Teachers' Resource Manual

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Science
Pull-out Worksheets

8
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 Contents
1. Crop Production and Management 10. Reaching the Age of Adolescence
Worksheet 1 (Engage)..........................3 Worksheet 1 (Engage)........................ 39
Worksheet 2 (Explore)..........................3 Worksheet 2 (Explore)........................ 40
Worksheet 3 (Extend)...........................4 Worksheet 3 (Extend)......................... 41
Worksheet 4 (Elaborate).......................5 Worksheet 4 (Elaborate)..................... 42
2. Microorganism: Friend and Foe 11. Force and Pressure
Worksheet 1 (Engage)..........................6 Worksheet 1 (Engage)........................ 43
Worksheet 2 (Explore)..........................7 Worksheet 2 (Explore)........................ 44
Worksheet 3 (Extend)...........................8 Worksheet 3 (Extend)......................... 45
Worksheet 4 (Elaborate)..................... 10 Worksheet 4 (Elaborate)..................... 45
3. Synthetic Fibres and Plastics 12. Friction
Worksheet 1 (Engage)........................ 11 Worksheet 1 (Engage)........................ 46
Worksheet 2 (Explore)........................ 12 Worksheet 2 (Explore)........................ 47
Worksheet 3 (Extend)......................... 13 Worksheet 3 (Extend)......................... 48
Worksheet 4 (Elaborate)..................... 14 Worksheet 4 (Elaborate)..................... 48
4. Materials: Metals and Non-Metals 13. Sound
Worksheet 1 (Engage)........................ 14 Worksheet 1 (Engage)........................ 49
Worksheet 2 (Explore)........................ 15 Worksheet 2 (Explore)........................ 50
Worksheet 3 (Extend)......................... 16 Worksheet 3 (Extend)......................... 51
Worksheet 4 (Elaborate)..................... 17 Worksheet 4 (Elaborate)..................... 52
5. Coal and Petroleum 14. Chemical Effects of Electric Current
Worksheet 1 (Engage)........................ 18 Worksheet 1 (Engage)........................ 53
Worksheet 2 (Explore)........................ 19 Worksheet 2 (Explore)........................ 54
Worksheet 3 (Extend)......................... 20 Worksheet 3 (Extend)......................... 55
Worksheet 4 (Elaborate)..................... 21 Worksheet 4 (Elaborate)..................... 56
6. Combustion and Flame 15. Some Natural Phenomena
Worksheet 1 (Engage)........................ 22 Worksheet 1 (Engage)........................ 57
Worksheet 2 (Explore)........................ 23 Worksheet 2 (Explore)........................ 57
Worksheet 3 (Extend)......................... 24 Worksheet 3 (Extend)......................... 58
Worksheet 4 (Elaborate)..................... 25 Worksheet 4 (Elaborate)..................... 59
7. Conservation of Plants and Animals 16. Light
Worksheet 1 (Engage)........................ 26 Worksheet 1 (Engage)........................ 60
Worksheet 2 (Explore)........................ 26 Worksheet 2 (Explore)........................ 61
Worksheet 3 (Extend)......................... 28 Worksheet 3 (Extend)......................... 62
Worksheet 4 (Elaborate)..................... 29 Worksheet 4 (Elaborate)..................... 63
8. Cell Structure and Functions 17. Stars and The Solar System
Worksheet 1 (Engage)........................ 30 Worksheet 1 (Engage)........................ 64
Worksheet 2 (Explore)........................ 31 Worksheet 2 (Explore)........................ 65
Worksheet 3 (Extend)......................... 32 Worksheet 3 (Extend)......................... 66
Worksheet 4 (Elaborate)..................... 33 Worksheet 4 (Elaborate)..................... 67
9. Reproduction in Animals 18. Pollution of Air and Water
Worksheet 1 (Engage)........................ 34 Worksheet 1 (Engage)........................ 69
Worksheet 2 (Explore)........................ 35 Worksheet 2 (Explore)........................ 69
Worksheet 3 (Extend)......................... 37 Worksheet 3 (Extend)......................... 70
Worksheet 4 (Elaborate)..................... 38 Worksheet 4 (Elaborate)..................... 71
 Answers
(Engage)
Worksheet 1 1. Crop Production and Management

1. (a) crop rotation (b) weeds (c) irrigation (d) silos

2. Uses: It is a cultivator. The cultivator is a tractor driven plough used for loosening and turning of the
soil.

Merit: It makes the ploughing of a field fast and easy.
3. (a) T (b) F (c) F (d) F
4. (a) fertilizer (b) NPK (c) Rhizobium (d) field fallow
5. (a) The plants of same type grown and cultivated in a field in large quantity are called crop.
(b) The science of farming, including cultivation of crop and rearing of animals is called agriculture.
(c) The watering of crops at different intervals is called irrigation.
(d) The process of loosening and turning up soil is called ploughing.
6. (a) The tasks performed by a farmer to obtain a good crop yield are called agricultural practices.
(b) The basic agricultural practices followed in India are:
l selection of soil l protection from weeds
l preparation of soil l pest control and disease protection
l seed selection and sowing l harvesting, threshing and winnowing
l irrigation l food grain storage
l manuring
(c) Trowel and harrow.
7. She should remember these points:

l turning of soil l sowing seeds at right depth
l regular irrigation in right amount
l crop protection from birds, pests and insects
(Explore)
Worksheet 2 1. Crop Production and Management
1. (a) moisture (b) heat (c) fungi
(d) animals (e) dried (f) contaminated
(g) sustaining (h) sun (i) microorganism (fungi)
(j) insects (moulds) (k) grain silos (l) gunny bags
(m) buffer
2. (a) Sickle Uses: Manual harvesting of crop
(b) Combine Uses: Threshing and winnowing
(c) Winnowing machine
Uses: Winnowing of grains to separate husk

3
 3. (a) (b) Grip Beam
Ploughshaft Handle

Bent plate
Ploughshare + handle
Hoe
Plough
4. (a) Amaranthus (chaulai), wild oat (javi), chenopodium (bathua), chickweed
(b) The loosening of soil makes air spaces between soil particles which allow roots to breathe easily.
(c) Field fallow – Leaving the soil uncultivated between two crops.
Crop rotation – Growing different crops alternately in same soil.
Mixed cropping : Growing two or more crops in same field at the same time.
All the above methods help in nutrient retention and replenishment of the soil.
(d) Kharif crop Rabi crop
l These are sown in rainy season (June to l These are sown in winter season (October to
September) March)

l Maize, paddy, cotton, pulses, groundnut l Wheat, gram, barley, potato

Science Around Us
(a) l Manure is a mixture of organic substances obtained from vegetable and animal waste. Manures are
rich in nitrogen, phosphorus and potassium. Manures improve soil texture and make it fertile.

l Compost is made from cattle waste and dry leaves. It makes the soil rich in humus.

l Fertilizer is chemical substance rich in specific nutrients added to the soil. Its prolonged use is

harmful and makes the soil infertile.

(b) Advantage: Manure and fertilizer make soil fertile and help in improving crop yield.

Disadvantage: Prolonged use of fertilizers reduces the self-replenishment capacity of soil and makes
it unfit for cultivation.
(c) Excessive use of fertilizers and weedicides is harmful to soil and kills the useful bacteria present in the
soil.
(Extend)
Worksheet 3 1. Crop Production and Management
1. (a) Sickle, combine
(b) Sprinkler system and drip system
(c) Cultivator, plough, hoe
2. (a) (i) Moat (ii) Rahat (iii) Dhekli
3. (a) Pump is the odd one. Other devices are manual devices used on field.
(b) Ocean is the odd one. Other sources are used for irrigation of fields.
(c) Cow-dung is the odd one. Others are chemical fertilizers.

4
 4. (a) (ii) (b) (vi)
(c) (v) (d) (iii)
(e) (vii) (f) (iv)
(g) (i)
5. (a) Agriculture involves cultivation of food crops while horticulture is the cultivation of ornamental
plants, flowers, nuts, fruits etc.
(b) In sprinkler irrigation, water is sprinkled through rotating nozzles in all directions. In drip irrigation,
water is released drop by drop.
(c) The seeds are scattered in the field in broadcasting, seed drill makes furrows in soil and sows the
seeds.
6. Small plantlets are new plants with 4.5 leaves which are transplanted from nurseries to the main field.
They are grown in nurseries to enable selective cultivation of healthy seedlings, so that better crop
production takes place.
Science Around Us
(a) These animals/insects are called pests, e.g. rodents (rats), insects (grasshoppers etc.), birds are pests.
(b) Farmers fence their fields to protect them from animals and use scare-crow to shoo away birds. They
use insecticides, pesticides and fungicides to protect against diseases, pests and insects.
(c) Examples of insecticides are : BHC (gamma xene), malathion, dimecron and polythion.
(d) l Insecticides are chemicals which kill insects only.
l Pesticides are sprayed at appropriate time of pest’s life cycle to control their growth.

l Fungicides are sprayed to prevent fungal diseases of crops.

l Rodenticides are used against rodents (rats) which attack the crops.

(Elaborate)
Worksheet 4 1. Crop Production and Management
1. Do it yourself.
2. Atmospheric De
on nit
f i xati Nitrogen rif
ica
ro g en tio
Nit Ammonification n
Ammonium
Salts
Animal
Nitrogenous Plant proteins proteins Nitrites and
compounds Nitration

Decomposers

on
Soil bacteria
ic ati
Compounds of rif
Nitrogen in the soil Nit

5
 (a) Process of conversion of free nitrogen into useful nitrogenous compounds.
(b) Formation of organic nitrogen compounds (amino acids) from inorganic compounds present in
environment.
(c) Conversion of organic nitrogen to ammonia by bacteria.
(d) Conversion of soil nitrates into nitrogen by bacteria or artificial fixation.
3. (a) Hulling – removal of outer covering of a seed of fruit.
Milling – process of grinding of grain into powdered form (flour).
Winnowing – process of removal of husk from grain.
(b) Plough – process of loosening and turning of soil.
Cultivator – Machine attached to tractor used for ploughing.
Hoe – Device used for weed removal and loosening of soil.
Leveller – Device used to process the ploughed land lightly to level it.
4. Advantages of soil preparation are:
l It loosens soil particles for better aeration and percolation.


l It brings nutrient rich soil on the top for crops.

l It promotes growth of useful bacteria and earthworms.

l It permits deeper root penetration.

5. Farming practices that are not environment friendly are:

l Overspray of pesticides as they kill useful soil organisms also.

l Overuse of fertilizers as it makes soil infertile over some time.

l Repeated sowing of crops one after the other uses up all soil nutrients.

6. Modern implements have made the farming work easier and faster than traditional ones. This has helped
to improve crop yield.
7. (a) Apart from efficient crop production, storage of grains and effective distribution are also important.
(b) l Use of good quality seeds.
l Use of modern agricultural techniques

l Sufficient means of crop protection.

l Use of modern equipments.

(c) Hybridization and tissue culture has helped to develop high yielding and disease resistant varieties.

(Engage)
Worksheet 1 2. Microorganism: Friend and Foe
1. (a) Chlamydomonas, Algae group (b) Paramoecium, Protozoan group
(c) Bread mould, Fungi group (d) Pencillium, Fungi group
(e) Bacteriophage, Virus group (f) Spirogyra, Algae group
2. (a) F (b) T (c) T (d) T
3. (a) Sodium benzoate, Potassium metabisulphite
(b) Pickle (mango or fruits), Pickle (carrot or vegetables)
(c) Jam, Jelly (d) Meat, Fish
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 4. (a) antibodies (b) Tuberculosis
(c) Anthrax (d) Fermentation
5. (a) Living organisms which cannot be seen by naked eyes are called microorganisms. They are
observed with the help of magnifying glass or microscope.
(b) (i) Process by which spoilage of perishable food items is prevented using chemical or physical
methods is called food preservation.
(ii) The process of injecting small quantity of weakened microbes in the body to immune it
against the disease is called vaccination.
(iii) The disease causing microorganisms are called pathogens.
(c) Diseases which get transmitted from one person to another through direct or indirect contact are
called communicable diseases e.g. tuberculosis, conjunctivitis.
(d) The process of breakdown of large organic molecules into smaller ones by the enzymatic action
in the absence of air is called fermentation. It is used in baking of cakes and making of wines.
(Explore)
Worksheet 2 2. Microorganism: Friend and Foe
1. (a) preservative (b) Rhizobium bacteria
(c) vector (d) antibodies
2. (a) Amoeba, Euglena (b) Bread mould, penicillium
(c) Amoeba (d) Fungi and bacteria
(e) Foot and mouth disease, Anthrax, Rinderpest
3. (a) (ii) (b) (iii) (c) (iv) (d) (i)
4. (a) Agar – agar, gelatin and sea-weed are used as thickening agents.
(b) Water – Entamoeba, Rotavirus
Soil – Actinomycetes, bacteriophage
Other organisms – Escherichia coli, salmonella
(c) Plasmodium vivax (Malaria), Entamoeba histolytica (Amoebic dysentry) and Giardia (Giardiasis)
(d) Yeast and microalgae mixed culture are rich in proteins. They are a potential source of protein
and used in food.
5. (a) Microorganisms are used in agriculture in the following ways –
l Nitrogen fixation by bacterium Rhizobium and blue green algae makes the soil fertile.
l Anaerobic bacteria convert organic waste into biogas and manure. Manure is used for soil
enrichment.
Biological decomposers decompose the dead plants and animals into simpler substances and
l

mix them in soil.

(b) Uses of microorganisms are:
l preparation of medicines
l preparation of curd, bread, cakes etc.
l production of wines and alcohol
l cleansing of environment by organic waste decomposition
l improving of soil fertility for agriculture.

7
Science Around Us
Pathogens enter our body through eyes, mouth, nose, urogenital openings, wounds or bites (which
breach the skin barrier). They spread through direct contact with skin, body fluids or sexual contact.
they also get transmitted by touch, droplet infection or use of common articles. Air, water and vectors
also carry pathogens into our body. Contaminated food, water, blood etc. carry disease causing germs.
Mosquites, flies, mites and ticks also transmit disease.
Examples of some pathogens are:
Fungi – Histoplasma, Aspergillus, crypto coccus.
Bacteria – Eschirichia Coli, Salmonella
Virus – Hepatitis C, HIV (Humanimmuno-deficiency virus), Zika.
(Extend)
Worksheet 3 2. Microorganism: Friend and Foe
1. (a)
Lactobacillus, yeast (b) Renin, yeast
2. (a)
Bacilli, spirilla, cocci (b) Between 1010 and 1011
(c)
Useful lactobacillus; Harmful – Mycobacterium tuberculosis
(d)
Rhizobium
3. (a)
We stop food from getting spoilt by using physical or chemical methods called food preservation.
(b)
Advantages of preserving food are – it prevents wastage of food, food can be stored for later use
and it can be stored for large number of buyers/consumers.
(c) (i) Bacteria living in our intestines help in the breaking of complex molecules and aid in digestion.
(ii) In tanning operations, Aspergillus, rhizobus, bacillus etc. are used in soaking, dehairing
bating and degreasing.
(iii) Anaerobic respiration of micro-organisms decomposes the organic waste into biogas and
manure.
4. Bacteria–They are found almost everywhere, even in human body. They are useful as well as harmful.

Cocci Bacilli Spirilla

Fungi–Fungi are saprophytes which grow by producing spores. While yeast helps in fermentations,
bread mould spoils the bread.

Bread mould Pencillium

8

Algae–Algae are unicellular as well as multicellular organisms.

Flagella
Basal
granule
Cytoplasm
Nucleus
Chloroplast
Pyrenoid
Cell wall Nostoc
Chlamydomonas

Protozoa–They exist in water, soil etc in colonies or alone.

Cilia

Macronucleus
Micronucleus
Oral groove
Cytosome
Waste
Food vacuole Cytopyne
Water vacuole

Amoeba
Paramoecium

Euglena

Virus–They have characteristics of both living and non-living organisms.

