Page 1 : CHAPTER 1 CROP PRODUCTION AND MANAGEMENT, Exercise Questions, 1. Select the correct word from the following list and fill in the blanks., float, water, crop, nutrients, preparation, (a) The same kind of plants grown and cultivated on a large scale at a place is, called the crop., (b) The first step before growing crops is the preparation of the soil., (c) Damaged seeds would float on top of the water., (d) For growing a crop, sufficient sunlight and water and nutrients from the soil, are essential., 2. Match items in column A with those in column B., A, , B, , (i) Kharif crops, , (a) Food for cattle, , (ii) Rabi crops, , (b) Urea and superphosphate, , (iii) Chemical fertilisers, , (c) Animal excreta, cow dung, urine and plant wastes, , (iv) Organic manure, , (d) Wheat, gram, pea, (e) Paddy and maize, , Answer:, (i) Kharif crops., , (e) Paddy and maize., , (ii) Rabi crops., , (d) Wheat, gram, pea., , (iii) Chemical fertilisers., , (b) Urea and superphosphate., , (iv) Organic manure., , (c) Animal excreta, cow dung urine and, plant wastes., , 3. Give two examples of each., (a) Kharif crop, (b) Rabi crop, Answer:, Kharif crops- Paddy and maize, Rabi crops- Wheat and Pea, 4. Write a paragraph in your own words on each of the following., (a) Preparation of soil, (b) Sowing

Page 2 : (c) Weeding, (d) Threshing, Answer:, a) Preparation of the soil is the first step in agriculture. Preparation of the soil is, done to loosen the soil, which is essential for the root penetration into the soil., This allows the roots to breathe easily. Loosening of the soil allows the growth, of earthworms and microorganisms, which will elp to keep the soil fertile by, adding humus to the soil. Loosening of soil also brings nutrient-rich soil to the, top layer, which is essential for the growth of plants., b) Sowing is an important process in crop production. First, healthy seeds are, selected before sowing. After selecting healthy seeds sowing is done by either, traditional methods or by using equipment’s seed drill., c) Removal of unnecessary plants from the field is called weeding. Weeds, compete with crop plants for nutrients and water. This will reduce the yield of the, desired crops. Weeds also interfere while harvesting and gets mixed with crops., Some weeds are poisonous to animals and humans. Tilling is a common method, which helps removal of weeds before sowing crops, manual methods like, physical removal of plants are used to remove weeds. Weedicides are sprayed to, get rid of weeds, but this method may affect the health of farmers because of, chemicals used as weedicides., d) Process of separating the chaff from the crop is known as threshing. Threshing, is carried by a machine called ‘combine’ which is a harvester as well as a thresher., Threshing is also done by winnowing where to blow of wind is used to separate, the chaff from crops., 5. Explain how fertilisers are different from manure., Answer:, Fertilizers, , Manure, , Fertilizer is an inorganic substance., , Manure is an organic substance., , Fertilizers are prepared artificially., , Manure is obtained by decomposition, of animal, plant and human waste., , Prepared in factories., , Prepared in fields., , Does not provide Humus to the soil., , Provide humus to the soil., , Rich in plant nutrients., , Relatively less plant nutrients., , Long term usage has adverse, effects on soil., , Long term usage improves soil, fertility.

Page 3 : 6. What is irrigation? Describe two methods of irrigation which conserve, water., Answer: The supply of water to crops at regular intervals is called irrigation., Methods of irrigation which conserve water are, a) Drip Irrigation: Here the water goes drop by drop directly into the roots this, method is very useful as it conserves the water and also helps in avoiding weeds., b) Sprinkler system: This method is in use in mainly uneven land where sufficient, water is not available. The perpendicular pipes, having rotating nozzles on top,, are joined to the main pipeline at regular intervals. When water is allowed to flow, through the main pipe under pressure with the help of a pump, it escapes from the, rotating nozzles. It gets sprinkled on the crop as if it is raining., 7. If wheat is sown in the Kharif season, what would happen? Discuss., Answer: Wheat crops may get destroyed if sown in Kharif season because of, unfavourable temperature, pests and adaptable conditions for the plants to grow., Kharif come during the rainy season, hence it is not a wise idea to grow wheat in, Kharif season., 8. Explain how soil gets affected by the continuous plantation of crops in a, field., Answer: Plants require nutrients for their growth. Without optimum nutrients, plants will die. Continuous plantation of crops results in depletion of certain, nutrients like Nitrogen, Phosphorus, Potassium etc. This results in the decrease, of yield due to loss of nutrients hence there should be a gap between crops in, order to get a good yield., 9. What are weeds? How can we control them?, Answer: In a field many other undesirable plants may grow naturally along with, the crop. These undesirable plants are called weeds. Weeds can be controlled by, methods called weeding. Tilling before sowing of crops helps in uprooting and, killing of weeds, which may then dry up and get mixed with the soil. Weeds are, also controlled by using certain chemicals, called weedicides., 10. Arrange the following boxes in proper order to make a flow chart of, sugarcane crop production., , Answer:

Page 4 : 11. Complete the following word puzzle with the help of clues given below., Down, 1. Providing water to the crops., 2. Keeping crop grains for a long time under proper conditions., 5. Certain plants of the same kind grown on a large scale., Across, 3. A machine used for cutting the matured crop., 4. A rabi crop that is also one of the pulses., 6. A process of separating the grain from chaff.

Page 5 : Answer:

Page 6 : NCERT EXAMPLERS, Multiple Choice Questions, 1. Which one of the following conditions is not essential to grow maize?, (a) High temperature, (c) Low temperature, (b) Humidity, (d) Rainfall, Answer: (c) Low temperature, 2. Propagation of ginger is generally done using, (a) Seed, (c)Root, (b) Stem (rhizome), (d) Leaf, Answer: (b) Stem (rhizome), 3. Which of the following statement is not true for organic manure?, (a) It enhances the water holding capacity of the soil., (b) It has a balance of all plant nutrients., (c) It provides humus to the soil., (d) It improves the texture of the soil., Answer: (b) It has a balance of all plant nutrients., 4. The term used for the process of separation of grains from the chaff is, (a) Sieving, (b) Threshing, (c) Winnowing, (d) handpicking, Answer: (c) Winnowing, 5. Read the statements given below., (i) Seeds require moisture for germination., (ii) Plants can absorb nutrients mostly in dissolved form., (iii) Irrigation protects crops from both frost and hot air currents., (iv) Irrigation improves soil texture., Choose the combination of statements which indicate the need to irrigate, crops., (a) i and ii, (b) i, ii, iii, (c) i, ii, iii, iv, (d) i and iii, Answer: (a) i and ii, 6. Which of the following tools would a farmer use to remove weeds from, the field?, (a) Hoe, (c) Axe

Page 7 : (b) Plough, (d) Cultivator, Answer: (a) Hoe, 7. Which of the following is not true for fertilisers?, (a) They increase the yield., (b) Their excessive use disturbs the balance of nutrients in the soil., (c) They are generally used in small quantity., (d) They are environment-friendly., Answer: (d) They are environment-friendly., 8. Given below are statements about the harmful effects of weeds on crop, plants., (i) They interfere with harvesting., (ii) They help crop plants to grow healthily., (iii) They compete with crop plants for water, nutrients, space and light., (iv) They affect plant growth. Choose the correct combination of, statements., (a) i, iii, iv, (b) iii only, (c) iii, iv, (d) i, ii, iii, iv, Answer: (a) i, iii, iv, 9. The process of loosening and turning of soil is called, (a) irrigation and manuring, (c) tilling and ploughing, (b) digging and winnowing, (d) harvesting and storage, Answer: (c) tilling and ploughing, 10. The monsoon season in our country is during the months, (a) April to December, (b) June to September, (c) November to March, (d) January to May, Answer: (b) June to September, 11. The system of irrigation wherein water is supplied drop by drop near, the roots of plants, is called, (a) pulley system, (b) drip system, (c) sprinkler system, (d) lever system, Answer: (b) drip system, Very Short Answer Questions

Page 8 : 12. Pick out the odd one from the following words given in the box and give, the reason for it., Plough, Seed Drill, Hoe, Chain Pump, Sickle, Answer: The answer is Seed drill. The seed drill is modern equipment used to, sow the seeds. Whereas Plough, Hoe, Chain pump and sickle are old and, traditional equipment’s used in agriculture., 13. If you are given a dry piece of land for cultivation what will you do, before sowing the seeds?, Answer: Before sowing, seeds land should be prepared for cultivation. Tilling, and ploughing are the first steps in preparing the land for cultivation. Ploughing, is done by using plough which is made of either wood or iron., 14. State whether the following statements are True or False. Correct the, false statements., (i) Using good quality seed is the only criterion to get a high yield., (ii) Growing different crops in different seasons in the same field will, deplete the soil of nutrients., (iii) All crop plants are sown as seeds in the field., (iv) Cells of root nodules of leguminous plants fix nitrogen., (v) Freshly harvested grains must be dried before storing., Answer:, (i) False, To get good yield appropriate agricultural practice, nutrients water is very, essential along with good quality seeds., (ii) False, It enriches the soil, (iii) False, Some crops need transplantation Ex: Ginger, (iv) False, Bacteria called as Rhizobium present in the root nodules of leguminous plants, fix nitrogen, (iv) True, 15. During which months do farmers grow mustard in India?, Answer: During October to March farmers grow mustard in India., 16. Which activity of the farmer can promote the growth of earthworms, and microbes in the field?, Answer: Loosening the soil/maintaining high moisture levels in the soil., Short Answer Questions, 17. Beera wants to practice crop rotation in his field. Suggest a Rabi crop, and a Kharif crop which will replenish his field with nitrogen. Which crop, replenishes nitrogen and why?, Answer: Kharif: Rice or Soyabean,, Rabi: Pea or Wheat., Pea/Soyabean are legumes that will fix nitrogen with the help of Rhizobium.

Page 9 : 18. Match the agricultural implements given in Column A with their use, given in Column B., Column A – Column B, (i) Sickle – (a) Ploughing, (ii) Hoe – (b) Sowing, (iii) Seed Drill – (c) Harvesting, (iv) Sprinkler – (d) Irrigation, Answer:, Column A – Column B, (i) Sickle – (c) Harvesting, (ii) Hoe – (a) Ploughing, (iii) Seed Drill – (b) Sowing, (iv) Sprinkler – (d) Irrigation, 19. What are organic foods?, Answer: Food crop grown without using any chemicals including fertilizers,, weedicides and pesticides are known as organic food., 20. From the word puzzle given as Fig. 1.1 find at least eight words which, are ‘farmer’s friends.’ Classify them into living and non-living., , Answer:

Page 10 : Living: Seed, Earthworm, Rhizobium, Microbes, Ox, Non-living: Plough, Urea, NPK, Manure, Hoe, 21. (a) Name the tool used with a tractor for sowing seeds in a field., (b) What are the advantages of using this tool?, Answer:, a) The seed drill is the tool used with a tractor for sowing seeds in a field., b) Advantages of seed drill are as follows, •, , It saves time and labour., • After sowing seeds are covered by soil which will protect seeds from., • Seeds are sown at uniform distance and depth. This avoids overcrowding, of the seeds in one location., 22. (a) Name the practice followed for large scale rearing of farm animals., (b) What facilities are provided to farm animals?, Answer:, a) Animal Husbandry, b) Animals should be provided with shelter, food and care., 23. Classify the following crops into Kharif and Rabi crops and write in the, tabular column given below: Maize, paddy, mustard, pea, gram, wheat,, groundnut, cotton., Answer:, Kharif, , Rabi, , Maize, , Mustard

Page 11 : Paddy, , Pea, , Groundnut, , Gram, , Cotton, , Wheat, , Long Answer Questions, 24. Despite favourable climatic conditions, a farmer’s crop failed to give a, good yield. Give the possible reasons for this., Answer: Possible reasons for failed crop despite favourable climatic conditions, are, 1. Weeds are not removed., 2. His land was not irrigated., 3. A farmer might not have used quality seeds., 4. The soil was not ploughed and tilled properly., 5. The farmer did not use appropriate fertilizer and manure., 25. As a part of the eco-club activity, students were asked to raise a kitchen, garden on the school premises. They were provided with some materials, given in the box. List the other materials you would require. How will you, plan the garden? Write the steps., Soln; Along with the given materials, students require seeds, vegetable seedling,, plants from the nursery, soil, manure and water., Steps to raise the garden, •, , Kitchen waste is collected and composted in a pit., • Suitable place to obtain sunlight is chosen to plant the plants., • Soil is dug with the help of spade., • Seeds are sown with adequate spacing., • Water the plants regularly, • Compost is added to the base of the plant, • Weeds are removed periodically., 26. Paddy is a major cereal crop in our country., (a) In which season is paddy cultivated?, (b) Discuss the method of sowing., (c) What measures must be taken to prevent spoilage and insect attack of, harvested grains?, Answer:, a) Paddy is cultivated in the rainy season., b) Seeds are first grown in a nursery and these plantings are transplanted in the, paddy field., c) After harvesting grains are sundried and are stored in jute bags or storage silos.

