of lightning strike., (b) A lightning conductor is a device which is fixed on the top of tall, buildings to protect them from damage due to lightning., (c) When the lightning strikes, the lightning conductor provides an, easy path for the charge to pass through to the earth and thus,, protects the building., (d) Safety measures to be taken during thunderstorm are:, (i) Do not take shelter under a tree because trees provide a good, conducting path for lightning., (ii) Do not take bath or shower during storms, as water is an, excellent conductor of electricity. , 3. (a) Volcano is a hole in the earth's crust through which the molten, rocks and hot gases under high pressure rush out., (b) The energy released during volcanic eruptions causes vibrations, in the crust. These vibrations can cause earthquakes in the area, around., HOTS (Higher Order Thinking Skills) Questions:, 1. Lightning takes place when two charged clouds come closer because, of the rapid flow of electric charges through the air between the two, oppositely charged clouds. It is seen as an intense spark of electricity in, the sky., 2. A car with closed windows is a safe place during lightning because the, body of the car acts as a conducting path for the lightning bolt or charges., 3. It is advised to switch off the TV sets during frequent lightning because, electrical lines are excellent conductors of electricity. So, lightning, can strike the circuits and consequently, the electrical devices and, appliances too., Application Based Questions:, 1. According to the given information, if the conductor is brought close to, the metal rod, it is charging an uncharged object by induction because the, charged object is close to the uncharged rod but not touching it., (a) The uncharged rod will take the opposite charge, i.e., it gets, negatively charged., (b) This is because of the positively charged conductor. The electrons, in the uncharged rod come to the surface, charging it negatively., , Teacher’s Resource Pack SCIENCE-8, , 69

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2. (a) The ebonite rod on being rubbed with wool will get negatively, charged. This when brought in contact with the brass rod,, will deliver the same charge to the leaves of gold. The gold leaf, that get charged by induction will carry the same charge and, thus, the negative charge will move the leaves apart due to, repulsion., (b) Gold leaves attain a negative charge., , 16. Light, Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 233, 1. (a), 2. (c), 3. (b), 4. (c), 5. (a), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 240, 1. (b), 2. (b), 3. (a), 4. (d), 5. (b), , SECTION A, CLASS RESPONSE, A. Oral questions:, 1. The process of sending back the light rays which fall on the surface of an, object is called reflection of light., 2. The phenomenon of splitting of white light into its component colours, on passing through a transparent medium like a glass prism is called, dispersion of light., 3. The band of seven colours formed on a white screen, when white light, passes through a prism (or any transparent medium) is called spectrum, of white light., B. Science quiz:, 1. Regular reflection of light, 2. Cataract is a condition of eyes in which the eye lens becomes cloudy (or, hazy)., 3. 60°, WORKSHEET, A. Tick (3) the correct options:, 1. (d), 2. (c), 3. (b), 4. (c), B. Circle the odd ones. Give reasons for your choice:, 1. Purple, → It is not the component of spectrum of light, whereas, others are components of spectrum of light., 2. Eardrum, → It is a part of human ear, whereas others are parts of a, human eye., 3. Tuberculosis → It is a disease associated with lungs, whereas others, are eye defects., , 70, , Teacher’s Resource Pack SCIENCE-8

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C., , Fill in the blanks:, 1. far point , 3. convex, , 2. hypermetropia, 4. kaleidoscope, , SECTION B, A., B., , C., , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (a), 2. (b), 3. (a), Very Short Answer Questions:, 1. Myopia and hypermetropia, 2. Green leafy vegetables, cod-liver oil, eggs, milk, curd, cheese, butter,, papaya and mango, 3. The near point of a normal human eye is about 25 cm., Short Answer Type-I Questions:, 1. The laws of reflection are as follows :, (i) The angle of incidence is equal to the angle of reflection., (ii) The incident ray, the normal at the point of incidence and the, reflected ray, all lie in the same plane., 2., , D., , 3. The ability of the eye lens to adjust its focal length, so as to see the, objects located anywhere is called the power of accommodation., Short Answer Type-II Questions:, 1., , Teacher’s Resource Pack SCIENCE-8, , 71

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2., , 3. A person with hypermetropia or far-sightedness can see distant (far, off) objects clearly but cannot see nearby objects distinctly. It is caused, when image of a nearby object is formed behind the retina and not at, the retina itself. It is corrected by using spectacles with a convex lens., 4. (a) The condition when either the cornea or the eye lens become, opaque due to some diseases or defects and a person cannot see,, is known as curable blindness. It can be cured., (b) No, it is not right to make fun of visually challenged people. If we, make fun of them, they may feel under privileged and hurt and we, should never hurt the feelings of other people. We should never, make fun of people or behave with them in a way we don't want, others to behave with us., E. Long Answer Questions:, 1. (a) Incident ray: The ray of light which falls on the mirror's reflecting, surface is called incident ray., (b) Reflected ray: The ray of light which is sent back after reflection, by the mirror surface at the point of incidence is called reflected, ray., (c) Normal at the point of incidence: The normal is a line drawn at, perpendicular or right angle to the mirror surface at the point of, incidence., (d) Angle of incidence: The angle which the incident ray makes with, the normal at the point of incidence is called the angle of incidence., (e) Angle of reflection: The angle which the reflected ray makes, with the normal at the point of incidence is called the angle of, reflection., , 72, , Teacher’s Resource Pack SCIENCE-8

