8 cbSe

Science (Based on NCERT Textbook)

Dheeraj Sexena M.Sc (Botany)

Full Marks Pvt Ltd (Progressive Educational Publishers)

New Delhi-110002

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Note from the Publishers FULL MARKS SCIENCE-8 has been thoroughly revised in view of the recent Examination Reforms propounded by the CBSE. The revised edition of this book is a complete support book based on NCERT text book. This provides all sorts of study-cum practice material and thus builds up strong confidence in the learner. It is an up-to-date, dependable and learner-friendly resource as per the guidelines of CBSE. Salient features of the book:  Chapterwise important points have been given under the heading Facts that Matter.  All NCERT textual questions have been solved.  Plenty of additional questions including Objective Type Questions and Assertion and Reason Type Questions have been given with answers.  At the end of every chapter some questions have been given under the heading Test Your Skills to test the students what they have learnt. The support website www.fullmarks.org is an added benefit for the users where one can get much more and also an opportunity to share one’s academic complexities.

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CONTENTS 1. Crop Production and Management ..................................................................................

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2. Microorganisms: Friend and Foe ..................................................................................... 25 3. Synthetic Fibres and Plastics .......................................................................................... 42 4. Materials: Metals and Non-Metals .................................................................................. 56 5. Coal and Petroleum .......................................................................................................... 71 6. Combustion and Flame .................................................................................................... 81 7. Conservation of Plants and Animals ............................................................................... 95 8. Cell—Structure and Functions ........................................................................................ 109 9. Reproduction in Animals .................................................................................................. 125 10. Reaching the Age of Adolescence ..................................................................................... 142 11. Force and Pressure ........................................................................................................... 160 12. Friction .............................................................................................................................. 176 13. Sound ................................................................................................................................. 190 14. Chemical Effects of Electric Current ............................................................................... 205 15. Some Natural Phenomena ............................................................................................... 219 16. Light ................................................................................................................................. 235 17. Stars and the Solar System.............................................................................................. 251 18. Pollution of Air and Water ............................................................................................... 269 • Chapterwise Additional Assertion and Reason Type Questions .................... 281

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Crop Production and Management

Facts that Matter

• Agriculture: The applied branch of biology which deals with cultivation of plants and rearing of animals is called agriculture. Generally, the art or practice of cultivating land is referred as agriculture. The branch of agriculture which deals with food, health and management of animals is known as animal husbandry. • Crop: When plants of the same kind are cultivated at one place on a large scale, it is called as a crop. • Crops are classified on the basis of the seasons as given below:  Kharif Crops: The crops which are grown during the monsoon (rainy) season (June‑September) are called kharif crops. For example, maize, millet (bajra) and cotton crops. Seeds of these crops are sown in the beginning of the monsoon season. After maturation, these crops are harvested at the end of the monsoon season (Oct.‑Nov.).  Rabi Crops: Crops which are grown during the winter season (October‑March) are called rabi crops. For example, wheat, gram and mustard. Seeds of these crops are sown in the beginning of the winter season. After maturation of crops, they are harvested at the end of the winter season (April‑May). • Agricultural Practices: All activities which farmers do for the cultivation of plants are called agricultural practices. For doing various activities, a farmer needs different types of tools. These tools which are involved in cultivation of plants are called agricultural implements. Farmers perform agricultural practices in a sequence. • Various Agricultural Practices: (i) Preparation of soil (ii) Sowing (iii) Adding manure and fertilisers (iv) Irrigation (v) Protection from weeds (vi) Harvesting (vii) Storage • Agricultural Implements:  Plough  Hoe  Cultivator  Seed drill • Implements used for traditional ways of irrigation:  (a) Moat (b) Dhekli (c) Rahat (d) Chain pump and (e) Motor pumps • Basic Practices of Crop Production (i) Preparation of Soil: Before sowing the crop seeds, the soil of fields is loosened and overturned. This process is called ploughing or tilling. Ploughing causes ventilation of soil and makes it suitable for the growth of small organisms living in it.  Plough: A large farming implement with one or more blades fixed in a frame, used to

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turn over and cut furrows in soil, is called plough. Plough may be made of only wood, Only iron or a combination of wood and iron (Fig. 1.1).  Ploughshare: The main cutting blade of a plough.