Page 12 : 27. Unscramble the words related to crop production and its management, and write in the boxes given beneath them., , Now, using the circled letters, form one word which is an activity carried out in, fields, after maturation of crops., Answer:, i), SILOS, ii), THRESHING, iii) IRRIGATION, iv), RIVER, 28. Given below is a conversation between two farmers Heera and Beera., Heera: Brother Beera, your maize crops look beautiful! They have grown, pretty fast., Beera: Yes, I have sprayed urea this time. What about you?, Heera: Well, I am still relying on good old cow dung. I am saving money on, buying a tractor., Beera: That’s good. Tractor saves a lot of time and labour., Heera: Yes, it’s been very labour intensive for me and now these weeds have, come up., Beera: Try weedicides, they are very effective., Now answer the following questions., 1. List the practices which are not environment-friendly and why?, 2. What is the advantage of modern agriculture implements over, traditional ones?, 3. Name one weedicide and the precaution farmers must take during its, application., Answer:, 1. Use of fertilizers, pesticides, weedicides and other chemical is not an ecofriendly way of cultivation as their usage will reduce the fertility of the soil, and also pose a threat to human health., 2. Modern agricultural practices lot and time and labour for the farmers., Modern agricultural practices impose the accuracy and efficiency of, farming procedures., 3. 2,4-D is a weedicide., Farmers should take following precautions before applying weedicide

Page 13 : •, , Cover Nose and Mouth, • Avoid excess usage of weedicide, 29. For discussion Despite being one of the growing economies, our country, still has a large section of the population going hungry and malnourished., Do you think an efficient crop production mechanism is the only solution to, this? Discuss in the class what else needs to be done to root out hunger and, malnutrition from our country., Answer: India, a growing economy with agriculture is the main contributor to its, growth. Agriculture is the science of cultivating plants, animals and other life, forms for food and other sources, despite large production of crops by agricultural, practices, people still go hungry and malnourished. This happens because of, inefficient crop production and management. In India, an increase in production, of food grains has been observed from 1960 to 2004. With efficient management,, crop production can be enhanced and improved to feed the country’s poor. A few, steps in this direction can be:, 1. Selection of high field seeds for planting the seeds with increased yield and, reduced growth period., 2. Management of crop production: The financial aspects of agriculture should be, made more approachable to farmers at all levels., 3. Information regarding the use of chemicals, manures, cropping patterns,, nutrient quality and irrigation facilities should be discussed and propagated, among farmers., 4 Protection of crops: The agricultural produce should be shared efficiently to, reduce the microbial or other organisms from infesting the produce. Pest and, weed control measures should be adopted., A large number of crops get spoiled during storage by different living and nonliving factors. Living factors include rodents, microbes and insects. Non-living, factors are moisture, temperature and hygiene of storage place. Keeping these, factors in mind, we can reduce the economic losses, increase the marketability, and feed the country’s poor., 30. Terms related to the agricultural practice are given below. Rearrange, them in the correct sequence., harvesting, sowing, manuring, tilling and ploughing, irrigation, de-weeding., Answer: The correct sequence of agricultural practices are, i) Tilling and Ploughing, ii) Sowing, iii) Manuring, iv) Irrigation, v) Weeding, vi) Harvesting, i) Tilling and ploughing: One of the most important tasks in agriculture is to, turn the soil and loosen it. This allows the roots to penetrate deep into the soil.

Page 14 : The loose soil allows the roots to breathe easily even when they go deep into the, soil. The process of loosening and turning of the soil is called tilling or ploughing., ii) Sowing: After tilling and ploughing healthy seeds are collected and they are, sown into considerable depth., iii) Manuring: Plants are manured with humus which improves the texture of the, soil and replenishes nutrients in the soil., iv) Irrigation: Irrigation helps to water the plants regularly which will help in, keeping the moisture of plants., v) Weeding: Weeds are removed before they get matured as they compete with, crops for water, nutrients and sunlight., vi) Harvesting: Cutting and gathering matured crops is known as harvesting., Harvesting can be done manually as well as by using harvesters.

Page 15 : CHAPTER 2 MICROORGANISMS: FRIEND AND FOE, , Exercise Questions, 1. Fill in the blanks., (a) Microorganisms can be seen with the help of a Microscope., (b) Blue green algae fix Nitrogen directly from air and enhance, fertility of soil., (c) Alcohol is produced with the help of Yeast., (d) Cholera is caused by Bacteria- Vibrio cholera., 2. Tick/Underline the correct answer., (a) Yeast is used in the production of, (i) sugar, , (ii) alcohol, , (iii) hydrochloric acid, , (iv) oxygen, , (b) The following is an antibiotic, (i) Sodium bicarbonate, , (ii) Streptomycin, , (iii) Alcohol, , (iv) Yeast, , (c) Carrier of malaria-causing protozoan is, (i) female Anopheles mosquito, , (ii) cockroach, , (iii) housefly, , (iv) butterfly, , (d) The most common carrier of communicable diseases is, (i) ant, , (ii) housefly, , (iii) dragonfly, , (iv) spider, , (e) The bread or idli dough rises because of, (i) heat, , (ii) grinding, , (iii) growth of yeast cells, , (iv) kneading, , (f) The process of conversion of sugar into alcohol is called, (i) nitrogen fixation, , (ii) moulding, , (iii) fermentation, , (iv) infection

Page 16 : 3. Match the organisms, Column B., A, (i) Bacteria, (ii) Rhizobium, (iii) Lactobacillus, (iv) Yeast, (v) A protozoan, (vi) A virus, , in Column A with their action given in, B, (a) Fixing nitrogen, (b) Setting of curd, (c) Baking of bread, (d) Causing malaria, (e) Causing cholera, (f) Causing AIDS, (g) Producing antibodies, , Answer:, , A, B, (i) Bacteria, (e) Causing cholera, (ii) Rhizobium, (a) Fixing nitrogen, (iii) Lactobacillus (b) Setting of curd, (iv) Yeast, (c) Baking of bread, (v) A protozoan, (d) Causing malaria, (vi) A virus, (f) Causing AIDS, 4. Can microorganisms be seen with the naked eye? If not, how can, they be seen?, Answer: Microorganisms cannot be seen by the naked eye because, they are very small. They can be seen by using a microscope., 5. What are the major groups of microorganisms?, Answer: Major group of microorganisms are as follows, 1. Bacteria, 2. Fungi, 3. Protozoans, 4. Algae, 5. Viruses, 6. Name the microorganisms which can fix atmospheric nitrogen, in the soil., Answer: Rhizobium, 7. Write 10 lines on the usefulness of microorganisms in our lives.

Page 17 : Answer: Uses of microorganisms are listed below, • They are helpful in cleaning up of the environment. For example,, the organic wastes (vegetable peels, remains of animals, faeces,, etc.) are broken down into harmless and usable substances by, bacteria., • Curd contains several microorganisms. Of these, the bacterium,, Lactobacillus promotes the formation of curd. It multiplies in, milk and converts it into curd., • Bacteria are also involved in the making of cheese, pickles and, many other food items., • Bacteria and yeast are also helpful for fermentation of rice idlis, and dosa batter., • Yeast reproduces rapidly and produces carbon dioxide during, respiration. Bubbles of the gas fill the dough and increase its, volume. This is the basis of the use of yeast in the baking industry, for making breads, pastries and cakes., • Microorganisms are used for the large-scale production of, alcohol, wine and acetic acid (vinegar)., • Antibiotics are being produced from bacteria and fungi., • Microorganisms are helpful in producing vaccines against, disease-causing agents., • Some bacteria are able to fix nitrogen from the atmosphere to, enrich the soil with nitrogen and increase its fertility., • Microorganisms decompose dead organic waste of plants and, animals to convert them into simple substances. These substances, are again used by other plants and animals. Thus, microorganisms, can be used to degrade the harmful and smelly substances and, thereby clean up the environment., 8. Write a short paragraph on the harmful effects of, microorganisms., Microorganisms cause diseases in plants and animals Ex; Cholera in, humans is caused by bacteria called Vibrio cholera. In animals, the, virus causes foot and mouth diseases. Microorganisms spoil the foods, by decomposing the food material. Some microorganisms spoil leather, and clothes. Microorganisms are responsible for food poisoning.

Page 18 : 9. What are antibiotics? What precautions must be taken while, taking antibiotics?, Chemical agents that kill or stop the growth of disease-causing, microorganisms are called antibiotics. Antibiotics should be taken only, on the advice of a qualified doctor. Also, one must complete the course, prescribed by the doctor.