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2. (a) Sclera: It is the outer most covering of the eye. It protects the vital, internal parts of the eye from external injuries., (b) Cornea: It allows the light to enter into the eyeball., (c) Iris: It regulates the amount of the light entering the eye by, adjusting the size of the pupil., (d) Choroid: It darkens the eye from inside and prevents any internal, reflection., (e) Retina: It contains rods and cones which are sensitive to light. The, cones are sensitive to bright light and can detect colour, while the, rods are sensitive to the intensity of light, i.e., the dim light., F. HOTS (Higher Order Thinking Skills) Questions:, 1. Vitamin A deficiency in diet is a cause to many eye problems. The vision, problems which can be caused are–, (a) night blindness, unable to see in dim light, (b) extreme dryness of the eye, (c) softening and clouding of the cornea, (d) can ultimately cause complete blindness, 2. Tall mirrors are placed in small offices to provide the sense of false, dimension (a sense of greater space, if the space is small)., 3. Yes, we can see a spectrum if monochromatic light falls on a prism,, because of the phenomenon of dispersion. Monochromatic rays of, light consist of seven colours which due to different wavelengths and, refractive indices, disperse at different angles forming a spectrum., 4. When we enter into a darkened cinema hall, the amount of light rays, coming from the large screen of cinema hall suffers diffused reflection, because of which we can't see the surroundings., 5. The convex eye lens is different from the glass convex lens because the, eye lens —, (i) is a delicate membrane-like structure, whereas glass lenses are, hard., (ii) has the ability to accommodate according to the distance of the, object, whereas the glass lens has a fixed role., G. Application Based Questions:, 1. If a student is unable to read a book, it shows that the he/she is suffering, from hypermetropia (far-sightedness), so cannot see close objects, properly. It can be corrected by using convex lens in the spectacles., 2. Myopia (short-sightedness). It can be corrected by using concave lens., Think And Answer, Tick (3) the correct options:, 1. (b), 2. (c), Teacher’s Resource Pack SCIENCE-8, , 73

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17. Stars and the Solar System, Think, Page No. 251, Planets in the solar system cannot move away from the Sun because of the, gravitational force between the planets and the Sun., Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 253, 1. (d), 2. (c), 3. (a), 4. (c), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 256, 1. (b), 2. (c), 3. (b), 4. (b), Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 259, 1. (b), 2. (a), 3. (b), 4. (d), , SECTION A, CLASS RESPONSE, A. Oral questions:, 1. The Stars, the planets, the Sun and the asteroids, meteors, meteorites,, comets, 2. Uranus and Venus, 3. Asteroids are small, irregular heavenly bodies of rocks and metals which, revolve around the sun in the gap between the orbits of Mars and, Jupiter., B. Science quiz:, 1. 1011 stars, 2. A comet is a small body of ice and dust that moves around the Sun in an, elliptical orbit., 3. Eris and Ceres, WORKSHEET, A. Tick (3) the correct options:, 1. (a), 2. (b), 3. (b), 4. (b), 5. (a), B. Circle the odd ones. Give reasons for your choice:, 1. Aryabhatta → It is an artificial satellite, whereas others are, heavenly bodies., 2. Earth, → Only Earth has life on it, whereas others do not, have., 3. Pole Star, → It is a single star, whereas others are constellations., C. Fill in the blanks:, 1. Sirius, 2. Hunter, 3. Halley's, 4. meteorite, , 74, , Teacher’s Resource Pack SCIENCE-8

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SECTION B, A., B., , C., , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (a), 2. (c), 3. (c), Very Short Answer Questions:, 1. (a) 123 °C, (b) – 233 °C, 2. Light year is the distance travelled by the light in a year., 1 light year = 9.46 × 1012 kilometres, Light year is a unit of distance not the unit of time., 3. Jupiter, 4. We can never see the backside of the moon from the Earth because the, moon rotates about its axis in about the same time that it takes to orbit, the Earth. This results in the same face of the moon turned towards the, earth at all times., Short Answer Type-I Questions:, 1. The Sun appears to be larger and brighter than other stars because it is, much nearer/closer to the Earth than any other star., 2. Mars is called the red planet because it is red in colour. The red colour, comes from iron oxide (rust) in its soil., 3. The Pole Star appears stationary as seen from the Earth because it lies, directly above the north pole close to the axis of rotation of the Earth., 4. The stars which appear in the form of closed groups and form, recognisable shapes and patterns are known as constellations. Ursa, Major and Orion are two important constellations., , D., , Short Answer Type-II Questions:, 1. (i) Ursa Minor is also known as 'Little Dipper' or 'Little Bear' during the, summer season. It is clearly seen in the northern part of the sky in, July., (ii) There are seven prominent stars in this constellation which form, the shape of a dipper., (iii) At the end of the tail of Ursa Minor is the Pole Star., (iv) The stars in Ursa Minor are closer and less brighter than in Ursa, Major., 2. The Earth is the only planet in the solar system on which life is known to, exist. Special environmental conditions required for existence of life on, earth are— (write any three)—, , (i) Earth is at the right distance from the Sun., , (ii) It has the right temperature range., , (iii) Presence of water, (iv) A suitable atmosphere, (v) A blanket of ozone, Teacher’s Resource Pack SCIENCE-8, , 75

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3. S. No. Parameters, , 4., , Meteors, , Meteorites, , (i), , Burning, , Meteors burn, completely before, they reach the surface, of the Earth., , Meteorites do not, burn completely on, entering the Earth’s, atmosphere and land, on the Earth’s surface., , (ii), , Size, , The size of this, heavenly body is very, small as compared to, the size of meteorites., , The size of this, heavenly body is very, big., , (iii), , Damage, , They do not cause any, damage., , They can create large, craters and cause a, lot of damage on the, Earth’s surface., , (iv), , Scientific, studies, , Not yet possible, , They help the, scientists to know, about the nature of, matter in outer space., , Planets are solid heavenly bodies which revolve around the, Sun in closed elliptical orbits., (ii) A planet has no light of its own. It shines because it reflects, the light of the Sun., (iii) Different planets have different sizes., (iv) Some planets have one or more natural satellites., (b) We learn to be disciplined, punctual and focused in life like these, heavenly bodies. They teach us to be energetic and spread the, warmth and light all around us., E. Long Answer Questions:, 1. (a) New moon : When the moon is in between the Earth and the Sun,, then the side of the moon, lit by the Sun is away from the Earth, and the side of the moon which is towards the Earth is dark. This is, called a new moon. New moon night is called 'Amavasya' in India., You cannot see the moon at all on new moon night, it is very dark, having no moonlight at all., (b) Crescent moon : The phase of moon when a small portion of moon, is lit by the Sun is called a crescent moon., (c) First quarter moon : After 7 days of new moon, the sunlit portion, of the moon facing the earth becomes bigger. So, we are able to, see half of the moon. It is called first quarter moon., , 76, , (a) (i), , Teacher’s Resource Pack SCIENCE-8

