Start Up Science

Class 7
Chapter Answer Keys
 Contents

S. No. Chapter Name Page No.

1. Nutrition in Plants 1

2. Nutrition in Animals 7

3. Fibre to Fabric 14

4. Heat 20

5. Acids, Bases and Salts 26

6. Changes around Us 34

7. Weather, Climate and Adaptations in Animals 40

8. Soil 46

9. Respiration in Organisms 52

10. Transportation of Materials 58

11. Reproduction in Plants 63

12. Motion and Time 69

13. Electric Current and Its Effects 74

14. Light 81

15. Winds, Storms and Cyclones 86

16. Water—A Precious Resource 92

17. Forests 98

18. Wastewater Management 103

19. Test Paper-I (Chapters 1 to 9) 108

20. Test Paper-II (Chapters 10 to 18) 111

 1. Nutrition in Plants

Answer Key

In-text Questions
Parts of a Plant (Page 1)
1. root; water; nutrients; soil erosion
2. stem; leaves; flowers; fruits; branches
3. leaf; food; photosynthesis; water; sunlight; carbon dioxide; chlorophyll
4. flower; fruit; seed(s)
Think and Answer (Page 2)
If plants stop producing food, then the heterotrophs will face food scarcity. This is because heterotrophs
are dependent on plants for food.
Think and Answer (Page 3)
1. Photosynthesis maintains a balance between oxygen and carbon dioxide as during photosynthesis,
plants take in carbon dioxide and give out oxygen in equal amounts. The equation for the process
of photosynthesis is as follows.
6CO2 + 6H2O Sunlight C6H12O6 + 6O2
→
Carbon dioxide Water Chlorophyll Glucose Oxygen
(from air) (from soil) (carbohydrate)
2. Plants have two types of vessels, i.e. xylem which transports water and minerals, and phloem
which transports food prepared by the leaves to all other plant parts.
Lab Activity (Page 5)
A. 1. The green parts of the leaf developed blue-black colour.
2. Chlorophyll
B. 1. Leaf Q
2. Carbon dioxide (CO2)
3. Potassium hydroxide (KOH) absorbs CO2 gas from the air present in the conical flask. It
eventually helps in determining the rule of CO2 during photosynthesis in this activity.
Think and Answer (Page 6)
Proteins are important for our body because they help in growth and development. They also help the
body to repair damaged cells and make new ones.
Quick Check (Page 6)
1. Heterotrophic nutrition
2. Chlorophyll

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 3. Croton
4. Nitrogen fixation
Quick Check (Page 8)
1. host
2. saprophytic
3. insectivorous
4. shelter; nutrients
Picture Study (Page 9)
A. Cuscuta (Amarbel)
B. Venus flytrap
C. Mushroom
D. Lichens
1. Cuscuta (Amarbel); host
2. insects; nitrogen
3. fungi
4. symbiotic

Apply Your Learning

A. Identify and Rectify (Page 10)
1. Pitcher plant
2. Bread mould
3. Croton
4. Lichen (This is labelled correctly.)
B. Observe and Answer (Page 10)
1. A: Venus flytrap B: Bread mould
2. Plant A eats insects.
3. A
4. B
C. Life Skills (Page 11)
Photosynthesis is important for the continuity of life on earth because plants are autotrophs and
all other organisms directly or indirectly depend on them for their food requirements. Plants also
release oxygen during photosynthesis which is essential for the survival of all living beings. If
photosynthesis were not to occur, heterotrophs would not get food and oxygen, and they would
die.
D. Reason Out (HOTS) (Page 11)
1. Leather shoes appear white when they are left in humid weather for a long time due to the
growth of fungi/moulds on their surface.
2. Venus flytrap can make its own food by the process of photosynthesis. It depends on insects
only for its nitrogen requirements. Hence, it is both an insectivorous plant and an autotroph.