Fig. 1.1 A plough.

 Hoe: A tool which is used for removing weeds and for loosening the soil.  Cultivator: Nowadays, ploughing is done through tractor driven cultivator. The use of cultivator saves labour and time (Fig. 1.2).

Fig. 1.2 Cultivator driven by a tractor.

(ii) Sowing of Seeds: For sowing, farmers obtain certified seeds from State Agriculture Department and Seed Corporation. Sometimes, farmers also select seeds from their own crop. For selection of seeds of most of the crops, seeds are put into a bucket of water. The seeds which float on water are rejected. These seeds are defective. The seeds which remain submerged in water are selected for sowing. The selected seeds are treated with chemicals such as agrosan or ceresan. This chemical treatment protects seedling from seed‑borne diseases. Seeds are sown either by handbroadcasting (spreading) or by using Fig. 1.3 Seed drill. seed drills (Fig. 1.3). Most commonly used seed drill is a long iron pipe 8

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having a funnel at the top. It is tied at the back of the plough [Fig. 1.4(a)]. A farmer does ploughing and simultaneously releases seeds from the funnel. Seeds thus released pass through iron pipe to the soil furrows which are formed by the plough.

Fig. 1.4(a) Sowing of seed: Simple method.

Fig. 1.4(b) Bullock-drawn big seed drill.

(iii) Adding Manure and Fertilisers: Like other plants, crop plants also obtain their mineral nutrients from the soil. Continuously cultivation of crops in a field causes deficiency of mineral nutrients in the soil. So, manure is added to the soil to make up for the deficiency of mineral nutrients. This process is called manuring. Manure is prepared from cow dung, urine and other wastes. Sometimes, soil becomes deficient in a particular mineral nutrient. It happens when same crop is grown in the same field, year after year. For example, that particular crop takes more phosphate, is grown in a field every year, the soil will become deficient in phosphorus nutrient. This type of deficiency of a particular nutrient is made up by adding chemical substances called fertilisers. For example: urea, super phosphate and NPK (Nitrogen, Phosphorus, Potassium). (iv) Irrigation: The supply of water to crops at regular intervals is called irrigation. The time and frequency of irrigation varies from crop to crop, soil to soil and season to season. Methods of Irrigation  Traditional methods: — Moat (pulley‑system) — Chain pump — Dhekli — Rahat  Modern methods: — Sprinkler system — Drip system (v) Protection from Weeds The unwanted plants in the fields are called weeds. Seeds of these weeds spread through the agencies like air, water, birds and other animals. Weeds share water, sunlight, space, nutrients with the crop plants. They compete with the crop plants and therefore, their removal is necessary. Otherwise, crop plants do not get sufficient space, water, sunlight and nutrient to grow. Weeds are removed out either by hand or with the help of an implement called harrow. Nowadays, certain chemicals are used to check the growth of crops. These chemicals are called weedicides, such as 2, 4‑D. (vi) Harvesting and Threshing: When crops get matured, they usually turn yellow, golden or brown. This is the time when crops should be cut. Cutting of crops when they mature, is known harvesting. Harvesting is either done manually by a sickle or through a machine called harvester. Harvested crops are further dried and then animals such as bullocks,

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buffaloes, camels are made to walk over them. The grains are separated from chaff with the help of wind (winnowing) (Fig. 1.6). The whole process of separation of the grains seeds from the chaff is known as threshing.

Fig. 1.5 Sickle—simple tool used for harvesting.

Fig. 1.6 Winnowing—separation of grains from chaff with the help of wind.

Big farmers use huge machines known as combine which can do both harvesting and threshing.  Special festivals associated with crop harvesting seasons are: Pongal, Baisakhi, Holi, Diwali, Nabanya and Bihu. (vii) Storage: Harvested grains obtained by threshing are dried in open. These dried grains are stored in gunny bags, and placed in properly ventilated cemented halls, known as godowns. Farmers keep dried grains in jute bags or metallic bins or mud bins. Large scale storage of grains is done in silos (Fig. 1.7) and granaries (Fig. 1.8). For storing large quantities of grains in big godowns, specific chemical treatment is used to protect them from pests and microorganisms.

