The Science Hub - SARASWATI HOUSE Material/978-93-5199-719-1_The_Science...Wheat Rabi crop 3. (a)...

(An imprint of New Saraswati House (India) Pvt. Ltd.)New Delhi-110002 (INDIA)

TEACHER’S MANUAL

Class 8

Tripti MehtaBSc, BEd, DCA

Science HubThe

(An imprint of New Saraswati House (India) Pvt. Ltd.)

R

ISBN: 978-93-5199-719-1

Preface Th e purpose of Th e Science Hub series (1 to 8) teacher’s resource pack is to empower teachers to make classroom teaching a holistic experience. it will enable teachers to explain the chapters in the most eff ective way, which will not only impart knowledge, but also ignite interest in the minds of young learners towards the subject. A wide array of resources complement these manuals, which makes learning an interesting process instead of a routine chore.

Teacher’s ManualTeacher’s Manual resources have been carefully prepared with an aim to make the process of teaching and learning interesting and intriguing for the teachers and learners alike. it comprises detailed lesson plans and answers to the coursebook along with solved worksheets and model test papers. Th ese have been prepared keeping in mind the explanation of the concepts and the level appropriateness of the topics. Easily available teaching aids are used to make teaching and learning an interactive and lucid process.Th e lesson plans give a topic-wise explanation of each chapter. its components are:

• Warm up section guides the teacher to start the topic in an interesting way.

• Specifi c learning objectives give the list of measurable aims of each chapter, which should be achieved aft er teaching the chapter.

• Concept explanation gives a detailed method of explaining the important concepts of the chapter using various teaching aids.

• Reinforce section allows the teacher to check the progress of the concepts learned by the students with the help of textual questions and worksheets and allows them to revisit and revise the concepts, if required.

• Explore section helps the learners to do various activities , oft en taking them beyond their classroom learning.

Teacher’s CDTeacher’s CD comprises animations, activities, fl ip book, detailed lesson plans and answers to the coursebook along with solved worksheets and model test papers.

Web SupportTh e web support consists of worksheets, model test papers, and answers to worksheets and model test papers. Th ese would help teachers in assessing students on the concepts taught in the class.

Contents

S.No. Chapters Pages

1. Crop Production and Management 5

2. Microorganisms: Friend and Foe 14

3. Synthetic Fibres and Plastics 22

4. Metals and Non-metals 29

5. Coal and Petroleum 35

6. Combustion and Flame 42

7. Conservation of Plants and Animals 50

8. Cell–Structure and Functions 58

9. Reaching the Age of Adolescence 66

10. Reproduction 74

Model Test Paper-i 86

11. Force and Pressure 90

12. Friction 97

13. Sound 102

14. Chemical Eff ect of Electric Current 109

15. Light 116

16. Some Natural Phenomena 124

17. Star and the Solar System 132

18. Pollution of Air and Water 139

Model Test Paper-ii 151

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Chapter 1Crop Production and Management

Specific Learning Objectives Aft er the completion of the chapter, students will be able to:

• Understand about crop production.• Know the type of crops that grow in diff erent seasons.• Know the steps involved in the agricultural practices.• Learn about animal husbandry

Warm upMake an attempt to have an interactive class by asking the students if they have visited any village and have seen the crops growing on the agricultural land. Ask the students, what is required by the plants to grow and from where do the plants get their food? Now, ask the students to complete the exercise given in the Warm-up section.

Concept Explanation:• Agriculture: Explain to the students, what agriculture means. Tell them that it is an art and

science of growing plant and rearing animals for food, clothing and other products. Due to the varied climatic conditions in india like temperature, humidity and rainfall, there are variety of crops grown in various parts of the country.

Preparation of the Soil

• Explain to the students that the soil is the most important requirement for the crops to grow. Th us, the preparation of the soil demands the loosening of the soil that makes it porous and helps the roots to penetrate and also helps the air easily reach the roots, which is very important for the health of the roots.

• Selection of seeds: Tell the students that good quality seeds should be selected to get good quality crops.

Adding Manure and FertilizersExplain to the students that plants take up nutrition from the soil. Manure and fertilizers have to be added in the soil to replace nutrients aft er every crop is harvested.

• Manure: Explain to the students that manure is an organic substance which can be obtained by the decomposition of plant and animal waste.

• Fertilizers: Explain to the students that fertilizers are chemical (inorganic) substances. Th ey are rich in particular nutrient. Judicious use of fertilizers helps farmers to get a very good yield but their excessive use leads to soil infertility and makes soil unfi t for growing crops.

• Weeds: Tell the students that weeds are harmful and useless plants which grow along with the crop and they compete with the crops for food, water, space and sunlight; therefore, it is very important to remove them.

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Irrigation• Explain to the students that the supply of water to the plants at regular intervals is called

irrigation. Root absorb water, minerals and fertilizers from the soil. Water is one of the important factors for seed germination. Nutrients dissolved in water are transported to various parts of the plant.

Storage

Explain to the students that it is important to keep the grains safe from moisture, rats, insects and microorganisms. The grains have moisture at the time of harvesting, which needs to be dried. if grains are not stored without drying, they may be attacked by the fungi and will get spoilt.Animal Husbandry Explain to the students that animal husbandry is the rearing of animals in the farm for food and clothing. in our country, animal farming is very common.

Reinforce• Help students develop values/skills (research and thinking) given in the values and Life skill

sections of the chapter. Discuss the terms and their meanings given at the end of the chapter. Discuss the answers in the class and explain them.

Explore• Ask the students to complete the questions and the projects given at the end of the chapter.

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Worksheet 1 1. Name two substances which increase nutrition in the soil?

2. Look at the picture and answer the following questions.

(a) identify the equipment shown in the picture. (b) Give the role of the above equipment in agriculture. (c) How oft en should one use the above tool on the agricultural fi eld?

3. Defi ne the following in one sentence each. (a) Mixed cultivation: (b) Crop rotation:

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Worksheet 2 1. Give two examples of each of the following. (a) Kharif crops (b) Rabi crops (c) Weeds (d) Fertilizers

2. What is organic farming?

3. Look at the picture and answer the questions that follow.

(a) identify the machine shown in the picture. (b) Give the role of the above machine in agriculture. (c) How does this machine make the work simpler? (d) What is the next step aft er the above activity on the fi eld?

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Answers to Coursebook

A. 1. (a) Tilling or ploughing (b) Rabi crops (c) Seed drill (d) Nutrients (e) Drip system (f) irrigation

2.

Column A Column BCombine harvester Harvesting and threshingKhurpi (trowel) WeedingSickle PloughingSprinkler irrigationWheat Rabi crop

3. (a) Crops (b) Ploughing (c) Plough, how, harrow or sickle (d) Sowing (e) Weedicide (d) Harvesting

B. 1. Weeds can be removed from the fi eld either by hand or with the help of implements such as trowel, harrow and hoe. Weeds can also be removed by using chemicals, known as weedicides.

2. Diff erent agricultural practices are as follows. (i) Preparation of the soil (ii) Selection and sowing of seeds (iii) Adding manures and fertilizers (iv) irrigation (v) Removal of weeds (vi) Harvesting (vii) Storage 3. Advantage of using fertilizers: Th ey are rich in nutrients that can be easily absorbed by the plants. Disadvantage of using fertilizers: Th ey do not increase humus in the soil. 4. Combine harvester is a machine which is used for both harvesting and threshing. 5. NSC stands for National Seeds Corporation which is involved in the production of good-quality

agricultural seeds. 6. (a) Before spraying weedicides, these must be diluted with water to the extent required and sprayed

in the fi elds with a sprayer. (b) Th e grains have moisture at the time of harvesting which needs to be dried in the sun before

storing in godowns. 7. Modern methods of irrigation are economical. Th ese methods are as follows. Sprinkler system: Sprinklers have perpendicular pipes with rotating nozzles. Th is system involves

pumping water under pressure and spraying it over the crops like rain. it helps in even distribution of water on the crops.

Drip system: it involves the use of pipes with very small holes. Th ese holes deliver water drop-by-drop at the base of each plant.

8. We obtain many products from animals. Here are some examples of food products obtained from animals.

Refer to Table given on page 17 9. Advantages of manure: Manure is preferred over fertilizers due to the following reasons. • Ithelpstomakethesoilporousduetowhichtheexchangeofgasesbecomeseasy. • Itenhancesthewater-holdingcapacityofthesoilandItalsoimprovesthesoiltexture. • Itdoesnotcausewaterpollutionwhenitgetsmixedwithwater.

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10. While sowing seeds, a few points must be kept in mind. Depth: Seeds should be sown at the correct depth, neither too shallow nor too deep. Distance: Seeds should be sown at an appropriate distance from one another so that the plants get

proper amount of sunlight, nutrients and water from the soil.

C. 1. The steps involved in these practices are as follows. (a) Preparation of the soil (b) Selection and sowing of seeds (c) Adding manures and fertilizers (d) irrigation (e) Removal of weeds (f) Harvesting (g) Storage (a) Preparation of the soil Plants absorb water, air and nutrients from the soil. Ploughing and levelling loosen the soil,

making it porous. Ploughing is the process by which the soil is turned, loosened and shuffled. After ploughing,

big chunks of soil called crumbs may remain in the soil. The soil is then levelled with the help of the leveller, ready for sowing and irrigation.

(b) Selection and sowing of seeds Good quality, healthy seeds should be selected to get good quality crops. Sowing is the process

of placing the seeds in the soil. Sowing can be done manually, using traditional tools or with the help of an implement called

seed drill. (c) Adding manure and fertilizers As crops grow in the fields, the nutrients are slowly used up. As a result, the level of the nutrients

in the soil may decrease. To avoid this situation, farmers add manure and fertilizers to the soil while preparing the soil.

(d) Irrigation After sowing, seeds need water for their growth. Rainfall is one of the main sources of water

for crops. For irrigation, water is obtained from wells, rivers, lakes and tube wells. irrigation is done using two methods: traditional and modern.

(e) Removal of weeds Some undesirable plants such as grass, wild oat, amaranthus (chaulai) also grow along with the

crops. These plants are known as weeds. Weeds start competing with the crops for air, sunlight and nutrients. So these need to be removed. The process of removing weeds is called weeding. it is done manually or by using chemicals.

(f) Harvesting After the crop matures, it is harvested. The process of cutting and gathering of crops is called

harvesting. Harvesting is done manually with the help of a sickle or by using a machine called harvester. After harvesting, the crop is subjected to threshing and winnowing to remove the grain from the chaff.

(g) Storage The grains have moisture at the time of harvesting which needs to be dried. if grains are stored

without drying, they may be attacked by fungi and will get spoilt.

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2. (a) Refer to table given on page 11 (b)

Mixed cultivation Crop rotationThe practice of sowing two or more different types of crops in a particular field at the same time, is called mixed cultivation.

The practice of growing two or more different crops in the same field, one after the other is called crop rotation.it is a good option to replenish the soil with nutrients.

For example, pea can be grown along with a cereal like wheat.

For example, wheat and paddy can be grown along with legumes.

(c) Threshing Winnowing

Threshing helps to loosen the seeds or grains from the chaff.

Winnowing helps to separate the grain and the chaff.

Threshing is done manually or with the help of a machine called thresher.

it is done manually or with the help of a winnowing machine.

(d) Sprinkler irrigation Drip irrigation

Sprinklers have perpendicular pipes with rotating nozzles.

it involves the use of pipes with very small holes.

This system involves pumping water under pressure and spraying it over the crops like rain.

These holes deliver water drop-by-drop at the base of each plant.

3. Spoilage of grains: if the harvested grains are stored without drying, they may be attacked by fungi and will get spoilt.

Factors responsible for spoilage of grains are as follows. (a) Moisture (b) Rats (c) insects (d) Microorganisms

Following steps must be taken to prevent the grains from getting damaged. 1. Before storing seeds, they need to be dried in the sun to remove moisture. 2. The place for storage should also be dry and free of pests. 3. Grains should be packed in gunny bags or bins to keep them away from rats.

4. Weeds: Some undesirable plants also grow along with the crops. These plants are known as weeds. Grass, wild oat, amaranthus (chaulai) are some examples of weeds. The process of removing weeds is called weeding. it is done manually or by using chemicals.

Manual weeding: Weeds can be removed from the field either by hand or with the help of implements such as trowel, harrow and hoe.

Using chemicals: The chemicals used to destroy weeds are called weedicides. Metachlor, dalapon and siziazine are examples of weedicides.

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5. The process by which free atmospheric nitrogen is converted into nitrogen compounds is called nitrogen fixation. Nitrogen fixation can be understood in the following steps.

in nature, nitrogen is fixed during lightning or by nitrogen fixing bacteria and blue-green algae. Leguminous plants such as pea have the nitrogen-fixing bacteria Rhizobium in their root

nodules. The bacteria fixes the atmospheric nitrogen and converts it into soluble nitrogen compounds, which can be easily absorbed by the plants from the soil and then used up for the formation of plant proteins.

There are two ways by which the nitrogen goes back into the atmosphere. One is the decomposition of animal excreta (which has nitrogenous waste) and secondly, when these plants and animals die, the bacteria and fungi decompose the nitrogen compounds present in them and release the free nitrogen back into the atmosphere.

Some of these nitrogen compounds are returned to the soil as well.

This is how the percentage of nitrogen remains balanced in the atmosphere.

6. Sowing is the process of placing the seeds in the soil. Sowing can be done manually, using traditional tools or with the help of an implement called seed drill.

Manual sowing: This is also called broadcasting. This involves direct sprinkling of seeds into the soil which get distributed unevenly. This may result in overcrowding.

Also, this method may not ensure that all seeds are sown at the correct depth. Traditional tools: For many years, farmers were using traditional tools for sowing seeds. A traditional

tool is shaped like a funnel attached to a pipe-like structure. This funnel is filled with the seeds which pass through the pipe having a sharp end. This sharp end pierces the field and places the seeds there.

Seed drill: it is a modern tool used for sowing. This is attached to the tractors. The advantages of using this tool are as follows.

it sows the seeds uniformly at equal distances and depths. it ensures that the seed gets covered with the soil after sowing. it also saves time and labour. it prevents the seeds from getting damaged or eaten up by the birds.

7. Soil is the most important requirement for the crops to grow. Plants absorb water, air and nutrients from the soil.

Soil is prepared before growing a crop so that the roots can get adequate air, water and nutrients. This preparation involves ploughing and levelling.

Tilling or ploughing: it is the process by which the soil is turned, loosened and shuffled. Plough (made of wood or iron) is used for tilling the soil and adding fertilizers in it. Plough and other tools such as how, harrow and sickle needed for the production of crops are called agricultural implements.

Levelling: After ploughing, big chunks of soil called crumbs may remain in the soil. They are broken with the help of a plank (made of wood or iron). The soil is then levelled with the

help of the leveller, ready for sowing and irrigation.

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D.

Nitrogen released by

bacteria in the soil

Nitrogen compounds in the soil

Fixed by lightning, nitrogen-fi xing bacteria

and blue-green algae

Excreti on and decompositi on

Absorbed by

Atmospheric nitrogen

Decompositi on of dead plants

Plants eaten by animals

E. 1. Wheat is a rabi crop and therefore, it does not require a huge amount of water. So, if it is grown in the rainy season it may die due to excess amount of water.

2. Natural fertilizers are obtained from plants and animals while chemical fertilizers are produced in factories using chemicals. Chemical fertilizers may get washed into the waterbodies. Which harms the aquatic animals. So the overuse of chemical fertilizers should be avoided. Th eir excessive use leads to soil infertility and makes the soil unfi t for growing crops.

3. Pea is a leguminous plant. Growing pea plant along with wheat crop helps in the enrichment of soil due to nitrogen fi xing property of leguminous plants. Th erefore, farmers grow pea plants along with wheat crops.

Answers to Worksheet

Worksheet 1 1. Manures, Fertilizers

2. (a) Plough (b) Plough is used to loosen the soil. (c) Ploughing should be done before sowing seeds.

3. (a) Practice of sowing two or more diff erent types of crops in a particular fi eld at the same time. (b) Practice of sowing two or more diff erent types of crops in the same fi eld one aft er the other.

Worksheet 2 1. (a) Paddy, Maize (b) Wheat, Gram (c) Wild oat, Grass (d) Urea, Potash

2. it is a form of agriculture that relies on techniques such as crop rotation, green manure, compost. 3. (a) Combine harvester

(b) it is used for both harvesting and threshing. (c) Th is machine threshes the crop at the time of harvesting. (d) Storage of crop is the next step.

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Specific Learning objectives Aft er the completion of the chapter, students will be able to:

• Know what are microorganisms? Why are they called so?• Know diff erent types of microorganisms.• Understand how microorganisms are useful and harmful to us.• How to prevent damage caused by microorganisms, for example, health and spoilage of

food.

Warm UpBegin the topic by asking students the questions such as, what do they know about microorganisms? Give them some clues that these microorganisms can be harmful for human life. What microorganisms do to us when we fall ill? Now ask the students to complete the exercise given in the warm-up section.

Concept Explanation• Explain to students that microorganisms are the living organisms that exist around us but they

are so tiny that they cannot be seen with our eyes, unless we take the aid of some magnifying tool like magnifying lens or microscope.

Microorganisms and Us• Explain to the students that microorganisms play a crucial role in our lives. Some are useful

and friendly while others are harmful for us, to the extent that they cause diseases. We need to understand and then take precautions against them.

Useful Microorganisms • Explain to the students that the microorganisms are useful to us in many ways such as in

food industry (for making curd, cheese, vinegar, coff ee, tea and bread), in medical industry, in agriculture and in environment cleaning.

Harmful MicroorganismsExplain to the students that microorganisms can be harmful in two ways.1. Cause diseases in plants, animals and human beings.2. Food spoilage (decay)

Food Poisoning• Explain to the students that the food gets spoilt due to the growth of microorganisms on it.

Th ey grow on the food and produce toxic substances. Th is leads to the poisoning of food and if this food is consumed, serious illness called food poisoning and sometimes death may result.

Chapter 2Microorganisms: Friend and Foe

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Food Preservation• Explain to the students that preservation of food is very important to prevent it from getting

spoilt. Food preservation methods kill the microbes or prevent them from multiplying. Different types of food require different methods of preservation.




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Worksheet 1 1. Based on the characteristics given, identify the type of microbe.

(a) Autotrophic and are present as scum on the water bodies.

(b) Th ese are killed by antibiotics.

(c) Th ese are saprophytic.

(d) Th ese are diffi cult to classify as living or non-living.

2. State the role of the following pathogen in our life.

(a) Bacteria

(b) Yeast (c) Algae (d) Protozoa (e) Virus

3. Mention.

(a) Any three antibiotics.

(b) Algae rich in proteins and other nutrients.

(c) Bacteria that helps in nitrogen fi xation.

(d) Microorganism used to make cheese.

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Worksheet 2 1. Name the microorganism that are responsible for these diseases.

(a) Polio

(b) Typhoid

(c) Citrus canker

(d) Septoria leaf blotch

(e) Apple scab

(f) Fin rot

(g) Anthrax

(h) Dengue

2. Name the food items that are preserved by the following preservation methods.

(a) Boiling

(b) Using sugar

(c) Canning

(d) Pasteurisation

(e) Dehydration

(f) Freezing

(g) Using salt

(h) Using chemical preservatives

(i) Using vinegar

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A. 1. (a) Penicillin, Tetracycline (b) Tuberculosis, Measles (c) Cholera, Typhoid (d) Anthrax, Fin rot

(e) Drying, Pasteurisation

2.

COLUMN A COLUMN BMicrobes Tiny organismsVirus MeaslesYeast FermentationPolio drops VaccinationPasteurisation Milk preservationAntibodies Produced in our bodyAntibiotics Obtained from microbesAnopheles and Aedes Malaria and dengue

3. (a) Microorganisms are living organisms that cannot be seen with naked eyes. Th ese can only be seen with the aid of a microscope.

(b) Microbes convert the dead organic matter of plants and animals into simple substances which go back into the soil and increase soil fertility. Th is also keeps our environment clean.

(c) When a person suff ering from common cold sneezes, pathogens spread in the air and they may enter the body of a healthy person and he/she may also get common cold.

(d) Drying in the sun removes water from the food and stops microbes from growing. B. 1. Fermentation: Th e process of conversion of a sugar into an acid or an alcohol by the action of

microorganisms is called fermentation. 2. By bacteria: Citrus canker; By virus: Yellow vein mosaic; By fungi: Rust of wheat 3. Antibiotics: Antibiotics are medicines that destroy microorganisms. 4. Sodium benzoate and sodium metabisulphite are used as preservatives. 5. Vaccines: Vaccines are prepared with dead or weakened disease-causing microbes. Vaccines protect

us from diseases. When a person is vaccinated, his/her body starts producing antibodies against the microbes.

6. Some bacteria such as Rhizobium and blue-green algae live in the root nodules of leguminous plants. Th ey help in nitrogen fi xation. Th ey absorb nitrogen from the atmosphere to enrich the soil and make nitrogen available for the plant as nitrates, which in turn are absorbed by the plant and used for protein formation.

7. Air is needed for the growth of microorganisms. 8. (a) Milk contains a sugar called lactose. it also contains a bacteria called Lactobacillus, which uses

lactose for energy and creates lactic acid as a by-product. it is the lactic acid which makes milk taste sour.

(b) Yeast is used in the preparation of bread. Yeast breaks down the sugar which results in the formation of alcohol and carbon dioxide. When this dough is baked, these bubbles escape, making the bread rise further and making it soft and fl uff y.

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(c) Food gets spoilt due to the growth of microorganisms on it. They grow on the food and produce toxic substances. This leads to the poisoning of food.

(d) Use of oil in pickles prevents the spoilage of food. When the pickle is covered with oil, the microbes are unable to come in contact with it.

(e) Black and green coating on bread occurs due to the action of microorganisms on it. (f) Drying of food before storage removes water from the food and stops microbes from growing. C. 1. Curd is prepared by the process of fermentation. The process of conversion of a sugar into an acid or

an alcohol by the action of microorganisms is called fermentation. Curd is formed due to a bacterium called Lactobacillus. When a spoonful of curd is added to warm milk, these bacteria multiply and convert the lactose sugar present in the milk to lactic acid. This way, milk gets converted into curd.

2. Commercial uses: Microorganisms are needed for the following activities. Making curd and cheese: Bacteria are used in making some of our popular food items such

as curd and cheese. These are made by the action of bacteria on milk. Curd and cheese are formed due to a bacterium called Lactobacillus. Paneer (cottage cheese) involves the use of Streptococcus bacteria. The process of conversion of a sugar into an acid or an alcohol by the action of microorganisms is called fermentation.

Making vinegar, coffee, tea and tobacco: Bacteria are also used in the preparation of vinegar (acetic acid), tea, coffee and tobacco.

Making bread: Yeast is used in the preparation of bread. Bread is prepared by kneading a mixture of flour, salt, sugar, yeast cells (microscopic fungus) and water into dough. Yeast breaks down the sugar which results in the formation of alcohol and carbon dioxide. When this dough is baked, these bubbles escape, making the bread rise further and making it soft and fluffy.

Making toothpaste: Toothpaste is made with the help of shells of diatoms (a type of algae). Xanthum gum, which is obtained from the bacteria Xanthomonas campestris, is also used to make toothpaste.

Making alcoholic beverages: Manufacturing of alcohol and alcoholic beverages like beer and wine requires fermentation of sugar present in barley and grapes using yeast.

3. Food preservation is the process of treating and handling food to stop or slow down its spoilage while maintaining its nutritional value, flavor and texture.

Four common methods of food preservation are as follows. Refrigeration and freezing: Microbes like bacteria and fungi cannot survive at low temperatures

so refrigerating at low temperatures and freezing help to preserve food for a long time. Food items such as fruits, vegetables and meat are preserved by using this method.

Using sugar: it is used to preserve jam, jellies and squashes. Microbes lose water due to osmosis. Boiling: Boiling kills the microbes. Milk and water are often boiled to kill microbes that may be

present in them. Canning: Storing food items such as jams, vegetables, fish and even cooked food in an airtight

can is an effective way of preserving them. 4. Pasteurisation: it is a process in which the foodstuff is heated at high temperature and then cooled

rapidly. The process was named after the French Chemist Louis Pasteur. Commercially available milk is first heated at 70°C for 15 to 30 seconds and then suddenly chilled and stored. This prevents the growth of bacteria.

5. Microbes convert the dead organic matter of plants and animals into simple substances which go back into the soil and increase soil fertility. This also keeps our environment clean. Some bacteria are used for treating sewage, as they break down the organic matter in the sewage into simple substances.

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6.

Disease Mode of

transmission Causative pathogen

Preventive measures

Anthrax Grazing Bacterium Proper vaccination

Typhoid Water Bacterium Maintaining proper sanitation. Taking vaccination.

Tuberculosis Air Bacterium Th e patient should be kept in isolation and the belongings should be separated from those of others. Vaccination for children.

Foot and mouth disease

Contact with aff ected animal and air

Virus Cleansing and disinfection of aff ected premises, equipment and vehicles and vaccination

Yellow vein mosaic

insect Virus Removing and destroying disease-aff ected plants and Controlling the insect vector by spraying chemicals

Chickenpox Air/contact Bacterium Th e patient should be kept in isolation and the belongings should be kept away from others. Vaccination should be given to the children.

Rinderpest Contact with aff ected animal,contaminated water and air

Virus Cleansing and disinfection of aff ected premises, equipment and vehicles and vaccination

D. Bacilli – Bacteria Spirilla– Bacteria Euglena– Protozoa

E. 1. if we do not take bath regularly, we may fall ill due to the growth of microorganisms. 2. (a) Th e reason for his illness is biting of mosquito.

(b) Th ey should use mosquito net and repellents. Th ey should spray insecticides. Th ey should also take care that water does not get collected or stagnated in their surroundings.

3. Th e green layer that covers some ponds and lakes is algae. Algae have chlorophyll so they appear green.


Worksheet 1 1. (a) Algae (b) Microorganisms (c) Fungi (d) Virus

2. (a) Lactobacillus bacteria is used to make curd. (b) Yeast is used to make bread. (c) Diatoms are used to make toothpaste. (d) Malaria disease is caused by Plasmodium protozoa. (e) Measles, chicken pox and dengue are caused by virus.

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3. (a) Penicillin, Tetracycline, Streptomycin (b) Chlorella (c) Rhizobium (d) Lactobacillus bacteria

Worksheet 2 1 (a) Virus (b) Bacteria (c) Bacteria (d) Fungi (e) Fungi (f) Bacteria/ Fungi (g) Bacteria (h) Virus 2. (a) Milk (b) Jam (c) Fish (d) Milk (e) Cereals (f) Fruits (g) Meat (h) Squashes (i) Vegetables

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• Know what are synthetic fi bres?• Learn about types and characteristics of synthetic fi bres.• Understand about plastic and its types and properties.• Understand the relation between plastics and the environment.