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 3. Animals cannot make their food from carbon dioxide and water in presence of light because
they lack the green pigment called chlorophyll. Chlorophyll is necessary to perform
photosynthesis.
E. Link and Learn (Geography) (Page 11)
Students are expected to do this on their own.
(Hint: They can take help from the atlas to accurately locate these types of forests.)
F. Mind Map (Page 11)

Types of Nutrition in Plants

Autotrophic nutrition Heterotrophic nutrition

Mode of nutrition in which an organism Mode of nutrition in which an organism
prepares its own food from simple is unable to make its own food and
substances like carbon dioxide and water. depends on other organisms for its food.

Parasitic plants Saprophytic plants Insectivorous plants Symbiotic plants

Plants that live on Plants that live and Plants that eat Plants that live in
other plants and feed on dead and insects. association with
obtain food from decaying organic other plants, and
them. matter. share shelter and
nutrients with them.

G. Integrating ICT (Page 11)

Students are expected to do this on their own.
H. Case Study (Page 12)
1. Nitrogen cycle is a process through which nitrogen is converted into many forms, continuously
passing from the atmosphere to the soil to organisms and back into the atmosphere. It
involves several processes such as nitrogen fixation, nitrification and denitrification.
2. Rhizobium bacteria
3. Mineralisation refers to the process of decomposition of organic nitrogen from manure and
other organic matter by microorganisms to form ammonium that can be readily used by
plants.
4. Compounds of nitrogen formed during nitrification are nitrite and nitrate.
5. Immobilisation is the reverse process of mineralisation.
6. Nitrogen is present in the atmosphere in gaseous form. However, atmospheric nitrogen cannot
be used by plants directly. It is first converted into usable form by the bacteria present in soil.
Then, it is absorbed by the plants from the soil along with water. This is why the nitrogen cycle is
important.

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Exercises
Stop and Reflect (Pages 13 and 14)
A. 1. (d) 2. (b) 3. (a)
4. (b) 5. (a)
B. 1. False (The leaves of a plant are the site of photosynthesis.)
2. True
3. False (In a croton plant, photosynthesis takes place only in green parts of the leaves.)
4. True
5. False (Oxygen gas is released into the atmosphere after photosynthesis.)
C. 1. (b)
2. (d) or (e)
3. (e) or (d)
4. (a)
5. (c)
D. 1. Parasitic plant
2. Symbiotic plant
3. Saprophytic plant
4. Symbiotic plant (or leguminous plant)
5. Insectivorous plant
E. 1. Mushroom
2. Mushroom
3. Cuscuta
4. Lichen
5. Pea plant
F. 1. Money plant, croton
2. Cuscuta, mistletoe
3. Sundew, venus flytrap
4. Nitrogen, phosphorous
5. Mushroom, yeast
Crisp and Accurate (Page 14)
A. 1. Nutrition is the process of taking in food by an organism and its utilisation by its body. The
two modes of nutrition are autotrophic nutrition and heterotrophic nutrition.
2. Photosynthesis is the process by which the leaves of plants absorb energy from sunlight
and convert it into food using raw materials like carbon dioxide from air and water from soil.
Oxygen is released during this process.
3. Nitrogen fixation is the process of conversion of atmospheric nitrogen into usable forms with
the help of certain bacteria present in the soil.
4. Saprophytic plants are the non-green plants that live and feed on dead and decaying organic
matter.