Fig. 1.7 Silos for storage of grains.

Fig. 1.8 Storage of grains in gunny bags in granaries.

• Animal Husbandry: Food can also be obtained from animals, for which animals are reared and provided with proper food, shelter and care. When this is done on a large scale, it is called animal husbandry. • Climatic Conditions: Temperature, humidity and rainfall are the climatic conditions, which vary from place to place. • Crumbs: The big pieces of soil in the plough field are called crumbs. • Plough Shaft: Long log of wood in the plough is called plough shaft. • Fertiliser: Fertilisers are chemical substances which are rich in a particular nutrient. • Harvest Festivals: The period of harvest is of great joy and happiness. This is celebrated by farmers as a festival. 10

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NCERT TEXTBOOK QUESTIONS SOLVED

Q1. 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 ____________. (b) The first step before growing crops is ____________ of the soil.

(c) Damaged seeds would ____________ on top of water. (d) For growing a crop, sufficient sun‑ light, ____________ and ____________ from the soil are essential. Ans. (a) crop (b) preparation (c) float (d) water, nutrients.

Q2. Match items in Column A with those in Column B.

Ans.

(i) (ii) (iii) (iv)

Column A Kharif crops Rabi crops Chemical fertilisers Organic manure

(i) (ii) (iii) (iv)

Column A Kharif crops Rabi crops Chemical fertilisers Organic manure

(a) (b) (c) (d) (e) (e) (d) (b) (c)

Column B Food for cattle Urea and super phosphate Animal excreta, cow dung, urine and plant waste Wheat, gram, pea Paddy and maize Column B Paddy and maize Wheat, gram, pea Urea and super phosphate Animal excreta, cow dung, urine and plant waste

Q3. Give two examples of each: (a) Kharif crop (b) Rabi crop Ans. (a) Paddy and maize. (b) Wheat and gram. Q4. Write a paragraph in your own words on each of the following: (a) Preparation of soil (b) Sowing (c) Weeding (d) Threshing Ans. (a) Preparation of soil: Soil is prepared before sowing the seeds. The soil is loosened to increase the absorption of water and manure. Loosening of soil particles adds humus and nutrients in the soil that increases crop yields. Tilling or loosening the soil is done by plough which is pulled by a pair of bulls. Tractor driven cultivators are also used to loosen the soil. (b) Sowing: After preparation of soil, it is ready for sowing of seeds. Healthy and clean seeds should be selected. Sowing is done by seed drill or funnel shaped

(c)

(d)

Q5. Ans.

tools. Seed drill is a modern instruments which can sow seeds at proper depth and distance. Weeding: The unwanted plants that grow along with the crops are called weeds. They hinder the growth of plant, by absorbing nutrients from the soil. Thus, it is necessary to remove them, otherwise, they may make the soil nutrient deficient. Process of removing weeds is called weeding. It can be done manually or by mechanical tools. Some chemicals like 2, 4‑D can also be used. Threshing: Separation of grains from the chaff is called threshing. When the crop mature, it is harvested, and cut along with the stalks. Grains are then, separated from the chaff using a winnowing machine. Explain how fertilisers are different from manure. (i) Manures are organic substances while fertilisers are chemical substances.

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(ii) Manures are prepared in fields, while fertilisers are prepared in factories. (iii) Manures contain all the nutrients, while fertilisers are rich in certain nutrients. (iv) Manures provide humus, while fertilisers do not provide it. Q6. What is irrigation? Describe two methods of irrigation which conserve water. Ans. The process of watering crop plants is called irrigation. Two methods of irrigation are: (i) Sprinklers: Sprinklers work as fountains. It has long perpendicular pipes, having holes at regular distances. When water is supplied, it comes out of the holes and sprinkled in the field. These holes have rotating nozzles which sprinkle water in all directions. It controls the wastage of water. (ii) Drip System: This system also conserve water, as it allows water to flow drop by drop directly near the roots of the plants. It is the best technique for watering fruit plants, in gardens and trees. Water is not wasted at all in this method. Q7. If wheat is sown in the kharif season, what would happen? Discuss.