Warm UpBegin the topic by asking students the questions like, what do they know about synthetic fi bres? Give them some clues about the kind of dresses that are made out of the synthetic fi bres and when can these be worn or are good to be used. Now ask the students to complete the exercise given in the warm- up section.

Concept Explanation• Explain to the students that the synthetic or man-made fi bres are obtained by using a

combination of chemicals. Th e raw materials to prepare synthetic fi bres are obtained from coal, petroleum (crude oil), and natural gas. Examples are polyester, rayon and nylon. Th e synthetic fi bre is a chain of small units called monomers, joined together to make a large unit called polymers.

Characteristics of Synthetic Fibre• Explain to the students that synthetic fi bres are easy to maintain, crease-resistant, elastic as

they do not lose their shape, durable, cheaper and dry very fast. Since they do not absorb water or sweat, synthetic fi bres are not very comfortable to wear during the hot and humid climates.

Types of Synthetic Fibres• Explain to the students that there are diff erent types of synthetic fi bres such as:

(a) Rayon (b) Nylon (c) Polyester (d) Acrylic (e) Spandex • Explain to the students the uses of diff erent types of synthetic fi bres. Also explain to them the

advantages and disadvantages of diff erent fi bres.Plastics

• Explain to the students that plastic is also a type of polymer. Th e use of plastic is replacing wood today. Look around your house. You will fi nd lots of goods made out of plastic. Th ey are found in diff erent shapes and sizes. Th e plastic can be melted, moulded, coloured, recycled, reused by heating. it can even be made into sheets and wires. Th ere are diff erent plastics with diff erent arrangement of small units. in some variety, it comprises linear linkage of small units and in others it could be cross-linked.

Chapter 3Synthetic Fibres and Plastics

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• Explain to the students that there are different type of plastics and also tell them the uses of plastics on the basis of their properties.

Plastic: Harmful Waste for the Environment• Explain to the students that the use of plastic is increasing day-by-day. Plastic is hazardous for

the environment. it is a non-biodegradable material as it cannot be decomposed by the natural process that is by the action of bacteria, which helps in the cleaning of the environment. it causes environmental pollution. if it remains on the earth crust, it makes the land non- productive. it is also harmful for the animals as they tend to eat the plastic bag along with the food contained in it. Burning of this material releases harmful gases into the environment, causing air pollution.




24

Worksheet 1 1. Give two examples of each of the following. 1. Synthetic fi bre 2. Plastic

2. Fill in the characteristics of the following fabrics.

POLYESTER NYLONWater absorbtion

Drying time Short period

Comfort in diff erent weathers

Shrinkage Low

Durability

Texture

Weight Light

3. Fill in the blanks.

(a) Plastics are for the life.

(b) Avoid throwing on the road or in the water.

(c) is a poor conductor of electricity.

(d) is popularly used as a coating on utensils to make it non-stick.

(e) is used to make shirts, skirts and other dress materials and is used to make formal suits for winter wear.

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Worksheet-2 1. Defi ne the following terms. (a) Polymers (b) Spandex (c) Acrylic (d) Bakelite (e) PET (f) PS

2. Name the materials used to prepare the following.

(a) Raincoat

(b) Parachute

(c) Packing material

(d) Containers for packing food

(e) insulators for electrical wires

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A. 1.

COLUMN A COLUMN BCotton Natural fi breNylon Synthetic fi breRayon mixed with cotton To make bedsheetsRayon To make carpetsPVC insulators on electric wiresMelamine Heat resistant

2. Natural fi bres- Cotton and wool Synthetic fi bres- Rayon and nylon

B. 1. Natural fi bres are preferred over synthetic fi bres because of the following reasons. Natural fi bres absorb a lot of sweat or water, and therefore, they can be worn during summer

and humid climates. Natural fi bres do not catch fi re easily and, therefore, it is safe to wear them either in the kitchen

or anywhere near a source of fi re. 2. Polymer (poly-many; mer-unit) is a large unit which is made up of a chain of small units (each of

which is a chemical substance) called monomers. 3. Th ermosetting plastics: Th is type of plastic can be moulded only once and thereaft er, it cannot be

melted or moulded again. in these plastics, heavy cross-linking between the smaller units is found. 4. Rayon is called artifi cial silk because this fi bre has properties as those of silk. 5. Cotton boll is the fruit of the plant.

6. (a) Polyester does not absorb water so it is not suitable for summer season. (b) Plastic is hazardous for the environment. it is a non-biodegradable material. As a result it

causes environmental pollution. By remaining on the earth’s crust, plastics make the land non-productive.

(c) Th e word Nylon is derived from the two cities that is New York and London because it was fi rst marketed in these places.

(d) Plastic are used over wood because of its properties which makes it the best and cheap material. (e) Bakelite and melamine can maintain their shape and size even at very high temperature because

in these plastics, diff erent polymer chains consisting of smaller units are cross-linked. (f) Since cotton and paper are obtained from plants, that is, their raw material is the same, so they

smell alike on burning. Wool is sheep's hair that is why, when it is burnt, it smells like burning hair.

C. 1. Although diff erent types of plastics diff er in some physical and chemical properties, the following properties are common to most of them.

Th ermal conductivity: Plastics are poor conductors of heat, and therefore, they are suitable for making handles of cooking utensils and for making containers used in microwave ovens.

Electrical conductivity: Plastics are poor conductors of electricity and this makes them suitable as covering materials on electric wires, appliances and cords for insulation.

27

Solubility in water: Plastics are insoluble in water, therefore, they are suitable for making containers for storing water like buckets, mugs and bottles.

2. This fibre is prepared from cellulose that comes from wood pulp. This fibre has properties as those of silk, therefore, this fibre is also called artificial silk.

3. Plastic goods are very common today. Their low cost, light weight and easy availability, make them a good substitute for wood and metals. Different types of plastics that we use in our daily lives and their uses are given in the following table.

Plastics Uses

Polythene (polyethylene) Making food containers, bottles of carbonated beverages and containers for microwave cooking

Polyvinyl chloride (PVC) Making insulators for electric wires, upholstery, floor covering and raincoats, shoes, handbags and furniture, pipes

Polypropylene (PP) Making medicine and ketchup bottles, containers for ice creams and yogurt

Polystyrene (PS) Making packaging material for delicate goods and thermocol

Bakelite Making electrical fittings like plugs, switches and switch boards

Melamine Making crockery and containers for serving food.

4. Though commodities made of plastic are handy, we should become aware of the harm that plastic causes to life on Earth. We need to take some effective preventive measures to reduce this type of pollution.

To bring a decline in its usage, we need to start using paper or cloth bags for shopping and other purposes as much as possible, and avoid bringing plastic bags at home.

Avoid and prevent dumping plastic in water and on land. Ensure proper disposal of plastic. Plastic which is disposed can be recycled and used in many different ways such as for tote bags,

wallets, or pouches. There are biodegradable plastic bags available, which can help to a considerable extent. These changes might be gradual but taking small steps can greatly contribute to the reduction of

plastic pollution. 5. We will recommend cotton clothes for workers in metal and chemical industries because of the

following reasons. Cotton allows better air circulation, which helps in absorbing and removing body moisture

caused by sweat. Cotton is light in weight. Being light-coloured will help the light to pass through instead of

being absorbed and hence we will not feel the heat as much. Cotton clothes do not catch fire easily which makes it safe to wear.

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D.

Reduce

Refuse

Reuse

Recycle

1. Th e picture depicts the principle of 4Rs- Refuse, Reduce, Reuse and Recycle. 2. Signifi cance of 4Rs principle in preventing plastic pollution: Reduce-Try to minimise the plastic goods or materials used as much as possible. Reuse-Try to reuse as much as possible the plastic items that can be reused. By doing this, you can

extend the use of items before they become waste. Recycle-Try to recycle all plastic items that can only be used once, and are recyclable. Refuse-Try to avoid buying plastic products that can harm you, your family and the environment. E. 1. Synthetic fi bres can catch fi re easily, so we should not wear synthetic clothes while working in the

kitchen. 2. Nylon fi bre is very strong and that is why it is used in making mountain climbing ropes. 3. Plastics are poor conductors of electricity and this makes them suitable for making utensil handles.


Worksheet 1 1. 1. Rayon, Nylon 2. Polythene, Bakelite 2. Polyester: No, No, No, More, lustrous, light Lylon: Yes, Long, Yes, More, lustrous, 3. (a) Very useful, daily (b) Plastic (c) Plastic (d) Tefl on (e) Terrycot, Terrywool

Worksheet 2 1. (a) Polymers are the large units that are formed from a chain of small units.

(b) Synthetic fi bre that is used to make tight-fi tting clothes. (c) Synthetic fi bre that resembles wool. (d) A thermosetting plastic that is used to make electrical fi ttings. (e) Polyethylene terephthalate is a popular polyester. (f) Polystyrene is a thermoplastic that is used to make packaging material.

2. (a) Polyester (b) Nylon (c) Polystyrene (d) Polythene (e) Bakelite

29


• Know what are metals.• Understand physical and chemical properties of metals.• Know what are non-metals • Understand physical and chemical properties of non-metals.• Know the uses of metals and non-metals.

Warm UpStart the lesson by asking students the questions like, what do they know about metals and non-metals? Give them some clues about the materials that are made out of the metals and non-metals. Now ask the students to complete the exercise given in the Warm-up section.Concept Explanation:

• Explain to the students that metals are hard and shiny such as iron, tin, copper, silver and gold.

• Non-metals are soft and dull such as phosphorus, sulphur and chlorine.• Th ere are certain elements that have some properties of metals and some properties of non-

metals. Such elements are called metalloids such as antimony, germanium and arsenic. Occurrence of Metals

• Explain to the students that the metals generally do not occur independently; they are found in combined state as minerals called ores. Ores have metals with lot of impurities. Rock salt (NaCl), dolomite (calcium carbonate and magnesium carbonate) are some ores. Some metals have oxides or sulphide in their ores like iron and aluminium. Some metals like silver, gold and platinum are not very reactive; they occur in free state in nature.

Occurrence of Non-Metals• Explain to the students that hydrogen, oxygen, nitrogen, silicon, carbon and sulphur are

generally found on the earth crust either in combined state or in elemental state. Like metals, non-metals are also extracted from their sources. Properties and uses of metals and non-metals can be discussed.

• Explain to the students about the physical and chemical properties of metals and non-metals. Also tell students to look around in their house and fi nd out the use of diff erent metals and non-metals.




Chapter 4Metals and Non-metals

30

Worksheet 1 Observe the given set-up and answer the q uestions that follow.

1. Identify the process taking place in the given set-up.

2. Defi ne the process.

3. How is the chemical reactivity of metals linked with their position in the activity series of metals?

4. What changes will you observe in the set-up aft er fi ve hours? Give reason.

5. Write the chemical equation taking place in the above reaction.

31

Worksheet 2 1. Fill in the blanks. (a) Carbon burns in the air to form . (b) Sodium and water form and hydrogen gas. (c) Metal, oxygen and moisture form . (d) Magnesium and oxygen form and . (e) Sodium and form sodium chloride

and .

2. Name the following. (a) Th e property by the virtue of which the metals can be beaten into sheets. (b) Non-metal used in pencils and dry cells. (c) Compounds formed by the reaction of acid and the base. (d) Th e process of slow eating of the metal due to the attack of atmospheric gas and moisture. (e) Th e series in which the metals are placed in their decreasing order of reactivity.

3. Write the chemical reactions of the following. (a) Copper + Oxygen (b) Sodium + Water (c) Zinc + Sulphuric acid (d) Copper + iron sulphate

32


A. 1. (a) Graphite (b) Sodium (c) Diamond (d) Graphite (e) Sodium

2.

COLUMN A COLUMN B

Aluminium Body parts of an aircraft iron MalleableGraphite ElectrodesZinc Dry cellsGold Exist in free stateSilver JewelleryCopper Cooking utensilsPhosphorus Matchboxes

B. 1. Mercury, gallium, francium, caesium and rubidium are the only metals that occur in a liquid state at room temperature. (You can write any one of the given metals.)

2. Basic oxides: Th e oxides of metals are basic oxides because when these oxides of metal react with water, they form bases. Th ese turn red litmus solution blue. Examples are copper oxide (CuO) and magnesium oxide (MgO).

3. Copper is a good conductor of electricity so it is used in making copper coils for electrical appliances. 4. Zinc is used for coating iron objects to prevent rusting of iron because zinc is more reactive than

iron. 5. Diamond is the hardest non-metal and that is why it is used to cut glass.

6. (a) Malleability: Th e property by virtue of which metals can be beaten into thin sheets is called malleability.

(b) Sonority: Th e property by virtue of which metals produce a ringing sound when struck with a hard object is called sonority.

(c) Ductility: Th e property of metals by virtue of which they can be drawn into wires is called ductility.

(d) Corrosion: Th e process of slow eating away of a metal due to the attack of atmospheric gases and moisture on its surface is called corrosion.

7. (a) Metals are ductile means they can be drawn into wires. (b) iron is placed higher than copper in the activity series; so it reacts with copper sulphate

solution. (c) Graphite is a good conductor of electricity so it is used in making electrodes in the dry cells. (d) Metals are sonorous means they produce sound when they are struck hard. C. 1. Aluminium is a useful metal because of the following properties. it is hard and solid at room temperature. it is malleable as it can be beaten into sheets, for example, aluminium foil. it is ductile and also a good conductor of heat and electricity; so it is used in making utensils. it is sonorous and has a very high melting point which makes it useful for making many things. it is non-corrosive in nature.

33

2. Metal Non-metal

Ductility Most metals can be drawn into thin wires, so they are ductile.

Non-metals are brittle and cannot be drawn into wires.

Conductivity of heat and electricity

Metals are good conductors of heat and electricity.

Non-metals are bad conductors of heat and electricity.

Malleability Most metals can be beaten into sheets.

Non-metals are brittle, they break on beating.

3. To show the rusting of iron Materials required: 1 test tube, salt, water, 1 iron nail Method: Take test tube and fill half of it with water. Now, add some amount of salt in the test tube

and mix it well. Now, put the nail in the test tube and leave it for at least 2-3 days. After 2-3 days, take out the nail and observe the change.

Observation: After 2-3 days you will notice that the nail of test tube rusts. Conclusion: iron objects rust in the presence of moisture and air. Presence of salt increases the

rusting or iron. 4. Activity series of metals: This is a series in which metals are arranged in the decreasing order of

their reactivity. The metals that are more reactive are placed higher in the activity series. The more reactive metals replace less reactive metals from their salt solutions.

1. Metal: Magnesium (a) Salt: Magnesium sulphate No reaction will take place in this case because no metal will displace itself. (b) Salt: Zinc sulphate Magnesium is more reactive than zinc so it will displace zinc from zinc sulphate solution

and magnesium sulphate and zinc metal will be obtained as final product. Magnesium + Zinc sulphate Magnesium sulphate + Zinc (c) Salt: Copper sulphate Magnesium is more reactive than copper so it will displace copper from the copper sulphate

solution and magnesium sulphate and copper metal will be obtained as final product. Magnesium + Copper sulphate Magnesium sulphate + Copper 2. Metal: Zinc (a) Salt: Magnesium sulphate No reaction takes place because zinc is less reactive than magnesium so it will not displace

magnesium metal from its salt solution. (b) Salt: Zinc sulphate No reaction will take place in this case because no metal will displace itself. (c) Salt: Copper sulphate Zinc is more reactive than copper so it will displace copper from its salt solution and zinc

sulphate and copper metal will be obtained as final products. Zinc + Copper sulphate Zinc sulphate + Copper 3. Metal: Copper (a) Salt: Magnesium sulphate No reaction takes place because copper is less reactive than magnesium; so it will not

displace magnesium metal from its salt solution.

34

(b) Salt: Zinc sulphate No reaction takes place because copper is less reactive than zinc, so it will not displace zinc

metal from its salt solution. (c) Salt: Copper sulphate No reaction will take place in this case because no metal will displace itself. 5. Displacement reaction: Th e chemical reaction in which a metal reacts with a salt solution and

displaces the metal present in it, is called displacement reaction. iron is placed higher than copper in the activity series, so it reacts with copper sulphate solution while copper does not react with iron sulphate solution.

Fe + CuSO4 FeSO4 + Cu iron Copper sulphate iron sulphate Copper Cu + FeSO4 No reaction Copper iron sulphate D. 1. Corrosion 2. iron + Oxygen (air) + Moisture (Water) Rust 3. Prevention of rust: Rusting of iron objects can be prevented by coating the iron objects with more

reactive metals, oil and grease. E. 1. Sodium metals form oxides at room temperature, as they are highly reactive metals. Th ey are kept

immersed in kerosene oil because if the metals come in contact with moist air, they can catch fi re. 2. Glass is a poor conductor of heat so wearing glasses protects workers from heat while they are

welding. 3. No, copper sulphate solution cannot be stored in an iron container because iron is more reactive

than copper and will displace copper from its salt solution and iron sulphate solution will be formed. 4. Pickles are acidic in nature and acid forms salt and hydrogen gas on reaction with metals which will

spoil the pickle.


Worksheet 1 1. Displacement reaction 2. Th e chemical reaction in which a metal reacts with a salt solution and displaces the metal present

in it. 3. Th e metals present at the top of the activity series are more reactive while metals present below

hydrogen in the activity series are less reactive. 4. iron of the knife will displace the copper of the copper sulphate solution and a brown deposition of

copper will be placed on the nail. 5. Fe + CuSO4 FeSO4 + Cu

Worksheet 2 1. (a) Carbon dioxide (b) Sodium hydroxide (c) Rust (d) Magnesium oxide

(e) Hydrochloric acid, Hydrogen gas 2. (a) Malleability (b) Graphite (c) Salt (d) Rusting (e) Activity series 2. (a) 2Cu + O2 2CuO (b) 2Na + H2O 2NaOH + H2

(c) Zn + H2SO4 ZnSO4 + H2 (d) Cu + FeSO4 CuSO4 + Fe

35

Specific Learning Objectives Aft er the completion of the chapter students will be able to understand:

• What are fossil fuels?• What is natural gas?• Disadvantages of fossil fuels and also how to conserve them.

Warm upStart the topic by asking the questions like, from where do we get energy for everything? Also ask them, have they ever heard about fuels? Now ask the students to complete the exercise given in the Warm-up section.

Concept explanation• Explain to the students that renewable resources are those that will either never get exhausted

or, can be replaced by natural process. However, all renewable resources are exhaustible if they are used faster as compared to their renewal.

• Explain to the students that non-renewable resources once used up cannot be replaced within a reasonable period of time. For example, coal, petroleum and natural gas.

Fossil Fuels• Explain to the students that coal, petroleum natural gas are called fossil fuels. Coal is formed

by the dead plants when buried for millions of years. Coal and petroleum are formed from the dead remains of plants and animals which remain buried in the deeper layers of the earth for millions of years as fossils, under high temperature and high pressure. So these are known as fossil fuels.

Coal• Explain to the students that coal is a fossil fuel. it is formed when the vegetation remained

buried and trapped in the deeper layers of the earth for millions of years, due to natural calamities like earthquake and volcanoes that result in the death of vegetation. Under high temperature, high pressure and less supply of oxygen, the vegetation got converted into coal. Th e slow process of conversion of wood into coal is called carbonisation.

• Coal is processed in the industry by destructive distillation to get some products such as coke, coal tar and coal gas.

Petroleum• Explain to the students that petroleum is formed from the dead remains of plants and animals

which remained buried and trapped in the deeper layers under water for millions of years. Absence of air, high temperature and high pressure transformed them into petroleum and natural gas. Petroleum is a thick black liquid found trapped in between the rocks called crude oil.

Chapter 5Coal and Petroleum

36

Natural Gas• Explain to the students that natural gas is found above petroleum which can be easily

transported through the pipes. it is stored under high pressure as compressed natural gas (CNG).

• Explain to the students that it is important to conserve petroleum. Explain to them the tips to conserve petroleum.




37

Worksheet 1 1. Fill in the blank cells in the table:

Constituents of Petroleum UsesLiquefi ed Petroleum gas (LPG) Fuel for home and industryGasolineKerosene

Fuel for heavy vehicles, electric generators

Residue lubricating oil paraffi n wax Asphalt (bitumen)

Lubricating machines, in paints, constructing roads

2. Write two uses of each of the following. (a) Coal tar (b) Coke (c) Coal gas (d) Natural gas

3. Write the names of diff erent types of coal and also mention the percentage of carbon in each type.

38

Worksheet 2 Look at the picture and answer the questions that follow.

1. What kind of fuel is obtained from the above set-up?

2. How is this fuel obtained?

3. Name the process for refi ning of petroleum.

4. What are the limitations of fossil fuels? Why are they called fossil fuels?

5. Give the detailed account of the statement, “Use of fossil fuels adds many undesirable substances in the atmosphere.”

39


A. 1. (a) Anthracite and bituminous (b) Coke and coal tar (c) Petrol and diesel (d) Coal and petroleum (e) Oxides of carbon and sulphur

2. COLUMN A COLUMN BFossil fuels ointmentsFractional distillation for making roadsParaffi n wax fossils of plants and animalsCoal tar fuel for vehiclesPetrol refi nery

B. 1. Petroleum: Petroleum is formed when the dead remains of marine plants and animals were buried and trapped inside the deeper layers of the earth for millions of years. it is a mixture of various hydrocarbons.

2. Coal tar: it is obtained as a by-product in the process of manufacturing of coke. it is a thick, black liquid with an unpleasant smell.

3. Uses of coke: Manufacturing steel Extraction of many metals 4. Coal gas is obtained when coal is processed to make coke. 5. Carbonisation: Th e slow process of conversion of wood into coal is called carbonisation.

6. (a) An ideal fuel is cheap and does not cause pollution. (b) Coal and petroleum are inexhaustible natural sources of energy. (c) Natural gas is not found along with coal deposits. (d) Sun and wind are natural renewable resources. (e) Coal is obtained from decayed dead remains of plants and animals.C. 1. Petroleum is formed when the dead remains of marine plants and animals were buried and trapped

inside the deeper layers of the earth for millions of years. Absence of air, high temperature and high pressure transformed the dead remains into petroleum and natural gas.

Refer Figure 5.2 from page 70 Constituents of petroleum: Petroleum gas (LPG), petrol, diesel, kerosene, gasoline, lubricating fuel,

paraffi n wax and asphalt. 2. Refi ning of petroleum: Petroleum is obtained as a crude oil which is a dark liquid. it is a mixture

of components such as petrol, diesel, kerosene, paraffi n wax, light oil, heavy oil, etc. Th e process of separating various components of crude oil in the fractionating column is called refi ning or fractional distillation. it works on the principle that diff erent compounds mixed in petroleum boil at diff erent temperatures. Th ese vapours are collected and condensed to obtain pure products. Th is process is carried out in a petroleum refi nery. Each fraction, thus obtained, is a mixture of many hydrocarbons which can be separated by various other methods to give diff erent products.

Refer Figure 5.3 from page 71

40

3. Natural gas is collected as a layer above petroleum which can be easily extracted and transported through pipes. it is mainly made up of hydrocarbons such as methane with traces of butane and propane. it is stored under high pressure as compressed natural gas (CNG). Natural gas is a very important fossil fuel because:

it is used for power generation. it is a less polluting fuel. Th erefore, it is used to run vehicles. it is used as a fuel in factories. it is also used in the manufacture of many chemicals such as hydrogen, ammonia and fertilisers. it is used in the manufacture of steel, glass and other products. 4. Disadvantages of fossil fuel: Th e two main disadvantages of fossil fuels are their limited availability

and air pollution caused due to their use. Burning of fossil fuels releases harmful gases, such as carbon monoxide and carbon dioxide. Due to carbon dioxide, the average temperature of the earth is increasing steadily. Th is is causing global warming, due to which the polar ice caps are melting and climate patterns are changing around the world. Release of harmful gaseous oxides such as sulphur and nitrogen oxides causes acid rain which makes the soil infertile and damages monuments. Carbon monoxide is a toxic gas which if inhaled can cause headaches and even death. Burning of fossil fuels also produces soot and suspended particles. Th ese get collected in our lungs and reduce our breathing capacity. Th ese can cause coughing, asthma and other respiratory diseases.

5. in india, the Petroleum Conservation Research Association (PCRA) has listed some tips to save petrol/diesel while driving.

Drive at a constant and moderate speed as much as possible. Switch off the engine at traffi c signals and during waiting time. Always maintain correct air pressure in the tyres. Regular maintenance of the vehicle also consumes less fuel. We can also save fossil fuels by using more alternate sources of energy, such as, solar energy,

hydropower, wind energy, tidal energy, geothermal energy, etc. D. 1. Petroleum 2. Fractional distillation process is used for refi ning petroleum. 3. Limitations of petroleum: it causes pollution on burning and also releases lots of toxic gases which

increases the temperature of the earth and result in global warming. E. 1. We cannot stop using petroleum and LPG fuels completely because these fuels are important

sources of energy for us. But we can minimise the use of these fuels as these fuels increase pollution. 2. Pressure cooker cooks food under high pressure. All the heat supplied to the cooker is trapped

inside it which is used in cooking food in shorter time. So, cooking in pressure cooker saves energy. 3. Th e government gives fi nancial assistance to people setting up a biogas plant but it does not give the

same amount of assistance to people using LPG because biogas is a renewable and non-polluting source of energy, also it is cheaper. While LPG is a non-renewable and polluting resource of energy and it is also expensive.

4. Renewable resources are those resources that will either never get exhausted or can be replaced quickly by the natural process while non-renewable resources, once used up cannot be replaced within a reasonable period of time. So, we should rely more on renewable resources and not on non-renewable resources for our energy needs.


Worksheet 1 1. Gasoline- Petrol-motor fuel and solvent for dry cleaning Kerosene- Domestic fuel and jet engine fuel Fuel for heavy vehicles, electric generators- Diesel

41

2. (a) it is used to make synthetic dyes. it is also used as a protective coating on roads. (b) it is used to make producer gas (nitrogen + carbon monoxide). it is used to manufacture steel. (c) it was used for cooking and lighting. (d) it is used for power generation. it is used as a fuel in factories. 3. Anthracite: 95-98%, Bituminous: 60-80%, Lignite: 25-40%

Worksheet 2 1. Petroleum 2. This fuel is obtained for oceans and seas. 3. Fractional distillation 4. Limited availability and air pollution are the two limitations of fossil fuels. They are called fossil

fuels because they turned into fossils when got buried under the layers of the earth for millions of years and they are used as fuels for getting energy.