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(d) Gibbous moon : When we see more than half of the moon, it is, called the gibbous moon (at 10th day of new moon)., (e) Full moon : After 14 days or after two weeks’ time of new moon, night, we are able to see the sunlit side of the moon, i.e., the full, part of moon facing towards the Earth. It is also called as 'Purnima', in India. The full moon night is very bright because the moonlight is, maximum on that night., 2. (a) An artificial satellite is a human-made object that has been, placed into the orbit around the Earth or some other planets to, perform specific functions. They are launched from the earth. Eg.,, Aryabhatta, Kalpana-I, etc., Differences between planets and satellites, , F., , S.No. Parameters, Planets, Satellites, (i) Type of, Planets are, Satellites are both natural, body, natural heavenly and artificial, i.e., humanbodies., made objects., (ii) Revolution Planets revolve, Satellites revolve around, around the Sun., the planets., (iii) Size of the Size of the, Size of the satellites is, body, planets is large as very small as compared, compared to the to the planets., size of satellites., (b) Uses of artificial satellites are as follows —, (i) In weather forecasting, (ii) For transmitting radio and television signals, (iii) For collecting information about other planets and about the, outer space, (iv) For navigation, (v) For remote sensing to locate minerals, underground water or, land mapping, HOTS (Higher Order Thinking Skills) Questions:, 1. Earth rotates about its axis which is 23½° (slightly tilted), so it appears to, rotate like a top. Uranus rotates at highly tilted rotational axis. Its axis of, rotation is inclined at 97°. This means it rotates almost on its sides, so it, appears to rotate or roll like a ball., 2. A constellation is not the part of solar system because the solar system, consists of the Sun, the eight planets, their satellites, the celestial bodies, like meteors, comets and asteroids under the effect of Sun's gravity., Other celestial bodies around Earth appear as the component of the, universe. As stars are the components of the universe, solar system is, also its component., , Teacher’s Resource Pack SCIENCE-8, , 77

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G., , Application Based Question:, Given, RJ = 11RE, 4, Volume of Jupiter = VJ = πR3J, 3,  RJ = 11 RE, , So, VJ = 4 π × (11RE )3, 3, 4, V = π × 11 × 11 × 11 × R3 = 1331 × 4 πR3, J, E, E, 3, 3, 4 3, ∴ Volume of Earth, VE = π RE, 3, ∴, , ⇒ , , VJ, VE, , 1331 ×, =, , 4 3, πR, 3 E, , 4 3, πR, 3 E, , VJ = 1331VE, , 18. Pollution of Air and Water, Multiple Choice Questions (MCQs). Tick (3) the correct options: Page No. 268, 1. (d), 2. (b), 3. (a), 4. (a), 5. (a), Multiple Choice Questions (MCQs). Tick (3) the correct options:, Page No. 269, 270, 1. (a), 2. (b), 3. (c), 4. (d), 5. (a), , SECTION A, CLASS RESPONSE, A. Oral questions:, 1. Coal and petroleum/dust, 2. Chlorine added to the water kills all the disease-causing microorganisms, (germs) present in water., 3. Carbon dioxide, methane and water vapour, B. Science quiz:, 1. Carbon dioxide, sulphur dioxide, carbon monoxide, oxides of nitrogen, 2. The contamination of water with harmful, unwanted substances like, domestic sewage, toxic industrial wastes and chemicals like pesticides, and fertilisers, which cause harmful effects on both living and non-living, objects is called water pollution., 3. The rainwater containing large amount of dissolved acids is called acid, rain., , 78, , Teacher’s Resource Pack SCIENCE-8

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WORKSHEET, A. Tick (3) the correct options:, 1. (b), 2. (c), 3. (a), 4. (c), B. Fill in the blanks:, 1. carbon dioxide, 2. temperature, 3. Chlorofluorocarbons, C. Match the following:, 1. (b), 2. (d), 3. (a), 4. (c), , SECTION B, A., B., , C., , D., , Multiple Choice Questions (MCQs) Scientific/Practical skills:, 1. (b), 2. (c), 3. (d), Very Short Answer Questions:, 1. Eutrophication, 2. Solar energy, 3. The oxides of sulphur and nitrogen and unburnt hydrocarbons produced, due to burning of fossil fuels causes acid rain., Short Answer Type-I Questions:, 1. Global warming is the rise in average temperature of the atmosphere of, the earth due to the increase in greenhouse effect., 2. Methods to control air pollution—, (i) Use catalytic converters in automobiles which convert the harmful, gases into harmless gases., (ii) We should grow more plants and trees to reduce carbon dioxide, concentration in the air., (iii) Replace use of wood, coal or kerosene with LPG for domestic use., (iv) Encourage the use of public transport., 3. Sedimentation, loading, filtration, chlorination and storage, 4. (i) Excessive use of fertilisers and pesticides should be discouraged., (ii) Dead bodies should not be disposed of in a river or a lake., (iii) Washing clothes, cleaning utensils or taking bath near water bodies, should be restricted., (iv) Domestic sewage should be treated before being released into, water bodies., Short Answer Type-II Questions:, 1. Damaging effects of ozone layer depletion are:, (i) Harmful ultraviolet radiations reaching the earth cause various, diseases in human beings such as cataract, skin cancer, dimming of, eyesight, etc., (ii) Harmful ultraviolet radiations can bring about changes in the gene, structure leading to mutations., , Teacher’s Resource Pack SCIENCE-8, , 79