Ans. Wheat does not require huge amount of water for growth. In contrary to it; in kharif season, rains are very frequent. So, wheat should not be grown in kharif season, otherwise, excess water may destroy the crop. Q8. Explain how soil gets affected by the continuous plantation of crops in a field. Ans. Plantation of crops in a field, continuously for many years can make the soil infertile as soil lose its nutrients does not get the time to replenish them. Thus, it makes Q9. What are weeds? How can we control them? Ans. Weeds are unwanted plants. They grow along with crops. They compete for nutrients and water with the main crop. Process of controlling growth of weeds is called weeding. Weeding is done manually by using khurpi and by using mechanical machines. Weeds can also controlled by using some chemical substances like 2, 4‑D. These chemicals are called weedicides and used to kill and destroy the weeds.

Q10. Arrange the following boxes in proper order to make a flow chart of sugarcane crop production.

Ans.

Preparation of soil

Ploughing the field

Sending crop to sugar factory

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Sowing

Harvesting

Manuring

Irrigation

Q11. 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 grains from chaff. Ans.

ADDITIONAL QUESTIONS SOLVED

I. Multiple Choice Questions

Choose the correct option: 1. The process of watering plants is called (a) sowing (b) manuring (c) tilling (d) irrigation. 2. Weeds are the: (a) main crop plants (b) insects and pests (c) unwanted plants growing along the crop (d) chemical substances. 3. Combines are used for: (a) sowing of seeds (b) harvesting the crops (c) threshing (d) both (b) and (c) 4. Separating grains from chaff is called: (a) winnowing (b) weeding

(c) tilling (d) harvesting. 5. Weedicides are used to destroy: (a) insects (b) weeds (c) pests (d) none of these. 6. Rabi crops are sown in (a) March, April (b) May, June (c) October, November (d) Any time. 7. Wheat and gram belong to (a) Rabi crops (b) Kharif crops (c) Both of these (d) None of these. 8. Examples of kharif crops are (a) Wheat and maize (b) Gram and maize (c) Paddy and maize (d) All of these. crop production and ManageMent n

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9. 2, 4‑D is a (a) Pesticide (b) Insecticide (c) Fungicide (d) Weedicide. 10. Seed drill is used to (a) sow the seeds (b) remove the weeds (c) remove the pest (d) mix manure in the soil. Ans. 1. (d) 2. (c) 3. (d) 4. (a) 5. (b) 6. (c) 7. (a) 8. (c) 9. (d) 10. (a).

II. Very Short Answer Type Questions

Q1. How green plants synthesise their food? Ans. Green plants synthesise their food on their own by the process of photosynthesis. Q2. Where do animals get their food? Ans. Animals get their food from plants and other animals. Q3. What do you mean by crop? Ans. Plants of same kind, are cultivated at a place, on a large scale, is called a crop. Q4. Name two broad cropping patterns. Ans. (i) Kharif crops (ii) Rabi crops. Q5. Give any two examples of kharif crops. Ans. (i) Paddy (ii) Maize. Q6. Give any two example of rabi crops. Ans. (i) Wheat (ii) Gram Q7. What are agricultural practices? Ans. The various steps followed to grow crops and storing the crop grains is referred to as agricultural practices. Q8. What do you mean by the tilling or ploughing? Ans. The process of loosening and turning of the soil is called tilling or ploughing. Q9. What is plough? Ans. The device used for tilling or ploughing is called plough. Q10. Name two materials used to make a plough. Ans. Wood and iron. Q11. What are crumbs? Ans. The big pieces of soil are called crumbs.

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Q12. Ans. Q13. Ans. Q14. Ans. Q15. Ans. Q16. Ans. Q17. Ans. Q18. Ans. Q19. Ans. Q20. Ans. Q21. Ans. Q22. Ans. Q23. Ans. Q24. Ans. Q25. An s.