5. Burning of fossil fuels provide lot of energy and along with energy it also produces lot of toxic gases to the environment.

42

Chapter 6Combustion and Flame

Specific Learning Objectives

Aft er the completion of the chapter, students will be able to understand:• What is combustion and what are its products.• Condition necessary for combustion and types of combustion.• What are the regions of a fl ame?• What is a fuel and also types of fuels?• Harmful eff ect of burning fuel.

Warm UpStart the topic by asking them the questions like, what do they know about combustion? What is involved in this process? Give them some clues as to what can combustion lead to? What are the regions of a fl ame? Now ask the students to complete the exercise given in the Warm-up section.

Concept Explanation

Combustion

• Explain to the students the process of combustion. Also tell them that the substances that react with oxygen and produce heat and light are called combustible substance, like magnesium, charcoal, paper, wood, kerosene, LPG, coal, charcoal, etc. Th e substances that do not produce heat and light on burning are called non-combustible substances, like rocks, mud, metals, etc.

• Explain to the students that fuels are mostly made up of hydrocarbon, that is, they are the compounds of carbon and hydrogen.

• Explain to the students that the lowest temperature at which the substance starts burning in the presence of oxygen is called ignition temperature.

• Explain to the students that the conditions necessary for the combustion are: 1. Substance should be combustible. 2. Presence of oxygen which supports combustion. 3. Heating the substance to its ignition temperature.

• Tell students that there are substances that have very low ignition temperature, like petrol, alcohol, kerosene and liquid petroleum gas (LPG). Th ey catch fi re very easily even with a small spark, therefore, they should be stored with great care.

43

Flame• Ask students if they have they observed different colours/zones in a candle flame. Tell them

that a candle flame has three zones, namely, non-luminous zone, luminous zone and dark zone.

• Also tell students the harmful effects of burning fuel.




44

Worksheet 1 1. Write two examples of each of the following.

(a) Solid fuel

(b) Liquid fuel

(c) Gaseous fuel

(d) infl ammable substances

2. List three things important to control fi re.

3. List any four characteristics of the good fuel.

4. Write the diff erent types of combustion.

45

Worksheet 2 1 Draw a labelled picture showing regions of the fl ame and also mention two

characteristics of each region.

Non-luminous zone

Luminous zone Dark zone

2. List the reasons for carbon dioxide to be an excellent fi re extinguisher.

46


A. 1. COLUMN A COLUMN BNon-polluting fuel CNGLuminous fl ame Yellow fl ameWhite phosphorus Spontaneous combustionNon-luminous fl ame Blue fl ameLiquid fuel LPG

2. (a) Water and carbon dioxide (b) Non-luminous zone and luminous zone (c) Matchstick and gas stove (d) Rock and metal (e) Petrol and kerosene B. 1. Combustion: Th e process of burning of a material in the presence of air or oxygen with the

production of heat and light is called combustion.

2.

Combustible substances Non-combustible substancesSubstances which can burn are called combustible substances.

Substances that do not produce heat and light on burning are called non-combustible substances.

Examples: Magnesium, charcoal, paper, wood, kerosene, LPG, coal and charcoal

Examples: rocks, mud and metals

3. Burning of wood creates many air pollutants which can result in respiratory problems. Moreover, incomplete oxidation during burning of wood creates carbon monoxide which is a poisonous gas. Burning of kerosene produces lesser amount of air pollutants. So, burning of kerosene oil is better than burning of wood.

4. Non-luminous fl ame: When the supply of oxygen is suffi cient, a substance burns with a non-luminous or a blue fl ame. A blue fl ame emits very little light. Th is type of fl ame leaves behind no residue.

5. Th e conditions necessary for combustion are: Th e substance should be combustible. Oxygen should be available to support combustion. Th e substance should be heated to its ignition temperature. 6. Ignition temperature: Th e lowest temperature at which the substance starts burning in the presence

of oxygen is called its ignition temperature. 7. (a) LPG is a better fuel than wood because of several reasons. Unlike wood, LPG burns without

smoke. Moreover, use of LPG as a fuel also rules out the chances of getting respiratory disorders which may happen when someone uses wood as a fuel. Storage and transportation of LPG are easier compared to that of wood.

(b) Some combustible substances, such as matchbox, kerosene, coal, wood, etc., do not catch fi re at room temperature because the room temperature is lower than the ignition temperature of these substances.

47

(c) Substances with lower ignition temperature such as petrol, alcohol, kerosene and liquefied petroleum gas (LPG) catch fire very easily, even with a small spark. Therefore, they should be stored properly.

(d) Firecrackers are an example of explosion because when we burn fireworks during celebrations, we ignite a cracker. A sudden reaction takes place in the cracker with the emission of heat, light, smoke and sound.

(e) This is the coolest part of a flame because no combustion takes place here. Being deep inside, it has vapours which are not burnt as they do not come in contact with oxygen.

(f) Burning of coal releases fine particulates of unburnt carbon in the air which causes respiratory diseases like asthma and bronchitis. incomplete combustion of coal releases carbon monoxide gas. it is a poisonous gas which can even cause death. Therefore, it is dangerous to burn coal in a closed room as it can kill people sleeping in the room.

C. 1. Fuel: Fuels are those substances that are used as a source of energy for various purposes at homes and industries. Wood, coal, petrol, LPG, kerosene, etc. are commonly used as sources of fuel. Fuels can be of three types on the basis of their physical state.

Solid fuels: Coal, wood, cow dung cakes, dead plants, etc., are solid fuels. Liquid fuels: Kerosene, LPG, petrol, diesel, etc., are liquid fuels. Gaseous fuels: Natural gas, water gas, coal gas, producer gas, biogas, etc., are gaseous fuels. 2. A candle flame can be divided into three zones. The formation of each zone depends on the amount

of air available. Each zone demonstrates a different colour. Non-luminous zone: This is the zone of complete combustion and the flame is blue in colour. it is

the outer part of the flame. This is the hottest zone and does not leave any mark on the object when it is placed on it. This zone emits very little light.

Luminous zone: This is the zone of incomplete combustion. This is the middle zone of a flame. This is a moderately hot zone. it leaves behind black soot and other residue.

This zone emits the most light. Dark zone: This is the coolest part of a flame and no combustion takes place here. it is the innermost

zone of the flame. it covers the area surrounding the wick. Being deep inside, it has vapours which are not burnt as they do not come in contact with oxygen. it emits no light.

Refer Figure 6.4 on page 86 3. Rapid combustion: When we strike a matchstick on the side of the match box or light a lighter near

the gas burner, what do we observe? The matchstick and the gas stove burn rapidly, producing heat and light. This type of combustion is called rapid combustion.

Spontaneous combustion: There are substances that burn suddenly into flames on their own, without the application of heat. This type of combustion is called spontaneous combustion. For example, phosphorus burns at room temperature.

Explosion: When we burn fireworks during celebrations, we ignite a cracker. A sudden reaction takes place in the cracker with the emission of heat, light, smoke and sound. This

type of combustion is called explosion. 4. Fire extinguisher: it is device used to control or extinguish fire. The most common extinguisher we

use is water. Fire caused due to electrical short circuit, petrol and oil cannot be controlled by using water. in such cases, water may conduct electricity and electrocute the person. Petrol and oil being lighter than water, will always float above the water surface and therefore, will continue to burn. in such cases, carbon dioxide is used as an extinguisher due to its following properties.

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it does not support burning. it is heavier than oxygen. Therefore, it covers the combustible material like a blanket and cuts

off the supply of oxygen. it does not harm the electrical equipment. Carbon dioxide can be stored at a high pressure as liquid in cylinders. When released, it expands and

cools down, forming a blanket around fire. it also brings down the temperature of the combustible material.

Other extinguishers used include soda-acid fire extinguisher. it contains sodium bicarbonate solution and sulphuric acid in a cylinder. These compounds react and release carbon dioxide which cuts off the oxygen supply to control the spreading of fire. Chemicals such as sodium bicarbonate and potassium bicarbonate are sprayed as dry powder near the fire which gives off carbon dioxide. Sometimes, even sand is used as a fire extinguisher.

5. The burning of fuels has the following harmful effects on the environment. Burning of hydrocarbons releases fine particulates of unburnt carbon in the air which causes respiratory diseases like asthma and bronchitis. incomplete combustion of these fuels releases carbon monoxide gas. it is a poisonous gas which can even cause death. it is dangerous to burn coal or wood in a closed room as it can kill people sleeping in the room. Combustion of fuels releases carbon dioxide in the environment which causes global warming.

Burning of coal, petrol and diesel releases sulphur dioxide gas and oxides of nitrogen. These oxides dissolve in rain and form acids. Such rain is called acid rain. it is harmful for the crops, plants, monuments, buildings and soil.

Using alternative sources of energy is recommended to reduce the effect of pollution and save the environment. Fuels like CNG are used in automobiles in place of petrol and diesel as such fuels are cleaner fuels and produce very small amount of harmful products.

D. 1. in the given picture, firefighters are extinguishing fire using fire extinguishers. 2. Firefighters are equipped with a wide variety of equipment to extinguish fire. Based on the source

of fire, firefighters use different materials to extinguish fire. 3. Water is mostly used to extinguish fire in most of the cases. 4. As a responsible citizen, we will give space to the fire brigade vehicle to go. E. 1. in case of a fire accident, the smoke produced contains harmful gases such as oxides of sulphur,

nitrogen and carbon which cause respiratory diseases like asthma and bronchitis. So, in case of a fire accident both flames and smoke are equally harmful.

2. (a) They should have left that area immediately. (b) There could be any reason for such as explosion such as Carelessness of any person improper safety measures 3. The gas inside the cylinder is in a liquid state that is why it is called liquefied petroleum gas. it is

liquefied because it is easier to store and transport a liquid, rather than a gas. 4. Luminous zone of flame is used to make kajal at home because this zone leaves behind black soot

and other residue. 5. Yes, we should use sand to put out fire caused due to electrical equipment because sand cuts off the

supply of air.

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Worksheet 1 1. (a) Coal, Wood

(b) Kerosene, LPG (c) Coal gas, Natural gas (d) Petrol, Kerosene 2. To control fi re, one must remove the combustible material, bring down the temperature of the

burning material below its ignition temperature and also cut off the supply of air. 3. it is readily available, burns easily in air, cheap and does not cause pollution. 4. Rapid combustion, spontaneous combustion and explosion

Worksheet 2 1. Students will do this section on their own. Non-luminous zone: it is the zone of complete combustion. it is the hottest zone. Luminous zone: it is the zone of incomplete combustion. it is a moderately hot zone. Explosion: it is the coolest part of the fl ame. it is the innermost zone of the fl ame. 2. Carbon dioxide does not support burning and it is heavier than oxygen, therefore, it is an excellent

fi re extinguisher.

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Chapter 7Conservation of Plants and Animals

Specific Learning objectives Aft er the completion of the chapter, students will be able to understand:

• What is biodiversity?• Deforestation and its consequences.• importance of conservation of forest and wildlife• Methods and policies to protect and conserve biodiversity.• Th e protected areas like biosphere reserves, national parks and wildlife sanctuaries.• Red Data Book • Recycling of paper and reforestation.

Warm UpMake an attempt to have an interactive class by asking the students if they understand the importance of conservation of plants and animals. Ask the students the reasons for conservation of an ecosystem. Now, ask the students to complete the exercise given in the Warm-up section.

Concept ExplanationExplain to the students that forests are a prime source of energy required for all life forms. Forests play a vital role in protecting the environment. Tell students the terms that are related with biodiversity and also explain endemic, endangered, extinct, vulnerable and threatened species.

• Explain to the students that deforestation is the removal of plant cover in the forests for the use of land for various purposes. Deforestation results in the loss of biodiversity.

Flora and Fauna

• Tell students about the fl ora and fauna and also explain the site which are earmarked to conserve them.

Ecosystem

• Explain to students that an ecosystem is made of all the plants, animals and microorganisms in an area along with the non-living components such as air, soil, temperature, water, etc. it is a self-sustaining functional unit of the biosphere.

Conservation

• Tell students about the government agencies that are working towards the conservation of plant and animal species.

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Recycling of Paper

• Ask students what they can do to conserve trees. Tell them the importance of trees and also mention the ways by which they can use paper wisely.




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Worksheet 1 1. Why does the passion for biodiversity compel someone to grow a fl ower or a

vegetable garden?

2. Is it necessary to have a large area to have a garden? How will you use small areas for making a green belt in your city?

3. Considering the present scenario, if you had some space in and around your house, what would be the fi rst thing that would occur in your mind?

4. Why is green belt important in a metropolitan city?

5. How does biodegradation of garden waste help the soil? What kind of organisms are involved in this process and how?

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Worksheet 2 1. What does IUCN stand for?

2. Write the nine categories of threatened species given by the IUCN Red List.

3. When do we celebrate Wild life Conservation week?

4. What is the need for conservation of plants and animals?

5. Defi ne reforestation.

6. Give diff erence between extinct species, endangered species and threatened species.

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A. 1. (a) False (b) True (c) True (d) False (e) True

2. COLUMN A COLUMN B

Deforestation increase in carbon dioxideBiodiversity All plants and animals in a regionProtected areas National parksTh reatened species EndangerediUCN Red Data Book

B. 1. Biodiversity: Th e abundance of various species of plants, animals and microorganisms in the natural environment of a specifi c region is called biodiversity.

2. Deforestation: Th e removal of plants in the forests for various purposes is called deforestation. 3. Th e international Union of Conservation and Natural Resources (iUCN) works towards assessing

the global conservation status of plant and animal species. it maintains a comprehensive list known as the iUCN Red List of Th reatened Species.

4. Th e preservation and careful management of plant and animals species in order to prevent their extinction is called conservation.

5. Life on earth relies on the interactions between diff erent plants and animals. Th erefore, if we want to survive on this planet for a long time, then we cannot aff ord the loss of biodiversity, which is one of the crucial environmental problems today.

6. (a) Due to deforestation, less carbon dioxide is used up and its increased amount in the atmosphere causes global warning. Carbon dioxide remains in the atmosphere and traps the heat refl ected by the earth. Th is aff ects the climate patterns and may lead to reduced rainfall and loss of fertility of the soil. As a result, the chances of natural calamities, such as fl oods and droughts increase.

(b) Due to deforestation, the soil particles are easily washed away by rain and wind, leading to soil erosion. in hilly areas, erosion can cause landslides. Th e fertile layer of soil is lost and the land becomes barren. if this situation continues for a long time, then the area converts into a desert and this process is called desertifi cation.

(c) Forests are one of the important natural resources on this earth. Covering the earth like a green blanket these forests not only produce innumerable material goods, but also provide several environmental services which are essential for life. Th erefore, forests are also called as green wealth.

(d) Plants and animals maintain the balance of our ecosystem. if any animal species has become extinct then this balance will get disturbed which will ultimately aff ect our survival on this earth.

C. 1. Consequences of deforestation are as follows. Plants take in carbon dioxide for photosynthesis. Deforestation removes the vegetation cover,

which increases the level of carbon dioxide in the atmosphere along with the temperature. it also disturbs the ecological balance in nature.

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Due to deforestation, less carbon dioxide is used up and its increased amount in the atmosphere causes global warning. This affects the climate patterns and may lead to reduced rainfall and loss of fertility of the soil.

Deforestation also leads to loss of habitat and in turn causes extinction of many plant and animal species.

Due to deforestation, the soil particles are easily washed away by rain and wind, leading to soil erosion. The fertile layer of soil is lost and the land becomes barren. if this situation continues for a long time, then the area converts into a desert and this process is called desertification.

Due to deforestation, transpiration cannot take place which makes the atmosphere dry, adversely affecting the water cycle.

Apart from man-made causes, many plant and animal species are also destroyed due to natural causes such as earthquakes, climate change, floods, droughts, cyclones, etc.

2. The Red Data Book keeps a record of all the endangered plants and animal species. This is done to highlight the species of plants and animals that are facing a threat of extinction. There are separate books for plants and animals. it also gives the status of their present population and the risk of extinction of various species. These books are revised periodically and are updated. The animals and plant species are categorised as being extinct, critically endangered, endangered and vulnerable species. The iUCN publishes the Red List of Threatened Species to check the growth or decline of the population of plants and animals. Some steps in the direction of wildlife conservation that can be taken are as follows:

Regularly survey and collect all the information about wildlife, especially, their number and growth.

Protect habitats by protecting forests. Delimit the areas of their natural habitat. Protect wildlife from pollution and natural hazards. impose complete restriction on hunting and capturing of wildlife. impose restrictions on export and import of wildlife products and severe punishment to be

given to those who indulge in this activity. Make special arrangements to protect those species whose number is very limited. Develop general awareness at national and international levels regarding protection of wildlife. Adopt a system of wildlife management through trained personnel. 3. A biosphere reserve is a special area of land or coastal environment in which multiple use of land is

permitted by dividing it into certain zones. The natural or the core zone consists of an undisturbed and legally protected ecosystem. There is a buffer zone surrounding the core zone. The transition zone is the outermost part of the reserve. This area allows active participation of

the government and local people. Some biosphere reserves, recognised by the UNESCO in india are Nilgiri, Sunderbans and Gulf of

Mannar. 4. National park: A national park is an area which is strictly reserved for the protection of the wildlife.

Human activities such as forestry, grazing, cultivation, etc., are not permitted here. Some famous national parks in our country are Jim Corbett and Dudhva in Uttar Pradesh and Tadoba in Maharashtra.

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Zoological garden: Zoological parks are special areas where animals are kept in enclosures or cages for public display. Many zoological parks or ‘zoos’ help in conservation and spread awareness about biodiversity. Some zoos also run programmes for breeding of endangered species. Famous zoological garden is National Zoological Park, Delhi.

Forest reserves: Forest reserves are those areas of land where commercial activities, such as obtaining wood and urbanisation are strictly prohibited so that the unique species of plants and animals can be conserved. Some examples of forest reserves are Hanumasagara Reserve Forest, Karanataka, and Begur Reserve Forest, Kerala.

Wildlife sanctuary: A wildlife sanctuary is a protected area that is reserved for the conservation of wildlife. Human activities, such as collecting timber and minor forest produce are permitted. Some wildlife sanctuaries are Periyar (Kerela), Ranipur (Uttar Pradesh), Chilika Lake (Odisha) and Sariska (Rajasthan).

5. We need paper in our daily life. This paper is obtained from trees which are being cut indiscriminately. The pulp and paper industry is so huge that trees are planted and grown specially to make paper.

Ways to save paper: By recycling and reusing the paper products, we can protect the trees from being cut down. if students save one sheet every day, then it will help in saving many trees in a year. By doing

so, we will not only save the trees but also save energy, chemicals and water that are used in manufacturing of paper.

Most of the used paper can be recycled to make cardboards, paperboard, packets, paper bags, etc.

D. 1. Deforestation is being shown in the picture. 2. Harmful effects of deforestation are as follows. it disturbs the ecological balance in nature. it becomes causes flood and drought. it leads to soil erosion and infertility. it also affects the water cycle. 3. Reforestation is the only method to restore destroyed forest by planting more trees. E. 1. Students were asked to keep quiet because noise disturbs the animals. And due to loud noise,

animals feel threatened. 2. Wetlands are among the most productive ecosystems in the world. An immense variety of species

of microbes, plants, insects, amphibians, reptiles, birds, fish and mammals can be part of a wetland ecosystem. Climate, geology and the movement and abundance of water help to determine the plants and animals that inhabit each wetland. Therefore, the government is trying to protect these areas.

3. Zoos are the special areas where animals are kept in enclosures or cages for public display. While in national parks and wildlife sanctuaries, animals live in their natural habitat and also remain conserved.

57


Worksheet 1 1. Having a garden or a vegetable garden around the house cools the surroundings. it also gives an

aesthetic appeal. Having greening around purifi es the air. Most of all this conserves biodiversity. 2. it is not necessary to have a large area to have a garden. A large number of potted plants can be kept

in the small area. Or the small area can be used to develop a kitchen garden. Or it can be just used to grow a patch of green grass.

3. i would use the space in and around my house to grow a garden and a kitchen garden. Th is will ensure that i have enough greenery around me.

4. A metropolitan city is a concrete jungle with fewer green belt. Th ere are buildings all around with less of free space. So here is a need to develop green belt in some areas because of the advantages that plants usually have, including purifying air and keeping the surroundings cool.

5. Biodegradation of garden waste produces manure which is a natural fertiliser and important for plants.

Manure comprises nutrients necessary for the growth of plants. it does not have the harmful eff ects that fertilisers have.

Earthworms usually are involved in this process as they convert the biodegradable waste into organic manure.

Worksheet 2 1. international Union of Conservation and Natural Resources.

2. Extinct Near threatened Extinct in wild Least concern Critically endangered Data defi cient Endangered Not evaluated Vulnerable

3. 1 – 7 October. 4. To maintain the balance in nature. 5. Reforestation is the restoration of the destroyed forest by planting new trees. 6. Extinct Species: Th e species that no longer exist anywhere on the earth are called extinct species.

Dodo bird and dinosaurs have become extinct long time ago. Endangered Species: Th ose species whose number has reduced to a critical level are called endangered

species. Bison, beaver, antelope, tiger, Asiatic lion and leopard are some of the endangered species. Th reatened Species: Species of plants and animals which are under the threat of becoming vulnerable

or endangered are called threatened species. Great indian Bustard, pygmy sloth and Sumatran rhinoceros are threatened species.

58

Chapter 8Cell–Structure and Functions

Specific Learning Objectives Aft er the completion of the chapter, students will be able to understand:

• What is a cell?• Discovery of the cell.• Organisms show variety in cell number, size and shape.• Cell structure and functions.• What are cell organelles and their functions?

Warm UpStart the topic by asking students the questions like, what do they know about cells? Give them some clues that cells are of diff erent shapes and sizes. Ask the students why is that so? Now ask the students to complete the exercise given in the Warm-up section.

Concept Explanation

Cell• Explain to the students that a cell is a fundamental structural and functional unit of all living

organisms. it is the smallest part of a living body which is capable of independent existence. Th e egg of a hen represents a single cell and is big enough to be seen with unaided eyes.

Cell Theory• Explain to the students that the cell theory states the following.

1. Th e cell is the structural and functional unit. 2. All cells develop from pre-existing cells. 3. Cells die and are replaced. 4. All life starts as a single cell.

Cell Organelles• Explain to the students that most parts of a cell have a defi nite shape, structure and function.

Such parts are called organelles. Cell organelles are living part of a cell.• Tell students that the cell membrane separates the contents of the cell from its surrounding

medium.• Also tell them that plant cells have a cell wall surrounding the cell membrane. it is made up

of cellulose and is a non-living part of the cell. it allows substances in the form of solution to enter and leave the cell.

• Explain to the students that the cytoplasm contains organelles like nucleus, mitochondria, vacuoles, plastids, golgi bodies, lysosomes and ribosomes.

59

Nuclear envelope

Nucleolus

Chromati n

Nuclear pore

Lysosome

Smooth endoplasmic

reti culum

Free ribosome

CentrioleGolgi body

Mitochondrion

Cytoplasm

Cell coat

Plasmamembrane

Rough endoplasmic reti culum

RibosomeNucleus

Animal Cell Plant cell

Prokaryotic cell• Explain to the students that in a prokaryotic cell, the nuclear membrane is not well organised

and the nuclear material is in the form of a chromatin mass in the centre without a membrane. Th e organisms with these type of cells are called prokaryotes. Example: bacteria and blue green algae.

Eukaryotic Cells• Explain to the students that the cells that have well-organised nucleus with nuclear membrane

are called eukaryotic cells (Eu: true; karyon : nucleus). Th e organisms with these type of cells are called eukaryotes. Example: all the organisms except bacteria and blue green algae.




60

Worksheet 1 1. Look at the diagram and the label the following parts. (a) Mitochondria (b) Plasma membrane (c) Ribosomes (d) Golgi apparatus (e) Nucleus (f) Cytoplasm (g) Lysosomes

2. Identify the type of cell and give reason for your answer.

3. Give two diff erences between a plant and an animal cell.

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Worksheet 2 1. Give the diff erence between prokaryotic cell and eukaryotic cell.

.

2. Draw the structure of a generalised cell.

.

3. Defi ne the following terms. (a) Cytoplasm (b) Organelles (c) Cell division (d) Chromosomes

62


A. 1. COLUMN A COLUMN BLysosomes intercellular digestionVacuoles Storage of water and foodPlastids imparts colour to the fl owers and leavesEndoplasmic reticulum Network inside the cellCell membrane Permits selected material

2. (a) Mitochondria and endoplasmic reticulum (b) Amoeba and yeast (c) Bacteria and blue green algae (d) Plants and animals (e) Chromoplast and leucoplast

B. 1. Protoplasm: Th e living part of the cell that is surrounded by the plasma membrane. 2. Cell organelles: Th e living parts of the cell that have defi nite shape, structure and function are called

organelles. 3. Th ese organelles have digestive enzymes and help in intercellular digestion and in destroying

foreign substances. 4. Cell wall is the non-living part of the plant cell. 5. Prokaryotic cells: Th e cells in which the nuclear membrane is not well organised and the nuclear

material is in the form of a chromatin mass, placed in the centre of the cell without a membrane. 6. (a) it is not necessary for animal cells to have a cell wall because of the following reasons.

Animal cells have other forms of support like exoskeleton and endoskeleton while plant cells do not have these so they require cell wall.

Animal cells require fl exibility for function and movement. Th is would not be possible if cells have cell wall as it would restricts fl exibility.

(b) Th e cell membrane has fi ne pores through which the substances move in and out of the cell. (c) Mitochondria is the site of cellular respiration and produce energy. Th erefore, it is called the

‘powerhouses of the cell’. 7. (a) Refer to Table given on page 111

(b) Prokaryotic cell Eukaryotic cell

in prokaryotic cells (pro: primitive; karyon: nucleus), the nuclear membrane is not well organised and the nuclear material is in the form of a chromatin mass, placed in the centre of the cell without a membrane. Organisms with such type of cells are called prokaryotes.

Eukaryotic cells (eu: true; karyon: nucleus) have a well-organised nucleus with a definite nuclear membrane. Th e organisms with these type of cells are called eukaryotes.

For example, bacteria and blue green algae are prokaryotes.

For example, all higher organisms, except bacteria, viruses and blue green algae are prokaryotes.