Page 19 : NCERT Exemplar Class 8 Science, MULTIPLE CHOICE QUESTIONS, 1. Which of the following reproduces only inside a host cell?, (a) Bacteria, (b) Virus, (c) Amoeba, (d) Fungus., Answer: (b) Virus, 2. A disease in human beings caused by a virus is _______., (a) Typhoid, (b) Influenza, (c) Dysentery, (d) Cholera, Answer: (b) Influenza, Explanation:, 3. Pathogenic micro-organisms present in host cells are killed by medicines, called, (a) Pain killer, (b) Antibodies, (c) Antibiotics, (d) Vaccines, Answer: (b) Antibiotics, 4. The two micro-organisms which live in symbiotic association in lichens are, (a) Fungus and Protozoa, (b) Alga and Bacteria, (c) Bacteria and Protozoa, (d) Alga and Fungus, Answer: (d) Alga and Fungus, 5. The gas released during the preparation of bread is, (a) Oxygen, (b) Carbon dioxide, (c) Nitrogen, (d) Sulphur dioxide, Answer: (b) Carbon dioxide, 6. The disease caused by a protozoan and spread by an insect is _________., (a) Dengue, (b) Malaria, (c) Polio, (d) Measles, Answer: (b) Malaria, 7. Paheli dug two pits, A and B, in her garden. In-pit A, she put a polythene, bag packed with some agricultural waste. In-pit B, she dumped the same

Page 20 : kind of a waste but without packing it in a polythene bag. She then covered, both the pits with soil. What did she observe after a month?, (a) Waste in pit A degraded faster than that in pit B., (b) Waste in pit B degraded faster than that in pit A., c) Waste in both pits degraded almost equally., (d) Waste in both pits did not degrade at all., Answer: (b) Waste in pit B degraded faster than that in pit A., , VERY SHORT ANSWER QUESTIONS, 8. Unscramble the jumbled words underlined in the following statements., (a) Cells of our body produce santiidobe to fight pathogens., (b) curbossulite is an air-borne disease caused by a bacterium., (c) Xanrhat is a dangerous bacterial disease., (d) Yeasts are used in the wine industry because of their property of, meronettinaf., Answer:, a. Antibodies, b. Tuberculosis, c. Anthrax, d. Fermentation, 9. Suggest a suitable word for each of the following statements., (a) Chemicals added to food to prevent the growth of microorganisms., (b) Nitrogen-fixing microorganism present in the root nodules of legumes., (c) The agent spreads pathogens from one place to another., (d) Chemicals which kill or stop the growth of pathogens., Answer:, a. Preservatives, b. Rhizobium, c. Carrier/ vector, d. Antibiotics, 10. Match the names of scientists given in Column A with the discovery made, by them given in Column B., Column A, Column B, (a) Louis Pasteur –, (i) Penicillin, (b) Robert Koch –, (ii) anthrax bacterium, (c) Edward Jenner –, (iii) Fermentation, (d) Alexander Fleming –, (iv) small pox vaccine, Answer:, Column A, Column B, (a) Louis Pasteur –, (iii) Fermentation, (b) Robert Koch –, (ii) anthrax bacterium, (c) Edward Jenner –, (iv) small pox vaccine, (d) Alexander Fleming –, (i) Penicillin

Page 21 : 11. Name one commercial use of yeast, Answer: Yeast is used in making bread and they are used in the fermentation of, alcohol., 12. Name the process in yeast that converts sugars into alcohol., Answer: Fermentation is the process in yeast that converts sugars into alcohol., 13. In the soil, which nutrient is enriched by blue-green algae, (cyanobacteria)?, Answer: Blue-green-algae enriches Nitrogen in the soil., 14. Why should we avoid standing close to a tuberculosis patient while he/she, is coughing?, Answer: Tuberculosis can spread through the air when the infected person, coughs. Hence, we avoid standing close to a tuberculosis patient while he/she is, coughing., 15. Polio drops are not given to children suffering from diarrhoea. Why?, Answer: If the children are suffering from diarrhoea oral polio drops will get, excreted due to frequent motions. Hence children with diarrhoea are not given, with polio drops., 16. Paheli watched her grandmother making mango pickle. After she bottled, the pickle, her grandmother poured oil on top of the pickle before closing the, lid. Paheli wanted to know why oil was poured? Can you help her, understand why?, Answer: Oils prevent the attack of bacteria which will help preserve the pickle, for a long period of time., Short Answer Questions, 17. Match the microorganisms given in Column A to the group to which they, belong in Column B., Column A, Column B, (a) Lactobacillus –, (i) Algae, (b) Aspergillus –, (ii) Protozoa, (c) Spirogyra –, (iii) Fungi, (d) Paramecium –, (iv) Bacteria, Answer:, Column A, Column B, (a) Lactobacillus –, (iv) Bacteria, (b) Aspergillus –, (iii) Fungi, (c) Spirogyra –, (i) Algae, (d) Paramecium –, (ii) Protozoa, 18. Classify the following into friendly and harmful microorganisms., Yeast, malarial parasite, Lactobacillus, bread mould, Rhizobium, Bacillus, anthracis, Answer:, Friendly, Harmful Microorganisms

Page 22 : Yeast, Malarial parasite, Lactobacillus, Bread mould, Rhizobium, Bacillus anthracis, 19. While returning from the school, Boojho ate chaat from a street hawker., When he reached home, he felt ill and complained of stomach ache and fell, ill. What could be the reason?, Answer: The probable reason is that the chaat was contaminated by pathogenic, microbes due to unhygienic conditions near the shop or the utensil used for, serving could have contaminated., The reason may be the contamination of food by pathogenic microbes., Contamination may be due to the unhygienic conditions near the shop or the, utensil used to serve the chaat., 20. What will happen to ‘pooris’ and ‘unused kneaded flour’ if they are left, in the open for a day or two?, Answer: Pooris and unused kneaded flour get spoiled due to microbial activity., Food gets fermented when kept open and it will be spoiled., 21. (a) Name two diseases that are caused by the virus., (b) Write one important characteristic of the virus., Answer:, a. Polio, HIV, b. A virus can reproduce only when it is inside the host cell., Long Answer Questions, 22. Observe the Fig. and answer the questions that follow., , (a) Write the name of the disease., (b) Name the causative agent of this disease?, (c) How does the disease spread from one plant to another?, (d) Name any two plant diseases and the microbes that cause them., Answer:, a. yellow vein mosaic of lady’s finger/okra, b. This disease is caused by a virus called yellow vein mosaic virus., c. This disease spread from one plant to another by insects., d. (i) Citrus canker caused by bacteria (ii) Rust of wheat caused by the fungus

Page 23 : 23. How do vaccines work?, Answer: When a disease-carrying microbe enters our body, the body produces, antibodies to fight the invader. The body also remembers how to fight the microbe, if it enters again. If dead or weakened microbes are introduced into a healthy, body, the body fights and kills the invading bacteria by producing suitable, antibodies. The antibodies remain in the body and we are protected from the, disease-causing microbes forever. This is how a vaccine works., 24. Observe the set up given in Figure and answer the following questions., (a) What happens to the sugar solution in A?, (b) Which gas is released in A?, (c) What changes will you observe in B when the released gas passes through, it?, , Answer:, a) Yeast ferments sugar to convert it to alcohol and carbon-di-oxide is released., b) Carbon-di-oxide, c), CO2, Coverts, limewater, milky., 25. Observe the Figure and answer the following questions., , (a) Name the microorganism and the group to which it belongs., (b) Name the food item on which the organism grows., (c) Does it grow well in dry or in moist conditions?, (d) Is it safe to eat infected bread?, Answer:, a) The image is of bread mould. It is a fungus, b) It grows on moist and stale bread, c) It grows well in moist conditions

Page 24 : d) No, it is not safe to eat infected bread because fungus produces a poisonous, substance which will spoil the food., 26. Give reasons for the following., (a) Fresh milk is boiled before consumption while processed milk stored in, packets can be consumed without boiling., (b) Raw vegetables and fruits are kept in refrigerators whereas jams and, pickles can be kept outside., (c) Farmers prefer to grow beans and peas in nitrogen-deficient soils., (d) Mosquitoes can be controlled by preventing stagnation of water though, they do not live in water. Why?, Answer:, a) Fresh milk is boiled to kill the harmful microorganisms in the milk. Packed, milk is pasteurized hence there is no need to boil the pasteurized milk., b) Raw vegetables easily get infected by microbes. Hence, they are kept in the, refrigerator as low temperature inhibits the growth of micro-organisms. In Jams, and pickle, there are sugar and salt which acts as preservatives. Hence, they do, not get infected easily., c) Beans and peas are leguminous plants which have Rhizobium in their root, nodules. Rhizobium fixes atmospheric Nitrogen to enrich the soil and its fertility, gets increases., d) Though mosquito do not live-in water, they lay their egg and their larvae grow, in water. Hence mosquitoes can be controlled by preventing stagnation of water., 27. How can we prevent the following diseases?, (a) Cholera, (b) Typhoid, (c) Hepatitis A, Answer:, a) Cholera can be prevented by following good personal hygiene and sanitation practices., b) Typhoid can be prevented by eating properly cooked food, by drinking boiled water and by, getting vaccinated against typhoid disease., c) Hepatitis can be prevented by drinking boiled water and by getting vaccinated., 28. Complete the following cycle given as the following Figure by filling the blanks (a),, (b), (c) (d)

Page 25 : Answer:, (a) Lightning fixes nitrogen., (b) Nitrogen-fixing bacteria and blue-green algae fix atmospheric nitrogen., (c) Nitrogenous waste from excretion and death., (d) Bacteria turn compounds of nitrogen into gaseous nitrogen.

Page 26 : CHAPTER 3 SYNTHETIC FIBRES AND PLASTICS, Multiple Choice Questions, Question. 1 Pick the synthetic fibre out of the following., (a) Cotton (b) Nylon (c)Jute (d)Wool, Answer. (b) Nylon Is a synthetic fibre. It is made without using any natural raw, material. Cotton, jute and wool are natural fibres., Question. 2 Which of the following is a source of rayon?, (a) Wool (b) PET (c) Wood pulp (d) Silk, Answer. (c) Wool pulp, Rayon is obtained by the chemical treatment of wool pulp (which contains, cellulose)., Question. 3 Polycot is obtained by mixing, (a) nylon and wool (b) polyester and wool (c) nylon and cotton (d) polyester, and cotton, Answer. (d) Polycot is obtained by mixing polyester and cotton., Polycot = polyester + cotton, Question. 4 Which is a thermosetting plastic?, (a) Melamine (b) Polythene (c) PVC (d) Nylon, Answer. (a) Melamine is a thermosetting plastic which when moulded once,, cannot be softened by heating., Question. 5 The material similar to silk in appearance is, (a) nylon (b) rayon (c) polyester (d) terylene, Answer. (b) Rayon resembles silk in appearance; therefore, rayon is also called, artificial silk., Question. 6 The most suitable material for the preparation of handles of, cooking utensils is- (a) polythene (b) PVC (c) nylon (d) Bakelite, Answer. (d) Bakelite is used for making the handles of various cooking utensils, because it is a poor conductor of heat and does not become soft on getting heated., Question. 7 Which of the following is not a common property of plastics?, (a) Non-reactive, (b) Light in weight, (c) Durable, (d) Good conductor of electricity, Answer. (d) Plastics are non-reactive, light in weight and durable but they do not, conduct electricity., Question. 8 Which of the following represents the correct match for items in, Column A with those in Column B.

Page 27 : Codes, (a) (a)-(ii), (b)-(iii), (c)-(i), (b) (a)-(iii), (b)-(i), (c)-(ii), (c) (a)-(ii), (b)-(i), (c)-(iii), (d) (a)-(iii), (b)-(ii), (c)-(i), Answer. (c) Nylon —-> Fibre, PVC —->Thermoplastic, Bakelite —>Thermosetting plastic, Question. 9 Which of the following groups contains all synthetic substances?, (a) Nylon, tprylene, wool, (b) Cotton, polycot, rayon, (c) PVC, polythene, bakelite, (d) Acrylic, silk, wool, Answer. (c) PVC, polythene and bakelite are synthetic substances., Question. 10 The material which is commonly used for making kitchen, containers is, (a) PVC (b) acrylic (c) teflon (d) PET, Answer. (d) PET is ‘poly-ethylene’ terephthalate’ PET as a plastic is very light, weight and is commonly used for making kitchen containers., , Very Short Answer Type Questions, Question. 11 Cotton is a natural polymer. What is its chemical name?, Answer. Chemical name of natural polymer of cotton is cellulose., Question. 12 A synthetic fibre which looks like silk is obtained by chemical, treatment of wood pulp. It is, therefore, known as artificial silk. What is its, common name?, Answer. Its common name is rayon. Rayon is often regarded as artificial silk., Question. 13 Terrycot is made by mixing two types of fibres. Write the names, of the fibres., Answer. Terrycot is made by mixing terylene and cotton., Question. 14 Plastic articles are available in all possible shapes and sizes. Can, you tell why?, Answer. Plastics can be easily moulded, so they are used to make a large variety, of articles (or objects) having different shapes and sizes., Question. 15 Plastic is used for making a large variety of articles of daily use, and these articles are very attractive. But it is advised to avoid the use of, plastic as far as possible. Why?

