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CCECCESCIENCE

Question Bank

8

(Based On NCERT Syllabus)

PREPARED BY

Rekha Lalla

TEACHER RESOURCE

MANUAL

Chapter-1 : Crop Production and Management

Objective Type Questions

A. Fill in the blanks.

1. agriculture 2. Weedicides 3. plantation 4. Kharif

5. seed drill 6. basin 7. Drip 8. Pests

9. winnowing 10. Bengal famine

NCERT Questions

11. crop 12. preparation 13. float 14. water and nutrients

B. Write whether the following statements are true or false.

1. False 2. False 3. True 4. False 5. True 6. False

7. False 8. False 9. True 10. True

C.Match the two columns to make correct pairs.

1. a. iii b. v c. iv d. i e. ii

NCERT Questions

2. a. iii b. i c. ii d. iv

3. a. v b. iv c. ii d. iii e. i

D. Multiple choice questions. Tick the correct option in each case.

1. b 2. b 3. d 4. c 5. b 6. d 7. c 8. c 9. c 10. c

NCERT Questions

11. b 12. c 13. d 14. b 15. c 16. a 17. d 18. b 19. b 20. c

21. c

E. Name them.

1. Maize 2. Wheat 3. Plough, hoe, cultivator, seed drill

4. Agriculture 5. Compost 6. Harvesting

Descriptive Questions

F. Very short answer questions.

1. (a) Two advantages of tilling the land.

(i) Allows easy penetration of roots. (ii) Lets air and water percolate easily.

(b) Two precautions to be taken while sowing seeds.

(i) Seeds should be free of infection. (ii) Sowing should be at the right depth.

(c) Two ways of saving water during irrigation.

(i) Using sprinklers for irrigation. (ii) Following drip irrigation technique.

(d) Two modern irrigation techniques.

(i) Using low density polyethylene to line the canals.

(ii) Following drip irrigation technique.

(e) Two traditional methods to improve soil fertility.

(i) Manuring the field. (ii) Crop rotation.

2. Seed drill ensures distribution of seeds at the right depth and right intervals.

3. If all the seeds are dropped in a bucket of water, the unhealthy ones will float while healthy ones would settle down.

4. Drip irrigation helps to save a lot of water which otherwise evaporates from the field. Here, the water flows through pipes with holes at regular intervals directly into the roots.

5. Fertilizers damage the soil, kill soil organisms and destroys soil fertility.

6. Manure makes the soil porous and increases its water holding capacity.

7. Weeds are unwanted plants in a crop field, which compete with crops for food and water.

8. Common pests that attack plants are organisms like rats, weevils, borers, etc.

9. Threshing is separation of grains from the harvested crop.®Jiwan Science CCE Question Bank Answer Key-8/1

®Jiwan Science CCE Question Bank Answer Key-8/2

10. In winnowing, grains are allowed to fall from a height. The chaff being light in weight, flies away and heavier grains fall down.

11. The harvested grains are stored in jute sacks or metal bins after being dried. Large scale storage is done in silos or granaries.

NCERT Questions

12. Chain pump, rest of all the equipments are directly related to cultivation.

13. The preparation of the soil is the first step before growing a crop. The first process is loosening and turning of the soil called tilling and ploughing. If the soil is dry it needs watering. The ploughed field may have big pieces of soil called crumbs. It is necessary to break these with a plank. The field is levelled for sowing as well as for irrigation purposes. Sometimes manure can be added before tilling. This helps in proper mixing of manure with soil. The soil is watered before sowing.

14. October to March.

15. The process of loosening and turning the soil is important to promote the growth of earthworms.

G. Short answer questions.

1. Distinguish between

a.

S.No. Kharif Crop Rabi Crop

1. They are sown between April and May. They are sown between September and October.

2. They are harvested after monsoon rain. They are harvested after winter.

3. Kharif crops are also known as monsoon crops. Rabi crops are known as winter crops.

4. These crops are totally dependent upon rainfall. These crops require irrigation.

5. The examples of kharif crops are rice, sunflower, The examples of rabi crops are wheat, gram, pea,sugarcane, soyabean, tea etc. mustard, barley etc.

b.

S.No. Fertilizer Manure

1. A fertilizer is an inorganic salt. Manure is a natural substance obtained by the decomposition of cattle dung, human waste and plant residues.

2. A fertilizer is prepared in factories. Manure can be prepared at household also.

3. A fertilizer does not provide any humus to the soil. Manure provides a lot of humus to the soil.

4. Fertilizers are very rich in plant nutrients like nitrogen, Manure is relatively less rich in plant nutrients.

phosphorus and potassium.

c. Mixed cropping, also known as inter-cropping or co-cultivation, is a type of agriculture that involves planting two or more of plants simultaneously in the same field. In general, the theory is that planting multiple crops at once will allow the crops to work together. Possible benefits of mixed cropping are to balance input and outgo of soil nutrients, to keep down weeds and insect pests, to resist climate extremes (wet, dry, hot, cold), to suppress plant diseases, to increase overall productivity and to use scarce resources to the fullest degree.

Crop rotation is the practice of growing a series of dissimilar types of crops in the same area in sequential seasons for various benefits such as to avoid the build up of pathogens and pests that often occurs when one species is continuously cropped. A traditional element of crop rotation is the replenishment of nitrogen through the use of green manure in sequence with cereals and other crops. It is one component of polyculture. Crop rotation can also improve soil structure and fertility by alternating deep-rooted and shallow-rooted plants.

2. Weeds compete with crops for food and water. They grow rapidly and deprive the crops of essential nutrients. So, they should be removed.

3. NPK fertilizers are mixed fertilizers. They contain nitrogen, phosphorous and potassium—which are necessary for plant growth.

4. Harvested grains will have a lot of moisture. If stored as it is, the grains will get mouldy and spoil. So, they should be first dried well and then stored.


5. Traditionally fields have been improved by agricultural practices like crop rotation and mixed cropping. In crop rotation two different categories of plants are grown alternately so that the soil is not deprived of the same nutrients season after season. In mixed cropping a main crop is grown along with two or more different crops in rows to enable the farmer to harvest varieties of crops at the same time maintaining soil fertility. The crops are chosen in such a way that their nutrient demands are different.

6. The process of cutting and gathering of crops is called harvesting. It is done when the grains are mature and ready.

7. Scattering of seeds by hand in a crop field is called broadcasting.

8. A leveller is used to crush the big lumps in the field and level out the soil.

9. Crops grown for commercial purposes like coffee, tea rubber, etc., are called plantation crops.

NCERT Questions

10. Beera can grow legume for one season end wheat for another season. This will help in replenishing the soil with nitrogen.

11.

13.a. Intensive animal farming.

b.

1. Food being the most important necessity of living beings, man's primary occupations for centuries, has been cultivation of plants to meet his requirements. The systematic method of cultivation is what is called agriculture. The practice of agriculture is completed in many stages like:

(i) Preparation of soil. (ii) Sowing of seeds.

(iii) Irrigation - supply of water. (iv) Providing manure/fertilizers.

(v) Controlling pests. (vi) Harvesting and storage of grains.

Each step involves a lot of challenge and hard work. With modern technology to provide support, man has been able to use more efficient time and labour saving methods in agriculture.

2. The various steps that are included in the process of agriculture in order to take care of the plants in the crop field, are called agriculture practices. They are:

(i) Preparation of the soil - tilling the land and levelling it to loosen the soil.

(ii) Sowing seeds - taking care of the spacing between seeds, etc.

Organic foods are foods that are produced using methods of organic farming – with limited modern synthetic inputs such as synthetic pesticides and chemical fertilizers, though organic pesticides.

12. a. Seed drill

b. The use of seed drills is beneficial because:

• It allows sowing seeds at an appropriate depth.

• Seeds at a depth cannot be picked by birds.

• Seeds sown in proper rows result in uniform growth and reduce overcrowding. Thereby, providing sufficient nutrients, water and sunlight to all plants.

•

•

•

•

•

•

•

•

H. Long answer questions.

The basic needs for the welfare of cattle are:

Adequate quantity and quality of water, food and air to maintain good health.

Social contact with other cattle. Cattle adapt to the familiar surroundings in which they live, including other cattle.

Sufficient space to stand, lie down, stretch and groom, and to perform normal patterns of behaviour.

Protection from predation.

Protection from disease or injury, and appropriate treatment if they occur.

Protection from adverse extremes of climate or unseasonal changes in weather conditions, where possible.

Precautions against the effects of natural disasters (e.g. storage of feed to protect against drought, provision of fire-breaks).

Protection from unnecessary, unreasonable or unjustifiable pain, suffering or injury.

14.Rabi crops-mustard, gram, wheat, pea.

Kharif crops-paddy, maize, cotton, groundnut.


(iii) Irrigation - according to the demand of the crop grown.

(iv) Adding manure and fertilizers to supplement the nutritional requirements.

(v) Controlling pests and weeding to protect the plants and ensure their well being .

(vi) Harvesting and storage of the grains after all the hard work.

3. Loosening and levelling of the soil ensures:

(i) Good ventilation for air and water to percolate .

(ii) Allows easy penetration of roots .

(iii) Helps in even distribution of nutrients .

(iv) Prevents soil erosion.

(v) Helps soil organisms to thrive .

(vi) Enables uniform irrigation of the field.

4. Some seeds like that of rice, tomatoes, etc., are sprinkled in a small plot of land where they grow into seedlings. When they are ready the seedlings are removed and planted in a prepared field at right distances. This is known as transplanting. It helps to choose healthy seedlings out of the whole lot and also plant them at right distances so that they get enough light, water and nutrients.

5. Various types of irrigation are:

(i) Surface irrigation (ii) Furrow irrigation (iii) Basin irrigation

(iv) Drip irrigation (v) Sprinkler irrigation.

Basin Irrigation: In this method, the whole field is flooded with water and nutrients.

Furrow Irrigation: Furrows (grooves) are made in the fields and water is allowed to flow through the furrows.

6. To make manure out of kitchen waste, we need (i) An old plastic container or a manure pit. (ii) Soil in the plastic container. Spread a layer of soil first and then keep adding all the wastes coming out of the kitchen like vegetable peels of discarded food, fruit peels, seeds, etc., cover these with soil intermittently. When the container is full, cover it with soil, close and leave for a month or two to decompose. The waste you've collected would have turned into manure at the end of the month.

7. The green revolution refers of the increase in food production and also production of non – food items in agricultural sector. It brought about dramatic increase in agricultural productivity due to the use of genetically improved varieties of seeds. India did its bit of research in improving the varieties of rice seeds which increased our grain production. Improvement in plant biotechnology has transformed India from a food deficit nation to one of the world's leading agricultural nations.

NCERT Questions

8. There are several reasons for a crop failure-seeds not good enough, seeds are planted deep, climatic conditions or global warming, erratic climatic conditions, diseased plant etc.

9. A kitchen garden can be grown even in old plastic bucket.

• Make tiny holes at the base and fill with mud. Loosen and level with khurpi. This is preparation of soil. The first step.

• Next you choose the seeds you want to cultivate and sow in the soil. The seeds should be of good quality.

• Water the plants with water-can everyday so that the soil remains moist and the seeds get water to germinate. This is irrigation.

• Add manure or fertilizer to make sure that all the nutrients are available for the growing plant.

• Keep watch every day, you will find tiny germinating plants, We need to protect the young plant. A spray of pesticide or a herbicide is necessary. Pull out the weeds.

10. a. Rice is sown during monsoon and harvested in October.

b. Seeds can be sown either by broadcasting or line sowing which are discussed below:

Broadcasting method: In this method seeds are broadcasted by hand over the well ploughed land once in east west and again north south direction to cover the area uniformly. Thereafter seeds are incorporated well in the top surface of soil so that they could be fully covered with a thin layer of soil having sufficient moisture for germination. It is one of the most popular methods of sowing but it has some difficulties in the intercultural operation.


Line Sowing method: This method is far superior to the broadcasting method because line sowing of crop facilitates the cultural operations and also enable to identify the weed seedlings even at early stage. In this method seeds are sown in the rows by keeping a proper distance using specific machine called seed drill. For this purpose various type of seed drill have already developed in our country drawn by machine or animal.

Depth of Sowing: The seeds of rice should be sown at 5 cm depth. Depth of sowing also varies with the size of seed. A thumb rule regarding depth of sowing is 4 times of the size of seeds.

c. The crop should be dried before storing to prevent from fungal and microbial growth. After drying the grains are stored in jute sacks or metal bins. Large scale storage is done in silos and granaries which have hundreds of tonnes of storage capacity. These are first treated with chemicals to avoid damage from pests and microbes. For storage at home dried neem leaves are a good option.

11. a. Preparation of soil : The preparation of soil is the first step before growing a crop. One of the most important tasks in agriculture is to turn the soil and loosen it. This allows the roots to penetrate deep into the soil. The loose soil allows the roots to breathe easily even when they go deep into the soil. The loosened soil helps in the growth of earthworms and microbes present in the soil. These organisms are friends of the farmer since they further turn and loosen the soil and add humus to it. Turning and loosening of soil brings the nutrient-rich soil to the top so that plants can use these nutrients.

b. Sowing : Sowing is the most important part of crop production. Before sowing, good quality seeds are selected. Good quality seeds are clean and healthy seeds of a good variety. Farmers prefer to use seeds which give a high yield. Nowadays the seed drill is used for sowing with the help of tractors. This tool sows the seeds uniformly at proper distances and depths. It ensures that seeds get covered by the soil after sowing. This prevents damage caused by birds. Sowing by using a seed drill saves time and labour.

c. Weeding : In a field many other undesirable plants may grow naturally along with the crop. These undesirable plants are called weeds. The removal of weeds is called weeding. Weeding is necessary since weeds compete with the crop plants for water, nutrients, space and light. Thus, they affect the growth of the crop. Some weeds interfere even in harvesting and may be poisonous for animals and human beings.

d. Threshing : In the harvested crop, the grain seeds need to be separated from the chaff. This process is called threshing. This is carried out with the help of a machine called 'combine' which is in fact a combined harvester and thresher.

12. S.No. Fertilizer Manure

1. A fertilizer is an inorganic salt. Manure is a natural substance obtained by the decomposition of cattle dung, human waste and plant residues.

2. A fertilizer is prepared in factories. Manure can be prepared at household.

3. A fertilizer does not provide any humus to the soil. Manure provides a lot of humus to the soil.

4. Fertilizer are very rich in plant nutrients like nitrogen, Manure is relatively less rich in plant

phosphorus and potassium. nutrients.

13.Irrigtion : All living beings need water to live. Water is important for proper growth and development of flowers, fruits and seeds of plants. Water is absorbed by the plant roots. Along with water, minerals and fertilisers are also absorbed. Plants contain nearly 90% water. Water is essential because germination of seeds does not take place under dry conditions. The supply of water to crops at different intervals is called irrigation. The time and frequency of irrigation varies from crop to crop, soil to soil and season to season.

Two methods of Irrigation which conserve water:

(i) Sprinkler System:

This system is more useful on the uneven land where sufficient water is not available. The perpendicular pipes, having rotating nozzles on top, are joined to the main pipeline at regular intervals. When water is allowed to flow through the main pipe under pressure with the help of a pump, it escapes from the rotating nozzles. It gets sprinkled on the crop as if it is raining. Sprinkler is very useful for sandy soil.


(ii) Drip system : In this system, the water falls drop by drop just at the position of the roots. So, it is called drip system. It is the best technique for watering fruit plants, gardens and trees. The system provides water to plants drop by drop. Water is not wasted at all. It is a boon in regions where availability of water is poor.

14.Wheat is a rabi crop, which is grown in the winter season . Rabi crops are generally sown from October to March and require less water, low temperature, less humidity and moderate sunshine. Whereas kharif crops are sown in the rainy season generally from June to September as these require a lot of water, excess temperature, humidity. Therefore, If wheat is sown in the kharif season, due to entirely adverse climatic conditions it will not yield any crop.

15.Continuous growing of crops makes the soil poorer in certain nutrients. Therefore, lateral farming of these crops, we have to add manure to the fields to replenish the soil with nutrients.

16.In a field many other undesirable plants may grow naturally along with the crop. These undesirable plants are called weeds. The removal of weeds is called weeding. Weeding is necessary since weeds compete with the crop plants for water, nutrients, space and light. Thus, they affect the growth of the crop.

To control weeds we can do the following things :

Tilling before sowing of crops helps in uprooting and killing of weeds, which may then dry up and get mixed with the soil. The best time for the removal of weeds is before they produce flowers and seeds. The manual removal includes physical removal of weeds by uprooting or cutting them close to the ground, from time to time using a khurpi. We can also use a seed drill for the same.

Weeds are also controlled by using certain chemicals, called weedicides. These are sprayed in the fields to kill the weeds. They do not damage the crops. The weedicides are diluted with water to the extent required and sprayed in the fields with a sprayer.

17.

I. Give reasons.

ucation of farmers through media, field workers and helping them to form self help groups for getting loans and marketing the produce.

3. The farmer uses a mixture of manure and fertilizers so that the nutrient which are not in manure are fulfilled by the fertilizers.

1.

2.

3.

This help to get enough sunlight, water and nutrients by preventing overcrowding in field.

If the grains are not dried before storage, the moisture present in them can destroy the grains. It will also provide a breeding ground for insects and bacteria.

A buffer stock scheme or storage of grains as buffer is an attempt to buy and store the grains when they are in surplus amount in the market and then sell them when there is shortage of food and the demand rises very much in order to stabilize the prices of the grains.

J. HOTS questions.

1. All seeds that are sown do not germinate. It is due to the fact that external agents can cause damage to the seeds. The probable reasons for non-germination of most of the seeds are:

(i) Defective seeds: The seeds that failed in germination could have been infested and defective .

(ii) Birds : Birds and certain others soil organisms might have eaten away the seeds.

2. Farmers in India especially in rural and remote areas have poor storage facilities. Government can help farmers as follows:

(i) Providing good quality seeds, fertilizers.

(ii) Improved irrigation facilities.

(iii) Providing electricity or providing assistance to generate electricity from alternate reserves like installing biogas plants, solar panels, wind mills, etc.

(iv) Procurement of the produce at a reasonable price.

(v) Improvement of storage facilities.

(vi) Above all, ed

Ploughing theField

6

Manuring

7

Preparation ofSoil

5

Sowing

4

Irrigation

6

Harvesting

7

Sending Crop to Sugar Factory

1

Chapter-2 : Microorganisms– Friends And Foe



1. biogas, manure 2. Glass, plastics 3. Rizhobium, leguminous

4. Lactobacillus 5. Fermentation 6. Dead, weakened

7. Antibodies 8. antigen 9. Edward Jenner

10. Penicillin, Alexander Flemming 11. Leeuwenhock

12. Fungi 13. Virus 14. Leguminous

15. Yeast, lactobacillus 16. Sodium benzoate, potassium metasulphide

17. salt 18. microbial growth 19. bacteria

20. Foot and mouth disease 21. vectors

22. B12

NCERT Questions

23. microscope 24. nitrogen 25. yeast


1. False 2. False 3. True 4. False 5. True 6. False


1. a. iv b. i c. v d. ii e. iii

NCERT Questions

2. a. v b. i c. ii d. iii e. iv


1. d 2. c 3. d 4. c 5. b 6. b 7. d 8. b 9. d 10. c

NCERT Questions

11. b 12. b 13. a 14. c 15. c 16. b 17. b 18. c 19. a 20. b

21. b 22. b

E. Name them.

1. Virus 2. Bacillus 3. Chlamydomonas

4. Anton Van Leeuwenhock 5. Euglena and volvox 6. Rhizobium



1. Rhizobium

2. Yeast

3. Fungi and bacteria

4. Bread mould

5. Virus are as good as non-living outside the body of a host .

6. Antibodies are cells produced to fight the antigens (microbes) which find entry in our body.

7. (i) Polio drops (oral polio vaccine).

(ii) DPT (Diphtheria, Pertussis Tetanus).

8. Inoculation is introduction of a small amount of microbe to stimulate antibodies in the body.

9. Diseases that are easily transmitted from one person to another through air, water, food, direct contact or

animals are called communicable. E.g. Jaundice and typhoid are spread through contaminated food and

water.

10. Sodium benzoate, potassium meta bisulphate.

11. Low temperatures in the refrigerator cause inactivity of microbes.

12. Bacteria are found in rod shape, spherical shape or spiral shape.®Jiwan Science CCE Question Bank Answer Key-8/7


G. Short answer questions.1. Organisms that are too small to be seen with the naked eyes are called microorganisms. They can be

seen with the help of a microscope.2. Vaccines stimulate our body to produce antibodies which provide immunity against certain serious illnesses.3. Viruses grow and show all signs of life while inside a host whereas outside a host they are as good as

non-living.4. Food to be canned is heated to about 110°C for a particular duration and then sealed in vacuum cans.

This eliminates the possibility of microbial growth.5. In dehydration, moisture is completely removed from foods and it helps to prevent growth of microbes.

Moisture is very important for microbial growth.6. Flies carry a lot of microbes on their hairy bodies. They are often seen in places where garbage and

sewage are dumped. After visiting such places, if they sit on food that we consume, the germs get deposited on the food and contaminate it.

7. The precautions that one should follow are:(i) Do not use the belongings of the infected person — his towel, sheets, utensils, etc., should be

washed separately.(ii) Avoid contact with the infected person. He should be quarantined until the infection subsides.

8. (i) Microbes are responsible for spreading a number of infectious diseases like typhoid, T.B, chickenpox, polio, etc.

(ii) Microbes bring about rotting of food. They spoil grains, vegetables and fruits, and cooked food.9. Microorganisms are classified into four major groups:

1. Bacteria 2. Fungi 3. Protozoa 4. AlgaeH. Long answer questions.

1. Pasteurization is a method of making milk germ free. It is done by heating milk upto 70° C rapidly and then cooling it suddenly below 10°C. This procedure helps to kill all microbes and also prevents their growth.

2. Pickling is the procedure of adding high concentration of salt to perishable items. Soil in high concentration will result in osmosis, that is, movement of water from the body of the organisms to outside. Thus the microbes are killed when they enter salt concentrated pickles .

3. Microbes are very useful to man in many ways. Many of our fermented foods get the texture and taste due to microbial action. Bread, idli, bhatura and nan are soft and spongy due to the action of yeast or the dough from which they are prepared. Curd or yogurt is a product of action of yeast and lactobacillus on milk. Vinegar and wine are beverages that are manufactured by introducing yeast in juices of fruits like grapes.

4. We can reduces the chances of contamination and infection by following certain precautionary measures like:(i) Washing our hands thoroughly with a disinfectant before eating.(ii) Food and drinks should be kept covered and eating exposed food has to be reduced.(iii) Water that we drink should be boiled, filtered or UV purified to ensure safety.(iv) Surroundings should be kept clean and tidy and no water should be allowed to stagnate.(v) Avoid contact with infected persons or their belongings.(vi) All necessary vaccines should be taken without fail.

5. Mangoes, when fresh will perish soon. When we receive a huge supply, they can be preserved as squashes, jams, and pickles. The mango slices can be canned by taking them to the nearest canning center. In squashes and jams sugar in high concentration prevents growth of microbes and they can be well preserved by adding a small quantity of chemical preventives. Pickles have high salt content which prevent microbial growth by preserving like this, the mangoes received in summers can be consumed throughout the year.

NCERT Questions 6. Microorganisms are quite useful in our lives in many way :

(i) Yeast - a microorganism is used for the large scale production of alcohol, wine and acetic acid (vinegar).

(ii) Lactobacillus- a bacterial microorganism helps us in truning milk into curd.(iii) Yeast a microorganism is used in baking industry for making breads, pastries and cake.(iv) Bacteria are also used for commercial production of antibiotics medicines like Streptomycin,

tetracycline and erythromycin.


(v) They help in increasing soil fertility.(vi) Microorganisms like Rhizobium and blue green algae are of great importance in agriculture.(vii) They increase soil fertility by fixing atmospheric nitrogen and converting it into nitrogenous

compounds.(viii) Certain bacteria convert compounds of nitrogen present in the soil into nitrogen gas which is

released to the atmosphere.(ix) Some microorganisms decompose the organic waste and dead plants and animals into simple

substances and clean up the environment.(x) Some microorganisms inside our bodies help in food digestion.

7. Microorganisms are harmful in many ways. Some of the microorganisms cause diseases in human beings, plants and animals. Such disease-causing microorganisms are called pathogens. Pathogens spread a number of microbial diseases or communicable diseases like cholera, common cold, chicken pox and tuberculosis from an infected person to a healthy person through air, water, food or physical contact. Some microorganisms spoil food, clothing and leather.

8. Antibiotics is a medicine which kills or stop the growth of the disease - causing microorganisms in human and animals. The antibiotics are manufactured by growing specific microorganisms and are used to cure a variety of diseases. Antibiotics medicines like Streptomycin, tetracycline and erythromycin are commercially produced from bacteria and fungi.Precaution in taking Antibiotics– It is important to remember that antibiotics should be taken only on the advice of a qualified doctor. We must finish the course prescribed by the doctor. If we take antibiotics when not needed or in wrong doses, it may make the drug less effective when you might need it in future. Also antibiotics taken unnecessarily may kill the beneficial bacteria in our body. Antibiotics, should not be taken for common cold and flu as these are caused by viruses and antibiotics are not effective against virus causing them.

I . Give reasons.1. Firstly, viruses don't carry out all of the living processes, which are growth, excretion, respiration,

reproduction, sensitivity, movement, nutrition. Secondly, they barely have any systems, due to their size, they are composed of only a layer of protein and a sample of genetic information. Also, they cannot reproduce on their own like cells can, by splitting up, or like humans, by releasing gametes (sex cells), they can only reproduce by getting inside a host and using its energy to replicate themselves. Another point is, they aren't living untill they get to a host. When they are outside of a host, on their own, they are dormant and pretty much useless, they can't do anything. To finalize, they have living and non-living characteristics, which makes them very hard to classify, and that is why they are on the border of living and non-living organisms.

2. Good hand washing is the first line of defense against the spread of many illnesses, from the common cold to more serious illnesses such as meningitis, bronchitis, influenza, hepatitis A, and most types of infectious diarrhea.

J. HOTS questions.

3. Yeast converts sugars into carbon dioxide and alcohol. Carbon-dioxide is also responsible for rising bread. As yeast begins to metabolize sugars in bread dough, the carbon dioxide gas is trapped within the gluten strands, creating bubbles, and causing a leavening action.

1. A forest has a large number of plants and trees. The old leaves, flowers, fruits keep shedding and they fall to the ground when they decompose and turn into useful nutrients for the plants and trees. In this way, the forest is a self sustaining system.

2. Freshly collected milk can get contaminated in many ways right from the container in which it is collected, by the udder of the cow, by the hands of the milking person and the atmosphere. The milk sold in sachets is pasteurized to kill all microbes and stored at low temperatures to avoid recontamination. So they are safe for a long time.

3. Both Ram and Raj are right. Fungi which are a reason for spoiling food are seen growing on bread, vegetables, fruits, cooked food and so on. There are some fungi which are sources of all our antibiotics and therefore they save our lives. So, fungi are both friends and foes to man.

4. When we cough or sneeze, we release a huge number of microbes in the droplets of silica that goes out. These droplets in the air are inhaled by healthy people who get infected. Thus the infection spreads in the community. So, it is a good practice to close the mouth while we cough or sneeze.