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C. 1. Refer Figure 8.7_page 112 and Figure 8.8_page 112 2. (a) Cell membrane: The cell membrane separates the contents of the cell from its surrounding

medium. (b) Chromosomes: They carry genes which help in the inheritance or transfer of characters from

parents to the offspring. (c) Nuclear membrane: This membrane is porous and allows the movement of materials between

the cytoplasm and nucleus. (d) Plastids: They are of several kinds. Most common ones are the chloroplast containing green

pigments called chlorophyll, which is essential for photosynthesis. it provides green colour to the leaves. Chromoplast imparts colour to the flowers and fruits such as red, orange, yellow and leucoplast stores starch in potato and is colourless.

(e) Cytoplasm: it holds the internal components of cells in place and protects them from damage. (f) Nucleus: it regulates and coordinates various activities of the cell. (g) Vacuole: They store water, useful minerals, pigments, many other substances and waste

products. (h) Endoplasmic reticulum: it helps in the synthesis, storage and transport of protein and fat in the

cell. (i) Ribosomes: These are the sites of protein synthesis. 3. Cells of organisms show variations is terms of their number, shape and size. Cell number: Larger the organism, the greater will be the number of cells in its body. Many

plants and animals are made up of a single cell, such as bacteria, Some very small plants and animals are made up of a few cells, such as Spirogyra and Volvox. Most plants and animals around us, including human beings, are made up of millions and billions of cells.

Cell size: Most cells are microscopic and cannot be seen with the naked eye. Cell size may vary from a micrometre (a millionth of a metre) to a few centimetre. A bacteria cell ranges in size from 0.1 to 0.5 micrometre. Nerve cells are the longest cells.

Cell shape: Cells show great variety in their shapes, such as polygonal, rectangular, disc-shaped, cuboid, thread-like, branched and even irregular. The shape of the cell depends on the function it performs. For example, human red blood cells are shaped like a disc to transport oxygen while human white blood cells are amoeboid in shape.

D. (a) Figure 1 represents a plant cell because it contains a cell wall. (b) Both of these cells contain cell membrane, cytoplasm, nucleus, endoplasmic reticulum, Golgi

bodies, mitochondria and ribosomes. (c) Cell wall, plastids and vacuoles are found only in plant cell.

(d) Figure 1 Figure 2 1. Mitochondrion 1. Nucleolus 2. Rough endoplasmic reticulum 2. Nucleus 3. Nucleolus 3. Ribosome 4. Vacuole 4. Cell wall 5. Cell wall 5. Chloroplast 6. Chloroplast 6. Plasma membrane 7. Golgi complex 7. Smooth endoplasmic reticulum 8. Nucleus 8. Mitochondria 9. Smooth endoplasmic reticulum 9. Peroxisome 10. Plasma membrane 10. Cytoplasm 11. Lysosome 11. Lysosome 12. Cytoplasm 12. Centriole 13. Plasmodesmata

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E. 1. When the cells become old or damaged, lysosomes burst and rapidly destroy the cell. 2. When one (or more) gene in the cell becomes damaged or altered, then the cell becomes abnormal.

Th e abnormal cell may then divide into two, then four, then eight, and so on. A group of abnormal cells may then form. if this group of cells gets bigger, it becomes a large clump of abnormal cells called a tumour which causes cancer. Th erefore, cancer is a disease.

3. Radhika would not be able to see the cells in the slide as staining highlights specifi c regions in the cells, which makes it easier for us to view the details.

4. (a) Cells performing similar functions collectively form tissues; tissues performing similar functions together form an organ and organs together form an organ system. So, two organ systems work diff erently in the same organism.

(b) Small structures (cell organelles) present inside cells perform diff erent functions. Th ese structures ultimately form organs and therefore they contribute towards the function of the organ.

5. Th ough Reena took an airtight jar, but while closing the lid some amount of air must have entered inside the jar which becomes responsible for the growth of fungus.


Worksheet 1 1. Animal Cell

(g) Lysosome

(d) Golgi body

(a) Mitochondrion

(f) Cytoplasm

(b) Plasma membrane

(c) Ribosome(e) Nucleus

2. Th is is an animal cell because it does not have cell wall.

3.

Plant cell Animal cellPresence of cell wall. Cell wall is absent.Plastids are present. Plastids are absent.

65

Worksheet 2 1.

Prokaryotic cell Eukaryotic cellTh e nuclear membrane is not well organised. Th ese cells have well organised nucleus with a

defi nite nuclear membrane.Example: bacteria and blue green algae Example: All higher organisms

2.

3. (a) Cytoplasm: Jelly-like liquid present between the cell membrane and the nucleus. (b) Th e living parts of the cell that have defi nite shape, structure and function. (c) A process by which a cell divides into two daughter cells. (d) Th read-like structures present in the nucleoplasm.

66

Chapter 9Reaching the Age of Adolescence

Specific Learning Objective Aft er the completion of the chapter, students will be able to understand:

• What is an endocrine system?• What is adolescence and puberty?• Role of hormone in initiating reproductive function.• Reproductive phase of life humans.• Menstruation or menstrual cycle.• Sex determination in a child.• Hormones other than sex hormones.

Warm UpAsk students what is growth? Ask them if they can feel any change in their body as they are growing? Ask them to complete the exercise given in the Warm-up section.

Concept Explanation

Endocrine System• Explain to the students that we have learnt about various systems in our body like digestive

system, circulatory system, respiratory system, etc. which support life and are essential for the survival of various species. Endocrine system controls many processes like growth, metabolism, development, behaviour and reproduction through the chemicals called hormones.

Adolescence• Explain to the students that the period of transition from a child to an adult is called

adolescence. During adolescence, the body undergoes various changes marked by secondary sexual characters. Th ese changes mark the onset of puberty.

• Tell students that the male hormone testosterone is released by the testes which brings about changes in boys like broadening of shoulders and growth of facial hair. in girls, the ovaries begin to produce female hormone or oestrogen which makes the breasts to develop. Th ese hormones are controlled by another endocrine gland called pituitary gland. Pituitary gland secretes many hormones; one of them controls the egg maturation in the ovary and production of sperms in the testes.

• Explain to the students that adolescents become capable of reproduction when testes and ovaries begin to produce sperms and egg called gametes. Th e production of gametes lasts much longer in males than in females. in females, the reproductive phase begins between 10 and 12 years of age and lasts till 45 to 50 years.

67

Mensturation • Explain to the students that with the onset of puberty, one ovum matures and is released by

one of the ovaries once every 28 days. This process is called ovulation. in case fertilization does not occur, the released egg and the entire uterus lining long with the blood vessels is shed off. This results into bleeding in women which is called menstruation. This cycle repeats every 28 to 30 days and is called menstrual cycle. This is also controlled by hormone.

Nutritional Health of an Adolescent• Tell students about the need of the physical and mental well-being of an adolescent. Also

mention why personal hygiene and exercise are important for the adolescents.




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Worksheet 1 1. Write the hormone secreted by the given glands. Also, mention their functions. (a) Pitutary gland (b) Pancrease (c) Th yroid (d) Adrenal (e) Ovary (f) Testes

2. Give reason why reproductive health is very important.

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Worksheet 2 1. List the changes that take place in the boys during adolescence.

2. List the changes that take place in the girls during adolescence.

3. What is the diff erence between menarche and menopause?

4. Explain the role of personal hygiene and physical exercise for the growth of adolescents.

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A. 1. 1. Target site 2. Pituitary gland 3. Menstrual cycle 4. Testosterone 5. Puberty 2.

COLUMN A COLUMN AGrowth of hair in the armpit Boys and girlsMenstruation Menstrual cycleBalanced diet NutrientsSelf-conscious AdolescentsChemical substances Hormones

B. 1. Adolescence: Th e period of transition from childhood to adulthood is called adolescence. 2. Characteristics of puberty are as follows. Development of secondary sexual characters increase in height Change in body shape Hair growth Voice change Development of sex organs increased activity of sweat and sebaceous glands Mental, intellectual and emotional maturity 3. Th e hormones secreted by the endocrine glands are directly poured into the bloodstream to make

them reach a particular part in the body, called the target site. Th e male hormone, testosterone is released by the testes which bring about the changes in boys, such as broadening of shoulders and growth of facial hair. in girls, the ovaries begin to produce the female hormone or oestrogen which helps in the development of breasts. in both boys and girls, hair grows in the armpits and pubic area. Th ese hormones are controlled by another endocrine gland called the pituitary gland. Th e pituitary gland secretes many hormones. One of them controls the maturation of eggs in the ovary and the production of sperms in the testes.

4. Ovulation: With the onset of puberty, one ovum matures and is released by one of the ovaries, once every 28 days. Th is process is called ovulation.

5. During puberty, the activity of sweat and sebaceous glands (oil glands) increases. it may result in excess sweating and occurrence of acne or pimple in adolescents.

6. (a) Hormones play a crucial role in bringing about the changes that help a child to grow into an adult. Th ese hormones are secreted by the reproductive organs and the entire process is controlled by the endocrine system.

(b) Since the girls start menstruating at puberty, they should consume food rich in calcium, iron and zinc.

(c) Drugs are addictive and have adverse eff ects on the body’s development. in some cases, using infected needles to take drugs can also cause AiDS.

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(d) Adolescents show increased activity of sweat and sebaceous glands which may lead to foul body odour. Therefore, it is important to maintain cleanliness and good personal hygiene. One should take bath every day to avoid bacterial infections.

C. 1. During adolescence, the body undergoes various changes and develops secondary sexual characters. These changes mark the onset of puberty.

Secondary sexual characters: During adolescence, male and female hormones are produced. in males, testes produce the male sex hormone called testosterone and in females, the ovary produces female sex hormones called oestrogen and progesterone. These hormones are responsible for the development of secondary sexual characters in males and females, and prepare them for reproduction.

Increase in height: There is a sudden increase in height in both the sexes; generally girls grow faster than boys, but both reach their maximum height by the time they attain the age of 18 years.

Change in body shape: As a result of growth, in boys, shoulders become broader. Their muscles become more prominent. in girls, the hips broaden, the pelvic region widens, breasts increase in size due to the development of mammary glands.

Hair growth: in both the sexes, hair starts growing in the armpits and in the pubic region. Boys develop facial hair, i.e., moustache and beard and hair on the chest.

Voice change: in boys, the voice box or the larynx increases in size, which results in the change in voice. The increase in size is more prominent in boys and the enlarged voice box can be observed as a protruding part of the throat called Adam’s apple. in girls, it is not visible as it is small in size. in general, girls have a high-pitched voice whereas boys have a deep voice.

Development of sex organs: in boys, testes and penis develop completely and testes start producing sperms. in girls, ovaries enlarge and start producing matured eggs.

2. (a) Insulin: it regulates the blood sugar level in the blood. Deficiency of this hormone causes diabetes.

(b) Adrenaline: it prepares the body for emergency situations like fight, flight or fear; helps the body to adjust to stress, etc.

(c) Oestrogen: it controls the development of secondary sexual characters in females. (d) Testosterone: it controls the development of secondary sexual characters in males. (e) Thyroxine: it helps in metabolism, growth and development. Deficiency of this hormone causes

goitre. 3. Menstrual cycle is the cycle of releasing a mature ovum at the end of 28 days. This is stimulated by

the oestrogen and progesterone hormones. During this period, the wall of the uterus becomes thick to receive the egg. Oestrogen helps in the development of breasts.

4. Adolescent can look after his/her physical and mental health in many ways. it is better for adolescents to enjoy some outdoor activities, such as walking, jogging and other outdoor games. it improves their blood circulation and keeps them fit and healthy. After all, a healthy mind resides in a healthy body.

5. Sudden changes in the body leave the adolescents in a state of deep thinking, confusion and insecurity. He/she becomes vulnerable and falls prey to drugs and wrong habits. Drugs are addictive and have adverse effects on the body’s development. in some cases, using infected needles to take drugs can also cause AiDS.

At this stage of life, one should be careful in selecting friends and should take guidance from their parents and elders. in case of any problem, they should communicate with their parents or counsellors. They should plan and try to involve themselves in creative and productive work of their interest.

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D. 1. Endocrine system 2. Th is system secretes hormones which play a crucial role in bringing about the changes that help

a child to grow into an adult. Th e endocrine system controls many processes such as growth, metabolism, development, behaviour and reproduction.

3.

Testis

Ovary

PancreasAdrenal gland

Th ymus

Th yroid glandParathyroid gland

Pituitary gland

E. 1. Yes, Reeta’s mother is right. During adolescence, adolescents spend more time thinking and become more independent and self-conscious. Sometimes, they may feel insecure while trying to adjust to the changes in the body and mind. Adolescents begin to experience emotional changes and they develop interest and attraction towards the opposite sex. All these developments are normal and are a part of growing up.

2. During puberty, the activity of sweat and sebaceous glands (oil glands) increases. it may result in excess sweating and occurrence of acne or pimple in adolescents. Th erefore, most of the acne and pimple treatment creams and face washes feature young teenagers in their advertisements.

3. Th e rate of thyroid hormone production is controlled by the pituitary gland. if there is an insuffi cient amount of thyroid hormone circulating in the body, then body starts showing abnormal functioning. Th erefore, thyroid test becomes a necessity in such situations. if something is diagnosed in this test, then proper care and medicines can control the secretion of thyroid hormone.

4. Sudden changes in the body leave the adolescents in a state of deep thinking, confusion and insecurity. He/she becomes vulnerable and falls prey to drugs and wrong habits. So, nowadays every school has a guidance and counsellor therapist who talk to adolescents and try to divert their minds in more creative and productive work of their interest.


Worksheet 1 1.

S. No. Gland Hormones Location Functions 1. Pituitary Growth

hormoneBase of the brain Growth and development of the body.

2. Pancreas insulin Near the liver Regulates the blood sugar level in the blood. Defi ciency of this hormone causes diabetes.

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3. Thyroid Thyroxine Base of the throat Metabolism, growth and development. Deficiency of this hormone causes goitre.

4. Adrenal Adrenaline Near the kidney Prepares the body for emergency situations like fight, flight or fear; helps the body to adjust to stress, etc.

5. Ovary Oestrogen Pelvic region it controls the development of secondary sexual characters in females.

6. Testes Testosterone Male genital organs it controls the development of secondary sexual characters in males.

2. Reproductive health is mainly regulated by the hormones. if a person is not healthy it results in the hormonal imbalance and becomes the reason for mental, emotional stress.

Worksheet 2 1. Broadening of shoulders, growth of facial hair and growth of hair in armpits and pubic area. 2. Development of breasts and growth of hair in armpits and pubic area. 3.

Menarche MenopauseThe first menstrual flow that begins at puberty.

The stoppage of menstruation at the age of 45-5o years.

4. Personal Hygiene: Adolescents show increased activity of sweat and sebaceous glands which may lead to foul body odour. Therefore, it is important to maintain cleanliness and good personal hygiene. One should take bath every day to avoid bacterial infections. Girls should take special care during menstruation.

Physical Exercise: it is better for adolescents to enjoy some outdoor activities, such as walking, jogging and other outdoor games. it improves their blood circulation and keeps them fi t and healthy. After all, a healthy mind resides in a healthy body.

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Chapter 10Reproduction

Specific Learning Objective Aft er the completion of the chapter students, will be able to understand:

• What is the importance of reproduction?• Modes of reproduction.• Male and female reproductive organs.• internal and external fertilization.• Development of an embryo.• Shell formation in the hen’s egg.• Viviparous and oviparous animals.• What is Metamorphosis?

Warm UpMake an attempt to have an interactive class by asking the students if they understand the role of reproduction in animals? How does the development of a child takes place in the womb? What are the diff erent stages during the development of a child? Now ask the students to complete the exercise given in the Warm-up section.

Concept Explanation• Explain to the students that reproduction is one such process which is essential for the

continuation of species. it is due to the reproductive process that the various species exist on the earth .Th erefore, reproduction is crucial to ensure the continuation of similar kinds of species generation aft er generation.

• Tell students that there are two modes of reproduction in animals, namely, asexual reproduction and sexual reproduction.

Asexual Reproduction

• Explain to the students that in the binary fi ssion, the adult parent cell on maturity divides into two daughter cells.

• in budding, a new bud arises from the parent body, which in time develops into a fully developed individual.

Sexual Reproduction

• Explain to the students that sexual reproduction occurs when two parents are involved. Males and females have diff erent reproductive organs. Male and female reproductive organs produce one reproductive cell called gamete. Th e type of reproduction which involves the fusion of the male and the female gametes is called sexual reproduction.

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• The male reproductive organs are as follows. 1. A pair of testes 2. Two sperm ducts 3. Penis

• The female reproductive organs are as follows. 1. A pair of ovaries 2. Oviducts (fallopian tubes) 3. Uterus




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Worksheet 1 1. Label the parts in the given diagram and answer the following questions.

(a) identify the given system. (b) State the functions of ovary. (c) What is fertilization? (d) Mention the role of the fallopian tube.

2. Give one or two words answer. (a) Master gland (b) Gland of emergency (c) Fight or fl ight hormone

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Worksheet 2 1. Defi ne the terms. (a) Foetus (b) Embryo (c) Fertilization (d) Zygote (e) infant (f) iVF (g) Metamorphosis

2. Give the functions of the following hormones. (a) insulin (b) Adrenaline

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A. 1. COLUMN A COLUMN Binternal fertilization HenExternal fertilization FishMetamorphosis LarvaOviduct FertilizationSperms Testis

2. (a) Dog and cow (b) Frog and fi sh (c) Human being and cat (d) Frog and fi sh (e) insects and frogs

B. 1. Reproduction: Reproduction is a process which is essential for the continuation of a species. 2.

External fertilization Internal fertilization

Fertilization that takes place outside the female body is called external fertilization.

Fertilization that takes place inside the body of a female is called internal fertilization.

Frogs and fish reproduce by external fertilization.

Human beings, cats, dogs, cows and hens reproduce by internal fertilization.

3. Metamorphosis: Th e transformation of a larva into an adult through such drastic changes is called metamorphosis.

4. Refer Figure 10.4_page 136 5. Th e male reproductive organs in a human being are as follows: A pair of testes Two sperm ducts Penis

6. (a) Th e hen sits on the egg for about three weeks to give warmth to the developing chick. Th is period is known as the incubation period.

(b) Eggs of frogs are very delicate and have a layer of jelly around them which holds them together and protects them.

(c) in frogs, at every stage of development, the organism has a diff erent structure. Th e transformation of a larva into an adult through such drastic changes is called metamorphosis.

(d) Amoeba is a single-celled organism which undergoes reproduction asexually by binary fi ssion. (e) Th e tail or fl agella helps the sperm swim the long way from the vagina to the fallopian tube

where it fertilizes the egg.C. 1. Refer Figure 10.5_page 136

Ovary: When a girl reaches puberty, the ovaries are stimulated by the pituitary gland to produce the female sex hormone oestrogen. Ovaries produce eggs or ova.

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Oviduct: Oviduct is the part where fertilization takes place. Uterus: Uterus is the part where the development of the baby takes place after fertilization of

gametes. 2. Refer Figure 10.10_page 141 3. Binary fission: in this type of reproduction, the adult parent cell, on maturity divides into two

daughter cells. in Amoeba, the process of reproduction begins by the division of the nucleus into two, followed by

the division of cytoplasm into equal amount. Then the cell membrane starts separating and finally two daughter cells are formed.

Refer Figure 10.1_page 134 4. Budding: in budding, a new bud arises from the parent body, which in time develops into a fully

developed individual. in Hydra, after development this bud gets detached from the parent body and survives independently. Refer Figure 10.2_page 135 5. Incubation period: The hen sits on the egg for about three weeks to give warmth to the developing

chick. This period is known as the incubation period. After this period, the developed chick breaks open the shell and is free to move.

D. 1. Ovary releases the egg. 2.

Zygote Embryo

The zygote is a single cell which starts the cell division, forming a ball of cells.

Zygote develops into tissues and organs which are called embryo.

3. When zygote is implanted in the uterus, the embryo attaches itself to the wall of the uterus and continues its development. it gradually develops body parts such as hands, face, legs, etc. The stage of the embryo in which the body parts are clearly visible is called foetus. The foetus continues to develop for about 40 weeks in a human being and when it is completely developed, the mother gives birth to the young baby.

4. The development of the baby takes place in uterus.

E. 1. Paramecium is a single-celled organism, in which asexual reproduction takes place through binary fission. in this type of reproduction, the parent cell is divided into two daughter cells. Therefore, the daughter organisms have the same characteristics like their parents.

2. Frogs lay eggs and sperms in pond. Sperms swim in water and when they come in contact with the egg, fertilization takes place. So, for the continuation of their species, water is necessary.

3. A newborn baby is unable to take care of itself, therefore a lot of care is needed for its growth and development.

4. Yes, in vitro fertilization and external fertilization are the same thing because in both cases fertilization takes place outside the body.

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Worksheet 1 1. 1.

Oviduct

Uterine well

Cervix

Vagina

Ovary

(a) Female reproductive system (b) Ovary releases the ovum. (c) When a sperm and an ovum fuse together, they form a zygote. (d) Sperm fuses with the ovum in the fallopian tube.

2. (a) Pituitary gland (b) Adrenal gland (c) Adrenaline

Worksheet 2 1. (a) Th e stage of embryo in which body parts are clearly visible is called foetus.

(b) Zygote later develops into a ball of cell which is called embryo. (c) Process in which a sperm fuses with an ovum and forms zygote. (d) A single cell which is formed by the fusion of a sperm and an ovum. (e) A very young child or baby. (f) in vitro fertilization is a technique used in which the sperm and the egg are fertilized in the

laboratory in a sterilized environment. (g) Th e transformation of a larva into an adult through such drastic changes is called metamorphosis.

2. (a) it regulates the blood sugar level in the blood. Defi ciency of this hormone causes diabetes. (b) it prepares the body for emergency situations like fi ght, fl ight or fear; helps the body to adjust

to stress, etc.

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Answers to Summative Assessment 1

A. 1. Harvesting 2. Fungi 3. Synthetic fi bres 4. Malleability 5. Lignite 6. ignition temperature 7. Biodiversity 8. Unicellular organisms 9. Adrenal gland 10. Budding B.

COLUMN A COLUMN BChlamydomonas AlgaeBakelite Th ermosetting plasticAnthracite CoalOxygen CombustionSonorous MetalsDodo ExtinctCell wall Plant cellAdam’s apple Voice boxOvaries OvumRice Kharif crop

C. 1. Traditional methods: Th ese methods are as follows. 1. Moat (pulley system) 2. Chain pump 3. Dhekli 4. Rahat (water wheel) 5. Canal irrigation 6. Furrow irrigation Modern methods: Sprinkler system and drip system are the modern methods of irrigation. 2. Microorganisms can be divided into fi ve major groups. Example Bacteria – Bacilli Virus – Tobacco mosaic virus (TMV) Fungi – Yeast Algae – Chlamydomonas Protozoa – Amoeba 3. Advantages of Synthetic Fibres Th ey have a lot of strength, and are less expensive and durable. Fabrics made of these fi bres do not wrinkle easily. Th ey are elastic in nature. Most synthetic fi bres can handle heavy loads without breaking. Disadvantages of Synthetic Fibres Th ey absorb very little sweat or water, and therefore, they cannot be worn during summer and

humid climates. Th ey catch fi re easily and, therefore, it is not safe to wear them either in the kitchen or anywhere

near a source of fi re. Th ese fabrics should be ironed carefully, because the fabric melts at high temperature. 4. Corrosion: Th e process of slow eating away of a metal due to the attack of atmospheric gases

and moisture on its surface is called corrosion. iron reacts with the oxygen and moisture of the

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atmosphere and forms a brown and flaky substance called rust. Rusting of iron is an undesirable reaction because the layer of rust formed falls off, exposing the metal to further rusting. Due to this, iron objects become weak with the passage of time.

5. Under high temperature, high pressure and less supply of oxygen, it was converted into coal which is actually a fossil. The slow process of conversion of wood into coal is called carbonisation.

Formation of coal: The steps involved in the formation of coal are as follows. Millions of years ago, trees and other plants died and got buried in the soil. These remains

were covered with mud and sand. This buried plant material formed a dark brown material called peat. This peat got compressed between layers of sediments and formed lignite. Further compression resulted in the formation of bituminous coal. This bituminous coal further compressed and formed anthracite. 6. To control fire, three things are required. They are as follows. 1. Removing the combustible material. 2. Bringing down the temperature of the burning material below its ignition temperature. 3. Cutting off the supply of air. 7. Deforestation: The removal of plants in the forests for various purposes is called deforestation. Consequences of deforestation are as follows. Deforestation removes the vegetation cover, which increases the level of carbon dioxide in the

atmosphere and also the temperature. it also disturbs the ecological balance in nature. Due to deforestation, less carbon dioxide is used up and its increased amount in the atmosphere

causes global warning. Deforestation also leads to loss of habitat and in turn causes extinction of many plant and

animal species. Due to deforestation, the soil particles are easily washed away by rain and wind, leading to soil

erosion. Due to deforestation, transpiration cannot take place which makes the atmosphere dry,

adversely affecting the water cycle. Apart from man-made causes, many plant and animal species are also destroyed due to natural

causes such as earthquakes, climate change, floods, droughts, cyclones, etc.

8. Refer Table given on page 111 9. Endocrine system: The endocrine system controls many processes such as growth, metabolism,

development, behaviour and reproduction through chemicals called hormones. Insulin- it is secreted by pancreas. it regulates the blood sugar level in the blood. Deficiency of this

hormone causes diabetes. Thyroxine – it is secreted by thyroid. it helps in metabolism, growth and development. Deficiency

of this hormone causes goitre. Adrenaline – it is secreted by adrenal glands. it prepares the body for emergency situations like

fight, flight or fear; helps the body to adjust to stress, etc. 10. in asexual reproduction, only one parent is involved. Asexual reproduction is of many types. Binary

fission and budding are two common types. Binary fission: it occurs in amoeba and paramecium. Budding: it occurs in yeast and hydra.

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D. 1. Food preservation is the process of treating and handling food to stop or slow down its spoilage while maintaining its nutritional value, flavor and texture. We can use some methods that can preserve food for a longer time. Various food preservation methods are as follows.

Drying or dehydration: Cereals, pulses, dry fruits, vegetables, fruits, fish, prawn are dried in the sun. This method removes water from the food and stops microbes from growing. The food is then stored and sold in airtight containers (cans) or packets. This prevents the attack of microbes.

Refrigeration and freezing: Microbes like bacteria and fungi cannot survive at low temperatures so refrigerating at low temperatures and freezing help to preserve food for a long time. Food items such as fruits, vegetables and meat are preserved by using this method.

Pasteurisation: it is a process in which the foodstuff is heated at high temperature and then cooled rapidly. Commercially available milk is first heated at 70°C for 15 to 30 seconds and then suddenly chilled and stored. This prevents the growth of bacteria.