RNA strand

Capsomeres

Influenza virus Tobacco Mosaic Virus

9
Science Around Us
(a) Wine making: Yeast contains enzyme invertase which breaks glucose into ethyl alcohol and carbon
dioxide.
(b) Curd from milk: The bacterium lactobacillus present in milk breaks down lactic acid and results in
curding of milk.
(c) Bread making: Yeast causes fermentation of dough and liberated carbon dioxide makes the dough to
rise. On baking, the gas escapes out, leaving the food/bread fluffy and porous.

(Elaborate)
Worksheet 4 2. Microorganism: Friend and Foe
1. Plant disease Causal organism Mode of transmission Preventive measures
(a) Tuberculosis Bacteria Droplet infection BCG vaccine
(b) Chickenpox Virus Air/contact Hygienic conditions, clean clothes
(c) Ringworm Worm food hygienic food
(d) Cholera Bacteria water, food prevention of water stagnation and
dirt accumulation.
(e) Typhoid Bacteria water, air proper disposal of excreta, hygienic
food.
(f) Polio Virus water polio vaccine.
2. (a) Acquired Immuno Deficiency Syndrome
(b) Virus (HIV)
(c) It affects the immune system of the body.
(d) No treatment for AIDS has been discovered so far, just preventive measures can be taken.
3. (a) Virus
(b) blue green algae.
(c) microbiology.
4. (a) The process of extraction of metals such as copper, zinc, lead etc. through the use of living
organisms is called bioleaching Bacteria used: Thiobacillus.
(b) Pulse polio programme is an immunization campaign of the government of India for fighting
poliomyelitis through vaccination. Polio drops contain attenuated virus. If diarrhoea is due to
virus, body’s response to infection may interfere with vaccination.
(c) Do it yourself
5. (a) Heating: Heating food at 110°C for half an hour kills food spoiling microbes. Food can be stored
for later use.
(b) Pasteurization: Milk is heated to 60-65°C for about 30 minutes. It kills bacteria present in it and
cooling it quickly inhibits bacterial growth.
(c) Cooling or Freezing: Vegetables, fruits, meat, curd and cooked food can be kept at low temperature
to retards bacterial growth and inactivate enzymes.
(d) Chemical process: Chemical preservatives kill the food spoiling microorganisms and help to
preserve food for long, even months.

10
 (e) Drying: Removal of moisture content of food retards the growth of food spoiling microorganisms,
It is done by sun drying and smoking.
(f) Canning: Food material, once heated to kill the germs, is canned under vaccum so that it remains
safe for longer periods.

(Engage)
Worksheet 1 3. Synthetic Fibres and Plastics
1. (a) (i) (b) (ii) (c) (iii) (d) (i)
2. (a) terrywool (b) terycot/polycot
(c) ester (d) terycot
3. (a) F (b) F (c) T (d) T
4. (a) Fibre: It is thin and long thread like material used to make fabrics.
(b) Plastic: It is a synthetic material which can be moulded into desired shape.
(c) Polymerisation: The process of linking smaller molecules into chains is called polymerisation.
(d) Biodegradable material: It is the material which can be decompose through natural processes.
(e) Non-biodegradable material: It is the material which cannot decompose to harmless substance
through natural processes.
5. Natural fibre Synthetic fibre
• These materials occur in nature and involve no man- • These are polymers which are made in laboratories
made materials. from small molecules chemically.
• e.g. cotton, jute, flax, wool • e.g. nylon, rayon, teflon, PVC.

6. Two groups of plastics are:

• Thermoplastic–These can be softened on heating and moulded repeatedly in desired shapes, e.g.
PVC, nylon, polythene.

• Thermosetting plastic–Once moulded into a shape these cannot be moulded on reheating, due to
formation of cross links between adjacent polymers.
7. Nylon Polyester
(i) It is very strong, elastic, lustrous and wrinkle- (i) It is strong and long lasting, prepared by ester
resistant. bonds.
(ii) It is not attacked by fungus/moth and does not (ii) It absorbs very little water and is wrinkle resistant
absorb water. e.g. terylene, decron, terene.
e.g. fishing net, tooth brush, bristles etc.

Rayon Acrylic
(i) It is made from wood pulp cellulose and is called (i) It has similar feel wool and is called artificial
artificial silk. wool.
(ii) It can be dyed in different colours, has silky texture (ii) It is lighter in weight, is cheaper and longer lasting
and is woven like silk fibre. than wool.
e.g. bandages, surgical dressing, tyre cord, etc. e.g. sweaters, shawls, blanket, carpet, etc.

11
 (Explore)
Worksheet 2 3. Synthetic Fibres and Plastics
1. (a) monomers (b) man-made (c) nylon (d) rayon
2. (a) (ii) (b) (iii) (c) (i) (d) (iv)
3. (a) Rayon (b) Polymer (c) Polythene (d) Plastic
(e) Polyester (f) Bakelite
4. (a) Polythene (b) Polyvinyl chloride
(c) Teflon (d) bakelite
(e) polystyrene
5. (a) Rayon is made from cellulose obtained from wood pulp. It is also blended with cotton.
(b) Polyester is made from petroleum products. It is prepared by reaction leading to ester bonds
between their repeated units.
(c) (i) natural fabric (ii) natural fabric
6. Polymer is a long chain like unit consisting of large number of small molecules joined to each other
by chemical bonds. The smaller molecules are called monomers.
–A–A–A–A
or
– (–A–)n—
e.g. – (–CH2 – CH2 –)n–
Science Around Us

Nylon Polyester

• fishing nets, parachute ropes. • sarees, dress material, curtains

• fabricating sheets, brush bristles. • sails of sail boats
• making elastic hosiery. • water hose for fire fighting
• socks, neckties, ropes, etc. • conveyor belts.

Rayon Acrylic

• manufacture of carpets • sweaters and shawls

• textile industry for fabrics • making blankets, warm bedsheets.
• manufacture of tyre cords. • carpets and mats
• making bandages and surgical dressings. • acrylic clothes.

12
 (Extend)
Worksheet 3 3. Synthetic Fibres and Plastics
1. e
S
a
A C R Y L I C
L
K
b f
P O L Y T H E N E
E
c
P O L Y M E R
d g
R A Y O N
L Y
E L
N O
E N

2. (a)Material: Terycot Reason: It is durable and absorbs sweat

(b) Material: Bakelite Reason: It is an insulator and does not melt/soften on heating.
(c) Material: Nylon Reason: It is very strong and does not absorb water.
(d) Material: Acrylic Reason: It has texture like wool, keeps warm and is cheaper
than wool.
(e) Material: Melamine Reason: It is unbreakable, hard and fire-resistant.
(f) Material: Melamine and nylon Reason: It is strong and hard (malamine). It is strong with
high tensile strength. (nylon)
3. Advantages Disadvantages
(a) They do not shrink. (a) They are non-biodegradable and cause soil and
water pollution.
(b) They are wrinkle free and abrasion free. They need (b) They catch fire easily and should be avoided in
little or no ironing. kitchen.
(c) They absorb very little water and dry quickly. (c) They do not absorb sweat and are not ideal for
summer season.
(d) They last longer as compared to clothes made from (d) They develop static electricity in winters and give
natural fibres. sparks. These can cause skin problems.
Science Around Us
Plastics are becoming material of choice because:-
• They are light weight as compared to wood, metals etc.
• They are strong and durable. They last longer due to their high tensile strength.
• Plastics are insulators and do not let heat and electricity to flow through then.
• Plastics are cheaper than metals.
• Plastic can be coloured as per choice and moulded in any shape.
• Plastics are not reactive to air, water, soil and bugs.
13
 (Elaborate)
Worksheet 4 3. Synthetic Fibres and Plastics
1. Do it yourself.
2. (a) It is a synthetic fibre of high elasticity. It is called lycra.
(b) It is used to make swimsuits, waist bands and disposable diapers.
(c) Carbon, hydrogen, nitrogen, chlorine, sulphur.
(d) Polyethylene terephathalate
3. • It causes soil pollution as it is non-biodegradable.
• It reduces water percolation into soil.
• It chokes the drains and war pipes.
• It pollutes rivers and oceans and harms aquatic life.
• It causes death of stray animals who chew plastic bags with food.
4. Following measures should be taken to prevent plastic pollution:-
• Avoid using articles made of plastic, such as carry bags and bottles.
• Reuse the plastic materials such as bags, cups and bottles.
• Do not discard plastic waste in the open or in waterbodies.
• Recycle plastic bags scientifically.
• Never burn any plastic waste as it produces toxic gases.
• Dispose off plastic waste carefully.
• Follow 4 R formula
– to minimize environment damage caused by plastic (Reduce, Reuse, Recycle and Recover)
• Minimise the use of plastics in the kitchen.
(Engage)
Worksheet 1 4. Materials: Metals and Non-Metals
1. (a) (iv) (b) (iv) (c) (i) (d) (ii)
2. g
F h
M
f
A E A
a
M E T A L R L
b
D U C T I L E
M I E
I L A
e
    M N I B
E I Z L
R U E E
C M R
d
G U
c
S O N O R O U S
L Y
D

14
 3. (a) (iii) (b) (iv) (c) (i) (d) (v) (e) (ii)

4. (a) Elements are classified on the basis of their physical and chemical properties.
(b) (i) Alloy: The substance formed by combining two or more elements whose properties are
entirely different from constituent elements.
(ii) Malleability: Ability of metals to be drawn into thin sheets is called malleability.
(iii) Ductility: Ability of metals to be drawn into thin wires is called ductility.
(iv) Sonority: Ability of metals to produce sonorous sound on being struck is called sonority.
(v) Corrosion: Reaction of metals surfaces with air and moisture leading to their conversion
into oxides is called corrosion.
5. The following measures must be taken to prevent rusting:-
• iron surfaces should be painted to cut contact with air.
• surfaces should be kept dry.
• layer of zinc can be galvanized on iron surface.
• regular monitoring should be done to prevent rusting.
6. Physical properties of metals are:-
(a) All metals except mercury are in solid state at normal pressure.
(b) Metals except copper and gold are silvery grey in colour.
(c) Metals have shiny appearance or lustre.
(d) Metals except sodium and potassium, are hard substances.
(e) Metals are strong with high tensile strength.
(f) Metals are malleable, ductile and sonorous.
(g) Metals are good conductors of electricity. Silver is bad conductor.

(Explore)
Worksheet 2 4. Materials: Metals and Non-Metals

1. (a) oxygen (b) water (c) blue (d) red (e) non-metals

2. Material Flattens/Breaks into pieces

(a) Iron nail Flattens

(b) Pencil Breaks into pieces

(c) Chalk Breaks into pieces

(d) Aluminum wire Flattens

(e) Copper wire Flattens

15
 3. (a) Phosphorus is stored in water as it is highly reactive. It reacts with oxygen even at room
temperature.
(b) Metals are sonorous and produce a ringing sound on being struck. Thus bells are made of metals.
(c) Metals have high density as the particles are closely packed together in fixed arrangement.
(d) Silver is a shiny metal with high lustre. It reflects light and is used for making mirrors.

4. (a) copper, silver (b) sodium, potassium (c) neon, argon

(d) Diamond (e) Bromine

5. (a) Metalloids are substances which show some properties of metals and some properties of non-
metals. e.g. boron, silicon.
(b) Sulphur is sometimes found in pure or native state. It also exists as sulphide and sulphate minerals.
6. Metals Non-metals
• Ductile, malleable, sonorous • Non-ductile, non sonorous, non-malleable
• Good conductors of electricity • Poor conductors of electricity
• Lustrous appearance • Dull appearance
• Strong with high tensile strength • Brittle with poor tensile strength.

Science Around Us
Silicon:- Making of solar cell panels, making glass, used in microelectronics and computer devices.
Phosphorus:- Manufacture of matchstick, rat poison, fertilizers, phosphoric acid
Sulphur:- Manufacture of gun powder and sulphuric acid, vulcanization of rubber.
Hydrogen:- Preparation of fuels, ammonia, hydrogenated oils.
(Extend)
Worksheet 3 4. Materials: Metals and Non-Metals
1. (a) (i) calcium (ii) magnesium
(iii) sodium (iv) copper
(b) (i) sulphur (ii) nitrogen
(iii) chlorine (iv) sulphur
2. (a) 2Fe + O2 + H2O → Fe2O3 + H2
(b) 2Mg + O2 → 2MgO
(c) 2Cu + H2O + CO2 + O2 → Cu (OH)2 + CuCO3
(d) S + O2 → SO2
(e) S + H2O → no reaction
(f) CuSO4 + Zn → ZnSO4 + Cu
3. (a) Metals: iron, calcium, potassium, sodium
Non-metals: iodine, oxygen, chlorine, carbon
(b) Iron (in haemoglobin)
(c) CO2 accumulates in the process of respiration, leading to metabolic action, it is a compound.
(d) Hydrogen, oxygen and carbon are essential for living beings.

16
 4. (a) Most reactive metals such as sodium and potassium react vigorously with oxygen, water and acids
even at room temperature. They generally do not react with bases/alkalies.
(b) Less reactive metals react only with steam, e.g. iron
3Fe + 4H2O → Fe3O4 + 4H2
(c) Copper does not react with water at all, even at high temperature.
Cu + H2O → no reaction.
Science Around Us
Iron:
• construction of buildings, bridges and strong structures
• making machines and alloys such as steel
Copper
• making electrical wires and cables, transformers etc.
• making cookware
Aluminium
• making alloys, utensils etc.
• aluminium foil for food packaging.
Zinc
• making alloys (brass, nickel, silver, aluminium, solder)
• making paints, rubber, cosmetics, electrical equipments.
(Elaborate)
Worksheet 4 4. Materials: Metals and Non-Metals
1. Au < Ag < Cu < H < Pb < Fe < Zn < Al < Mg < Na < Ca < Ba < K
2. (a) ZnSO4 + Cu (b) FeSO4 + 6Cu
(c) No reaction (d) No reaction
(e) No reaction (f) 2Al2 (SO4)3 + 6Cu
(g) 2NaOH + H2 (h) MgSO4 + H2
3. (a) Aluminium can be beaten into thin sheets suitable for making foils.
(b) Metal is a good conductor of electricity and conducts heat into the liquid.
4. Alloy Metals present Used in
(a) Brass copper, zinc making pipes, screws etc.
(b) Steel Iron, nickel, chromium Surgical instruments
(c) German silver Copper, nickel, zinc Machine fitting, tableware etc.
(d) Aluminium alloys aluminium, copper, magnesium body of aeroplanes
(e) Solder zinc, lead joining metals

5. The reaction in which a more reactive metal displaces a less reactive metal from its salt solution is
called displacement reaction.
e.g. Mg + CuSO4 → MgSO4 + Cu
Copper cannot displace zinc present in zinc sulphate because copper is less reactive than zinc.
17
 6. (a) Rusting is a chemical change in which iron reacts with moist air resulting in the formation of iron
oxide on its surface. This corrodes the metal surface.
[Fe + O2 + H2O → FeO + Fe2O3]
(b) Corrosion of copper or copper alloys due to exposure to atmosphere, leads to formation of cuprite
on its surface. It runs the colour of surface from brown to green.
Silver gets tarnished by a black layer of silver sulphide and oxide on its surface due to presence
of sulphurous gases in the atmosphere
7. Electroplating: It is the process of depositing a thin layer of metal over an object of cheaper metal with
the help of electric current for the purpose of decoration or prevention of corrosion. Silver or gold
plating on brassware and electroplating of iron with nickel are common examples of electroplating.

Anodising is an electrolytic process used to increase the thickness of metal surfaces with an oxide layer
which helps to prevent them from corrosion and damage. Since it occurs at anode electrode, it is called
anodising. Aluminium and its alloys are anodised to prevent their corrosion.
4 Cu + O2 → 2 Cu2O
2 Ag + O2 → Ag2O
2 Ag + H2S → Ag2S + H2
(Engage)
Worksheet 1 5. Coal and Petroleum
1. (a) (iv) (b) (iii) (c) (iii) (d) (iv)
2. (a) F (b) T (c) T (d) T
3. (a) Petroleum (b) Fractional distillation
(c) natural resources (d) biogas
4. (a) fuels (b) carbon monoxide
(c) electricity (d) coke, coal gas, coal tar
(e) viscous liquid, unpleasant.
5. (a) Fuel: The material which burns to produce energy mainly in the form of heat is called fuel.
(b) Petroleum: The fossil fuel which is obtained from dead remains of plants and animals under the
sea bed.
(c) Natural gas: It is a mixture of lower hydro-carbons accruing deep inside the earth’s crust near
or above an oil field.
(d) Refining of Petroleum: The process of separation of useful products of petroleum through
distillation is called refining of petroleum.