Chapter-3 : Materials in Daily Life – Synthetic Fibres, Fabrics and More



1. Monomer 2. polymerisation 3. cellulose 4. proteins

5. coal, natural gas 6. artificial silk 7. monomers 8. cotton,silk

9. cellulose 10. polyester 11. nylon, terelene, acrylic 12. Thermostat

13. Plastics 14. forming beads 15. Wool 16. Acrylic

NCERT Questions

17. man-made and artificial 18. petrochemicals 19. polymer


1. True 2. False 3. False 4. True 5. False

NCERT Questions

6. True 7. True 8. True 9. False


1. a. iii b. iv c. ii d. i

NCERT Questions

2. a. iv b. iii c. i d. ii

3. a. iii b. iv c. v d. ii e. i


1. b 2. d 3. c 4. b 5. b 6. c 7. a 8. d

NCERT Questions

9. b 10. b 11. c 12. d 13. a 14. b 15. d 16. d 17. b 18. c 19. c

E. Name them.

1. Polymers 2. Plastics 3. Metalloid

4. Noble Metals 5. Polymerization



1. Plants (cotton, jute), animals (sheep, goat ), Insects (silkworm).

2. Acetylene, butylenes, propylene and naphthalene.

3. Very long chains of matter containing many small units are called polymers.

4. Being very strong and most elastic of synthetic fibers, nylon is fit for use in ropes and parachutes.

5. The first synthetic polymer prepared was nylon.

6. Melamine the thermo set plastic used in dinner ware.

7. Plastic wastes are dumped in Landfall sites.

8. Water resistant and corrosion resistant.

9. Plastic have poor electrical conductivity. They are used as insulators.

10. PVC stands for polyvinyl chloride.

NCERT Questions

11. Cellulose

12. Rayon

13. Terylene and cotton

14. Plastic is a material which can be moulded into various shapes and sizes because of this property it is called plastic.

15.

a. Rayon

b. Polymer

c. Terylene

d. Plastic®Jiwan Science CCE Question Bank Answer Key-8/10


e. Polyester

f. TeflonG. Short answer questions.


1.

1. Majority of synthetic fibres are made from petroleum derivative like acetylene, butylene, etc. The raw material used is subjected to very high temperatures. Thus, they are melted and dissolved in a solvent. The molten liquid is forced through very fine holes in a spinneret. The fibres obtained are spun into yarns.

fibres

2. Rayon is lustrous as silk, it absorbs moisture, is strong and easy to dye.

3. (i) Nylon is a thermoplastic polymer. Polyester can be thermoplastic or thermoset depending on the chemical structure.

(ii) Nylon fabrics have a more natural feeling than polyester ones.

(iii) The polyester fabrics are more wrinkle resistant than the nylon fabrics.

(iv) Nylons are always synthetic but polyesters can be producing by natural ingredients also. One of the major ingredients is the cutin obtained from the plant cuticles.

4. Use of acrylic fibres (i) Can be knitted to make sweaters, shawls and socks. (ii) Transparent plastics can be used in place of glass.

5. Synthetic melt forming beads when burnt.

6. Plastics are classified as thermoplastics and thermoset plastics on the basis of their reaction to heat.

7. Plastics are (i) Strong, durable and corrosion free (ii) They are poor heat and electrical conductors. (iii) They produce static charges on rubbing.

NCERT Questions

8. Nylon fibres are strong, elastic and light in weight. It has a lustrous and easy to wash. Nylon fibres are used to make many articles such as socks, ropes, tents, toothbrushes, car seat belts, sleeping bags, curtains etc. Nylon is also used for making parachutes and ropes for rock climbing. If we compare strength of a nylon thread and a steel wire of same thickness or diameter, a nylon thread is stronger than steel wire as it can support more weight than a steel wire.

9.

S.No. Can be recycled Cannot be recycled

1. plastic toys telephone instruments

2. carry bags plastic bowls

3. ball point pens plastic covering on electrical wires

4. plastic chairs electrical switches

10. Metals like iron get rusted when left exposed to moisture and air. But plastics do not react with water and air. They are not corroded easily. That is why they are used to store various kinds of material, including many chemicals.

11. Rana should buy a cotton shirt made for summer. As synthetic material soak less water than the natural fabrics like cotton, this will result in discomfort to him as water from body perspiration will not be soaked by the shirt made of synthetic material. Where as shirt made from cotton will soak the perspiration very rapidly and transfer it to outside, for surface vaporization, this will give him cooling comfort.

Natural fibres are fibers that are found in nature. Ex: Wool, silk, and cotton etc.

They are good absorbents and so able to absorb heat, temperature, cold, sweat etc., depending on conditions and nature of fibres.

No spinning process is required for filament production.

Comfortable in use.

Their length is naturally obtained and it is not possible to change the fibre structure.

These fibres are man made or simply prepared in lab. Ex: Nylon, Teflon etc.

They do not have such pores as they are made up of chemicals and so do not act as good absorbents.

Melting, wet or dry spinning processes are used for filament production.

Not as comfortable as natural fibres.

Their lengths can be controlled by man and the fibres can easily be changed to different structures.

Natural FibreS.No. Synthetic Fibre

1.

2.

3.

4.

5.


2. (i) Polyester is very durable and strong.

(ii) It blends easily with natural fibres and so can be used in making blended fabrics.

(iii) Quick drying and wrinkle proof.

(iv) Does not shrink in water. Due to these properties, polyester is preferred in fabrics.

3. Plastics are non-biodegradable. The waste generated by extensive use of plastics gets accumulated on

land and water and pose a serious threat to land and aquatic organisms. They can also cause toxicity in

the environment when burnt. Animals feed on them accidentally and choke to death. Chemicals used in

toys made of cheap plastic is believed to affect a child's health.

4. Plastic does not absorb water, so it will protect us from rain if used in raincoats, umbrellas and tents. They

also dry easily and do not fade or shrink. Being strong, tents, umbrellas and raincoats made of plastic,

last long.

NCERT Questions

5. While natural fibres are obtained from plants and animals, synthetic fibres on the other hand, are

obtained by human beings from the chemical processing of petrochemicals. Petrochemicals when

processed, results in different type of synthesised products like Petrol, Kerosene, Grease, Bitumen and

polymers. Synthetic fibres are made from synthetic polymers. That is why these are called synthetic or

man-made fibres.

6. Plastic containers are mostly used for storing a food item, water, milk, pickles, dry food along with others

like medicines and chemicals. Due to light weight, lower price, good strength, durability and easy

handling plastic containers are convenient for use. Metals like iron get rusted when left exposed to

moisture and air. But plastics do not react with water and air. They are not corroded easily. That is why

they are used to store various kinds of material, including many chemicals. After use or breakage, later

they can be sold as scrap and be recycled to make new products again.

7. Plastic is also a polymer like the synthetic fibre. All plastics do not have the same type of arrangement of

units. In some it is linear, whereas in others it is cross-linked.

Thermoplastics: Plastic which gets deformed easily on heating and can be bent easily are known as

thermoplastics. Thermoplastics do not undergo chemical change in their composition when heated and

can be molded again and again. Polythene and PVC are some of the examples of thermoplastics. These

are used for manufacturing toys, combs and various types of containers.

Thermosets: Plastics which can be moulded only once, and after solidification, can not be softened by

heating, are called thermosetting plastics. Two examples are bakelite and melamine. Bakelite is a poor

conductor of heat and electricity. It is used for making electrical switches, handles of various utensils, etc.

Melamine is a versatile material. It resists fire and can tolerate heat better than other plastics. It is used

for making floor tiles, kitchenware and fabrics which resist fire.

8. (a) Saucepan handles : Saucepan handles are made from a type of thermosetting plastics, called

bakelite. It is is a poor conductor of heat and electricity. In cooking, while using saucepan with a

bakelite handle protect us from heat burns and also if we are cooking on a electric stove then it also

saves us from electric shocks.

(b) Electric plugs/switches/plug boards. They are also made from a type of thermosetting plastics,

called bakelite. As stated above, It is a poor conductor of heat and electricity. It resists fire and can

tolerate heat better than other plastics. Hence it prevent possible fire in electrical installations due to

overheating and also saves us from receiving electric shock while using them.

9. The list of polymers in our house is never ending. The versatility of plastic is responsible for its wide use.

Scientists have been able to create many different varieties of plastics, some as soft as sponge, some as

hard as rock, some as clear as glass and some as flexible as cotton. It is achieved by changing the

molecular structure of polymers. Thermoplastics are moulded into different shapes as polythene, PVC,

polystyrene, Teflon etc. Bakelite is used for making utensil handles, electrical switches, radios,

telephones etc. Melamine is used for making kitchen wares.

10. Plastic is non-biodegradable product. Plastic takes several years to decompose, it is not environment

friendly. It causes environmental pollution. Besides, the burning process in the synthetic material is quite

slow and it does not get completely burnt easily. In the process it releases lots of poisonous fumes into the

atmosphere causing air pollution. We should avoid the use of plastics as far as possible. We should make

use of bags made of cotton or jute when you go for shopping. In our homes, offices and industries, the

biodegradable and non-biodegradable wastes should be collected separately and disposed off separately.

11. Collect lids of cardboard boxes and prepare a pan. Collect threads of cotton, silk, nylon and polyester of

equal length and thickness. Attach the selected threads one by one to the pan and add weights to the

pan. If you don't have weights, use sealed packets of salt or sugar of known weights. Note down how

much weight each thread is able to bear before breaking. The thread which is able to take up more weight

has the highest tensile strength.

I. Give reasons.

1. Nylon is exceptionally strong, easy to wash, resistant to damage from oil and many chemicals, low in

moisture absorbing, long lasting, and light weight.

2. Bakelite handles are used in making electrical heating appliances because it has very good electrical

insulating properties.

3. Plastics are normally used on wires in order to act as insulators. Electrical wires need jacket insulation to

protect them from the elements and other stresses. Plastic is preferred over other materials because of

its good moisture resistance, flexibility and insulating properties.

4. Drainage pipes made of plastic is used as it can be constructed in a range of sizes and is very durable,

even when exposed to chemicals.

5. Plastics and glass are non-reactive so they are used to store chemicals.

NCERT Questions

6. 'Manufacturing synthetic fibres is actually helping conservation of forests because synthetic fibres are

man-made fibres. These fibres are made from petrochemicals. For manufacturing synthetic fibres

cutting of trees or killing of animals is not required and hence we conserve our natural environment.

7. By burning plastics, poisonous fumes are released that cause air pollution. So we should use plastic

judiciously.

J. HOTS questions.

1. A forest has a large number of plants and trees. The old leaves, flowers, fruits keep shedding and they fall

to the ground when they decompose and turn into useful nutrients for the plants and trees. In this way, the

forest is a self sustaining system.

2. Freshly collected milk can get contaminated in many ways right from the container in which it is collected,

by the udder of the cow, by the hands of the milking person and the atmosphere. The milk sold in sachets

is pasteurized to kill all microbes and stored at low temperatures to avoid recontamination. So, they are

safe for a long time.

3. Both Ram and Raj are right. Fungi which are a reason for spoiling food are seen growing on bread,

vegetables, fruits, cooked food and so on. There are some fungi which are sources of all our antibiotics

and therefore they save our lives. So fungi are both friends and foes to man.

4. When we cough or sneeze, we release a huge number of microbes in the droplets of silica that goes out.

These droplets in the air are inhaled by healthy people who get infected. Thus the infection spreads in the

community. So it is a good practice to close the mouth while we cough or sneeze.


Chapter-4 : Metals and Non-Metals



1. Hydrogen, oxygen 2. Silica, magnetite 3. metal oxides 4. Moisture

NCERT Questions

5. reactive 6. good, electricity 7. more 8. hydrogen


1. True 2. False 3. False 4. False 5. False

NCERT Questions

6. False 7. True 8. False 9. False 10. True

11. False 12. True 13. True 14. True


1. a. iv b. v c. iii d. vi e. ii f. i

2. a. iii b. iv c. i d. v e. iiD. Multiple choice questions. Tick the correct option in each case.

E. Name them.1. Sodium 2. Diamond 3. Lead 4. Graphite5. Mercury 6. Copper 7. Sodium 8. Bromine



1. d 2. c 3. a 4. d 5. c 6. d 7. b 8. c 9. a 10. bNCERT Questions

11. a 12. c 13. c 14. d 15. d 16. c 17. b 18. a 19. d 20. c21. d 22. b 23. a 24. c

1. Diamond.

2. Copper is a metal which is hard, ductile and a good electrical conductor. Phosphorous is a non-metal which is brittle, not ductile and can't conduct electricity.

3. Ions are charged atoms.

4. Sodium readily reacts with oxygen and moisture in the air. So, it is stored in kerosene.

5. Iron rusts when it reacts with oxygen of air in the presence of water.

NCERT Questions

6. Potassium and sodium.

7. Sulphur and phosphorus.

8. Chlorine, a greenish yellow gas , generally used in the form of tablets is used to dis-infect water.

9. Iodine.

10. Copper does not react with water but it reacts with atmospheric oxygen though at a very slow rate. When it reacts with oxygen it forms a layer of black copper oxide. Copper is a ductile metal that has a high electrical and thermal conductivity.

11. Bells are hollow objects which have a shape of a deep inverted cup widening at the lip. Most of them are made of metal because it allows them to vibrate like a spring when struck, a necessary quality as the clapper may strike the bell at speeds of up to 965.6km per hour.

12. Mercury.

13. Zinc.


1. All non-metals are not colourless. Some like bromine are brown, iodine is violet and graphite is grey.

2. Ions are formed when an atom either loses or gains electrons. When an atom loses electrons, it is negatively charged and when it gains electrons, it is positively charged.

3. Metals and non metals are elements that have different chemical and physical properties with the metals being placed on the left side of the periodic table while the non metals are on the right. One of the main differences is that chemically, non metals have 4 to 8 electrons in their outer shell while metals have 1 to 3.


4. Reactivity series is an arrangement of metals in order of their ability to react with air, water and other chemicals. The higher the metal in the series, the more reactive it is. For example, sodium is more reactive than iron and so it is placed higher than iron in the list. Reactivity–potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, etc.

5. Corrosion is damage caused to metals due to the action of air or water or chemical. It can be prevented in any of the following ways: (i) Oiling and greasing (ii) Painting (iii) Galvanizing (iv) Anodizing (v) Alloying.

6. To find out if an oxide is acidic or basic we use indicators like the litmus paper. An acidic oxide will turn blue litmus red whereas basic oxide will turn red litmus blue.

7. A chemical reaction in which a less reactive metal is displaced by a more reactive metal is called displacement reaction. For example, when Na ( more reactive metal) reacts with zinc oxide (ZnO) (zinc is the less reactive metal out of the two), Na takes the place of Zn and form Na O.2

2Na+ZnO ® Na O+Zn2

Zn+CuSO ® ZnSO +Cu4 4

More recative ® Zn

Less reactive ® Cu8. Gold is a noble metal that is chemically unreactive, highly malleable and ductile and is very lustrous. So,

it makes beautiful jewellery.9. (a) When diluted sulphuric acid is poured on a copper plate, copper as a metals reacts with acids and

produce metal salts - CuSO (a blue crystalline solid) and hydrogen gas.4

Cu (Copper) + H SO (Sulphuric Acid) ® CuSO (Copper sulphate ) + H (Hydrogen gas)2 4 4 2

(b) When Iron nails are placed in copper sulphate solution, Iron (Fe) replaces copper (Cu) from copper sulphate (CuSO ). That is why, nails come out copper plated and the blue colour of copper sulphate 4

disappears and the solution turns from blue to light yellowish.

Copper sulphate (CuSO ) + Iron nail (Fe) ® Iron Sulphate (FeSO + Copper (Cu)4 4

10.For detecting the type of gas, Saloni has to place a thumb over the tube, making sure that the test tube is upright. After this she has to carefully pour a small amount of clear lime- water into the tube, if the lime-water will turn milky, the gas produced is carbon dioxide. Burning charcoal will produce carbon dioxide as shown in equation below :C + O = CO .2 2

11. It turns green because of the process of oxidation.12. a. Iron b. Conductor.13.No, because wood is not a good conductor of electricity.14.When Iron nails are placed in copper sulphate solution, Iron (Fe) replaces copper (Cu) from copper

sulphate (CuSO ). That is why, nails come out copper plated and the blue colour of copper sulphate 4

disappears and the solution turns from blue to light yellowish.15.Iron is an ingredient in many mineral and vitamin supplements.

H. Long answer questions.1. Metals are good conductors of electricity and heat. Because of this property, they are used in electric

wires and as cooking utensils. Among metals, silver and copper are very good conductors of heat as well as electricity. Copper, being less expensive is used as electrical wires. Iron rusts easily and therefore is not used for wiring and cooking.

2. Reaction of metals with water:(i) Sodium and potassium react readily with water to give hydroxides of the metal and release

hydrogen. This reaction is accompanied with a lot of heat.

Na + H O ® Na OH + H 2 2 2

K + H O ® KOH + H2 2

Magnesium and aluminium react with warm water forming respective oxides and hydrogen.

2Al + 3H O ® Al O + 3H2 2 3 2

Mg + H O ® Mg O + H 2 2 2

Mostly non-metals do not react with water.3. When zinc is added to copper sulphate, copper is displaced by zinc. It is because zinc is more reactive

than copper. This reaction results in formation of zinc sulphate which is colourless. The blue copper


sulphate solution loses it colour.

CuSO + Zn ® ZnSO + Cu 4 4

(Blue) (Colourless)4. Alloys are homogenous mixtures of two or more metals to get a new metal with new properties. By

making alloys we can obtain metals which gain new properties—like iron which rusts can be alloyed with nickel, chromium and carbon to get stainless steel which is chemically un reactive and is extremely useful and cheap. Brass is an alloy of copper that has excellent sonorous property and is used in making temple bells. Alloys have increased the use of metals.

5. a. Utility of metals: Metals form such an important place in our lives. Right from the coins we use metals in the aeroplanes, ships, heavy machinery etc. If we look around, the common household equipments and utensils, decorative items, knives, scissors, garden implements, door handles, taps, showers are all made of metals. Precious metals are used in making jewellery. Copper and aluminium are widely used in electrical wiring, lead and tin are used in solders. So, metals are indispensable.

b. Utility of Non-metals- Hydrogen is used in welding torches. Oxygen is used in the manufacture of acids and in making acetylene lamps. Nitrogen is used in making fertilizers. Sulphur is used in manufacture of chemical compounds, match sticks, dyes, gunpowder, etc. Graphite is used in pencils, dry cells and in making brake linings. Iodine is used as an disinfectant and as a bleaching agent. Noble gases like helium are used to fill balloons and argon is used to fill in the bulbs. Neon advertisement signs are also a common feature now. Phosphorus is used in fireworks industry.

6. All reactive metals combine with oxygen to form oxides. Very reactive metals like sodium, potassium react readily and vigorously with

Zinc, on heating strongly reacts with O to give Zn O 2 2

Iron undergoes very slow oxidation in the presence of moisture to give rise to rust.Non-metals like sulphur and phosphorous react vigorously in air to produce their respective oxides.

oxides and also can catch fire instantaneously.

4Na +O ® 2Na O2 2

Magnesium burns in air to produce magnesium oxide.

2Mg +O ® 2MgO 2

S + O ® SO (sulphur oxide) 2 2 2 2

P + 5O ® 2P O (Phosphorous pentoxide) 2 5 2 4 2 2 5

Carbon and hydrogen react with oxygen to give carbon dioxide and water respectively.

C + O ® CO 2 2

2H + O ® H O 2

NCERT Questions7.

Metals are malleable and can be beaten into thin sheets through heating and hammering.

Non-Metals are non malleable, brittle and can not be beaten into thin sheets through heating and hammering.

Metals are hard except sodium and potassium which are soft.

Non-Metals are generally soft except diamond which is very hard.

1. Appearance Metals have luster. Non-Metals do not have luster.

PropertiesS.No. Non-metalsMetals

2. Hardness

3. Malleablility

Metals are good conductor of electricity.

Non-Metals are poor conductor of electricity.

Metals are good conductors of heat.

Non-Metals are poor conductor of heat.

Metals are ductile and can be drawn into wires.

Non-Metals are not ductile and can not be drawn into wires.

4. Ductility

5. Heat Conduction

6. Conduction of

Electricity


8. Iron (Fe) replaces copper (Cu) from copper sulphate (CusO ). That is why, nails come out copper plated 4

and the blue colour of copper sulphate disappears and the solutions turns from blue to light yellowish.

I. Give reasons.

Copper sulphate (CuSO ) + Iron nail (Fe) => Iron Sulphate (FeSO ) + Copper (Cu)4 4

9. Oxygen, water, blue, red, non-metals.

1. Because copper is one of the best conductors of electricity and it has a high melting point so it won't melt with the heat from the flow of electricity when used for electric wires.

2. Gold has high density than water so it sinks in water whereas the density of lead is low and it float on water.

3. Silver is lustrous and shiny so it is used for making jewellery.

4. a. Mercury does not wet glass, this makes the thread move up and down without breaking.

b. It is a shining metal and easily seen.

c. It is a liquid up to 300 deg C.

5. Cooking utensils are made out of metal because metal is an excellent heat conductor. Metal also can withstand a lot higher temperatures then other materials and doesn't burn.

6. Silver is a very expensive and rare metal. So, it is not used for wiring in electrical installations in spite of being a good conductor.

7. Graphite is a brittle substance and so can't be drawn into wires. So, it is not used in electrical wiring.

NCERT Questions

8. Aluminium foils are used to wrap food items : The property of metals by which they can be beaten into thin sheets, is called malleability. Aluminium is a metal. Aluminium foils are made exploiting this property. They keep food items warm and safe from contamination.

9. Immersion rods for heating liquids are made up of metallic substances: Metal are good conductors of electricity and heat. So, when we supply electric power to immersion rods, inside element gets heated. Heat so generated is transferred from metallic surface of rod to water.

10. Copper cannot displace zinc from its salt solution: Zinc is more reactive than copper. A more reactive metal can replace a less reactive metal, but a less reactive one cannot replace a more reactive metal. Therefore Copper cannot displace zinc from its salt solution.

J. HOTS questions.

1. The unknown metal is aluminium. Since aluminium is more reactive than zinc and iron, it can displace these two from their salt solutions. But magnesium is more reactive than aluminium and so it can't be displaced by aluminium.

2. Tomato is acidic in nature. Iron reacts with the acid in the food and forms salts. That is why the container gets corroded and develops spots.

3. Helium is used in place of hydrogen because hydrogen is an explosive gas. It can catch fire and burn rapidly which is not safe in balloons. Helium is unreactive and so it is safer to use in flying balloons.

NCERT Questions

4. Metals react with acids and produce metal salts and hydrogen gas. Aluminium is a metal and lemon contains citric acid. So, if we store lemon pickle in an aluminium utensil after some time utensil metal will get corroded due to reaction and lemon pickle inside will not be fit for human consumption.

5. Nitric acid is used as a cheap means in jewellery shops to quickly spot low-gold alloys and to rapidly assess the gold purity. Gold which is not pure such as coloured gold or artificial gold, can be easily oxidized and dissolved by nitric acid, leading to colour changes of the gold-alloy surface along with loss in weight.

So here, in first probability, their gold jewellery is not pure. In another probability, if they had pure gold jewellery, then, they have been cheated by goldsmith in the guise of polishing the old jewellery. Pure gold do not react with any acid including nitric acid, but pure gold does react with aqua regia, a mixture of concentrated nitric acid and hydrochloric acid. Goldsmith, who are not fair in dealing, make use of aqua regia to wash the gold jewellery. In this cleaning process, a small amount of gold along with surface impurities, if any, gets dissolved in the aqua regia -acids mixture solution. For polishing they use buffing machines. Gold jewellery so polished is returned to customers which is of less weight as a part of it already dissolved in aqua regia. The dissolved gold is extracted by them later.

Chapter- 5 : Coal and Petroleum



1. absence 2. Anthracite 3. Coal tar 4. pesticides

5. hydrogen, carbon monoxide, methane 6. ammoniacal liquor

7. Coal gas, coal tar, coke 8. Carbon 9. Carbon monoxide 10. fractions

11. Sun and wind 12. fossil fuels 13. exhaustible

14. compressed natural gas

NCERT Questions

15. coal, petroleum, and natural gas 16. refining

17. CNG 18. Carbonization 19. fossil fuels 20. unpleasant

21. Ammonia and coal gas 22. Destructive distillation 23. Pollution



NCERT Questions

6. False 7. False 8. True 9. True 10. False 11. True

12. True 13. True


1. a. ii b. iii c. v d. i e. iv

2. a. iii b. iv c. i d. ii


1. c 2. a 3. c 4. b 5. c 6. a 7. d 8. b

NCERT Questions

9. d 10. c 11. d 12. d 13. c 14. d 15. a 16. a 17. c

18. d 19. c

E. Name them.

1. Compressed 2. Fractional distillation 3. Coal gas 4. Energy crisis

5. Ammoniacal liquor 6. Exhaustible 7. Solar 8. Coal gas

9. Thermal power plants 10. Greenhouse Effect

NCERT Questions

11. Bitumen


1. Combustion takes place when fuel reacts with the oxygen in air to produce heat. The heat created by the

burning fuel is used in the operation of equipment such as furnaces, kilns, boilers and engines. Along

with heat, carbon dioxide and water are created as by products of the exothermic reaction in combustion.

2. Natural gas and coal.

3. Carbon dioxide is the main greenhouse gas responsible for global warming.

4. The chemical composition of acid rain is carbonic acid, nitric acid and sulfuric acid. The chemical

composition can vary based on the location of the rain and the pollution in the area. The main two gases

that cause acid rain are sulfur dioxide and nitrogen oxide.

NCERT Questions

5. Use a separating funnel since the petrol floats above the water. Just let the mixture stand. Petrol and

water are not soluble, so they will eventually separate. Since the petrol is lighter than water, it forms a

layer on top.




6. Compressed Natural Gas. CNG is better than Petrol because it has very low moisture content, it's cheap

and easy to transport.

7. Kerosene

8. a. COAL b. PETROLEUM c. REFINERY d. KEROSENE e. SUNLIGHT


1. Fuels formed as a result of decay of buried plants and other living organisms that thrived millions of years

ago, are called fossil fuels. For example: coal and petroleum are fossil fuels.

2. Energy from the sun, wind and bio gas are renewable sources.

3. Jharkhand and Odisha are states in India which are rich in coal reserves.

4. Coal is obtained from coal mines. It has certain impurities mixed in it. Coke is a product of destructive

distillation of coal. It is richer in carbon content and hence is a better fuel. It also acts as a reducing agent.

5. Coal tar is used for metalizing roads and as a starting material for making pesticides, explosives, dyes,

paints, etc.

6. The major fuels obtained from petroleum are : petrol, kerosene, diesel and petroleum gas.

7. Oil spill is leakage of crude oil in massive quantity into the ocean due to ship wrecks or accidents. It can

also occur on land due to leakage from tankers carrying crude oil.

8. Solar energy and wind energy are two good alternate sources.

9. CNG refers to compressed natural gas. The gas obtained from under the ground is compressed and

stored in cylinders as CNG.

NCERT Questions

10. CNG - compressed natural gas, is stored under high pressure as compressed natural gas (CNG). CNG

is a very important fossil fuel because it is easy to transport through pipes. CNG is used for power

generation. It is now being used as a fuel for transport vehicles because it is less polluting. It is a cleaner

fuel. Similarly, LPG- Liquified Petroleum Gas is used as fuel for home and industry as it is less polluting

and easy to transport and to use.

11. Those resources which are present in unlimited quantity in nature and are not likely to be exhausted

easily by human activity are inexhaustible natural resources (sunlight, air etc.) .

12. Exhaustible-Coal, natural gas, petroleum, minerals, forests.

Inexhaustible-Air, sunlight, oxygen.

13. Coke is used as a fuel, burns with almost no smoke. As a reducing agent, in manufacture of gaseous

fuels like producer gas and water gas.

14. Coal has many important uses worldwide. The most significant uses of coal are in electricity generation,

steel production, cement manufacturing and as a liquid fuel.

15. It is crude oil as it is always trapped between rocks and under the ocean.

16. Dense forests, flooding, soil, soil, temperature, pressure, temperature.


1. Coal and petroleum have been derived from dead plants and animals. Millions of years back, huge

forests that existed on earth could have got buried due to some natural calamities and surely, over many

thousands of years got converted to coal due to the prevailing heat and pressure under the earth.

Similarly aquatic organisms that had got buried under the ocean have been converted to petroleum. Due

to this reason, they are called as fossil fuels.

2. Various fractions of the crude oil are separated by the process of fractional distillation. It is done by

heating the crude oil to a temperature of about 350°C in a fractionating tower. As it boils, the vapours pass

up the column of the tower. The different fractions cool and condense at different heights in the column,

depending on their boiling points. Each fraction is then separated and purified further.

3. Coal is formed from dense forests that must have got buried due to some natural phenomena some

300–400 million years ago. They were subject to heat and pressure from the top layers of the earth and

were acted upon by anaerobic bacteria. The conversion of these buried plants and animals look place


over millions of years and we are able to use them now. The organisms buried in different depths

experienced different pressure and temperature conditions and hence their characteristics also show

differences. The deeper the deposits, the higher the carbon in them.