Using common salt: it is used to preserve meat, fish, vegetables, pickles and chips. Presence of salt causes loss of water from the microbes which results in the death of microbes.

Boiling: Boiling kills the microbes. Milk and water are often boiled to kill microbes that may be present in them.

Using sugar: it is used to preserve jam, jellies and squashes. Microbes lose water due to osmosis. Using chemical preservatives: Chemical preservatives such as sodium benzoate and sodium

metabisulphite are used in squashes and ketchups. Using oil and vinegar: Use of oil and vinegar prevents the spoilage of food. When the food is covered

with oil and vinegar, the microbes are unable to come in contact with the food items such as meat, fish, vegetables and fruits.

Canning: Storing food items in an airtight can is an effective way of preserving it. Food items such as jams, vegetables, fish and even cooked food are canned and sold in market.

2. Microorganisms are beneficial for us in a number of ways. Their uses can be divided into four categories such as commercial, medicinal, agricultural and environmental.

Commercial uses of microorganisms are as follows. Making curd and cheese: Bacteria are used in making some of our popular food items such as curd

and cheese. These are made by the action of bacteria on milk. Curd is formed due to a bacterium called lactobacillus.

Cheese is also made using lactobacillus. Paneer (cottage cheese) involves the use of Streptococcus bacteria.

Making vinegar, coffee, tea and tobacco: Bacteria are also used in the preparation of vinegar (acetic acid), tea, coffee and tobacco.

Making bread: Yeast is used in the preparation of bread. Yeast breaks down the sugar which results in the formation of alcohol and carbon dioxide. When this dough is baked, these bubbles escape, making the bread rise further and making it soft and fluffy. Baking the expanded dough at 180°C kills the yeast and stops fermentation. The alcohol evaporates during the packing process.

Making toothpaste: Toothpaste is made with the help of shells of diatoms (a type of algae). Xanthum gum, which is obtained from the bacteria Xanthomonas campestris, is also used to make toothpaste.

Making alcoholic beverages: Manufacturing of alcohol and alcoholic beverages like beer and wine requires fermentation of sugar present in barley and grapes using yeast. This process results in the formation of alcohol and carbon dioxide.

Medicinal uses of microorganisms are as follows. Making medicines and vaccines: Antibiotics are medicines that destroy microorganisms. They are

prepared using bacteria and fungi. Penicillin is an antibiotic certain disease-causing prepared

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from the fungi called Penicillium notatum. Some other known antibiotics are tetracycline and streptomycin (both obtained from Streptomyces bacteria).

Making food supplements: Chlorella (a type of algae) is rich in proteins and other nutrients and thus used as a food supplement.

In human body: Lactobacillus acidophilus live in human intestines, where they help to digest food and destroy disease-causing microbes.

Agricultural uses of microorganisms are as follows. Some bacteria such as Rhizobium and blue-green algae live in the root nodules of leguminous

plants. They help in nitrogen fixation. They absorb nitrogen from the atmosphere to enrich the soil and make nitrogen available for the plant as nitrates, which in turn is absorbed by the plant and is used for protein formation. Nitrogen is one the main elements in proteins.

Environmental uses of microorganisms are as follows. Microbes convert the dead organic matter of plants and animals into simple substances which go

back into the soil and increase soil fertility. This also keeps our environment clean. Some bacteria are used for treating sewage, as they break down the organic matter in the sewage

into simple substances. 3. Following steps can be taken to manage the plastic waste in the environment. Reducing the usage of plastic and increasing the use of these plastic objects that can be recycled

are the best ways of handling the challenge. Segregation of waste helps in identifying the type of waste that can be recycled, for example lot

of plastics can be reused by melting and remoulding into desired shapes. Use separate garbage bins for different types of wastes—biodegradable and non-biodegradable. Follow the principle of 4Rs—Refuse, Reduce, Reuse and Recycle. 4. Reaction of Metals and Non-metals with Acids Metals: Metals react with acids and form salt and hydrogen gas. Metal + Acid Salt + Hydrogen gas Non-metals: Non-metals do not react with acids. Reaction with Bases Metals: Very few metals such as zinc, aluminium and lead react with strong bases such as sodium

hydroxide to produce compounds of that metal and hydrogen gas. Non-metals: The reactions of non-metals with bases are complex. You will learn about them in

higher classes. 5. On the basis of the carbon content present in coal, it is classified into the following types. Anthracite: This type of coal has about 95-98 per cent of carbon and has very less amount of

moisture in it. Due to this, it provides more heat and is regarded as the highest grade. it is mainly used for heating.

Bituminous: it contains about 60-80 per cent of carbon and has more moisture in it. it is also used for power generation and in manufacturing of another fuel called coke.

Lignite: This type of coal has the least carbon content; about 25-40 per cent. it is mainly used for power generation.

6. A candle flame can be divided into three zones. The formation of each zone depends on the amount of air available. Each zone demonstrates a different colour.

Non-luminous zone: This is the zone of complete combustion and the flame is blue in colour. it is the outer part of the flame. This is the hottest zone and does not leave any mark on the object when it is placed on it.

85


Dark zone: This is the coolest part of a flame and no combustion takes place here. it is the innermost zone of the flame. it covers the area surrounding the wick.

Refer Figure 6.4 from page 86 7. The preservation and careful management of plant and animals species in order to prevent their

extinction is called conservation. Conservation emphasises the protection of ecosystems and the original habitats of living beings. This includes protection of a typical ecosystem through a network of protected areas, land or sea. These are managed by the government and other agencies. The government makes rules and policies to protect and conserve them.

india has approximately 381 protected areas as Biosphere Reserves, National Parks and Wildlife Sanctuaries for this purpose. Forests help in sustaining thousands of lifeforms including plants and animals. Wildlife is a natural resource that helps to maintain ecological balance. Human beings have been exploiting forests to satisfy their needs. This has led to a decline in the number of many species of plants and animals. it is, therefore, very important to conserve plants and animals.

8. (a) Nucleus: in addition to inheritance, the nucleus regulates and coordinates various activities of the cell.

(b) Mitochondria: They are the site of cellular respiration and produce energy. Therefore, they are called the ‘powerhouses of the cell’.

(c) Lysosomes: These organelles help in intercellular digestion and destroying foreign substances. When the cells become old or injured, lysosomes burst and rapidly destroy the cell; hence they are also called suicidal bags.

(d) Plastids: Most common ones are the chloroplasts that provide green colour to the leaves. Chromoplast imparts colour to the flowers and fruits such as red, orange, yellow and leucoplast stores starch in potato and is colourless.

9. With the onset of puberty, one ovum matures and is released by one of the ovaries, once every 28 days. This process is called ovulation. Menstrual cycle is the cycle of releasing a mature ovum at the end of 28 days. This is stimulated by the oestrogen and progesterone hormones. During this period, the wall of the uterus becomes thick to receive the egg. in case, it is fertilized, it gets implanted in the uterus for further development. This results in pregnancy. in case, fertilization does not occur, then the released egg and the entire uterus lining along with the blood vessels is shed off. This causes bleeding in women for 4 to 6 days which is called menstruation. This cycle repeats every 28 to 30 days and is called the menstrual cycle. This is also controlled by hormones.

Refer figure 9.3 from page 126 10. The transformation of a larva into an adult through such drastic changes is called metamorphosis. Metamorphosis in frog occurs in three stages during its development from an egg to an adult. These

changes are controlled by the hormone called thyroxine. Egg Tadpole (larva) Adult frog Tadpole and the adult frog are very different in morphology. Butterflies and moths also go through these stages of development. Egg Caterpillar (larva) Pupa - Adult Refer figure 10.10 from page 141

E. (a) 1. Sperm is shown in the given picture. 2. Refer Figure 10.4 from page 136 3. Sperms fuses with ovum and form a zygote which ultimately converts into a baby. (b) 1. Adam’s apple is shown in the given picture. 2. This is responsible for deep voice in boys.

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Model Test Paper-I1. Fill in the blanks: (1 × 5 = 5) (a) Th e chemicals used to destory weeds are called ____________ . (b) Th e process of conversion of a sugar into an acid or an alcohol by the action of micro-organisms is

called ____________ . (c) ____________ was the fi rst man-made fi bre. (d) Th e properly by virtue of which metals can be beaten into thin sheets is called ____________ . (e) Th e slow process of conversion of wood into coal is called ____________ .

2. Diff erentiate between: (2 × 5 = 10) (a) Natural fertilizers and chemical fertilizers (b) Metals and non-metals (c) Plant cell and animal cell

3. Explain in one or two sentence. (1 x 5 = 5) (a) Oviparous animals (b) External fertilization (c) Ovulation (d) Mitochondria (e) Reforestation

4. Answer the following questions briefl y. (2 × 5 = 10) (a) Defi ne corrosion. (b) Mention the properties of polyster. (c) What is metamorphosis? (d) What are secondary sexual characters? (e) What are the conditions necessary for combustion?

5. Answer the following questions in detail? (3 × 5 = 15) (a) How are microorganisms useful for us? (b) Mention the properties of plastics. (c) How can we conserve fossil fuels? (d) Describe the structure of a fl ame? (e) What is deforestation? What are its causes?6.

(a) What does the given picture depict? (b) Mention the various stages indicated in the picture.

1

2

4

5

3

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Answers

1. (a) weedicides (b) fermentation (c) Nylon (d) malleability (e) carbonisation

2. (a) Natural fertilizers Chemical fertilizersThese are obtained from plants and animals.They are not rich in absobrable nutrients that can be taken in by plants.They increase humus in the soil.Manure, compost and bark of neem are examples of natural fertilizers.

There are produced in factories.They are rich in nutrients that can be easily absorbed by plants.They do not increase humus in the soil.Urea, potash and NPK (nitrogen, phosphorus, potassium) are examples of chemicals fertilizers.

(b) Metals Non-metalsPhysical stateMetals are generally solid at room temperature.Exceptions are mercury, gallium, caesium etc. that are liquids.

All non-metals occur as solids or gases at room temperature. Bromine is the only exception that is a liquid at room temperature.

LustreMost of the metals have lusture, that is, they shine.

Non-metals do not have a lusture. They have a dull surface.

Hardness and strengthMost metals are generally hard and strong. Sodium, potassium and magnesium are soft metals.

Non-metals with the exception of diamond are generally soft.

MalleabilityMost metals can be beaten into sheets. Non-metals are brittle. They break on beating.DuctilityMost metals can be drawn into thin wires. Non-metals are brittle and cannot be drawn

into wires.

(c) Plant cell Animal cellPresence of a cell wall.Plastids are present.They have one or two large vacuoles.Nucleus is present in the periphery of the cell.

Centrosome is absent.

Cell wall is absent.Plastids are absent.Vacuoles are generally absent.Nucleus is generally present in the centre of the cell.Centrosome is present.

3. (a) Oviparous animals Animals that lay eggs which hatch into offspring are called oviparous animals. Examples are birds,

frogs, fish.

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(b) External fertilization Fertilization that takes place outside the female body is called external fertilization. (c) Ovulation With the onset of puberty, one ovum matures and is released by one of the ovaries, once every 28

days. This process is called ovulation. (d) Mitochondrea These are tiny spherical rod-shaped structures. They are the site of cellular respiration and produce

energy. Therefore, they are called the ‘powerhoues of the cell.’ (e) Reforestation is restoration of the destroyed forest by planting new trees.4. (a) Some metals react with oxygen and the moisture present in the atmosphere. This phenomenon is

called corrosion. Metal + Oxygen + Moisture → Rust (b) it is strong, lustrous, easy to maintain, light, easy to wash and dry. This fabric does not get wrinkled easily. it does not absorb water so can be washed and dried easily and quickly. (c) Newly born animals such as birds and mammals show features similar to their parents. But this is not

true for all animals. Some insects and frogs have different stages of development from the egg to the adult stage. At every stage of development, the organism has a different structure. The transformation of a larva into an adult through such drastic changes is called metamorphosis.

(d) The characters that distinguish a child from an adult are called secondary sexual characters. These changes help in distinguishing between males and females. These changes are controlled by hormones.

(c) The conditions necessary for combustion are as follows: The substance should be combustible. Oxygen should be available to support combustion. The substance should be heated to its ignition temperature.5. (a) Microorganisms are beneficial to us in many ways. Commercial uses Making acid and cheese: Bacteria are used in making some of our popular food items such as curd

and cheese. Curd is formed due to a bacterium called lactobacillus. Bacteria are also used in the preparation of vinegar, tea, coffee and tobacco. Yeast is used in the preparation of bread. Toothpaste is made with the help of shells of diatoms. Yeast is used to make alcoholic beverages through fermentation. Medicinal uses Antibiotics are prepared using bacteria and fungi. Penicillin is derived from a fungi called Penicillium

notatum. Tetracycline and streptomycin are derived from Streptomyces bacteria. Agricultural uses Rhizobium bacteria and blue-green algae help in nitrogen fixation in leguminous plants. Environmental uses Microbes convert the dead organic matter of plants and animals into simple substances which go

back into the soil and increase soil fertility. This also keeps our environment clean. (b) Different types of plastics differ in some physical and chemical properties. Following properties are

common to most of them. Thermal conductivity: Plastics are poor conductors of heat. They are therefore used in making

handles of cooking utensils.

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Electrical conductivity: Plastics are poor conductors of electricity so they are used as covering materials on electrical appliances.

Solubility in water: Plastics are insoluble in water. So they are used as containers for storing water. Reactivity: They are non-reactive as they do not react with water and air and do not get corroded.

So they are used in making storage containers. (c) in india, the Petroleum Conservation Research Association (PCRA) has listed some tips to save

petrol/diesel while driving. Drive at a constant and moderate speed as far as possible. Switch off the engine at traffic signals and during waiting time. Always maintain correct air pressure in the tyres. Regular maintenance of the vehicles also consumes less fuel. We can save fossil fuels by using alternate sources of energy like solar, energy, hydropower, etc. (d) A candle flame can be divided into three zones. The formation of each zone depends on the amount

of air available. Non-luminous zone: This is the zone of complete combustion and the flame is blue in colour. it is

the outer part of the flame. This is the hottest zone and does not leave any mark on the object when it is placed on it. This zone emits very little light.


Dark zone: This is the coollest part of a flame and no combustion takes place here. it is the innermost zone of the flame. it covers the area surrounding the wick. Being deep inside, it has vapours which are not burnt as they do not come in contact with oxygen. it emits no light.

(e) The removal of plants in the forests for various purposes is called deforestation. Deforestation is caused due to natural or human activity. Reasons for deforestation are:

To obtain wood for fuel and making furniture. To manufacture paper. To acquire land for urbanisation. Forest fires caused due to high temperature and dried leaves. Loss of vegetation due to overgrazing of cattle.6. (a) The given picture shows ovulation and fertilization in human beings. (b) 1. Once a month, an ovum is released from the ovary by a process called ovulation. 2. The ovum moves into the oviduct (fallopian tube). 3. During sexual intercourse, the male transfers sperms in the vagina through the penis. The sperm

travels through a narrow opening called cervix into the uterus and then the oviduct. 4. A single sperm fuses with the ovum in the oviduct and fertilization takes place. The fertilized

ovum continues its journey down the oviduct, into the uterus. 5. The fertilized ovum implants itself into the uterus wall and develops into a human embryo.

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Chapter 11Force and Pressure

Specific Learning Objective

Aft er the completion of the chapter, students will be able to understand:• What is force and what are its eff ects?• What is pressure and how does it vary?• What is atmospheric pressure?

Warm UpStart the topic by asking them the questions on, what do they know about the force? Have they ever applied force anywhere? Have they pushed or pulled objects; what do they think they have done? Now ask the students to complete the exercise given in the Warm-up section.Concept Explanation

• Explain to the students that we use force to perform day to day activities like pushing, pulling, lift ing, compressing, kicking, shutting, opening, etc. Each of these actions usually results in some kind of change in the motion of the object.

• Explain to the students the eff ect of force and also the types of force by giving daily life examples.

1. Force can make the stationary objects move. 2. Force can change the direction of the moving objects.

• Explain to the students that the eff ect the force will produce on the object will depend on the following factors.

1. Th e magnitude of the force 2. Th e area on which the force is appliedPressure

• Explain to the students about the concept of pressure and also explain the pressure exerted by liquids with the help of activities and experiment 1.

Atmospheric Pressure• Explain the concept of atmospheric pressure with the help of Experiment 2 on page 156. Also

tell students that atmospheric pressure varies at diff erent altitudes. Also, give the daily life applications of pressure.




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Worksheet 1 1. Fill in the blanks.

FORCE

FRiCTiONAL FORCE

CONTACT NON-CONTACT

2. Write the eff ects of force.

3. Diff erentiate between contact force and non-contact force.

4. Give examples of the following forces. (a) Muscular force (b) Magnetic force (c) Frictional force (d) Electrostatic force (e) Gravitational force

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Worksheet 2 1. Design an activity to show the eff ect of atmospheric pressure.

2. A tumbler fi lled with water has an inverted tube with mercury. (a) if the air pressure is more outside what will be the level of mercury? (b) if the air pressure is less outside what will be the level of mercury in the tube?

3. Explain the pressure exerted by gases by giving daily-life example.

4. Mention any two applications of pressure.

5. Why do astronauts wear pressurised suits in space?

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A. 1. COLUMN A COLUMN B

Magnet Attracts iron nailsPascal Unit of pressureGravitational force Planets around the sunPressure Force per unit areaElectrostatic force Force between electric charges

2. (a) Barometer (b) Newton (N) (c) Magnetic force (d) Pressure B. 1. A pull or a push on an object is called force. Th e eff ects of force are as follows. Force can make a

stationary object move. Force can change the direction of a moving object. Force can slow down or completely stop a moving object. Force can change the shape of an object.

2. Contact force: Examples of contact forces are muscular and frictional force. Non-contact force: Examples of non-contact forces are frictional and gravitational forces. 3. Atmospheric pressure is defi ned as the pressure exerted on an object by the weight of the air above

it. Th e atmospheric pressure at a place is due to the force exerted by the air column on the unit area. 4. Liquid pressure is the increase in pressure at increasing depths in a liquid. As we go deeper in the

sea, the pressure increases. Pressure increases with depth. 5.

Force PressureA pull or a push on an object is called force. Pressure is defi ned as the force per unit area.Th e standard unit of force is newton (N). Th e Si unit of pressure is pascal (Pa) which is

newton per square metre or N/m2. 6. (a) As we go deeper in the sea, the pressure increases. Pressure increases with depth. Th e pressure

exerted by water deep under the sea is much greater than that at the sea level. (b) Due to gravitational force, the object falls on the ground when it is thrown upwards. (c) Air exerts pressure inside the balloon which becomes responsible for the bursting of balloon. (d) Smaller the area of contact, the greater is the eff ect of force. Th erefore, to minimise the eff ect of

force, the pillars of bridges and fl yovers have a broad base. (e) High rise building exerts more pressure, therefore, to maintain the balance, the foundation of

such buildings should be strong and wide. As we know that greater the area of contact, smaller is the eff ect of force.

(f) Due to electrostatic force, tiny bits of paper get attracted when brought close to a solution.

C. 1. Th e eff ects of force are as follows.Force can make a stationary object move: When you take the bicycle out of its stand, you can make it move. When you kick a stationary football, you make it move. if the football is already moving, you can make it move faster by giving it a push in the direction in which it is moving. Th us, a force can make a stationary object move, and it can also make an already moving object move faster.

Force can change the direction of the moving object: A player kicks the moving football to the other direction while playing. Th e kick is the force he applies to change the direction of the motion of the football.

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Force can slow down or completely stop a moving object: A football player slows down or stops a moving football by applying force in the opposite direction to the motion of the moving football.

Force can change the shape of an object: if you squeeze a sponge, the force applied will change its shape. Things also get broken by applying force. For example, objects made of glass and clay break easily if we apply force on them.

2. There are two types of forces: contact force and non-contact force. Contact force: Force that acts on an object only when the force is in contact with the object is termed

as contact force. Examples are muscular and frictional force. Non-contact force: Force that acts on an object without any physical contact is termed as non-

contact force. Examples are magnetic, frictional and gravitational forces. 3. Take an empty plastic bottle and fill it with water up to the brim. Close the mouth of the bottle

tightly with a lid. Prick a small hole in the centre of the bottle so that water starts flowing out of the bottle. After some time, the flow of water from the hole will automatically stop though there is still a lot of water in the bottle. Now loosen the lid of the bottle. The water again starts oozing out of the hole. This shows that when water was removed, there was not enough air to push more water out of bottle. As the lid was loosened, air entered the bottle and pushed the water out of the bottle. This shows that air exerts pressure.

4. When two surfaces in contact move with respect to each other, the resistance to the motion experienced is called friction. When you slide an object on a surface, there is a force acting in the opposite direction which slows it down; this is called frictional force.

Frictional force helps us to move. This force is effective when the surface is firm and rough. This is why it is difficult to walk on smooth surfaces like smooth tiles and ice; we slip on them.

Water or oil on the surface also reduces the effect of friction. Similarly, it is difficult to walk on sand, because the friction does not come into play while we walk on sand.

5. Some applications of pressure are as follows. Syringes are used to take blood for blood tests. The pressure of the blood forces the blood to

move into the syringe when its plunger is withdrawn. As the area of the edge of a knife’s blade is extremely small, this creates a pressure high enough

for the blade to cut through a material. 6. Given, force = 30 N Area = 50 m2

We know that pressure = Force / Area = 30 N / 50 m2 = 0.6 N/m2

7. Given, force = 200 N Pressure = 600 Pa We know that pressure = Force / Area So, area = Force/Pressure = 200 N/600 Pa = 0.33 m2

D. Due to atmospheric pressure the water in the glass in (iii) case will not spill out. E. 1. Heaver objects fall faster. if you drop a heavy and light object together, the heavy one will get to the

ground first. 2. As we know that greater the area of contact, smaller is the effect of force. Therefore, dams are made

stronger and thicker at the bottom than at the top. 3. On the moon, there is no pressure, so we would not be able to suck juice.

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Worksheet 1 1.

FORCE

FRiCTiONAL FORCE

CONTACT NON-CONTACT

MUSCULARFORCE

MAGNETiCFORCE

FRiCTiON

GRAViTATiONALFORCE

2. Th e eff ects of force are as follows. Force can make a stationary object move. Force can change the direction of a moving object. Force can slow down or completely stop a moving object. Force can change the shape of an object. 3. Contact force: Force that acts on an object only when the force is in contact with the object is

termed as contact force. Examples are muscular and frictional force. Non-contact force: Force that acts on an object without any physical contact is termed as non-

contact force. Examples are magnetic, frictional and gravitational forces. 4. (a) Horse pulls a cart

(b) Separate recyclable waste iron objects from garbage dumps (c) Writing on a paper (d) Electric air purifi ers in factories to purify air in chimneys (e) Stand and walk on the earth surface

Worksheet 2 1. Aim: To demonstrate the presence of atmospheric pressure. Material required: Glass, water and a tough cardboard (4”

by 4”) Method: • Filltheglasswithwaterandcovertheglass

with the cardboard. Place hand on the cardboard fi rmly to support it and now invert the glass upside down, keeping the hand in place. Slowly, remove your hand from the cardboard and note down your observations.

Observation: • Th ecardboardwillnotfallfromtheglass.it will appear as though the cardboard is stuck to the glass.

Conclusion: • Th ecardboardisheldontotheglassduetothe atmospheric pressure.

Water

Tumbler

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2. (a) The level of mercury will fall down. (b) The level of mercury will rise. 3. Blow air into a balloon, you will observe that the balloon gets inflated. This shows that the air exerts

pressure on the walls of the balloon. 4. Syringes are used to take blood for blood tests. The pressure of the blood forces the blood to move

into the syringe when its plunger is withdrawn. As the area of the edge of a knife’s blade is extremely small, this creates a pressure high enough for the blade to cut through a material.

5. As we go to the higher altitudes, the length of the air column above us decreases. As a result, weight reduces and therefore, atmospheric pressure also decreases. if there is sudden change in the atmospheric pressure, the blood vessels burst due to the pressure inside our body. This is the reason why astronauts wear pressurized suits, as there is no air and air pressure in space.

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Chapter 12Friction


• What is friction and what are the factors aff ecting it?

• Static and sliding friction.

• Advantages and disadvantages of friction.

• Steps taken to reduce and increases friction.

Warm Up Ask the students if they are aware of the concept of friction? How are they able to walk without falling? Why are they not able to walk on the sand? Now, ask the students to complete the exercise given in the Warm-up section.

Concept Explanation • Explain to the students that friction force is eff ective when the surface is fi rm and rough.

Friction is caused due to the two surfaces that are irregular. Even though they appear smooth, they have irregularities in them which lock into each other.

• Explain to the students that which of the two would be easier? To move the box at rest or to move the box when it is already in motion?

• Explain to the students that in certain cases it is important to reduce friction, whereas in some cases it is important to increase friction, on the basis of advantages and disadvantages.

• Explain to the students that the motion of aircraft and ships is opposed by friction due to air and water. Th e streamlined body helps them to overcome friction.




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Worksheet 1 1. List the steps to increase the friction.

2. List the steps to reduce friction.

3. Give diff erences between sliding and rolling friction.

4. Write any two advantages of friction.

5. Write any two disadvantages of friction.

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Worksheet 2 1. Give reasons for the following. (a) When the fl oor has oil spilled on it, we slip when we try to walk. (b) Aircraft reduces friction. (c) Rajesh tried to hold the oily rods and his hand slipped. (d) Seema advised her father to change his car tyres. (e) Wearing out of shoe soles.

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Grooved shoe sole WalkingBall bearing Change sliding friction to rolling frictionOil and grease LubricantsAeroplane and ships Streamlined structure reduces frictionFriction Opposes the movement

2. (a) Friction (b) Ball bearing (c) Lubricant (d) Fluid friction

B. 1. Friction: Th e resistance to motion experienced when two surfaces in contact move with respect to each other is called friction.

2. Th e following are some other advantages of friction. Vehicles like cars and buses can move on the road due to the force of friction between the tyres and the road. Th e brakes in the cycles and heavy vehicles work due to friction.

3. Aft er rubbing hands we feel heat which is due to friction. 4. Fluid friction: Friction due to air or water is called fl uid friction. 5. Streamlined body of sea animals helps them to handle the fl uid friction.

6. (a) Lubricants such as oil and grease are used to reduce friction. (b) Frictional force is eff ective when the surface is fi rm and rough. Friction is caused due to two

surfaces that are irregular. On a rough surface, there are many irregularities and the force of friction is greater.