18
 6. Exhaustible resources–These are present in limited quantity and are likely to get exhausted over a
period of time. e.g. fossil fuels.
Inexhaustible resource– These are present in unlimited quantity and are not likely to get exhausted.
e.g. solar energy.
7. Properties of a good fuel are:
• It has a high calorific value.
• It does not produce toxic gases/solid residue.
8. Oil is lighter than water, for its density is less than that of water. Also, oil does not get dissolved in
water. Thus it floats over water forming a layer over water surface.
(Explore)
Worksheet 2 5. Coal and Petroleum
1. (a) distillation tower (b) crude oil (c) paraffin wax
(d) coal (e) moth repellant (f) carbonisation
2. f
D
i
e h
C e P
a
F o s s i l f u e l s
a e t
g b
l l B R e f i n i n g
c
i C o k e
d
P e t r o l
u e
m u
e m
n
3.(a) The demand of fossil fuel has increased due to increased population and increased dependence of
people on energy sources. Fossil fuels need to be conserved as they are limited in nature and are
likely to get exhausted.
(b) LPG – cooking fuel, fuel in gas geysers
CNG – vehicle fuel, cooking fuel
(c) Limitations of fossil fuels are:
• They are exhaustible natural resources and should be used judiciously.
• They produce harmful gases on burning.
• Their transportation to remote areas is difficult.
(d) Pollutants emitted by fossil fuels-
• cause respiratory problems to human beings.
• kill the birds and small animals.
• cause global warming.
• result in acid rain which affects monuments, buildings, soil and waterbodies.
19
Science Around Us
Crude oil is extracted from oilfields under the seabed
and brought to the surface through pipelines. It is sent
Distillation tower (8) (2) Petroleum gas
to distillation tower for refining and separation of its
components. The oil is heated to high temperature and Oil vapours (9) (3) Kerosene
the vapours are allowed to rise up in the distillation Furnace (10) (4) Petrol
tower. As the vapours rise, the components of
(5) Diesel
crude oil start separating at different temperatures.
Lubricating oil, paraffin wax, diesel, petrol, kerosene Crude oil (1) (6) Paraffin wax
and petroleum gas are some such products obtained (7) Lubricating oil

from oil. It is due to a variety of products obtained

from petroleum that it is also called black gold.

(Extend)
Worksheet 3 5. Coal and Petroleum

1. Constituents of Petroleum Uses

Petrol Automobile fuel, solvent for drycleaning
Kerosene domestic fuel, illuminant
Diesel fuel for trucks, buses, railways, generators etc.
Lubricating oil lubricants for machines
Paraffin wax making candles, polish for shoes, grease
Bitumen road, surfacing, roofing

2. (a) Jharkhand, Odisha, West Bengal (b) Assam, Gujarat, Tamil Nadu
(c) Gujarat, Kerala, Karnataka (d) Assam, Maharashtra, Gujarat.
3. Dead remains of plants Anaerobic thermal Increased temperature
and animals decomposition and pressure

Carbonisation Further degradation and Increased temperature

compression and pressure due to
sedimentation on surface

Increased carbon content Fossils fuels are formed

4. (a) Carbonisation: Anaerobic thermal degradation of wood is called carbonisation.

(b) Destructive distillation: The breaking up of a fuel by heating it to high temperature in the absence
of air is called destructive distillation.
(c) Fractional distillation: The distillation of petroleum to separate its useful products by passing
its vapours to distillation tower is called fractional distillation.

20
 5. Physical Features Coal Physical Features Petroleum
• Black coloured solid fuel • Black coloured viscous liquid which does not flow.
• Brittle • Lighter than water
• Burns without flame • has unpleasant odour.
6. Coke–It is Greyish black residue left in boiling tube which has 98% carbon and has no moisture or
volatile matter.
Coal tar– It is a black tarry material which is highly viscous with unpleasant odour and consists of
different carbon compounds.
Coal gas– It is the gaseous product consisting of hydrogen, methane and carbon monoxide.
Science Around Us
(a) Yes we need to worry because the replenishment of coal over this period is not possible due to the
conditions prevailing today. Thus we will run short of coal reserves in the years to come.
(b) The coal mines are found in Jharkhand (Jharia, Bokaro), Odisha, Madhya Pradesh and West Bengal
(Raniganj)
Varieties of coal are:
Anthracite: It is hard coal of bright black colour. It has the highest carbon content and is of best quality.
Bituminous: It is household coal. It has lower calorific value than anthracite.
Lignite – It is brown coloured soft coal and has still lower calorific value.
Peat: It is light brown coloured coal with least carbon content.

(Elaborate)
Worksheet 4 5. Coal and Petroleum

1. SOLID FUEL LIQUID FUEL GASEOUS FUEL

Definition. A fuel which exists Definition: A fuel which exists in Definition: A fuel which exists in
in solid form in natural state is liquid form in natural state is gaseous in natural state is called
called solid fuel. called liquid fuel. gaseous fuel.
Examples: coal, fuel wood etc. Examples: petrol, diesel Examples: coal, gas, natural gas

2. (a) The vegetation dies and forms peat.

The peat is compressed between sediment layers and forms lignite

Further compression forms sub-bituminous coal.

Sub-bituminous coal is further compressed and bituminous coal is formed.

Anthracite formation occurs

(b) The geological time period which is called carbon bearing time and tasted about 300 million years
ago is called carboniferous age.
3. (a) Carbon dioxide (b) Carbon monoxide (c) Sulphur oxides
(d) Nitrogen oxides (e) Unburnt carbon particles (f) Smoke

21
 4. Fuel Kj/Kg Fuel Kj/Kg
Petrol 45000 Kerosene 45000
Diesel 45000 Biogas 35000-40000
CNG 50000 LPG 55000
5. CNG is considered a cleaner fuel than petrol as it does not produce nitrogen oxides or sulphur oxides
on burning.
6. • Drive at constant and moderate speed
• Do not use accelerator quite often.
• Get four vehicle serviced regularly.
• Switch off the engine at traffic lights or when waiting.
7. • Natural gas is used as domestic and industrial fuel.
• It is used for obtaining hydrogen on industrial scale.
• It is used for manufacturing carbon black.
• It is a raw material for making petro-chemicals and fertilizers.
8. (a) Fossil fuels can be conserved in the following ways:-
• Using as little fuel as possible for our work.
• Avoiding wastage of fuel
• Switching off engines at traffic signals.
• Using less electricity and electrical gadgets.
• Switching to renewable sources of energy.
•   Adopting public transport and car pool.
• Campaigning for adoption of energy saving methods.
(b) Advantages of judicious use of energy:-
• It prevents pollution and global warming.
•   It helps to save fuel for future.
(Engage)
Worksheet 1 6. Combustion and Flame
1. (a) (ii) (b) (iv) (c) (iii) (d) (ii)
2. (a) (iii) (A) (b) (i) (C) (c) (ii) (B)
3. Material Combustible Non-Combustible
Wood 
Paper 
Iron nails 
Kerosene oil 
Stone piece 
Straw 
Charcoal 
Matchsticks 
Glass 

22
 4. (a) fuel (b) heat (ignition temperature)
(c) air/oxygen (d) remove
5. (a) Combustion: The process by which a substance chemically combines with oxygen with
simultaneous evolution of heat and light is combustion.
(b) Ignition temperature: The lowest temperature upto which a substance must be heated before it
catches fire is ignition temperature.
(c) Calorific value: The amount of energy given by a fuel per unit mass on its combustion is called
calorific value.
6. (a) A flame is the shining zone in which the combustible gaseous material undergoes combustion
producing heat and light.
(b) When a combustion process is so rapid that a lot of energy is released in the form of sound along
with heat and light, it is called explosion.
(c) Zones of a candle flame are: complete combustion zone, central incomplete combustion zone and
inner dark no combustion zone.
(d) Two parts of a candle are:
• Wax– This acts as a fuel for burning the candle.
• Wick– The candle flame burns on the wick as wax is used up.

(Explore)
Worksheet 2 6. Combustion and Flame
1. (a) Calorific (b) paraffin (c) Luminous (d) Ignition
2. (a) chemical, oxygen (b) minimum, ignition
(c) low, combustible (d) burning
3. (a) False. Air is necessary for combustion
(b) True.
(c) False: inner zone is the zone where unburnt substances are formed.
4. • Smokeless chulha uses biogas instead of cow dung cakes as fuel.
• It has high efficiency.
5. (a) (ii) (C) (b) (iii) (B) (c) (i) (A)
6. (a) Do it yourself.
(b) When the person is wrapped in a blanket, it cuts the oxygen supply to his clothes and the burning
stops.
(c) Conditions for combustion are: presence of a combustible substance, presence of air/ oxygen,
attainment of ignition temperature.
(d) Burning of candle involves formation of a flame as wax vaporises.
Burning of coal does not involve formation of a flame as coal does not vaporise.
7. (a) Magnesium oxide (white coloured ash)
(b) Energy is released in the form of heat and light.

23
Science Around Us
(a) He should first soak some paper in kerosene and put on the fuelwood, so that wood gets enough heat
to start burning. It won’t be possible to start fire without paper and kerosene as wood has high ignition
temperature
(b) Kerosene and molten wax vaporise when they get heated up. This leads to formation of flames and they
start burning.
(Extend)
Worksheet 3 6. Combustion and Flame
1. (a) carbon dioxide, heat, light, sound
(b) carbon monoxide, heat, light, sound
2. Do it yourself
3. (a) (i) kilo joule/kg (ii) joule
(b) Fuel Calorific value Fuel Calorific value
(kj/kg) (kj/kg)
(a) LPG (i) 50000 (b) fuel oil (i) 45000
(b) Cow dung cake (ii) 7000 (d) Kerosene (ii) 45000
(c) CNG (v) 50000 (f) wood (vi) 22000
(d) alcohol (vii) 35000 (h) Hydrogen gas (viii) 150000
4. The goldsmith is blowing into the flame while melting the gold material.
5. Incomplete combustion has following disadvantages:
• It results in production of carbon monoxide gas which is toxic.
• It causes wastage of energy of the fuel.
6. It is difficult to burn a heap of green grass as it has moisture content which keeps its temperature low
and a lot of heat needs to be supplied to burn it.
7. The following are the types of combustion:
(a) Rapid combustion– It is the combustion which occurs in a short time with evolution of large
amount of heat and light, e.g. LPG burning.
(b) Slow combustion: It is the combustion in which no light is produced and temperature of the
substance remains almost unchanged, e.g. digestion.
(c) Incomplete combustion: It is the combustion reaction occurring in insufficient quantity of air,
e.g.
2C + O2 → 2CO
(d) Complete combustion: It is the combustion reaction occurring in a sufficient quantity of air e.g.
C + O2 → CO2
Science Around Us
The foamite fire extinguisher or dry powder extinguisher or pyrene fire extinguisher or soda acid extinguisher
are kept in buildings. In soda acid fire extinguisher, the container holds sodium bicarbonate solution. The
screwed cap contains a plunger mechanism covered by safety guard. A glass phial containing sulphuric acid
lies the beneath the plunge. When plunge is struck, the glass phial breaks and the acid and sodium bicarbonate
mix. This produces carbon dioxide with pressurises the space above the liquid. The liquid forces out the nozzle
and extinguishes the fire. Soda acid fire extinguisher is the most common type of fire extinguisher.

24
 (Elaborate)
Worksheet 4 6. Combustion and Flame
1. (a) The candle keeps burning in (i). It extinguishes in cases (ii) and (iii).
(b) The flame flickers and gives smoke because in candle burns in insufficient oxygen and finally
when there is lack of oxygen, it extinguishes.
(c) The flame goes off because oxygen is required for combustion. When oxygen becomes less/scarce,
the combustion stops.
2. (a) Potassium chlorate, sulphur, starch and glue.
(b) White phosphorous ignites spontaneously in air and catches fire.
(c) Combustion starts when heat produced by friction during rubbing ignites the match head.
3. (a) The fireworks are filled with chemicals (lead oxide) and when gun powder is suppressed, the gas
present in it is released with a large popping sound.
(b) Acid rain causes diseases to human beings as it is harmful for skin. It makes the soil medium
acidic and affects plant growth.
4. (a) Conditions on which candle flame depends are as under:
• combustion of wax vapours
• rising of molten wax through the wick by capillary action.
• yellow colour of flame and its being luminous.
(b) The three zones of the candle flame are:-
• Outermost non-luminous zone of complete combustion of wax vapours, hottest part of candle
flame.
• Central luminous zone of incomplete combustion of wax vapours, bright yellow, having
moderate temperature.
• Inner dark zone of no combustion around the wick, least hot with unburnt carbon particles.
5.    
Knob

Bottle
Sulphuric
Acid

Container

Sodium
bicarbonate
solution

A soda-acid type fire extinguisher

25
 (Engage)
Worksheet 1 7. Conservation of Plants and Animals
1. (a) biosphere (b) Forest (c) deforestation (d) Uttarakhand
2. (a) Royal Bengal Tiger (b) Blue bull (c) Chinkara deer
These are found in Pachmarhi Biosphere Reserve.
3. (a) Wild dog (b) Spotted deer (cheetal)
(c) Silver fern (d) Hyena
4. (a) Kaziranga (b) Migration (c) Biosphere (d) Sanctuary
5. (a) Species: The organisms of similar types and functions, living in same habitat and capable of
interbreeding form a group called species.
(b) Biosphere: The variety of animals, plants and microorganisms along with their variability and
non-living components constitute the biosphere.
(c) Conservation: It means using a resource without depleting it and preventing its wastage and
overexploitation.
(d) Ecosystem: The biosphere consists of a vast network of well interconnected ecosystems. It is a
self-sustaining functional unit of biosphere consisting of living and non-living components.
6. The aim behind conservation of plants and the environment to:
• maintain the ecological balance of the place.
• prevent natural disasters such as drastic climate change arising out of loss of plants and animals.
7. Trees in the forests are cut due to following reasons:
• increased demand for wood and timber.
• increased demand land for factories, houses, roads and dams.
• increased mining activity
• forest fires.
8. Products which we get from forests includes timber, fuelwood, medicines, gums, raisins, paper, fruits
vegetables, rubber, etc.
9. Animals lose their natural habitate due to deforestation. It causes rise in temperature which makes their
survival difficult. Increased chance of natural calamities makes their survival tough.

(Explore)
Worksheet 2 7. Conservation of Plants and Animals
1. (a) Indian gaint squirrel
Feature – long feathery tail
(b) Sal, wild mango
(c) bison, flying squirrel

26
 2.

1.

1.

1.
2. 2.

2. 3.
3. 3.

1 Corbett National Park 2 Ranthambore National Park

3 Kanha National Park
1 Keoladeo Bird Sanctuary 2 Manas Wildlife Sanctuary
3 Sunderbans wildlife Sanctuary
1 Cold Desert 2 Great Reserve of Kutch
3 Pachmarhi Biosphere Reserve
3. (a) forests, mountains, riverbeds (b) deforestion.
(c) grazing, poaching (d) protected, favourable
(e) laws, plans, rules
4. (a) overgrazing (b) deforestation
(c) afforestation (d) afforestation
5. (a) A forest is considered useful to mankind as it helps to purify air, regulate climate, replenish
groundwater, maintain soil fertility and control floods.