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 5. The association between two different plants for shelter and nutrients is called symbiotic
association or symbiosis.
B. 1. The compounds present in food that are essential for the growth of an organism are called
nutrients. Carbohydrates, proteins, fats, vitamins and minerals are the nutrients we get from
food.
2. Different components of photosynthesis are carbon dioxide, water, chlorophyll and sunlight.
3. Insectivorous plants are mostly found in areas where the soil is deficient in nitrogen and they
trap insects to meet their nitrogen requirements.
4. Amarbel is a type of parasitic plant. It lives on other plants and obtain food from them.
5. The concentration of minerals like potassium, phosphorus and nitrogen decreases in the soil
as plants take them up. This reduces the fertility of the soil and hence it is necessary to add
them from time to time. This is the reason why farmers add fertilisers and manure to the soil.
Think and Explain (Page 14)
1. The mode of nutrition in which an organism prepares its own food from simple substances
like carbon dioxide and water is called autotrophic nutrition. It is derived from two words, auto
meaning self and trophos meaning nourishment. The organisms that prepare their own food are
called autotrophs or producers.
The mode of nutrition in which an organism is unable to make its own food and depends on
other organisms for its food is called heterotrophic nutrition. It is derived from two words, heteros
meaning other and trophos meaning nourishment. The organisms that are directly or indirectly
dependent on other organisms for their food are called heterotrophs or consumers.
2. Green plants prepare their own food by the process of photosynthesis. During photosynthesis,
the leaves of plants absorb energy from sunlight and convert it into food using raw materials like
carbon dioxide from air and water from soil. Oxygen is released during this process.
The equation for the process of photosynthesis is as follows.
6CO2 + 6H2O Sunlight C6H12O6 + 6O2
→
Carbon dioxide Water Chlorophyll Glucose Oxygen
(from air) (from soil) (carbohydrate)
3. Heterotrophic plants are of four types.
• Parasitic plants: These plants live on other plants and obtain their food from them. They are
also called parasites. The parasite derives its food from the host. Cuscuta is a parasitic plant.
• Saprophytic plants: These are the non-green plants that live and feed on dead and decaying
organic matter. They are also known as saprophytes. Mushroom is a saprophyte.
• Insectivorous plants: These are the plants that eat insects. Insectivorous plants are green
in colour and are mostly found in areas where the soil is deficient in nitrogen. These plants
obtain nitrogen by trapping insects and digesting them. Pitcher plant is an insectivorous
plant.
• Symbiotic plants: These are the plants that live in association with other plants, and share
shelter and nutrients with them. This association between two different plants for shelter
and nutrients is called symbiotic association or symbiosis. Lichen is an example of symbiotic
association.
4. The leaves of a pitcher plant are modified into a pitcher-like structure with a lid-like leaf tip that can
open or close the mouth of the pitcher. The inner surface of the pitcher possesses hair pointing

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 downwards. When an insect enters the pitcher, the lid closes and the insect gets trapped in the
hair. The insect gets digested by the digestive juices secreted by the pitcher plant.
5. Symbiotic plants are the plants that live in association with other plants, and share shelter and
nutrients with them. This association between two different plants for shelter and nutrients is
called symbiotic association or symbiosis. An example of symbiotic association is lichen. It is
composed of fungus and algae. Shelter, water and minerals are provided to the algae by the
fungus. In return, food is provided to the fungus by the algae. In this manner, both the plants
benefit from each other.

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 2. Nutrition in Animals

Answer Key

In-text Questions
Components of Food (Page 15)
Components of Food Category Sources Functions
Carbohydrates Energy-giving food Wheat, potato and bread Provide energy to the
body
Fats Energy-giving food Egg yolk, cashew nuts and Provide energy more
almonds than carbohydrate
Proteins Body building food Milk, soya beans and meat Growth and repair of
body
Vitamins Protective food Spinach and strawberry Protect body against
diseases
Minerals Protective food Milk, spinach, pulses and Essential for growth and
eggs development
Roughage (or fibre) No nutritive value Fruits, whole grains and To get rid of undigested
pulses food

Think and Answer (Page 16)

A bee ingest its food by using its feeding tube to suck nectar from flowers.
Do and Learn (Page 17)
Name of the Animal Type of Food Eaten Mode of Feeding
Ant Insects, insect eggs, sap of plants and Chewing
fruits
Crow Insects, spiders, fruits, nuts and Swallowing
vegetables
Wall lizard Insects and mosquitoes Swallowing
Snail Leaves and insects Scraping
Housefly All types of food, animal and human Siphoning
fecal matter

Think and Answer (Page 18)

Tooth enamel is the hardest substance in the body.