(c) Streamlined body shape reduces the air and water resistance and therefore reduces friction. (d) Gravel on the wet ground reduces the friction and therefore helps in walking. (e) Due to friction, a lot of heat is produced which becomes responsible for the wear and tear of

tyres. C. 1. We will shift heavy box with the help of rollers because rolling friction is smaller than the sliding

friction. 2. Disadvantages of friction are as follows. it causes wear and tear in the moving parts in machinery and automobiles. Th ere is wastage of energy and fuel, because frictional force comes into play in the moving

parts of the machinery. Shoe soles and tyres wear out due to friction. Friction produces a lot of heat. Th e friction should be minimised to prevent the machines from

getting damaged. 3. Following things are done to increase friction. Tyres have grooves in them to increase friction. Th is prevents skidding of vehicles. We spread sand or gravel on wet or slippery ground during rainy season. Th is increases friction. Players and athletes have spikes in their shoe soles to increase friction. Weightlift ers and gymnasts rub a rough and coarse material on their hands to improve their

grip by increasing friction.

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4. When an object is at rest, the frictional force will be larger to make it slide. Whereas the frictional force will be less in the case of the moving box because the two surfaces do not get enough time to interlock with each other, therefore, less force will be needed to keep it moving.

D. 1. Rolling friction is always less than the sliding friction so it is diffi cult to shift the box in fi gure A. 2. Yes, the person in fi gure B would fi nd it easy to transport the box because rollers lower the frictional

force. E. 1. When we rub our hands, we feel heat due to friction force. 2. When it rains, the roads become wet and the force of friction becomes less which can make us fall.

So, we should be more careful while walking on the road when it rains.


Worksheet 1 1. Following steps are take to increase friction. Tyres have grooves in them to increase friction. Th is prevents skidding of vehicles. We spread sand or gravel on wet or slippery ground during rainy season. Th is increases friction. Players and athletes have spikes in their shoe soles to increase friction. Weightlift ers and gymnasts rub a rough and coarse material on their hands to improve their grip by

increasing friction. in workshops or industries, workers also use rough material while lift ing goods. 2. Following steps should be taken to reduce friction. To reduce the friction in the machinery, it should be regularly oiled and greased. Th is is called

lubrication. Oil, grease and graphite are used in reducing friction. Th ese are called lubricants. While playing carrom, talcum powder is used on the board to reduce friction.

Ball bearings can be used to reduce friction. Th ey change the sliding friction to rolling friction when these are placed between the moving surfaces because the rolling friction is less than the sliding friction. Th at is why rollers are used in suitcases, and vehicles have wheels to reduce friction. Rolling the luggage is easier than lift ing or sliding.

Polishing of rough surfaces makes them smooth and reduces friction. Streamlined shape of objects in water or air like in ships, boats and aircraft overcomes friction due

to air or water called fl uid friction. Birds and fi sh have a naturally streamlined body which helps them to handle the fl uid friction.

3. Sliding friction: Th e frictional force off ered when sliding an object is called sliding friction. Rolling friction: Th e frictional force off ered when rolling an object is called rolling friction. 4. Th e brakes in the cycles and heavy vehicles work due to friction. it is possible to light a matchstick

due to friction. 5. it causes wear and tear in the moving parts in machinery and automobiles. Th ere is wastage of

energy and fuel, because frictional force comes into play in the moving parts of the machinery.Worksheet 2

1. (a) Oil reduces the friction therefore, we slip when we try to walk. (b) Streamlined shape of aircraft overcomes friction due to air. (c) Oil reduces the friction and therefore, Rajesh was unable to hold the oily rods. (d) Th e tyres of the car got damaged due to the friction and therefore, Seema advised her father to

change his car tyres. (e) Due to frictional force, shoe soles get worn out.

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Chapter 13Sound


• What is sound and how is it produced?• Sound requires a medium to travel. • Speed of sound and echo.• Characteristics and types of sound.• What is noise pollution and how to reduce it?

Warm Up Ask the students if they are aware about how sound is produced? How are they able to hear the sound? Now, ask the students to complete the exercise given in the Warm-up section.

Concept Explanation

Sound• Explain to the students that we hear diff erent types of sounds from our surroundings. We can

also identify the source from where the sound comes. Sounds are of diff erent nature, some are natural like rattling of leaves, some are produced by the instruments and some originate from animals and human. Each sound has its own characteristics which enables us to identify them. Sound plays a very important role in our lives

Sound Requires a Medium to Travel• Explain to the students that the closer the molecules in a medium, faster the vibrations

will be transferred to the other molecules. Th erefore, denser the medium, faster will be the movement of sound waves. Th e speed of sound is maximum in solids, lesser in liquids and least in gases.

Echo• Explain to the students that when you visit the hill stations, you must have experienced echo.

When you shout loudly standing on a hill, you hear it back in some time. it is simply the refl ection of sound by the hill or a tall building at a distance.

• Explain to the students that when you keep your hand on the speaker of a music system or touch your throat while speaking, you will feel a vibration. Th erefore, sound is produced due to vibration, which can be heard.

Characteristics of Sound• Explain to the students that vibration and oscillation can be understood by using a pendulum.

Vibrations are very fast and it is very diffi cult to observe them.

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• Explain to the students about the loudness and pitch. We are aware about the amplitude and frequency. The larger the amplitude, the louder would be the sound, the smaller the amplitude lower will be the sound.

• Explain to students about the different characteristics of sound by using daily-life examples.




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Worksheet 1

1. Give diff erences between compressions and rarefactions.

2. When you shout loudly standing on a hill, you hear it back in some time. Why?

3. Defi ne the following. (a) Time period (b) Frequency (c) Audible sound (d) Amplitude

4. How can we reduce noise pollutions? Give any two methods.

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Worksheet 2 1. Identify the types of instruments.

(a)

(c)

(e)

(b)

(d)

(f)

(h)(g)

(a) (b) (c) (d) (e) (f) (g) (h)

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A. 1. (a) infrasonic waves (b) Amplitude (c) Noise (d) Time period (c) Wind instruments


Pitch FrequencyTrumpet Wind instrumentGuitar Stringed instrumentLoudness AmplitudeBlaring loudspeakers Noise pollution

B. 1. When you keep your hand on the speaker of a music system or touch your throat while speaking, you will feel a vibration. Th erefore, sound is produced due to vibration, which can be heard. While speaking, the air forces itself through the slit, the vocal cords vibrate and sound is produced.

2. Human ear can hear the sound in the frequency range from 20 Hz to 20,000 Hz or 20 kHz. 3. Harmful eff ects of noise pollution: Noise pollution causes health hazards. For example, too much of

noise has many adverse health eff ects, such as headache, restlessness, discomfort, insomnia (lack of sleep), hypertension, anxiety and many more health problems. Constant exposure to loud noise can cause partial or complete deafness.

4. Musical instruments produce pleasant sounds and have frequencies with defi nite ratio. Th ey use vibration of various kinds to produce music. Th ey are of three types such as stringed

instruments, wind instruments and percussion instruments. 5. Th e speed of the sound depends on various factors such as temperature, nature and physical state

of the substance. 6. (a) Sounds below 20 Hz are infrasonic waves and we can hear only sound which ranges from 20

Hz to 20,000 Hz. (b) Higher the frequency, the greater will be the shrillness of a voice. Th e voice of a woman has a

high frequency, and therefore, her voice is shriller. (c) Sound needs a medium like a solid, liquid or gas to travel. it cannot travel through a vacuum

because sound travels by producing a vibration in the molecules of the medium and there are no molecules in vacuum.

(d) Closer the molecules in a medium, the faster the vibrations will be transferred to the other molecules. Th erefore, denser the medium, the faster will be the movement of the sound waves. Th e speed of sound is maximum in solids, lesser in liquids and least in gases.

C. 1. Sound travels in the form of a wave and waves are characterised by three quantities, namely, amplitude, speed and frequency. Amplitude and frequency can be understood by the oscillations of a simple pendulum. Th e to and fro movement of the pendulum around the central point is called oscillation.

Amplitude: Th e maximum displacement of the ball from its mean position during an oscillation is called the amplitude of the oscillation. Th e maximum displacement is when the ball is at extreme position. Th e oscillation is small if the ball moves a small distance and the oscillation is large if the ball moves a larger distance.

Time period: Th e time taken by the ball to complete one oscillation is called time period. it is very diffi cult to measure the time period of one oscillation. Th erefore, measure the time period for 10 oscillations and divide it by 10. Th is will give the time period of one oscillation.

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Frequency: The number of oscillation per second is called the frequency of oscillation. The Si unit of frequency per second is called Hertz (Hz) in honour of the German physicist, Heinrich R Hertz. For example, if a pendulum makes 10 oscillations in one second then its frequency is 10 Hz.

Refer figure 13.4 from page 174 2. Refer figure 13.3 from page 173 Our ears are the sensory organs that help us to hear various sound. The structure of the ear can be

broadly classified into three parts: the outer ear, the middle ear and the inner ear. Outer ear: The part of the outer ear that is visible to us is called pinna. The pinna collects the sound

waves and directs them to the ear tube. Ear drum (tympanum) is present at the end of the ear tube which vibrates when sound waves strike it. it transmits the sound to the middle ear.

Middle ear: it has three bones connected with each other. These three bones are attached in such a way that they move when the ear drum vibrates and send the sound waves to the inner ear.

Inner ear: The inner ear is filled with a liquid. When this liquid vibrates, it excites tiny hair in the inner ear. Here the vibrations are transformed into electrical impulses which are then transferred to the brain through the auditory nerve.

3. Refer Experiment 3 on page 172 4. Sustained presence of harmful, unwanted or annoying noise in the environment is called

noise pollution. Major sources of noise pollution are vehicles, machines, bursting of crackers, loudspeakers, television, radio, desert coolers and air conditioners. Harmful effects of noise pollution: Noise pollution causes health hazards. For example, too much of noise has many adverse health effects, such as headache, restlessness, discomfort, insomnia (lack of sleep), hypertension, anxiety and many more health problems. Constant exposure to loud noise can cause partial or complete deafness.

5. When you keep your hand on the speaker of a music system or touch your throat while speaking, you will feel a vibration. Therefore, sound is produced due to vibration, which can be heard. The part in the throat which produces sound is called larynx or voice box. The voice box is situated in the neck at the upper end of the wind pipe. There are two vocal cords that are stretched in the larynx such that they have a slit in between for the passage of air.

While speaking, the air forces itself through the slit, the vocal cords vibrate and sound is produced. Different sounds are produced due to the muscles attached to the vocal cords. When the muscles are tight and thin or loose and thick, the sound produced will be different.

D. Guitar and violin – Stringed instruments Drums – Percussion instrument Shehnai – Wind instrument

E. 1. in some musical instruments, sound is produced by the vibrating air column inside the instrument. These instruments are called wind instruments. The pitch of the sound depends on the length of the vibrating air column.

2. When air is blown between two sheets of papers, the sheets are pulled together and an air column is formed which acts as a passage for the sound vibrations.

3. in percussion instruments, sound is produced by a vibrating skin or membrane. The pitch of the sound depends on the tension in the membrane and if the membrane is stretched more than its strength, it will get damaged. So, percussion instruments are able to produce only a limited range of frequencies.

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Worksheet 1 1. Th e areas where they lie together are called compressions and the areas where they lie away from

each other are called rarefactions. 2. When you shout loudly standing on a hill, you hear your sound returning back to you in some time.

it is simply the refl ection of sound by the hill or a tall building at a distance. 3. (a) Th e time taken by the ball to complete one oscillation is called time period.

(b) Th e number of oscillation per second is called the frequency of oscillation. (c) Human ear can hear the sound in the frequency range from 20 Hz to 20,000 Hz or 20 kHz.

Such sound is called audible sound. (d) Th e maximum displacement of the ball from its mean position during an oscillation is called

the amplitude of the oscillation. 4. By putting silencers in vehicles and other machines. Vehicles should avoid honking near residential

areas, hospitals, schools and community areas.

Worksheet 2 (a) Stringed instrument (b) Percussion instrument (c) Wind instrument (d) Percussion instrument (e) Stringed instrument (f) Wind instrument (g) Stringed instrument (h) Wind instrument

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Chapter 14Chemical Eff ect of Electric Current


• What is electric current? • Do liquids conduct electricity?• Good and poor conductor of electricity?• Magnetic eff ect of the current• Electrolysis—chemical eff ect of electric current.• Uses of electrolysis.• Electroplating and its uses.

Warm Up Ask the students if they are aware about what is electricity? How is electricity conducted? How does the bulb glow in a circuit? Are there any eff ects of electricity? Now, ask the students to complete the exercise given in the Warm-up section.

Concept Explanation

Electric Current• Explain to the students that we know what is electric current? We also know that there are

materials that allow the passage of electric current through them and some do not allow the electric current to pass through them.

• Explain to the students that they are cautioned by their parents not to touch electric wires with wet hands. Th is is because the liquids conduct electricity. Th e pure water or distilled water is a poor conductor of electricity

Heating Effect of Electric Current• Ask students if they know how does the bulb glow? Explain to the students that when there is

a circuit where the bulb is placed, it glows due to the heating eff ect of the current.

Magnetic Effect of Electric Current• Explain to the students that when a compass is placed near the wire in which the current

fl ows, the needle shows defl ection even if the current is weak. Th is shows the magnetic eff ect of the current.

Electrolysis• Explain to the students that the process of electrolysis is very interesting. By doing Experiment 4,

we will be able to see the eff ect of electric current through the liquids called electrolytes. it is the process of breaking down of an electrolyte chemically on passage of electric current.

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Electroplating• Explain to the students that there are many objects that we get from the market which look

shiny and attractive. For example, bicycle, gas stoves, show pieces and cutlery. They look attractive as a result of electroplating. Explain the process of electroplating with the help of Experiment 5.

• Explain to the students that, electrolysis and electroplating are very useful to protect inferior metals and improve the appearance of many objects.




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Worksheet 1 1. Fill in the blanks.

Electrolysis

(Negatively chargedelectrode)

Electrolyte(Cations) (Anions)

(Positively chargedelectrode)

2. Defi ne the following terms. (a) Electrolysis (b) ions (c) Electrolyte (d) Electroplating

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Worksheet 2 1. What will be the following in the electrorefi ning of copper? Anode Cathode Electrolyte

2. Give any three uses of electrolysis.

3. Make a simple circuit to demonstrate electroplating.

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A. 1. COLUMN A COLUMN BElectrolyte LiquidsCathode Negative electrodeAnode Positive electrodeAnion Negative ionsCation Positive ions

2. (a) ions (b) Electrorefi ning (c) Electroplating (e) Cations (d) Anions

B. 1. (a) Electrodes: A solid electric conductor through which an electric current enters or leaves an electrolytic cell or other medium.

(b) Cathode: Negatively charged electrode is called cathode. (c) Anode: Positively charged electrode is called anode. (d) Electrical conductivity: Th e measure of the ability of a substance to allow the fl ow of an electric

current is called electrical conductivity. (e) Electrolyte: Th e liquid that conducts electricity in the liquid state and breaks up chemically during

the process is called an electrolyte. 2. iron and copper can be electroplated. 3. in electrolysis, battery is used to get electric current. 4. Conductors: Materials that allow the electric current to pass through them are called conductors.

Tap water and acids are good conductor of electricity. 5. (a) Pure water is a poor conductor of electricity. So to make it a good conductor of electricity,

dilute acid is added into it. (b) Pure water does not get ionised on passing electric current so it is a poor conductor of electricity. (c) LED works even when the current is weak while bulbs do not glow due to the weak fl ow of

current. Th erefore, LED is a better option than bulbs for testing conduction. (d) Lime juice and vinegar both are acids which get ionised on passing electric current. So these

are good conductors of electricity. (e) Sodium chloride solution ionises into sodium and chloride ions on passing electric current. So

it is a good conductor of electricity. (f) You can get electric shock while operating electrical appliances with wet hands because water

is a good conductor of electricity. C. 1. Electrolysis is used in industry for the production of metals and non-metals. For example, metals

are extracted from their compounds like copper from copper sulphate and aluminium from aluminium chloride.

Refer fi gure 14.2 from page 185 2. Th e method in which one metal is used to coat another metal using an electric current is called

electroplating. Th e method involved in electroplating is as follows. Th e object to be coated is made the cathode. Th e metal to be deposited on the object is taken in the form of an electrode and made the

anode.

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Th e electrolyte contains salts of the metal to be coated. ions of the metal are attracted by the cathode and therefore move towards the object and get

deposited on it. Electroplating is used for refi ning of impure metals. it can be used to refi ne metals like copper,

silver and gold. Th e method is called electrorefi ning. in this process, the pure metal is made into cathode and the impure metal is made into anode. Th e charged particles move from the anode to the cathode. Th e pure metal gets deposited at the cathode. Th e impurities collect below the anode and are called anode mud.

Refer fi gure 14.3 from page 188 3. (a) impure copper is used as anode.

(b) Copper sulphate is used as electrolyte. (c) Pure copper is used as cathode. Picture in folder D. 1. Electrorefi ning is being depicted in the given picture. 2. Electrorefi ning is used for refi ning of impure metals. 3. in this process, the pure metal is made into cathode and the impure metal is made into anode.

Th e charged particles move from the anode to the cathode. Th e pure metal gets deposited at the cathode.

4. Copper from the anode loses electrons and enters the solution. Th ese electrons will get accepted by the copper ions at cathode and form copper metal which gets deposited on cathode. Th erefore, cathode is made of pure metal because it is not possible that cathode loses electrons.

5. Anode mud: Th e impurities that collect below the anode and are called anode mud.

E. 1. Electrodes are used to conduct electricity in the solution and carbon is used in the form of graphite which allows the electrons to fl ow through it. Also, carbon is cheaper and its graphite form is chemically inert in nature, so these do not cause any change in the reaction.

2. Th e effl uent that eliminate from the electroplating contaminates water, air and soil. Th e electroplating industry mainly releases cadmium, lead and mercury which are toxic and also a lot of waste water and sludge are released in the environment which cause pollution.


Worksheet 1 1.

Electrolysis

(Negatively chargedelectrode)

Cathode Anode

Negatively charged ionsPositively charged ionsElectrolyte(Cations) (Anions)

(Positively chargedelectrode)

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2. (a) Th e process of breaking down of an electrolyte chemically on the passage of electric current is called electrolysis.

(b) Atoms or a group of atoms with a positive or a negative charge are called ions. (c) Th e liquid that conducts electricity in the liquid state and breaks up chemically during the

process is called an electrolyte. (d) Th e method in which one metal is used to coat another metal using an electric current is called

electroplating.

Worksheet 2 1. Anode- impure copper, Cathode- Pure copper, Electrolyte- Acidifi ed copper sulphate solution 2. Uses of electrolysis: Electrolysis is used in industry for the production of metals and non-metals. For example, metals are extracted from their compounds like copper from copper sulphate and

aluminium from aluminium chloride. Electrolysis is used to coat dull metals with other metals to make them look shiny and attractive by

the method of electroplating. it is also used in purifying of metals. 3. Aim: To construct a simple circuit to demonstrate electroplating. Material required: Beaker, copper sulphate solution, sulphuric acid, one copper plate, one article

which is to be electroplated, battery and conductors Method: • Connect the article and the copper plate to the terminals of the batterywith

the wires. Now dip them in the beaker containing copper sulphate solution and add a few drops of dilute sulphuric acid. Allow the current to pass through the solution in the beaker and observe aft er 15 to 20 minutes.

Observation: • Youwillobserveacoatingofcopperonthearticle.

Conclusion: • Whenthecurrentstartsflowinginthesolution,thecoppersulphatedissociatesinto copper and sulphate. Th e copper ions move towards the electrode connected to the negative terminal of the battery. From the other electrode, an equal amount of copper gets dissolved in the solution. Th erefore, the loss of copper from the solution is restored. Th e process continues and the copper gets transferred from the copper plate to the article.

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Chapter 15Light


• What is light?• What are regular and diff used refl ections?• Laws of refl ection and lateral inversion.• Characters of the image formed with plane mirror.• Multiple refl ection.• Structure of an eye and defects of the eye.

Warm Up Ask the students if they know what is light? Which light is called white light? Have they seen refl ections? How do we observe things around us? Now, ask the students to complete the exercise given in the Warm-up section.

Concept explanation • Explain to the students that light rays fall on the things around us and are refl ected and when

these refl ected rays fall in our eyes, we are able to see things. • Explain to the students about the regular refl ection with the help of mirror and also about

diff used refl ection with the help of the examples. For example, we are able to see things inside the room even though the sun rays do not reach directly inside the room.

• Explain to the students that there are two laws of refl ection. 1. Th e incident ray, refl ected ray and normal all lie on the same plane. 2. Angle of incidence is equal to the angle of refl ection.

• Explain to the students the lateral inversion with the help of an example.• Tell them to stand in front of the mirror. Ask them to lift their right hand and note what

happens? Tell them that they will observe that their image will show left hand being raised. When they lift the left hand their image shows their right hand being raised.

• Explain to the students about the characteristics of refl ection from the plane mirror and multiple refl ections.

• Explain to the students that the sunlight is referred to as white light. it consists of seven colours known as ViBGYOR.

• Explain to the students the structure and defect of eyes.• Tell students about the Braille system which is used by visually challenged people.

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118

Worksheet 1 1. Label the given picture of an eye.

2. Defi ne the following terms. (a) Pupil (b) Retina (c) Blind spot (d) Optic nerve (e) Lens

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Worksheet 2 1. Give reasons of the following. (a) Objects appear of a particular colour only. (b) Refl ections are irregular. (e) Sun rays are called white light. (d) Eye care is important. (e) Th e images formed with the plane mirror show lateral inversion.

2. Give diff erence between myopia and hypermetropia.

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Retina image formationOptic nerve impulsesPupil Light rays enterMyopia Short sightedHypermetropia Long sightedLens Bending of light

2. (a) Refl ection: When a ray of light hits a mirror, or any polished surface, it bounces off the surface. Th is phenomenon is called refl ection of light.

(b) Refraction: Th e change in the direction of the path of a light ray when it passes from one transparent medium to another is called refraction.

(c) Dispersion: Th e process of splitting of white light into many colours is called dispersion. (d) Spectrum: Th e band of colours produced when a white light is split up is called spectrum. (e) Persistence of vision: Th e image produced in the human eye is retained for a very short period

of time aft er the object is removed. Th is phenomenon is called persistence of vision. B. 1. Irregular refl ection: When the beam of light falls on rough surfaces, the light is refl ected in diff erent

directions. Th is type of refl ection is called diff used refl ection. Refer fi gure 15.3 on page 194 2. it carries impulses from the eyes to the brain. 3. When you lift the left hand, your image shows your right hand being raised. Th is shows that the

refl ected image undergoes left -right inversion called lateral inversion. 4. Spectrum: Th e band of colours produced when a white light is split up is called spectrum. A rainbow

is an example of a spectrum. Water droplets in the sky split the sun rays and form a spectrum, which appears as a rainbow to us.

5. Multiple refl ection: By varying the angle between the two mirrors, we can get any number of images. Th is is a case of multiple refl ection.

6. (a) Bright sunlight can be harmful for our eyes. Long exposure to bright sunlight can lead to pain and irritation of eyes and cataract. So we should wear sunglasses when going out in bright sunlight.

(b) Th e image formed by a plane mirror is upright, erect, virtual and of the same size as the object. Th erefore, we should see ourselves in plane mirror.

(c) By varying the angle between the two mirrors, multiple images can be obtained due to multiple refl ection.

(d) To get infi nite number of images, hair salons have parallel mirrors. (e) A periscope has two plain mirrors. Th e refl ection from these two mirrors helps us to see

objects that cannot be seen directly. Periscopes are used in submarines, tanks and by soldiers in bunkers.

C. 1. Uses of plane mirrors: Plane mirrors are used as looking glass. Plane mirrors are used to make kaleidoscope, a toy which produces beautiful patterns from

coloured paper, pieces of glass or small coloured beads. Plane mirrors are also used in constructing periscope which is used in submarines. Plane mirrors are used in solar cookers.

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2. The number of images formed by a mirror can be calculated by a simple formula. N = (360/angle) – 1 The number of images formed when the angle between the mirrors is 90°: N = (360 – 90) – 1 N = 4 – 1 N = 3

3. Types of eye defects: Myopia: This is also called short sightedness. in this defect, the person cannot see the objects that

are far away clearly. This defect can be rectified by wearing spectacles with concave lenses. Hypermetropia: This is also called long sightedness. in this defect, the person cannot see the nearby

objects clearly. This defect can be rectified by wearing spectacles with convex lenses. 4. images formed by a plane mirror has the following characteristics. Erect: The image formed with the plane mirror is upright or erect. Size: The image is of the same size as the object. Distance of the image as compared to that of the object: The distance between the mirror and the

image is the same as that between the mirror and the object. if the object moves closer to the mirror, the image seems to move closer. if the object moves away, even the image seems to move further away.

Virtual: The image formed is virtual; it cannot be seen on the screen. Lateral inversion: The image shows lateral inversion, the right side of the object appears to be the left

side of the image. 5. Refer Figure 15.10_page 199 6. The number of images formed by a mirror can be calculated by a simple formula. N = (360/angle) – 1 (a) 45º The number of images formed N = (360/angle) – 1 = (360/45)-1 = 7 (b) 30º The number of images formed N = (360/angle) – 1 = (360/30)-1 = 11

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(c) 60º Th e number of images formed N = (360/angle) – 1 = (360/60)-1 = 5 D. 1. Dispersion is being depicted in the given picture. 2. We can see this phenomenon when light passes through a prism. When a beam of light is passed

through a prism, it splits into a band of seven colours. 3. A rainbow is an example of dispersion. Water droplets in the sky split the sun rays and form a

spectrum, which appears as a rainbow to us.

E. 1. if the refl ected ray becomes the new incident ray, then the new refl ected ray would be perpendicular to the surface of the plane mirror.

2. New stainless steel plate acts as a plane mirror because it is lustrous and due to this we are able to see ourselves in this plate not in the old one.


Worksheet 1 1.

Ciliary body

Iris

Pupil

Cornea

Lens

SuspensoryLigament

ScleraChoroid

Reti na

Fovea centralis

Opti c disc (blind spot)

Blood vessels

Opti c nerve

2. (a) Th e inner aperture that we can see in the centre of the eye is known as pupil. it is a small hole through which the light enters.

(b) Th is lies behind the eyeball. Th e image is formed on the retina. (c) Th is portion does not have any rods and cones. Th is is a position on the retina where image

formation does not take place. (d) it carries impulses from the eyes to the brain. (e) Th is is the transparent tissue between the pupil and the retina. Th e lens helps in focusing the

light that passes through the pupil into the eye.