Page 28 : Answer. The disposal of plastic waste is a major problem because plastic is nonbiodegradable, it takes several years to decompose. Thus, cause environmental, pollution. So, we should avoid use of plastics, as for as possible., Question. 16 Why is it not advisable to burn plastic and synthetic fabrics?, Answer. Burning of plastics and synthetic fabrics produces lots of poisonous, gases causing air pollution. So, it is not advisable to burn plastic and synthetic, fibres., Question. 17 Select the articles from the following list which are, biodegradable., (a) Paper, (b) Woollen clothes, (c) Wood, (d) Aluminium can, (e) Plastic bag, (f) Peels of vegetables, Answer. The biodegradable articles are: (a) paper (b) woollen clothes, (c) wood (f) peels of vegetables, Question. 18 A bucket made of plastic does not rust like a bucket made up of, iron. Why?, Answer. Plastic is non-reactive material. When left exposed to moisture and air,, it does not react with air and water which are essential for corrosion, therefore, does not rust., , Short Answer Type Questions, Question. 19 Rohit took with him some nylon ropes, when he was going for, rock climbing. Can you tell why he selected nylon ropes instead of ropes, made up of cotton or jute?, Answer. Nylon ropes are strong, elastic and lighter as compared to cotton and, jute ropes. A nylon thread is actually stronger than a steel wire of similar, thickness., Question. 20 A lady went to the market to buy a blanket. The shopkeeper, showed her blankets made up of acrylic fibres as well as made up of wool., She preferred to buy an acrylic blanket. Can you guess why?, Answer. Acrylic blankets are cheap, light in weight, more durable and are, available in variety of colours and designs. They can be easily washed at home., Question. 21 PVC (polyvinyl chloride) is a thermoplastic and is used for, making toys, chappals, etc. Bakelite is a thermosetting plastic and is used for, making electrical switches, handles of various utensils, etc. Can you write the, major, difference, between, these, two, types, of, plastics?, Answer. Thermoplastics get deformed easily on heating and can be bent easily, on heating. On the other hand, thermosetting plastics when moulded once cannot, be softened on heating., Thermoplastics, →, Polythene, and, PVC, →, Thermosetting plastics → Bakelite and melamine

Page 29 : Question. 22 Fill in the blanks., 1. A polymer is a chain of many small units joined together which, are called monomers., 2. The synthetic fibres are also known as man-made fibres., 3. The first fully synthetic fibre was nylon., 4. A fibre similar to wool is acrylic., 5. A plastic used for making crockery is melamine., Answer., Question. 23 Match items in Column A with the terms of Column B., , Answer. The, correct, matching, is, as, given:, (a)—(iii), (b)—(iv), (c)—(v), (d)—(ii), (e)-(i), Question. 24 Unscramble the jumbled materials. words given below, related, to synthetic, (a), Anory, (b), Lopmery, (c), Relyteen, (d), Laspict, (e) Yespolter (f) Felton, Answer., (a), Rayon, (b), Polymer, (c), Terylene, (d), Plastic, (e) Polyester (f) Teflon, , Long Answer Type Questions, Question. 25 State whether the following statements are True/False., 1. The fabric tery wool is obtained by mixing terylene and wool., 2. Synthetic fibre do not melt on heating., 3. It is risky to wear synthetic clothes while working in the kitchen., 4. Most of the plastics are biodegradable., Answer., 1. True, 2. False, synthetic fibres melt on heating., 3. True, a disadvantage as synthetic fibre is that they melt on heating., 4. False, most of the plastics are non-biodegradable., Question. 26 Write the importance of synthetic polymers in our life., Answer. The importance of synthetic polymers in our life are as follows:

Page 30 : 1. Nylon It is used for making ropes for rock climbing, fishing nets,, raincoats, parachutes and tyre cords, etc., 2. Acrylic It is used for sweaters, track suits, linings for boots and gloves, and In furnishing fabrics and carpets., 3. Terylene It is used in textile industry to make clothes like sarees,, tapestry and dress material. It is also mixed with natural fibre like, cotton and wool to make more variety of clothes., 4. Plastics It is used to store food item, water, milk, pickles, dry food,, etc., Plastic, containers, seem, most, convenient., This is because of light weight, low price, good strength and easy, handling as compared to metals. Plastics are used in cars, air crafts, and spacecrafts., Question. 27 Despite being very useful, it is advised to restrict the use of, plastic. Why is it so? Can you suggest some methods to limit its, consumption?, Answer. It is advised to restrict the use of plastic because of the following, reasons:, 1. The articles mades of plastics are non-biodegradable. They do not, decompose (or rot) easily. This causes a great problem in the disposal, of plastic wastes., 2. The burning of plastic wastes gives out harmful gases which pollute, the air. So, it is not advisable to dispose of the used plastic articles by, burning., Question. 28 Write an activity to show that synthetic fibres are stronger than, the cotton fibres., Answer. Activity Take threads of cotton and nylon (synthetic fibres) of about, same length and thickness. Hang cotton, thread from a stand. Attach a pan at the, other end of the thread., Add weights, one by one, to the pan until the thread breaks (see fig.) note the total, weight required to break the cotton thread. This gives a measure of the tensile, strength of the thread. Repeat the same with nylon thread.

Page 31 : Conclusion, Much more weight is required to break the nylon thread showing that nylon thread, has a greater strength that the cotton thread., Question. 29 Crossword Puzzle Complete the crossword given below with, the help of clues., Across, 1. Substance used as synthetic wool. (7), 2. A plastic used for making containers and carry bags. (9), 3. Substance made up of large number of smaller molecules. (7), 4. Another name for this compound is artificial silk. (5), Down, 5. A type of fibre obtained naturally from cocoon. (4), 6. A synthetic fibre classified as polyester. (8), 7. A polymer used for making ropes. (5)

Page 32 : Answer.

Page 33 : CHAPTER 4 MATERIALS – METALS AND NON-METALS, Exercise Questions, 1. Which of the following can be beaten into thin sheets?, a), b), c), d), , Zinc, Phosphorus, Sulphur, Oxygen, , Answer: a) Zinc, 2. Which of the following statements is correct?, a), b), c), d), , All metals are ductile., All non-metals are ductile., Generally, metals are ductile., Some non-metals are ductile., , Answer: (c) Generally, metals are ductile., 3. Fill in the blanks., (a) Phosphorus is a very reactive non-metal., (b) Metals are good conductors of heat and electricity., (c) Iron is more reactive than copper., (d) Metals react with acids to produce hydrogen gas., 4. Mark ‘T’ if the statement is true and ‘F’ if it is false., (a) Generally, non-metals react with acids., , (False), , (b) Sodium is a very reactive metal., , (True), , (c) Copper displaces zinc from zinc sulphate solution. (False), (d) Coal can be drawn into wires., , (False), , 5. Some properties are listed in the following table. Distinguish between, metals and non-metals on the basis of these properties., Properties, Metals Non-metals

Page 34 : 1. Appearance, 2. Hardness, 3. Malleability, 4. Ductility, 5. Heat Conduction, 6. Conduction of Electricity, Answer:, Properties, 1. Appearance, 2. Hardness, , Metals, Non-metals, Lustrous, Dull, Hard, Soft, Have, property, of Do not have a property of, 3. Malleability, Malleability, Malleability, Have, property, of Do not have the property of, 4. Ductility, Ductility, Ductility, 5. Heat Conduction, Good conductor of Heat Bad Conductor of Heat, 6., Conduction, of Good conductor of The bad conductor of, Electricity, electricity., electricity., , 6. Give reasons for the following., (a) Aluminium foils are used to wrap food items., (b) Immersion rods for heating liquids are made up of metallic substances., (c) Copper cannot displace zinc from its salt solution., (d) Sodium and potassium are stored in kerosene, Answer:, a) Aluminium is malleable and can be drawn into thin sheets hence Aluminium, foils are used to wrap food items, b) Immersion rods for heating liquids are made up of metallic substances because, metals are good conductors of heat and electricity., c) Copper cannot displace zinc from its salt solution because Zinc is more reactive, than copper.

Page 35 : d) Sodium and Potassium are highly reactive metals which readily reacts with, atmospheric Oxygen to catch fire hence Sodium and Potassium are stored in, kerosene., 7. Can you store the lemon pickle in an aluminium utensil? Explain., Answer: Pickle consists of acids which react with Aluminium metal to produce, salt and Hydrogen. Hence pickle is not stored in aluminium utensil., 8. Match the substances given in Column A with their uses given in Column, B., A, B, (i) Gold, (a) Thermometers, (ii) Iron, (b) Electric wire, (iii) Aluminium, (c) Wrapping food, (iv) Carbon, (d) Jewellery, (v) Copper, (e) Machinery, (vi) Mercury, (f) Fuel, Answer:, A, (i) Gold, (ii) Iron, (iii) Aluminium, (iv) Carbon, (v) Copper, (vi) Mercury, , B, (d) Jewellery, (e) Machinery, (c) Wrapping food, (f) Fuel, (b) Electric wire, (a) Thermometers, , 9. What happens when, (a) Dilute sulphuric acid is poured on a copper plate?, (b) Iron nails are placed in a copper sulphate solution?, Write word equations of the reactions involved., Answer:, (a) No reaction occurs when dilute sulphuric acid is poured on a copper plate., However, when concentrated sulphuric acid is poured on a copper plate,, hydrogen gas evolves along with the formation of blue coloured copper

Page 36 : sulphate crystals. The chemical reaction for the reaction between, concentrated sulfuric acid and copper is:, Cu + H2SO4 (conc.) → CuSO4 + H2, (b) Iron being more reactive displaces copper from copper sulphate. In this, reaction, the blue colour of copper sulphate fades and there is a deposition, of copper on the iron nail., Fe + CuSO4 → FeSO4 + Cu, 10. Saloni took a piece of burning charcoal and collected the gas evolved in, a test tube., (a) How will she find the nature of the gas?, (b) Write down word equations of all the reactions taking place in this, process., Answer:, a) In a test tube containing gas, add a few drops of water. Now cover the test tube, and shake well. After shaking, test the solution with blue litmus. It will change, from blue to red. Thus, gas is acidic in nature., b) Charcoal reacts with oxygen to form carbon dioxide gas., C + O2 → CO2, 11. One day Reeta went to a jeweller’s shop with her mother. Her mother, gave old gold jewellery to the goldsmith to polish. Next day when they, brought the jewellery back, they found that there was a slight loss in its, weight. Can you suggest a reason for the loss in weight?, Answer: In order to polish the gold ornament, it is to be dipped into a liquid, called aqua regia (a mixture of hydrochloric acid and nitric acid). On getting, dissolved in the environment of aqua regia, the outer layer of gold dissolves and, an inner shiny layer appears. The dissolving of the layer causes a reduction in the, weight of the jewellery.