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(iii) Harmful ultraviolet radiations cause damage to early developmental, stages of fishes, crabs and other animals., 2. The main causes of water pollution are :, (i) Industrial sewage: The discharge of untreated industrial sewage, directly into water bodies is one of the main cause of water, pollution., (ii) Domestic sewage: Liquid wastes from domestic activities, such, as kitchen and toilets, are discharged into rivers through sewage, systems causing water pollution., (iii) Human activities: Bathing of human beings and animals in or near, lakes, rivers, etc., pollutes the water bodies., (iv) Agricultural wastes: In modern agriculture, we use large quantities, of pesticides and fertilisers than required by the plants. Excess of, these inorganic chemicals find their way to water bodies which, results in water pollution., (v) Oil spill: Oil spills from huge tankers is one of the major cause of, water pollution which affects the marine plants and animals., 3. The damaging effects of acid rain are :, (a) Acid rain increases the acidity of soil and thus, affects the plant and, animal life living in it. It leads to the loss of soil fertility., (b) Acid rain makes the water of lakes and rivers acidic leading to, destruction of aquatic plants and animals., (c) Acid rain destroys monuments and buildings., (d) Acid rain promotes corrosion of metallic objects like railway bridges, and gates., 4. (a) No, Mr Mehta should not shift to petrol instead of CNG because, CNG is a cleaner fuel and is good for the environment as it produces, less pollutants than coal, petrol, etc., (b) It is right to use catalytic converters in the cars because they convert, the harmful gases into harmless gases., E. Long Answer Questions:, 1. Harmful effects of air pollution are as follows:, (i) Carbon monoxide is a very poisonous gas. When inhaled in excess, it, can kill a person without warning as it is a colourless and odourless, gas., (ii) Oxides of sulphur (sulphur dioxide and sulphur trioxide) cause, respiratory problems and damage lungs., , (iii) Oxides of nitrogen cause lung congestion., (iv) Fumes coming out of chemical industries cause irritation in eyes,, nose and throat., , 80, , Teacher’s Resource Pack SCIENCE-8

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(v) Particles of lead oxide present in the automobile exhausts can, affect the brain of children and cause mental disorder., (vi) Particles of dust in air can cause bronchitis., 2. Eutrophication: Washing away of fertilisers into water bodies causes, increase in growth of algae and other weeds in water bodies. Due to, respiration carried out by algae, a large amount of dissolved oxygen in, the water is consumed. Death of algae further reduces the amount of, oxygen in the water. This is because microorganisms use the oxygen for, the decomposition of dead algae. Once the level of dissolved oxygen, falls, fishes and most other aquatic animals die due to suffocation., This loss of dissolved oxygen from water in water bodies is called, eutrophication., , Biological magnification: Pesticides and insecticides like DDT are, poisonous chemical substances which are used in large quantities to, kill pests and protect the plants from diseases. Excess of pesticides find, their way to water bodies through rainwater. The pesticides enter the, food chain at the producer level (plants) and get accumulated in the, body of organisms in increasing concentrations along the food chain. In, an aquatic food chain, phytoplanktons are consumed by zooplanktons, which are further consumed by small fishes. The small fishes are, consumed by large fishes, which in turn are eaten by fish-eating birds., At each level, the concentration of pesticides increases. This increase in, the concentration of harmful chemical substances like pesticides in the, body of living organisms at each trophic level of a food chain is called, biological magnification., 3. (a) The phenomenon due to which the earth's atmosphere traps solar, radiations because of the presence of gases like carbon dioxide,, water vapour, methane and chlorofluorocarbons is called greenhouse effect. Carbon dioxide, CFC (chlorofluorocarbons) and, methane are the greenhouse gases., (b) Global warming is the rise in average temperature of the, atmosphere of the earth due to the increase in greenhouse effect., Harmful effects of global warming are:, (i) Polar caps would melt and water would flow into the seas. If, the level of water in the seas increases, low lying areas near, the coasts would be submerged., (ii) Climate and rainfall pattern would change., (iii) It affects agriculture and the production of food., F. HOTS (Higher Order Thinking Skills) Questions:, 1. If there was no greenhouse effect, earth's surface would be too cold to, sustain life., Teacher’s Resource Pack SCIENCE-8, , 81

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G., , 2. The excessive use of fertilisers causes eutrophication. Since, fertilisers, are rich in nutrients, and when with the flow of water they are washed, to the water reservoirs, they provide nutrients to the aquatic flora, causing increased algal growth, which increases the biological oxygen, demand., Due to insufficient oxygen, organic decaying happens causing, deterioration of water bodies. This is called eutrophication., 3. Using water from wells for drinking purpose is safe in comparison to, river water. This is because river water contains heavy minerals and, toxic wastes., Application Based Question:, The house near the park should be preferred over the house on the roadside., This is because, the houses on the roadside are more prone to both air and, noise pollution., The people living on the roadsides will be affected more by the fumes, released by automobile exhausts than the people living near the park. Also,, the continuous movement of vehicles on the road and the sound of their, horns would cause disturbances leading to noise pollution., , Periodic Assessment-1 (Based on Chapters 1 to 4), A., B., , C., , D., , Tick () the correct answers:, 1. (a), 2. (a), 3. (b), 4. (c), Fill in the blanks:, 1. ploughing, 2. Lactobacillus, Very short answer questions:, 1. The process of conversion of sugar into alcohol by the action of microbes, , like yeast, is called fermentation., 2. Substances that cannot be broken down easily into simple, harmless, substances through natural processes such as action of bacteria are, called non-biodegradable substances., Short answer questions:, 1. The unwanted plants which grow along with a cultivated (main) crop, in a field are called weeds Cyperus and Achyranthus are two common, weeds., 2. When an iron object is left in damp air (or moisture) for a considerable, time, it gets covered with a reddish brown flaky substance. This is called, rusting of iron., Iron, +   Oxygen + Water, →, Hydrated iron, (metal), , 82, ,     from damp air, , oxide (rust), , Teacher’s Resource Pack SCIENCE-8