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Worksheet 2 1. (a) An object appears to be of a particular colour because it absorbs all the colours except the one

it is made up of. (b) When the beam of light falls on rough surfaces, the light is reflected in different directions and

results in irregular reflections. (c) Sunlight consists of seven colours known as ViBGYOR which appear to our eyes as white. (d) Eyes are a very important organ of our body. Eye health has a very strong relationship with the

food we eat. So we should eat healthy food to take proper care of eyes. (e) The image shows lateral inversion, the right side of the object appears to be the left side of the

image. 2. Myopia: This is also called short sightedness. in this defect, the person cannot see the objects that

are far away clearly. This defect can be rectified by wearing spectacles with concave lenses. Hypermetropia: This is also called long sightedness. in this defect, the person cannot see the nearby

objects clearly. This defect can be rectified by wearing spectacles with convex lenses.

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Chapter 16Some Natural Phenomena


• What is lightening? • What is an electric charge?• How to charge an electrically neutral object?• How to test for the charges on an object• Safety measures during lightening.• What is an earthquake? What causes earthquake?• How can an earthquake be measured?

Warm Up Ask the students if they know what is lightning? When does lightning take place? Have they experienced tremors? What is the reason for tremors? Now, ask the students to complete the exercise given in the Warm-up section.

Concept Explanation• Explain to the students that during rainy season they must have seen lightning in the sky

along with the storm. Th ey must have also seen sparks in the loose plugs, switch boards and many electrical appliances. During winters they must have noticed that when the woollens or polyester clothes are rubbed or removed with a jerk they produce a spark. Lightning is also a kind of spark. Th is phenomenon is seen in the air during rainy season.

• Explain to the students that the concept of electric charge can be understood by rubbing and charging a body.

• Explain to the students that an electrically neutral object can be charged by friction, conduction and induction.

• Explain to the students that like charges repel and unlike charges attract each other. • Explain it with the help of a simple example. Tell students to rub the scale with their hair

and then put it close to the bits of paper. Now, ask them what do they observe? Why did this happen?

• Explain to the students the test for the charges on an object. When we bring two charged objects, if they get attracted to each other, this does not mean that both the objects are charged like we saw in the case of comb and the pieces of paper. Th erefore, only when objects repel, then it is certain that both the objects have charges.

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• Explain to students about the safety measures they need to take during lightning. Also mention the steps they should take during an earthquake. Tell students about “DROP, COVER and HOLD ON” as given in the innovator’s corner.




126

Worksheet 1

1. How can an object be charged? Give two methods.

2. Answer the following. (a) What is a gold leaf electroscope? (b) List two uses of gold leaf electroscope. (c) Draw a labelled diagram of a gold leaf electroscope.

(d) How does a gold leaf electroscope work?

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Worksheet 2 1. Give reasons for the following. (a) Lightning (b) Earthquake (c) Lightning conductors are used in the buildings. (d) Seismograph is used to measure the intensity of earthquake. (e) During earthquake, take cover under a heavy table. (f) One should not take bath during lightning. (g) Avoid being under the trees during lightning.

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A. 1. (a) Protons (b) Electrons (c) Seismology (d) Seismograph (e) Electroscope 2.

COLUMN A COLUMN BMaterials AtomsCharges by friction RubbingEpicentre Maximum intensityEarthquake DestructionEarthing Discharge to the earthElectroscope Test for the charge

B. 1. Earthquake: An earthquake is a sudden movement or a fracture in the crust and the upper layer of the mantle (together called lithosphere).

2. india is divided into 4 seismic zones: zones 2, 3, 4 and 5. Zone 5 is highly prone to the earthquake with the highest level of seismicity whereas Zone 2 is

associated with the lowest level of seismicity. 1. Guwahati – Assam – Zone 5 2. Srinagar - Jammu and Kashmir – zone 5 3. Delhi - Zone 4 4. Mumbai – zone 4 5. Chennai – Zone 3 6. Pune - Maharashtra 7. Kochi - Kerala 8. Kolkata - West Bengal 9. Th iruvananthapuram - Kerala 10. Patna - Bihar 3. Objects around us are electrically neutral as atoms have an equal number of positive and negative

charges. Electrically neutral objects can be charged by friction, conduction and induction. 4. (a) Fault zone: Th e boundaries of the plates are the weak zones where the earthquake is more likely

to occur. Th ese are known as seismic zones or fault zones. (b) Focus: Th e location where the earthquake begins. (c) Epicentre: Th e point at which the intensity of an earthquake is maximum is called the epicentre. (d) Plate tectonics: Th e theory that the surface of the earth is made of plates that move with respect

to one another. (e) Seismic zones: Th e boundaries of the plates are the weak zones where the earthquake is more

likely to occur. Th ese are known as seismic zones or fault zones. (f) Seismology: Th e branch of science concerned with earthquakes and related phenomena is

called seismology. 5. (a) During lightning, we should avoid going in open places because lightning has negative charge

which gets attracted towards the positive charge of the earth and if you are in open then you may get hurt.

(b) Landslides occurs due to earthquake because of the sudden movement of the crust.

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(c) in earthquake-prone areas, the buildings should be made with lighter materials because it may cause less loss of lives.

(d) Taking cover under a table may save you from the heavy objects that may fall. (e) A very large amount of electric current is generated during a lightning strike. The enormous

amount of heat produced makes the air expand suddenly. This causes a wave of vibrations (called a shock wave), which is the cause of the thunder that we hear. Thus, we see that lightning is accompanied by large amounts of electric current and very high temperatures, both of which are very dangerous.

C. 1. Objects around us are electrically neutral as atoms have an equal number of positive and negative charges. Electrically neutral objects can be charged by the following methods.

Charging due to friction: This is done by rubbing one material with another. Rubbing a glass rod with silk and an ebonite rod with wool are the most common examples. When a glass rod is rubbed with silk, the negative charges get transferred to the silk and the glass rod is left with positive charges. Similarly, when the ebonite rod is rubbed with fur, the negative charges go from the wool to the ebonite rod. Therefore, the ebonite rod becomes negatively charged and the wool is left with positive charge.

Refer figure 16.2 on page 206 Charging by conduction: Charging of an object can also be done by touching an object with a charged

body. For example, if we take a charged glass rod and touch it with the object to be charged, the charge from the glass rod will get transferred to the object and the object will get positively charged. This is called charging by conduction.

The nature of the charge acquired will be the same as that of the charging body. Refer figure 16.3 on page 207 Charging by induction: This is done without touching the charged body with the object. For example,

a charged glass rod is brought close to the metal object, without touching it. 2. To test whether a body has a positive or a negative charge: Take a charged object and touch the

charged electroscope. if the gold leaves diverge, the body is charged. Touch the disc with negatively charged ebonite rod. The leaves get negatively charged and diverge.

Now bring the body with an unknown charge close to the disc. Observe the divergence. if the divergence increases, then the body has similar charge. if the leaves collapse then the body has

opposite charge. Refer figure 16.4 on page 208 3. The boundaries of the plates are the weak zones where the earthquake is more likely to occur. These

are known as seismic zones or fault zones. Refer figure 16.8 on page 211 Earthquake tremors are caused due to the shifting of earth plates below the earth crust. The earth

layers are not in one piece; they are broken into fragments. The earth is divided into as many as seven large plates and several small plates. Therefore, when these plates move or shift, they cause tremors on the surface. These plates are called tectonic plates. When these plates go apart, rub against each other or collide with each other, they result in a disturbance on the earth’s crust which shows up as an earthquake.

Vibrations caused by an earthquake travel in the form of waves within the earth or along the surface of the earth. These waves are called seismic waves.

130

4. Here are some things that you can do to protect yourself during an earthquake. if you are indoors, take cover under a heavy table or a cot. Keep away from heavy objects that

might fall. if you are indoors in a public place, you should try to take cover under a sturdy object. Running

to the exit may cause a stampede, which could be very dangerous. if you are outdoors in a public place, move away from buildings, electric poles and trees which

could fall down. if you are in a vehicle, stay inside. Vehicles should keep away from bridges, overpasses and

tunnels. Avoid stopping under trees, light posts, power lines or signboards. 5. During lightning, it is important to take the following precautions. Hide in a safe place till lightning stops. Safe places could be houses and cars with the windows

closed. if you are unable to fi nd a safe place, then squat down. Avoid being in the open, under the trees

or near the poles; they are not safe. You should not carry any pointed metal as in an umbrella. Avoid touching anything that is metallic, electrical wires, pipes and telephone cords inside the

house. All these objects being good conductors are likely to transfer the charges. Use of electric appliances should be avoided. All gadgets like computers and televisions should

be unplugged. Do not take a bath during lightning and avoid touching the running water.

6. (a) Professional and responsible behaviour is being shown by the weather department. (b) Courage, compassion and humanity are expressed by people who come forward to help victims.

D. 1. Earthquake is being shown in the given picture. 2. Shift ing of earth plates is the possible reason behind this.

E. 1. Ravi did the right thing because the car acts like a cage. Th e metal in the car will shield Ravi from any external electric charge and thus prevent the lightning from striking the car.

2. Yes, the magnitude of the earthquake determines the damage caused. Th e magnitude of this scale is between 0 and 9. Earthquake that measures from 0 and 3 on the scale cannot be noticed. Earthquake of magnitude 4-5 is considered moderate. Earthquake of magnitude 5-7 generally moves the lighter objects and causes mild damage to weak structures. Th e intensity above 7 is disastrous and destroys property and life.


Worksheet 1 1. Object can be charged by friction and conduction.

2. (a) Th e gold leaf electroscope is used to measure the charge and also used to fi nd out the nature of the charge. Th e gold leaf electroscope has a metal disc attached to a metal rod. Th is rod passes into a bell jar through a tightly fi tted rubber stopper. Two metal thin strips are fi xed at the bottom of the metal rod made up of copper, brass or gold. Th e base of the jar has tin foils attached and the electroscope rests on the wooden base.

(b) To measure the charge: Th e amount of divergence of the leaves is a measure of the amount of charge in the body.

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To find out the nature of the charge: This is possible only when the electroscope is charged with a known charge. if the charges are same, the gold leaf will show divergence.

(c) Golden leaf electroscope

+

+

+

+

+

+

+

+ + + +

++

+

Gold leaf

InsulatorDisc

(d) To test whether a body has a positive or a negative charge: Take a charged object and touch the charged electroscope. if the gold leaves diverge, the body

is charged. Touch the disc with negatively charged ebonite rod. The leaves get negatively charged and

diverge. Now bring the body with an unknown charge close to the disc. Observe the divergence. if the divergence increases, then the body has similar charge. if the leaves collapse then the

body has opposite charge.

Worksheet 2 1. (a) During a thunderstorm, there is movement of clouds and air currents. The positive charges are

above the clouds and negative charges are below the clouds. There are positive charges on the ground too. When a large amount of charges accumulate, the air is unable to stop the negative charges from moving towards the positive charges on the earth. The charges meet, producing streaks of light and sound. These streaks of light are called electric discharges.

(b) Earthquake tremors are caused due to the shifting of earth plates below the earth crust. The earth layers are not in one piece; they are broken into fragments.

(c) Lightning conductors are devices used to protect the buildings. These are the rods installed above the building which extend and are buried underground, so that at the time of lightning the charges gets transferred to the ground through them.

(d) Seismograph is a simple vibrating rod or a pendulum, which starts vibrating when the tremor occurs. A pen is attached to the vibrating system, which records the seismic waves on the paper which moves under it. When the scientists study these waves, they are able to construct a complete map of the earthquake and can also estimate the power that caused destruction.

(e) During earthquake, one should take cover under a heavy table so that he or she can be saved from harm of life.

(f) Water is a good conductor of electricity so one should not take bath during lightning. (g) Avoid being under the trees because they are not safe as lightning may fall on them.

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Chapter 17Star and the Solar System


• What is universe? • What are stars, galaxies and constellation?• Why do the phases of moon occur?• What are asteroids, comets, meteors and meteorites?• About artifi cial satellites and their uses.

Warm up Ask the students if they know what are stars? Have they seen galaxies? What is the position of the sun in the solar system? Now, ask the students to complete the exercise given in the Warm-up section.

Concept Explanation • Explain to the students that the universe has stars, planets, moons, and celestial bodies. it is

huge and it is diffi cult to measure it. Th e branch of science that deals in the study of objects in the universe is called astronomy

• Explain to the students that stars are seen in the sky in groups. Th e group of stars is called galaxy. it contains millions and billions of stars.

• Explain to the students that the diff erent shapes of the bright part of the moon as seen during the period of one month is called phases of the moon.

• Explain to the students that moon does not produce its own light, whereas the sun and the stars have their own light, therefore, they are called luminous body and the moon is called the non-luminous body. Th e moon shines because it refl ects the light of the sun falling on it.

• Explain to the students that the moon is earth’s satellite. Th e surface of the moon is uneven with lot of steep and high mountains. Ask them how to identify them. Th e moon has no life as there is no atmosphere or water to support life.

• Tell students that the objects that are closer to us appear bigger and the ones that are far away look smaller even though they are of the same size. it is their distance from the earth that makes them look diff erent in size. Th e sun and the stars emit light of their own.

• Help students to recall that when we were young our grandparents made us aware about the stars in the sky. Th e fi rst star that they usually show us is in the name of Dhruv tara.

• Explain to the students that when they observe very carefully, they will see some stars forming shapes in groups. Th e stars forming a group with a specifi c shape is called constellations. Tell students to identify some constellations in the night sky.

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• Explain to the students that the sun and celestial bodies together form the solar system. it consists of large number of bodies such as planets, constellations, galaxies, comets, asteroids and meteors. The gravitational attraction between the Sun and these objects keeps them revolving around the sun. Earth is also the part of solar system, as it revolves around the Sun.




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Worksheet 1 1. Label all the planets.

2. Defi ne the following terms. (a) Stars (b) Galaxies (c) Satellites (d) Meteors (e) Asteroids

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Worksheet 2 1. Name the following. (a) Constellation which looks like the letter W or M. (b) Constellation which is called the Hunter. (c) Constellation also known as Big Dipper.

2. Write any three diff erences between inner and outer planets.

3. What is a light year?

4. Write any three applications of artifi cial satellites.

5. Mention the phases of the moon. Why do the phases of the moon occur?

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Great Bear SaptarshiComets Bright head with a tailOrion Th e hunterCassiopeia Egyptian queenVenus Hottest planetSaturn Large number of satellites

2. (a) Venus (b) Mercury, Venus, Mars, Jupiter and Saturn (c) 9.46×1012 km (d) Asterism

B. 1. Universe: Th e universe is a huge wide-open space that holds everything from the smallest particle to the biggest galaxy. Th e universe has stars, planets, moons, and other celestial bodies.

2. Millions of stars make galaxies. 3. Solar system: Th e sun and the celestial bodies together form the solar system. it consists of planets,

constellations, galaxies, comets, asteroids and meteors. 4.

Meteors CometsAs meteoroid falls, it burns up as a result of the enormous heat generated. Th is makes a streak of light called meteor or a shooting star.

Th ese are made of small chunks of ice and dust that revolve around the sun in the elliptical orbit. Th ey are characterised by a small solid part (called the head) surrounded by a cloud of glowing gases (called the coma).

5. Light year: A light year is the distance travelled by light in one year. Light year is used as a unit in astronomy.

1 light year = 3 × 108× 365 × 24 × 60 × 60 m = 9.46 × 1015 m or 9.46 × 1012 km

6. (a) Mercury is very hot during the day because the atmosphere on Mercury is very thin, allowing a lot of heat to be absorbed during the day.

(b) Th e moon has no life as there is no atmosphere or water to support life. (c) Stars are luminous objects so they give out light. (d) Stars are seen in the sky in groups. Th e group of stars is called galaxy. Stars form shape of some

objects of the earth. Th ese shapes are called constellations. (e) Pole star appears almost stationary to us. it does not move at all. So, sailors use this star to fi nd

direction. C. 1. Group of stars making shapes of objects of the earth are called constellations. Some of the

constellations are as follows. Ursa Major: it is also known as Big Dipper, the Great Bear or Vrihat Saptarshi. Th is is one of the

most famous constellations which can be seen during summer. Th ere are seven stars in the Ursa

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Major. it appears like a big ladle or a question mark. Ursa Minor: it is also called the Lesser Bear. One part of this constellation comprising a group of

seven stars is called the Little Dipper or Laghu Saptarshi. The Pole star is present in this constellation. Orion: This is one of the constellations which is well known and can be seen during winter in the

late evenings. it has seven to eight bright stars. it is called the Hunter. Cassiopeia: This is a constellation located in the northern sky. it is visible during the winter. it

looks like the letter W or M. The five stars in the constellation form an image of an Egyptian queen Cassiopeia.

2. Star: The luminous objects that are seen as points of light in the night sky are called stars. The sun is also a star. The stars emit light of their own. While the planets do not emit light of their own.

Galaxy: Stars are seen in the sky in groups. The group of stars is called galaxy. Milky way galaxy: if you look up at the night sky, in a place far away from pollution, you will see a broad band of light. This band is called the Milky Way galaxy, named so because it looks like a trail of milk split across the sky. We also belong to the Milky Way galaxy. it contains millions of stars.

3. The different shapes of the moon are called the ‘phases of the moon’. The day the moon is visible like a complete disc, it is called a full moon day. After this day, the moon starts thining down. On the fifteenth day, the moon is not visible. This day is called a new moon day. Next day, a very thin portion of the moon appears in the sky. This is known as the crescent moon. Till the fifteenth day, the moon continues to grow larger, that is, the lit side of the moon becomes bigger every night and when the half moon can be seen (like a semicircle), it is called first quarter. it keeps increasing and becomes round on the fifteenth day and we get the full view of the moon. This is called full moon. This cycle continues day after day. The changes that are seen every day are due to the relative position of the sun, the earth and the moon, which changes every day.

When the moon is between the earth and the sun, we do not see the moon. it is called the new moon. When the earth comes between the sun and the moon on the fifteenth day after the new moon, it is called full moon.

4. Natural satellite: A natural satellite is a celestial body that orbits another celestial body which is bigger. The moon is the only natural satellite of the earth.

Artificial satellite: The artificial satellite is a device placed in orbit around the earth, moon, or another planet. The artificial satellites are man-made. They are launched from the earth. They revolve around the earth much closer than its natural satellite, that is, the moon.

5. Moon is about one-fourth the size of the earth. When astronauts visited the moon, they found that the surface was dusty and there was no life. The surface was uneven with a lot of steep and high mountains. These can be equated with the mountains on the earth. The moon has no life as there is no atmosphere or water to support life. The moon completes one rotation on its axis as it completes one revolution around the earth in 27.3 days. it also rotates on its own axis. its distance from the earth is about 3,84,400 kilometers.

D. 1. Refer figure 17.4 and 17.2 on page 223 Orion: This is one of the constellations which is well known and can be seen during winter in the

late evenings. it has seven to eight bright stars. Ursa Major: it is also known as Big Dipper, the Great Bear or Vrihat Saptarshi. This is one of the

most famous constellations which can be seen during summer. There are seven stars in the Ursa Major. it appears like a big ladle or a question mark.

E. 1. There is not atmosphere on the moon so streak of light will not form there because it will not burn up.

2. The stars are not visible to us during the day because of the following reasons. Stars are very far from us. Brightness of the sun dims the light of the stars.

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Worksheet 1 1.

Sun

Mer

cury

Venu

s

Eart

h

Mar

s

Jupi

ter

Satu

rn

Ura

nus

Nep

tune

2. (a) Th e luminous objects that are seen as points of light in the night sky are called stars. (b) Stars are seen in the sky in groups. Th e group of stars is called galaxy. (c) A satellite is a moon, planet or machine that orbits a planet or star. (d) When the earth’s orbit crosses the path of a meteroid, it falls through the earth’s atmosphere.

As it falls, it burns up as a result of the enormous heat generated. Th is makes a streak of light called meteor or a shooting star.

(e) Th ese are large pieces of rock or metal. Th ere is large gap between the Mars and Jupiter. Th is gap is occupied by a large number of small objects called asteroids.

Worksheet 2 1. (a) Cassiopeia (b) Orion (c) Ursa major

2.

Inner planets Outer planetsTh ey are smaller in size. Th ey are very large in size.Th ey are closer to the sun as compared to the outer planets.

Th ey are much farther away from the sun as compared to the inner planets.

Th ey are very dense, mostly made of rock. Th ey are very light and made up of gases.

3. A light year is the distance travelled by light in one year. Light year is used as a unit in astronomy. 4. Application of artifi cial satellites: Research satellites measure fundamental properties of outer space, e.g., magnetic fi elds, fl ux of

cosmic rays and micrometeorites, and properties of celestial objects that are diffi cult or impossible to observe from the earth.

Communication satellites provide a worldwide linkup of radio, telephone, and television. Weather satellites, or meteorological satellites, provide continuous, up-to-date information about

large-scale atmospheric conditions such as cloud cover and temperature profi les. 5. Full moon, gibbous moon, crescent moon, and new moon are the phases of the moon. Th e changes

that are seen every day are due to the relative position of the sun, the earth and the moon, which changes every day.

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Chapter 18Pollution of Air and Water


• What is air pollution? • Reasons for air pollution.• Th e beauty of Taj Mahal is decreasing due to the air pollutants. • What is green house Eff ect and what causes global warming?• What changes can be made to reduce air pollution?• What is water pollution and reasons for water Pollution.• What is Ganga Action Plan and its objectives?• What changes can be made to reduce water pollution?

Warm Up Ask the students if they know what is pollution? Have they observed air pollution? Have they seen polluted water bodies? Why should one need fresh air and clean water? Now, ask the students to complete the exercise given in the Warm-up section.

Concept Explanation• Explain to the students that air is one of the most crucial requirements for life. We can stay

without food and water for some time, but it is diffi cult to survive without air. We are aware about the percent of various constituents of air. Oxygen is very important for survival.

• Explain to the students that we are living in the modern world. Due to the growing population the needs of people are increasing. Th e modernization is leading to setting up of factories and industries to manufacture goods that we need. As a result, there is lot of waste and pollution generated. Th e increase in the number of vehicles for personal use and transportation is also adding to the problems. Explain to them about the other air pollutants.

• Explain to the students that during winter season, in the northern part of india, people experience fog in the morning which continues to be there for almost half the day. Th is is nothing but smog, which is the combination of the smoke and fog. Smoke may contain oxides of nitrogen and sulphur. it combines with the other air pollutants and with fog forming the smog.

• Ask students the reason why Taj Mahal is getting decolourised?• Explain to the students that the sun rays enter the atmosphere which acts like a greenhouse

and they are unable to escape as they remain trapped inside it. With the result the house remains warm throughout providing required temperature for the plants to grow. Th is is called the Greenhouse Eff ect. Th e heat radiations then remain in the atmosphere resulting into gradual increase in the temperature of earth’s atmosphere. Th is is called Global warming.

• Explain to the students that success stories are the best means of creating awareness amongst people regarding the importance of reducing air pollution.

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1. Government declared the use of CNG and unleaded petrol in Delhi. This has reduced the air pollution remarkably in the city, which was known to be the most polluted city in the world.

2. Fossil fuels as we have learnt had been hazardous for the lives of people, therefore, we should switch over to the alternative fuels to avoid air pollution, for example, solar energy, hydropower and wind energy.

• Explain to the students that water is also a precious resource like air is for life. Due to increase in population and industrial and agricultural activities, the demand of water is increasing day by day, leading to scarcity of water. Water is also getting polluted due to the human activities. The production of goods and the waste generated as a result is going into the water bodies, which is spoiling the quality of water. The substances that pollute the water are called water pollutants.

• Explain to the students that Ganga is one of the most famous rivers of india. Millions of people depend on river Ganga for water and livelihood. Many people go to the bank of river Ganga for rituals like taking a dip in the holy water and for cremation. The River Ganga passes through many towns and the cities. The residents throw large quantities of waste, untreated sewage, dead bodies and many harmful things into the river. Pollution level of the river have been rising over the years.

• Explain to the students that water that appears to be clean and clear, may not be fit for drinking. it may be free of solid impurities but it may still have germs in it, like disease causing microorganisms. Therefore, it is crucial to treat the water before using it for the purpose of drinking. The Municipal Corporation treats the water before supplying it to the households.




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Worksheet 1

1. Complete the given fl ow chart. Also mention the role of missing air pollutants in air pollution.

Sources Of Air Pollution

Power Plants

Chemical Industry

(a) (b) (c)

(d)

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

2. Mention any two eff ects of air pollution.

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Worksheet 2 1. Complete the given fl ow chart and also mention the role of missing water pollutants

in water pollution.

Food Processing

industrial Chemical

Waste

Sources of Water Pollution

(a) (b)

(c)

(d)

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

2. Mention any two eff ects of water pollution.

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A. 1. (a) Sulphuric acid and nitric acid (b) Potassium permanganate and chlorine tablets (c) Oxides of sulpur and nitrogen (d) Boiling and chlorination (e) Detergents and fertilizers


Methane Greenhouse gasPoisonous gas Carbon monoxideParticulate matter Respiratory diseasesOxygen Supports lifeNitric acid Acid rain

B. 1. Global warming: When the sunrays enter the earth’s atmosphere, these get trapped in this blanket of carbon dioxide. Th is gas traps the heat and does not allow it to escape. Th e heat radiations remain in the atmosphere, resulting in the gradual increase in the temperature of the Earth. Th is phenomenon of increase of the earth’s temperature due to greenhouse gases is called global warming.

Acid rain: Air pollution is caused by automobiles and chemical industries which emit sulphur dioxide and nitrogen dioxide. Th ese gases react with water vapour in the atmosphere and form acids such as sulphuric and nitric acid. Th ese are responsible for acid rain.

2. Boiling, chlorination and electric water fi lters are used at home to purify water. 3. Greenhouse eff ect: Th e phenomenon whereby the earth’s atmosphere traps solar radiation because

of the presence of gases like carbon dioxide, water vapour and methane is called the greenhouse eff ect. Th ese gases are called greenhouse gases.

4. Due to the burning of fossil fuels and cutting of trees, the concentration of carbon dioxide is increasing in the atmosphere. Th e increase in the concentration of carbon dioxide and other gases is responsible for global warming.

5. Burning of fossil fuels such as coal and petroleum in thermal power plants and automobile exhaust release oxides of sulphur and nitrogen into the air which are responsible for air pollution.

6. Many detergents and fertilizers contain phosphates. When these enter the waterbodies, they promote rapid growth of algae. Th is process is called eutrophication. Aquatic weeds multiply in the waterbodies, which reduces the oxygen content of the water, leading to the death of aquatic plants and animals.

7. Oil leaks from boats and ships leave a trail of oil on the water surface and pollute rivers and oceans. Spilled oil can harm living things because its chemical constituents are poisonous.