Page 37 : CHAPTER 5: COAL AND PETROLEUM, Exercise Questions, 1. What are the advantages of using CNG and LPG as fuels?, Answer: The advantages of using CNG and LPG as fuels are as follows, • CNG and LPG burn easily., • CNG and LPG give a lot of heat energy when burnt., • CNG and LPG can be transported easily through pipelines., • CNG and LPG are clean fuels and they do not release smoke when burnt., 2. Name the petroleum product used for surfacing of roads., Answer: Bitumen is used for surfacing of roads., 3. Describe how coal is formed from dead vegetation. What is this process, called?, Answer: Dense forests got buried under the soil due to natural processes, millions, of years ago. More and more soil got deposited over them and they got, compressed more. This led them to get exposed to very high temperature and, pressure. They slowly got converted into coal under these extreme conditions., The whole process of formation of coal from dead vegetation is known as, carbonization., 4. Fill in the blanks., (a) Fossil fuels Coal, Petroleum, and natural gas., (b) Process of separation of different constituents from petroleum is called, refining., (c) Least polluting fuel for a vehicle is Compressed Natural Gas (CNG)., 5. Tick True/False against the following statements., (a) Fossil fuels can be made in the laboratory., (False), (b) CNG is more polluting fuel than petrol., (False), (c) Coke is the almost pure form of carbon., (True), (d) Coal tar is a mixture of various substances., (False), (e) Kerosene is not a fossil fuel., (False), 6. Explain why fossil fuels are exhaustible natural resources., Answer: The process of formation of fossil fuels requires millions of years. Dead, vegetation and animals that get buried deep inside the earth require high, temperature and pressure for the formation of fossil fuels, which cannot be done, in the laboratory. Thus, fossils are limited. Therefore, the use of fossil fuels at a, rapid rate will lead to their exhaustion., 7. Describe the characteristics and uses of coke., Answer: Characteristics:, i) Coke is tough., ii) Coke is porous., iii) Coke is black in colour., Uses:, i) In the manufacture of steel.

Page 38 : ii) In the extraction of metals (as a reducing agent)., 8. Explain the process of the formation of petroleum., Answer: Dead organisms that got buried in the sea millions of years ago got, covered with layers of sand and clay. Due to lack of air, high temperature and, high pressure, these dead organisms got transformed into petroleum and natural, gas., 9. The following table shows the total power shortage in India from 1993–, 1999. Show the data in the form of a graph. Plot shortage percentage for the, years on the Y-axis and the year on the X-axis., S.No., Year, Shortage (%), , Answer:, , 1., , 1993, , 7.7, , 2., , 1994, , 7.5, , 3., , 1995, , 8.2, , 4., , 1996, , 7.1, , 5., , 1997, , 7.7, , 6., , 1998, , 9.1, , 7., , 1999, , 11.2

Page 39 : CHAPTER 6: CONSERVATION OF PLANTS AND ANIMALS, Exercise Questions, 1. Fill in the blanks., (a) A place where animals are protected in their natural habitat is called, Sanctuary., (b) Species found only in a particular area is known as endemic., (c) Migratory birds fly to faraway places because of climatic changes., 2. Differentiate between the following., (a) Wildlife sanctuary and biosphere reserve, (b) Zoo and wildlife sanctuary, (c) Endangered and extinct species, (d) Flora and fauna, Answer:, (a), Wildlife sanctuary, Biosphere Reserve, An area within which wild animals, An area constructed for the conservation, are protected from external dangers, of biodiversity, like hunting, Adequate habitat and protection are Several life forms like plants, animals, and, provided for the wild animals living micro-organisms, conservation, are, in a sanctuary, possible in a reserve, Eg: Corbett national park, Eg: Nilgiri Biosphere reserve, (b), Zoo, Wildlife Sanctuary, Animals are kept in artificially, An area within which wild animals are, constructed facilities for public, protected from external dangers like hunting., exhibition., It is an artificial habitat and the The animals are conserved within their, animals may or may not adapt to natural habitat itself. So, they won’t have a, the new conditions., problem with their surroundings., (c), Endangered Species, Extinct Species, The species which are on the verge of The species of animals or plants that, extinction are called as Endangered no longer exist are called Extinct, species., species., Eg: Caribbean monk seal, Great Auk,, Eg: Bengal Tiger, Blue Whale, etc., Passenger pigeon., (d), Flora, Fauna

Page 40 : It is the collective name for the plant It is the collective name for the animal, life from a particular area., life from a particular area, Eg: Spurge and Hogweed from the Eg: Langur, Tiger, Tahr from the, Nilgiris region, Nilgiris region., 3. Discuss the effects of deforestation on the following., (a) Wild animals, (b) Environment, (c) Villages (Rural areas), (d) Cities (Urban areas), (e) Earth, (f) The next generation, Answer:, (a) Effects of deforestation on wild animals: Removal of trees and plant life, from a particular area for the construction of industries, agriculture or for other, such purposes is termed as Deforestation. Plantlife forms an integral part of the, ecosystem and these plants form the natural habitat of various animals of that, ecosystem. Destroying the plant life will ultimately threaten the existence of, animals in that particular ecosystem and may lead to their extinction., (b) Effects of deforestation on the environment: In plants, Photosynthesis takes, place by the absorption of CO2 from the earth’s atmosphere. The percentage of, CO2 in the atmosphere increases rapidly if the plant life of an area is destroyed., Increased concentrations of CO2 result in the trapping of excessive heat radiations, within the Earth’s atmosphere contributing to global warming. This results in the, rise of the temperature of the Earth and disturbs the water cycle which occurs in, nature. Hence, rainfall pattern changes leading to droughts and floods., (c) Effects of deforestation on villages: The soil particles are held together in a, place by the roots of the plants, trees and other vegetation. In the event of water, flow or a high-speed wind over the top layer of the soil, the soil particles get, removed easily as there are no plants to hold it in place. Thus, soil erosion is, increased by deforestation activities. Soil loses fertility and loses humus. Hence,, a fertile land, fit for agriculture turns into a desert., (d)Effects of deforestation on cities: The risk of natural calamities like floods, and drought in urban areas is increased by deforestation. It will also lead to global, warming because of increased CO2 levels in the atmosphere. This is a result of, continuous pollution from automobiles and industries. The water cycle in the, vicinity is also affected., (e) Effects of deforestation on Earth: Deforestation leads to increased chances, and occurrences of desertification, droughts and floods. Carbon Dioxide level in, the earth’s atmosphere also increases which leads to global warming. The water, cycle is disrupted and there is also an increased risk of natural calamities., (f) Effects of deforestation on the next generation: Our Environment is slowly, changed by the activities of deforestation, both directly and indirectly. Soil

Page 41 : erosion, global warming, desertification, drought, greenhouse effect, floods and, many other problems are caused only because of deforestation. Ultimately, the, next generation will be facing the consequences of deforestation., 4. What will happen if, (a) we go on cutting trees, (b) the habitat of an animal is disturbed, (c) the top layer of soil is exposed, Answer:, (a) If we go on cutting the trees: If we go on cutting the trees, the animals will, lose their natural habitat as an essential part of their ecosystem are destroyed. This, reduces the biodiversity of the affected areas. The temperature of the Earth also, increases and gives way to global warming. Global warming, in turn, affects the, water cycle. Hence, rainfall pattern changes leading to droughts and floods. Risks, of soil erosion, global warming, desertification, greenhouse effect increases., (b) If the habitat of an animal is disturbed: All the basic necessities for an, animal, like food, water, shelter and protection is provided by the habitat in which, the animal lives-in disturbing the habitat of the animal forces it to move to another, place in search of food, water, shelter and protection. The animal, in due course,, may get killed by other animals., (C) If the top layer of the soil is removed: Removing the top layer of the soil, gradually exposes the lower layers of the soil. The lower layers of the soil are, hard and rocky in nature and are less fertile. This is because of the reduced, quantity of humus. Soil erosion on a continued basis will turn it barren and, infertile., 5. Answer in brief (a) Why should we conserve biodiversity?, (b) Protected forests are also not completely safe for wild animals. Why?, (c) Some tribals depend on the jungle. How?, (d) What are the causes and consequences of deforestation?, (e) What is Red Data Book?, (f) What do you understand by the term migration?, Answer:, (a) The number and variety of various life forms such as plants, animals and, micro-organisms in the area are called Biodiversity. Both plants and animals have, a mutual dependence on each other for their survival. As they are related to one, another, destruction of one will automatically destroy the other. Hence,, biodiversity has to be conserved in order to maintain nature’s balance., (b) People who live near the forests depend on the resources of the forests in order, to fulfil their day-to-day needs. Therefore, it is not safe for animals living in, protected forests. The animals would be threatened by the presence of the human, population. This results in the killing of wild animals and selling their products, for huge sums of money.

Page 42 : (c) The forests provide food, fodder and other resources to the tribal people. It is, inevitable for them to depend on forests and their resources for everyday needs., (d) Causes of deforestation: There are a lot of causes for deforestation. A few of, them are listed below., i. In order to accommodate the ever-expanding urban population, forest areas, are often cleared and converted into lands for various uses., ii. For agricultural activities like crop cultivation and cattle grazing, forest, lands are cleared., iii. Firewood is a major product from the forests and it is one of the main, reasons for cutting the trees on a large scale., Consequences of deforestation: There are a lot of fatal consequences caused by, deforestation. A few of them are listed below., 1. Soil erosion, 2. Loss of Biodiversity, 3. Floods, 4. Droughts, 5. Global warming as a result of climate change, 6. Disruption of the water cycle, (e) Red data book is basically a sourcebook which has an international list of all, plant and animal species which are endangered, that is, on the verge of extinction., The International Union for Conservation of Nature and Natural resources, (IUCN) maintains the books and adds/ removes the names of the species by, conducting a comprehensive survey., (f) The movement of an organism or a group of organisms from its natural habitat, to another place on a standard basis at a particular time of each and every year is, known as migration. The organisms do so in order to avoid uninhabitable, conditions of climate or for the process of breeding., 6. In order to meet the ever-increasing demand in factories and for shelter,, trees are being continually cut. Is it justified to cut trees for such projects?, Discuss and prepare a brief report., Answer: No. Cutting trees in order to meet the ever-growing demands of the, human population is not at all justified. There are a vast number of organisms like, wild animals, insects, and birds living in the forests. The forests provide good, quality air for both animals and humans. This is because of the process of plants, respiration by which, they consume the harmful carbon dioxide and give out good, quality Oxygen. Thus, keeping greenhouse gases and global warming under, check. The roots of the flora of the forests help in preventing soil erosion. Natural, Calamities such as floods and droughts could also be prevented by their presence., They help in increasing the soil’s fertility and conserving the biodiversity of the, ecosystem., Overutilization of forests and its resources by cutting a large number of trees in, order to satisfy the demands of the ever-increasing human population, leading to, many long-term problems like

Page 43 : •, , Soil erosion, • Greenhouse effect, • Global warming, • Floods, • Droughts, Besides the above-listed problems, the effects of large-scale deforestation will be, leaving an everlasting mark on the face of human civilization. The balance of, nature is disturbed by the destruction of trees. Hence, it is of utmost priority and, importance to conserve forests., 7. How can you contribute to the maintenance of green wealth of your, locality? Make a list of actions to be taken by you., Answer: I can take care of the green cover of my locality by growing plants in, my locality. I shall motivate the people of my neighbourhood to plant more trees, and take care of the existing trees by creating awareness about the importance of, plant life in an ecosystem. In order to make this possible, I would initiate the, proceedings and organize weekly events on the same. Creating awareness among, the children and youth would be of top priority as they will easily understand the, issues that we are facing. Planting new trees is as important as looking after the, existing ones. So, my volunteers and I would water the plants and trees on a, regular basis., 8. Explain how deforestation leads to reduced rainfall., Answer: Removal of trees and plant life from a particular area for the, construction of industries, agriculture and other purposes is termed as, Deforestation. Photosynthesis in plant life, takes place by the absorption of, CO2 from the earth’s atmosphere. When the plant life is destroyed, the Carbon, Dioxide levels in the atmosphere will increase drastically leading trap of heat, radiation which causes global warming. This rise in temperature will affect the, water cycle. Disturbance in the water cycle will lead to a chain of events and in, the end, the rainfall pattern changes and results in droughts., 9. Find out about national parks in your state. Identify and show their, location on the outline map of India., Answer: Periyar National Park located in the state of Kerala.