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Periodic Assessment-2 (Based on Chapters 10 to 13), A., B., C., , D., , Tick () the correct answers:, 1. (a), 2. (c), 3. (c), 4. (a), Fill in the blanks:, 1. gravitational force, 2. motion, Very short answer questions:, 1. The force acting along the two surfaces in contact which opposes the, motion of one object over the other is called the force of friction., 2. Pitch is the characteristic of sound by which you can distinguish a shrill, sound from a grave (hoarse) sound even though the two sounds have, the same loudness., Short answer questions:, 1. The physical quantity which measures the effect of force per unit area is, called pressure. Its unit is pascal (Pa)., 2., , Infrasonic sounds, , Ultrasonic sounds, , The sounds (inaudible to humans) The sounds (inaudible to humans), having frequency less than 20 Hz having frequency more than, are known as infrasonic sounds., 20000 Hz are known as ultrasonic, sounds., , Half Yearly Examination (Based on Chapters 1 to 9), A., , Very short answer questions:, 1. Amaranthus, convolvulus, 2. Streptomycin, tetracycline, 3. A polymer is a very large unit formed by the combination of a large, number of smaller molecules (called monomers) joined end to end by, chemical bonds., 4. Graphite, 5. Petroleum is called ‘black gold’ due to its great commercial importance., 6. Cloth, wooden stick, 7. Increase in the concentration of carbon dioxide may lead to an increase, in global temperature which is called global warming., 8. Water hyacinth, 9. Organisms made up of a single cell are called unicellular organisms., Amoeba, Paramecium, Euglena, bacteria, yeast are few examples of, unicellular organisms., 10. Pink headed duck and the cheetah, 11. Genes are present in chromosomes., , Teacher’s Resource Pack SCIENCE-8, , 83

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B., , Short answer type I questions:, 1. The crops that are sown in the winter season are called rabi crops. Rabi, crops are sown at the beginning of winter season (October/November), and harvested in March-April. Rabi crops do not depend on monsoon, rains for growth. Wheat, gram, pea, mustard and linseed are rabi crops., 2. Two uses of yeast are:, (a) It is used in the baking industries for making breads, pastries and, cakes., (b) It is also used in day-to-day household food items like idli, dhokla,, etc., 3. Plastics which easily get deformed (become soft) on heating and can be, bent easily are known as thermoplastics., Plastics which once moulded into a shape do not become soft on heating, and cannot be moulded again are called thermosetting plastics., 4. Copper is used for making utensils, car radiators and calorimeters., Aluminuim is used for making paints to prevent rusting of iron., 5. Destructive distillation is the process of breaking coal by heating it, to high temperature in the absence of air. It produces coke, coal tar,, ammoniacal liquor and coal gas., C. Short answer type II questions:, 1. Parameters, , Fertilisers, , Manure, , Nature, , These are inorganic salts., , It is a natural organic, substance., , Amount of, nutrients, present, , These are rich in plant, nutrients like nitrogen,, phosphorus and, potassium., , It contains less amount of, essential plant nutrients., , Preparation These are prepared in, factories., , It is prepared in fields, by the decomposition of, animal wastes, human, wastes and plant residues., , Cost, , It is cheap., , These are costly., , 2. The process in which metal is eaten up by the action of air, moisture or, a chemical on their surface is called corrosion., , Prevention of corrosion, Corrosion of metals can be prevented by preventing their contact with, air and water. It can be done as follows:, (i) Oil, grease or paint is applied on the surface because it keeps the, metal away from air and moisture., , 84, , Teacher’s Resource Pack SCIENCE-8

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3., , 4., , 5., , 6., , 7., , (ii) A layer of zinc is deposited on the surface of iron object by dipping, it in molten zinc. This process is known as galvanisation., (a) The slow chemical process of the conversion of the dead vegetation, (remains of dead plants) into coal, under the influence of high, temperature and pressure is called carbonisation., (b) Uses of coal, (i) Coal is used in railway engines to produce steam to run the, engine., (ii) Coal is used in many houses in villages as fuel to cook food in, chulhas., (iii) Coal is used in thermal power plants to produce electricity., (iv) Coal is used in many industries to produce organic compounds, such as phenol, benzene, toluene and naphthalene., Conservation is the wise and careful use of resources. We need to, conserve the fossil fuels, keeping in mind their limited availability., (i) We should reduce the use of fossil fuels and use these fuels only, when absolutely necessary., (ii) We should encourage the use of renewable sources of energy like, wind energy, solar energy and hydroenergy to meet our energy, needs., (iii) We should use more fuel-efficient machines., Three conditions which are necessary for combustion are as follows :, (i) the presence of a combustible substance, (ii) the presence of a supporter of combustion, (iii) attainment of ignition temperature of the combustible substance, These three conditions, necessary for combustion, are also called, triangle of fire., (a) Water cannot be used to extinguish fires in electric wiring caused, by an electrical short-circuit. This is because water is a conductor, of electricity. When it is poured over burning electrical wires, or appliances, it causes electric shocks to the people involved in, the firefighting operations. This electric shock can even kill the, people., (b) It is dangerous to sleep in a closed room with coal burning inside,, on a cold winter night. This is because no fresh air can enter the, room and when coal burns in an insufficient supply of oxygen (due, to closed room), a lot of carbon monoxide is produced. This can, lead to suffocation or may even cause death., Species that are at a high risk of getting extinct, in near future, due, to decline in their number and a drastic change in habitat are called, endangered species., , Teacher’s Resource Pack SCIENCE-8, , 85

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Species that already exist in low numbers and may become endangered, if the causative factors like habitat destruction, environmental, disturbance or illegal hunting continue to operate are called vulnerable, species. For example, hippopotamus, polar bear, golden langur, chinkara, deer, blood pheasant are vulnerable species., 8. S. No., , Prokaryotic cells, , Eukaryotic cells, , (i), , These cells do not have a, well organised nucleus due, to the absence of nuclear, membrane., , These cells have a well, organised nucleus with, nuclear membrane., , (ii), , Bacteria and blue-green algae, are examples of prokaryotic, cells., , Plants, animals, fungi,, protozoa, etc., are eukaryotic, cells., , 9., , 10. (a), , , , , D., , 86, , Organs in the male reproductive system are:, (i) A pair of testes, (ii) Two sperm ducts, (iii) Urethra, (iv) Penis, Organs in the female reproductive system are:, (i) A pair of ovaries, (ii) Oviducts, (iii) Uterus, (iv) Vagina, (b) Function:, Testes: It produces male gametes called sperms and also produces, the male sex hormone called testosterone., Ovary: It makes the female gametes called ova or eggs and, also secretes the female sex hormones called oestrogen and, progesterone., Long answer questions:, 1. (a) The process by which spoilage of food is prevented using chemical, or physical methods is called food preservation. Sodium benzoate,, citric acid and potassium metabisulphite are common food, preservatives., Teacher’s Resource Pack SCIENCE-8