27
 (b) Migration is the seasonal movement of animals from one habitat to another to overcome
unfavourable conditions. Birds migrate to find food and hospitable climate where they can lay eggs.
Arctic Torn migrates from Arctic Circle to Antarctic and back in a year. It is called the champion
of migration.
Science Around Us
The following measures can be adopted to conserve forests:-
• overgrazing by animals must be stopped in the forests.
• Large-scale cutting of trees must be banned.
• Seedlings should be planted on deforested land during rainy season.
• Van Mahotsavas should be observed regularly.
• Forest fires must be controlled immediately.
• Pollution of soil, water and air must be controlled.
(Extend)
Worksheet 3 7. Conservation of Plants and Animals
1. (A) (iii) (e) (B) (iv) (d) (C) (v) (a) (D) (i) (b) (E) (ii) (c)
2. (a) trees (b) several (c) 17 (d) save
(e) recycle (f) trees (g) water (h) resources
(i) substitute
3. Trees in the forest are cut due to following reasons:-
• increased demand for wood and timber.
• increased demand for land for factories, houses, roads and dams.
• increased mining activity
• forest fires.
4. (a) A National park is the area reserved for preserving flora, fauna, landscape and historic objects while
a wildlife and bird sanctuary is reserved for protection of wild animals and birds in their natural
habitat.
(b) A Botanical park is meant for the preservation of plants of various varieties while a Zoological
park ensures preservation of animals of various varieties. The bio reserve is a protected area for
conserving biodiversity, including plants, animals, environment and microbes.
5. The illegal killing of wild animals for the sake of entertainment and for commercial use is called
poaching. The hunters look for skin, ivory, leather, tusk, meat and fur while poaching.
6. To control poaching, government has acquired some areas under its protection and strict punishment,
including imprisonment and fine, has been imposed on poachers. The endangered, threatened, vulnerable
and rare species have been categorised for greater protection.
Science Around Us
The biosphere reserve is a multipurpose protected area developed to conserve biodiversity. Its main functions
are to:
• conserve biodiversity and integrity of plants, animals and microorganisms.
• enducate, train and create awareness about environmental aspects and ecofriendly living. It may contain
other protected areas in it too.
28
 (Elaborate)
Worksheet 4 7. Conservation of Plants and Animals
1. (a) Do it yourself
(b) (i) dinosaurs (ii) dodo bird
(c) (i) Indian rhinoceros (ii) Asiatic lion
(iii) crocodile (iv) Bengal tiger
(v) Golden langur (vi) Chinkara deer
(d) (i) Bison (ii) Indian giant squirrel
(iii) Flying squirrel
(e) (i) Golden cat (ii) Indian pied hornbill
(iii) Crestless Himalayan porcupine.
2. (a) International Union of Conservation of Nature and Natural Resources
(b) 103 (data of 2015)
(c) 150-200 per year
(d) (i) Elephant
(ii) Indian rhinoceros
(iii) mink, rabbit, squirrel
(iv) Crocodile, python
(e) (i) 89 (ii) 492 (iii) 12
3. The environmental laws passed by Government of India are:

• National Green Tribunal Act 2010

• Air prevention and Control of Pollution Act 1981.

• Water prevention and Control of Pollution Act 1974.

• Environment Protection Act.
4. Project Tiger is a tiger conservation programme launched in 1973 by the Indian government to ensure
viable population of Bengal Tigers in their natural habitat. The numbers of tigers has improved
significantly to 2226 from 1411 and the process is still going on. It aims at conservation of habitat,
prevention of poaching, unit monitoring for the purpose of conserving tiger for economic, scientific,
culture, aesthetic and ecological values.
5. (a) Natural calamities caused due to human activities are:-
• floods in rivers due to sedimentation of erosioned soil
• disturbed rainfall patterns.
• drought due to continuous farming and overgrazing
• increased temperature of earth
(b) IUCN classfies the species of plants and animals in endangered, vulnerable, rare and threatened
categories. It publishes these information pieces in Red Data Book to create awareness about
endangered species.

29
 (c) The book published by IUCN provding all information about the endagered species of plants and
animals is called Red Data Book. The Red list contains the species names which features as Red List.
(d) Hotspots are the parts of biosphere which are rich in variety of species of plants and animals. The
three hotspots in India are:-
Pachmarhi, Satpura and Nandankanan Biosphere Park.
(Engage)
Worksheet 1 8. Cell Structure and Functions
1. (a) (ii) (b) (iv) (c) (i) (d) (iv)
2. M I C R O S C O P E L R
A Z S I Y P J B Y P P Z
X B W B C R I X Q H H O
C H L O R O P H Y L L X
Y Q S S P K E T N O O M
T F V O N A H F T O E U
O R H M E R U U V N M I
P U G E T Y M W G Y H Z
L D C H R O M O S O M E
A L T I B T E J O C D P
S J F K B E R X Y L E M
M A S A R S Q G C L O H

3. (a) Robert Hook (b) Cell organelles

(c) Chloroplast (d) Vacuole
4. (a) Cell is the basic structural unit of an organism. It is the structural and functional unit of life, capable
of performing all biological activities in a living organism.
(b) Unicellular – Amoeba, Paramoecium, Euglena
Multicellular – Plants, animals, algae
(c) 1. Lysosome 2. Centrosome 3. Mitochondria, 4. Ribosome, 5. Golgi bodies, 6. Endoplasmic
reticulum.
(d) Vacuoles are the sac like structures present in cytoplasm which store soluble food, waste and
secretions of cell.
(e) Nucleus is a cell part floating in the cytoplasm which controls all life functions occurring in a
cell and transmits hereditary characters to next generations. It is made of nuclear membrane,
Chromosomes, nucleolus, nucleoplasm.
5. Cell well– Cell wall is found only in plant cells. It is a rigid outer wall made of cellulose which protects
the cell against atmospheric conditions and temperature variations.

Cell membrane– It is a thin delicate outer boundary of cell which gives shape to cell and helps in
selective exchange with the surroundings.

Cytoplasm– It is a thick jelly like fluid in cell membrane in which all cell organelles are suspended
and all life functions occur.

30
 (Explore)
Worksheet 2 8. Cell Structure and Functions
1. (a) multicellular organisms (b) stain
(c) zygote (d) tissue
(e) white blood cell
2. (a) Amoeba
(b) Paramoecium
(c) Amoeba moves by building finger like projections on its body called pseudopodia.
(d) The hairs called cilia help the paramoecium to move fast.
3. Living cells Non-living cells
Endoplasmic reticulum Wax
Mitochondcia Resin
Vacuoles Gum
Cytoplasm cell wall
Plasma membrane
Golgi bodies
Centrioles
Plastids

4. Cell → Tissue → Organ → organ system → Organism.

5. (a) Mitochondria, Lysosome, Chloroplast, Golgi bodies, Ribosome
(b) Cell wall, Nucleus, Mitochondria, Lysosome, Vacuole
(c) Yeast, Euglena, Paramoecium, Amoeba, Hydra
6. (a) Single cell controls are functions of the body in single called organism.
Specialised cell controls different functions of the body in multi-called organism.
(b) Hen’s egg consists of shell through which gaseous exchange occurs. It has egg yolk rich in proteins
and fat. The egg white/albumen is rich in proteins.
      (c) Plant cell Animal cell
It has a rigid non living cell wall The cell wall is absent.
It has one or two large vacuoles It has small or no vacuoles
It has plastids. Plastids are absent
Centrosomes and lysosomes are absent Centroiomes and lysoromes are present.

Science Around Us
Centrosomes and lysosomes are present in animal cells but not in plant cell. Lysosomes help in cellular digestion
and are called the suicidial bags of the cell. Centrosomes help in cell reproduction.
Similarly, cell wall is present only in plant cell and not animal cell. It is made of cellulose and protects the
cell against imperative variation, high wind speed and atmospheric moisture. Plastids occur in plants cells
only. Green plastids (chloroplast) help in photosynthesis. Colourless plastids (leucoplast) help in food storage.
Coloured plastids (chromoplasts) give colour to fruits and flowers.
31
 (Extend)
Worksheet 3 8. Cell Structure and Functions
1. (a) Red blood cell (b) Nucleus (c) Vacuole (d) Nerve cell
(e) Muscle cell (f) Red blood cell (g) Cilia
1. Lysosome
   2.
1. Cytoplasm 2. Cytoplasm

2. Chloroplast 3. Centrosome
3. Cell wall 4. Mitochondria
4. Mitochondria
5. Chromosome
5. Endoplastmic
reticulum
6. Endoplasmic
6. Nucleus reticulum
7. Golgi apparatus 7. Nucleolus

8. Golgi bodies
8. Cell membrane
9. Ribsome
9. Vacuole
10. Ribosomes
10. Cell membrane

A Plant Cell An Animal Cell

(a) Nuclear membrane is porous to allow passage of certain materials in and out of cell.
(b) Cell membrane has semi-permeable properties.
3. (a) Prokaryotic cells don’t contains well defined nucleous or internal membranes.
The cells have descended from oldest forms of life on earth; for example archae bacteria.
Eukaryotic cells have well defined membrane of nucleus, DNA and cell organelles, it is a complex
and large cell, e.g. plant cell.
(b) No, cells in elephant are not bigger than those, but they are more in number.
4. Wash the scalpel and scrap the inner surface or cheek gently. Place the scrapings on a clean slide and
spread it with the help of a needle. Put a drop of water and spread on the scraping with a needle. Put a
drop of methylene blue and glycerine. Cover with a converslip and process it gently. Observe under a
microscope first in low power and then in high power.
Cell membrane

Nucleus

Cytoplasm

32
Science Around Us
(a) Nerve cell: It is a long elongated cell with branches, which carries electrical impulses between brain
or spinal cord and the budy organs.
(b) Muscle cells: These are spindle shaped cells which combine to form muscular tissue. These can be
straited or unstriated.
(c) Skin cell: It is a flat thin, irregular shaped cell which spreads as a cover over the body in the form of a
layers.
(d) Sperm cells: It is a cell with a pointed head and a tail. The tail helps to move the cell and the head helps
it to enter the ova during fertilization.
(e) White blood cells: These are irregular shaped cells of different types which perform different functions
in a cell.
(Elaborate)
Worksheet 4 8. Cell Structure and Functions
1. Onion peel cells Intestinal villi tissue
Nerve cell Kidney organ
Xylem tissue Heart organ
2. (a) 55-60 (b) Mycobacteria
(c) 7 (d) 170, 130
(e) 10–3
3. Tissue is a group of two or more types of cells specialised to perform a particular function.

• Plant tissue: Vascular tissues called xylem and phloem, are used in transportation of food and water
in plant body.

• Animal tissue: Muscular tissues (striated, unsteriated and cardiac) tissues form the heart and muscles
of the body.
4.

33
 5. (a) They are thread like structures found in nucleus of the cell. There are 25 pairs of chromosomes
in humans.
(b) They contain basic hereditary units which are responsbile for passing genetic characteristics from
parents to the offsprings.
(c) Genes are the hereditary units found on chromosomes. DNA (Deoxyribonucleic acid) are the units
of chromosomes.
6. The crops which are modified using genetic enginnering methods to introduce some desirable traits are
called GM crops. e.g. BT cotton, alfalfa, sugar beet, canola etc.
7. Bt cotton is a genetically modified crop. Bt means Bacillus thuringiens is the bacterium containing a
gene called st gene. It makes cotton resistant to bollworm. It also ensures higher yield. But the pink
bollworm is not affected by Bt variety of cotton and still affects it.
(Engage)
Worksheet 1 9. Reproduction in Animals
1. (a) (i) (b) (iv) (c) (ii) (d) (iv)
2. (a) Royal Bengal Tiger
Name of animals Name of young ones Lay eggs/Give birth to babies

(a) Human beings baby Give birth to babies

(b) Cats kitten Give birth to babies

(c) Dogs puppy Give birth to babies

(d) Lions cub Give birth to babies

(e) Hens chicken lays eggs

(f) Butterflies larva lays eggs

(g) Cows calf Give birth to babies

(h) Frogs tadpole lays eggs

(i) Ducks duckling lays eggs

3. (a) Asexual reproduction: The mode of reproduction in which a single organism is able to reproduce
one or more of its kind is called asexual reproduction.
(b) Sexual reproduction: The mode of reproduction in which both parents (male and female) are
needed to reproduce individuals of the same kind.
(c) Internal fertilization: When fertilization of female gamete by male gamete occurs inside the
body of the female, it is called internal fertilization.
(d) External fertilization: When fertilization of egg takes place outside the female body, it is called
external fertilization.
4. (a) Reproduction helps living beings to produce individuals of same kind which is important for
sustenance of species. In its absence, the species will cease to exist.
(b) Male reproductive parts, testes, vas deferens, urethra, penis.
Female reproductive parts, ovary, oviduct, uterus, vagina.

34
 5. Budding in Hydra: A bulb like projection is formed on the body of the organism called bud. The nucleus
of the parent body divides into two and one goes into the bud. The bud gradually matures and detaches
itself from the parent body and becomes an independent individual.

Budding in Hydra
Binary fission in Amoeba: the mature cell splits into two daughter cells. The nucleus first divides into
two parts and then cytoplasm divides, each containing a nucleus. The constriction deepens and leads
to the formation of two daughter cells. The daughter cells grow into mature cells again.

Binary fission in Amoeba

(Explore)
Worksheet 2 9. Reproduction in Animals
1. A M E T A M O R P H O S I S I
K A D F N C W V C Y E G E B B
G P Y I C H X F D T E Z O S U
E B I N A R Y F I S S I O N D
S R E P R O D U C T I O N G D
T O B H E M O D Z X N R N A I
A A O B L O U D J C A G Q M N
T G J H R S W I B V R O I A G
I S C L K O S N V N Y P D T O
O J T I K M U G G O A H K E E
N Q J A I E R P N W L M M S P
O P A R T U R I T I O N B C S
P Q T K H G A S T O T I O N T

2. (a) sperm, ovum (b) asexual (c) Hydra (d) nutrition, maturation
(e) daughter
35
 3. The organisms which lay eggs that later develop into young ones are called oviparous animals e.g.
frog, hen, crow, etc. The organisms which give birth to young ones are called viviparous animals. e.g.
human beings, cows, buffaloes, etc.
4. Advantages
Internal fertilization External fertilization
The foetus develops inside female body and is not likely The fertilized eggs/foetus are likely to be killed due to
to be killed by predators. climatic conditions or attack by predators. The fertiliza-
tion is also not sure.
Disadvantages
Only one egg is fertilized at a time. A number of individuals can be born in one time.

Science Around Us
The transformation of larva into an adult butterfly and of tadpole into a frog occurs through many drastic
changes. This is called metamorphosis.
Difference: The adult form of butterfly develops wings while the frog develops hind limbs and fore limbs.

Adult butterfly

Eggs
Pupa

Caterpillar

Life cycle of butterfuly

Early stage of Tadpole

Eggs
Late stage of Tadpole

Frog

Life cycle of frog

Similarities: The adult form is entirely different from other stages of life.

36
 (Extend)
Worksheet 3 9. Reproduction in Animals
1. (a) F
External fertilization can occur in water.
(b) T
(c) F
Human sperm has a head, middle piece and a tail.
(d) F
In adult human females, a single mature egg is released by each ovary into an oviduct every month.
2. Release of mature egg into oviduct by each ovary in four weaks.
↓
Male release sperms in the body of female during mating.
↓
The sperm fuses with ovum in the process of fertilization.
↓
The nucleus of cell and sperm fuse to form single nucleus and finally leads to formation of zygote.
3.

Plasma membrane
Acrosome

Head Nuclear/chromosomal
material

Neck Centrioles

Middle Mitochondria
piece

Tail

A Human Spermatozoan
4. (a) When ovum does not fuse with sperm, the released egg and thickened lining of uterus is shed off
in the form of bleeding called menstruation.
(b) Fishes and frogs lay hundred of eggs out of which only some get fertilized. In hen internal
fertilization occurs after which egg is laid.

37
 5. After fertilization the zygote is formed. It divides repeatedly and gives rise to a ball of cells which begin
to form groups. These groups form tissues and organs. This developing structure is called embryo.
The embryo gets embedded in the wall of uterus. The embryo develops in the uterus while remaining
attached to the uterine wall.
Science Around Us
Two ovaries are situated in the abdominal cavity. They produce one mature ovum every four weeks. The thin
coiled fallopian tube or oviduct joins the uterus and ovary. It passes ova into uterus by ciliary action. The
uterus receives the ovum and contains the developing fectus.
In males, there are two testes, lying inside the scrotum, which produce sperms. The sperm duct (vas deferens)
carries sperms to urethra by muscular action of the walls. Vas deferens carries the sperms along with fluid
secreted by seminal vesicles (called semen). This duct opens in urethra which passes through penis. The penis
has erectile tissue which delivers male reproductive cells in the vagina of female body.