Page 44 : 10. Why should paper be saved? Prepare a list of ways by which you can save, paper., Answer: If one ton of clean white paper is to be produced, seventeen full-grown, trees are cut down. Trees play a major role in maintaining a balance in nature. So,, it is essential to save paper in order to protect the trees and avoid the impact of, the loss of trees on the living organisms that depend on these trees., Ways to save paper:, • Collection and recycling of used paper., • Using both sides of a paper for writing., • Spreading awareness about the importance of paper among school children, and youth., • Intelligent and proper use of paper., 11. Complete the word puzzle., Down, 1. Species on the verge of extinction., 2. A book carrying information about endangered species., 5. Consequences of deforestation., Across, 1. Species which have vanished., 3. Species found only in a particular habitat., 4. Variety of plants, animals and microorganisms found in an area.

Page 45 : Down, 1. Endangered, 2. Red Data Book, 3. Deserts, Across, 1. Extinct, 2. Endemic, 3. Biodiversity

Page 47 : CHAPTER 7: FORCE AND PRESSURE, Exercise Questions, 1. Give two examples each of situations in which you push or pull to change, the state of motion of objects, Answer: Examples of situations in which you push or pull to change the state of, motion of objects., 1. Pull situations, a) In order to open a drawer, we have to pull it. This action changes the state of, motion of the drawer., b) To draw water from the well, the rope is pulled. This action changes the state, of motion of the bucket., 2. Push Situations, a) A football is pushed by the foot of a player. This action changes the state of, motion of the ball., b) In order to change the place of the heavy box from one room to another, we, have to push it. This action changes the motion of the box., 2. Give two examples of situations in which applied force causes a change in, the shape of an object., Answer: The forces which change the shape of an object are as follows:, i) By pressing the clay between the hands, it deforms., ii) The shape of the plastic bottle changes by squeezing it., 3. Fill in the blanks in the following statements., 1., 2., 3., 4., , To draw water from a well we have to pull at the rope., A charged body attracts an uncharged body towards it., To move a loaded trolley, we have to pull or push it., The north pole of a magnet repels the north pole of another magnet., , 4. An archer stretches her bow while taking aim at the target. She then, releases the arrow, which begins to move towards the target. Based on this, information fill up the gaps in the following statements using the following, terms.

Page 48 : muscular, contact, non-contact, gravity, friction, shape, attraction, (a) To stretch the bow, the archer applies a force that causes a change in its shape., (b) The force applied by the archer to stretch the bow is an example of muscular, force., (c) The type of force responsible for a change in the state of motion of the arrow, is an example of a contact force., (d) While the arrow moves towards its target, the forces acting on it are due to, gravity and that due to friction of air., 5. In the following situations identify the agent exerting the force and the, object on which it acts. State the effect of the force in each case., (a) Squeezing a piece of lemon between the fingers to extract its juice., (b) Taking out paste from a toothpaste tube., (c) A load suspended from a spring while its other end is on a hook fixed to, a wall., (d) An athlete making a high jump to clear the bar at a certain height, Answer:, a) We make a muscular force to extract the juice of the lemon by squeezing it. As, a result, the shape of the lemon gets changed., b) To take out paste from the toothpaste tube we use our muscular force. This, muscular force acting on the toothpaste tube leads to a change of its shape., c) Here, the suspended load exerts a force on the spring and pushes the spring, downwards. As a result, the spring gets stretched. Hence, its shape gets changed., d) The feet of the athlete exert the muscular force on the ground, which pushes, the ground. This allows him to jump over the bar. As a result, his state of motion, gets changed., 6. A blacksmith hammers a hot piece of iron while making a tool. How does, the force due to hammering affect the piece of iron?

Page 49 : Answer: A blacksmith uses his muscular force while hammering a hot piece of, iron. The muscular force changes the shape of the iron so that it can be given the, desired shape., 7. An inflated balloon was pressed against a wall after it has been rubbed, with a piece of synthetic cloth. It was found that the balloon sticks to the wall., What force might be responsible for the attraction between the balloon and, the wall?, Answer: When an inflated balloon rubbed with a piece of synthetic cloth, it, becomes charged. A charged body attracts an uncharged body. When this charged, balloon is pressed against a wall, it sticks to the wall. Thus, the electrostatic force, acts between the charged balloon and the wall., 8. Name the forces acting on a plastic bucket containing water held above, ground level in your hand. Discuss why the forces acting on the bucket do, not bring a change in its state of motion., Answer: For holding the bucket of water above the ground, we use muscular, force. This muscular force acts against the force of gravity that pulls the bucket, towards the ground. The two forces are equal in magnitude but opposite in, direction. Therefore, the net force on the bucket is zero. Hence, there is no change, in the state of motion., 9. A rocket has been fired upwards to launch a satellite in its orbit. Name the, two forces acting on the rocket immediately after leaving the launching pad., Answer: The force of gravity is the one which acts on the rocket to pull it towards, the ground and the other one is the force of friction due to earth’s atmosphere,, which opposes its motion., 10. When we press the bulb of a dropper with its nozzle kept in water, air in, the dropper is seen to escape in the form of bubbles. Once we release the, pressure on the bulb, water gets filled in the dropper. The rise of water in, the dropper is due to, (a) pressure of water., (b) gravity of the earth., (c) shape of rubber bulb., (d) atmospheric pressure

Page 50 : Answer:, a) Due to the atmospheric pressure, there is a rise of water in the dropper., When all the air escapes from the nozzle, the atmospheric pressure which is acting, on the water forces the water to fill the nozzle of the dropper.

Page 51 : NCERT Exemplar, Multiple Choice Questions, 1. In Fig 11.1, two boys A and B are shown applying force on a block. If the, block moves towards the right, which one of the following statements is, correct?, (a) The magnitude of force applied by A is greater than that of B., (b) The magnitude of force applied by A is smaller than that of B., (c) The net force on the block is towards A., (d) The magnitude of force applied by A is equal to that of B., , Answer: (a) Magnitude of force applied by A is greater than that of B., 2. In the circuit shown in Fig.11.2, when the circuit is completed, the hammer, strikes the gong. Which of the following force is responsible for the, movement of the hammer?, (a) gravitational force alone, (b) electrostatic force alone, (c) magnetic force alone, (d) frictional force alone, Answer: (c) magnetic force alone, 3. During dry weather, while combing hair,, sometimes we experience hair flying apart. The, force responsible for this is, (a) force of gravity., (b) electrostatic force., (c) the force of friction., (d) magnetic force., Answer: (b) electrostatic force., 4. Fig.11.3 shows a container filled with water. Which of the following, statements is correct about the pressure of water?

Page 52 : (a) The pressure at A > Pressure at B > Pressure at C., (b) The pressure at A = Pressure at B = Pressure at C., (c) The pressure at A < Pressure at B > Pressure at C., (d) The pressure at A < Pressure at B., Answer: (d) Pressure at A < Pressure at B, 5. Two objects repel each other. This repulsion could be, due to, (a) frictional force only, (b) electrostatic force only, (c) magnetic force only, (d) either a magnetic or an electrostatic force, Answer: (d) either a magnetic or an electrostatic force, 6. Which one of the following forces is a contact force?, (a) force of gravity, (b) force of friction, (c) magnetic force, (d) electrostatic force, Answer: (b) force of friction, 7. A water tank has four taps fixed at points A, B, C, D as shown in Fig. 11.4., The water will flow out at the same pressure from taps at, (a) B and C, (b) A and B, (c) C and D, (d) A and C, Answer: (a) B and C, 8. A brick is kept in three different ways on a, table as shown in Fig. 11.5. The pressure, exerted by the brick on the table will be, (a) maximum in position A-C, (b) maximum in position B, (c) maximum in position, (d) equal in all cases., Answer: (a) maximum in position A-C, , Very Short Answer Questions, 9. A ball of dough is rolled into a flat chapatti. Name the force exerted to, change the shape of the dough., Answer: Muscular Force., 10. Where do we apply a force while walking?, Answer: While walking we apply force on the ground., 11. A girl is pushing a box towards the east direction. In which direction, should her friend push the box so that it moves faster in the same direction?, Answer: Towards the east.

Page 53 : 12., In the circuit shown in Fig.11.6, when the key is closed, the compass, needle placed in the matchbox deflects. Name the force which causes this, deflection., , Answer: Answer is Magnetic force., 13. During dry weather, clothes made of synthetic fibre often stick to the, skin. Which type of force is responsible for this phenomenon?, Answer: Answer is Electrostatic force, 14. While sieving grains, small pieces fall down. Which force pulls them, down?, Answer: Force of gravity., 15. Does the force of gravity act on dust particles?, Answer: Yes, the force of gravity act on dust particles., 16. A gas-filled balloon moves up. Is the upward force acting on it larger or, smaller than the force of gravity?, Answer: The upward force is larger than the force of gravity., 17. Does the force of gravitation exist between two astronauts in space?, Answer: Yes, the force of gravitation exists between two astronauts in space., , Short Answer Questions, 18. A chapati maker is a machine which converts balls of dough into chapati., What effect of force comes into play in this process?, Answer: Force works on the dough to convert it to chapati., 19. Fig.11.7 shows a man with a parachute. Name the force, which is responsible for his downward motion. Will he come, down with the same speed without the parachute?, Answer: Force of gravity is responsible for his downward, motion. If he comes down without parachute his speed will be, higher.

Page 54 : 20. Two persons are applying forces on two opposite sides of a moving cart., The cart still moves with the same speed in the same direction. What do you, infer about the magnitudes and direction of the forces applied?, Answer: Force applied is of equal magnitude in the opposite direction hence the, cart moves with the same speed in the same direction., 21. Two Thermocol balls held close to each other move away from each, other. When they are released, name the force which might be responsible, for this phenomenon. Explain., Answer: Two Thermocol balls held close to each other move away from each, other, which is because of electrostatic force. The balls having similar charges, move away due to repulsion between similar charges., 22. Fruits detached from a tree fall down due to force of gravity. We know, that a force arises due to the interaction between two objects. Name the, objects interacting in this case., Answer: Earth and fruits., 23. A man is pushing a cart down a slope. Suddenly the cart starts moving, faster and he wants to slow it down. What should he do?, Answer: He should apply a force to pull the cart up the slope., 24. Fig. 11.8 shows a car sticking to an electromagnet. Name the forces acting, on the car? Which one of them is larger?, , Answer: Magnetic force (in the upward direction) force of gravity or the weight, of the car (downward) act on car. Magnetic force is larger than the force of, gravity., , Long Answer Questions, 25. An archer shoots an arrow in the air horizontally. However, after moving, some distance, the arrow falls to the ground. Name the initial force that sets, the arrow in motion. Explain why the arrow ultimately falls down., Answer: Archer puts muscular force to stretch the string. This will change the, shape of the arrow. When the string is released, arrow regains its original position, which gives it the initial force to set the motion. Because of gravitational from it, comes down towards after some time.

Page 55 : 26. It is difficult to cut cloth using a pair of scissors with blunt blades., Explain., Answer: The blunt blade has a larger area than shard edged blades. Because of, this, blunt blade produces a low pressure which makes it difficult to cut the cloth., Whereas in sharp blade surface area is much is very less which increase the, pressure produced. This makes the cutting of cloth easier with sharp blades., 27. Two rods of the same weight and equal length have different thickness., They are held vertically on the surface of sand as shown in Fig.11.9. Which, one of them will sink move? Why?, , Answer: In Rod B area of contact is smaller. Hence the weight of the rod (Force), produces more pressure. In Case of the rod, the same force produces less pressure., 28. Two women are of the same weight. One wears sandals with pointed heels, while the other wears sandals with flat soles. Which one would feel more, comfortable while walking on a sandy beach? Give reasons for your answer., Answer: Women’s height are same and they apply the same weight when they, walk. But women wearing sandal with a flat heel will be more comfortable while, walking on a sandy beach. This is because flat soles have larger area compared, to the sandals with pointed heels. Also, the pressure exerted by the pointed heels, will be more compared to that with sandals having flat soles. This pressure will, make the sandals with pointed soled sink in the sand which will make difficult to, walk on sand., 29. It is much easier to burst an inflated balloon with a needle than by a, finger. Explain., Answer: The pressure exerted on an inflated balloon by the needle will be more, as it has a smaller area of contact compared to the finger. This larger pressure, pierces the surface of the balloon easily which will make the balloon burst., 30. Observe the vessels A, B, C and D shown in Fig.11.10 carefully.