Name any three tools used in agriculture. Plough, hoe, cultivator. Write two uses of plough. (i) It is used for tilling of soil. (ii) It is used to remove the weeds. Write two uses of hoe. (i) It is used to remove the weeds. (ii) It is used to loosen the soil. What is traditional tool used for sowing? The tool used traditionally for sowing seeds is a funnel shaped tool. What is manure? Manure is a natural substance obtained by the decomposition of plants, animals, and human waste. What do you mean by manuring? The process of providing manure to replenish the soil with nutrients is called manuring. What are fertilisers? Fertilisers are the chemical substances which are rich in a particular nutrient. Which one is better, to use manure or to use fertilisers? Using manure is better than using fertilisers. What do you mean by the term irrigation? The supply of water to crops at regular intervals is called irrigation. Is the time and frequency of irrigation same for all the crops? The time and frequency of irrigation varies from crop to crop. Name some sources of water for irrigation. Wells, tubewells, ponds, rivers and canals are some sources of irrigation. Mention traditional methods of irrigation. (i) Moat (ii) Chain pump (iii) Dhekli (iv) Rahat (lever system) What is the use of pumps? Pumps are mainly used for lifting water. What are the modern methods of irrigation? (i) Sprinkler system (ii) Drip system.

Q26. What are weeds? Ans. The unwanted plants growing naturally along with the main crop are called weeds. Q27. What is weeding? Ans. The process of removal of weeds is called weeding. Q28. What are weedicides? Ans. The chemical substances which are used to control weeds are called weedicides. Q29. Name a weedicide which is commonly used by the farmers. Ans. The weedicide commonly used by the farmers is 2, 4‑D. Q30. Define harvesting. Ans. Cutting of crops after its maturation is called harvesting. Q31. What is threshing? Ans. The process by which grains are separated from the chaff is called threshing. Q32. Name the machine which is a harvester and a thresher. Ans. Combine. Q33. What is winnowing? Ans. It is a process of separation of grains from the chaff. Q34. Name some harvest festivals. Ans. Pongal, Baishakhi, Nabanya, and Bihu are some harvest festivals. Q35. What do you mean by storage? Ans. The process of keeping harvested grains for a long time by saving them from moisture, insects, rats and microorganisms is called storage. Q36. Why is it necessary to dry grains before storage? Ans. The grains are properly dried in the sun to reduce the moisture in them. This prevents the attack by insects, pests, fungi and bacteria. Q37. Name two devices which are used to store grains at large scale. Ans. (i) Silos (ii) Granaries. Q38. Name some animals which provide food. Ans. Cow, buffalo, hen, fish, etc. Q39. Name two milk yielding animals. Ans. (i) Cow (ii) Buffalo.

Q40. Mention the name of three animals which provide meat. Ans. Goat, hen and fish. Q41. What do you mean by animal husbandry? Ans. Rearing of animals at home or forms by providing them with proper food, shelter and care refers to animal husbandry. Q42. Name a vitamin, which is found in cod liver oil. Ans. Vitamin D. Q43. Which time is best for weeding? Ans. The best time for weeding is before crop plants produce flowers and seeds. Q44. Name two main parts of the plough. Ans. (i) Plough share (ii) Plough shaft. Q45. Name a fertiliser, which is rich in nitrogen. Ans. Urea.

III. Short Answer Type Questions

Q1. Why do we have to eat food? Ans. Food provides us energy. The energy provided by food is utilised by the organisms for carrying out their various body functions, such as digestion, respiration and excretion. We get our food from plants and animals. Q2. Explain: (i) Kharif crops, (ii) Rabi crops. Ans. (i) Kharif crops: The crops which are grown in the rainy season (June to September) are called kharif crops. Paddy, maize, soyabean, groundnut, cotton are some of the major kharif crops. (ii) Rabi crops: The crops sown in the winter season (October to March) are called rabi crops. Wheat, gram, pea, mustard and linseed are some of the major rabi crops. Q3. List various agricultural practices. Ans. The agricultural practices are listed below: (i) Preparation of soil (ii) Sowing (iii) Adding manure and fertilisers (iv) Irrigation crop production and ManageMent n

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Full Marks Pvt Ltd (Progressive Educational Publishers)

9, Daryaganj, New Delhi-110002 Phone: 011- 40556600 (100 Lines) Website: www.fullmarks.org E-mail: [email protected]