(1) Oviduct
(2) Ovary (1) Vas deferens
(3) Uterus
(4) Vagina (2) Penis
(5) Abdominal (3) Urethra
cavity
(4) Testes
(6) Vaginal tube
Fig. (i) Fig. (ii)

(Elaborate)
Worksheet 4 9. Reproduction in Animals
1. (a) unfertilized (b) Thyroxine, Protactin (c) twins
2. (a) Finn Dorsett sheep clone named Dolly, formed by cloning.
(b) • Nucleus from mammary gland cell is inserted into the egg without nucleus.
• Nucleus of ewe egg is removed for insertion into the egg. (from Scottish black face ewe)
• The egg is modified.
• The Modified egg is implanted into Scottish blackface ewe.
• After gestation, Dolly is born.
3. The freshly released egg and sperms are collected and kept together for few hours. If fertilization occurs,
the zygote is developed for a week and placed in mother’s uterus for development of baby. The term
is misleading as the baby does not develop in a test tube.
4. (a) Fertilization
(b) It is possible that only one of label A enters B during the process of fertilization.
5. (a) Oviduct is blocked and sperms can’t reach the egg.
(b) The male partner is not able to produce enough sperms.
(c) The ovum fails to implant on the uterine wall.
6. (a) In-vitro fertilization
(b) Gamete Intra Fallopian Transfer

38
 7. Gender issues and myths common in underdeveloped countries are as follows:-

• Girls should not go to temple, kitchen or gatherings during menstruation.

• Mother is responsible for the birth of a girl child.

• Girls and boys should keep away from each other.
8. Adolescent pregnancy results in mental and physical problems to the mother. She is mentally not
prepared and physically weak to bear a child. This leads to pregnancy complications, poor health of
mother and baby, malnutrition and mental stress.
9. In males, sex chromosomes consist of one X and one Y type chromosome. In females, it consists of
both X type chromosomes.
When a sperm carrying X-chromosome fertilizes an egg, it develops into a female baby. When a sperm
carrying y-chromosome fertilizes an egg, the zygote develops into a male baby. Thus whether a baby
is a girl or boy depends on type of sperm that fertilizes the ovum.
Male Female
XY XX
↓ ↓
X Y X X

↓ ↓
XX XY
↓ ↓
female (girl) male (boy)
(Engage)
Worksheet 1 10. Reaching the Age of Adolescence
1. (a) adolescence (b) larynx
(c) blood (d) thyroid, pancreas, adrenal
(e) male
2.
X S T V A W G W A X
K E N D O C R I N E
S T B B V U R Y F H
M H U B U Z E G Q Z
H Y S T L C U I Y L
P R I S A N D G L E
G O D C T C D A A F
F I L J I E K N R P
I D R G O L O T Y M
A D R E N A L I N E
K A Q B O M H S X J
D W A R F I S M N I
P P I T U I T A R Y

39
 3. (a) F (b) F (c) T (d) T (e) F
4. (a) Adolescence: The period of life when body undergoes changes leading to reproductive maturity
is called adolescence.
(b) Hormone: The chemical regulators secreted by ductless glands are called hormones.
(c) Puberty: The period of life during which body grows rapidly is called puberty.
(d) Adolescence: The period of life when body undergoes changes leading to reproductive maturity
is called adolescence.
(e) Gland: The chemical regulators are secreted in the body by glands.
5. (a) The personal hygiene helps to keep one healthy and prevents the possibility of catching infectious
diseases. It prevents spread of diseases and keeps a person socially active, cheerful and stress free.
(b) The hormone in insects helps in metamorphosis during their life cycle.
(c) The onset of puberty is controlled by hormones. The hormones are responsible for secondary male
and female sexual characteristics.
(d) Male: Testes gland secretes testosterones.
Female: Ovary secretes oestrogen and mammary glands function by the control of pituitary glands.
(e) The bleeding in women due to breakdown of thickened inner wall of uterus and its blood vessels
is called menstruation.
(f) Pituitary gland secretes hormones which stimulate gonads to release testosterone in males and
oestrogen in females. It is the master gland which stimulates thyroid for thyroxine production.
(Explore)
Worksheet 2 10. Reaching the Age of Adolescence
1. (a) Adrenal, Adrenaline (b) Pancceas, Insulin
(c) Thyroid, Thyroxine
Pituitary
_________________
2.
_________________
_________________
Thyroid

_________________
Pancreas
Ovary and testis
_________________
Adrenaline
_________________

(a) The glands which release their secretions through ducts are called exocrine glands.
(b) The glands which release their secretions in blood stream are called endocrine glands.
(c) Endocrine glands secrete hormones in blood stream.
Exocrine glands secrete hormones through ducts.
(d) The hormone reaches a specific body part such as an organ, tissue or cell. Such part is called target
site.
3. (a) Drug: Drugs are medicines or external chemicals taken by people to get rid of some physical or
mental stress.
(b) Drug abuse: Sometimes people get addicted to certain types of drugs. This is called drug abuse.
(c) Growth Hormones: The hormones (Thyrotropic hormone, TTH) secreted by pituitary gland is
called growth hormone as it stimulates the secretion of thyroxine in the body.
40
 4. (a) The physical features which help to distinguish the male from the female are called secondary
sexual characters.
(b) Pancreas is called duel gland as it is both exocrine as well as endocrine. It secretes pancreatic
juice through duct and insulin in bloodstream.
5. Physical changes that occur in boys and girls at puberty are:-
• Increase in height of boys and girls.
• Growth of pelvic bones, hips and breasts in girls; muscles in boys.
• Increased activity of sweat and sebaceous glands, appearance of acne and pimples.
• Development of male and female sex organs in boys and girls respectively.
• Hoarse voice of boys and shrill voice of girls.
Science Around Us
Dietary requirements of adolescents include:-
• cereal and grains for carbohydrates, vitamins, minerals and roughage.
• pulses, soyabean, gram etc. for proteins, minerals and vitamins.
• vegetables such as spinach, carrots, tomatoes, salads etc.
• Eggs, meat and fish
• Milk and milk products for fat, calcium and phosphorus.
• Fruits such as grapes, mangoes, bananas etc.
(Extend)
Worksheet 3 10. Reaching the Age of Adolescence
1. (a) goitre (b) deficiency of iodine in food
(c) thyroid; thyroxine (d) metabolic rate and growth
(e) use of iodised salt
2. 100
PERCENTAGE OF FULL HEIGHT

95 Age Percentage of full Height in cm

height
90
ys Boys Girls Boys Girls
Bo
85
8 70 75 114 110
80 10 75 85
75 14 90 98
70 16 98 99
65 18 100 100
8 9 10 11 12 13 14 15 16 17 18
AGE IN YEARS
GIRLS
BOYS

3. (a) A-Anterior pituitary gland, B-posterior pituitary gland.

(b) Hypothalanum
(c) A–gonadotropin hormone, growth hormone, prolactin, thyroid, LH, FSH, ACTH
B–oxytocin, vasopressin

41
 4. (a) Menopause: The stoppage of menstural flow and other associated events in the body of a female
is called menopause.
(b) Menarche: The beginning of menstruation at puberty in females in called menarche.
5. Adolescents become capable of reproduction. The testes in boys and ovaries in girls begin to produce
sex cells called gametes. In boys, the male sex organs (tests and penis) develop completely. Sperm
production begins in testes. In girls, ovaries enlarge and eggs begin to mature. The ovaries start releasing
mature eggs.
Science Around Us
There are two ovaries in the abdominal cavity. These produce one mature ovum each after four weeks. This
is called ovulation. The walls of uterus become every thick to receive the fertilized egg if fertilization occurs.
If fertilization does not happen, the released egg and the thickened lining of uterus along with blood vessels
are shed off. This causes bleeding called menstrual flow. It last for 4-7 days, and occurs once in about 28-30
days. This cycle of changes, occurring in uterus every month, i.e. 28 days and marked by menstrual flow, is
called menstrual cycle.

(Elaborate)
Worksheet 4 10. Reaching the Age of Adolescence
1. (a) It indicates family planning.
(b) The objectives of family welfare centre are to preserve and strengthen the family as a unit, to
develop caring relationships and to prevent personal and family problems.
(c) The population of India is large and rising at an alarming rate. So birth control is advised.
(d) Population growth is caused due to lack of education, lack of knowledge of contraceptive methods,
taboos associated with girl child, teenage.
2. (a) diabetes; insulin hormone
(b) sugar metabolism in the body.
(c) Insulin and sugar regulators are given by doctors to such patients.
3. Low boy-girl ratio is caused by prenatal sex determination and female foeticide due to want of male child
by parents. This poor ratio results in societal imbalance and increased sexual crimes against women.
4. The process by which amniotic fluid is sampled using a hollow needle inserted into uterus to screen for
foetal abnormalities is called amniocentesis. It helps in diagnosing problems in the growing foetus and
taking necessary remedial action. It is banned in India as it is more used for prenatal sex determination
here and leads to female foeticide.
5. (a) Adrenaline: It helps the body to prepare to fight or run fast.
(b) Oestrogen: It controls the mammary glands and development of breasts and secondary female
sexual characteristics.
(c) Progesterone: It controls the production of ova in ovaries and menstrual cycle.
(d) Testosterone: It controls the growth of facial hair and secondary male sexual characters along
with sperm production.
6. Adolescents must do brisk walking, running, cycling, swimming, skipping and dancing. They should
play outdoor games like badminton and volleyball. They should wash their body parts regularly, specially
girls during menstruation. They should wear clean clothes and undergarments.
42
 7. (a) Adolescents sometimes feel confused or insecure due to stress caused by emotional pressure and
take drugs for relief from stress. They also resort to this practice under peer pressure.
(b) Cocaine, heroin, tobacco and alcohol. The drugs are taken orally, inhaling or by injection
(tranquillisers)
(c) Drugs are addictive. They affect the nervous system, behavioural patterns, emotional values and
sexual desires of teenagers.
(d) To stay away from drugs, they should share and discuss their problem with their elders and friends.
They should keep themselves busy in creative and constructive work.
(e) They can reform themselves through counselling, rehabitation and medical treatment.

(Engage)
Worksheet 1 11. Force and Pressure
1. (a) muscular (b) downward (c) opposite (d) force
2. (a) Boys are pushing a box.
(b) No, the directions of motion are different.
(c) The box will move to left in (i). It will not move in (ii) if force is acting equally on both sides.
3. (a) Muscular force
(b) The force is applied by holding the load.
(c) Pushing a rock and catching a ball are examples of this force.
(d) Moulds, Mushroom
(e) Sandalwood, Mistletoe
4. (a) True (b) False (c) False (d) True
5. (a) Force is an effort applied in the form of push or pull on a body which changes its state of rest or
motion.
(b) Unit of force is newton (N).
(c) Contact forces: Muscular force, Frictional force, buoyant force.
(d) Non-contact forces: Gravitational force, magnetic force, electrostatic force.
(e) Frictional force is the force which acts between two surfaces in contact and opposes the motion of
one surface over the other, e.g. friction in machine parts produces heat; friction prevents us from
slipping while walking.
(f) Frictional force is essential for walking. If there was no friction between our feet and ground, we
would keep on slipping and never be able to walk.
6. Effects of forces are:
(a) Change in shape– squeezing a lemon, blowing a balloon etc.
(b) Change in rest state– pushing a toy car, pulling a box etc.
(c) Change in direction– hitting a football or cricket ball.
(d) Change in state of motion stopping a moving-bicycle, catching a ball.
(e) Change in speed– increasing or decreasing rate of motion of a swing.

43
 (Explore)
Worksheet 2 11. Force and Pressure
1. (a) magnitude, direction (b) Atmospheric
(c) gravitational (d) repel, attract
2. (a) pull (b) push
(c) push (d) pull
(e) pull
3.
(a) Upper hook
(b) Pointer

(c) Spring
(d) Scale

(e) Lower hook

(a) Spring balance

(b) We measure weight with it.
(c) The spring gets stretched on suspending weight and the pointer gives a reading.
(d) It will point at ‘30’ marker on the scale.
4. (a) it exerts less pressure on the shoulder since greater the area, less is the pressure.
(b) lower the edge area, greater will be the pressure exerted and cutting will be easier.
5. (a) moving a toy car.
(b) increasing the speed of a vehicle.
(c) hitting a ball with bat.
(d) squeezing a lemon.
6. (a) Frictional force acts between two surfaces opposing their relative motion. It is a contact force.
Gravity is the force exerted by earth on all objects. It is a non contact force.
(b) Balance forces. When a number of forces acting on a body produce zero net effect, they are called
a combination of balanced forces. e.g. gravitational force and reaction force acting on a book are
balanced and it stays at rest.
Science Around Us
Contact forces Muscular force helps us to hold things and to do almost every work in our daily life which
involves muscular action. Frictional force enables us to stay on ground without skidding.
Non-contact forces. Gravitational force keeps us bound to earth else we would fly away in space with rotation
of earth. Magnetic force is important in technology, electronic devices. etc. electrostatic force is involved in
many natural phenomena occurring on the earth.

44
 (Extend)
Worksheet 3 11. Force and Pressure
1. (a) (iv) (b) (iii) (c) (i) (d) (vi)
(e) (ii) (f) (v)
2. (a) Observation: As water level in the tube rises, the baloon at the bottom inflates.
Conclusion: As height of water column increases, pressure exerted by it also increases.
(b) Observation: The balloon gets inflated upto a certain thickness as water flows into it.
Conclusion: Water exerts pressure on the walls of the container.
3. It works on the principle that a freely suspended magnet always points in N-S direction. This is due to
the magnetic field of the earth.
4. Fig. (i) The force acts in direction of motion of ball and increases its speed.
Fig. (ii) The force acts in opposite direction to motion of ball and reduces its speed and changes direction.
Fig. (iii) The force acts at an angle to motion of ball and turns it by an angle.
Fig. (iv) The force acts on both sides and changes the shape of the ball.
5. (a) The thrust acting per unit area of a surface is called pressure. Its unit is pascal (Pa).
[Pressure = Force/Area]. 1 Pa = 1 Nm–2. It is called Pa in remembrance to Blaise Pascal.
(b) Weight is the force with which an object is attracted to earth.
• Weight and gravitational force are equal at a place.
• Weight is zero where there is no gravitational force, e.g. in free space.
Science Around Us
Gravitational force is helpful in the following ways.
• It keeps us bound on earth, otherwise we would keep on suspended in space.
• There would be no atmosphere on earth if there was no gravitation to hold it.
• Water on earth would fly about in the absence of gravitation.
(Elaborate)
Worksheet 4 11. Force and Pressure
1. (a) Electrostatic force.
(b) It is the force existing between charged bodies.
(c) It is attractive when opposite charges face each other. It is repulsive when like charges face each
other.
2. (a) Pressure = Force/Area = 300 N/2m2 = 150 N/m2
(b) (i) Area of base = 10 cm × 5 cm = 50 cm2 = 0.005 m2;
F = 1.5 N.
P = F/A = 1.5/0.005 = 300 Pa.
(ii) Area of base = 15 cm × 10 cm = 150 cm2 = 0.0150 m2;
F = 1.5 N.
P = F/A = 1.5/0.0150 = 100 Pa.

45
 3. Fig. (i): Balanced force, so the box will not move.
Fig. (ii): Unbalanced force, so the box will move upwards with a net force of 8 N.
Fig. (iii): Unbalanced force, so the box will move forward with a net force of (2 + 6) 8N.
4. Gravitational force causes him to come downwards. But his speed will not be the same as without a
parachute because air exerts upward buoyant force on the parachute.
5. (a) The increased wind speed results in reduced air pressure above the rooftop. So the roof top flies
away.
(b) When the meteor falls towards the earth, it gains heat due to friction with earth’s atmosphere.
Hence it starts burning.
6. Applications of force and pressure in daily life are:

• We exert force and pressure on the earth all the time.

• There principles help in designing of ships, boats and submarines.

• Atmospheric pressure acts on our body all the time.