Page 56 : The volume of water taken in each vessel is as shown. Arrange them in the order, of decreasing pressure at the base of each vessel. Explain., Answer: B, D, A, C. Because the pressure of a liquid column depends upon the, height of the liquid column and not on volume of the liquid.

Page 57 : Chapter 8 Friction, Exercise Questions, 1. Fill in the blanks., (a) Friction opposes the motion between the surfaces in contact with each other., (b) Friction depends on the nature of surfaces., (c) Friction produces heat., (d) Sprinkling of powder on the carrom board reduces friction., (e) Sliding friction is lesser than the static friction., 2. Four children were asked to arrange forces due to rolling, static and, sliding frictions in a decreasing order. Their arrangements are given below., Choose the correct arrangement., (a) rolling, static, sliding, (b) rolling, sliding, static, (c) static, sliding, rolling, (d) sliding, static, rolling, Answer: (c) static, sliding, rolling, 3. Alida runs her toy car on dry marble floor, wet marble floor, newspaper, and towel spread on the floor. The force of friction acting on the car on, different surfaces in increasing order will be, (a) wet marble floor, dry marble floor, newspaper and towel., (b) newspaper, towel, dry marble floor, wet marble floor., (c) towel, newspaper, dry marble floor, wet marble floor., (d) wet marble floor, dry marble floor, towel, newspaper, Answer: (a) wet marble floor, dry marble floor, newspaper and towel., 4. Suppose your writing desk is tilted a little. A book kept on it starts sliding, down. Show the direction of frictional force acting on it., Answer: When book slides down on the desk, a frictional force acts between the, book and the surface of the desk. The direction of the friction force on the book, is opposite to the direction of its motion and acts in an upward direction. It is, shown in the diagram below., , 5. You spill a bucket of soapy water on a marble floor accidently. Would it, make it easier or more difficult for you to walk on the floor? Why?, Answer: It is possible to walk on the floor because of the friction present between, our feet and the ground. For walking, we push the ground in a backward direction

Page 58 : with our feet. The force of friction pushes it in the forward direction and allows, us to walk. The force of friction decreases between the ground and the feet when, there is soapy water spilt on the floor. Hence, it becomes difficult to walk on the, soapy floor., 6. Explain why sportsmen use shoes with spikes., Answer: Sportsmen use shoes with spikes because of the better grip given by, spikes while running. This is because the force of friction between the shoes and, the ground increases with the help of spikes., 7. Iqbal has to push a lighter box and Seema has to push a similar heavier, box on the same floor. Who will have to apply a larger force and why?, Answer: Due to the interlocking of the irregularities on the two surfaces in, contact, the force of friction arises. On the floor when a heavy object is placed,, the interlocking of irregularities on the surface of the box and floor become, strong. This is because the two surfaces in contact are pressed harder. Hence,, more force is required to overcome the interlocking. Thus, to push the heavier, box, Seema has to apply greater force than Iqbal., 8. Explain why sliding friction is less than static friction, Answer: When irregularities present in the surfaces of two objects in contact get, interlocked with each other, friction come into play. The time given in sliding, for interlocking is very small. Thus, interlocking is not strong. Therefore, less, force is required to overcome this interlocking. Due to this reason, sliding friction, is less than static friction., 9. Give examples to show that friction is both a friend and a foe., Answer:, Advantages of the friction, a) Due to friction, we are able to walk., b) We are able to write because of the friction between the tip of the pen and, paper., Disadvantages of friction, a) Because of friction, the tires and soles of shoes wear out., b) Friction produces heat between different parts of the machines. This can, damage the machines., 10. Explain why objects moving in fluids must have special shapes., Answer: When a body moves through a fluid, it experiences an opposing force, which tries to oppose its motion through the fluid. This opposing force is known, as the drag force. This frictional force depends on the shape of the body. By, giving the objects a special shape, the force of friction acting on it can be, minimized. Hence, it becomes easier for a body to move through the fluid.

Page 59 : NCERT Exemplar, Multiple Choice Questions, 1. Whenever the surfaces in contact tend to move or move with respect to, each other, the force of friction comes into play, (a) only if the objects are solid., (b) only if one of the two objects is liquid., (c) only if one of the two objects is gaseous., (d) irrespective of whether the objects are solid, liquid or gaseous., Answer: (d) irrespective of whether the objects are solid, liquid or gaseous., 2. In Fig.12.1, a boy is shown pushing the box from right to left. The force of, friction will act on the box, (a) from right to left (←), (b) from left to right (→), (c) vertically downwards (↓), (d) vertically upwards (↑), Answer: (b) from left to right (→), 3. To sharpen the blade of a knife by rubbing, it against a surface, which of the following will, be most suitable?, (a) stone, (b) plastic block, (c) wooden block, (d) glass block, Answer: (a) stone, 4. A toy car released with the same initial speed will travel farthest on, (a) muddy surface, (b) polished marble surface, (c) cemented surface, (d) brick surface, Answer: (b) polished marble surface, 5. If we apply oil on door hinges, the friction will, (a) increases, (b) decreases, (c) disappear altogether, (d) will remain unchanged, Answer: (b) decreases, 6. Which of the following statements is incorrect?, (a) Friction acts on a ball rolling along the ground., (b) Friction acts on a boat moving on water., (c) Friction acts on a bicycle moving on a smooth road., (d) Friction does not act on a ball moving through air., Answer: (d) Friction does not act on a ball moving through air.

Page 60 : 7. A boy rolls a rubber ball on a wooden surface. The ball travels a short, distance before coming to rest. To make the same ball travel longer distance, before coming to rest, he may, (a) spread a carpet on the wooden surface., (b) cover the ball with a piece of cloth., (c) sprinkle talcum powder on the wooden surface., (d) sprinkle sand on the wooden surface, Answer: (c) sprinkle talcum powder on the wooden surface., 8. In a large commercial complex, there are four ways to reach the main, road. One of the paths has loose soil, the second is laid with polished marble,, the third is laid with bricks and the fourth has a gravel surface. It is raining, heavily and Paheli wishes to reach the main road. The path on which she is, least likely to slip is, (a) loose soil., (b) polished marble., (c) bricks., (d) gravel., Answer: (d) gravel., , Very Short Answer Questions, 9. Two blocks of iron of different masses are kept on a cemented floor as, shown in Fig.12.2. Which one of them would require a larger force to move, it from the rest position?, , Answer: The larger force will be required to move the heavier block., 10. Will force of friction come into play when a raindrop rolls down a glass, window pane?, Answer: Yes, force of friction comes into play when a raindrop rolls down a glass, window pane., 11. Two boys are riding their bicycles on the same concrete road. One has, new tyres on his bicycle while the other has tyres that are old and used., Which of them is more likely to skid while moving through a patch of the, road which has lubricating oil spilt over it?, Answer: The bicycle with worn-out tyres is more likely to skid., 12. Fig.12.3 shows two boys applying force on a box. If the magnitude of the, force applied by each is equal, will the box experience any force of friction?

Page 61 : Answer: Force of friction will be zero as the net force on the box is zero., 13. Imagine that an object is falling through a long straight glass tube held, vertical; the air has been removed completely from the tube. The object does, not touch the walls of the tube. Will the object experience any force of, friction?, Answer: No, the object will not experience any force of friction., , Short Answer Questions, 14. You might have noticed that when used for a long time, slippers with, rubber soles become slippery. Explain the reason., Answer: After using slippers for a long time, soles become smooth. This, decreases the friction between the sole and floor. Therefore, slippers become, slippery., 15. Is there a force of friction between the wheels of a moving train and iron, rails? If yes, name the type of friction. If an air cushion can be introduced, between the wheel and the rail, what effect will it have on the friction?, Answer: Yes, there exists a rolling force between the wheels of a moving train, and iron rails. If an air cushion is introduced between the wheel and the rails, the, friction will decrease., 16. Cartilage is present in the joints of our body, which helps in their smooth, movement. With advancing age, this cartilage wears off. How would this, affect the movement of joints?, Answer: With advancing age, this cartilage wears off. This increases the friction,, which will lead to difficulty in movement and will cause joint pain., 17. While playing tug of war (Fig.12.4), Preeti felt that the rope was slipping, through her hands. Suggest a way out for her to prevent this.

Page 62 : Answer: She may rub soil to increase friction between the rope and her hand., 18. The handle of a cricket bat or a badminton racquet is usually rough., Explain the reason., Answer: To have a better grip on the bat it should be rough because rough surface, decreases the friction and allow to have a firm grip on the bat., 19. Explain why the surface of mortar and pestle (silbatta) used for grinding, is etched again after prolonged use?, Answer: To increase friction to make it more effective for grinding again., 20. A marble is allowed to roll down an inclined plane from a fixed height., At the foot of the inclined plane, it moves on a horizontal surface (a) covered, with silk cloth (b) covered with a layer of sand and (c) covered with a glass, sheet. On which surface will the marble move the shortest distance. Give the, reason for your answer., Answer: A marble moves to the shortest distance on the floor covered with sand, as it offers maximum friction against its motion., 21. A father and son pushed their car to bring it to the side of the road as it, had stalled in the middle of the road. They experienced that although they, had to push with all their might initially to move the car, the push required, to keep the car rolling was smaller, once the car started rolling. Explain., Answer: Because initially they had to apply force to set the card in motion but, once the car started rolling, they had to apply force only to balance rolling friction, of the car, the value of which is very less., Long Answer Questions, 22. When the cutting edge of a knife is put against a fast rotating stone to, sharpen it, sparks are seen to fly. Explain the reason., Answer: Heat is produced as a result of friction between a knife and the rotating, stone. As the speed of rotation increases the amount of heat generated also, increases which result in the sparks., 23. We have two identical metal sheets. One of them is rubbed with, sandpaper and the other with ordinary paper. The one rubbed with, sandpaper shines more than the other. Give reason.