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(b) Advantages of Food Preservation, (i) It decreases the wastage of food by avoiding spoilage., (ii) It increases the storage period of food materials., (iii) Nutritional value of the food is retained for a long period., (iv) It ensures the food availability at distant places and during the, off season., 2. Advantages of synthetic fibres, (a) High tensile strength: Synthetic fibres are very strong and have high, tensile strength (as they can hold large weight without breaking) in, comparison to natural fibres like cotton and wool., (b) Low water absorption: Synthetic fibres absorb very little amount, of water (moisture). Due to this, a wet cloth of synthetic fibre dries, out rapidly., (c) Good elasticity: Most of the synthetic fibres are fairly elastic and, flexible as they can be stretched or compressed to some extent., On releasing the force applied, they regain their original shape and, size., , (d) Wrinkle-resistant: Most synthetic fibres do not get crumpled, easily during washing or wearing. They are wrinkle-free and keep, permanent creases., , (e) Abrasion-resistant: Most of the synthetic fibres have a high, abrasion (wear and tear) resistance. So, the clothes made of, synthetic fibres are long lasting or durable., , (f) Moth-resistant: Most of the synthetic fibres are not attacked by, moths and moulds., , (g) Lightweight: Most synthetic fibres are quite lightweight. Natural, fibres are comparatively heavy., , (h) Inertness: Most synthetic fibres are chemically more inert than the, natural fibres., (i) Less expensive: Synthetic fibres are less expensive and more, affordable than the natural fibres., 3., , Parameters, , Metals, , Non-metals, , Reaction with Most of the metals react, oxygen, with oxygen to form, basic oxides., , Non-metals react with, oxygen to form acidic or, neutral oxides., , Reaction with Metals react with water, water, to form metal hydroxide, or metal oxide and, hydrogen gas., , Non-metals do not react, with water under normal, conditions., , Teacher’s Resource Pack SCIENCE-8, , 87

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Reaction with Metals react with acids, acids, to form respective salts, and hydrogen gas., , Non-metals do not react, with acids., , Reaction with Reactive metals react, bases, with bases to form their, respective salts and, hydrogen gas., , Reaction of nonmetals with bases is, complicated., , Displacement Metals show, reaction, displacement reaction., , Most of the nonmetals do not show, displacement reactions, but certain more reactive, non-metals displace less, reactive non-metals from, their salt solutions., , 4. The clearing of forests (by cutting down forest trees) over a wide area is, called deforestation. Deforestation has taken place due to the following, reasons:, • To build homes, factories, roads and dams for the increasing, human population, • To obtain wood as fuel and for making furniture and paper, • To obtain more agricultural land for cultivation of crops for the, growing population, • For mining of minerals such as coal, petroleum and ores, All the above causes of deforestation are human-made causes. There, are some natural causes of deforestation also like forest fires, severe, droughts, attacks of insects and pests., Consequences of deforestation, • It causes soil erosion and makes the soil infertile. Due to gradual, erosion of fertile topsoil, the land gets converted into a desert. This, is called desertification., • Deforestation increases the level of carbon dioxide in the, atmosphere and disturbs the natural balance of gases in the, atmosphere. Increase in the concentration of carbon dioxide may, lead to an increase in global temperature which is called global, warming. Global warming disturbs the water cycle, reduces rainfall,, causes drought and melting of glaciers., • It decreases the water-holding capacity of the soil and can cause, floods., • Forests are natural habitat of many species of animals. Cutting, down trees destroys the homes of these species which poses a, threat to their survival, , 88, , Teacher’s Resource Pack SCIENCE-8

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5., , nucleus, , nuclear envelope, (two membranes), nuclear pore, nucleolus, , cell wall, , nucleoplasm, smooth, endoplasmic, reticulum, cytoplasm, , plasma, membrane, rough, endoplasmic, reticulum, chloroplast, , mitochondrion, vacuole, dictyosome, cell sap, , E., , Practical skill based questions:, 1. When we add a piece of aluminium to a freshly prepared solution of, sodium hydroxide, we observe tiny bubbles of hydrogen gas in the, solution on bringing a burning match stick near the mouth of test tube,, the gas burns fire with a pop sound., 2. (a) Dry leaves, Dry leaves have low ignition temperature because there is no moisture, content in them, whereas the green leaves have moisture content which, increases their ignition temperature., , Yearly Examination (Based on Chapters 2, 4, 5, 10 to 18), A., , Very short answer questions:, 1. Acquired Immuno Deficiency Syndrome, 2. Male sex hormone: testosterone, Female sex hormones: oestrogen and progesterone, 3. Two types of non-contact forces are:, (i) Magnetic force, (ii) Electrostatic force, 4. An echo is the repetition of the original sound heard after the sound is, reflected from a distant, dense and rigid object (such as a high building,, cliff, etc)., 5. Flute, shehnai/trumpet, 6. The method of coating the metal’s surface with a thin layer of superior, metal with the help of electric current is called electroplating., 7. Largest planet: Jupiter, Brightest plant: Venus, Teacher’s Resource Pack SCIENCE-8, , 89