• It helps birds, aeroplanes, jet planes etc. to fly.
7. Atmospheric pressure is measured with the help of a device called barometer. There is variation in
atmospheric pressure. It is higher in planes than on hills. This happens due to reduced weight of air
above the measurement point.
8. Uses of air pressure: It helps to keep us on the ground. It helps in inflating tyres, playing
reed instruments, flushing toilets, operating barometer, breathing, drinking through straw etc.
Change in atmospheric pressure could cause change in weather conditions, ocean tides etc.

(Engage)
Worksheet 1 12. Friction
1. (a) True (b) False (c) False (d) True (e) False
2. (a) sprinkling talcum powder (b) lubricating oil
(c) polishing (d) rollers
3. (a) grooves on the tyre surface
(b) sprinkling sand
4. (a) motion (b) roughness (c) heat
(d) reduces (e) less
5. (a) Friction acts in opposite direction to motion of book.
(b) Friction opposes motion of the book.
(c) No, friction is not same for all type of surfaces. Rough surfaces offer more friction than smooth
surfaces.
6. Friction is the contact force which opposes relative motion of a surface over another. Types of friction
are: static friction and dynamic friction (sliding and rolling).

46
 7. Properties of friction are:

• It acts in opposite direction to that of motion.

• It opposes the motion of a body over a surface.

• It depends on roughness of surfaces.

• It depends on weight of a body.
8. Advantages of friction are:

• It enables us to walk on ground without slipping.

• It enables us to write on board or on paper.

• It helps us to hold things and do tasks such as fixing a nail on the wall.

• It helps in movement and stopping of vehicles.

(Explore)
Worksheet 2 12. Friction
1. (a) Friction is produced only when two solid bodies are in contact.
(b) When an object moves through water, it experiences friction due to water.
(c) Aeroplanes have streamlined bodies that ensure minimum friction and allow them to fly freely.
2. (a) Increases (b) Increases (c) Decreases (d) Increases
3. (a) (i), (iv) (b) (ii), (iii), (vi)
(c) (vii), (viii) (d) (v)
4. (a) The distance covered is more on smooth table.
(b) The smooth table offers lesser friction to cell than clothpiece. So cell travels longer distance on
table.
5. Friction increases when weight increases. The loaded mat has greater friction with ground and is difficult
to drag.
6. Friction between two surfaces placed over one another at rest is called static friction. Its value increases
as force is applied to move the object.
F No
Motion

Static Friction

Science Around Us
Disadvantages of friction in our daily life are:
• It causes wear and tear of machine parts as they slide against each other.
• It generates unwanted heat and leads to wastage of energy.
• It results in tearing of shoe soles.
• The tyres of vehicles get worn out.
• Sometimes friction between dry leaves causes forest fires.

47
 (Extend)
Worksheet 3 12. Friction
1. (a) Wet muddy road becomes slippery due to lack of friction. Thus it is difficult to walk on.
(b) Oily surface offers less friction and the pen slides off. This makes it difficult to write on it.
(c) Banana peel has less friction with ground. So one is likely to slip on it.
2. (a) The pictures depict the act of swimming, rowing boat, flying plane and flying of bird, all moving
in streamlined shape through water or air.
(b) All figures have streamlined shape which reduces friction with air or water.
(c) It is the same principle, but followed in water (in (i) and (ii)) and in air ((iii) and (iv)) respectively.
Water offers more friction than air.
(d) No. Friction offered by liquids and gases is lesser than that offered by solids.

3. F Sliding F Rolling
F motion
(no motion) motion

Sliding friction Rolling friction

Static friction
Friction is a self-adjusting force. When applied force is gradually increased, friction also increases and
the body remains stationary. This is called static friction. e.g. When a heavy box is pushed, it does not
move. The force required to move a body is slightly more than the limiting friction. When the body
just slides over the other, it is called sliding friction. When rollers are used and the body rolls over a
surface, it is called rolling friction.
Static friction > Sliding friction > Rolling friction
Science Around Us
Friction has to be reduced in the following cases:
• Machine parts are oiled, greased or lubricated so that they move smoothly without getting heated up.
• Ball bearings are used between sliding parts to reduce friction.
• Powder is sprinkled on carrom board to move the striker freely.
• Shapes of boats and planes are streamlined to reduce friction due to air or water.
• Graphite powder is used in machines to reduce friction.
(Elaborate)
Worksheet 4 12. Friction
1. (a) Lubricants
(b) A lubricant is a substance applied between moving parts to reduce friction.
(c) The application of this product reduces friction between machine parts.
(d) No, some friction always remains though it reduces considerably.
2. (a) Rolling friction is less than sliding friction.
(b) Area of contact of rollers with surface is less and irregularities do not get interlocked.
(c) Rollers are used to move the luggage easily.
48
 3. (a) The reading of spring balance shows a constant value.
(b) The reading of spring balance reduces as friction offered by table is less now.
(c) The reading increases as friction between jute cloth and table is more.
(d) Motion of a ball rolling on floor; ball bearings in machines.

4. Advantageous Disadvantages

– Safe ride without slipping. – Wear and tear of tyres.

– Application of brakes due to friction between brake – Riding against wind makes it difficult to ride.
lining and wheel rim.

5. Friction is a necessary evil. It helps to fix the nails and screens. It ensures safe driving without skidding
and walking without slipping. But, it causes wear and tear of machine parts and also reduces efficiency
of machines by producing unwanted heat.
6. If there was no friction, it would cause us slip everytime we tried to walk. It would be impossible to
stop a moving body, to write, to hold anything, to fix a nail or a screw etc.
7. Friction is increased in the following situations.

• Soles of shoes and tyres are corrugated and rough to provide better grip on ground.

• Brake pads are made rough to increase friction so that the vehicle can be stopped easily.

• Wrestlers and kabaddi players rub their hands with soil for better and firm grip on the opponent’s
body.

• Sand is sprinkled on slippery surfaces so that people and vehicles do not skid on wet roads.

(Engage)
Worksheet 1 13. Sound
1. (a) Membrane (b) String (c) String
2. (a) Pleasant (b) Unpleasant (c) Unpleasant
3. (a) vibrations (b) eardrum (c) vocal cords (d) trees (e) higher
4. (a) Three characteristics of sound are loudness, pitch and quality. Loudness depends upon amplitude
of vibration while pitch depends upon frequency of vibration. Quality of sound is called tone and
is different for sounds coming from different sources.
(b) Propagation of sound means travelling of sound waves through a medium from the source of
sound to the recipient.
(c) Characteristics of vibration are amplitude, time period and frequency.
5. Types of sound around us are:

• Music from various sources like microphone, loudspeaker, television.

• Sound of people produced by vibration of their vocal cords.

• Sound produced by musical instruments produced by vibration of membrane, string or wind.

• Sound produced by machines, cars, aeroplanes, horns etc.

• Sound produced by flowing water, chirping of birds, rustling of leaves, fluttering of flag etc.

49
 6. When the sound produces an unpleasant and discordant effect in our ears and mind, it is called noise.
The sound which produces pleasant effect on our ears is called music.
7. Instruments produce different types of sounds. Some of them are:

• A guitar produces sound when its strings vibrate. It is called string instrument. Other examples are
sitar, violin etc.

• A drum produces sound when its membrane vibrates. It is called percussion instrument other
examples are mridangam, tabla etc.

• A flute produces sound when its air column vibrates. It is called seed instrument. Other examples
are shehnai, harmonium etc.
• Instruments such as manjira, cymbals etc are just beaten to produce sound.


• A bell produces sound when hit with a hammer.

(Engage)
Worksheet 2 13. Sound
1. (a) Yes
(b) It feels to vibrate.
(c) The water surface has small ripples.
(d) These changes occur because the dish vibrates on being hit with a spoon.
2. (a) (iii) (b) (i) (c) (iv) (d) (v) (e) (ii)
3. (a) (ii) (b) (iv) (c) (iii) (d) (iv)
4. 1. Ear pinna 2. Oval window
3. Ear drum 4. Auditory canal
5. Air way 6. Auditory nerve
7. Cochlea 8. Ear bones
5. Astronauts talk with the help of special devices in space. They use such system because there is no
medium in outer space through which sound waves can propagate.
6. (a) Loudness depends on amplitude of vibration which produces that sound. Greater the amplitude of
vibration, louder is the sound produced.
(b) The shrillness of sound is called its pitch. The pitch depends on frequency of sound. Higher the
frequency, shriller is the sound.
(c) Quality of sound is called its tone. It helps to distinguish between sounds produced by different
sources.
Science Around Us
Echo occurs in hills when the sound gets reflected by hill rocks and reaches our ears after some time lag so
that we can distinguish between original sound and echo. The minimum distance to hear an echo is 17.2 m.
Speed of sound = 344 m/s in air; Minimum time lag required to distinguish echo = 0.1 s.
Sound travels from source to hill and back, i.e. distance = 2d
2d = Speed × Time lag
344 × 0.1
d= = 17.2 m
2

50
 (Extend)
Worksheet 3 13. Sound
1. (a) (viii ) (b) (vi) (c) (iv) (d) (v)
(e) (iii) (f ) (i) (g) (ii) (h ) (vii)

2. Name of the Musical instruments Vibrating part producing sound

Drum Membrane

Veena Strings

Sitar Strings

Mridangam Membrane

Shehnai Air column

Jal Tarang Water column

Kartal Whole body of instrument

3. Fig. (i) The tuning fork is at rest in non vibrating state.

Fig. (ii) On being struck with rubber pad, the prongs of tuning fork start vibrating.
Fig. (iii) When the vibrating tuning fork is touched at water surface, ripples are produced.
Fig. (iv) When a thernocole ball is brought near vibrating prongs, it moves away by vibrating prongs.
4. (a) Vibrations in stretched string produce sound.
(b) Frequency of vibration is dependent on length of air column. Smaller the air column, higher is
the frequency and longer the air column, lesser is the frequency.
5. Yes sound needs a medium to travel.
(i) Sound travels in the form of longitudinal waves in dry air at a speed of 340 m/s.
(ii) Speed of sound is greater in sea water than in air, ≈ 1500 m/s.
(iii) Speed of sound is maximum in iron ≈ 5100 m/s.
(iv) Sound travels at a speed of 1540 m/s through blood.
6. Sound waves are collected by the outer ear and reach the eardrum. The sound waves strike the eardrum
and it starts vibrating. The vibrations are passed to the oval window made of three bones. These magnify
the force of vibrations. Since the oval window has lesser area than the eardrum, it increases pressure on
liquid in the cochlea. The vibrations of cochlear fluid affect the auditory nerves and signals are carried
to the brain. This enables us to hear the sound.
Science Around Us
Sound waves are mechanical waves and need a material medium to propagate. Sound is produced by vibrations.
When a part of a medium, (Solid, liquid or gas) vibrates, it causes the neighbouring particles to vibrate and
the disturbance is carried to the other end of the medium. This carries energy from one part of the medium to
the other and sound propagates.

51
 (Elaborate)
Worksheet 4 13. Sound
1. (a) Speed of sound = 330 m/s.
Time taken = 5 s
Distance = Speed × Time
= 330 m/s × 5 s
= 1650 m
(b) Time period =  Time taken to complete 1 oscillation
= 2 min/60
= 120s/60 = 2s
1 1
Frequency = = = 0.5 Hz
Time period 2
Average
Rocket City Hair Radio Light Loud
2. SOURCE Whispering sound at
engine traffic dryer (TV) vehicle thunder
home
SOUND
>130 >90 >90 >80 >70 >100 >20 50-60
LEVEL (dB)

3. (a) Whales and dolphins communicate in water by sending ultrasonic signals to each other.
(b) The rate of travel of an object at speed greater than that of sound is called supersonic speed.
Supersonic waves create shock waves in air which generate enormous amount of sound energy.
This is called sonic boom.
4. The following are the characteristics of vibrations:
(a) Amplitude: The maximum displacement of a body from its mean position is called amplitude of
oscillation.
(b) Time Period: Time taken by pendulum particle to complete an oscillation is called time period.
(c) Frequency: Number of oscillations made by an oscillating body in one second is called frequency.
5. Uses of ultrasonic vibrations in industry are:
• cleaning of hard to reach places such as spiral tubes.
• detection of flaws in metals
• detection of impurities in ores
• preparation of SONAR devices used in defence technology.
6. (a) Noise is produced by irregular vibrations and causes noise pollution. Its hazards are:
• hearing loss-prolonged exposure to high noise level leads to hearing loss.
• fatigue due to lack of sleep and irritation
• anxiety and stress
• high blood pressure, arrythmias.
(b) Following are the ways to reduce noise:
• setting up of industries away from residential areas.
• planting more trees
• using carpets and draperies
• restricting the use of loudspeakers, amplifiers and horns.

52
 (Engage)
Worksheet 1 14. Chemical Effects of Electric Current
1. (a) (iii) (b) (i) (c) (iv) (d) (ii) (iv)
2. (a) The electrolyte splits up due to electricity. The cations
get reduced at cathode and anions get oxidised at anode. –
+
Depositions and evolution of gas can be seen at both the
electrodes depending upon the electrolyte used.
(b) Anode attracts negative ions as it is positive electrode. Cathode cathode
attracts positive ions as it is a negative electrode.
anode

3. (a) No (b) Yes (c) No electrolyte

4. (a) Electric current is defined as the flow of electrons in a particular direction.
(b) The materials which allow electricity to flow through them are called conductors.
Examples:conductor (silver, copper)
insulator (paper, plastic)
5. The chemical effects of electric current are:

• Splitting of electrolyte into its ions during electrolysis.

• purifying of metals in electrorefining.

• Depositing a layer of metal over another in electroplating.
6. Two thick wires were taken and placed in a trough containing acidulated water. Two test tubes filled
with acidulated water were kept over the open ends of wires and other ends of wires were connected
to battery terminals. After some time, gases started collecting in the test tubes at both electrodes by
downward displacement of water. It was found that volume of hydrogen and oxygen gases are in the
ratio 2 : 1.

53
 (Explore)
Worksheet 2 14. Chemical Effects of Electric Current
1. (a) T (b) F, All liquids are not good conductors of electricity.
(c) T (d) T
2. S.No. Material Deflection in compass needle (Yes/No) Conductor (Yes/ No)
1. Lemon Juice Yes Yes
2. Vinegar Yes Yes
3. Tap water Yes Yes
4. Distilled water No No
5. Vegetable oil No No
6. Milk No No
7. Honey No No
8. Orange juice Yes Yes
9. Ink No No
10. Curd water (whey) Yes Yes

3. LED starts emitting light when very weak current flows through it. It is used in fairy lights and in
sensitive detectors.

Bulb

Negative
Terminal
Positive
Terminal

4. (a) A substance which gives ions when melted or dissolved in water is called electrolyte.
(b) The process of decomposition of an electrolyte on passing electricity is called electrolysis.
(c) The positively charged ion is called cation.
(d) The negatively charged ion is called anion.
5. (a) Water contains dissolved salts which could conduct electricity causing electric shock and even
short circuit.
(b) Two thick wires were taken and placed in a trough containing acidulated water. Two test tubes
filled with acidulated water were kept over the open ends of wires and other ends of wires were
connected to battery terminals. After some time, gases started collecting in the test tubes at both
electrodes by downward displacement of water. It was found that volume of hydrogen and oxygen
gases are in the ratio 2 : 1.
Science Around Us
• Car wheel is electroplated by chromium to give it strength and lustre.
• Brass tap is electroplated with chromium to give lustre and prevent corrosion.
• Artificial jewellery is electroplated with gold to increase its decorative value.
• Iron objects are electroplated with nickel to prevent corrosion.