Page 63 : Answer: Friction between plane paper and the metal sheet is less compared to, the friction between sandpaper and metal. This friction acts on the top layer of, metal sheet which will remove the top layer to make the metal shine., 24. While travelling on a rickshaw, you might have experienced that if the, seat cover is very smooth, you tend to slip when brakes are applied suddenly., Explain., Answer: If the seat cover is very smooth then the friction between the seat and, our body is very less. Because of this, we tend to slip when brakes are applied in, a rickshaw., 25. Two friends are trying to push a heavy load as shown in Fig.12.5. Suggest, a way which will make this task easier for them., , Answer: Their work can be made easy by putting rollers below the heavy load, because the rolling friction is smaller than the sliding friction., , CHAPTER 9: SOUND, Exercise Questions, 1. Choose the correct answer., 1. Sound can travel through, (a) gases only, (b) solids only, (c) liquids only, (d) solids, liquids and gases, Answer: (d) solids, liquids and gases, 2. Voice of which of the following is likely to have a minimum frequency?, (a) Baby girl, (b) Baby boy, (c) A man, (d) A woman, Answer: (c) A man, 3. In the following statements, tick ‘T’ against those which are true, and ‘F’, against those which are false., (a) Sound cannot travel in vacuum. (T/F)

Page 64 : (b) The number of oscillations per second of a vibrating object is called its, time period. (T/F), (c) If the amplitude of vibration is large, sound is feeble. (T/F), (d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F), (e) The lower the frequency of vibration, the higher is the pitch. (T/F), (f) Unwanted or unpleasant sound is termed as music. (T/F), (g) Noise pollution may cause partial hearing impairment. (T/F), Answer:, a) True- A medium is required for sound to travel, b) False- A vibrating object whose number of oscillations per second is known as, its frequency. The time taken to complete one oscillation is called a time period., c) False- The Square of the amplitude of vibration is proportional to the loudness, of sound. Sound is loud when the amplitude of vibration is large. For feeble, sound, the amplitude is small., d) True- Sounds of all frequencies are not audible to human ears. The range of, frequencies which are audible to human ears is between 20 Hz and 20,000 Hz., Sounds outside these frequencies are not audible to human ears., e) False- Higher the frequency, higher is the pitch of the sound as the pitch is, proportional to its frequency. For high pitched sound, its vibrating frequency is, high and for low pitched sound, its vibrating frequency is small., f) False- Music is a melodious and pleasing sound which is pleasant to hear., Noises are unpleasant sounds., g) True-Noises are unwanted and unpleasant sounds, which cause temporary, hearing impairment when heard continuously for a long period of time., 4. Fill in the blanks with suitable words., (a) Time taken by an object to complete one oscillation is called time period., (b) Loudness is determined by the amplitude of vibration., (c) The unit of frequency is Hertz., (d) Unwanted sound is called Noise., (e) The shrillness of a sound is determined by the frequency of vibration., 5. A pendulum oscillates 40 times in 4 seconds. Find its time period and, frequency, Answer: The number of oscillations per second of the vibrating body is known, as the frequency of oscillation., Frequency = Total number of oscillations, Total time taken, = 50/5, = 10 Hz, Time period is the time taken to complete one oscillation. It is also the inverse of, frequency., Time period = 1/ Oscillating frequency, = 1/10, = 0.1 s

Page 65 : ∴ frequency = 10 Hz, Time period = 0.1 s, 6. The sound from a mosquito is produced when it vibrates its wings at an, average rate of 500 vibrations per second. What is the time period of the, vibration?, Answer: Time period is defined as the time taken to complete one oscillation. It, is also the inverse of frequency., Time period = 1, Oscillation frequency, Oscillation frequency = 500 Hz, Time period = 1/500 = 0.002 s, 7. Identify the part which vibrates to produce sound in the following, instruments., (a) Dholak, (b) Sitar, (c) Flute, Answer:, a) Dholak- It consists of a head which is a stretched membrane. Vibrations are set, into these stretched strings when the head is beaten gently, these vibrations, produce sound and thus Dholak produces sound., b) Sitar – It is a musical instrument. Stretched strings are part of it. Vibrations are, produced when the string is plucked when played. These vibrations produce, sound, thus sitar produces sound., c) Flute – It’s an instrument which has holes in it. It is a hollow pipe. The air, inside the pipe is set into vibration when air is blown over its mouth and this, produces a pleasant sound., 8. What is the difference between noise and music? Can music become noise, sometimes?, Answer: Music is sound which is pleasant to hear. Sounds from flutes, pianos, and violins are pleasant to hear., Noise are sounds which are unpleasant to hear., Sounds which are unpleasant to hear are:, (a)Sounds from bus horns and truck horns., (b)Electrical generator sounds., (c)Gunshot sounds., (d)Jackhammer sounds, Yes, sometimes when the music is played at high volumes, it becomes noise., 9. List sources of noise pollution in your surroundings., Answer: Noise pollution sources are, (a) Bus and car horns., (b) Firecrackers and loudspeakers., (c) High volumes in televisions and transistors., (d) mixers at home

Page 66 : e) Sirens from factories, 10. Explain in what way noise pollution is harmful to human., Answer: A number of health issues are associated with noise pollution. They are, as follows, (a) Stress, (b) Headache, (c) Hearing loss, (d) Insomnia, (e) Hypertension, 11. Your parents are going to buy a house. They have been offered one on, the roadside and another three lanes away from the roadside. Which house, would you suggest your parents should buy? Explain your answer., Answer: It is better to buy the house which is three lanes away from the roadside, as there will be less noise as compared to the one on the main road. The noises, can be caused by vehicles. As the distance between the source and the listener, increases, the intensity of noise decreases. So it’s better to buy the house which, is three lanes away., 12. Sketch larynx and explain its function in your own words., Answer:, When we swallow something, the larynx, moves. There are two vocal cords inside the larynx., The air passes through a small gap which is present, in between them. The lungs force the air into the gap, when we speak and this vibrates the vocal cord, due, to which sound is produced., 13. Lightning and thunder take place in the sky at the same time and at the, same distance from us. Lightning is seen earlier and thunder is heard later., Can you explain why?, Answer: Speed of the light is more than the speed of sound. Thus, lightning is, seen first which is accompanied by thunder later.

Page 67 : NCERT Exemplar, Multiple Choice Questions, 1. A list of mediums is given below., (i) wood, (ii) water, (iii) air, (iv) vacuum, In which of these mediums can sound travel?, (a) i & ii only, (b) i, ii & iii only, (c) iii & iv only, (d) ii, iii & iv only, Answer: (b) i, ii & iii only, 2. The loudness of a sound depends on:, (a) its amplitude., (b) its frequency., (c) its time period., (d) its speed., Answer: (a) its amplitude., 3. Which of the following statements are correct?, (i) Sound is produced by vibrations., (ii) Sound requires a medium for propagation., (iii) Light and sound both require a medium for propagation., (iv) Sound travels slower than light., (a) i & ii only, (b) i, ii & iii only, (c) ii, iii & iv only, (d) i, ii & iv only, Answer: (d) i, ii & iv only, 4. An object is vibrating at 50 hertz. What is its time period?, (a) 0.02 s, (b) 2 s, (c) 0.2 s, (d) 20.0 s, Answer:, Answer is (a) 0.02 s, 5. In order to reduce the loudness of a sound, we have to, (a) decrease its frequency of vibration of the sound., (b) increase its frequency of vibration of the sound., (c) decrease its amplitude of vibration of the sound.

Page 68 : (d) increase its amplitude of vibration of the sound., Answer: (c) decrease its amplitude of vibration of the sound., 6. The loudness of sound is measured in units of, (a) Decibel (dB), (b) Hertz (Hz), (c) Metre (m), (d) Metre/Second (m/s), Answer: (a) Decibel (dB), 7. The loudness of sound is determined by the, (a) amplitude of vibration, (b) the ratio of amplitude and frequency of vibration, (c) frequency of vibration, (d) product of amplitude and frequency of vibration, Answer: (a) amplitude of vibration, 8. 1 hertz is equal to, (a) 1 vibration per minute, (b) 10 vibrations per minute, (c) 60 vibrations per minute, (d) 600 vibrations per minute, Answer: (c) 60 vibrations per minute, 9. Pitch of sound is determined by its, (a) frequency, (b) amplitude, (c) speed, (d) loudness, Answer: (a) frequency, 10. Ultrasound has a frequency of vibration, (a) between 20 and 20,000 Hz, (b) below 20 Hz, (c) above 20,000 Hz, (d) between 500 and 10,000 Hz, Answer: (c) above 20,000 Hz, , Very Short Answer Questions, 11. Lightning can be seen as the moment it occurs. Paheli observes lightning in, her area. She hears the sound 5 s after she observed lightning. How far is she from, the place where lightning occurs? (speed of sound = 330 m/s)., Answer:, Distance=330ms x 5s, =1650m, 12. Does any part of our body vibrate when we speak? Name the part.

Page 69 : Answer: Larynx or vocal cords vibrate when we speak., 13. Boojho saw a cracker burst at night at a distance from his house. He heard the, sound of the cracker a little later after seeing the cracker burst. Give the reason, for the delay in hearing the sound., Answer: Speed of light is faster than the speed of sound, hence Boojho heard the, sound of the cracker a little later after seeing the cracker burst., 14. When we hear a sound, does any part of our body vibrate? Name the part., Answer: When we hear a sound our eardrum vibrates., 15. Name two musical instruments which produce sound by vibrating strings?, Answer: Sitar and Veena, , Short Answer Questions, 16. A simple pendulum makes 10 oscillations in 20 seconds. What is the time, period and frequency of its oscillation?, Answer:, Time period: 2 s, frequency : 0.5 oscillations/sec, Explanation:, A pendulum makes 10 oscillations in 20 seconds., So it makes 1 oscillation in 2010, sec = 2sec, Time period=2 sec, Frequency= 1t, = 12, = 0.5 Hz, 17. We have learnt that vibration is necessary for producing sound. Explain why, the sound produced by every vibrating body cannot be heard by us?, Answer: Everybody has its own range of frequency. But we can only hear, frequencies in the range of 20hz to 2000 Hz so we cannot hear the sound of a few, vibrating bodies., 18. Suppose a stick is struck against a frying pan in a vacuum. Will the frying pan, vibrate? Will we be able to hear the sound? Explain., Answer: The frying pan will vibrate. We will not be able to hear the sound of, vibration because sound cannot travel in a vacuum., 19. Two astronauts are floating close to each other in space. Can they talk to each, other without using any special device? Give reasons., Answer: In space there will be no medium for sound waves to travel and it will, be the vacuum. Sound cannot travel in vacuum hence sound cannot be heard, without any special device., 20. List three sources of noise pollution in your locality., Answer: Industrial sirens, Vehicle honking and bursting crackers.

Page 70 : Long Answer Questions, 21. We have a stringed musical instrument. The string is plucked in the middle, first with a force of greater magnitude and then with a force of smaller magnitude., In which case would the instrument produce a louder sound?, Answer: The amplitude of vibration determines the loudness of the sound. When, a string is plucked with greater force amplitude of string will be larger. This, makes the sound louder., 22. How is the sound produced and how is it transmitted and heard by us?, Answer: Sound is produced when the body starts vibrating by any force. This, vibration produces waves which travel through a medium to reach the destination, (Our ear) where it will be heard., We hear the sound by our ears. The shape of the outer part of the ear is like a, funnel. When sound enters it, it travels down a canal at the end of which there is, a thin stretched membrane. It is called the eardrum. The eardrum is like a, stretched rubber sheet. Sound vibrations make the eardrum vibrate. The eardrum, sends vibrations to the inner ear. From there, the signal goes to the brain. That is, how we hear., 23. An alarm bell is kept inside a vessel as shown in Fig. 13.1. A person standing, close to it can distinctly hear the sound of the alarm. Now if the air inside the, vessel is removed completely how will the loudness of alarm get affected for the, same person?, , Answer: Air needs a medium to get transmitted. If we slowly remove the air, inside the bottle. Sound will not be having medium to travel as it will be the, vacuum. Due to vacuum loudness of the sound decrease gradually with the, quantity of the air in the bottle., 24. The town hall building is situated close to Boojho’s house. There is a clock, on the top of the town hall building which rings the bell every hour. Boojho has, noticed that the sound of the clock appears to be much clearer at night. Explain., Answer: When sound is initiated speed, pitch, loudness all are initiated with, vibration. During the day time there is a number of vibrations around us. This, results in a decrease of the amplitude of vibrations. During the night there will be, no such disturbances which will make the sound clearer.

Page 71 : 25. Suggest three measures to limit noise pollution in your locality., Answer:, i) Trees must be planted along the roads and around the buildings., ii) Use of horns should be minimised., iii) Silencers must be installed in transport vehicles and industrial machines.