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8. Two uses of artificial satellites are:, (i) They are used for weather forecasting., (ii) They are used for transmitting radio and television signals., 9. Air and sunlight, 10. When sodium metal reacts with oxygen at room temperature, it forms a, basic oxide called sodium oxide., 11. Copper wires are used in household electric wiring because it is a good, conductor of electricity., B. Short answer type I questions:, 1. Skiers use long and flat skis to slide over snow. This is because the skis, have a large area of contact which reduces the pressure on the snow, and enables the skier to slide over the snow without sinking in the snow., 2., , Sliding friction, , Rolling friction, , It is the opposing force that, comes into play when one object, is actually sliding over the surface, of another object., , It is the opposing force that, comes into play when one object, is actually rolling over the surface, of another object., , 3. Those musical instruments in which vibrating skin or membrane, produces a musical sound are called percussion instruments. For, example, tabla, dholak, mridangam, drum, etc., 4. The main limitations of fossil fuels are:, (i) Limited availability: They are available in limited quantity. So, if, they are used at their present rate of consumption, the known, reserves of these fossil fuels will last only a few hundred years, causing energy crisis., (ii) Air pollution: The burning of fossil fuels produces gases like carbon, dioxide, carbon monoxide, sulphur dioxide and smoke., 5. Two uses of electrolysis are:, (i) It is used in the extraction of metals from their ores., (ii) It is used for refining metals., C. Short answer type II questions:, 1. The three secondary sexual characters in males are:, , (i) Hair grow under armpits and in pubic region between the thighs., (ii) Hair also grow on other parts of the body like chest and face., (iii) Body becomes more muscular due to development of muscles., The three secondary sexual characters in females are:, , (i) Hair grow under armpits and pubic region., (ii) Ovaries start to release eggs (or ova)., (iii) Menstrual cycle (MC) or monthly period starts., , 90, , Teacher’s Resource Pack SCIENCE-8

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2. (a) The physical quantity which measures the effect of force per unit, area is called pressure. Its unit is pascal (Pa)., , (b) Here, force (F) = 200 N, , Area of contact (A) = 5 m2, , , We know that, pressure (P) =, , Force (F), Area (A), , 200, 5,            = 40 N/m2 or 40 Pa, 3. Advantages of friction are:, (i) It helps us walk., (ii) The friction between the tyres of vehicles and the ground helps, them move on the ground without slipping., (iii) It helps us to write., (iv) It is the force of friction which holds screws and nails in the wood., (v) It is the force of friction between the brake lining and the drum of, the wheel of vehicles that stops it on applying brakes., , So,            , P=, , 4., , 5. Chlorofluorocarbons (CFCs) which are used in refrigerators, air, conditioners and aerosol sprays when released in air, damage ozone, layer of the atmosphere., Damaging effects of ozone layer depletion are:, (i) Harmful ultraviolet radiations reaching the earth cause various, diseases in human beings such as cataract, skin cancer, etc., (ii) Harmful ultraviolet radiations can bring about changes in the gene, structure leading to mutations., (iii) Harmful ultraviolet radiations cause damage to early developmental, stages of fish, crabs and other animals., Teacher’s Resource Pack SCIENCE-8, , 91

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6. Noise from any source that causes disturbance or discomfort of any kind, in the environment is called noise pollution., Harmful effects of noise pollution are:, (i) It causes nervous tension, irritation, earache, headache and high, blood pressure., (ii) It may cause lack of concentration in work or studies., (iii) Loud music during night disturbs our sleep., (iv) Prolonged exposure to high level noise can affect the eardrum and, may lead to temporary or even permanent loss of hearing., 7. The process of separating various constituents or useful fractions of, petroleum is known as refining of petroleum., Petroleum refineries in India are located at Chennai, Cochin, Mathura,, Digboi, Mumbai, Koyali, Haldia, Barauni, etc., 8. Three uses of natural gas are:, (i) It is used as a starting material for the manufacture of a number of, chemicals and fertilisers., (ii) It is used for manufacturing of carbon black which is used in rubber, industry as a strengthening agent., (iii) It is used to obtain hydrogen on industrial scale which is used in, manufacturing of ammonia., 9. The displacement reactions is a chemical reaction in which a more, reactive element displaces a less reactive element from its compound, (salt solution)., For example,, , , (i)   CuSO4, , +, , (ii)    2KBr, , +, , copper sulphate, (blue solution), , potassium, bromide, , Zn, , →, , zinc, , zinc sulphate, (colourless solution), , Cl2, , →, , chlorine, , ZnSO4, , +, , 2KCl, , +, ,      potassium, chloride, , Cu, copper, , Br2, , Bromine, , 10. Lactobacillus bacteria help make curd from milk. Curd is formed when a, protein called casein, present in milk, clumps together to form solidified, mass. Casein coagulation (clump formation) takes place only when the, milk is acidic. A spoonful of curd contains the bacteria Lactobacillus, which promote the formation of curd from milk., Lactobacillus multiplies, , milk + curd →,   , , 92, , (containing, Lactobacillus, bacteria), , using the non-fat, components of milk to, produce acidic product, , casein coagulates, , Milk → Formation of, becomes in acidic milk, curd (from, acidic, milk), Teacher’s Resource Pack SCIENCE-8

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D., , Long answer questions:, 1. We know that chromosomes are present inside the nucleus of every, cell. Chromosomes are thread-like structures that carry information in, the form of genes. All human beings have 23 pairs of chromosomes in, the nucleus of their cells. Out of these 46 chromosomes, 44 are called, autosomes., Autosomes are identical in males and females. Remaining two, chromosomes are called sex chromosomes. They are represented as X, and Y chromosomes., • In females, the cells contain two identical X chromosomes. So, the, sex chromosomes in females are represented by XX., • In males, the cells contain two different chromosomes X and Y. So,, the sex chromosomes in males are represented by XY. Each gamete, contains only one sex chromosome. An egg (female gamete), always contains X chromosome whereas a sperm (male gamete), may contain either X or Y chromosome., • If the sperm having X chromosome fertilises the egg, the zygote, would have two X chromosomes. It develops into a female child., • If the sperm carrying the Y chromosome fertilises the egg, the, zygote would have one X and one Y chromosome. It develops into, a male child figure., , So, the sex of a baby totally depends on the father’s sperm and not on, the mother’s egg., 2. A push or a pull on an object is called force. Effects of force are:, (i) Force can cause motion in a stationary object (object at rest), (ii) Force can stop a moving object., (iii) Force can change the direction of motion of the moving object., (iv) Force can change the speed of a moving object., (v) Force can change the shape and size of an object., 3. An earthquake is a sudden shaking of the earth’s crust which lasts for, a very short time. It is caused by a disturbance deep inside the earth’s, crust., Teacher’s Resource Pack SCIENCE-8, , 93