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Do and Learn (Page 18)
Students are expected to do this on their own.
(Number of teeth can slightly vary from one person to other.)
Quick Check (Page 19)
1. frog
2. pseudopodium
3. 32
4. enamel
Think and Answer (Page 21)
Yes, liver and pancreas are endocrine glands. It is because they excrete hormones and digestive juices
containing enzymes which help in the digestion of food.
Quick Check (Page 22)
1. Rectum
2. Stomach
3. Small intestine
4. Mouth
Picture Study (Page 23)

mouth salivary gland

oesophagus

liver stomach

gall pancreas
bladder
large
intestine
appendix
small
intestine
anus
rectum

1. digestive
2. stomach

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 3. small
4. large

Apply Your Learning

A. Observe and Label (Page 24)
small large
rumen intestine intestine
oesophagus

stomach

1. Cellulose 2. Rumen
3. Cud 4. Rumination
B. Identify and Answer (Page 24)
1. Incisors 2. Canine
3. Premolars 4. Molars
1. 4 (Molars) 2. 2 (Canines)
3. 1 (Incisors) 4. 3 (Premolars)
C. Life Skills (Page 25)
We can take care of our mouth and teeth in the following ways.
• We should clean our teeth with a brush and dental floss at least twice a day.
• We should rinse our mouth with water after every meal.
• We should eat raw vegetables and fresh fruits to cleanse the teeth.
• We should avoid eating too much sweets, chocolates and soft drinks, especially at night.
D. Reason Out (HOTS) (Page 25)
1. Our stomach produces hydrochloric acid for digestion but it does not burn because mucus
covers the inner lining of the stomach. Mucus protects the stomach from HCl.
2. Absorption of digested food occurs in the small intestine. The inner wall of the small intestine
has a number of finger-like projections called villi which increase the surface area of the small
intestine. This leads to an increase in the absorption of food in the small intestine.
E. Link and Learn (General Awareness) (Page 25)
1. Humans and rabbits have monogastric digestive system.
2. Avian digestive system
3. There are four compartments in a ruminant digestive system.

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10
Digestive System in Human Beings

Mouth Anus
F. Mind Map (Page 25)

Oesophagus Small intestine

Ingestion of food Performs egestion
monogastric stomach.

Passes food to Absorption of

the stomach digested food
Digestive System in Human Beings

Rectum
Tongue

Stores undigested waste

Help to sense
taste, mix the
chewed food with
saliva and swallow Stomach Pancreas
the chewed food
Large intestine
Secretion Convert
of digestive carbohydrates,
Salivary glands juices and proteins and fats Absorption of
digestion into simpler forms water and salts
Converts starch of proteins
into sugar

Gall bladder
Liver
Stores bile juice
Digestion of fats
compartments in their stomach. Their stomach may be either three-chambered or a simple
4. Animals that have ruminant digestive system have four compartments in their stomach.
On the other hand, animals that have pseudoruminant digestive system do not have four
G. Integrating ICT (Page 25)
Students are expected to do this on their own.
H. Case Study (Page 26)
1. Cooked vegetables take the least time to get digested.
2. Processed meat takes the maximum time to get digested.
3. Cottage cheese can be used to make traditional dishes as well as pasta, rolls and dips; and
eggs can be used to make omelette, scrambled eggs and toasts.
4. Water can be digested in 5 to 10 minutes, while fruit juice takes 20 to 40 minutes to get
digested.
5. Nuts are important because they are a good source of proteins. Almond is one such nut. It
takes around 2.5 to 3 hours to get digested.
6. Students are expected to do this on their own.