54
 (Extend)
Worksheet 3 14. Chemical Effects of Electric Current
1. (a) In (ii), (iv), (vi), the bulb will glow as the electrolyte used in each is conducting in nature.
(b) In others, the electrolyte is non-conducting and thus the bulb does not glow.
2. Q G E L E C T R O D E
T A G P I Q G T H R L
E L E C T R O L Y T E
S V H Y U L L X G P C
U A F I G F D K E F T
L N J R O D P D D O R
P I Q H S N L S L H O
H Z Z I C M A F X V L
U A C N R B T A E P Y
R T R N V E I W O O T
I I T A A W N I E N I
C O J A S B G S B Y C
A N H Z C P V A G L C
C K F J A N O D E P E
I T L R L Q N B K M L
D C M C A R B O N T L

3.(a) We can use detector such as battery bulb, magnetic compass or LED to detect electric current. If
the bulb glows or the compass needle shows deflection, then the current passes through the object.
(b) The liquids that conduct electricity are solutions of acid, base and salts because these substances
can dissociate into their ions on passing electric current and conduct electricity.
4. Rajesh can connect the circuit as shown. The two copper
electrodes connected to terminals of battery are immersed in
distilled water contained in the trough. A torch bulb (used as
indicator) is connected in the circuit as shown. If the bulb glows,
it means water contains dissolved salts and it is not distilled
water. If bulb does not glow, it means water is distilled and
hence non-conducting.

Science Around Us
LED bulbs are available in different colours. They are used in fairy
lights used for decorative purposes. They are used in lighting circuits, in night lamps, in traffic lights and
solar lamps. Emergency lights also use LED light panel. LED is also used as indicator to detect weak current
in a circuit.
CFLs are preferred LED as they are more luminous as compared to LED, and used for purposes which require
high intensity of light such as reading.

55
 (Elaborate)
Worksheet 4 14. Chemical Effects of Electric Current
1. (a) Electrorefining (b) strip (c) impure (d) pure
(e) cathode (f) dilute (g) electrolyte (h) ions of
(i) anode (j) pure (k) Impurities (l) copper

2. (a) (1) Metal cap (1) External circuit

(2) Seal
(3) Carbon rod

(4) MnO2 + C
(2) Cathode (zinc)

(5) NH4Cl paste

(3) Anode (copper)

(6) Outer card

(4) Electrolyte
(dil. H2SO4)
(7) Zinc
Voltaic cell
Dry cell

(b) The electrolyte is in the form of paste in a dry cell. e.g. Lechlanche cell.
The electrolyte is in the form of solution in a wet cell. e.g. voltaic cell.
The electrolyte is in the form of solution in a galvanic cell, but anode and cathode electrolytes are
kept separately.
3. (a) Zn (s) → Zn2+ (aq) + 2e–
(b) 2MnO2 (s) + 2e– + 2NH4Cl (aq) → Mn2O3 (s) + 2NH3 (aq) + 2H2O (aq) + 2Cl–
(c) 2MnO2 (s) + 2NH4Cl → Mn2O3 (s) + 2H2O (l) + 2NH3 (aq)
(d) 1.5 V
4. (a) To detect weak current, a magnetic compass needle (between coil of wire) or an LED bulb can be
used in place of bulb.
(b) When current is passed through copper sulphate solution, it dissociates into Cu2+ and SO42– ions
(cations and anions respectively).
5. Chromium is used for electroplating brass objects, such as bathroom fittings, car parts, cycle parts etc.
It gives hardness to the surface, resistance to scratches and shiny appearance to these articles.
6. The major concern associated with electroplating on commercial level is that the waste generated in
electroplating industry is highly polluting. Though there are government guidelines for the disposal of
these chemicals, these wastes are unfortunately discarded in waterbodies.
Chromium is used for electroplating brass objects, such as bathroom fittings, car parts, cycle parts etc.
It gives hardness to the surface, resistance to scratches and shiny appearance to these articles.

56
 (Engage)
Worksheet 1 15. Some Natural Phenomena
1. (a) True (b) False (c) True (d) True
2. (a) charges (b) Benjamin Franklin, 1952
(c) sparks, sound (d) Lightning
3. (b) Closed car or bus (d) A house or a building
4. (a) Seismograph (b) Measurement of seismic waves
(c) Charles Richter
(d) The wavy line depicts vibrations generated by earthquakes.
(e) The device works by recording the seismic waves on an instrument called seismograph.
5. (a) The study of charges at rest is called static electricity.
(b) The relative movement of different parts of lithosphere producing high intensity shock waves is
called earthquake.
(c) The device used to detect the presence of charges on a body is called electroscope.
6. (a) Glass rod acquires positive charge and silk acquires negative charge.
(b) When cotton is subbed with ebonite, cotton gets negatively charged and ebonite gets positively
charged.
(c) When two objects are charged by friction or rubbing, they require equal and opposite charges.
7. An electroscope is a device that can be used to check whether or not an object is carrying a charge. When
the metal head of the electroscope is touched with a charged body, it gets charged due to conduction.
The acquired charge redistributes on the electroscope and flows down to the gold leaves from the disc.
Leaves acquire like charge and diverge away. This indicates that electroscope is charged. When the
metal head is touched by hand, the charge on gold leaves is neutralised due to earthing and the gold
leaves come close again. This is called discharging of electroscope.

(Explore)
Worksheet 2 15. Some Natural Phenomena
1. Object rubbed Material used for Attracts/Does not Charged/Not charge
rubbing attract bits of paper
(a) Refill of a pen Polythene Attracts Charged
(b) Eraser Wool Attracts Charged
(c) Plastic scale Dry hair Attracts Charged
(d) Metallic scale Silk cloth Does not attract Not charged

2. (a) (v) (b) (iv) (c) (i) (d) (iii) (e) (ii)
3. (a) The balloons repel each other. (b) The balloons have acquired like charge.
(c) Like charges repel each other.
4. (a) static (b) current (c) earthing (d) fault zone, seismic

57
 5. (a) Strong earthquake can cause severe loss to life and property in the form of collapse of buildings
and trees, damage to nuclear reactors and by floods in rivers.
(b) Lightning is believed to have played a significant role in the evolution of life on earth. It helps to
fix nitrogen and fertilization of plants by providing it nitrates.
6. Benjamin Franklin flew a kite made of silk cloth into the clouds on a thunderous day. He tied a metallic
key to the silk thread of the kite. Whenever there was a flash of lightning in the clouds, he received an
electric shock and the key was found to be warmed up. This helped him prove that lightning and thunder
are caused by electric charges in the clouds. When the key was touched, the charge passed through his
body into the earth giving him an electric shock.
7. Lightning in the sky affects radio, television transmission/reception. Due to atmospheric disturbances,
we get crackling noise on radio/TV. We should not use TV during lightning as TV antennae are prone
to lightning strike. Similarly, wired telephones should not be used.
Science Around Us
The earth is a geoid-shaped planet made of 12 tectonic plates which are in constant relative movement. When
the break line (fault zone) between two plates suddenly moves, brushes past or overlap, or the magma rises
up between two plates pushing them apart, vibrations. These vibrations are called seismic waves. The waves
travel outward and through the earth surface as well as along the surface at varying speeds resulting in tremors
in the earth. These are known as an earthquake. The occur all the time, all over the earth, but most of them
are not even noticed.

(Extend)
Worksheet 3 15. Some Natural Phenomena
1. (a) Static charges (b) Electric current
(c) Epicentre (d) Seismic waves
(e) Tectonic plates
2. (a) The two refills will attract. (b) The uncharged body is attracted by the charged body.
3. (a) The two will attract as the balloon has negative charge while the refill has positive charge.
(b) Unlike charges attract each other.
4. (a) Electrostatic force
(b) Fig. (i) Charging by induction when the comb induces opposite charge on paper bits.
Fig. (ii) Charging by friction when rod and silk are rubbed together.
Fig. (iii) Charging by friction when ebonite and wool are rubbed together.
5. (a) Following methods can be used to detect the charge on a body:
• bringing it close to bits of paper.
• bringing it close to metal head of electroscope.
• touching it with the metal head of electroscope.
(b) The above test proves that detection of the charge is possible by conduction or induction.
6. A body can be charged by three methods.
• Charging by friction: When two uncharged bodies are rubbed, they acquire equal and opposite
charges.

58

• Charging by conduction: When a charged body is touched with the uncharged body it acquires like
charge due to redistribution of charges.

• Charging by induction: When a charged body is kept close to an uncharged body it induces opposite
charge on close/nearer end of the uncharged body.
Science Around Us
The huge masses of clouds get electrically charged due to the rubbing or friction with air and the presence
of dust, carbon and other charged materials in the air. When clouds carrying opposite charges approach
each other, a large quantity of charge flows from one cloud to another through air. Since air is an insulator,
charges flow only when mutual interaction of charges is so high that it breaks the insulation of air. When this
happens, tremendous amount of energy is released in the form of heat and light and is seen as an instant spark
of electricity in the sky.

(Elaborarte)
Worksheet 4 15. Some Natural Phenomena
1. (a) Gujarat 2001, Odisha 2005, Maharashtra 1993
(b) Japan 2011, Indonesia 2004, Chile 1960
2. (a) (4) Surface (b) (2) Epicentre

(3) Crust
(1) Hypocentre

(2) Mantle (3) tremors

(1) Core

(a) Fig. (i) Structure of earth

Fig. (ii) Conduction of quake tremors
(b) Tsunami occurs when an earthquake occurs on seabed.
Earthquake occurs under the earth’s crust.
(c) The instrument which records the seismic waves due to an earthquake is called seismograph.
(d) The scale which gives a measure of energy released at earthquake’s centre is called Richter Scale.
(e) The earthquake of magnitude 4 is a mild earthquake.
The earthquake of magnitude 6 is a major earthquake having intensity 100 times more than that
of magnitude 4.
(f) 8 and above, 0 – 3
3. (a) An electroscope has been developed to detect the presence and nature of charge on a body.
(b) Lightning occurs when there is an electric discharge in the air.
Examples: (i) Spark produced in a lighter. (ii) Spark produced in a socket when the pin is loose.
(c) No. lightning would not occur if air was good conductor as no heat and light would be produced
during conduction of electricity through them.
59
 4. Safety measures during an earthquake are:
• Take shelter under a table and be there until the vibrations stop. If in outdoors, squat on the ground
and cover your head.
• If in bed, stay there and cover your head with a pillow.
• Stay away from tall and heavy objects, cupboards etc.
• Don’t use stairs or lift to move out.
• If in a car or bus, don’t come out and drive slowly to clear area.
5. To protect from lightning, following measures can be taken.
• keep away from tall trees, high buildings or electric poles
• unplug the TV set, computers or wired phones
• avoid contact with running water electron
• never use umbrella with metallic head
• never stand near window or balcony with metallic railings.
6. In an atom, there are two type of charged particle, positive and negative. While +
neutron is neutral particle negative charge particle, electron revolve around
nucleus which is positively charged due to presence of proton and neutron.
Electrons revolve in circular pushs known as orbit around nucleus.

Nucleus
(proton and neutron)

(Engage)
Worksheet 1 16. Light
1. (a) (i) (b) (iii)
2. (a) energy, see (b) direction (c) direction of light
(d) luminous, non-luminous (e) lateral
3.

Fig. (i) Fig. (ii)

(a) Fig. (i) irregular Fig. (ii) regular

(b) Fig. (i) rough Fig. (ii) smooth/polished
(c) Fig. (i) wall, paper Fig. (ii) mirror, shiny metal
4. (a) carrot (b) night blindness

60
 5. (a) • Illuminated objects are the ones which reflect light falling on them, e.g. moon.
• Luminous objects are the ones which emit light of their own, e.g. sun.
(b) The image in which left appears right and right appears left is said to be laterally inverted.
6. (a) The ray of light coming from a source towards a surface is called incident ray.
(b) The ray of light bounced back from a surface into the medium is called reflected ray.
(c) The imaginary perpendicular drawn at the point of incidence on the relfecting surface is called
normal.
(d) Angle between incident ray and normal is called angle of incidence.
Angle between reflected ray and normal is called angle of reflection.
7. The sense of sight is important to connect with the outside world. The part of retina where optic nerves
join the retina and which has rods or cones is called blind spot.
8. Image formed by plane mirror has following characteristics:
• Image is virtual and erect.
• Image is laterally inverted.
• Image is of same size as object.
• Distance of object from mirror = Distance of image from mirror.
(Explore)
Worksheet 2 16. Light
1. (a) white light (b) seven (c) violet (d) indigo
(e) blue (f) green (g) yellow, orange (h) red
(i) dispersion (j) rainbow
2. (a) (iv) (b) (i) (c) (ii) (d) (iii)
3. (a) Angle of incidence = 45°
Incident ray Normal Reflected ray

i r

(b) The distance between mirror and object = Image distance (in plane mirror)
Thus, distance = 20 cm.
4. (a) the pupil has to expand a lot and this causes strain in the eyes.
(b) it can damage the eye lens and retina leading to blindness.
(c) it helps to remove dust, dirt and germs from the eyes.
5. (a) • Incident ray, reflected ray and normal, all lie in the same plane.
• Angle of incidence is equal to angle of reflection.
(b) Uses of plane mirror as:
• looking glass
• mirror in periscope and kaleidoscope.

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 6. Periscope is based on the principle of multiple reflection of light. It is used in submarines to detect
surface activities and to look around in crowd or behind the wall.
7. Retina has rod cells and cone cells.
Cone cells help us to detect the colours of objects seen by us.
Rod cells help us to respond to light of different intensities.
Science Around Us
A Kaleidoscope consists of three thin mirror strips connected edge to edge to form a triangular cavity. One end
is closed with a triangular glass piece and some broken pieces of colour glass or plastic are poured in it. The
other end is then closed with paper and a hole is made in the centre to observe the inside of the kaleidoscope.
Now, when one observes through the hole, coloured patterns are seen. When the kaleidoscope is rotated, the
patterns change.
It is a fun scientific toy for young learners.
(Extend)
Worksheet 3 16. Light
1.(a) It shows multiple reflection of light, a phenomenon caused by placing two mirrors inclined at an
angle to each other.
360
(b) If q = angle between mirrors, number of images, N = –1
q
(c) Angle between the mirrors 0° 30° 60° 90°
Number of images Infinite 11 5 3

2.

Ciliary muscles (1)

Iris (2)

Eye lens (3)

(5) Optic nerve
Cornea (4)

(6) Retina

S.N. Eye parts Function

(a) Cornea It helps to protect the eye lens and cause most of the bending of light entering the eye.
(b) Iris It regulates the amount of light entering the eye.
(c) Pupil It constricts or enlarges to regulate the amount of light which enters the eye.
(d) Retina It is the screen on which the image is formed.
(e) Optic nerve It is the nerve which carries signals from retina to brain.
(f) Eye lens It is the crystalline lens made of living cells through which refraction of light takes
place.

3. He is Louis Braille. He developed the Braille method so that visually impaired people could read using
the sense of touch. It involves use of symbols which represent alphabet and their combinations. The
text is arranged in the form of symbols in rectangular array called Braille cell.

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 4. (a) When the image of the object keeps on changing at a rate greater than 16 images per second, the
object is perceived as moving.
(b) The eye of the butterfly and crab are unique as they can detect fast moving objects and distinguish
between ultraviolet and polarised light, which a human eye cannot.
(c) Day birds have more cones than rods to see easily during the day. Night birds have more rod cells
than cone cells to see during the night time.
5. To take care of eyes, one should take the following steps:
• don’t watch television or use mobile gaming for long hours.
• wear spects while going through dusty places and during bright sunshine.
• never keep the book too close or too far from the eyes while reading.
• wash your eyes regularly with fresh water and never rub your eyes.
Science Around Us
Just after the rain, a large number of tiny water droplets remain suspended in the air and each droplet acts like
a tiny prism. When the sunlight passes through these drops, then due to dispersion and total internal reflection,
it splits into a pattern of seven constituent colours. This is known as rainbow.
(Elaborate)
Worksheet 4 16. Light

1.

Incident Ray

Prism
e
Glass Slab
The incident ray enters from air to glass and since glass has greater optical density than air, refraction
occurs. Again as light passes from glass to air, it again gets refracted due to its movement from optically
denser medium to air.
2.