4. Natural gas is the gaseous product of decomposition of buried organisms under the ground. It is mainly

methane and has very little impurities. As a result, it undergoes complete combustion and so is

considered cleaner.

5. Among the fossil fuels, India is rich in coal reserves. It is the 14th largest producer of coal in the world.

The major coal producing states in India are Jharkhand, Odisha, West Bengal, Andhra Pradesh,

Chhattisgarh and Madhya Pradesh. Oil reserves in India are limited to Assam, Gujarat and in Arabian

Sea, off the coast of Mumbai. We are finding more natural gas reserves in Godavari-Kaveri basin,

Rajasthan and Tripura High. In comparison to the energy consumption, the fuel reserves are very limited

and some are heading towards energy crisis. To avoid such a situation, it is very essential that we turn to

renewable sources and consume the existing fossil fuel reserves.

6.

NCERT Questions

7. A long time back, about 300 million years ago the earth had dense forests in low lying wetland areas.

Due to natural processes, like earthquakes, flooding, these forests got buried under the soil, rocks and

other land masses. With the passage of time, as more soil deposited over them, they were compressed.

The temperature also rose as they sank deeper and deeper. Under high pressure and high temperature,

dead plants got slowly converted to coal. As coal contains mainly carbon, the slow process of conversion

of dead vegetation into coal is called carbonisation. Since it was formed from the remains of vegetation,

coal is also called a fossil fuel.

8. The formation of fossil fuels is a very slow process, takes million of years in nature. We have limited

reserves of fossil fuels in nature . Fossil fuels are exhaustible natural resources, as limited fossil fuels

reserves like coal, petroleum, natural gas are being depleted very fast by human activities like rapid

urbanization, industrialization and transportation.

9. Coke is a tough, porous and black substance. It is almost pure form of carbon. Coke is used in the homes

for cooking, heating and in industries, for manufacturing of steel and extraction of many metals. Earlier it

was also used in steam engines for rail transportation. It is also used in thermal power plants to

produce electricity.

40°C

110°C

180°C

260°C

340°CHeatedcrude oil

Refinery gasUsed as fuel

PetrolUsed in cars

NaphthaUsed in chemical

production

KeroseneUsed as jet fuel

Diesel oilFuel for diesel engines

ResidueFuel for ships lubricating

oil, road surfaces.

1. Coal Gas- Main constituents are H CH and CO.2 4

2. Liquid Ammonia.

3. Gas Carbon.

4. Coke (greyish Black).

5. Coal Tar (black Terry material).

Different products Uses

As a fuel in cooking food, street lighting.

To make fertilizers.

Carbon electrodes in batteries.

As a fuel and as a reducing agent in steel

manufacturing produce fuel gas like water

gas (CO+H ) and producer gas (CO+N ).2 2

For producing Carbide like CaC ,SiC, and 2

Al C .4 3

To make plastics, paints, dyes, naphthalene

balls and explosives, perfumes.

S.No.


10. Petroleum was formed from organisms living in the sea. As these organisms died, their bodies settled at

the bottom of the sea and got covered with layers of sand and clay. Over millions of years, absence of air,

high temperature and high pressure transformed the dead organisms into petroleum and natural gas.

11.

intensive to recover as it lies deep below the surface, usually around 300 feet below land

level and deposits can only be a few centimetres thick.

14. "Greenhouse Effect." is caused by many different gasses in the atmosphere, most importantly water

vapor, carbon dioxide (CO ), methane (CH ) and a few others. These gasses trap heat in the 2 4

12.

13. The three fossil fuels, oil, natural gas and coal, were formed millions of years ago when dead plants and

animals were trapped under deposits and became buried underneath land. Compression over time

fossilised the remains, creating carbon-rich fuel sources. All fossil fuels are finite - the deposits that exist

cannot be replenished when they are used. With further use, all are in danger of running out.

The question of when each one will actually run out, however, is a tricky one. There are many different

opinions and calculations and none really agree on the exact timing. Many different factors need to be

considered including how much of each deposit is left in the earth, how fast we are using each fossil fuel at

the moment, and how this is likely to change in the future. If we start switching to alternative fuel sources that

are renewable rather than non-renewable, the reserves that we have will obvious last longer.

Natural Gas: Some experts believe that current natural gas deposits fill around 6000 trillion cubic feet

that could, with the current level of usage, last for about 50 years.

Oil: The world could still have oil reserves that would fill 800 million barrels, with about half of that in the

Middle East. Because we use oil to manufacture many materials, including plastics, we use oil at a much

faster rate than either natural gas or coal.

Coal: Coal is the fossil fuel with the greatest reserves and coal reserves are spread all over the Earth. It is

very labour

1991 1992 1993 1994 1995 1996 1997

0010203040506070809101112

Perc

enta

ge :

Y-a

xis

Graph: Power shortage (%) in India from 1991-1997

Years : Y-axis

atmosphere, keeping it much warmer than it would be without a greenhouse effect (about 60 degrees

warmer in fact.) Every time we burn a fossil fuel (coal, oil, natural gas), we release carbon dioxide--a

major greenhouse gas. The general equation for this is pretty simple: C + O = CO . Carbon (C) is the 2 2

main ingredient in all fossil fuels, and oxygen (O ) is required for anything to burn. 2

So, as we burn fossil fuels, we put more and more CO into the air. This makes the greenhouse effect 2

stronger, so in essence it causes more heat to be trapped within the atmosphere. This, in turn, causes

temperatures to rise.

15. a. Drive at the speed limit.

b. Try to avoid traffic on busy days or times when it is raining, windy or barometric pressure is high.

c. Get rid of any unnecessary weight in your car or truck like golf clubs or unnecessary tools and

materials.

d. Avoid wasting fuel from pressing the gas to regain the speed lost from braking when following closely

(tailgating) which forces you to correct your following distance by applying your brakes, slowing

forward motion.

e. Every time you punch the gas to quickly accelerate after stopping you are burning extra fuel and

increasing tire wear.

f. Drive smoothly.

g. Change your air filter.

h. Keep the tires inflated to the proper pressure to increase your traveling distance on a tank of gas.

i. Check your tyre pressure more often when the outside temperature changes greatly (Hot tyres will

have high pressure from expanding air -- but if air is let out to the proper pressure, then when cooled

they will become too low in the cooler conditions so deflate them when cooler).

j. Keep your car tuned-up at manufacturer recommended intervals to optimize your mpg.

16. Petrol and other petroleum products are limited natural resources. These resources take millions of year

to form. So, once used up, we cannot get them back or replenished. Whereas sunlight is an inexhaustible

natural resources. It can not be exhausted and thus, can be used for the well being of the mankind.

17. a. Highly compact portable source of energy used for most forms of mechanical transportation.

b. Excellent source of organic molecules for building plastics, medicines, rubber, fiber, etc.

c. Can withstand high heats without breakdown making it useful as lubricants like motor oil and grease .

d. Residuals make excellent surface for asphalt roads and waterproof roofing materials.

e. Certain components make excellent solvents for paint, industrial use etc.

f. Other components (propane, butane) make excellent compact source of portable cooking fuel and

heating in areas that do not have infrastructure for natural gas delivery.

g. Natural gas is used to make fertilizers used in agriculture and household detergents .

h. Compared to most other fuel sources it is still one of the most economical -in other words the costs to

produce it are relatively cheap compared to other energy sources.

i. Production of oil has much less impact and a smaller footprint on the earth surface than production of

coal from strip mining.

j. If not for the discovery of oil, all whales would likely be extinct, because they were the primary source

of lamp oil for lighting before oil, and are still recovering from hunting in the 1800's.

k. The oil industry has been a source of much advanced technology and many new products that have

changed our lives for the better.

l. During WWII oil produced in Texas was the major source of fuel supply for the Allied Forces and

without that advantage over both the Germans and Japanese, the world might look very different

today. At that time the US was the major supplier of oil in the world.

m. Natural gas wells are the world's supply of helium gas.



n. Oil refining produces the world's supply of elemental sulphur as a by product, used for many

industrial applications.

I. Give reasons.

1. It is a fuel that produces less fumes in its paraffin form, therefore it is considered environmentally more,

friendly than coal and wood. Despite this, it does emit some poisonous gases. These include nitrogen

dioxide, sulfur dioxide and carbon monoxide. All three of these can cause damage to the body if breathed

in. Kerosene is a non-corrosive fuel, safe to store for a long time.

2. Some substances have a lower combustion point and therefore they catch fire much more easily and

faster as compared to other substances. The temperature at which a substance catches fire is the most

important parameter in determining the combustibility of different substances.

3. Because water is a good conductor of electricity. So, if added to a fire it will spread the electricity further

and therefore the fire.

4. Dry Leaves burn easily because they contain less or no moisture in them. Green Leaves have a lot of

moisture in them. So, they don't burn easily.

5. We wrap a blanket around a person whose clothes caught fire because it cuts the supply of oxygen with

fire as fire can only burn when it is in contact with oxygen. In order for a fire to burn, all three elements of

the fire triangle must be present: heat, fuel and oxygen. If anyone is cut off the fire will be put out. As the

fire blanket completely surrounds the person whose clothes caught fire, it seals the person's body

surface around the fire and cut's off the oxygen supply to the fire, thereby putting it out. Hence fire blanket

acts as a fire extinguisher and stops the fire from spreading.

J. HOTS questions.

3. A combustible substance is the one which can burn. It does not necessarily mean that it would produce

large amount of heat without leaving any residue. Thus, all fuels are combustible but not all combustible

substances are fuels. A good fuel produces large amounts of energy and does not leave behind any

undesirable substances. Also, it is cheap and is readily available

4. Synthetic fuel is a category of fuels that includes any fuel "produced from coal, natural gas or biomass

feed stocks through chemical conversion" Many synfuels also burn cleaner than conventional fuel.

But there are also disadvantages. While they can burn cleaner, producing synthetic fuels often

causes just as much, if not more, pollution than traditional gasoline. Synfuels still remain more

expensive to produce than conventional fuels, mostly because more research, development and

investment are necessary to make production economically viable. Extra-heavy oil is one of several

sources of syncrude, a type of synthetic fuel that closely resembles crude oil. Producing gas-to-

liquids fuels (or GTL) involves a process of converting natural gas into liquid, petroleum-based fuels.

Shale oil is another form of syn crude produced from marlstone, a naturally occurring rock that is

commonly called oil shale.

.

1. Combustion of coal is an oxidation reaction in which coal combines with oxygen of air to give rise to CO . 2

So, the end products are CO , and energy and ash. Destructive distillation of coal is carried out in the 2

absence of oxygen. It gives rise to coke, coal gas and coal tar. In this reaction the fuel coal is not used up,

but it is made purer. In combustion, the fuel is completely used up.

2. Natural gas is a fuel which has methane and certain gases which are not mixed with much impurities.

When it burns it undergoes complete combustion and so does not release polluting products in the

atmosphere. So, it is considered a cleaner fuel.

Chapter- 6 : Combustion-Fire, Flame and Fuels



1. Antoine Lavoisier 2. Michael Faraday 3. Spirit/LPG/Paper 4. Red Phosphorus

5. spontaneous 6. slow 7. complete 8. complete

9. water and energy 10. hottest 11. Calorific value 12. Wood, paper, etc

13. LPG, hydrogen 14. Residue

NCERT Questions

15. pollution 16. Kerosene 17. ignition temperature 18. water

19. chemical, oxygen 20. fire, blanket 21. minimum, ignition 22. low, inflammable

23. combustible 24. Ignition 25. paper 26. Calorific value


1. True 2. False 3. True 4. True 5. False

6. True 7. False

NCERT Questions

8. True 9. True 10. True

11. False 12. False 13. False 14. True 15. False

16. True 17. False 18. True

C. Match the two columns to make correct pairs.

1. a. iv b. vi c. v d. iii e. i f. ii

2. a. iii, A b. ii, C c. i, B


1. c 2. d 3. a 4. d 5. c 6. b 7. c 8. a 9. c 10. d

NCERT Questions

11. d 12. b 13. c 14. c 15. d 16. a 17. c 18. b 19. c 20. d

21. d 22. b 23. d 24. d 25. c

E.Name them.

1. Calorific value 2. Inflammable 3. Spontaneous combustion

4. Fire extinguisher



1. The amount of energy released when unit mass of a fuel is burnt is called its calorific value.

2. A substance that doesn't undergo combustion is a non-combustible substance.

3. Minimum temperature at which a fuel catches fire is its ignition temperature.

4. A good fuel should have high calorific value.

5. The middle zone of a flame gives us light.

6. The candle will extinguish inside a closed jar due to absence of oxygen.

7. A flame has a glow due to the presence of unburnt carbon particles which glow.

NCERT Questions

8. a. DIESEL b. GLASS c. MATCHSTICK d. HEAT and FLAME e. CALORIFIC


1. Carbon monoxide is given out during incomplete combustion of carbon.

2. Luminous zone of a flame has unburnt carbon particles which glow.



3. The zone above the luminous zone of a candle flame is the hottest region. So, a matchstick ignites very

quickly in it.

4. Water acts as a coolant and brings down the ignition temperature, helps in cutting off oxygen supply.

5. When a substance burns, if soot deposits on the surface of the container kept over it, then we can say

that the combustion is incomplete.

6. Hydrogen is used as a fuel in rocket propellants since it has a very high calorific value and is very light in

weight.

7. A good fuel should :

(i) have light calorific value.

(ii) should be economically priced.

(iii) should be easily available.

(iv) easy to transport.

(v) should have ignition temperature higher than room temperature.

NCERT Questions

8. For combustion to take place we need:

(i) Oxygen supply : No combustion will take place in the absence of oxygen or air.

(ii) Combustible substance : Each combustible material needs a specific temperature at which it can

start burning which should be reached for combustion to take place.

9. A goldsmith use outermost zone of the flame with a metallic blow-pipe for melting gold and silver as it is

the hottest part of flame.

10. Calorific value of the fuel = Amount of heat energy produced / Weight of the fuel burnt

= 180,000 /4.5 kJ/kg

= 40,000 kJ/J

11. A candle flame is less hot near the wick as this is innermost zone of unburnt wax vapours. Whereas outer

most part of flame is the zone of complete combustion and is the hottest. Therefore, in case of Ramesh,

water will get heated in a shorter time than that of Abida.

12. In Jar B the candle remain lighted for a longer time.

13. Outermost zone of the flame is best suited for boiling water quickly.

14. Our cities generally have high numbers of automobiles vehicles. The use of diesel and petrol as fuels in

automobiles is a major cause of air pollution today. During combustion, these fuel release unburnt

carbon particles. These fine particles are dangerous pollutants causing respiratory diseases, such as

asthma. Incomplete combustion of these fuels gives carbon monoxide gas. It is a very poisonous gas.

Combustion of most fuels releases carbon dioxide in the environment. Increased emission of carbon

dioxide in the air is one of the major cause for global warming.

The use of diesel and petrol as fuels in automobiles is being replaced by CNG (Compressed Natural Gas),

because CNG produces the harmful products in very small amounts. CNG is a cleaner fuel. It has high fuel

efficiency. Hence use of CNG in automobiles has reduced pollution in our cities to a noticable extent.

15. Combustible-charcoal, wood, paper, cardboard, candle, glass.

Non-combustible-Chalk, stone, iron rod, copper coin,

16. It will not produce any flame but it will soon be covered with black soot indicating incomplete combustion.

17. Burning of coal in closed room (lack of oxygen) produces Carbon mono-oxide (CO) in the absence of

oxygen. Carbon mono-oxide is poisonous to humans and it does not have any smell. It is also called as

silent killer gas. The fumes/smoke because of burning can cause lung damage or even death due to

smoke inhalation.

18. Fuel efficiency is a form of thermal efficiency, meaning the efficiency of a process that converts chemical

potential energy contained in a carrier fuel into kinetic energy or work.



1.

Different parts of a candle flame

Zone of non-combustion: This is the dark zone that lies around the wick. It contains unburnt gas particles.

No combustion takes place here as no oxygen is available.

Zone of partial combustion: In this zone, the hydrocarbons present in the oil gas decompose into free

carbon and hydrogen. The unburnt carbon particles impart a pale yellow colour to the flame. This is the

luminous part of the flame.

Zone of complete combustion (blue) : This is the non-luminous thin zone of the flame. It is the outermost

hottest region in the flame that is invisible. Here, carbon and hydrogen are completely oxidized to

Carbondioxide and water vapour.

Carbon + Oxygen ® a Carbon monoxide (blue flame)

Carbon monoxide + Oxygen ® a Carbon dioxide + Water (vapour)

2. Large scale burning of fossil fuels results in:

(i) Excess amount of CO in the atmosphere leading to global warming. It is a phenomenon that can 2

cause irreparable damage to the earth.

(ii) Fossil fuels are non-renewable. So, once exhausted, they will leave us in a state of energy crisis.

(iii) Incomplete combustion of fossil fuels produces a toxic gas carbon monoxide which can cause health

problems.

(iv) Products of combustion of petroleum release harmful oxides of sulphur and nitrogen that cause acid

rain which can corrode buildings, spoil air, water and land and are also traced to a number of human

diseases.

3. A good fuel should:

(i) Be easily available. The supply should be in plenty.

(ii) Burn moderately in air. Not rapidly or explosively or too slowly.

(iii) Has low calorific value. High heat energy per unit mass.

(iv) Should burn leaving no residue for maximum efficiency.

(v) Ignition temperature should not be too high, best should be higher than room temperature.

(vi) Should be non-polluting and non-toxic.

4. When rain water dissolves traces of acid in air to make it acidic we call it acid rain. It is believed to take

place due to excessive use of fossil fuels. When fuels of petroleum are burnt, they release oxides of

sulphur and nitrogen which combine with the moisture in the air to produce acids which dissolve in

rain water. This kind of rain is harmful to the soil since plants can't grow in acidic soil. Water bodies like

Outer zone ofcomplete combustion(blue)

Middle zone ofpartial combustion(yellow)

Innermost zoneof unburnt wax vapours(black)

Hottest Part

Moderately Hot

Least Hot

Wax Candle

Diagram of different zones of candle flames

lakes and ponds turn acidic killing aquatic organisms and we also end up having respiratory illnesses.

A lot of damage is also done to heritage structures and monuments due to the corrosive effect

of acids.

5. Yes, to some extent, the process of rusting can called slow combustion .The Rusting of iron is a oxidation

process. In this iron using oxygen and water, gets oxidized and is rusted out. It is a slow process which

does produce heat at a very slow rate. The combustion process is also a oxidation process and a

chemical reaction by which fuel and an oxidizer react and produce heat or light. Combustion needs

heat, an oxidizer, and fuel. Combustion is much faster than rusting.

6. Our cities generally have high numbers of automobiles vehicles. The use of diesel and petrol as fuels in

automobiles is a major cause of air pollution to day. During combustion, these fuel release unburnt

carbon particles. These fine particles are dangerous pollutants causing respiratory diseases, such as

asthma. Incomplete combustion of these fuels gives carbon monoxide gas. It is a very poisonous gas.

Combustion of most fuels releases carbon dioxide in the environment. Increased emission of carbon

dioxide in the air is one of the major cause for global warming.

The use of diesel and petrol as fuels in automobiles is being replaced by CNG (Compressed Natural Gas),

because CNG produces the harmful products in very small amounts. CNG is a cleaner fuel. It has high fuel

efficiency. Hence use of CNG in automobiles has reduced pollution in our cities to a noticable extent.

7.

8. CO , being heavier than oxygen, covers the fire like a blanket. Since, the contact between the fuel and 2

oxygen is cut off, the fire is controlled. For fires involving electrical equipment and inflammable materials like

petrol, carbon dioxide (CO ) is the best extinguisher. The added advantage of CO is that in most cases it 2 2

does not harm the electrical equipment. It not only forms a blanket around the fuel fire and cut off oxygen

supply, it also brings down the temperature of the fuel. That is why it is an excellent fire extinguisher.

9. The glass containing petrol will catch fire instantly.

10. You should not put water on an oil fire because the water, instead of mixing with the oil and reducing the

intensity of the flame, settles below the oil, thus allowing the oil to continue burning. The water may also

begin to heat up and convert into steam, which expands quickly and can carry the fire further, thus

making things even worse.

11. Conditions under which combustion take places :

1. Some Fuel is is required for combustion. During combustion a fuel substance reacts with oxygen to

give off heat. The fuel may be solid, liquid or gas.

2. Oxygen in air is essential for combustion. Combustion can not take place in the absence of air

(oxygen).

3. For combustion, an inflammable substance must be heated to its ignition temperature. Ignition

temperature is the lowest temperature at which a combustible substance catches fire.


LPG Wood as Fuel

1. LPG is a costly fuel but dily available,

combustible and easy to transport in

cylinders and tanker.

2. LPG is more energy efficient.

3. Its calorific value is 55000 kJ/kg.

4. It cause less air pollution and prevent

deforestation by supplementing the fuel

need in place of wood as fuel.

5. It is an exhaustible natural resource.

rea Wood is a cheap fuel, not readily available in cities and not readily combustible.

Wood as fuel in not much energy efficient.

Its calorific value is 17000-22000 kJ/kg

It causes air pollution and deforestation.

It is not an exhaustible natural resource as trees can be grown in 5-10 yrs.

S.No.


In general any fire extinguisher uses any or all of the following methods:

1. Removing the combustible substance.

2. Cooling the burning substance to below its ignition temperature.

3. Cutting off the supply of air oxygen.

12.Solid fuels: Solid fuels left some ash or residue after combustion. The solid fuels and their calorific values

are given below.

Liquid fuels: Most of the liquid fuels in use are the hydrocarbons which exist in the liquid phase at room

temperature. The liquid fuels and their calorific values are given below.

Gaseous fuels: Some of the gaseous fuels exist naturally at room temperature and some are made by

the treatment of coal. The gaseous fuels and their calorific values are given below.

13 I will choose CNG for the vehicle as it is cheap, it leaves less residue and is eco-friendly. CNG is a

cleaner fuel; compared to petrol and diesel. CNG produces lesser amount of harmful gases on

burning. Due to this, CNG is now being used in automobiles in many cities; which has helped in

reducing pollution in our cities.

14. Wood as fuel use is discouraged due to deforestation and pollution. Wood has traditionally been used as

kitchen fuel and is still predominantly being used in rural areas. 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. LPG is much better because it burns without

giving smoke. It produces lesser amount of air pollutants. Complete oxidation during burning of LPG

does not lead to carbon monoxide production.

15. Forest fires are caused due to sparks between tree leaves. Dry leaves have rough surface. Due to wind,

they undergo friction and spark is emitted.

I. Give reasons.

NCERT Questions

1. As water may conduct electricity and harm those trying to douse the fire.

2. As LPG is a affordable, readily available, combustible and easy to transport in cylinders and tanker. LPG

is more energy efficient. Its calorific value is 55000 kJ/kg where as that of wood is just 17000-22000

kJ/kg. It causes less air pollution and prevent deforestation by supplementing the fuel need in place of

wood as fuel.

Fuel Calorific Value(Kcal/kg)

Peat Coal 2500

Lignite Coal 3500

Bituminous Coal 3000

Anthracite Coal 7500


Gasoline 11,200

Paraffins 11,100

Diesel 11,000

Fuel Oil 10,500


Coal gas 11,200

Coke oven gas 11,100

Producer gas 11,000

Blast furnace gas 10,500


3. Because for burning or combustion, a substance must me heated to its ignition temperature. Paper

wrapped around an aluminium pipe does not catch fire as on heating, it is unable to attain the ignition

temperature due to transfer of heat to aluminium pipe which is good conductor of heat.

4. A heap of green leaves contains a lot of water and has very high ignition temperature. Water is a natural

fire extinguisher and do not let leaves catch fire easily where as dry leaves contains no water and have

low ignition temperature and catch fire easily.

5. A firecracker is a small explosive device primarily designed to produce a large amount of noise. They

have fuses, and are wrapped in a heavy paper casing to contain the explosive compound.

J. HOTS questions

NCERT Questions

1. Rising of a lot of soot indicates that paper undergoes incomplete combustion. Paper is made of cellulose

which does not burn completely. It can't make a good fuel. It also leaves behind ash.

2. Both cotton and paper burn incompletely giving out a lot of soot. They are plant products and to use them

as fuel we need to destroy a large number of plants or their products which are otherwise useful to us.

The calorific value of paper and cotton are not as good as fossil fuels. They don't have the qualities that a

good fuel should have. Therefore though they burn, they can't be used as a fuel.

3. The discolouration of the marble used in Taj Mahal has been attributed to the traces of acid found in the

air due to the exhaust coming out of the petroleum refinery in the vicinity. Over many years the presence

of acid in air and resultant acid rain have caused corrosion to the marble making it yellow.

4. There are three things required for fire 1- flammable material 2- heat 3- oxygen .during summer

atmospheric temp is high which causes heat and dry leafs and grass are flammable material this cause

of forest fire.

5. Matchsticks mainly contain red phosphorous on the top . And as phosphorous has very low ignition

temperature about 35 degree C , it is used to glow matchstick by rubbing the phosphorous through rough

surface . This leads to friction and the matchstick glows.

Chapter- 7 : Conservation of Plants and Animals



1. Biosphere 2. South-west 3. Leopard, jaguar 4. Hybridization

5. Deforestation, natural calamities

NCERT Questions

6. wildlife sanctuaries 7. endemic species 8. climatic


1. False 2. True 3. False 4. True 5. False

6. True 7. True 8. False 9. False 10. True

NCERT Questions

11. True 12. False 13. False 14. False


1. a. v b. iv c. ii d. iii e. i


1. b 2. a 3. c 4. c 5. b 6. a 7. c 8. c 9. d 10. d

NCERT Questions

11. a 12. c 13. b 14. b 15. a 16. d 17. c 18. a 19. c 20. b

21. b

E. Name them.

1. Conservation 2. Habitat 3. Extinct 4. Biodiversity

5. Desertification



1. Forest fires.

2. (i) Industrialization (ii) To build homes for increasing population.

3. Paper is a product of trees. Many hundreds of trees are cut to produce paper. So, it leads to extensive

deforestation. If we take care to save paper, we can definitely save some of the trees.

4. Reasons for wildlife poaching: (i) Valuable products of the animals like skin and horn (ii) Hunting as a sport.

5. IUCN: International Union for Conservation of Nature and Natural Resources.

NCERT Questions

6. The following are the advantages and necessities of forest conservation:

1. Forest conservation support life on earth.

2. It maintains quality of water and air, the basic essentials of existence of life.

3. Stability in soil is possible by trees, enables the land based plants and animals to live.

4. From their biodiversity grows wealth in the form of food, medicines, essential for human health.

5. It acts as carbon sinks absorbing carbon dioxide and keeps global warning at body.

6. Forests influence climate and reduce extremes of temperature. They conserve soil and regulate

moisture and stream flow. It prevents soil erosion and floods.

7. Forests also supply raw materials to so many industries like pulp to make paper, newsprint, saw

milling, matches, medicinal herbs.

8. It is the source of wood for use in houses construction and fuel wood.

9. Forests help in main export items like teak, paper, paper boards, natural resins, seeds obtained from

forests.


1. Wildlife sanctuary are areas where animals are protected from any disturbance to them and their habitat.

2. Wildlife sanctuaries provide protection and suitable living conditions to wild animals. Here killing (poaching) or capturing of animals is strictly prohibited.

Wildlife Sanctuary Biosphere Reserve

Biosphere reserve are large areas of protected land for conservation of wildlife, plant and animal resources and traditional life of the tribals living in the area.

Biosphere reserves like a complete ecosystem that take care of biodiversity comprising plants, animals and microorganisms generally found in an area.

S.No.


10. Forests are also source of revenue to the Government in the form of royalty, from leases of forest

products.

11. It also provides employment to a large many people.

7. There are things that every one of us can do! Planting trees is an easy way to help. When we reduce the

amount of products we use and buy, fewer trees are cut down to make new products. If we take care of

the things that we already have, and repair them when they are broken, we don't need to buy more.

When we recycle products like paper, (after we can no longer use and reuse them) we prevent new trees

from being cut down.