Exercises
Stop and Reflect (Page 27 and 28)
A. 1. (a)
2. (b)
3. (d)
4. (c)
5. (d)
B. 1. False (Liver is the second largest organ of the body.)
2. True
3. False (Amoeba uses its false feet to engulf the food particles.)
4. True
5. False (Large intestine absorbs water from the undigested food.)
C. 1. (d)
2. (a)
3. (e)
4. (b)
5. (c)
D. 1. Skin
2. Canine
3. Tooth enamel
4. Iodine solution
5. Gall bladder
E. 1. Salivary glands
2. Liver
3. Stomach
4. Pancreas
5. Stomach

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F. 1. Pancreas, liver
2. Cow, goat
3. Premolars, incisors
4. Sweet, sour
5. Stomach, oesophagus
(Answers may vary. Accept all logical answers.)
Crisp and Accurate (Page 28)
A. 1. Digestion is the process in which complex food is broken down into simple and soluble form.
2. Digested nutrients are absorbed into the blood vessels and transported to the tissues of the
body through the process of absorption.
3. Ingestion is the process of taking food inside the body of an organism.
4. In assimilation, the body uses absorbed nutrients to form complex substances that are
required for the growth and functioning of the body.
5. Egestion is the process in which undigested food is removed from the body.
B. 1. Saliva is the watery substance secreted by the salivary glands in the mouth. Saliva contains
the amylase enzyme, which helps in the breakdown of starch present in food into simple
sugar.
2. Human beings ingest food through the mouth. Digestion begins when food is chewed in
the mouth. The buccal cavity or the mouth consists of teeth, tongue and salivary glands. The
salivary glands in the mouth add saliva which helps in the breakdown of starch into simple
sugars.
3. The inner lining of the stomach secretes mucus, hydrochloric acid and digestive juices
(pepsin).
4. The tongue perform the following functions.
It helps us to sense taste with the help of taste buds.
It helps in mixing the chewed food with saliva.
5. Liver is reddish-brown in colour and is located in the upper part of the abdomen on the
right side. It is the second largest organ in the body. It secretes bile juice which helps in the
digestion of fats. Bile juice is stored temporarily in a sac-like organ called gall bladder which is
connected to the liver with the bile duct.
Think and Explain (Page 28)
1. Different animals use specialised structures to ingest or take in food inside their bodies. Some of
the ways by which different animals ingest food are given below.
• Amoeba uses pseudopodium (or false feet) to engulf the food particles.
• A butterfly uses its feeding tube to suck nectar from flowers.
• A frog uses its sticky tongue to catch insects.
• A mosquito uses its feeding tube to suck the blood of animals.
• A spider weaves a web to catch its prey.
• A snake swallows its food as a whole.
• Humans use their hands to ingest food in the mouth.

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2. There are four different types of teeth in the mouth which are described below.
• Incisors: They are located in the front and used for cutting and biting food.
• Canines: These are the sharp teeth located next to incisors on both sides of the jaw. They are
used in piercing and tearing of food.
• Premolars: They are located next to canines and help in chewing and grinding food.
• Molars: These are located next to premolars. They also help in chewing and grinding food.
3. Digestion and absorption of food takes place in the small intestine. It is a highly coiled tube about
7.5 m long. It secretes digestive juices and also receives secretions of the liver and pancreas. The
digested food is absorbed by the walls of the small intestine. The inner wall of the small intestine
has a number of finger-like projections called villi. These increase the surface area for absorption
of digested food. The food gets absorbed by the villi and then transported to different organs of
the body with the help of blood vessels.
4. In grass-eating animals like cow, sheep, goat and buffalo, cellulose is digested by a unique
method. A cow swallows its food after chewing once and stores it in a part of the stomach known
as rumen. Here, the food is partially digested and is called cud. The cud is then brought back to
the mouth of the animal in small lumps and chewed properly. This process of chewing the cud
is called rumination, and such animals are called ruminants. During this process, the cud mixes
with the saliva and after chewing it thoroughly, it goes back into the stomach. It is then digested
further by other organs of the digestive system.
5. Amoeba is a unicellular organism with an irregular shape. Amoeba moves and captures food with
the help of one or more finger-like projections called false feet or pseudopodia. It does not have
a mouth or digestive system and feeds on other microscopic organisms. When it senses food, the
pseudopodia surround the food particle and takes it inside the body. The food particle in amoeba
forms a food vacuole. Digestive juices are secreted into the food vacuole, which breaks down the
food into simpler substances. Then, absorption and assimilation of digested food takes place and
amoeba grows in size. The undigested food is thrown out with the help of a temporary vacuole.