F
F

Fig. (i) Fig. (ii)

Convex lens: Image is • real and inverted • highly diminished
Concave lens: Image is • virtual and erect • highly diminished
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 3. Optical aids are the aids which help people see clearly, e.g. spectacles and contact lenses. Non-optical aids
are also developed for people with impaired vision, e.g. tactual aids (using sense of touch such as Braille).
4. The bird appears to be inside the cage because as the cardboard twists rapidly, the next image appears in
time faster than 1/16th of a second. Then due to persistence of vision, the bird is perceived to be inside
the cage.
5. (a) When the torch is lighted on the pupil of someone’s eyes, it starts constricting.
(b) The size of pupil becomes smaller to cut the excess light entering the eye.
(c) The pupil of the eyes becomes larger in size to allow greater amount of light enter the eye when
the torch is switched off.
(d) The ability of the eye to retain the image of object for 1/16th of the second after we stop looking
at it, is called persistence of vision.
Accommodation is defined as the ability of the eye to focus on the nearby as well as far off objects.
6. Defects in vision occur when people are not able to see the nearby or far off objects clearly. These are
called myopia and hypermetropia respectively.
• Myopia: The person can see nearby objects clearly, but not the far off objects.
• Hypermetropia: The person can see far off objects clearly, but not the nearby objects.
In myopia, the patient wears concave lens of appropriate power.
In hypermetropia, the patient wears convex lens of appropriate power.
(Engage)
Worksheet 1 17. Stars and The Solar System
1. (a)
(i) (b) (iii) (c) none of these is correct
(d)
(iii) (e) (i) (f) (ii)
2. (a)
Jupiter, Saturn, Uranus, Neptune, Mercury, Venus, Earth, Mars
(b)
Mercury, Venus, Earth, Mars (c) Uranus, Saturn, Neptune, Jupiter
(d)
Mars (e) Jupiter
3. (a)
The part of galaxy with sun at its centre and planets, asteroids and comets revolving around it, is
called solar system.
(b) A source of light which produces heat and light by nuclear reactions is called star.
(c) A celestial body revolving around the sun is called planet.
4. (a) The fixed path along which a body revolves is called orbit.
(b) Time taken by a satellite to complete one revolution around sun/planet is period of revolution.
Time taken by a body to complete one rotation on its axis is period of rotation.
(c) The natural satellite of a planet is called moon.

5.

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 6. Venus rotates on its axis from east to west. Thus sun appears to rise in the west and set in the east on
Venus.
7. Sun Earth

• It is the only planet of solar system on which

• It is a star and is at the centre of solar system.
life exists.
• It is a huge ball of burning gases. • 71% of earth is made of water.
• Its atmosphere contains nitrogen, oxygen,
• It is the source of all energy for us
carbon dioxide, hydrogen etc.
• It generates heat by nuclear fusion reaction. • Its temperature is optimum to support life.
• It causes day and night, season change,
• It is also called blue planet.
illumination of moon and planets etc.

(Explore)
Worksheet 2 17. Stars and The Solar System
1. (a) Pole star is visible in the northern part of the sky.
(b) It appears stationary from earth while all other stars appear to move from east to west. This is
because it is at the imaginary axis of earth’s rotation.

2. (a) Surya (b) Budh (c) Shukra (d) Prithvi

(e) Chandra (f) Mangal (g) Brihaspati (h) Shani
3. (a) smaller, less than that (b) 29
(c) once (d) 3,84,000 (e) solar eclipse
4. (a) Moon (b) Moon
(c) Uranus, Neptune (d) Venus, Uranus
(e) Saturn (f) Jupiter
5. (a) Three stars form the handle of the dipper and four stars form its bowl.
(b) Orion is called hunter because the stars are arranged to resemble a hunter. Three middle stars form
its belt and four stars form the shoulder and legs.
(c) A group of small number of stars which form a recognizable pattern is called constellation. e.g.
Ursa Major, Orion.

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 6. Asteroid: These are rock pieces which revolve around the sun between the orbits of Mars and Jupiter.
They are about 0.1 million in number.
Meteor: It is a heavenly body of small pieces of stones, rocks and gases travelling at high speed. It
starts burning when it enters earth’s atmosphere due to friction with air.
Meteorite: The part of meteor which does not burn completely in earth’s atmosphere and reaches the
surface is called meteorite.
Science Around Us

The axis of rotation of earth is tilted at 23/2° to the vertical. The face towards the sun has day and that away
from sun has night. The position of northern and southern hemisphere keeps on changing as they move on
elliptical orbit. When N-hemisphere is tilted towards sun, it has summer and S-hemisphere has winter. When
S-hemisphere is tilted towards sun, it has summer and N-hemisphere has winter.
On March 21 and September 22, duration of day and night is equal in both hemispheres.
(Extend)
Worksheet 3 17. Stars and The Solar System
1. (a) Celestial (b) Niel Armstrong
(c) Astronomical Unit (AU) (d) Arizona
(e) Sputnik 1 (f) Ceres
(g) No such meteoroid.
Average distance from Time taken to complete
2. Planet
one orbit around the Sun
Number of moons known
Sun (million km)
Mercury 58 88 days –
Venus 108 225 days –
Earth 149 365.25 days 1

66
 Mars 228 687 days 2
Jupiter 778 12 years 50
Saturn 1427 29.5 years 62
Uranus 2871 84 years 27
Neptune 4498 165 years 14

3. (a) It completes one revolution in 76 years and comes close to sun.

(b) 1986
(c) 2062
4. (a) International Astronomical Union (b) Polar Satellite Launch Vehicle
(c) Pluto is no longer considered to be a planet because of its very small size and very long period of
revolution around the sun. It is now called a dwarf planet.
(d) Star produces its heat and light due to nuclear reactions occurring on it. It is a huge body very
far away from earth. Shooting star produces heat and light as it burns due to friction in earth’s
atmosphere. It is very small and burns completely before reaching the surface.
5. Natural Satellite Artificial Satellite

• It occurs naturally. • It is a man made satellite.

• It revolves at a large distance from the planet. • It revolves closer to the planet.
• It is of no practical use. e.g. moon. • It is launched with specific purpose e.g.
Sputnik 1

6. Mercury is a small planet revolving closest to the earth. It has thin atmosphere. Its day temperature is
over 400°C and night temperature is about –170°C. There is no life on Mercury. It completes a revolution
in 88 days.
7. Moon has no/very weak gravitational pull. So it cannot hold any atmospheric gases and water on its surface.
Science Around Us
(a) Aryabhatta was the first Indian Satellite
Other satellites are: Chandrayaan, MoM, Kalpana Chawla 1, INSAT series.
(b) Applications of artificial satellites are:
• weather forecasting • communication (TV, cell phone, Fax etc.)
• remote sensing and land mapping • space research
(Elaborate)
Worksheet 4 17. Stars and The Solar System
1. (a) 1 Light year = Distance travelled by light in 1 year
= Speed of light × time
= 3,00,000 km/s × 365 × 24 × 3600 = 9.46 × 1012 km
(b) Time taken by light to reach earth
Distance between sun and earth 1.476 × 1011
= = = 492 s = 8.2 minutes.
Speed of light 3 × 108

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2. Mangalyaan Mission Chandryaan Mission

Launch from: Sriharikota Launch from: Satish Dhawan Space Centre

Launch date: 5\11\2013 Launch date: 20\10\2018
From Earth to: Mars From Earth to: Moon

Objective: Deep space communication, navigation, Objective: Design and develop a spacecraft to orbit
e x p l o r a t i o n o f s u r f a c e f e a t u re s , the moon, increase scientific knowledge
morphology etc. about Mars.

3. (a) Mars (Olympus Mons) (b) Deimos and Phobos

(c) Titan, (d) 88
(e) No rings seen; 27 moons (f) Saturn
(g) 318 and 1321 times (h) Pluto and Eris
4. Comets are heavenly bodies which revolve around the sun in very large, highly elliptical orbits. These
have very long period of revolution. When a comet comes close to sun, it appears like a bright glowing
ball with long glowing tail, consisting of dust and gases. Its tail always points away from the sun. e.g.
Halleys Comet, Shoemakers levy 9.
5. (a)

Direction of
sunlight

Different Phases of Moon

(b) When moon revolves around the earth, we see only that part of moon which is illuminated by
the sun. When the rays of sun fall directly on moon we see its full bright disc called full moon.
When we see that part of moon when sunlight does not reach at all, it is called new moon. The
phases occurring from new moon to full moon are called waxing phases and from full moon to
new moon are called waning phases.
(c) Neap tide occurs just after first and third quarter of moon phases. When sun and moon are in line
with each other, they produce tides in ocean called spring tides.
(d) The proxigean spring tide occurs three or four times in a year. The moon’s perigee, i.e. when it is
closest to earth in its orbit, coincides with spring tide. It produces 25% rise in the tide.

68
 (Engage)
Worksheet 1 18. Pollution of Air and Water
1. (a) (i) (b) (ii) (c) (ii) (d) (ii)
2. (a) Waste Water Treatment Plant
(b) At places where water is disposed off in rivers.
(c) It is helpful in controlling river pollution and groundwater contaminations.
3. (a) False (b) True (c) False (d) True
4. Carbon monoxide, Sulphur oxides, nitrogen oxides, dust particles
5. Compressed Natural Gas (CNG) Liquefied Petroleum Gas (LPG)
6. (a) Smog is a combination of smoke and fog. It is formed due to excessive pollution in the air at the
time of fog.
(b) The pollutants which do not get broken into harmless substances naturally are non-biodegradable
pollutants. e.g. DDT, lead etc. The pollutants which get broken into harmless substances by natural
agents are biodegradable. e.g. organic pollutants.
7. River removal of suspended impurities sedimentation filtration

Supply to houses Water mains chlorination/ozonisation aeration

8. Plantation of tree saplings is the main activity during van Mahotsav.
9. Water, in recent years, has become polluted due to following reasons:

• discharge of untreated domestic sewage in rivers and lakes which contains food waste, detergents,
microbes (bacteria, fungi, virus and parasites).

• discharge of toxic industrial waste into rivers and lakes.

• excessive use of fertilizers and pesticides in agriculture which flow down to river with rainwater.

• addition of acids, alkalies and dyes.

• contamination by toxic metals-lead, arsenic, cadmium, mercury, nickel etc.
(Explore)
Worksheet 2 18. Pollution of Air and Water
1. (a) (iv) (b) (v) (c) (i) (d) (vi)
(e) (ii) (f) (vii) (g) (iii)
2. (a) All the events cause global warming because green gases including carbon dioxide etc. are evolved
in these processes. These also result in raising the temperature of environment to high degrees.
(b) A large portion of forest vegetation catches fire which spreads very fast. It is harmful not only for
green cover, but also to the wildlife and settlements close to these areas.
(c) A volcanic eruption leads to release of massive dust, smoke, ashes and harmful gases in the air,
polluting it.

69
 3. To improve air quality in cities, following measures can be taken:
• improving quality of fuels in automobiles.
• use of catalytic converters in automobiles and industries
• replacing wood, charcoal, coal and kerosene with LPG
• planting more trees
• using better technology to control the level of pollutants in emissions
• using CNG in automobiles and renewable sources to generate electricity.
4. Causes of air pollution are:
• burning of fossil fuels, automobile exhausts, industrial emissions
• burning of wastes–plastic, rubber, agricultural stub
• mining and construction
• vapours of organic solvent, paints and varnish industry.
5. The increased concentrations of carbon dioxide in air results in an increase in the earth’s temperature.
This rise in temperature due to presence of excessive carbon dioxide, methane and water vapour in air
is called greenhouse effect and leads to global warming. It can be reduced by planting more trees and
reducing the consumption of fossil fuels.
Science Around Us
It is not possible to completely prevent and eliminate air pollution. But it can be controlled by taking following
steps:
To improve air quality in cities, following measures can be taken:
• improving quality of fuels in automobiles.
• use of catalytic converters in automobiles and industries
• replacing wood, charcoal, coal and kerosene with LPG
• planting more trees
• using better technology to control the level of pollutants in emissions
• using CNG in automobiles and renewable sources to generate electricity.
(Extend)
Worksheet 3 18. Pollution of Air and Water
1. • Archaeological Survey of India

• Chlorofluorocarbon

• Suspended particulate matter

• Parts per million
2. (a) Fig. (i) filtration candle Fig. (ii) Reverse Osmosis/UV filtration
Fig. (iii) Reverse Osmosis Fig. (iv) Boiling
(b) Water is purified in the treatment plants in the following ways:
• Removal of suspended impurity: Water is mixed with some alum and allowed to stand. Heavy
impurities settle down and upper layer is taken for filtration.
• Filtration: Water is allowed to pass through thick layers of sand and gravel.
• Aeration: It helps to kill harmful microorganisms.
• Chlorination: Chlorine is added to water to kill germs.
70
 (c) Four processes to kill germs are:
• Aeration: When air under pressure is blown in water, it kills pathogens.
• Chlorination: Chlorine tablets are added to water to kill germs
• Boiling: Water boiled for 10-15 minutes kills germs present in it.
• Reverse Osmosis: It is used to purify water for domestic use.
(d) Chlorine is added in 0.1 – 10 mg/litre concentration.
3. (a) High wind, water and overgrazing cause foliage destruction.
(b) It increases rate of global warming on earth.
(c) Camp fire results in foliage destruction.
4. (a) Nitrous oxide – 2%, Methane – 5%, Other gases – 3%, CFCs – 37%, Carbon dioxide – 53%
(b) They cause respiratory diseases, acid rain and deplete ozone layer.
(c) Gaseous pollutants are gaseous compounds while particulate pollutants are solid particles suspended
in air.
Science Around Us
The Ganga Action Plan was launched in 1985 to cleanse the river Ganga. It aimed at reducing pollution in
the river. It was found that ecology of Ganga had been greatly damaged. The process of cleaning the river is
still going on.
In Kanpur, 5000 industrial units including fertilizers, sugar, detergent, textile, leather and paint discharge their
effluents into river Ganga. This toxifies the river and causes great harm to it.
(Elaborate)
Worksheet 4 18. Pollution of Air and Water
1. (a) Water hyacinth is called terror of Bengal. It is an exotic shrub and competes with native species
and eliminates them. It occurs easily in hot and humid climate of Bengal.
(b) The marble statues and structures get slowly corroded due to acidic rainwater falling on them.
This is known as marble cancer.
(c) Lead poisoning causes brain and neurological disorder, behavioural changes, kidney impairment
and gastrointestinal illness.
It is caused by occupational exposure (paint industry, mines, smelting plants and water from old
lead pipes.
(d) The release of liquid petroleum hydrocarbon in marine ecosystem forming a layer of oil on ocean
water is called oil spill. Its known cases are:
• Arabian Sea Oil Spill with 400 million tonnes of oil spilled.
• Gulf of Mexico spill with 5.1 million gallons of oil spilled.
(e) The toxicity from mercury consumption in body is called mercury poisoning, the known cases are:
• A 48. year old professor died of mercury poisoning due to accidental exposure to organic mercury
compound.
• 3 year old child suffered mercury poisoning due to excessive intake of antibiotics.

71
 2. (a) DDT sprayed in the field enters the waterbodies and becomes a part of food chain.
(b) DDT sprayed in the field.
(c) Man, who consumes the fish, gets DDT in his body by the process of biological magnification.
(d) The level of pollutants present in the food keeps on increasing by accumulation at each trophic
level of food chain. This is called biomagnification.
3. (a) 4.2 million, air (b) 100 mg, above 100 mg
(c) Delhi and Kanpur (d) brain damage in children; bronchitis
4. (a) Electrostatic precipitator and scrubber are particle collection devices used in steel, gypsum and
power industry for cleaning of air.
(b) Pure air is free of any harmful pollutants and greenhouse gases.
Polluted air is concentrated with harmful pollutants and greenhouse gases.
(c) Ozone layer gets depleted due to excessive use of hydrocarbon, refrigerants, chlorofluorocarbons
and propellants.
(d) Kyoto Protocol is an international treaty which commits state parties to reduce greenhouse gas
emissions based on scientific consensus.
5. Discolouring of white marble of Taj Mahal is due to oxides of nitrogen and sulphur released by industrial
units around it and by Mathura Refinery. These oxides react with water vapour in atmosphere and form
sulphuric and nitric acids. These acids come down as acid rain and corrode the marble of the monument.
6. General measures to check water pollution are:
• never throw garbage in river/lakes and clean them regularly.
• plant trees and plants along river banks.
• treat the toxic industrial waste chemically to remove harmful substances.
• discourage excessive use of fertilisers and pesticides.
• never wash clothes, clean utensils or bathe on river bank.
• sewage should be treated in sewage treatment plants before discharge.

72