8. Regeneration occurs within a short period after harvest.

9. Corbett National Park.


1. Species:

a. A set of animals or plants having close similarity and can interbreed among themselves are called a

species. Eg., All dogs belong to a species.

b. The species which has completely been wiped out of the earth are extinct species. Eg. dodo bird.

c. Vulnerable Species : The species of organisms which are becoming less and can soon become

endangered is not taken if care. Eg. wild yak, black buck.

d. Endangered species: The species whose number has dwindled to near extinction levels. E.g. Rhino,

Bengal tiger.

2. Loss of biodiversity is due to:

(i) Deforestation: Large scale deforestation by man for his innumerable requirements leads to loss of

the natural habitat of many species of plants and animals.

(ii) Illegal hunting and poaching of animals like the rhinoceros and elephants.

3. Forest reserves have been established with the aim of protecting the flora and fauna of a region. The

forest reserves are governed by legislations which protect and preserve the nature with the aim to stop

felling of trees, hunting of animals and theft of valuable plants and animals products.

4. (i) Wildlife Sanctuaries: Wildlife sanctuaries are protected forests all across the world to preserve

certain plants and animal species. India has about 510 wildlife sanctuaries where hunting and

poaching are illegal. The government has also initiated projects for protection of specific species of

wildlife like Project Tiger for preserving and increasing tiger population and Project Elephant to

preserve elephant population. In these sanctuaries these animals are also provided with all the

facilities to help in their healthy survival.

(ii) National Parks : National parks are protected government owned areas (land or sea) which are

protected from various development activities. India has now 96 national parks. The first national

park was established in 1936 under the name of Hailey National Park, now known as Jim Corbett

National Park.eg., Gir National Park in Gujarat is known for the Asiatic lion.

5. (a) Wildlife Sanctuary and Biosphere Reserve :


(b) Zoo and wildlife sanctuary:

(c) Endangered and Extinct species:

(d) Flora and Fauna:

6. We should conserve biodiversity, because biodiversity represent whole ecosystem comprising land,

water, air, fauna and flora, Each component of this biodiversity chain is interdepedent on each other for a

sustainability.

7. Even protected forests are not safe for wild animals because people living in the neighbourhood

encroach upon them and destroy them.

8. Some tribals depend on the jungle as they live in the deep forest like primitive people had lived in

ancient time. They are still away from the basic amenities of modern life. Forest provide them food items

like seed grains, fruit, raw vegetables and other products like honey, meat of hunted wild animals for

themselves, fodder for theirs animals, wood fuel for heating and cooking even clothing using natural

fibres, leaves and animal skins.

9. The main causes of deforestation are exploitation of forest resources by the human being to meet the

ever growing requirements of an increasing population, rapid urbanization, industrialization. The

consequences of deforestation will result in putting in danger, the whole existence of human being along

with biodiversity on the planet earth.

10. Red Data Book is the source book which keeps a record of all the endangered animals and plants.

11. Migration is the phenomenon of movement of a species from its own habitat to some other habitat for a

particular time period every year for a specific purpose like breeding.

12. Wildlife refers to all living organisms in their natural habitat other than cultivated plants and domesticated

animals.

1. The plants found in a particular area are termed flora of that area. They are naturally occurring and have a indigenous plant life cycle.

Flora Fauna

The animals found in a particular area are termed fauna of that area.

S.No.

1. Zoo is man-made places where animals are kept in artificial setting instead of their natural habitat and provided protection.

2. Zoo can be in the middle of a urbanised city.

Zoo Wildlife Sanctuary

Wildlife sanctuary provides protection and suitable living conditions to wild animals just like in theirs natural habitat.

Wildlife sanctuary can be in the wild.

S.No.

1. Animals Species whose numbers are diminishing to a level that they might face extinction are known as the endangered species.

2. Eg. vultures, the Great Indian bustard, Southern Ground Hornbill.

Endangered Species Extinct Species

Extinct species are those animal species which became extinct a long time ago due to sudden climatic changes.

The dinosaurs are the extinct species, which were very large sized animals and were in plenty but vanished from this earth due to their inability to adjust to changes around.

S.No.


Importance of wildlife

1. To maintain ecological 'balance of nature' and maintain food chain and nature cycle.

2. It has economic value. Many wild plants provide useful substances like timber, paper, gums etc. And

they also have wide applications in ayurveda and other branches of medicine. Wild animals products

are tusk, ivory, leather, honey etc.

3. Most important contribution of wildlife for human progress is availability of large gene pool for the

scientists to carry breeding programmes in agriculture, animal husbandry and fishery.

4. Wildlife provides aesthetic value to man.

5. Wildlife of a country is its cultural asset.

13.Due to indiscriminate destruction of the natural home of animals or plant many species have either been

wiped out or facing threat to their survival. The plants and animals surviving in a specific area are called

endemic species. They are under great threat due to destruction of their habitat.

14.Each species, no matter how small, all have an important role to play in the ecosystem. An ecosystem is

defined by the network of interactions among organisms, and between organisms and their

environment, they can be of any size.

15. Invasive species seem to have traits or combinations thereof that enable them to out compete native

species. The competition sometimes is about rates of growth and reproduction; species other times

interact with each other more directly.

16.Soil erosion is a major environmental issue because it can lead to water pollution. Soil erosion results in

the loss of soil fertility and makes the land barren. There are more than 25 million hectares of barren

lands in the world now. Soil erosion also leads to desertification. Desertification refers to increase of

desert areas.

17.The Parliament has enacted the Forest (Conservation) Act, 1980, to check further deforestation and

conserve forests and to provide for matters connected therewith or ancillary or incidental thereto.

18.Biological diversity, or the shorter "biodiversity," (bio-di-ver-si-ty) simply means the diversity, or variety,

of plants and animals and other living things in a particular area or region.


1. Forests are the natural habitats of wild animals. When forests are destroyed for development activities,

the wild animals become homeless and so they are either forced to migrate and if not, they perish. So,

forest conservation is the most important initiative in wildlife conservation. Forests provide protection,

food and suitable environment for all animals which can not be artificially created. So, forest

conservation is most essential for wildlife conservation.

2. Project Tiger is a conservation project, launched in 1973. The main aim was to identify and create a list of

sites that were natural habitats of tigers and then devising ways to restore them. It has been a successful

attempt which has helped in the recovery of the habitat and consequent increase in tiger population in

the reserve areas.

3. Red Data Book is a catalogue containing a comprehensive list of rare, threatened, and endangered

species which has been published by International Union for conservation of nature and natural

reserves. The Red Data Book is a list of endangered wildlife species in various countries of the world.

This gives information such that immediate action for saving them needs to be initiated.

4. Endemic Species: Plant and animal species confined to specific geographic areas are called endemic

species. North East India, the Western Ghats and the Himalayas are very rich in endemic species.

Identification and protection of endemic species involves protection of their habitats. The lion tailed

macaque endemic to South-west India has been ranked among the most threatened primates due to

destruction of its habitat. Giant panda is endemic to China, it is its natural home. The Great India Bustard,

endemic to India, is classified as endangered.


5. Animals migrate to escape from conditions which are unfavourable, when food becomes scarce.

Sometimes migration takes place when the habitat of the organisms is destroyed. Many fishes and

aquatic animals migrate for breeding purposes too. For example, the Arctic tern which breeds in the

Arctic and sub-Arctic regions, spends its winter in the Antarctic travelling a distance of 19,000 km. Its

annual trip back and forth sums up to 74,000 km. Siberian cranes are often seen in India during winter.

They migrate from Siberia to avoid the severe cold.

NCERT Questions

6. (a) Wild animals : Deforestation deprives wild animals of their natural habitat as result of which they may

migrate to other areas or may face extinction.

(b) Environment : Deforestation is disturbing the whole set of our eco-system, leading to major

environmental changes like Global warming.

(c) Villages (Rural areas) : Deforestation results in less rain fall, which means less water for human and crop

irrigation. Domestic cattle will have no fodder. Floods and soil erosion caused by deforestation will

further adversely effect the rural economy and they may resort to migration to cities in great numbers.

(d) Cities (Urban areas) : Deforestation is making water scarcity a major problem in the cities. In the

absence of an ecosystem for recycling and over grown urban areas and industries, cities are

already facing air pollution and scarcity of resources obtained from forests. Rural migration caused

by the depleted resources there, is adding further burden. In future cities may face water scarcity,

inadequate supplies of food grains, vegetables and other products like milk.

(e) Earth : Deforestation is changing earth temperature due to global warming. This may endanger the

the complete ecosystem comprising of land, living beings, water, air and other resources.

(f) The next generation : Deforestation will offer great challenges to the next generation in the form of

scarcity of water due to less rainfall, air pollution, lesser food, lesser organic raw materials, increased

temperature, natural calamities or disasters floods, droughts and storms due to climatic changes.

7. (a) Trees are the most important part of our ecosystem directly responsible for recycling of polluted air

we breath, rainfall augumenting our water reserves which are used for drinking as well as crop

production, supply of organic raw materials in the form of food, wood and medicine, providing food

and shelter to animals and birds. Trees also prevent soil erosion and floods. Cutting of trees in a

longer run will result in catastrophic consequences for the existence of mankind along with whole

spectrum of diversity envolvng living being and plants on this planet earth.

(b) Each species of animal is part of an ecosystem chain with diverse elements in the form of land, air,

water, flora and fauna. Each part essentially play its role as a team member to support the co-

existence of natural diversty in a wholistic and balanced term. If the habitat of an animal is disturbed,

it will resort to migrate to some other place for food and shelter. This will disturb the ecosystem of that

particular area resulting in long term consequences.

(c) If the top layer of soil is exposed, rain water will directly hit the ground and impact of this will cause

further loosening of humus rich top soil layer. First, this will result in soil erosion in the form of mud

flush and reduced soil fertility, secondly it will deprive groundwater reserves from recharging as

water will flow down without any seapage or percolation.

8. It is not justified to cut the trees at present rate for such projects. Trees as a part of forest are the most

important part of our ecosystem. Worldwide, reduced forest cover have already started showing its

devastating effects in terms of climatic changes. We must reduce our dependency on our forest resources

to meet the ever-increasing demand in factories and for shelter. We should look for some other alternatives

for the same. We have to start reforestation at much larger scale taking it as a top priority.

9. We can plant trees in open spaces, park, along the side of road and motivate others.

We can make use of roof water or water from kitchen for water harvesting to recharge the ground water

table. We can recycle our organic waste from kitchen for making compost and use it in our kitchen

garden or plants. We can reduce use of paper. We can save it, reuse used paper and recycle it.


10. Deforestation increases the temperature and pollution level on the earth. It increases the level of carbon

dioxide in the atmosphere. Ground water level also gets lowered. Deforestation disturbs the whole

ecosystem. As we know, plants need carbon dioxide for photosynthesis. Fewer trees would mean that

less carbon dioxide will be used up resulting in its increased amount in the atmosphere. This will lead to

global warming as carbon dioxide traps the heat rays reflected by the earth. The increase in temperature

on the earth disturbs the water cycle and may reduce rainfall.

11. It takes 17 full grown trees to make one tonne of paper. Therefore, we should save paper. Paper can be

recycled five to seven times for use. If each student saves at least one sheet of paper in a day, we can

save many trees in a year. We should save, reuse used paper and recycle it. By this we not only save

trees but also save energy and water needed for manufacturing paper. Moreover, the amount of harmful

chemicals used in paper making will also be reduced. We can also save paper by using Information

technology for storage of printed data, books in digital form.

12. Because the plants and trees that are on earth breathe out O (Oxygen) and breathe in CO (Carbon 2 2

Dioxide) and we breathe out CO and breathe in O so we basically share the gases and because they 2 2

are being cut down they are not able to breathe in the CO that we breathe out so that is going into the 2

atmosphere contributing to the greenhouse effect and slowly poisoning us.

13. Deforestation plays several roles in the flooding equation because trees prevent sediment runoff and

forests hold and use more water than farms or grasslands. Tree roots absorb water from the soil, making

the soil drier and able to store more rainwater. Tree roots hold the soil in place, reducing the movement of

sediment that can reduce floods.

I. Give reasons.

1. Extinction is always a part of the nature: weak species must go extinct in order to make strong species

able to survive. Now a day's more species are disappearing at a much faster rate than ever before. The

reason for this is us. By contaminating, over hunting, destroying ecosystems, etc., we are forcing many

species to the extinction. Scientists agree that the number of species that are extinct because of us could

easily approach the number of species that became extinct at the end of the Cretaceous (all dinosaurs,

plus many other reptiles and birds). So, animals are becoming endangered because of humans.

2. The IUCN maintains a Red Data Book which contains a record of animals which are known to be in

danger. It includes endangered, vulnerable, rare, extinct etc., species of plants and animals. It helps to

create awareness about the various species. Also, the information about status of the species in danger

helps in increasing concern and implementing ways to protect and preserve them.

3. Invasive species are a major threat to our environment because they can change an entire habitat,

placing ecosystems at risk. They can crowd out or replace native species that are beneficial to a habitat.

They can damage human enterprise, such as fisheries, costing the economy millions of rupees.

J. HOTS Questions.

1. It is very important to include the local people of a place in conservation activities because they are very

much a part of the ecological system and understand the local area, climate, and the behaviour patterns

of animals and the commonly identified plant species. They have a sense of belonging and if guided well,

take pride in improving their surroundings. The culture of the local people is also related to their own

surroundings and so these can be used in conservation activities.

2. Sanctuaries promise to take in and care for any animals that have been abused, neglected, or

abandoned and to keep them for life. Zoos are created specifically to exhibit animals to the public. They

collect animals, taking into consideration conservation needs, the potential for scientific research, and

which species the public likes best. Zoos buy, sell, trade, borrow, loan out, and breed animals.

3. Deforestation includes a more difficult way of keeping many people alive this is because rainforest's

provide plants which we use as our medicines. On the other hand, we need the resources that it provides

e.g. Paper, we need paper to write on. So, deforestation cannot be stopped completely.

Chapter- 8 : Cell: Building Blocks of Our Life



1. Robert Hooke 2. Leeuwenhoek 3. Amoeba, paramecium

4. fly 5. much more 6. tissues, organs

7. organs 8. tissue 9. cell wall

10. cytoplasm 11. tissues 12. Chloroplast

13. unicellular 14. electron microscope 15. specimen

16. Golgi bodies


1. False 2. False 3. True 4. False

NCERT Questions

5. True 6. False 7. False 8. True


1. a. iv b. v c. vi d. iii e. ii f. i

NCERT Questions



1. c 2. b 3. d 4. b 5. c 6. c 7. d 8. d 9. c 10. d

NCERT Questions

11. c 12. b 13. c 14. d 15. c 16. d 17. b 18. d 19. a 20. a

21. b 22. a 23. b 24. d 25. c 26. c 27. d 28. a 29. d 30. d

31. d 32. c 33. c 34. b

E. Name them.

1. Plasma membrane 2. Chromoplasts 3. Egg of ostrich 4. Nucleus

NCERT Questions

5. Chloroplasts 6. Compound microscope 7. Nucleus

8. Cell membrane 9. Genes



1. Cells of different tissues are different in shape and size because they perform different functions. The shape and size are suited to the area they function.

2. Stains are used in slides to enable us to see the specimen clearly against the background.

3. Chromosomes are thread like structures which carry the hereditary units called the genes, which are responsible for all our characteristics.

4. A tissue is a collection of similar cells performing a set function.

5. Amoeba and paramecium are unicellular.

6. Prokaryotes are primitive organisms in which the nucleus is not well defined and genetic material is absent.

7. Endoplasmic reticulum acts as the transport system in this cell.

8. The cell wall in plant cell protects it against forces of nature like wind, humidity and temperature conditions.

9. The object to be viewed in a microscope is called specimen.

10. Centrosome is a cell organelle found in animal cells just above the nucleus. It helps in cell division.

NCERT Questions

11. Genes in a cell are found in the chromosome. Chromosomes come in pairs, and there are hundreds of them made up of DNA (deoxyribonucleic acid). In humans, a cell nucleus contains 23 pairs of chromosomes.



12.Kingdom Protista.

13.The function of a cell wall is to act as a pressure vessel, preventing over-expansion when water enters

the cell. They are usually found in bacteria, plants, algae and fungi amongst other organisms.


1. Plastids are different coloured organelles found only in plant cells. They are chloroplasts containing

green coloured chlorophyll. Chromoplasts which have colours other than green, like orange, red, etc.,

and leucoplasts which are colourless.

2. Lysosomes are called suicidal bags since they secrete digestive enzymes that are capable of destroying

the whole cell, at times.

3. Cell division takes place chiefly in region of growth. In plants they are the root and the shoot tips, and in

animals, the ends of bones and layers of skin cells.

4. The cover slip helps to keep the specimen protected and prevents the lens of the microscope from

coming in contact with the specimen.

5. Blood is a liquid tissue having a liquid portion called the plasma in which various cells are suspended.

They are the red blood cells, white blood cells and the platelets.

6. Every multi-cellular organism is made up of a huge collection of cells. When similar cells group together

to perform a function we call it a tissue. When different tissues collect together to perform a major

function, we call it an organ. e.g., stomach is an organ consisting of muscular tissue, nervous tissue,

connective tissue (blood) and epithelial tissue. Similarly when many organs group together to perform a

very important function, we call it an organ system. Digestive system is one such system made up of food

pipe, stomach, intestines, etc.

7. Inheritance refers to the transfer of certain characteristics from one generation to another. This is

responsible for strong resemblances between members of the same family.

NCERT Questions

8. Human nerve cell, also known as neuron, is branched like structure. A typical neuron possesses a cell

body (often called the soma), dendrites, and an axon. Dendrites are thin structures that give rise to a

complex "dendrite tree". An axon is a special cellular extension that arises from the cell body at a site

called the axon hillock. The cell body of a neuron frequently gives rise to multiple dendrites, but never to

more than one axon, although the axon may branch hundreds of times before it terminates.

Functions: The nerve cell or neuron processes and transmits information through electrical and chemical

signals, thereby helping to control and coordinate the working of different parts of the body. Neurons are

the core components of the nervous system, which includes the brain, spinal cord, and peripheral

ganglia and play a vital role in sensing touch, sound, light and other through sensory organs that then

send signals to the spinal cord and brain. Motor neurons receive signals from the brain and spinal cord,

cause muscle contractions, and affect glands. Interneuron connects neurons to other neurons within the

same region of the brain or spinal cord.

Sketch of the human nerve cell- Neuron

Nucleus

Myelin sheath

Schwann cell

Axon

SomaNode ofRanvier

Axon terminal

Dendrite


9.

10. Eukaryotes ( eu + karyon meaning true nucleus ) are made up of eukaryotic cells, which, like onion cells and cheek cells have a well organised nucleus with a nuclear membrane. All organisms other than bacteria and blue green algae are called eukaryotes. Whereas Prokaryotes (pro + karyon - primitive nucleus) are made up of prokaryotic cells, in which nuclear material exists without nuclear membrane. The organisms with these kinds of cells are called prokaryotes. These are of type primitive nucleus. Examples are bacteria and blue green algae.

11. Chromosomes are found in nucleus. They are thread-like structures carry genes and help in inheritance or transfer of characters from the parents to the offspring. The chromosomes can be seen only when the cell divides.

12. a. It represents a animal cell. b. It represents an eukaryotic cell.

13. A– Cell Wall B– Cell Membrane C– Vacuole D– Nucleus E– Cytoplasm

14. Cell – RBC, WBC, Nerve cell.

Tissue – Blood, muscle.

Organs – Heart, hand, brain, blood vessels.

15. Cell wall, cell membrane, cytoplasm, cell organelles, nucleus, chromosomes.


1. The three major components of a cell are:

(i) The outer boundary (The plasma membrane and the cell wall): The outer boundary forms a barrier between the inner contents of the cell and the surrounding. Allows certain substances to enter and exit. So, we call it selectively permeable.

(ii) The cytoplasm and the cell organelles suspended in it: The jelly like substance inside the plasma membrane which carries all the cell organelles is called the cytoplasm. It also contains salts, proteins, sugar and other nutrients required by the cell.

(iii) The nucleus : It is the control centre of the cell containing thread like strands called chromosomes. The chromosomes are made up of complex substances called deoxyribonucleic acid. They are the hereditary units which travel from one generation to another.

S.No. Animal Cell Plant Cell

1. Cell wall absent. Cell wall present.

2. Chloroplasts are absent. Chloroplasts are present.

3. Centrosome is present and helps in cell division. Centrosome is absent.

4. Small vacuoles or absent. Large vacuoles to store food.

2. Nucleus is a dense spherical structure suspended in the cytoplasm. It controls all cell activities. Each nucleus is surrounded by a nuclear membrane which is selectively permeable. The nuclear membrane contains semi solid material called nucleoplasm. The centre of the nucleus is nucleolus. The nucleoplasm has a network of threads called the chromatin network which carry the DNA.

3. The term organelle means a tiny organ. The term is used to refer to the tiny structure found suspended in the cytoplasm. The cell generally contains organelles like endoplasmic reticulum which helps in storage

Cell Membrane

Nucleus

Cytoplasm

Centrosome

Ribosomes

Golgi Body

Vacuole

Mitochondria

Animal Cell

Cytoplasm

Ribosomes

Golgi Body

Cell Wall

Cell Membrane

Vacuole

Nucleus

Chloroplast

Mitochondria

Plant Cell

Sketches of Animal and Plant Cells

cell membrane

vacuole

nucleus

cytoplasmchloroplast

cell membrane

cell well

(a) (b)


and transport of materials with in the cell, mitochondria in which energy is released through oxidation, ribosome which make proteins and nucleus which controls all activities.

4. Plastids are of three types. They are chloroplasts, chromoplasts and leucoplasts. Chromoplasts contain the green pigment, chlorophyll; Chromoplasts are present in portions of plants coloured other than green and leucoplasts are found in the roots and colourless portions.

5. Cell division is a process in which a single cell divides into two daughter cells. So, cell division is a very important phenomenon by which growth and development of an individual takes place. Cell division is also very important for repair and replacement of damaged cells and wound healing.

6. A slide is prepared by collecting the necessary material and equipment first. They are glycerine, a dye like methylene blue, coverslips and clean slides, microscope and of course the specimen to be viewed. For observing living objects, we use a wet mount. On a clean slide a drop of water is placed and then a small quantity of the specimen is taken and thoroughly mixed with the drop of water. Alternately the specimen is carefully placed in the water. Then a drop of glycerine and a drop of the dye are added. The specimen should then be covered with a coverslip very slowly and gradually, taking care to avoid air bubbles. Then a filter paper should be used to blot out any excess fluid. The slide thus prepared should be placed on the stage of microscope and then the low power lens is brought in place. Using the eyepiece (lens) we focus the object until the object is clearly visible.

7. a

NCERT Questions

8. Every living organism has many organs, which performs different functions such as digestion,

assimilation and absorption. Different organs of perform specific functions. For example, roots help in

the absorption of water and minerals. Leaves, are responsible for synthesis of food. Each organ is

Present (formed of cellulose)

Rectangular (fixed shape)

One, large central vacuole taking up 90% of cell volume.

Plant cell have chloroplasts because they make their own food

Present

Cell wall and a cell membrane

Lysosomes usually not evident

It is very rare

Cell wall

Shape

Vacuole

Chloroplast

Plastids

Plasma Membrane

Lysosomes

Cilia

Absent

Round (irregular shape)

One or more small vacuoles (much smaller than plant cells)

Animals cells don't have chloroplasts

Absent

only cell membrane

Lysosomes occur in cytoplasm.

Present

Features Animal Cell Plant CellS.No.

1.

2.

3.

4.

5.

6.

7.

8.


further made up of tissues which in turn, are made up of cells. This is for the reason, why in in a living

organism, cell is the basic structural unit.

9. The chloroplasts are found only in plant cells, because, chloroplasts contain green pigment called

chlorophy, which is essential for photosynthesis in plants leaves for making food. As we know there are

several small coloured bodies in the cytoplasm of the cells of plant leaf. They are scattered in the

cytoplasm of the leaf cells. These are called plastids. They are of different colours. Some of them contain

green pigment called chlorophyll. Green coloured plastids are called chloroplasts.

10. Each cell organelle is responsible for a specific function and the collective work of all the cell organelles

is very important for making the cell work as a single unit.

11. Cell wall is the additional layer found around the outside of plant cells and bacteria. It is used to filter the

absorption and secretion of items in and out of the cell. It also provides protection to the cell.

12. The number of cells in an elephant runs into billions and trillions. Human body also has trillions of cells

which vary in shapes and sizes. Different groups of cells perform a variety of functions. Organisms made

of more than one cell are called multicellular organisms. The number of cells being less in smaller

organisms does not in any way affect the functioning of the organisms. An organism with billions of cells

begins life as a single cell which is the fertilised egg. The fertilized egg multiplies and the number of cells

increase as development proceeds. A single celled organism performs all the necessary functions that

multicellular organisms perform.

I. Give reasons.

1. Cells have different shapes because they do different things. Each cell type has its own role to play in

helping our bodies to work properly, and their shapes help them carry out these roles effectively.

2. The primary concern of cell division is the maintenance of the original cell's genome.

3. Many organs and tissues in the body can recover after injury without intervention. But some cells of the

central nervous system are so specialized that they cannot divide and create new cells. As a result,

recovery from a brain or spinal cord injury is much more difficult. The complexity of the central nervous

system makes the formation of the right connections between brain and spinal cord cells very difficult.

NCERT Questions

4. Nails are usually made up of thick and multiple layers of a type of protein known as Keratin and are

composed of dead tissues. They are devoid of any nerves and blood vessels and therefore we do not feel

any pain while the nails are being cut.

J. HOTS questions

1. While observing the slides, we need to look at the outermost boundary. The specimen having a thick

outer boundary is a plant cell because only plant cells have a cell wall which stays thick.

2. Before the discovery of the microscope, man's understanding of life was restricted to what he could see

around him. The invention opened the doors to the world of microorganisms. The primitive microscope

could magnify only to a limited range. With the improvement of technology the range of magnification

increased and the world of microorganisms also expanded. Initially with the compound microscope we

could see only the microorganisms but not its detailed structure. Electron microscope was a discovery

which took us further ahead enabling us to see all cell organelles and study their detailed structures. So,

we can say that technological development is very closely associated with scientific advancement.

3. Head injuries can be serious and require urgent medical attention. A hard blow to the head from a fall,

knock or assault can injure the brain, even when there are no visible signs of trauma to the scalp or face.

The brain is a soft and delicate organ. A hard blow to the head can injure the brain or spinal cord even

when there are no visible signs of trauma to the scalp or face. That's why all head injuries are considered

serious and should be assessed by your doctor or the nearest hospital emergency department.

4. A unicellular organism has only one cell, which means that it has to carry out all functions of life in a single cell.

Multicellular organisms have specialised cells to perform various function. Certain actions or functions carried

out by a multicellular organism in order to maintain life like RBCs carry oxygen and nephron filter, neuron

regulate brain etc. Cells in a multicellular organism have the ability to specialize certain functions for the living.

Chapter- 9 : Reproduction in Animals



1. binary fission 2. multiple fission 3. Yeast

4. One, Two 5. hermaphrodite 6. sperm, eggs

7. fertilization 8. zygote


1. True 2. False 3. True

NCERT Questions

4. False 5. True 6. True

7. False 8. True 9. False



1. a. vi b. v c. i d. ii e. iii f. iv


1. c 2. a 3. c 4. d 5. b 6. a 7. a 8. d

NCERT Questions

9. a 10. b 11. c 12. c 13. d 14. b 15. c 16. a 17. d 18. a

19. b 20. a 21. a

E. Name them.

1. Ovary 2. Oviduct 3. Testes 4. Uterus



1. Male gametes are formed in the testes.

2. Ovum is fertilized in the fallopian tubes.

3. After fertilization, the ovum becomes a zygote.

4. Amoeba and paramecium reproduce by binary fission.

5. Yeast and hydra reproduce by budding.

6. Hormones are chemical messengers in the body. They are produced in endocrine glands.

7. Division of amoeba into two is called binary fission.

8. Birds like crow, hen and reptiles like crocodiles.

9. Growth spurt (sudden increase in height ) is seen both in boys and girls. Boys have a change in voice and

development of beard (facial hair). Girls develop breasts and show bodily changes.