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 3. Fibre to Fabric

Answer Key

In-text Questions
Types of Fibres (Page 29)

A B C
Wool
Name of fibre: A. __________________ Flax
B. __________________ Nylon
C. __________________
Natural
Type of fibre: A. __________________ Natural
B. __________________ Synthetic
C. __________________
1. Plant fibres like cotton and jute are obtained from plant sources. Animal fibres, on the other hand,
are obtained from animal sources i.e. hair/fur of animals.
2. Summer: cotton
Winter: wool
Think and Answer (Page 30)
Woollen clothes trap air and do not allow the heat of the body to escape. Thus, woollen clothes keep
us warm.
Think and Answer (Page 30)
Fleece is the fine soft under-hair of animals such as sheep and goat, that provides wool, whereas, hair
is the outer covering of all animals.
Quick Check (Page 33)
1. sheep, goat 2. Rampur Bushair/Marwari
3. scouring 4. sweaters
Think and Answer (Page 33)
Silk keeps us warm in winter and cool in summer because it is a good absorbent and good insulator of
heat.
Quick Check (Page 35)
1. Anthrax
2. Caterpillar/Silkworm

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 3. Mulberry leaves
4. Sericulture
5. Reeling of silk
Picture Study (Page 36)

Llama Yak Camel

1. These animals give us wool.

2. These animals protect themselves from cold weather conditions with the help of thick fur present
on their bodies.
3. Merina wool
4. Patanwadi, Nali

Apply Your Learning

A. Image Study (Page 37)
1. Shearing 2. It is done during early summer.
3. Wool 4. Sweaters and shawls
B. Label the Diagram (Page 37)

Cocoons are treated Raw silk threads are

Silk moth lay eggs reeled
with hot water to
soften silk filaments

Further treatment to
Egg hatch to give larvae
yield soft filaments that
that eat mulberry leaves
are used to produce yarn
Larvae spins cocoon
around it

Caption: ______________________________
Sericulture

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C. Life Skills (Page 38)
Shearing does not hurt the sheep because this process is similar to shaving. Only the extra layer of
hair that grows above the skin is removed and the skin as such is not hurt.
D. Reason Out (HOTS) (Page 38)
1. Silk is called queen of fibres because it is soft, light in weight and lustrous.
2. When we visit a hill station, we wear woollen clothes because they trap the body heat and
keep us warm in the cold weather.
E. Link and Learn (Page 38)
Students will do it on their own. (Hint: Students can take help from the Internet as well as atlas.)
F. Mind Map (Page 38)

Steps Involved in the Production of Wool

1. Shearing: Removal of fleece

2. Scouring: Washing of sheared skin with hair

3. Sorting: Sorting and grading of dried hair on the basis

of length, texture, colour and fineness

4. Dyeing: Dyeing fleece in desired colour

5. Combing/Carding: Straightening of dyed fibres

6. Spinning: Spinning of strands to make thread

G. Integrating ICT (Page 38)

Students will do it on their own.
H. Case Study (Page 39)
1. 2015
2. 47.9 million kg
3. 2019
4. 2019
5. India is the ninth largest producer of wool in the world.