8. Eff ects of global warming: Global warming has become a matter of concern as it is causing a change in the climate pattern too. Th e Gangotri Glacier in the Himalayas and the polar ice caps are melting due to global warming and the sea level is increasing. Th is will cause gradual drowning of many small islands and coastal areas.

9. Sunlight, wind and water are renewable sources of energy.

C. 1. Some of the harmful eff ects of air pollution on plants and animals are listed in the following table.

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Refer Table on page 241 2. Creating awareness amongst people is the best means of reducing air pollution. The government

declared the mandatory use of CNG and unleaded petrol in Delhi. This has reduced the air pollution remarkably in the city, which was known to be the most polluted city in the world.

Burning of fossil fuels is hazardous for the lives of people. Therefore, we should switch over to the alternative fuels to avoid air pollution. For example, solar energy, hydropower and wind energy.

We should also reduce the usage of personal vehicles and use public transport or carpools. 3. Refer case study given on page 243 4. Water that appears to be clean and clear, may not be always fit for drinking. it may be free of solid

impurities but it may still have disease-causing microorganisms. Therefore, it is crucial to treat the water before using it for the purpose of drinking. The Municipal Corporation treats the water before supplying it to the households. Water supplied in our homes generally comes from the rivers and is not pure. it contains impurities like sand, slit and clay; soluble impurities like salts and also microorganisms. So, water needs to be treated before supplying it to our homes, which is done in big purification plants.

Reasons of water pollution: industries that use chemicals, make paper and process food, produce waste materials such as

metals and synthetic compounds. Lead and mercury are very harmful for life, which reach the waterbodies when the pollutants are discharged and thus pollute the water.

Many detergents and fertilizers contain phosphates. When these enter the waterbodies, they promote rapid growth of algae. This process is called eutrophication. Aquatic weeds multiply in the waterbodies, which reduces the oxygen content of the water, leading to the death of aquatic plants and animals.

Oil leaks from boats and ships leave a trail of oil on the water surface and pollute river and oceans.

Bathing animals and washing clothes in or near lakes and rivers make these waterbodies dirty. 5. Water pollution can be checked through following measures. Trees should be planted to prevent

water runoff. There should be separate drainage for sewage which should be treated before discharging it in water. Agro-chemicals, such as pesticides and fertilizers should be used judiciously to reduce eutrophication. There should be more use of bio-fertilizers and bio-pesticides. industrial and factory waste should be treated before discharging it in the waterbodies.

6. Water supplied in our homes generally comes from the rivers and is not pure. it contains impurities like sand, slit and clay; soluble impurities like salts and also microorganisms. So, water needs to be treated before supplying it to our homes, which is done in big purification plants. Purification of water can be done physically (boiling) and chemically (chemical tablets and electric water filters).

Boiling: it is the easiest way to purify water. Water should be boiled at 100°C for at least 10-15 minutes to kill microorganisms.

Refer figure 18.14 _page 247 Addition of chlorine tablets: Chlorine tablets or potassium permanganate can be added to water to

kill microorganisms. Refer figure 18.15_page 248 Electric water filters: Electric water filters have a micro-porous filter, carbon and a source of

ultraviolet radiation. Micro-porous filter removes physical impurities such as dust, rust, dirt and mud. Carbon absorbs organic impurities. Ultraviolet radiation kills microorganisms.

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Refer figure Fig 18.16_page 248 7. Effects of water pollution: Harmful effects of water pollution on living beings are as follows. Untreated domestic sewage: When released into waterbodies, sewage provides support for the

growth of a number of organisms that cause waterborne diseases. Oil spills: These lead to the destruction of marine life. Moreover, the cleaning up process also

causes a lot of damage to marine habitat. Industrial waste: This contains a lot of toxic substances that make water unfit for drinking. Ignition of arms and weapons: it produces a large amount of mercury. When water contaminated

with mercury is used for drinking by animals and human beings, it causes numbness of lips and tongue.

Fertilizer-rich runoff: Fertilizer-rich runoff from agricultural fields contains organic matter. The process of washing away of fertilizers into water bodies is called leaching. The entry of nutrient-rich water results in a thick growth of algae, called algal bloom, leading to eutrophication.

Water pollution can be checked through following measures. Trees should be planted to prevent water runoff. There should be separate drainage for sewage which should be treated before discharging it in

water. Agro-chemicals, such as pesticides and fertilizers should be used judiciously to reduce

eutrophication. There should be more use of bio-fertilizers and bio-pesticides. industrial and factory waste

should be treated before discharging it in the waterbodies. D. 1. Purification of water is being depicted in the given picture. 2. Purification of water: 1. Large impurities are removed by sedimentation and decantation. 2. Finer impurities are removed by filtration. 3. Chlorination is done to kill the germs. 4. Water is stored in big tanks. 5. Clean water is supplied to our homes. E. 1. Greenhouse trap the sunrays and prevent them from going back. So the temperature of greenhouse

is warmer than the surroundings. So, plants in cold countries get adequate warmth and grow well. 2. Ravi’s friend did the right thing because tap water contains a lot of impurities and germs which are

harmful for us. 3. Yes, i agree with this. Green plants release oxygen during photosynthesis and use up the available

carbon dioxide. This used up carbon dioxide is more than the carbon dioxide they release during breathings. So by using up the atmosphere carbon dioxide, green plants reduce greenhouse effect.

4. Ozone layer absorbs the harmful ultraviolet radiation of the sun and protects us. But ozone layer depletion will allow the harmful UV rays to reach to us directly which can cause skin cancer on long exposure.

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Worksheet 1 1. (a) Burning of fossil fuels such as coal and petroleum in thermal power plants and automobile

exhaust release oxides of sulphur and nitrogen into the air. (b) Burning of fuels which are rich in carbon such as fi rewood, coal and petroleum releases carbon

dioxide and carbon monoxide into the atmosphere. (c) Volcanic eruptions, forest fi res and dust storms are some of the natural sources of air pollution.

Th ese release harmful particulate matter into the atmosphere. (d) Freons or chlorofl uorocarbons (CFCs) are commonly used as coolants in air conditioners and

refrigerators and as propellants in aerosol spray cans. Th ese also pollute the air. 2. Global warming and acid rain occur due to air pollution.

Worksheet 2 1. (a) industries that use chemicals, make paper and process food, produce waste materials such as

metals and synthetic compounds. Lead and mercury are very harmful for life, which reach the waterbodies when the pollutants are discharged and thus pollute the water.

(b) Many detergents and fertilizers contain phosphates. When these enter the waterbodies, they promote rapid growth of algae. Th is process is called eutrophication. Aquatic weeds multi ply in the waterbodies, which reduces the oxygen content of the water, leading to the death of aquatic plants and animals.

(c) Oil leaks from boats and ships leave a trail of oil on the water surface and pollute river and oceans.

(d) Bathing animals and washing clothes in or near lakes and rivers make these waterbodies dirty. 2. Eff ects of water pollution: Untreated domestic sewage: When released into waterbodies, sewage provides support for the

growth of a number of organisms that cause waterborne diseases. Oil spills: Th ese lead to the destruction of marine life. Moreover, the cleaning up process also causes

a lot of damage to marine habitat.

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Answers to Summative Assessment-2

A. 1. iii. 2. i. 3. ii. 4. iv. 5. ii. 6. iii. 7. ii. 8. ii. B. 1. Pressure increases with depth. 2. Force of friction is less on smooth surfaces. 3. Th e number of oscillations per sound is called the frequency of oscillation. 4. Pure water is a poor conductor of electricity. 5. Refl ections are regular when the beam of light falls on a smooth surface like a mirror. 6. Like charges repel each other. 7. Jupiter is the largest planet of the solar system. 8. Carbon dioxide is a greenhouse gas. C. 1. Gravitational force: Th e force with which objects pull each other is called gravitational force. We are

able to walk and stay on the Earth because of gravity. Th is is the force that is constantly exerted on us by the Earth and is called gravitational force or the force of gravity. Th is force makes the planets move around the Sun and also makes the moon move around the Earth.

2. Th e following are some other advantages of friction. Vehicles like cars and buses can move on the road due to the force of friction between the tyres

and the road. Th e brakes in the cycles and heavy vehicles work due to friction. Disadvantages of friction: it causes wear and tear in the moving parts in machinery and automobiles. Th ere is wastage of energy and fuel, because frictional force comes into play in the moving parts of

the machinery. 3. Sound travels in the form of a wave and waves are characterised by three quantities, namely,

amplitude, speed and frequency. Amplitude: Th e maximum displacement of the ball from its mean position during an oscillation is

called the amplitude of the oscillation. Time period: Th e time taken by the ball to complete one oscillation is called time period. Frequency: Th e number of oscillation per second is called the frequency of oscillation. Th e Si unit

of frequency per second is called Hertz (Hz). 4. Uses of Electroplating Electroplating is used for refi ning of impure metals. it can be used to refi ne metals like copper,

silver and gold. Th e method is called electrorefi ning. Electroplating is used for protecting the metals that get easily corroded by coating them with a

metal that does not corrode. Electroplating with gold and silver is used for cutlery, decorative pieces like statues and

jewellery made out of cheaper metals. 5. Lateral inversion: When you lift the left hand, your image shows your right hand being raised. Th is

shows that the refl ected image undergoes left -right inversion called lateral inversion. Characteristics of the image formed with a plane mirror are as follows. Erect: Th e image formed with the plane mirror is upright or erect. Size: Th e image is of the same size as the object.

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Distance of the image as compared to that of the object: The distance between the mirror and the image is the same as that between the mirror and the object. if the object moves closer to the mirror, the image seems to move closer. if the object moves away, even the image seems to move further away.

Virtual: The image formed is virtual; it cannot be seen on the screen. Lateral inversion: The image shows lateral inversion, the right side of the object appears to be the left

side of the image. 6. Objects around us are electrically neutral as atoms have an equal number of positive and negative

charges. Electrically neutral objects can be charged by the conduction, friction and induction. 7. Group of stars making shapes of objects of the earth are called constellations. Some of the constellations are as follows. Ursa Major: it is also known as Big Dipper, the Great Bear or Vrihat Saptarshi. This can be seen during summer. There are seven stars in the Ursa Major. it appears like a big ladle

or a question mark. Ursa Minor: it is also called the Lesser Bear. One part of this constellation comprising a group of

seven stars is called the Little Dipper or Laghu Saptarshi. The Pole star is present in this constellation. Orion: This is one of the constellations which is well known and can be seen during winter in the

late evenings. it has seven to eight bright stars. it is called the Hunter. Cassiopeia: This is a constellation located in the northern sky. it is visible during the winter in the

early part of the night. it looks like the letter W or M. 8. Greenhouse effect: The phenomenon whereby the earth’s atmosphere traps solar radiation because

of the presence of gases like carbon dioxide, water vapour and methane is called the greenhouse effect. These gases are called greenhouse gases. These greenhouse gases are responsible for trapping the heat and causing global warming.

D. 1. Pressure is defined as the force per unit area. The Si unit of pressure is pascal (Pa) which is newton per square metre or N/m2.

Some applications of pressure are as follows. Syringes are used to take blood for blood tests. The pressure of the blood forces the blood to

move into the syringe when its plunger is withdrawn. As the area of the edge of a knife’s blade is extremely small, this creates a pressure high enough

for the blade to cut through a material. Skis have a large area to reduce the pressure on the snow. that the skis do not sink into the snow

too deep. 2. Decreasing friction: Wear and tear of an object reduces its life. Wear and tear due to friction depends on two factors: the

roughness of the two surfaces in contact and the amount of time the two surfaces rub against each other.

To reduce the friction in the machinery, it should be regularly oiled and greased. Ball bearings can be used to reduce friction. Polishing of rough surfaces makes them smooth and reduces friction. increasing friction: it is difficult to walk on smooth surfaces like smooth tiles, ice and wet or oily fl oor. We slip

and fall on such surfaces because friction does not come into play. Sometimes, it is necessary to increase the friction to avoid accidents.

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Following things are done to increase friction. Tyres have grooves in them to increase friction. This prevents skidding of vehicles. We spread sand or gravel on wet or slippery ground during rainy season. This increases friction. Players and athletes have spikes in their shoe soles to increase friction. 3. Musical instruments produce pleasant sounds and have frequencies with definite ratio. They use

vibration of various kinds to produce music. They are of three types. Stringed instruments: in these musical instruments, sound is produced by a vibrating string. The

pitch of the sound depends on the length of the vibrating string. The loudness of the sound is increased by the air chamber present in them. Sitar, guitar, violin and sarod are some examples of stringed instruments.

Wind instruments: in these instruments, sound is produced by the vibrating air column inside the instrument. The pitch of the sound depends on the length of the vibrating air column. Flute, shehnai and saxophone are some examples of wind instruments.

Percussion instruments: in these instruments, sound is produced by a vibrating skin or membrane. The pitch of the sound depends on the tension in the membrane. Tabla, drums and mridangam are some examples of percussion instruments.

4. Refer Experiment 3_page 184 5. Refer page 199 6. Here are some things that you can do to protect yourself during an earthquake. if you are indoors, take cover under a heavy table or a cot. Keep away from heavy objects that

might fall. if you are indoors in a public place, you should try to take cover under a sturdy object. Running

to the exit may cause a stampede, which could be very dangerous. if you are outdoors in a public place, move away from buildings, electric poles and trees which

could fall down. if you are in a vehicle, stay inside. Vehicles should keep away from bridges, overpasses and

tunnels. Avoid stopping under trees, light posts, power lines or signboards. 7. Solar system: The sun and the celestial bodies together form the solar system. it consists of planets,

constellations, galaxies, comets, asteroids and meteors. Sun: The sun is the closest star from the earth. There is a massive nuclear reaction taking place in

the sun, converting the hydrogen gas into helium gas. it is the fundamental source of energy on earth as it emits huge amount of heat and light.

Planets: From far, the planets look like stars but they do not have a light of their own. The stars shine but the planets do not. The planets keep changing positions with respect to the stars. Hence, they were named planets, which means ‘wanderers’ in Greek.

Mercury: This is the closest planet to the sun. it is the smallest planet of our solar system. it is very difficult to observe it because it is hidden due to the glare of the sun.

Venus: Venus is near the earth. it is the brightest planet in the sky. Sometimes it appears in the eastern sky before sunrise and sometimes in the western sky just after the sunset.

Therefore, it is also called the morning or the evening star because it appears bright. Earth: This is the only planet which has environmental conditions that support life. These conditions

are air, water, suitable temperature and ozone layer. it appears blue and green due to the water and the vegetation on the planet.

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Mars: it is known as the red planet as it appears red in colour because it contains large amount of iron oxide. This planet is visible to the naked eye.

Jupiter: it is the largest planet of the solar system. 1300 Earths can be placed inside Jupiter. Saturn: it is the second largest planet in the solar system. Saturn appears yellowish in colour. Saturn is often called the ‘ringed planet’ because it has rings which are not visible with the naked

eyes. Uranus: This planet was identified by the British astronomer William Hershel in 1781. it can be seen

with the naked eyes but not very easily. Uranus also has rings. Neptune: it was identified by the German astronomer Gottfried Galle in 1846. it cannot be seen

with the naked eyes. it looks like a star with the help of pair of binoculars and looks like a small bluish circle through a powerful telescope. it has two known satellites.

8. Due to the growth in population and increase in industrial and agricultural activities, the demand for freshwater is increasing day by day, leading to its scarcity.

Water is also getting polluted due to human activities. The waste generated as a result of increased production of goods is thrown into the waterbodies, which is leading to the deterioration in the quality of water. The substances that pollute the water are called water pollutants.

Steps to reduce water pollution: Refer page 244 & 245

E. 1.

2. Refer figure 15.2 and 15.3 from page 194 3. Refer figure 16.6 from page 210 4. Refer figure 13.4 from page 174

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Model Test Paper-II 1. Match the following. 1×10=10

Column A Column BContact force AnionStringed instrument Mars and JupiterNegatively charged ion HunterSeismograph Frictional forceAsteroid belt Air pollutionGlobal warming EarthquakeOrion SitarEcho Anode mudimpurities Multiple reflectionsKaleidoscope Sound

2. Tick (√) the correct option. 1×5=5 (a) Which of the following parts of the eye through which light enters? (i) Cornea (ii) Pupil (iii) Retina (iv) Sclera (b) Gold leaf electroscope is used to measure (i) Earthquake intensity (ii) Charge of an object (iii) Seismic waves (iv) Lightning (c) Which of the following celestial bodies is not considered as a planet anymore? (i) Uranus (ii) Neptune (iii) Pluto (iv) Mars (d) Which of the following is a bad conductor of electricity? (i) Pure water (ii) Tap water (iii) Vinegar (iv) Salt solution (e) Which of the following helps to reduce friction? (i) Ball bearing (ii) Grooves in tyres (iii) Spikes in shoe soles (iv) Gravel on road

3. Write one word for the following. 1×10=10 (a) Pressure exerted on an object by the weight of the air above. (b) Reflection of the sound by the hill. (c) A liquid that conducts electricity due to the presence of ions. (d) The process of splitting of white light into many colours. (e) The point at which the intensity of an earthquake is maximum. (f) Meteoroid hitting the earth surface as a solid piece. (g) The phenomenon of increasing earth’s temperature due to greenhouse gases. (h) Force per unit area. (i) Atoms or a group of atoms with a positive or a negative charge. (j) Water which is treated and is suitable for drinking.

4. Answer the following questions in 1-2 lines. 2×10=20 (a) Give differences between conductor and insulator. (b) What is refraction?

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(c) What is persistence of vision? (d) Explain charging of an object by induction. (e) Write the names of all tectonic plates. (f) Write the names of fi rst artifi cial satellite and fi rst indian artifi cial satellite. (g) When was Th e Ganga Action Plan launched? (h) Explain why magnetic force is a non-contact force. (i) How does the friction help in writing on the blackboard? (j) Write the frequencies of audible and inaudible sound.

5. Answer the following in brief. 3×8=24 (a) Write the steps to reduce air pollution. (b) What are meteors, meteoroids and meteorites? (c) Explain the magnitude of earthquake. (d) Explain the method of electroplating. (e) How loudness and pitch are related to amplitude and frequency of the sound wave? (f) On what factors does the pressure depend? (g) How ball bearing reduces the friction? (h) What is braille system?

6. Answer the following in detail. 5×4=20 (a) Explain how to construct a simple electroscope with the help of an experiment. (b) Explain the phases of the moon with the help of a diagram. (c) How to make a kaleidoscope? Show an activity. (d) How does sound travel and how is it produced?

7. Look at the given picture and answer the following questions. 11

(a) What does the picture depict? 1 (b) Label the given picture. 4 (c) Explain the picture. 4 (d) What type of refl ection is it showing? 2

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Answers

1. Column A Column B

Contact force Frictional forceStringed instrument SitarNegatively charged ion AnionSeismograph EarthquakeAsteroid belt Mars and JupiterGlobal warming Air pollutionOrion HunterEcho Sound impurities Anode mudKaleidoscope Multiple reflections

2. (a) ii (b) ii (c) iii (d) i (e) i 3. (a) Atmospheric pressure (b) Echo (c) Electrolyte (d) Dispersion (e) Epicentre (f) Meteorite (g) Global warming (h) Pressure (i) ions (j) Potable water 4. (a) Conductors are the materials that conduct electricity such as tap water due to the presence of ions

while insulators are the materials that do not conduct electricity such as pure water. (b) The change in the direction of the path of a light ray when it passes from one transparent medium

to another is called refraction. (c) The image produced in the human eye is retained for a very short period of time after the object is

removed. This phenomenon is called persistence of vision. (d) This is done without touching the charged body with the object. For example, a charged glass rod

is brought close to the metal object, without touching it. (e) Pacific plate, North American Plate, South American Plate, African Plate, Antarctica Plate, indian-

Australian Plate and Eurasian plate. (f) First artificial satellite: Sputnik-1 First indian artificial satellite: Aryabhatta (g) The Ganga Action Plan was launched in Varanasi on 14 June 1985. (h) Magnetic force is applicable even when magnet is not touched with iron or nickel, hence, it is called

a non-contact force. (i) Due to the rough surface of the blackboard, when the chalk rubs the blackboard, some chalk

particles stick to the blackboard. (j) Audible sound: 20 Hz-20,000 Hz inaudible sound: Below 20 Hz and above 20,000 Hz 5. (a) Creating awareness amongst people is the best means of reducing air pollution. The government declared the mandatory use of CNG and unleaded petrol in Delhi. This has reduced the air pollution remarkably in the city, which was known to be the most polluted

city in the world. Burning of fossil fuels is hazardous for the lives of people. Therefore, we should

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switch over to the alternative fuels to avoid air pollution. For example, solar energy, hydropower and wind energy. We should also reduce the usage of personal vehicles and use public transport or carpools.

(b) Meteoroids are smaller than comets. When the earth’s orbit crosses the path of a meteoroid, it falls through the earth’s atmosphere. As it falls, it burns up as a result of the enormous heat generated. Th is makes a streak of light called meteor or a shooting star. Most of the meteoroids fully burn up before they reach the lower atmosphere. Sometimes, a meteoroid does not fully burn up and it hits the earth surface as a solid piece. Th is is called a meteorite.

(c) Th e magnitude and the intensity of the earthquake are measured using the Richter scale. Th e magnitude of this scale is between 0 and 9. Earthquake that measures from 0 and 3 on the scale cannot be noticed. Earthquake of magnitude 4-5 is considered moderate. Earthquake of magnitude 5-7 generally moves the lighter objects and causes mild damage to weak structures. Th e intensity above 7 is disastrous and destroys property and life.

(d) Th e method involved in electroplating is as follows. Th e object to be coated is made the cathode. Th e metal to be deposited on the object is taken in the form of an electrode and made the anode.

Th e electrolyte contains salts of the metal to be coated. ions of the metal are attracted by the cathode and therefore move towards the object and get deposited on it.

(e) if the frequency of the vibration is high, the sound will be shrill and have a higher pitch and if the frequency of vibration is low then the sound will have a lower pitch. Th e larger the amplitude, the louder would be the sound, the smaller the amplitude, lower would be the sound. Th e loudness of the sound produced by a vibrating object depends on the amplitude of vibration.

(f) How much eff ect the force produces on the object depends on the following factors. Th e magnitude of the force Th e area on which the force is applied

(g) Ball bearings can be used to reduce friction. Th ey change the sliding friction to rolling friction when these are placed between the moving surfaces because the rolling friction is less than the sliding friction.

(h) Th e most popular resource for visually challenged people is the Braille system. Th ere is Braille code for common languages. Many indian languages can be used using this system. Visually challenged people learn this system by beginning with letters followed by special characters and letter combinations. it is a method that depends upon touching; each character has to be memorised. Th e text is produced by hand or machine.

6. (a) Aim: To construct a simple electroscope. Materials required: Glass bottle with wider mouth, small cardboard,

paper clip, two small strips of aluminium foil Method: Take the bottle and the cardboard. Pierce the cardboard

with a paper pin so that the paper pin can be inserted. Now open the paper clip and hang the aluminium foil on the clip. Cover the bottle with the cardboard. Fold the clip so that it stays partly above the cardboard. Bring a charged plastic strip near the clip and observe.

Observation: Similar charges will show repulsion and the aluminium foil strips will repel each other and become wide open. Repeat this with other charged bodies to test the charges on the body. Such a device that can be used to test for the presence of charge on an object is known as electroscope. Th e metal clip acts as a good conductor of electricity and transfers the electric charge from the charged object to another. Now touch the clip with the hand. You will observe that the foil collapses.

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Conclusion: When you touch the clip, it loses the charge which travels to the earth through your body. So, you can say that, the foil gets discharged. When a charged object comes in contact with a body which is not charged, electric charges jump from the charged body till the charges on the two bodies are equalized. This process is called discharging. When a body comes in contact with the earth, either directly or indirectly, then the charges are discharged to the earth. The process of transfer of the charge from the charged body to the earth is called earthing.

(b) The different shapes of the moon are called the ‘phases of the moon’. The day the moon is visible like a complete disc, it is called a full moon day. On the fifteenth day, the moon is not visible. This day is called a new moon day. Next day, a very thin portion of the moon appears in the sky. This is known as the crescent moon. it keeps increasing and becomes round on the fifteenth day and we get the full view of the moon. This is called full moon. This cycle continues day after day. When the moon is between the earth and the sun, we do not see the moon. it is called the new moon or amavasya.

When the earth comes between the sun and the moon on the fifteenth day after the new moon, it is called full moon or poornima.

(c) Take three rectangular mirror strips, each measuring about 15 cm long and 4 cm wide. Join them together forming a triangle. Take a circular cardboard and fix the mirrors on the cardboard. Make sure that the cardboard is slightly longer than the mirrors. Make a circular cardboard disc having a hole in the centre, so that you can see through it. Paste a piece of transparent plastic sheet under the cardboard disc to make it durable. Fix a circular plane glass at the other end, touching the glass. Now place some glass pieces and close this by putting another circular glass on it, leaving enough

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space for the movement of glass pieces. Now when you see from the other end, you will be able to see various patterns when you rotate it. A particular pattern is never repeated. Th is can also be wrapped in a colourful paper to make it attractive.

(d) Let us understand this with an example. When a loudspeaker is switched on, a membranein the loudspeaker vibrates, that is, moves backwards and forwards. Th is causes the surrounding air molecules to vibrate. A sound wave travelling through air pushes these molecules close together and then pulls them away from each other. if we imagine the air molecules to be like small balls, a sound wave travelling through air alternatively pushes these balls together and then pulls them away from each other. Th e areas where they lie together are called compressions and the areas where they lie away from each other are called rarefactions. As the sound wave propagates, the molecules only vibrate about a mean position, they themselves do not move from one point to another. it is this eff ect that propagates and reaches our ears.

Production of sound: Sound is produced due to vibration, which can be heard. Th e part in the throat which produces sound is called larynx or voice box. Th e voice box is situated in the neck at the upper end of the wind pipe. Th ere are two vocal cords that are stretched in the larynx such that they have a slit in between for the passage of air. While speaking, the air forces itself through the slit, the vocal cords vibrate and sound is produced. Diff erent sounds are produced due to the muscles attached to the vocal cords. When the muscles are tight and thin or loose and thick, the sound produced will be diff erent.

7. (a) Laws of refl ection is being depicted in the given picture. (b)

Refl ected ray

Normal

Incident ray

Mirror

θθ

(c) Th e incident ray, the refl ected ray and the normal all lie on the same plane. Th e angle of incidence is equal to the angle of refl ection.

(d) in the given picture, mirror is used so uniform refl ection is shown.

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