10.A nymph or a metamorph is a stage in incomplete metamorphosis when a young one develops into a

form similar in structure to the adult but lacks some of its features such as wings and sexual organs.

NCERT Questions

11. In the female reproductive parts, the embryo gets embedded in the wall of the uterus for further

development, where it continues to develop in the uterus, finally to form a foetus.

12.The transformation of the larva into an adult through drastic changes is called metamorphosis. For

example tadpoles or caterpillars in early stages differ a lot in features than their adult stage later in the

form of frog and moth.



13.During fertilisation the nuclei of the sperm and egg fuse to form a single nucleus. This results in the

formation of a fertilised egg or zygote. Zygote is the beginning of new individual.

14.Egg, silkworm, pupa, silkmoth.

15.Reproduction is important because without it, a species would not survive over time. Individuals must

reproduce to ensure that they will continue on over generations of time.

16.Dog is a viviparous animals. They do not lay eggs. The mother gives birth to young ones.

17.Frogs and toads lay eggs in jelly-like masses, and unless the eggs are covered with water, they will dry up

and die. Eggs become much bigger after they are laid because the eggs absorb water and swell to

several times their original volume. The jelly around the eggs keeps them safe in water.


1. a. Reproduction: The process of producing members of one's own kind is known as reproduction. It is a

characteristic of living beings.

b. Fertilization: The process of fusion of the male gamete with the female gamete is known as

fertilization.

c. Embryo: After the fertilization, the zygote divides and forms a ball of cells which travels to the uterus

and gets implanted in the uterine wall and begins to grow. At this stage it is called an embryo.

d. Zygote: The cell formed by fusion of male and female gamete is known as the zygote.

e. Metamorphosis: The process of development of an adult through various stages such as larva and

pupa from an egg is called metamorphosis.

f. Hermaphrodite: The organism which carries both male and female reproductive organs in the same

body, is called a hermaphrodite.

2. Asexual reproduction refers to the process of reproduction in which only one parent is involved and the

offspring produced are identical to the parent. No reproductive cells are involved.

3. Fishes and frogs lay millions of eggs because the eggs are laid in water. A lot of them are eaten away as

food by aquatic animals. Many of them get carried away by the force of water and do not get a chance to

fertilize. So, only a few get fertilized and develop into adults.

4. The age between thirteen and nineteen years, also known as teenage is known as the period of

adolescence. It is the stage between a child and the adult.

5. Placenta is a tube shaped organ through which a foetus receives food and oxygen from the mother's

blood and releases the waste into it.

6. In budding, a small bud grows out from the side of the mother's body, and eventually breaks off as an

independent organism. In fragmentation, the mother's body itself divides into two or more sections and

each section develops into a fully grown organism. Hydra and yeast reproduce by budding. Planaria,

liver fluke reproduce by fragmentation.

7. Hormones are chemicals which are produced in endocrine glands and they coordinate a lot of our body

functions.

8. Viviparous organisms give birth to fully developed young ones. The development of the young one takes

place inside the mother's body. E.g. humans, dogs, cats etc. Oviparous organisms lay eggs and

development of the young one takes place outside the body of the mother. E.g. birds and reptiles.

9. Fertilization occurs when a male gamete meets the female gamete. The nuclei of the two gametes fuse

to produce a new cell which is called the zygote.

10. Incomplete metamorphosis is the one in which an insect develops from the egg into a nymph, which is

similar in structure to the adult but lacks some of its features like the wings and sexual organs which

develop later. E.g. development of cockroach.


NCERT Questions

11.

12. The transformation of the larva into an adult through drastic changes called metamor. For example

tadpoles or caterpillars in early stages differ a lot in features than their adult stage later in the form of from

and moth.

13.

14. Single, asexual, body, nucleus, binary.

15. Human beings do not have to undergo metamorphosis as the body parts similar to those in the adults are

present from the time of birth. But in the case of butterfly and frog they have to pass through drastic

transformation to become the adult. This change is called metamorphosis.

16. The process of fertilisation is the meeting of an egg cell from the mother and a sperm cell from father. So,

the new individual inherits some characteristics from the mother and some from the father. So, the baby

has the characters of both parents.

17. In hydra the new individual develops from as outgrowth from a single parent. Since the new individual

develops from the buds this type of asexual reproduction is called budding. Amoeba is a single celled

organism. It begins the process of reproduction by the division of its nucleus into two nuclei. This is

followed by division of its body into two each part receiving a nucleus. Finally two amoebae are produced

from one parent amoeba. This type of asexual reproduction in which an animal reproduces by dividing

into two individuals is called binary fission.

18. The sperm has a long tail, which it uses to swim up the woman's cervix while looking for an egg to

fertilize. It also has a streamlined body that makes it more agile and a pointy tip that enables it to

penetrate the egg for fertilization.


1. Female reproductive system consists of a pair of ovaries, the oviduct or the fallopian tubes and the

uterus. Ovaries lie in the lower abdomen. It produces the egg or the ovum. The oviduct is a funnel

shaped tube which carries the egg to the uterus.

Uterus: The uterus is a hollow organ in which the fertilized egg is embedded and develops into the

foetus. The neck of the uterus is called the cervix.

2. Animals which give birth to fully developed young ones like the humans and most of the mammals are

called viviparous. In these the young ones develop inside the mother's womb and are then born. Animals

1. The stage of fertilization, in which fusion

of ovum and sperm take place, is called a

zygote.

2. Zygote is a single nucleus cell and is the

first step in the process of reproduction.

The stage of fertilization, in which fusion

of ovum and sperm take place, is called

a zygote.

Zygote is a single nucleus cell and is the

first step in the process of reproduction.

Zygote FoetusS.No.

1. Fertilization that takes place inside the

female body is cal led internal

fertilization. This is observed in human

beings and other animals. Eg. hen, cows

and dogs.

Fertilization that takes place outside the

female body is called external

fertilization. Eg. frogs, fish, starfish etc.

Internal Fertilization External FertilizationS.No.


which lay eggs are called oviparous. In these animals, eggs come out of the body of the mother and then

the young ones hatch out as in the case of hen eggs and eggs of most of the birds.

3. In hydra the method of reproduction is asexual. A small bud develops from the side of the parent body

and it grows in size and eventually breaks off to give rise to an independent new individual.

4. S.No. Sperm cell Egg cell

1. Male gamete. Female gamete.

2. Smaller in size. Larger in size.

3 Produced in testes. Produced in ovary.

4. Can move with the help of tail the Does not move. It stays inside.

ovary attached to its head.

5. Elongated. Spherical in shape.

5. After the formation of a zygote, it divides and forms a ball of cells which travels to the uterus and gets

implanted in the uterine wall. Here it begins to grow. At this stage it is called an embryo. The uterus is well

prepared to receive the embryo by building up a thick cushion like lining rich in blood vessels. As the

embryo continues to grow, its cells differentiate into muscle cells, blood cells, nerve cells, etc. Various

tissues and organs form from these cells. The growing embryo is now called the foetus. The foetus

receives food and oxygen from the mother's blood and releases the waste into it through a tube shaped

organ called placenta. When the development is complete in about 38 weeks, the baby is ready to be

born. This is the journey of a zygote from its formation to the birth of the baby.

6. Hormones are chemicals that control and coordinate our body functions. Hormones are responsible for

growth and development, sexual maturity, production of gametes, development of secondary sexual

characteristics and so on. They are produced in endocrine glands and are transported to a target site

through blood.

7. S.No. Sexual Asexual

1. Two parent take part. Single parent.

2. Variation occurs in offspring. Offspring are genetically identical to each other

and to their parent.

3. Fertilization takes place. No Internal fertilization or external fertilization.

4. Gametes are involved. No gametes.

5. Mixing of hereditary material. No mixing of hereditary material .

NCERT Questions

8. The process of reproduction in organisms is essential for the continuation of theirs respective species.

The reproduction in organisms is very important as it ensures the continuation of similar kinds of

individuals, generation after generation. In larger context, reproduction in various species of animals

and plants kingdom, forms part of ecosystem and which helps in maintaining it, by evolution chain.

9. In human beings, the reproductive organs in the female include ovaries, oviducts and uterus. The

reproductive organs in male include testes, sperm ducts and penis. In human beings, female,

produces every month, female gametes called ova inside her ovaries. Ova which is a single matured

egg is released into the oviduct by one of the ovaries. The testes in male produce male gametes

called sperms.

Embedding & Development

of the embryo in the uterus

Embryo

Uterus wall


The fusion of ovum and sperm is called fertilization. The fertilized egg is called a zygote. The zygote

divides repeatedly to give rise to an embryo. The embryo gets embedded in the wall of the uterus for

further development. The stage of the embryo in which all the body parts are identifiable is called foetus.

Human beings and others animals such as cows and dogs which give birth to young ones are called

viviparous animals.

10. Asexual Reproduction: The type of reproduction in which only a single parent is involved is called

asexual reproduction.

Two methods of asexual reproduction are as follows :

Budding: The type of asexual reproduction in which new individuals develop from the buds, is called

budding. In hydra, new individuals develop from buds.

Binary Fission: The type of asexual reproduction in which an animal reproduces by dividing into two

individuals is called binary fission. Amoeba reproduces by dividing itself into two.

I. Give reasons.

1. Asexual reproduction is the process by which an organism creates a genetically similar or identical copy

of itself without a contribution of genetic material from another individual. This means it doesn't involve

meiosis, ploidy reduction, or fertilization but only one parent is involved genetically. In comparison to

sexual reproduction, asexual reproduction produces less variation of individual organisms.

2. Hormones are chemical substances made by special glands and which pass all over the body through

the bloodstream. The marked changes in the body and in the way we behave at puberty is entirely due to

Ovum

Female reproductive organs in humans

Oviduct

Uterus

Sperms

Testes

Sperms

Ovary

Fertilization

Penis

hormones. The testis in the male and the ovaries in the female become active, and secrete testosterone

or oestrogens respectively. These hormones are mostly responsible for young people developing from

children into young adults. Puberty is a time of great change. Not only does the body alter from a child-

like shape to a more adult one, but things like friendships, attitudes to others (of both sexes) and to one's

parents all change quite dramatically because of hormones.

3. As a baby develops in the womb, the placenta develops in the womb, too. The placenta plays a crucial

role for foetal well-being. Without a healthy placenta, positioned correctly in the uterus, the baby could

not develop correctly. The placenta develops and attaches to the uterine wall. As the uterus expands, the

placenta grows and repositions itself in conjunction with uterine growth.

J. HOTS questions.

1. A butterfly develops from an egg after passing through a number of stages like larva and pupa. The

process of developing through different stages is called metamorphosis. A chick develops inside the

egg. The hen incubates the eggs and the embryo grows and reaches maturity in 21 days. It then breaks

the shell and emerges out.

2. Traditionally, majority of communities in India have a preference for a male child over a female child. A

male was considered as the bread winner and protector of a family. Female was considered a burden

since a lot of money was spent on the marriage of the girl, as dowry. In today's context, it does not

have much significance. Girls are no more the weaker sex. Therefore the preference for a male child

is totally unjustified.


Chapter- 10 : Reaching the Age of Adolescence




1. True 2. True 3. True 4. True 5. True


1. a. v b. iv c. i d. ii e. iii



1. b 2. d 3. b 4. a 5. a 6. d 7. c 8. c 9. b 10. a

NCERT Questions

11. b 12. a 13. b 14. d 15. c 16. d 17. d 18. a 19. d

E. Name them.

1. Menopause 2. Zygote 3. Ovulation

NCERT Questions

4. Target site 5. Exocrine gland 6. Hormones

7. Menstrual Cycle 8. Testosterone



1. Ultrasonic scanners are used to monitor the growing foetus in the mother's womb. They are helpful in

finding developmental defects in the growing foetus.

2. Hormones are secreted in the endocrine glands.

3. Hormones are carried to target sites through blood.

4. Menarche is the onset of puberty, marked by the first menstrual flow in females.

5. Metamorphosis is the development of a young animal after passing through various stages of growth like

larva, pupa, etc.

6. Due to the activity of oil and sweat glands, the adolescent boys and girls develop acne and pimples on

the skin.

7. Drug abuse is intake of chemicals that produce physical mental, behavioural or emotional changes in the

user. It is very harmful and sometimes causes complete dependence on them which is known as

addiction.

NCERT Questions

8. The secretions of endocrine glands responsible for changes taking place in the body are called

hormones. Hormones are chemical substances, which are released by endocrine glands directly into the

blood stream. The changes which occur at onset of puberty and adolescence are controlled by

hormones.

1. Testosterone 2. Glycogen 3. liver 4. Adolescence

5. Acne, Pimples 6. larynx 7. Menopause 8. 38

9. Thyroxine 10. healthy, Junk 11. adolescence

12. Progesterone and testosterone 13. larynx 14. Hormones, target

15. Sweat and oil glands 16. Reproductive

NCERT Questions

17. fertilized egg 18. blood stream, body part

19. testosterone, secondary sexual characters 20. pituitary gland



9. The period of life, when the body undergoes changes, leading to reproductive maturity, is called

adolescence. Adolescence begins around the age of 11 and lasts upto 18 or 19 years of age. Since this

period covers the 'teens', adolescents are also called 'teenagers'. In girls, adolescence may begin a year

or two earlier than in boys. Also, the period of adolescence varies from person to person. The

Adolescence is marked by the onset of puberty in which growth of the reproductive organs , change in

body size, change in body height, change in Voice etc takes place.

10.a. Menarche, Menopause b. Metamorphosis

c. larynx d. Adrenalin


1. Adams apple is protruding of the voice box at the week region due to growth of the voice box in

adolescence which changes the voice. It is one of the secondary sexual characteristic noticeable in

boys. It is not seen is girls because the voice box of the girls remains small.

2. Sex chromosomes of boys contain a X and a Y factor. It is represented as XY. The females have both X

factors in their sex chromosome. It is represented as XX.

3. Onset of puberty in girls is marked by starting of the menstrual cycle.

4. The physical changes that accompany the onset of puberty are called as secondary sexual

characteristics. For e.g., boys, the growth of facial and body hair, change in voice growth etc., are

secondary sexual characteristics.

5. a. Ovulation: The release of egg from the ovary.

b. Menopause: The cessation of menstrual cycle at the age of 45-50 years.

c. Puberty: The beginning of reproductive phase in humans.

d. Pregnancy: The period of development of a foetus in the mother's womb.

6. The gender of a child is determined by how the gametes combine. A female gamete carrying X

chromosome combining with a male gamete carrying X chromosome results in a girl child whereas a

female gamete (X) embanking with a male gamete carrying Y chromosome results in a male child.

7. Pregnancy takes place when the male and gamete fuse, and the zyote formed, gets implanted and starts

developing in the mother's uterus and grows.

NCERT Questions

8. Menstruation is elimination of the unfertilized egg along with the inner lining of the uterus. It occurs every

28 days when a girl reaches adolescence till the menopause.

9. List changes in the body that take place at puberty.

a. Increase in Height - The most visible change during puberty is the sudden increase in body height.

b. Change in Body Shape - The onset of puberty is marked by characteristic changes in body shape. In

boys, the shoulders of boys generally broaden . In girls, the region below the waist becomes wider. In

boys, the muscles of the body grow more prominently than in the girls. Thus, changes occurring in

adolescent boys and girls are different.

c. Voice Change - At puberty, the voice box or the larynx begins to grow.Boys develop larger voice

boxes than girls, Generally, girls have a high pitched voice, whereas boys have a deep voice.

d. Increased Activity of Sweat and Sebaceous Glands- During puberty the secretion of sweat glands

and sebaceous glands (oil glands) increases. Many young people get acne and pimples on the face

at this time because of the increased activity of these glands in the skin.

e. Development of Sex Organs- At puberty, male sex organs like the testes and penis develop

completely. The testes also begin to produce sperms. In girls, the ovaries enlarge and eggs begin to

mature. Also ovaries start releasing mature eggs. During this period change in Secondary Sexual

Characters results in development of breasts in girls and apperance of facial hair (moustache and

beard) boys.


f. Reaching Mental, Intellectual and Emotional Maturity - The puberty is marked by adolescence

stage, in which a person becomes more thoughtful, conscious and independent than before.

10.Teenage girls should eat around 1800 calories a day, but eating the same things each day isn't healthy.

For a balanced diet, teen girls should eat a variety of foods every day. Girls should eat foods from all food

groups each day and limit their intake of fat. No more than 35 percent of the calories a teenager eats in a

day should come from fat.

11. Increased Activity of Sweat and Sebaceous Glands- During puberty the secretion of sweat glands and

sebaceous glands (oil glands) increases. Many young people get acne and pimples on the face at this

time because of the increased activity of these glands in the skin.

Development of Sex Organs- At puberty, male sex organs like the testes and penis develop completely.

The testes also begin to produce sperms. In girls, the ovaries enlarge and eggs begin to mature. Also

ovaries start releasing mature eggs. During this period change in Secondary Sexual Characters result in

the development of breasts in girls and apperance of facial hair (moustache and beard) boys.

12.Eating well is often hard for teens. Hanging around with friends, frequenting fast food outlets and

snacking can lead to excessive intake of fat, sugar and calories and insufficient intake of important

vitamins and minerals. Adolescence is a time of increased nutrient needs. During the rapid growth of

puberty, the body has increased need for calories and key nutrients including protein, calcium, iron,

folate and zinc. Iron and calcium are particularly important nutrients for your body during adolescence.

13.a. nutrients b. thyroxine c. ductless d. deep

14.


1. During adolescence, significant changes occur at physical, emotional and intellectual levels. At physical

level, there is:

(i) Growth spurt resulting in height and weight gain.

(ii) Development of secondary sexual characteristics such as voice change and hair growth, muscular

development in boys and breast development, broadening of pelvis, etc., in girls.

(iii) At emotional and intellectual level there is:

(a) High rate of intellectual development leading one to explore and experiment with things around.

(b) High degree of independence.

(c) Emotional outbursts and responses due to the hormonal changes occurring in the body.

2. The menstrual cycle happens every 28 days. The sequences of events are (i) An egg matures in the

ovary and becomes ready for ovulation. At the same time the uterus lining thickens with blood vessels.

(ii) Ovulation occurs. (iii) The uterus lining thickens, further ready to receive the fertilized egg. (iv) The

egg that is released passes through the oviduct and reaches the uterus. (v) If no embryo is implanted, the

blood lining of the uterus breaks down and passes out of the vagina. This is called the menstrual cycle.

XX

XX XY

XY

YXXX

A ____XX Female

XX chromosomes— Female child XY chromosomes— Male child

B ____XY Male


3. Four endocrine glands are:

Pituitary gland: called as the master gland, produces growth hormones, ant diuretic hormones and the

reproductory hormones. It controls the activities of all the other endocrine glands, and hence the name

master gland. It is located at the base of the brain.

Thyroid gland: Is present at the base of the neck region and produces a hormone called thyroxine. It

controls the rate of metabolism and the rate at which glucose is used up in respiration.

Ovary: Female reproductive organs. It produces the hormones oestrogen and progesterone and

controls ovulation, secondary sexual characteristics, functions of uterus and soon.

Testes: Male reproductive organ, produces the hormone testosterone which controls sperm production

and the secondary sexual characteristics in men.

4. Insects like butterfly, moth, silkworm, etc., have a lifecycle in which they undergo metamorphosis and

pass through various stages of development. These are controlled by hormones. In frogs the thyroxine

hormone is responsible for the various stages of development. The hormones also help in moulting in

insects.

5. Adolescence is a period in which there is a sudden growth spurt and therefore the nutritional demands

are very high. The diet should contain high protein and energy foods along with sufficient quantity of

minerals and vitamins like calcium, phosphorous, iron and vitamin A, B, C and D. Since the appetite at

this stage is very large, the intake of balanced food should be insisted upon and junk food should

be avoided.

6. Addiction means getting used to ingestion of certain chemicals which leave one craving for more of it. It

then becomes difficult to remain without it. During adolescence the desire to explore and experiment

results in getting addicted to certain drugs. These drugs produce mental, physical, behavioural and

emotional changes in the user and are very harmful for the body. Nicotine, cocaine, marijuana are some

of them. The drugs sometimes are injected through needles and can spread HIV, a deadly virus among

the users. So, addiction is a curse and should be avoided at all costs.

NCERT Questions

7.

S.No. Names of Endocrine Glands Type of Hormones Secretions

1. Pituitary gland Growth Hormone & Hormone Stimutors

2. Pancreas Insulin

3. Thyoid Thyroxine

4. Adrenals Adrenalin

5. Testes Testosterone

6. ovaries Estrogen

8. The sex hormones are also known as male hormone (testosterone) and female hormone (estrogens).

These are secreted by testes and ovaries in male and female respectively. These hormones are

responsible for the male and female secondary sexual characters. Further, the sex hormones, under the

control of hormones from the pituitary gland, secrete many hormones, one of which makes ova mature in

the ovaries and sperms form in the testes.

9.

S.No Body changes in Boys Body changes in Girls

1. Broad shoulders Development of mammary glands

2. Wider chest Acne and pimples on face

3. Growth of pubic hair Development of sex organs

4. Development of muscles Growth of pubic hair

5. Growth of facial hair Wider region below waist

6. High pitched voice


10. a. controls the release of sex hormones. Pituitary gland

b. is responsible for the secondary sexual characters in boys. Testes

c. prevents diabetes Pancreas

d. maintains the correct salt balance in the blood Adrenal gland

11.

S.No Food items Major Nutrient Functions

1. Pulses and nuts Protein Growth and Maintenance

2. Oranges and amla Vitamins Repair of tissues

3. Sugar, roti Carbohydrates Providing energy

4. Oils Fat Help in keeping is warm

5. Vegetables Vitamin and Minerals Protection from diseases

12. a. a frightened person

b. growth of a child to adult

c. development of caterpillar to moth prothoracico tropic and ectozoon hormone

d. development of tadpole to frog

13. In females the reproductive phase of life begins at puberty(10 to 12 years of age) and generally lasts till

the age of approximately 45 to 50 years. the ova begin to mature with the onset of puberty. One ovum

matures and is released by one of the ovaries once in about 28 to 30 days. during this period, the wall of

the uterus becomes thick so as to receive the egg, in case it is fertilised and begins to develop. This

results in pregnancy. If fertilisation does not occur, the released egg and the thickened lining of the uterus

along with its blood vessels are shed off. This causes bleeding in women which are called menstruation.

14. Boys at the age of puberty develop secondary sexual characters like Adam's apple. John is a growing up

boy so he has developed Adam's apple.

15. a. First line b. Second line

c. After the age of 8 years, the height of girls outpaces the height of boys till the age of 12 years. After

age of 12 years, the height of boys increases at slightly faster rate and becomes almost equal to that

of girls at 16th year. After 16th year, the boys continued to grow more in height till the age of 20 years.

d. This pattern may be more or less true for each individual

16. Sweat and oil glands become active leading to body odour and oily skin. This bring along the problems

like acne and pimples.

Endocrine Glands and their location

Pituitary

Thyroid

AdrenalPancreas

Ovaries (females only)

Testes (males only)

17. In our country the legal age for marriage is 18 years for girls and 21 years for boys. This is because

teenage mothers are not prepared mentally or physically for motherhood. Early marriage and

motherhood cause health problems in the mother and the child. It also curtails employment opportunities

for the young woman and it may cause mental agony as she is not ready for responsibilities of

motherhood.

I. Give reasons.

1. The master gland of the human body is the pituitary gland located in the brain. This is because it secretes

hormones that operate the endocrine system, which comprises of the thyroid gland, gonads and adrenal

glands. The hypothalamus regulates the pituitary gland.

2. Pelvic area broadens to prepare the body for carrying baby in the womb in future.

3. During puberty the secretion of sweat glands and sebaceous glands (oil glands) increases. Many young

people get acne and pimples on the face at this time because of the increased activity of these glands in

the skin. So, it is advisable that teens should have a balanced diet.

NCERT Questions

4. Adolescence is a period of much activity in the body and mind which is normal part of growing up. So,

kids feel confused or insecure. If anybody suggests that take this drug to get relief, just say no unless

prescribed by the doctor. Drugs are addictive. If taken you may feel like taking them again and again.

They harm the body in the long run. They ruin health and happiness.

J. HOTS questions.

1. In adolescence, the larynx or the voice box of the boys becomes larger resulting in voice change. The

voice becomes deeper and hoarse. Sometimes the larynx can protrude out and is called the Adam's

apple. This is one of the secondary sexual characteristics brought about due to the reproductive

hormone.


Chapter- 11 : Force and Pressure





1. a. v b. iv c. i d. iii e. ii


E. Name them.

1. Force 2. Force of friction 3. Mass 4. Pressure



1. contact 2. motion 3. opposite 4. direction

5. opposite, like 6. force/area 7. pascal 8. high heeled

9. depth 10. salt 11. Fluids 12. decrease

13. pressure 14. transmitted equally 15. Liquids,gases 16. Barometer

17. area 18. 760mm 19. gravitational force 20. gravitational force

21. iron and steel

NCERT Questions

22. pull 23. attracts 24. push 25. repels

1. False 2. True 3. True 4. False 5. False

6. True 7. True 8. False 9. True 10. True

1. d 2. c 3. d 4. d 5. a 6. d 7. a 8. b 9. d 10. c

NCERT Questions

11. a 12. c 13. c 14. a 15. c 16. c 17. c 18. a

1. a. Force causes rate of change of motion.

b. Changing the size and shape.

c. Changing the direction of motion.

d. Stopping a moving object.

e. Change in shape is caused.

2. Anything that causes change in the position, shape, size and form of an object can be called a force.

3. Opening a door, hammering a nail on the wall are examples of contact forces.

4. GEM stands for the three non-contact forces. They are :

G – Gravitational force E – Electrostatic force M – Magnetic force

5. When two forces of equal magnitude are acting in opposite direction, the forces get cancelled. The net

force will be the difference in the magnitude of the two forces.

6. Electrostatic force refers to the attraction or repulsion that exists between two charged bodies.

7. Gravitational force and magnetic force are non-contact forces.

8. Opposite poles of a magnet attract and like poles repel. Similarly, opposite charges attract and similar

charges repel.

9. Force applied in direction opposite to the direction of motion of an object can cause change in direction at

times.

10. North pole of a magnet is attracted towards the south pole because of the magnetic field that is present

around a magnet.



11. A ball that is hit will start moving from stationary position or will either change direction or move faster if

already in motion.

NCERT Questions

15. We apply

1. a. Force: Any push or pull which can cause disturbance in the position, form, shape or size of an object.

b. Gravitational force: The force that exists between the earth and the object is gravitational force. It

also exists between all the heavenly bodies.

c. Magnetic force: Force exerted by a magnet on another magnet or other magnetic substances is

called magnetic force.

2. A rubbed ruler develops charges in the process of rubbing. Therefore it is able to attract bits of paper

which is neutral.

3. When two forces act on an object from the same direction, they get added and the net force is the sum of

the two forces.

F1 + F2 = net force

4. Effects of force:

(i) Force can move a stationary object.

(ii) Force can stop a moving object.

(iii) Force can change the direction of an object.

(iv) Force can change the shape or size of an object.

(v) Force can change the speed of a moving object. It can make it faster or slower in motion.

5. No. When two forces act in the same direction, they get added as the net force. So, the net force

increases. When the same two forces act in the opposite direction, the forces cancel each other and the

net force is the difference between the magnitude of the two forces.

6. A sharp nail is easier to hammer since it exerts more pressure due to smaller area in contact.

7. The larger the area on which the force acts, the less is the pressure. Conversely the smaller the area, the

larger will be the pressure.

8. In fluids, pressure increases with depth. The maximum pressure is exerted at the base of a container

containing a fluid.

9. The pressure exerted by the column of air surrounding the earth on the surface is called atmospheric

pressure.

10. Our bodies exert force equal to what atmosphere exerts on us in the opposite direction. Therefore, we

don't feel the effect of it.

12. a. A goalkeeper saving a goal.

b. Hockey player flicking a ball.

13. a. A lump of dough on a plate.

b. A rubber band suspended from a hook.