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Exercises
Stop and Reflect (Page 40)
A. 1. (a)
2. (c)
3. (b)
4. (c)
5. (d)
B. 1. False (Sweaters are made using the long fibres of wool.)
2. True
3. False (We obtain wool from Angora rabbit.)
4. True
5. False (Organza is a variety of silk.)
C. 1. (e)
2. (a)
3. (b)
4. (c)
5. (d)
D. 1. Marwari
2. Patanwadi
3. Rampur Bushair
4. Lohi
5. Bhakarwal
E. 1. Shearing
2. Combing/Carding
3. Scouring
4. Sorting
5. Spinning
F. 1. Sheep, Yak
2. , Patanwadi
3. Wool, Silk
4. Sericin, Fibroin
5. Crepe, Muga
Crisp and Accurate (Page 41)
A. 1. In spinning, wool threads are formed by spinning two, three or four strands of wool as per the
required thickness.
2. The breeding and management of silkworms for the production of silk is called sericulture.
3. In sorting, the dried hair obtained after scouring is graded and sorted on the basis of length,
colour, texture and fineness.

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 4. The process by which parents are selectively chosen in order to obtain certain special features
in their offspring is called selective breeding.
5. The risks and hazards faced by people at their workplace are termed as occupational hazards.
B. 1. Plant fibres like cotton and jute are obtained from plant sources while animal fibres are
obtained from animal sources i.e. hair/fur.
2. The thick coat of hair on the sheep traps air as it is a poor conductor of heat. Hence, the coat
does not allow the heat of the body to escape and shields the animal’s body from cold.
3. The fibres for making wool are provided by the fine soft under-hair. Some breeds of sheep
are specially chosen to give birth to sheep that possess fine soft under-hair only. This process
by which parents are selectively chosen in order to obtain certain special features in their
offspring is called selective breeding.
4. Sheep are reared in the Indian states of Gujarat, Rajasthan, Jammu and Kashmir, Himachal
Pradesh and Punjab.
5. Shearing is the process in which fleece along with the thin uppermost layer of skin is removed.
However, the process by which the sheared skin with thick coat of hair is washed thoroughly
in machines to remove grease, dirt and dust is called scouring.
Think and Explain (Page 41)
1. Production of wool from sheep includes the steps given below.
• Shearing: In this process, fleece along with the thin uppermost layer of skin is removed. This
is mainly done in early summer once a year. It is done with a manual razor or blade or with
clippers. The hair grows again before the onset of winters.
• Scouring: In this process, the sheared skin with thick coat of hair is washed thoroughly in
machines to remove grease, dirt and dust.
• Sorting: In this process, the dried hair obtained after scouring is graded and sorted on the
basis of length, colour, texture and fineness.
• Dyeing: The natural fleece of the sheep is white, brown or grey in colour. It is dyed in the
desired colours.
• Combing/Carding: The dyed fibres are straightened by passing them through metal teeth.
This process is known as carding. The soft fluffy fibres called burrs are also removed in this
process.
• Spinning: Wool threads are formed by spinning two, three or four strands of wool as per the
required thickness. Sweaters are made from the longer fibres of wool. Woollen clothes are
spun and woven by the shorter fibres of wool.
2. The life cycle of a silk moth has four stages. They are the egg, the caterpillar, the pupa and the
adult. The female silk moth lays hundreds of eggs on mulberry leaves. After about twenty days,
they hatch into larvae. These hatched larvae are known as silkworms or caterpillars. They feed
on mulberry leaves for about six weeks and their size increases. At this stage, they are ready to
enter the next stage of their life cycle called pupa. The silkworm holds itself by weaving a net
around its body. It weaves the net by swinging its head from side to side in the form of eight. The
silkworm secretes a wet sticky substance of protein during this movement. On exposure to air, this
substance hardens and becomes silk fibre. The pupa gets covered by these silk fibres to form the
cocoon. Once the cocoons are spun, pupae turns into adult moths. Finally, the silk moth cuts open
the cocoon and flies away.