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Causes of earthquake, The main causes of earthquake are:, • Movement of the tectonic plates,, • Volcanic eruptions,, • Dislocation (or faults) of the crust and, • Underground nuclear explosion, (a) Movement of the tectonic plates: The surface of the earth is not, one continuous piece, but it is broken into many large pieces called, tectonic plates. It is more like a jigsaw of blocks that fit together., The world is divided into seven large tectonic plates and several, smaller plates. Due to the slow movement (convection current), inside the earth, these plates move with respect to one another by, about a few inches in a year like rafts on a gentle ocean. While this, may seem very small, the magnitude of energy developed by this, ‘small’ movement is enormous., The movement sometimes causes the edges of the tectonic, plates to grind each other with a force. They may get deformed,, displaced, crushed or fractured. They may also slide/slip under each, other. They may even move apart. Such changes in the plates, send a tremor or set up vibrations through the crust causing, earthquakes., (b) Volcanic eruptions: Volcano is a hole in the earth’s crust through, which the molten rocks and hot gases under high pressure rush out., The energy released during volcanic eruptions causes vibrations in, the crust. These vibrations cause earthquakes in the area around., Such earthquakes occur at the time of volcanic eruption or, before it., (c) Dislocation (or faults) of the crust: Over millions of years, the, movements of the tectonic plates have created weak points in the, earth’s crust called faults. Most faults occur along the boundaries, of the tectonic plates and these are the zones where earthquakes, occur. These weak zones are also known as seismic or fault zone., (d) Underground nuclear explosions: Under-ground nuclear, explosions cause very powerful vibrations. These vibrations cause, earthquake in the area around the nuclear explosion site., 4. (a) The characteristics of the image formed by the plane mirror are:, (i) The image on a plane mirror is of the same size and shape as, the object., (ii) The image on a plane mirror is erect., (iii) The image formed on a plane mirror is virtual, i.e., the image, cannot be obtained on a screen., , 94, , Teacher’s Resource Pack SCIENCE-8

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(iv) The image formed on a plane mirror is at the same distance, behind the mirror as the object is in front of it., (v) The image on a plane mirror is laterally inverted with respect, to the object., (b) Plane mirrors are often used,, (i) as looking glass., (ii) as reflectors in solar cookers., 5. Nitrogen cycle, Nitrogen is needed for the formation of proteins, amino acids and, nucleic acids., The cyclic process of nitrogen being fixed, used by plants and animals, and later returned to the atmosphere, is referred to as the nitrogen, cycle., It involves following steps– nitrogen fixation, nitrogen assimilation,, ammonification, nitrification and denitrification., (a) Nitrogen fixation, Our atmosphere has 78% nitrogen gas. Plants and animals cannot, take atmospheric nitrogen directly. It has to be first converted, into useful nitrogen compounds which can be easily absorbed., The conversion of free atmospheric nitrogen into nitrogenous, compounds is known as nitrogen fixation. Nitrogen fixation occurs, by following two ways:, , Teacher’s Resource Pack SCIENCE-8, , 95

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(i) , Lightning: When lightning strikes, nitrogen and oxygen of, atmosphere react and form oxides of nitrogen. These dissolve, in rainwater and form nitric acid. Nitric acid reacts with, limestone in the soil and converts into nitrates., , , (ii) , Biological nitrogen fixation: Certain plants such as peas,, beans, pulses (leguminous plants) contain Rhizobium bacteria, in their root nodules. The bacterium can take atmospheric, nitrogen and convert it into nitrogen compounds. Some, cyanobacteria like Nostoc and Anabaena also fix atmospheric, nitrogen into nitrates., (b) Nitrogen Assimilation, Plants absorb nitrates from the soil with water with the help of roots, and convert them into plant proteins. The herbivorous animals eat, green plants and convert the plant proteins into animal proteins., The herbivorous animals are then eaten by carnivorous animals., The process of conversion of inorganic nitrogen compounds into, organic compounds that become a part of living organism is called, nitrogen assimilation., (c) Ammonification, When plants and animals die, the proteins present in them are, converted into ammonium compounds by the putrefying bacteria, and fungi (decomposers) found in the soil. This process is called, ammonification. We can define ammonification as conversion of, complex organic compounds like proteins into ammonia., (d) Nitrification, Ammonium salt in the soil is converted first into nitrites by, Nitrosomonas bacteria. The nitrites are then converted into, nitrates by Nitrobacter bacteria. These bacteria are called nitrifying, bacteria. The nitrates, so formed in the soil, can once again be, absorbed by the plants. This process is called nitrification. So, the, conversion of ammonia into nitrates is called nitrification., (e) Denitrification, Some of the nitrates are absorbed by plants. Rest of the nitrates in, the soil are converted by Pseudomonas bacteria into nitrogen gas, , 96, , Teacher’s Resource Pack SCIENCE-8

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which escapes into the atmosphere. The conversion of nitrates into, free nitrogen gas by denitrifying bacteria (Pseudomonas) is called, denitrification., Thus, the nitrogen cycle maintains the percentage of nitrogen in, the atmosphere more or less constant., E. Practical skill based questions:, 1. No, distilled water does not conduct electricity. We can make it, conducting by adding –, • salts like common salt, copper sulphate, sodium nitrate, zinc, chloride, etc., • acids like dilute hydrochloric acid, nitric acid, sulphuric acid, etc., • bases like sodium hydroxide, ammonium hydroxide, potassium, hydroxide, etc., 2. To show that liquids exert pressure on the base of the container, , Things needed: A transparent glass tube, rubber balloon, thread and, water, , Method: Take a transparent glass tube opened at both ends. To one end, of the tube, tie a rubber balloon with the help of a thread. Now, hold the, tube in vertical position and pour some water into it., , Observation: You observe that the rubber balloon bulges out [Fig. (a)]., Now, pour more water in the tube. You see that the size of the bulge, increases [Fig. (b)]., , , Conclusion:, (a) The liquids exert pressure on the base of the container in which, they are poured., (b) Pressure exerted by water at the bottom of the container depends, on the height of its column. More is the height, more is the pressure, and vice versa., , Teacher’s Resource Pack SCIENCE-8, , 97