14. Contact force-muscular force is applied on the dough to make chapattis.

16. Her friend should also apply force in the same direction to make it move faster.

17. Electrostatic force.

18. Electromagnetic force.

19. Gravitational pull.

20. Yes.

21. The upward force acting on it is larger than the gravitational force.

22. No, the gravity is zero in space.


frictional force which is always opposite to the direction of force applied.


NCERT Questions

11. (a) shape (b) muscular (c) contact (d) gravity, friction

12.

13. The force due to hammering changes the shape of the piece of iron.

14. The force which is responsible for the attraction between the ball and the wall is electrostatic force. When

we rub the balloon by a synthetic cloth, it gets charged. When it is taken near the wall, it will get attracted

towards the uncharged wall because of the electrostatic force which is the force exerted by a charged

body on another uncharged body.

15. The force acting on a plastic bucket containing water held above the ground level are :

a. Gravitational force: It is acting downwards.

b. Muscular force: It is applied by our hands to lift the bucket in upward direction.

Although these forces are acting on the bucket but no change is found in its state of motion because the

forces are balancing each other and as a result net force becomes zero.

16. Two forces acting on the rocket immediately after leaving the launching pad are:

a. Frictional force due to air.

b. Force of gravity pulling in downward direction.

17. Atmospheric pressure.

18. Muscular force.

19. They are both applying equal amount of force.

20. Two thermocol balls are attached together with electrostatic force, they can be separated when the

electrostatic force is decreased.

21. The force which occurs by interacting between two objects is frictional force.

22. The cart will stop only if it is pushed from the opposite direction by a greater force.

23. Gravitational pull is responsible for bringing down the man, while the friction in the air is pulling him

down, with the parachute it add more friction slowing him down because air resistance works against

very large area of the parachute. While gravity is pulling the man 32 ft/sec the cat of pushing air out of the

way slows his progress down towards the ground. A free falling skydiver that has not yet opened his

parachute can make his downward speed vary between about 110 mph 225 mph using air pressure.

24. Magnetic force is acting on the car. The magnet forms an area of attraction around itself, called magnetic

field, which attracts magnetic objects without any direct contact.


1. Pressure is the force acting per unit area. Pressure, force and area are related to one another. Force

applied on a small area creates more pressure, while the same force applied on a larger area create less

pressure. So, pressure mainly depends on the area at which the force is applied.

S.No.

1.

2.

3.

4.

Squeezing a piece of lemon between the fingers to extract its juice.

Taking out paste from a toothpaste tube.

A load suspended from a spring while its other end is on a hook fixed to a wall.

An athlete making a high jump to clear the bar at a certain height.

Fingers

athlete

load

Fingers

Situation Agent

lemon

athlete's body

spring

Object

toothpaste tube

The effect of the force is that the juice is extracted from the lemon.

Object

The effect of the force is that the tootpaste is coming out from the tube.

The effect of the force is that the spring expands as the other end is one a hook fixed to a wall.

The effect of the body is that the athlete will jump on the other side of the bar at a certain height.


2. Pressure needs to be reduced for comfort in many instances. For example, flat soled shoes are more

comfortable to wear since the pressure exerted on the ground is less whereas shoes with pointed heels

exert higher pressure. All cutting tools like knives, scissors, etc., should have sharp edges to

accomplish the task more efficiently since they exert more pressure.

3. The force exerted by the air column above the earth per unit area is known as atmospheric pressure. The

column of air reduces as the altitude increases and so at higher altitudes the air pressure experienced is

very less. The atmospheric pressure is maximum at the sea level and reduces as the altitude increases.

4. Take an empty can with lid. Pour some water and let it boil till steam escapes. After a while fix the lid

tightly. Dip it in a tub of ice cold water. The can immediately gets crushed. When the steam escapes from

the tin, air inside the tin is driven out. So, when cold water is poured steam condenses creating a partial

vacuum. The pressure is higher outside the can and so the air rushes and exerts pressure on all sides of

the can, crushing it.

5. Pressure exerted by fluids increases with depth. Take an empty plastic water bottle, a sharp tipped nail to

pierce. With the help of the nail punch holes at four different levels in the bottle one below the other.

Place the bath in a tray and fill it with water watch how water, flows out of each hole. We can see that

water flowing out of the bottommost hole covers the longest horizontal distance and water flowing out of

the top most hole covers the smallest horizontal distance. It proves that at the base of the bottle, water

has the highest pressure. So, the pressure exerted by fluids increases with depth.

NCERT Questions

6. The muscular force makes arrow to more for word horizontally. In the air the arrow faces. Air friction and

constant gravitational pull. So, gradually the arrow looses its motion and falls down on the earth due to

the gravitational pull.

7. When a force acts on a large area, it spreads across the entire area, while reducing the area helps to

concentrate the force on smaller area. That is why is difficult to cut with a blunt scissor as it requires more

force and energy.

8. A lady wearing high heeled shoes exerts greater pressure on the ground than if she wears flat soled

shoes. All the pressure acting on a smaller area produces larger pressure. So, the lady with high heeled

shoes will find it difficult to walk on a sandy beach.

9. Bursting an inflated balloon with finger requires more effort than with a needle. The difference is because

of the area (in this case the pointed needle) on which the applied force is acting. When a force acts on a

large area it spreads across the entire area, while reducing the area helps to concentrate the force on a

smaller area, so with a needle smaller effort can create greater force.

10. B will sink more in the sand as the area is smaller so it will put a large amount of force on the sand.

11. 60 ml>50ml>300ml>500ml.The 60 ml will have the highest pressure. This is because the more wider the

container for keeping water the lesser the pressure at the base. The water exerts pressure at the base

so it increases with the amount of water above it.

I. Give reasons.

1. A blunt knife has larger surface area than the sharp one. Hence the force applied will have its effect on

larger area causing it difficult to cut vegetables. When there is larger surface area the pressure exerted is

less and when surface area is small the pressure exerted is more.

2. Every magnetic substance has its own magnetic field depending on its pole strength in which its effect

can be experienced.

3. Tanks weigh 40 + tons; If they used wheels they would often get stuck. They use caterpillar tracks

because they are quieter and have better grip. Battle tanks use tracks to spread their weight on soft

ground this prevents the sinking of land under the weight of the tank.

4. As there is less friction on the muddy road it is difficult to walk on it. Water reduces the friction of the soil.

5. Ski boards are flat and long to have larger surface area on which the force is distributed and so pressure

will reduce.

6. At high altitudes, the air pressure is less in comparison to the pressure exerted by the body, which is

more and so the blood capillaries break to cause nose bleeding.

7. The base and walls of the dams should be thick because the maximum pressure of water is exerted on

the base. The water stored in the reservoirs will exert equal pressure on all sides too. So, to safeguard

the reservoirs and dams from breaking, they should be built with strong thick walls.

8. Space is devoid of air and so one doesn't experience any air pressure there. But body fluids will exert

pressure from inside and so the blood vessels can burst and cause extreme bleeding. To avoid this,

special space suits are essential.

9. Aeroplanes fly at very high altitudes air pressure is very low. Is devoid of the differential pressure

between the human body and the atmosphere, the air cabins are pressed and maintained at normal

atmospheric pressure.

J. HOTS questions.

1. There is always frictional forces which act by themselves will slow down the body.

F = ma. Taking this into account even if we say that a acceleration is zero even then the net force applied

to the object of mass m. It is often that two or more balancing forces are applied which cancel each other.

The same situation can be observed in an aeroplane where the aircraft may accelerate until the drag

caused by pushing through the air, trying to slow the aircraft exactly balances the force from the engine

resulting in a settled and steady speed. This stable speed denotes zero acceleration by definition. A

body in uniform motion has no net force acting on it that means that either there are no force at all or else

that all the force acting on it add up to zero.



Chapter- 12 : Friction



1. rolling 2. static 3. friction 4. heat

5. fluid 6. drag 7. reduce 8. lubricant

9. frictional force 10. contact

NCERT Questions

11. motion 12. roughness 13. heat 14. reduces

15. less than



6. False 7. True 8. True


1. a. iii b. iv c. i d. v e. ii


1. c 2. a 3. d 4. c 5. c 6. a 7. c 8. d 9. d 10. b

NCERT Questions

11. c 12. a 13. a 14. a 15. a 16. c 17. c 18. d 19. d 20. d

E. Name them.

1. Static friction 2. Lubricant 3. Ball bearings 4. Friction



1. Pendulum comes to rest after many oscillations due to the resistance offered by air.

2. The friction experienced by a stationary object is called static friction.

3. Sliding friction is higher than rolling friction.

4. Invention of wheel is a major achievement because it gave us a tool with which friction could be reduced

drastically.

5. Soapy water reduces friction by forming a smooth layer over the hand and soil becomes very difficult to

have a grip on the tap.

6. Tyres wear out sooner on rough surfaces.

7. Rubbing our palms produces heat. The friction between the palms is responsible for the heat and so we

feel warm.

8. Lubricants are those which smoothen out the roughness of a surface and help to reduce friction.

9. Drag is the friction experienced by objects moving in air or water.

10. Skid free floors provide friction which will make them less slippery and it is safer to use them.

NCERT Questions

11. The block with 2 units would require a larger force to move it from the rest position.

12. No the box will not experience any force of friction.

13. The raindrops will stick to the window as the force of friction is working on them.

14. Yes, the air also has friction.


1. Friction is the force that opposes motion.


2. The force of friction depends on:

(i) The weight of the body. (ii) The nature of surfaces in contact.

3. Striking a matchstick – Friction is useful.

Peddling bicycle – Friction is harmful.

Application of brakes – Friction is useful in moving car.

Driving a nail into the wall – Friction is useful.

Dragging a suitcase – Friction is harmful on the ground.

4. Two undesirable effects of friction are:

(i) Friction produces heat.

(ii) Friction causes wear and tear.

5. Objects moving in air or water like airplanes and ships face resistance from them. This can be termed as

fluid friction.

6. It is the friction between the nail and the wall or furniture that helps to hold the nail.

7. Sand paper is rough and so it helps to engage in between the surface irregularities and even out while

we rub it back and forth on a surface.

8. An eraser is able to take off a very thin layer of the written part (pencil lead) due to the friction between the

paper and itself. So, we get the paper cleaned out.

9. Certain pens are more comfortable to hold because of a firm grip they provide between our fingers and

the surface of the pen.

NCERT Questions

10. When the writing desk is tilted a little, the book kept on, due to force of gravity acting on it in the downward

direction, starts sliding down, The direction of frictional force acting on it will be opposite to that of sliding

motion of book or the force of gravity acting on it i.e. upward ;

11. We know that for a comfortable walk on some surface, we need force of friction. A marble floor has

already very smooth surface and exerts comparatively less frictional force. The soapy water spilled on

the marble floor will further decrease the frictional force it may offer. Therefore, it would make more

difficult for anyone to walk on the floor.

12. In case of the heavier box, the surface of heavier box will be pressed harder against the floor surface,

than lighter box. Therefore, force offered by the heavier box due to static friction will be more, hence

Seema has to apply a larger force.


13. Yes, there is friction between the train wheel and the rail. Air cushions will slow down the speed of

the train.

14. Deteriotion of cartilage results in osteoarthritis. The pits and cracks in the cartilage deepen and cause

large areas to deteriorate and wear away completely. This allows the 2 bone surfaces to rub together.

With time, these surfaces become smooth and polished from the constant grating upon each other. The

bones lose their ability to fit smoothly together, which keeps them from moving easily. The joint begins to

lose its normal shape, and the space between the joint narrows causing difficulty in moving.

15. Preeti should rub her hands on limestone powder or soil to get that extra grip and for increasing the

friction.

16. The roughness increases friction and helps the player in getting the grip for the game.

17. The surface of mortar and pestle (silbatta) used for grinding is etched to increase the friction so that the

masalas can be ground properly and finely.

18. a. On a silk cloth the marble will move smoothly.

b. It will be difficult for a marble to move on a sand as the friction is high, it can sink into the sand.

c. On a glass sheet also it can move smoothly as the friction is very less.

19. We know that the friction is caused by the interlocking of irregularities in the two surfaces. For an object

sliding on some surface, the contact points on its surface, do not get enough time to lock into the contact

points on the other surface. So, the sliding friction is less than the static friction. That is why we require

less force on a moving car than when it was standing.


1. Friction can be increased by (i) Increasing the roughness of a surface. For e.g., skid free tiles are

purposely made rough to avoid slipping or over speeding. (ii) Friction can be increased by providing

grooves in car tyres and shoe soles in order to prevent them from sliding smoothly.

2. Friction is caused by irregularities present on a surface. When two surfaces move past each other,

getting interlocked at various ridges and grooves, they control each other's motion. This is friction. When

we smear oil on a surface, the particles of oil get into the grooves and fill up the irregularities. This helps

smoothen out a surface.

3. Ball bearings are small metal balls which are free to roll, placed between moving parts of machines as in

a bicycle wheel. They reduce friction enormously and enable smooth and efficient functioning of

machines.

4. Grooves in the tyres of vehicles allow the cars to stay on road and makes it possible to drive. They

provide enough friction to keep the vehicles balanced. If tyres were perfectly smooth and so also the

roads, the vehicles would keep moving even when the driver attempted to stop it. That would be very

dangerous.

5. When we suddenly apply brakes in a moving car, the tyres that are rolling suddenly come to a halt

increasing the friction between the road and the tyres. The rubbing of the surface with lot of friction

produces the screeching noise.

NCERT Questions

6. We know that the friction is caused by the interlocking of irregularities in the two surfaces. For an object

sliding on some surface, the contact points on its surface, do not get enough time to lock into the contact

points on the other surface. So, the sliding friction is less than the static friction .

7. Friction as a friend:

1. It helps in normal walking.

2. It helps in smooth driving, breaking and steering of Vehicles.

3. It helps in pulling of weight using rope and pulleys.


4. It is must for building construction, without friction no building could be constructed.

5. Friction helps in, producing a fire by stricking a match stick.

Friction as a foe:

1. It wears out almost every materials of general use in daily life, which may include domestic

appliances, shoes, cloths, stationary or any machine.

2. It produces heat. When a machine is operated, heat generated causes much wastage of energy.

3. Some times, it may require additional arrangements to minimise friction for better efficiency through

application of lubricants, ball bearings, special coating, or suitable shapes etc., hence cause extra

cost.

4. It increases over all cost of transportation in deserts, water or air.

5. A lot of slip injuries occur on a wet or icy surface.

8. When objects move through fluids such as air or water, they have to overcome fluid friction acting on

them. In this process they lose energy and overall efficiency decreases. In order to save the energy,

being wasted against fluid friction, objects moving in fluids, are modified and given special shapes. Such

modified shapes which are also known as streamlined shapes or aerodynamic shapes help in reducing

fluid friction to a greater extent.

9. Heat caused by the friction that is created when the knife is rubbed on the stone. This is the reason for

the sparks.

10. An ultra-fine grade of sandpaper (1200 to 3000 grit) if rubbed will create more friction on the surface of

metal the ordinary paper will not have any effect on the metal. So, the metal rubbed with sand paper

will shine.

11. Smooth surfaces are surfaces that have less contact with things touching them and thus have less

friction. Less friction means there are fewer contact points to stop the motion. So, we keep slipping on a

smooth rickshaw seat.

12. Wheels reduce friction. Real friction we have to work against is between the four wheels and their axles.

So, it is easier to push the heavy load.

I. Give reasons.

1. The amount of traction which can be obtained for an auto tire is determined by the coefficient of still

resistance amongst the tire and the road. The force of friction is strong-minded by the constant of kinetic

resistance and is usually significantly less. In gliding resistance, an object is dragged over the ground,

and the object is therefore moving in relation to the ground. The surface area of the underside of the

object is in constant contact and motion with respect to the ground, and it is this underside surface

dragging along the ground that creates the friction.

2. Friction is always more on a rough surface compared to a smooth surface. This is because rough

surface offers more resistance to the movement of an object over it compared to a smooth surface.

3. Because oil is a lubricant which reduces friction between our hands and glass.

NCERT Questions

4. The sportsmen use shoes with spikes, to increase the force of friction between the ground and shoe.

Increased force of friction makes the grip of shoe with ground, very strong. This prevent sportsman from

slipping or skidding during play and also helps in proper application of muscular force.

5. When the tread on the soles or the soles of new shoes themselves start to wear out, shoes can become

slippery as the friction becomes less so tend to slip. So, the slippers with a rubber sole become slippery

when used for a long time.

J. HOTS questions.

1. Friction is very much needed in certain surfaces and instances to protect us whereas it is undesirable in

certain places. We all know that friction is very important for us to keep our balance on earth. A

frictionless surface will never be able to let us walk. We'll keep slipping as we do on a slab of ice. Friction

is necessary for good grip while we want to climb rocks, play on a monkey bar, work with tools, and write

with a pen and so on. Even a sweaty hand will make these tasks uncomfortable. On the other hand,

friction between machine parts results in energy wastage. It heats up the parts, causes wear and tear

and leads to inefficiency. So, friction is a force we use in certain areas and can best be avoided in certain

other areas.

2. Ice surface will have very little friction because it is very smooth. It is very easy to skid and fall on ice we

can't hope to walk on it without falling a few times. Sand will offer a very large amount of friction. So,

walking on sand is very tough since a lot of effort is used up in overcoming the friction between the legs

and sand. Ice offers too little friction whereas sand offers a lot of friction. Both are difficult for motion.

3. In rainy season the roads are wet. The presence of water on roads reduces friction. The tyres of vehicles

also get water entering in the grooves. As a result, it takes longer time for the vehicle to come to a stop

after the brakes are applied. Therefore it is advisable to avoid high speed driving during rainy season.



Chapter- 13 : Sound



1. hertz 2. louder 3. frequency 4. pitch

5. Bats, elephants 6. ultrasonic 7. auditory nerve 8. tympanic membrane

9. vibrations 10. solids 11. larynx 12. shorter

13. vacuum 14. sonorous 15. wave 16. different

17. 20,000hz 18. medium

NCERT Questions

19. time period 20. amplitude 21. hertz 22. noise pollution

23. frequency


1. False 2. False 3. True 4. False 5. False

6. True

NCERT Questions


12. False 13. True


1. a. iii b. iv c. i d. ii


1. a 2. d 3. c 4. c 5. b 6. d 7. a 8. d 9. d 10. c

NCERT Questions

11. d 12. c 13. c 14. a 15. a 16. a 17. c 18. a 19. a 20. c

21. a 22. c

E. Name them.

1. Sound 2. Waves 3. Frequency 4. Noise 5. Larynx



1. (i) Musical instruments like sitar and flute.

(ii) A temple bell.

(iii) Cymbals

(iv) A whistle.

2. A vibration is the disturbance causing to and fro motion in an object.

3. The larynx or the voice box is the human organ producing sound.

4. The external ear, middle ear and the inner ear.

5. 20 Hz is the lowest frequency of human hearing range.

6. Inserting sharp objects into the ears causes damage to the tympanic membrane.

7. A medium is particulate matter like solid, liquid or gas through which sound can travel.

8. The number of vibrations produced per second by a body is called its frequency.


NCERT Questions

9. (a) Dholak: Dholak has stretched membranes which vibrate (to and fro) to produce sound.

(b) Sitar: A sitar is a musical instrument which has stretched strings. When these strings vibrate, they

produce sound.

(c) Flute: A flute is a wind or reed musical instrument which uses air column to produce sound.

10. d = vt , 330m/s X 5sec =1.6 km.

11. Vocal chords vibrate when we talk.

12. Since light travels faster than sound we see the cracker burning first and then listen to the sound.

13. Ektara, Violin.


1. Amplitude refers to the extent of displacement of a vibrating body.

2. The number of oscillations made by a body in one second is called frequency. It's unit is Hertz (Hz).

3. The higher the frequency, the higher the pitch.

4. The speed of sound is influenced by temperature, physical state of matter and nature of the material.

5. Ultrasonic means sound frequencies above 20,000 Hz.

6. Audible sounds are sound frequencies that the human ear can pick up. They are between 20Hz –

20,000Hz. Inaudible sounds are sound frequencies below 20Hz and above 20,000 Hz.

7. Noise pollution refers to the presence of unwanted disturbing sounds in the environment which cause

health problems. Examples of such sound are vehicular traffic, loud music over public address systems,

landing and taking off of aircrafts.

NCERT Questions

8. Frequency is the number of oscillations per second of a vibrating body.

It is denoted as:

Frequency of oscillations is defined as the number of oscillations of a vibrating body in one second. It is

given by Frequency = number of oscillations/total time taken

= 40/4 Hz

= 10 Hz

The time taken to complete one oscillation (to and fro) is known as time period.

Time period = 1/frequency of oscillation

= 1/10 sec

= 0.1 sec (...Answer)

9. The time taken to complete one oscillation (to and fro) is known as time period.

Time period = 1/frequency of oscillation

= 1/500 sec

= 0.002 sec

10. Some sources of noise pollution are:

• loud-speakers.

• honking of horns.

• sound of machines.

• loud music.

• loud volume of television.


• sound of shooting of gun.

• sound of fire-crackers.

11. Time taken by the particle

10. Period =

Time taken /Number of oscillations made by the particle

= = 2 S

Frequency = 1/ 2 = 0.5Hz.

12. Every vibrating object does not produce sound that we can hear. It is because the human ear can only

pick up vibrations between 20 Hz and 20,000 Hz. So, any frequency below 20 hz(infrasonic) or beyond

20,000Hz (ultra sonic)are not heard by us.

13. If we a stick is struck against a frying pan in vacuum, sound is made but sound needs a medium to travel.

So, we cannot hear the sound.

14. Astronauts use radios as there is no air. Air is used to travel sound waves. Without air the astronauts are

not able to hear each other.

15. 1. Loudspeaker at religious functions.

2. Loudspeakers at wedding ceremonies.

3. Construction work in neighbourhood.


1. Unwanted, disturbing and annoying sounds in the environment is called noise pollution. It is responsible

for a number of ailments like hypertension, impaired hearing, sleeplessness, heart ailments, etc. The

noise in our environment is due to excessive use of machinery, vehicles, honking on roads, loud public

address systems on festival days and public meeting. With regulations in place these can be minimized.

2. In our surrounding, we can reduce the noise level by adopting the following measures:

(i) Do not honk unnecessarily.

(ii) Play your T V, radio, music system, etc., at a low volume.

(iii) Make sure that your vehicles are fitted with silencers.

(iv) Noise creating industries should be moved away from dense residential areas.

(v) Partying and celebrating festivals with loud music and entertainment late at night should be avoided.

(vi) Government regulations should be strictly adhered to.

3. Sound needs a medium to travel. Choose a cardboard box and fix a transparent glass or polythene on

one side. The box should be connected to a vacuum pump through a tiny opening on one of the sides.

Choose an alarm clock, set the alarm and place it inside the box. Start the vacuum pump when the alarm

starts ringing. Slowly you'll hear the sound turning faint as air is pumped out.

NCERT Questions

4. The noise pollution is harmful to humans in many ways as it may cause :

1. Lack of sleep.

2. Hypertension (high blood pressure).

3. Anxiety.

4. Mood Disorders leading to depression.

5. Temporary or even permanent impairment of hearing.

20

10


5. In humans, the sound is produced by the voice box or the larynx. It is a hard bump like structure deep

inside the throat, located at the upper end of the windpipe. Two vocal cords are stretched across the

voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air. When

the lungs force air through the slit, the vocal cords vibrate, producing sound. Muscles attached to the

vocal cords can make the cords tight or loose. When the vocal cords are tight and thin, the type or quality

of voice is different.

6. The light travels at a speed of 300000000 m/s where as sound travels at a speed of 340 m/s.

Due to this reason, at the event of a lightening and thunder, taking place in the sky at the same time and

at the same distance from us, lightning is seen earlier and thunder is heard later .

7. Speed of sound is 330 m/s and speed of light is 300,000,000 m/s. Therefore light travels much faster

than sound and is seen earlier.

8. Sound is produced by vibrations. These vibrations are transferred to the nerves in the inner ear. The

nerves carry the messages to the brain, enabling us to interpret the sounds that we hear.

9. The person standing nearby will not hear any sound as sound needs a medium to travel.

10. Sound needs medium to pass through. In night less opposition is offered as compared to day time. At

night there is less activity then in the daytime. Everything has calmed down at night including you. You

aren't deeply involved something which allows you to be more aware of your surroundings.

Vocal Cords

Trachea(Wind Pipe)

Epiglottis

Cartilage

Sketch of the Larynx or Voice Box

Speed of Light = 300000000 m/s

Speed of Sound = 340 m/s

At the event of a lightening adn thunder, at

the some time and distance from us, lightning

is seen earlier and thunder is heard later

11. To reduce the noise in locality :

• We should grow trees along road sides.

• We should make sure that our vehicles are fitted with silencers.

• Playing loud music at public address system should be discouraged.

I. Give reasons.

1. When we touch the prong of a tuning fork, we stop its vibrations therefore the sound stops.

2. A pendulum swings with a frequency below 20 Hz. That is why the sound is not picked up by human ear,

and we do not hear it.

3. There is no air beyond earth's atmosphere. Therefore, the sounds from there can't be transmitted to

the earth.

4. When we bang a door, the extent of displacement is more. Since the amplitude is more the sound

is louder.

5. Music is rhythmic sound, and is therefore pleasant. Vehicular traffic produces vibrations which are

irregular with a mixture of different amplitudes frequencies. Therefore, it is unpleasant.

J. HOTS questions.

1. Ear has a very delicate membrane at the end of the ear canal called the tympanic membrane. This is

responsible for transmitting sound frequencies into the inner ear. Inserting sharp objects will result in

puncturing the membrane. It will cause deafness.

2. Sound travels in air at the speed of 364 m/sec whereas the train travels at a speed less than this.

Therefore, sound reaches earlier before the actual train.



Chapter- 14 : Chemical Effects of Electricity




1. False 2. False 3. False 4. True 5. False


Insulator – Rubber, plastics, dry air, cotton, ebonite.

Conductor – Silver, aluminium, acids, moist air, brass.


1. d 2. d 3. a 4. b 5. c 6. b 7. a 8. a

9. a 10. d

NCERT Questions

11. a 12. d 13. a 14. d 15. a 16. d 17. b 18. d

E. Name them.

1. Electrolyte 2. Good electrolyte 3. Cathodes 4. Anodes 5. Electroplating



1. (i) Ion: An atom which carries a charge either by gaining electrons or losing electrons.

(ii) Insulator: A material which is a poor conductor of electricity.

(iii) Electrolysis: The process of splitting a chemical solution into its component chemicals.

(iv) Electroplating: The process of coating a metal over another for improving its properties, using the

process of electrolysis.

(v) Electrolyte: A solution capable of conducting electric current.

2. Common salt breaks into sodium ions and chloride ions during electrolysis of its solution. NaCl= Na + Cl.

3. Anode is the electrode connected to the positive terminal of a battery.

4. An electric circuit has a source of electricity (battery) and conducting wires.

5. Electrolysis of water gives hydrogen and oxygen.

6. Chemical effect of electric current refers to the chemical change that can be caused due to electricity.

7. Electroplating car parts which are generally made up of steel helps to prevent corrosion as well as gives

them a shiny and rich look.

8. A neutral atom is that which has equal number of protons and electrons.

9. Charged ions are attracted towards the oppositely charged terminals during electrolysis. Positives ions

move towards cathode (–ve) and negative ions move towards anode (+ve).

10. Zinc is coated on iron because iron can rust and corrode. Zinc is a metal which does not react with

atmospheric agents. So, it is used to coat iron to increase iron's durability.

11. Electroplating is used in coating silver articles with gold to make it look more expensive.

1. circuit 2. protons and electrons 3. positively, ion 4. anion, negatively

5. NaCl 6. Positively 7. Chemical

8. acids, bases and salts 9. Chemical 10. electricity 11. Salt

12. Zinc 13. Cations 14. Hydrogen, oxygen 15. Negative

16. Cathode 17. Ions

NCERT Questions

18. acids, bases and salts 19. chemical 20. negative 21. electroplating

22. cathode 23. electroplating 24. good conductor 25. chromium


NCERT Questions

12. Pure water will conduct a very small amount of electricity due to the self ionisation of water. In pure water,

a very small amount of H O molecules will split into H+ and OH- ions. These are free moving charged 2

particles and will hence allow electricity to be conducted. On the whole though, the conductivity of pure

water is so low that it is essentially an insulator.

13. Zinc coatings for iron and steel provide excellent corrosion resistance.

14. Pure water does not conduct electricity very well. However, when certain substances are dissolved in

water, the solution does conduct electricity. Sugar as a non electrolyte substance does not produce ions

when dissolved in water. A solution of sugar contains molecules of sucrose, but no ions. The absence of

ions in a sugar aqueous solution makes it a non electricity conductor fluid.

15. When we close the circuit, the electric field is set up in the entire closed circuit instantly with the speed of

electromagnetic wave which causes electron drift at every portion of the circuit. Due to it, the current is

set up in the entire circuit instantly.


1. An electric circuit is a continuous pathway of electric current. It has components like a source of

electricity (battery), connecting wires, a key or switch and components which convert the electrical

energy to other usable forms like a bulb, fan, TV, etc.

2. Conductivity of a metal is due to the presence of free electrons which can flow. No chemical change

occurs in an electrolyte. The conductivity is due to ionization of the components which in turn help in the

flow of electrons. A chemical change helps in conductivity.

3. Electrolysis of water gives rise to hydrogen gas at the cathode and oxygen gas at the anode.

4. Major uses of electrolysis are :

(i) In separation of components of a salt

(ii) To make hydrogen from water

(iii) In electroplating

(iv) In refining impure metals

(v) In extraction of certain metals like aluminium from its ore.

5. Anode – The electrode is connected to the positive terminal of a battery. It attracts negatively charged ions.

Cathode – The electrode connected to the negative terminal of a battery. It attracts positively charged ions.

6. When current passes through an electrolyte, a chemical change occurs. The electrolyte breaks up into

ions (charged particles). For example, sodium chloride breaks into sodium ions (Na ) and chlorine ions

(Cl ). Since ions are charged they conduct electricity very easily.

7. Commonly used metals in electroplating are:

(a) Zinc – Used for galvanizing iron to stop corrosion of iron.

(b) Silver – Used for coating inferior metals to give it a rich and expensive look.

NCERT Questions

8. Lemon juice, Vinegar, Common Salt Solution.

9. • The Liquid is either bad or poor conductor of electricity.

• The connections are loose.

• The bulb is fused.

• The cells being old or used up, are not producing electric current.

10. We know that pure water is a poor conductor of electric current. The presence of some impurities in the

form of some salt or acid, turns it to a good conductor. The seawater and the drinking water both contains

salt impurities dissolved in them. The salt concentration in seawater is much more as compare to the

normal drinking water. The presence of excess of salt in seawater makes it as better conductor of

electricity than drinking water. Thus, the child testing the the drinking water and the seawater, finds

compass needle deflecting more in the case of seawater, due to excess flow of current in the tester.


11. Impure Copper plate should be connected to positive terminal. Pure copper plate should be connected

to negative terminal of electrode. Copper ions are positively charged and will attract to negative

electrode terminal.

12. When two resistances (or loads like bulb) are connected in parallel there resistance decreases, and in

series it increase. Eg: if two 5 ohm resistances are connected 1) in series it becomes= R1+R2=10 ohms

2)Parallel it becomes(R1*R2 )/(R1+R2) = 25/10 = 2.5ohms that means resistance decreases in parallel

combination and increases in series combination. So, lower the resistance higher will be the current and

vice-versa ( V=IR where V is constant). Since the voltage is constant bulbs in parallel combination will

get more current and bulbs in series combination will get less current. Hence bulbs connected in parallel

will glow brighter than those bulbs which are connected in series.

13. LED stands for light emitting diodes which consume very less current. In fact they can be damaged by

large currents. So, if LED is glowing that means the Liquid B is not a strong electrolyte, as LED glows

even when the solution is a weak electrolyte.

14. Spoon should be connected as cathode and a silver bar is the anode. During electrolysis positively

charged silver ions move to the spoon and deposit over it.

15. Cans in which food items are sold in the market are iron coated with a layer of tin. Tin is not very reactive

and so the food does not undergo any change.

16. Greenish spot developed in the potato is always connected to the positive terminal. The current produce

a chemical effect in the potato. So the set up A is correct.

17. In circuits B and D the bulb will glow as iron nail and steel spoon are good conductors of electricity but

coal and eraser are bad conductors of electricity so the bulb will not glow.


1. Flow of current takes place when electrons flow from a point when they are in excess to a point where

they are in deficit. For the electrons to flow a conducting pathway is a must.

2. Purification of copper is done by electrolysis.

The electrolyte used – Copper sulphate

The anode – Impure copper

The cathode – Pure copper. The anode and cathode are connected to a source of electricity. When the

current is passed, the electrolyte CuSO ionizes to Cu and So ions. Copper ions move towards the 4 2 4

cathode and get deposited on pure copper. The SO combine 4 with copper in the anode and form 4

CuSO . Ionization takes place again and this goes on until all the copper from the impure rod gets 4

deposited on the cathode. The impurities settle down at the base of the solution.

3. An electrolytic cell: Materials Required: A 9 volt battery, 2 metal strips or graphite rods, an electrolyte like

salted water, a bulb and a switch, connecting wires.

Anode Cathode

Electrolyte

Power Supply

+ ––e


Method: Make a circuit by connecting the two electrodes to connecting wires. Insert a switch and a bulb

in the circuit. Dip the electrodes in the electrolyte. When the switch is on, the bulb lights up. It proves that

the current passes through the cathode, anode and electrolyte, completing the circuit.

4. Electroplating is a method of coating one metal over another by using the process of electrolysis. In this

an inferior metal or that which coated with a metal which is superior and non–corrosive is used. It is

widely used in the following areas:

(i) All bathroom fittings are plated with chromium to prevent corrosion and to impart a shiny

appearance.

(ii) Silver articles and jewellery are coated with gold.

(iii) Cans in which food materials are packed are coated with a layer of tin to prevent chemical reaction

(iv) Iron pipes and tubes are galvanized, that is coated with tin to enable it to be used for cooking acidic

foods.

5. Electroplating a copper chain with silver.

Materials Required: A silver rod, copper chain, silver nitrate solution, a beaker, should be filled with silver

nitrate solution. Take a battery; connect the silver rod to the anode and the chain to be electroplated as

cathode. Dip both into the solution and pass current. After a while we can observe the silver getting

deposited on the chain and if the reaction continues for sufficiently long period the chain gets coated with

silver. On passing electricity the silver ions forming out of AgNO move towards the cathode and get 3

deposited there. Silver from anode will get into the solution by combining with – [NO ] ions and this 3

process will continue as long as the silver rod can last. Thus, an inferior metal like copper can be given a

coating of a superior metal like silver and look very rich.

NCERT Questions

6. The rain water, mixed with chemical impurities such as acids or salts in the air and ground surface,

becomes good conductor of electricity. Therefore it would not be safe for the electrician to carry out

electrical repairs outdoors during heavy downpour, as risk of electric shock due to leakage of current,

working on a wet surface, will be always there.

7. The rainwater is supposed to be as good as distilled water. But now a days due to increased level of air

pollution, a lot of impurities or pollutants are present in the air. These impurities may be acidic or may

contain some salt. All these impurities in the form of either acid or salt, get dissolved with the rainwater,

and make it good conductor of electricity. This is the reason, why Paheli found the compass needle

showing deflection on testing with a tester.

8. The list of electroplated objects around us:

(i) The Gold Plated Artificial Jewellery.

(ii) The chromium plated Automobiles parts such as Wheel Rim, Engine Parts and Carriage etc.

(iii) The chromium plated kitchen and bathroom fixtures, such as Tapes, Showers, Water Sinks, and

Racks.

(iv)Tin platted iron cans, used for storing food.

(v) The copper plated metal decorations for home and offices.

(vi) The shaving blade with titanium coating on cutting age.

(vii)The chrome plated Surgical Instrument.

9. Some liquids are good conductors of electricity and some are poor conductors. Most liquids that conduct

electricity are solutions of acids, bases and salts. The passage of an electric current through a

conducting liquid causes chemical reactions.

10. During electrolysis positively charged copper ions move to the carbon rod and get deposited. A deposit

of copper forming on the cathode. This will often be powdery and uneven. You should explain that, if the

current used is much lower, then the solid coating is shiny, impermeable and very difficult to rub off; this

process forms the basis of electroplating.

Bubbles of gas (oxygen) are formed at the anode.2+ -Cathode reaction: Cu (aq) + 2e → Cu(s)

+ -Anode reaction: 2H O(l) → O (g) + 4H (aq) + 4e2 2

With carbon (graphite) electrodes, the oxygen usually reacts with the anode to form CO . If copper is 2

used for the electrodes, the copper anode dissolves. The reaction is the reverse of the cathode reaction.

The results of this experiment can lead to a discussion about electroplating and the electrolytic refining

of copper.

11. The electrode with thick rod of impure copper should be attached to the positive terminal of battery

because in electroplating process, when electric current is passed through the copper sulphate

solution, copper sulphate dissociates into copper and sulphate. The free copper gets drawn to the

electrode connected to the negative terminal of the battery and gets deposited on it. An equal amount

of copper gets dissolved from the other electrode with thick rod of impure copper, in the solution.

Thus, the loss of copper from the solution is restored. As the process keeps going , the copper gets

transferred from positive electrode with thick rod of impure copper to the other electrode made up of

thin plate of pure copper.

12. When the free ends of the tester do not touch each other, there is an air gap between them. There will be

no deflection as air is a poor conductor of electricity. But during lightning, an electric current passes

through air and deflection is seen in the compass. Air is indeed a poor conductor but not always under

certain conditions the electric current do pass through air also.

13. If Boojho has taken distilled water then the electric current will not pass, as distilled water is free of salts

and is a poor conductor. But the water we get from the sources such as taps, hand pumps, wells and

ponds is not pure. It may contain several dissolved salts in it. Small mineral salts are naturally present in

it. This water is thus a good conductor of electricity. So, even if he has forgotten to add the lemon juice

gas bubbles of oxygen and hydrogen ions will arise near electrodes confirming that chemical reaction is

taking place.

14. a. The deflection indicates that the solution is poor conductor of electricity. The current through the

circuit is too weak, the filament does not get heated sufficiently and the bulb does not glow. Material is

conducting the current but the current is too weak to glow a bulb.

b. The bulb will glow when the current passes through it. Due to the heating effect of current, the

filament of the bulb gets heated to a high temperature and starts glowing. However, if the current

through a circuit is too weak, the filament does not get heated sufficiently and does not glow.

c. The increase in magnetism is proportional to the number of coils.

d. The current will increase the bulb will get brighter.

15.


I. Give reasons.

1. Zinc is coated on iron to avoid corrosion in car parts in iron used for construction of bridges etc.

2. Water being a good conductor of electricity increases the chances of electric shock if we handle electrical

appliances with water or wet hands.

3. Chromium plating is itself costly and making automobile parts from chromium would be very expensive

and cost of objects having chromium part would be again very expensive and will not be affordable by

maximum percentage of people.

NCERT Questions

4. The deflection of magnetic needle indicates electric current is flowing through the wire. It means the

liquid or the solution is a good conductor of electricity. When the free ends of a tester are dipped into a

solution, electric circuit is completed and an electric current passes through the solution.

J. HOTS Questions.

1. Solid NaCl cannot conduct electricity. So, it should be either molten or dissolved in water.

2. Distilled water has no salts in it. Pure distilled water forms very weak ions which can't conduct current.

So, it is a poor conductor.

3. Water, being a good conductor will conduct electricity and if there is any leakage due to short circuit

during rainy season we'll receive electric shock. So, we should not touch electric poles.

4. Wood is an insulator of electric current. So, it is safer to use it as handles to avoid electric shock in case of

faulty appliances.



Chapter- 15 : Some Natural Phenomena



1. hair 2. thunder 3. negatively charged 4. static

5. electric shock 6. lightning conductor 7. tectonic plates 8. seismology

9. richter 10. tsunami 11. negative, positive 12. earthing


1. True 2. False 3. False 4. False 5. True


NCERT Questions

9. False 10. True 11. False 12. False 13. True

14. True 15. True 16. True 17. True


1. a. iv b. iii c. v d. ii e. i


1. b 2. c 3. b 4. c 5. d 6. a 7. c 8. b 9. b 10. a

11. b 12. b 13. c 14. d 15. a 16. c 17. b 18. d 19. a

E. Name them.

1. Seismograph 2. Electroscope 3. Electric discharge 4. Static charge

5. Seismology 6. Earthing



1. Lightning is an atmospheric discharge of electricity, which typically occurs during thunderstorms, and

sometimes during volcanic eruptions or dust storms.

2. Epicentre is the point vertically above the plates where an earthquake arises.

3. When a glass rod is rubbed with silk, electrons from glass transfer to silk and so glass is positively

charged and silk is negatively charged.

4. Electroscope is used to detect charged bodies.

NCERT Questions

5. In India weak zone pass through Kashmir, western and central Himalayas the whole of north-east, Runn

of Kachch, Rajasthan and Indo-Gangetic Plain.

6. Although some major earthquakes are preceded by foreshocks, there is currently no reliable method to

accurately predict the time, location, and magnitude of a quake.

7. When charged straw is brought near uncharged straw it induces opposite charge in the uncharged straw

thus attracting it towards itself.

8. If we replace the aluminium strips with the plastic strips there will not be any change in the position of the

plastic strips as the plastic is a non conductor so it will not transfer the charge from the paper clip to the

plastic strips.

9. Rub a dry drinking straw with a cotton cloth and bring it close to any small object. As a result of rubbing

against each other, they became charged so these objects can attract small pieces of paper and other

light particles.


1. Waves that are generated due to the tremors or jolts under the ground when earthquake is in progress,

are called seismic waves.


2. The jerks under the earth are due to geological processes that cause rocks to break underground with

tremendous energy release.

3. Seismograph is an instrument used to measure the magnitude of seismic waves.

4. In India the earthquake prone zones pass through Kashmir, western and central Himalayas, the whole of

northeast, Rann of Kachch, Rajasthan.

NCERT Questions

5. We know that some objects can be charged by rubbing with other objects.The electrical charges

produced by rubbing are called static charges. A woollen sweater while taking off comes in contact with

the surface of inner clothes like shirts etc., which are either made of cotton or synthetic material. Due to

rubbing, or friction between the surfaces of cloth materials, where inner cloth lose some charge in the

form of lose electrons, and the sweeter acquires excess of static charge. This excess of static charge,

accumulated in sweater, when it comes near or in contact with body, gets discharged to either back or to

ground through body, producing electric sparks with crackling sound.

6. Destructive energy of an earthquake is measured on the Richter scale. The earthquake measuring 3 on

Richter scale may be recorded by a seismograph and it is not likely to cause much damage as it will

result in mild tremors of very low intensity on the earth surface. The earthquake measuring 7 or more on

Richter scale can cause severe damage to life and property.

7. At the event of thunderstorm prediction, while going out, We should avoid carrying an umbrella, as

lightening has great affinity to strike at any available metal object in the open. An umbrella with pointed

metal tube and wire frame structure inside, offers an ideal situation for a lightning strike in a

thunderstorm.

8. The metal columns used during construction, electrical wires and water pipes in the buildings also

protect us to an extent from lightning. But we should not touch them during a thunderstorm.

9. Air is a bad conductor of electricity under normal conditions. But, during some adverse conditions even

air conducts electricity. During lightning, the temperature and hence kinetic energy of the air molecules

increases. This results in ionizing of air molecules and hence they get converted into plasma state. In

this state, air molecules become good conductor of electricity and hence the lightning comes to Earth.

Even good insulators will eventually break down under very high voltages. Lightning is the visible effect

of air in electrical breakdown.

10.

11. Even the metal columns used during the construction, electrical wires and water pipes in the buildings

also protect us during the thunderstorm. So, it is not always necessary to install a lightning conductor.

Lighting conductor

Copper plate


12. Free or nearly-free electrons on stuff like wool are getting rubbed off onto you so that your body holds

some sort of net total electric charge. When you touch a metal door (or any piece of metal) then the

electrons want to spread out to balance themselves between you and the metal. Since the metal

conducts electricity very well, they fly off you very quickly which heats up the air in between you and the

metal, giving you the painful "shock" feeling.

13. A lightning rod (also called lightning conductor) is just part of a lighting diversion system meant to protect

building from damage due to a lightning strike. Included in the system is the metal cable or rod that

extends down into the ground and electrodes in the earth to safely dissipate the energy away. Often

buildings prone to being struck by lightning will have a network of lightning rods and conductors. The

idea is that the electricity will take the path of least resistance and thus bypass the structure of the

building as it travels to the ground. But also, the configuration of tip of the lightning rod is such that it is a

good receptor for lightning.

14. In an electroscope if we have already brought a negatively charged body in contact with the metal clip it is

charged negatively. If now we are bringing positively charged body close to the metal clip the

electroscope will collapse.

15. When you touch the metal strip with hand you will find a change in the foil strips. They come back to their

original state. Repeat charging the foil strips and touching the paper clip. Every time you will find that the

foil strips collapse as soon as you touch the paper clip with hand. The reason is that the foil strip loses

charge to the earth through the body. We say that the foil strips are discharged.


1. Earthquakes generally occur at the boundaries of the various plates (also called tectonic plates) which

are in continuous motion. When they brush against one another or when they get disturbed due to

pressure build up, this result in earthquake.

2. The degree of damage during an earthquake depends on factors like (i) Time of day – working hours will

see very heavy casualties (ii) Magnitude and duration of the event (iii) Distance from the epicentre – the

closer the place is, heavier the damage (iv) Type of construction – Brick and stone constructions cause

greater damage than timber constructions. (vi) Type of soil – Lose soil will let things bury faster into the

earth and (vii) The preparedness of the people. If people are well prepared with mock drills then

response to the event will help them to rescue a lot of people.

3. The boundaries of the tectonic plates along which the quakes are most likely to occur are the weak ones.

The plates are in continuous motion and when rub against each other, it can trigger an earthquake.

These weak zones are also called fault zones. In India, these pass through Kashmir, western and central

Himalayas, the whole of north east, Rann of Kachch, Rajasthan and Indo-Gangetic Plains.

NCERT Questions

4. The three measures to protect ourselves from lightning are as follows:

1. We should avoid driving or sitting in open vehicles, like motorbikes, tractors, construction machinery,

open car etc., as they being made up of metal, may induce lightening strike, hence are not safe.

Similarly open fields, tall trees, shelters in parks, elevated places do not protect us from lightning

strokes.

2. We should secure, high rise building with lightening conductor. At the same time, we should avoid

carrying umbrella during thunderstorms as lightening may strike its pointed end of metal pipe.

3. In a forest, we should take shelter under shorter trees to an extent as possible. In an open field, we

should stay away from trees, metal poles or structures and squat low on the ground, placing hands

on knees with head between the hands.

4. In an open field, we should stay away from trees, metal poles or structures and squat low on the

ground, placing hands on knees with head between the hands.


5. We know that like charges repel and unlike charges attract each other. Therefore, a charged balloon

is repelled by another charged balloon, whereas an uncharged balloon, in the presence of a charged

balloon gets induced with opposite charge, is attracted by another charged balloon.

6.

The instrument which is used to detect a charged body, is called electroscope. Such instrument can be

made very easily. As shown in the figure, the mouth of empty jam bottle is covered with a piece of

cardboard slightly bigger in size than the mouth of the bottle. A stretched paper clip, is inserted in the

middle of cardboard as shown. Two small strips of aluminium foil about 4 cm × 1 cm each are hanged by

the lower end of paper clip inside the bottle. When a charged refill is brought in contact with the upper

end of paper clip and as metals are good conductors of electricity, the aluminium foil strips receive the

same charge from the charged refill through the metal body of paper clip . The aluminium foil strips

carrying similar charges repel each other and they become wide open, thus showing the presence of a

charge in refill body.

7. Lightning is produced in thunderstorms when liquid and ice particles above the freezing level collide, and

build up large electrical fields in the clouds. Once these electric fields become large enough, a giant

"spark" occurs between them (or between them and the ground) like static electricity, reducing the

charge separation. The lightning spark can occur between clouds, between the cloud and air, or

between the cloud and ground.

A simple electroscope to detect a charged body

Ball-Pen Refill

Metal Wire or Paper Clip

Aluminium Foil Strips


As seen in the photo above, cloud-to-ground lightning usually occurs near the boundary between the

updraft region (where the darkest) clouds are, and the downdraft/raining region (with the lighter, fuzzy

appearance). Sometimes, however, the lightning bolt can come out of the side of the storm, and strike a

location miles away, seemingly coming out of the clear blue sky.

As long as a thunderstorm continues to produce lightning, you know that the storm still has active

updrafts and is still producing precipitation. The temperature inside a lightning bolt can reach 50,000

degrees F, hotter than the surface of the sun. Objects that are struck by lightning can catch on fire, but

since the flash is so brief, objects can also show little or no evidence of burning at all.

8. If you're indoors, stay there. Get under and hold onto a desk or table, or stand against an interior wall.

Stay clear of exterior walls, glass, heavy furniture, fireplaces and appliances. The kitchen is a particularly

dangerous spot. If you're in an office building, stay away from windows and outside walls and do not use

the elevator.

9. Lightning can strike telephone cords as it is an electrical discharge. During thunderstorms contact with

these should be avoided. It is safer to use mobile phones and cordless phones. However, it is not wise to

call up a person who is receiving your phone through a wired phone.

10. An ebonite rod is a thin, round stick made of hard, black rubber. Replacing the metal clip with ebonite will

not have any effect on the aluminium strips. As the ebonite rod is an insulator.

I. Give reasons.

J. HOTS questions.

1. A charged plastic comb will attract water flowing out of the tap that is why the stream of water bends

towards the comb.

2. A charged rod will pass its charges to the leaves of the electroscope when contact is made. Both the

leaves get the same charge and so they repel and diverge.

3. Our body can easily transfer the charges to the earth. So, when touched with fingers, the charges from

the electroscope are removed and so the leaves fold back.

4. Tall trees have a chance of attracting the discharge that occurs during lightning and so it is not advisable

to take shelter under them especially tall ones.

5. Lightning conductors absorb all the charges released during lightning and safely pass them to the

ground. So, the tall structures do not get affected or damaged by lightning.

1. During thunderstorms, clouds come closer to the earth especially in hilly regions, the charges can jump

towards the earth through trees, air or buildings. So, it is best to avoid elevations, tall trees, building

structures or even hold an umbrella which can attract charges. Assuring a squatting position is the safest

way of avoiding any serious consequences.

2. Lightning produces a large flash of light across the sky in various patterns accompanied by loud noise

and looks very spectacular like the display of fireworks. Since lightning involves jumping of electric

charges between clouds and clouds or between clouds and earth, objects on earth can end up

receiving these charges and can get electrocuted, and buildings can catch fire. It is one of the deadly

aspects of lightning.


Chapter- 16 : Light



1. Multiple 2. Kaleidoscope 3. dispersion

4. seven 5. refracts 6. violet, indigo, blue, green, yellow, orange, red

7. Light,normal vision 8. reflection of light 9. luminous

10. erect, virtual, laterally 11. Multiple

NCERT Questions

12. 2 13. left ear, left hand 14. large

15. less


1. True 2. True 3. False 4. True 5. False 6. False


1. a. ii,B b. iii, C c. iv, A d. i, D

D.Multiple choice questions. Tick the correct option in each case.

1. d 2. d 3. c 4. b 5. c

NCERT Questions

6. a 7. b 8. a 9. b 10. a 11. a 12. a

13. a 14. b 15. b

E. Name them.

1. VIBGYOR 2. Lateral inversion 3. Second cranial nerve 4. Braille



1. (a) Luminous objects are those which emit their own light.

(b) Non-luminous objects do not have their own light.

(c) It is the phenomenon of rebounding of light rays after striking a medium.

(d) The scattering of reflected rays from a rough or uneven surface is called diffusion.

(e) Incident Ray: Light rays that come from an object and strike a reflecting surface are called incident

rays.

NCERT Questions

2. Iris.

3. The impression of an image does not vanish immediately from the retina. It persists there for about 1/16

of a second. So, if still images of moving objects are flashed on the eye at a rate faster than 16 per

second, then the eye perceives object as moving. So, his fingers appear blurred.

4. When the two mirrors are aligned at a 0-degree angle with each other (i.e., a parallel mirror system),

there is an infinite number of images. Each image is the result, or an image of an image of an image or an

image of an image of......

5. As per the laws of reflection

The angle of incidence ∠i = angle of reflection ∠r

Here as given ∠i + ∠r = 60°

∴ ∠i + ∠i = 60 °

or ∠i = 60/2 = 30 °

Hence, angle of incidence of a ray = 30 degree.

6. 12 cm.



1. The rebounding of light when it strikes an opaque surface is called reflection.

2. Light falling on a surface diffuses if the surface is irregular and the rays disperse in different directions.

3. The image in a plane mirror can be caught on a screen, you'll find out that it is not possible. In other

words, an object in front of the mirror cannot be seen on the wall behind. It proves that the image formed

on a plane mirror is virtual.

4. Sir Isaac Newton, an English physicist was the one who proved that rainbow is a result of dispersion of

light.

5. Braille script is a system using raised dots. It puts to use the sense of touch in place of the sense of sight.

NCERT Questions

6. We cannot see objects in the dark room without the presence of light or a lighted object itself. We may

see an object only when, the light from an object enters our eyes. The light may have been emitted by the

object directly (luminous objects.), or may have been reflected by it (illuminated objects). Similarly, we

cannot see outside objects, sitting inside the darkroom, if there is no opening or passage for any

incidental light from outside. However, outside the darkroom, in open, we can easily see the objects, due

to either reflected light from the surface of illuminated objects or direct light from luminous objects such

as sun, candle, torch etc. Nearly everything we see around is seen due to reflected light.

7. (a) Polished wooden table g regular reflection

(b) Chalk powder g diffused reflection

(c) Cardboard surface g diffused reflection

(d) Marble floor with water spread over it g regular reflection

(e) Mirror g regular reflection

(f) Piece of paper g diffused reflection

In case of objects with smooth, polished and shiny surfaces, like polished wooden table, marble floor

with water spread over it and mirror, when a incident beam of light strikes on their surfaces, regular

reflection takes place. Whereas, in case of objects with rough surfaces, such as chalk powder,

cardboard surface, piece of paper etc, when a incident beam of light strikes on their surfaces, irregular

reflection takes place. It is caused by the irregularities in the reflecting surface.

8. As per the laws of reflection.

The angle of incidence ∠i = angle of reflection ∠r

Here as given ∠i + ∠r = 90°

∴∠i + ∠i = 90 °

or ∠i = 90/2 = 45 °

Hence angle of incidence of a ray = 45 degree

9. If a candle is placed between two parallel plane mirrors, we will see an infinite numbers of images of

candles.

10.

30°

N

incidental ray

30°

N

incidental ray

90°

60°

60°

N

Reflected ray

30°

11.

As Boojho is not standing in front of plane mirror, incident ray, reflected ray and the normal drawn at the

point of incidence to the reflecting surface, does not lie in the same plane, therefore he can not see him

self. He can see the image of objects situated at P, Q as incident ray, reflected ray and the normal drawn

at the point of incidence to the reflecting surface, lie in the same plane. Similarly, incidental ray from R,

will not be reflected to reach point A, hence will not be seen by Boojho.

12.

A (Boojho) P Q

R

Fig. 16.20

P Q

R

A(Boojho)

A

B

C

Fig. 16.21

(Boojho)

(Paheli)



1. (a) A virtual and lateral image of an object situated at A, will be formed , behind the mirror surface. The

image will be exactly at the same distance, as the distance of real object at position A and

reflecting surface of the mirror.

2. (b) Yes, as incidental ray from object A, is reaching at B as reflected ray, therefore Paheli at B, can

see this image.

3. (c) Boojho can also see this image, as reflected rays from object at A is reaching at C.

4. (d) The point of convergence, of reflected rays reaching at point B and C, is same and at same

distance behind the mirror. Therefore, When Paheli moves from B to C, the image of A will not

change its position.

13.Dispersion of light can be defined as the separation of a visible light beam into its constituent colours, for

example Red, Orange, Yellow, Green, Blue, Indigo and Violet colours are obtained when a white light

beam is dispersed. Dispersion of light happens when a light beam passes through a dispersive medium

such as a prism. A rainbow is formed when light is dispersed through raindrops.

14.

15.Yes, the image of the hair cut can be seen by the child. The hair dresser is using the two plane mirrors to

reflect the image.

16.The most notable feature of nocturnal animals is the size of their eyes. Large eyes, with a wider pupil,

larger lens and increased retinal surface can collect more ambient light. For example, an owl's eyes fill

over one half its skulls. Likewise, some species have evolved tubular eyes as a means of increasing their

size. By expanding the eyes in this way, they are very tightly fit in the socket. As such, many nocturnal

Laws of Reflection

(i) The angle of incidence is equal to the angle of reflection.

(ii) Incident ray, reflected ray and the normal drawn at the point

of incidence to the reflecting surface, lie in the same plane

Angle of incidence (i)

Incident Ray Reflected Ray

Angle of Reflection (r)

Normal

i(x) r(y)

B

C (Boojho)

(Paheli)

Ax

x

Ciliary muscles

Iris

Lens

Cornea

Retina

Optic Nerve


animals cannot move their eyes within the orbit. Instead, they have evolved extraordinary rotational

ability in the neck. Owls, for example, can rotate their neck through 270°. Some animals of the night have

acquired a spherical lens and widened cornea to compensate for reduced eye movement. A spherical

lens projects an equally clear image regardless of the light's incoming direction. This combined with a

wide cornea effectively increases the animal's field of view allowing the head and eyes to remain

motionless.

17.The lens in the human eye is a convex lens, but it is flexible and when it is acted on by the ciliary

muscle around it, the lens can be "flattened" to change the focus or when the muscle is relaxed the

lens can assume a more spherical shape. This is how our eyes focus on objects nearer or farther

away.

In a healthy eye, the lens brings light into the eye and helps to focus it onto the retina at the back of the

eye. The lens is a clear, disk-like structure located behind the iris and the pupil. In order for an image or

an object to be seen, the light reflected from the object is filtered through the lens of the eye which

focuses the light onto the light-sensitive membrane of the retina. The light from the image activates the

membrane of the retina and is transformed into nerve signals. The nerve signals travel along the optic

nerve and are translated by the brain and the final picture of the object is "seen".

In order for the light to hit the retina and form a complete and clear picture in the brain, the lens must be

transparent so that all of the light reflected from the image makes it to the retina.

18.Cataracts occur when there is a buildup of protein in the lens that makes it cloudy. This prevents light

from passing clearly through the lens, causing some loss of vision. Since new lens cells form on the

outside of the lens, all the older cells are compacted into the center of the lens resulting in the cataract.

Surgery is the only effective method of treating vision loss caused by cataracts. Cataract surgery is a

common procedure that involves removing the clouded lens of the eye (the cataract). The lens makes it

possible for the eye to focus. The lens can be replaced with an artificial lens called an intraocular lens

implant (IOL). Sometimes an IOL is not used, and eyeglasses or contact lenses can compensate for the

lens that is removed. Surgery is often not needed or can be delayed for months or years. Many people

with cataracts get along very well with the help of eyeglasses, contacts, and other vision aids.


1. Laws of Reflection:

(i) The angle of incidence is equal to the angle of reflection.

(ii) The incident ray and the normal at the point of incidence all fall in the same plane.

Verification:

Fix a white sheet of paper on a drawing board and fix it with board pins. Draw a line XY in the center of the sheet

and place a strip of mirror over it with the help of a stand. At the center of XY, mark a point O and draw a

perpendicular ON. This is the normal line. Using the protractor, measure 45 degree from the normal and draw a

line OS. This is the incident ray. Place 2 pins P and P on OS with a gap of 2 cm between them. Make sure that

the pins are straight. Look at the images of the pins in the mirror. Get the images of the pins in a straight line and

place 2 more pins in such a way that all the four appear in the same straight line. Mark the position of P and P2

and connect the points to O. This is the reflected ray. Measure the angles —<SON and <BON and you will find

that both are the same. So, we know that angle of incidence is equal to angle of reflection. Extend the reflected

ray or on the paper and then fold a portion of the paper. You'll notice that the extended ray's path does not fold

with the paper. It proves that the incident ray, reflected ray and the normal lie in the same plane.

2. Seven colours of the rainbow (VIBGYOR) recombine to give white light. It can be demonstrated with a

colour wheel.

Materials required: A large round tin or tin lid, strong card board, red, blue, green paints, pencil, string.

Method:

(i) Use the tin lid and draw a circle on the card.

(ii) Draw 3 lines from the center and make 3 equal parts. Paint one red, other green, and the third blue.

(iii) Make 2 holes on either side of the center point. Pass a string through and make a loop at each end of

the string.

(iv) Put one hand in each of the loop and turn the card to twist the strings tightly.

(v) Now, pull your hands apart so the string unwinds and turns the colour wheel. When turned quickly

and continuously, the wheel appears white.

Note: The same card can be painted with all the 7colours and the result will be the same.

3. Braille is a system of providing literacy for the visually impaired. Since reading and understanding

becomes an impossible task for visually impaired, a system of using a 6 – cell with raised dots specific for

each alphabet, common words and punctuation was developed by LOUIS BRAILLE. He was a young

French boy who became blind at the age of three, due to eye injury. This creation revolutionized the

communication for blind people and transformed the lives of millions of blind people. For e.g., in Braille

system all the alphabets are given notations as shown in the figure.

4. When we see an object each image stays on our retina for1/16 of a second. If more than 16 images fall on

the retina in one second, they blend with each other and give a sensation of continuity. Motion pictures

are made in this manner.

NCERT Questions

5.


1.

2.

3.

Regular reflection Diffused reflection

When all the parallel rays reflected from a plane surface are parallel, the reflection is known as regular reflection.

When all the parallel rays reflected from a place surface are not parallel, the reflection is known as diffused or irregular reflection.

Reflection from a smooth surface like that of a mirror is an example of regular reflection images are formed by regular reflection.

Reflection from a rough surface, like that of a cardboard, is an example of irregular reflection. It is caused by the irregularities in the reflecting surface.

Images are formed by regular reflection. Images are not formed by irregular reflection.

S.No.

6. A kaleidoscope is made up of three rectangular mirror strips about 15 cm long and 4 cm wide each. This

mirrors, as shown in the figure, are joined together to form a prism. This assembly may be housed inside

a circular cardboard tube or tube of a thick chart paper. The length of tube is slightly longer than the

mirror strips. One end of the tube is covered by a cardboard disc having a hole in the center, through

which we can see. Other end of the cardboard tube is covered by a circular plane glass plate touching

the edge of mirror strips. Now several small pieces of coloured glass (broken pieces of coloured

bangles) are put inside. Close this end of the tube by a ground glass plate. Allow enough space for the

colour pieces to move around. Your kaleidoscope is ready. When we peep through the hole, we will be

able to see a variety of patterns in the tube. Interesting feature of a kaleidoscope is that we will never see

the same pattern again.

7.

8. .a. 3 mirrors.

b. Mirrors should be placed at B, C and D.

c. Fix the plane mirror strips at the corners with reflecting sides facing one another at 45 degree angle.

d.

e. No, he will not be able to see the objects if any of the mirror are removed.

Object to be seen

Eye


Plain Mirror Strips Circular cardboard Tube

Broken pieces of coloured Bangles

Cardboard Disc with Hole

Plain Mirror Disc

Ground Glass Disc

Making a Kaleidoscope

Ciliary muscles

Iris

Lens

Cornea

Optic Nerve

Human eye

Retina


9. a. The direction of incident ray is wrong.

b. The angle of reflection is greater than the angle of incidence which is not possible.

c. The normal line should be making an angle of 90 degree to the line representing the mirror at the

point where the incident ray strikes the mirror.

10. Persistence of vision is the process which enables us to perceive motion in a cartoon film. Persistence of

vision is the phenomenon in which the image of the object is retained on the retina for a very short period

of time i.e. 1/16th of a second even after the object is removed.

11. A Kaleidoscope operates on the principle of multiple reflections. An optical toy producing symmetrical

patterns by multiple reflections in inclined mirrors enclosed in a tube. A kaleidoscope is an optical device

used for the illustration of the image-forming properties of inclined mirrors that have been combined. It is

an important tool for pattern designers and is commercially available as a toy.

12. A plane mirror shows the left of an object to be right and right of the object to be left. We call this lateral

inversion. So, the word REST will appear like

13.

I. Give reasons.

1. The word AMBULANCE is written like this on the vehicles (as shown) because images in a plane mirror

are laterally inverted. So, when seen through the rear view mirror the image will read in the reverse

manner as AMBULANCE. This helps people driving on roads to give way to ambulances which may be

carrying critical patients.

AMBULANCEWRITTEN AS IN FRONT OF AMBULANCE

REST

Ciliary muscles

Iris

Lens

Cornea

Optic Nerve

Human eye

Retina

2. Puddles of water on roads refract sunlight falling on them and get reflected back. They refract once again

on emerging out of water. This makes them disperse into seven colours and we see flashes of colours.

3. If two mirrors are placed an angle to each other with an object at the centre each mirror forms an image

and images of the images are also formed and we get multiple images.

4. The image formed by a mirror can be real or virtual. A real image is inverted (upside down), appears in

front of the mirror, and may be larger or smaller than the object. A real image may be projected onto a

screen. A virtual image is erect (upright), appears to be behind the mirror, and may be larger or smaller

than the object. A virtual image in a mirror has the sides reversed; that is, the left side of the object will

appear as the right side of the mirror image. The image in a looking glass is a virtual image. A virtual

image cannot be projected.

J. HOTS questions.

1. If the light approaches the mirror along the normal (perpendicular to the mirror), then it reflects back in

the same direction from which it came. In that event, the angle of reflection is still equal to the angle of

incidence, they're both zero.

2. Angle of incidence = 45 degree and angle of reflection = 45 degree.



Chapter- 17 : Stars and the Solar System



1. Moon 2. Moon, Sun, Earth 3. Big 4. Meteoroids

5. Buzz Aldrin, and Neil Armstrong

NCERT Questions

6. Neptune 7. Mars 8. Satellite

9. Stars 10. Mars and Jupiter


1. True 2. True 3. False 4. False 5. True


NCERT Questions

9. False 10. True 11. False 12. True 13. False

14. False 15. False 16. False 17. True 18. True

19. True 20. False


1. a. iv b. iii c. i d. v e. ii

2. a. iv,v b. i c. iii, vi d. vii e. ii


1. b 2. a 3. d 4. b 5. d 6. a 7. c

NCERT Questions

8. c 9. a 10. a 11. d 12. d 13. c 14. c 15. a 16. d 17. a

E. Name them.

1. Venus 2. Jupiter 3. Mars 4. Neptune 5. Earth



1. Huge collection of stars moving away from one another are called galaxies.

2. 88 constellations have been identified so far.

3. Our solar system lies in the milkyway galaxy.

4. The pole star is considered to be in fixed position.

5. A light year is the distance travelled by light in one year.

6. Venus and Uranus rotate in a direction opposite to that of other planets.

7. Asteroids are found between the orbits of Mars and Jupiter.

8. Comets are made of balls of frozen gas, dust and rocks.

9. Jovian planets are Jupiter, Saturn, Uranus and Neptune. These are also known as outer planets.

10. The moon orbits around the earth every 27.3 days.

NCERT Questions

11. Venus, if it is visible as an evening star, can be found in the western part of the sky only, just 1-3 hours

after sunset.

12. Constellations are groups of stars that appear to form recognisable shapes. Constellations were

devised by ancient people to easily recognise stars in the sky. The constellations were named as per

theirs shapes resembling familiar objects of that time. We can easily identify some constellations in the


night sky if know how a particular constellation looks like and where to look for it. Two constellations are

Ursa Major and Orion.

13. 1. Asteroids 2. Comets

14. All stars, and our own Sun is just an example, are hot balls of glowing plasma held together by their own

gravity. And the gravity of a star is very intense. Stars are continuously crushing themselves inward, and

the gravitational friction of this causes their interiors to heat up. So, they are always giving light.

15. Paheli is right if you find an unusually bright non-twinkling object in the night sky along this path, it is

probably a planet.

16. He will be able to see the full moon again after 29 days.

17. Given in the pages

18.

19.

Pole Star

S

U

N

New Moon Day or

Amavasya

Full Moon Day or

Poornima

B

A C

D

Moon

Earth

Rays

DayNight



NCERT Questions

4. Yes, in real, all the stars in the sky move. As we know, all the celestial bodies comprising our solar

system, Stars, Constellations and galaxies, are part of big Universe, which is ever expanding. Every

celestial object with in Universe, in order to overcome the gravitational pull of other celestial object

around, has to move in some relative motion. The pole star, which is also moving, but appears to be

stationary from the Earth, because it is situated close to the direction of the axis of rotation of the Earth.

From earth, all others stars appear to move from east to west as earth makes rotation from west to east

around its axis.

5. The death of a star (a supernova) would appear as a brightening over hours.Stars not massive enough to

explode as supernova would eventually fade from view, but that would take millions to billions of years.

6. At night when the sky is clear and the moon is not there, you may sometimes see bright streaks of light in

the sky. These are shooting stars called meteors. They are usually small object that occasionally enters

the earth's atmosphere. At that time it has a very high speed. The friction due to the atmosphere heats it

up. It glows and evaporates quickly. That is why the bright steak lasts for a short time.

7. The moon keeps changing its shape because the position of the moon and the sun's reflection on it

keeps changing. The moon orbits around the earth every 29 and a half days and during this revolution we

see the light reflected from the sun at different angles and in different shapes. This is what forms the

phases of the moon.

8. Moon rises and sets at different times depending on what phase it is in, meaning where the Moon is

located relative to the Sun and Earth. In fact, for some phases the Moon can be seen in the day time!

Each unique phase rises/sets at a different time. So, Paheli may not be able to see the moon at the same

position.


1. A unique combination of conditions has allowed life to evolve on earth. First the earth is formed

around a star at a perfect distance to foster life. If it would have been close gamma rays and

ultraviolet rays would induce genetic mutation, cancer and other deadly diseases. The heat would

evaporate oceans and raise the surface temperature too high for survival. If the earth was too far from

the sun, ocean would freeze over and it would be too cold for anything to thrive. Water is very

important. Organic compound and amino acids(the basis of all life forms) were able to form from

molecules floating freely in early earth's ocean. Water is the most basic need of any plant and animal

on the planet. Also the size of the earth is important, if it was too big the crushing gravity would make

the life hard to sustain, if it was too small it probably would not hold oceans or atmospheres. The

moon is responsible for tides and without it the early organic compounds that evolved today's life may

not have formed. So, the combination of size, gravity, air, water and nutrient make life sustainable

on earth.

1. Light from a star travels a long distance before we see it. Due to disturbances caused by the atmosphere

of the earth the light seems to flicker.

2. The Pole star lies in the axis of rotation of the earth. So, it appears stationary while all the other stars

appear to be moving from east to west. So, sailors and travellers relied to it for finding their way.

3. Constellations are groups of stars which always stayed together and showed a definite pattern. They

were observed by star gazers who named them after the pattern they presented. Orion is a constellation

which appears like a warrior.


2.

NCERT Questions

3. The stars are located at far greater distance from each other. It is convenient to express distances of stars

in light years. For example, The Sun is nearly 150,000,000 kilometres away from the Earth. Alpha

Centauri, the next nearest star , is at a distance of about 40,000,000,000,000 km from the Earth. This

distance is not convenient to express in normal units of length. To measure such large distances, we

make use of another unit known as light year, which is the distance traveled by light, in one year with a

speed of 300,000 km per second. So, using this unit, the distance of Alpha Centauri is about 4.3 light

years, which is very convenient to express.

A star is eight light years away from the Earth implies that, for light, which travels with speed of 300,000

km per second, it takes 8 years to reach Earth. In other way, the distance between star and earth is

around 9460800000000 km (365 X 24 X 60 X 60 X 3,00, 000 Km).

4.

Let the radius of the Earth = r

∴ The radius of Jupiter = 11r3Volumes of earth = 4/3√π(r)

3Volumes of Jupiter = 4/3√π(11r)3 3Ratio of the volumes of Jupiter and the Earth4/3√π(11r) = 4/3√π(r)

= 1331 : 1

∴ Jupiter can accommodate 1331 numbers of Earths

5. The correct position of the planets is given below :

The correct sketch of Solar System

Uranus

Neptune

Saturn

Jupiter

Earth

Mercury

Sun

Mars

Venus

Orion- Constellation(with relative position of prominent stars)

Ursa Major- Constellation(with relative position of prominent stars)


6. No, moon will not have phases if it had its own light. The moon does not shine by its own light, but by the

reflected light of the sun. We see the moon because the sunlight falling on it gets reflected towards us.

We therefore see only that part of the moon from which the light of the sun is reflected towards us. If it had

light of its own it will keep on shining all the time.

7. The tails are always directed away from the sun. gas (ions) tail points straight away from sun. Dust tail

curves towards orbital path. The tail gets longer the closer the comet gets to the sun.

8. a. Western sky

b. Eastern sky

9.

10. We always see the same side of the moon due to tidal locking. The moon follows a synchronous rotation

as it rotates on its axis. The period it takes to rotate on its axis is the same period it takes to rotate around

the earth and this is why we only see one side.

11. The gravitational force between two heavenly bodies will become 9 times more as the gravitational force

between any two bodies in the universe is inversely proportional to the square of distance between them.

It would increase or decrease the solar radiation and shorten or lengthen the year.

I. Give reasons.

1. The moon does not have its own light. It only reflects light from the sun. So, depending on its position in

relation to the sun, the part of the moon visible from earth keeps changing. That is why the moon seems

to wax and wane.

2. Saturn shows 3 prominent rings made of dust and ice. So, it is called the ringed planet.

3. As the comet approaches the sun, it heats up and leaves behind a stream of hot glowing gases and dust

particles which gives the appearance of a long tail.

4. Mercury does not have an atmosphere. Venus has an atmosphere of CO which absorbs the heat and 2

makes the planet very hot.

J. HOTS questions.

1. The stars of a constellation are millions of miles away from the earth. So, when we see them they appear

as though they are close to one another even though they are far away from each other.

2. Meteorites give information to scientists about the nature of material of which the solar system was

formed.

3. The cosmonauts who landed on moon had to wear specially designed, pressurized suits to protect them

from low gravity and absence of atmospheric pressure.


Chapter- 18 : Pollution of Air and Water



1. untreated 2. pollutant 3. carbon monoxide

4. groundwater recharge 5. carbon dioxide, nitrous oxide, methane


1. False 2. True 3. False 4. True


1. a. iii b. iv c. i d. v e. ii


1. d 2. c 3. d 4. d 5. a 6. d 7. c

NCERT Questions

8. d 9. c 10. b 11. c 12. a 13. a 14. b 15. d 16. b

17. b 18. d 19. b 20. a

E. Name them.

1. Global warming 2. Air 3. Chlorofluorocarbon 4. Pollutants



1. Carbon monoxide is present as 0.03 % in air.

2. Methane and carbon dioxide are green house gases.

3. When we breathe in carbon monoxide, it binds with RBCs and causes disruption in transport of oxygen.

4. Nicotine is the carcinogen in cigarettes.

5. Smog is a mixture of smoke and fog.

6. The Ganga Action Plan (GAP) was launched by the Government of India in 1985.


1. When we add huge amount of organic matter in water bodies they decompose using up a lot of dissolved

oxygen, and leave no oxygen for aquatic life. Weeds grow fast in such water due to organic matter

availability, further reducing the available oxygen. This phenomenon is called eutrophication.

2. Oil spills float on water since the density of oil is less than that of water. This stops oxygen from dissolving

in water. So, there is extensive damage to marine and aquatic life.

3. Sewage treatment plants help to remove the organic matter from the waste water so that they can be

decomposed separately and the water (light part ) will mix with rivers.

4. Rivers can be saved by taking the following steps:

a. No sewage should be directly discharged into the rivers.

b. Sewage should be treated in sewage treatment plants.

c. Industrial effluents should be treated and neutralised before letting out into the rivers.

d. Polluting industries should be shifted away from banks of rivers.

e. Limited use of fertilizers and chemical pesticides should be advocated.

f. Dumping dead bodies in the rivers should be banned.

g. Polluting cultural activities like immersion of idols made of synthetic materials should be avoided.

5. Oxides of sulphur and nitrogen which are mixed in the automobile exhaust can form acids on mixing in

rain water. Such acidic rain water is harmful to the environment and is called acid rain.

6. Smog includes fumes coming from burning of fuel mixed in water vapour. It affects visibility by forming a

thick layer in the atmosphere and contains harmful and poisonous gases.


7. CFCs (chlorofluorocarbons) were extensively used in refrigerators and air conditioners as a coolant in

aerosol cans, plastic foams and insulating materials.

8. Due to depletion of ozone layer, more harmful ultraviolet rays will enter the earth's atmosphere and

destroy all forms of life. Ozone helps to filter out the UV rays.

NCERT Questions

9. Water gets contaminated in the following ways:

a. Various industrial units dispose off the chemicals in rivers. These chemicals are harmful and

poisonous and contaminate water.

b. Water gets contaminated when sewage is disposed off (without any treatment) in rivers.

c. Ground water gets contaminated by harmful insecticides and pesticides sprayed by farmers and it

becomes unfit for drinking.

10. Air pollution should also be checked at individual level:

a. At at individual level, we can plant trees as trees reduce air pollution.

b. We can use public transportion and encourage car pooling so that air pollution can be reduced.

c. Instead of going by cars and scooters for short distances, we can go by foot or by bicycles.

d. By saying no to crackers we can minimise air pollution as well as noise pollution.

e. We should not burn garbage and dry leaves. The burning of dry leaves and garbage release green

house gases which are responsible for global warming.

11. Transparent water is not always fit for drinking. It may contain harmful microorganisms and other

pollutants. We should purify water before drinking. Water can be purified with the help of water purifier or

by boiling it.

12. Excessive quantities of chemicals (fertilizers, weedicides, pesticides etc.) washed from the fields enter

into ponds. These act as nutrients for algae to flourish. Once these algae die, they serve as food for

decomposers like bacteria. A lot of oxygen in these ponds gets used up. This results in a decrease in the

oxygen level which kills aquatic organisms.


1. Major measures necessary for controlling air pollution are:

a. All vehicles should have periodic pollution checks.

b. The automobile engines should be designed to convert harmful exhaust gases to harmless gases.

c. Change over to less polluting fuels like the CNG in place of petrol or diesel.

d. Development of public transport systems to reduce the use of cars and two wheelers.

e. Planting more and more trees.

f. Ban on cigarette smoking in public places.

g. Industrial chimney smoke should be treated to make it harmless before it goes into the air.

h. Polluting heavy vehicles should be phased out.

2. Smoke contains carbon dioxide, carbon monoxide, oxides of nitrogen and sulphur and SPM

(Suspended Particulate Matter).

Carbon dioxide: Is responsible for increasing the temperature of the atmosphere resulting in global

warming, with consequences like melting of polar caps, rise in the level of water in the oceans and

submergence of landmass.

Carbon monoxide: Poisonous gas which can even cause death in higher concentration.

Oxides of Sulphur and Nitrogen: Their presence in air causes burning of eyes, skin irritation, respiratory

illnesses and corrosion of metals. In higher concentration, it causes acid rain.

NCERT Questions

3. We can take following measures:

a. Water should be treated properly to make it free from germs, chemical and physical impurities.

b. Enforce laws to treat water and chemicals before disposing into water bodies.


c. Proper maintenance of pipes supplying tap water to avoid any corrosion and leakage.

d. Organize awareness programmes to keep water resources clean.

4. S.No. Pure Air Polluted Air

1. Free from harmful and poisonous gases. Increased levels of harmful and poisonous

gases.

2. Fit for breathing and good for health. Unfit for breathing and may cause

diseases like asthma, cancer etc.

3. Pure air is good for crop production and wild life. Polluted air is a threat to our ecosystem. It

affects crops, wildlife as well as aquatic life.

5. When harmful gases like sulphur dioxide and nitrogen dioxide, react with moisture present in air, they

form nitric acid and sulphuric acid. These acids when drop down on earth along with rain, is called acid

rain. Acid rain causes skin irritation, inhibits germination of plants, causes corrosion to bridges and

building. It changes the fertility of the soil, destroys plants and aquatic life.

6. Greenhouse effect is a process by which solar radiation is absorbed by green house gases and is

transmitted to all directions. This increases the temperature of the surroundings and is responsible for

global warming. Gases like CO , Methane, ntirous oxide, water vapours trap heat radiation and are 2

called greenhouse gases. Green houses are often used for growing flowers, vegetables and plants

(specially in cold region). Now because of increase in concentration of greenhouse gases in our

environment is adversely affecting the climate.

7. Continuous increase in temperature of the earth due to increase levels of green house gases is known

as global warming. Global warming in one of the biggest concern worldwide. Scientists believe climate

shifting, melting of glaciers (eg. Gangotri glacier), sudden floods in coastal areas are due to global

warming. The Kyoto Protocol is one such agreement made among the countries to reduce emission of

greenhouse gases.

Thermal radiationinto space: 195Solar Radiation

absorbed by Earth2235 W/m

67

168 324

Heat and energyin the atmosphere 452

Greenhouse gasabsorption: 350

Directly radiatedfrom surface: 40

Earth's land and ocean surfacewarmed to and average of 14°C

TheGreenhouse

Effect


8. The industries located around Agra like rubber processing, automobile, chemicals and especially the

Mathura oil refinery, were producing pollutants like sulphur dioxide and nitrogen dioxide, thus forming

acid rain. It corroded the marble of Taj Mahal monument. The suspended particles and ash(soot) from

Mathura refinery caused yellowish colour to Taj marbles. This is popularly called "Marble cancer

phenomenon". Supreme Court has taken several steps to save Taj from pollution.

I. Give reasons.

1. Thermal pollution is the change in the water temperatures of lakes, rivers, and oceans caused by made-

man industries or practices. These temperature changes may adversely affect ecosystems by

contributing to the decline of wildlife populations and habitat destruction. Any practice that affects the

equilibrium of an aquatic environment may alter the temperature of that environment and subsequently

cause thermal pollution.

2. Red blood cells absorb carbon monoxide molecules faster than they can absorb oxygen molecules, so

when there is a high concentration of carbon monoxide in the air, red blood cells may "replace" oxygen

with carbon monoxide. When oxygen cannot enter red blood cells, our essential organs suffer and may

shut down if oxygen is not absorbed, possibly resulting in death.

3. Global climate change has already had observable effects on the environment. Glaciers have shrunk,

ice on rivers and lakes is breaking up earlier, plant and animal ranges have shifted and trees are

flowering sooner. Global temperatures will continue to rise for decades to come, largely due to

greenhouse gasses produced by human activities. The Intergovernmental Panel on Climate Change

(IPCC), which includes more than 1,300 scientists from the United States and other countries, forecasts

a temperature rise of 2.5 to 10 degrees Fahrenheit over the next century.

Freshwater availability projected to decrease in Central, South, East and Southeast Asia by the 2050s;

coastal areas will be at risk due to increased flooding; death rate from disease associated with floods

and droughts expected to rise in some regions.

4. Yes, it is renewable because the amount of it on earth is always the same. It only changes in form and in

quality, so even though fresh water is becoming scarce and polluted water is increasing, it´s still water

and in the same amount. What the real question is that: how to keep the amount of fresh unpolluted

water steady and even increasing.

J. HOTS questions.

1. Waste organic matter in water is decomposed in water and a lot of dissolved oxygen is used up because

of that. That makes water deficient in oxygen. Moreover, the presence of decomposed organic matter

support weed growth further, reducing the oxygen supply. So, rivers, lakes, ponds, become unfit for

aquatic life and eventually turn into dead zones.

2. Cigarette smoking is very harmful since the smokers are inhaling a chemical called nicotine which is

poisonous and causes lung diseases. This is also responsible for killing millions of people every year

and affecting even non–smokers who breathe the air in which the smoke is mixed. So, to create

awareness amongst smokers, the warning is printed.

3. Lead is added to petrol for smooth combustion. But while petrol is burnt, lead compounds are released in

the atmosphere and it has been traced to a number of health problems connected to the nervous system

and kidneys. So, unleaded petrol has been introduced as a step toward greener environment.

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