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3. People working in the wool industry are at a high risk of contracting Sorter’s disease. It is a fatal
blood disease caused by a bacterium Anthrax. People working in the silk industry suffer from
respiratory problems. This is due to inhalation of vapours from boiling of cocoons. This results in
asthma and bronchial ailments. Also, during reeling, the workers constantly dip their hands in
boiling water. Due to this, their skin starts to peel off. This results in blistering and scabbing.
4. For rearing silkworms, the eggs laid by female silk moths are kept in hygienic conditions, and
under suitable temperature and humidity. Once the eggs are warm enough, larvae (silkworms)
hatch out. These are fed chopped mulberry leaves. Once they grow in size and develop glands,
they spin a cocoon around themselves.
5. The cocoons are collected after the complete development of silkworms. They are kept under the
sun or boiled or exposed to steam. This process releases the silk fibres from the cocoons and is
known as reeling the silk. Reeling is done in special machines. Then the silk fibres are spun into silk
threads which are woven to get silk cloth.

19
 4. Heat

Answer Key

In-text Questions
Properties of Matter (Page 42)
Conductors water, metal

Insulators wood, plastic

1. Yes
2. Plastic; insulator
Do and Learn (Page 44)
S. No. Name of the Object Hot/Cold

1. Ice tray in the refrigerator Cold

2. Serving spoon in a frying pan Hot

3. A glass filled with cold coffee Cold

4. Pack of frozen snacks Cold

5. Pan containing boiled milk Hot

(Students can add a variety of different things.)
Numerical Corner (Page 45)
1. 32°F = (32 – 32) × 5/9
= 0°C
2. 68° F = (68 – 32) × 5/9
= 20°C
3. 122˚F = (122 – 32) × 5/9
= 50°C
Think and Answer (Page 45)
We should not touch the bulb of the thermometer while taking a reading because the temperature of
one's body may affect the actual reading. Due to the body temperature, the mercury expands in the
bulb and thus results in incorrect reading.

20
Quick Check (Page 47)
1. heat, light
2. cold-blooded
3. 32°F to 212°F
4. clinical
In the Lab (Page 48)
Does It Become Hot? Conductor/
Name of Object Material of the Object
Yes/No Insulator
Steel fork Metal Yes Conductor
Plastic spoon Plastic No Insulator
Wooden scale Wood No Insulator
Divider Metal Yes Conductor

Think and Answer (Page 48)

Conduction of heat is fastest in solids because the particles are very closely packed.
Think and Answer (Page 49)
Mercury is used as thermometric fluid.
Thermos Flask (Page 52)
1. Thermos flask is different from a regular flask because it can keep liquids like hot water, tea and
coffee, at the same temperature for a long duration of time.
2. No, the transfer of heat through the walls of this flask is not possible because the walls and lid
are made of an insulating material. The inner and outer coatings of the flask are reflective and
thus prevents radiation. Conduction and convection are also prevented due to the presence of
vacuum chamber.
3. Yes, the tea will remain hot.
Quick Check (Page 52)
1. Mercury
2. Sea breeze
3. Radiation
Picture Study (Page 53)
A. Clinical thermometer

B. Digital thermometer

C. Laboratory thermometer

1. mercury 2. Celsius, Fahrenheit 3. B

4. A 5. C

21
Apply Your Learning
A. Image Study (Page 54)
1. Yes, the direction of breezes that blow during the day and night are different.
2. During day time, breeze blows from sea towards the land.
3. During the night, the breeze blows from land towards the sea.
4. Convection
B. Observe and Answer (Page 54)
1. Wood/Bakelite
2. Woollen clothes, preferably dark colours like black, should be worn in winter as they absorb
more heat energy.
3. Mercury thermometers are replaced by digital thermometers because mercury is a toxic
metal. Disposal of mercury is also difficult.
4. Convection and radiation
C. Life Skills (Page 55)
Heat is important to all aspects of life for both plants and animals. We require heat energy for
cooking, heating, drying as well as for generating electricity.
D. Reason Out (HOTS) (Page 55)
1. Flow of heat does not take place if two substances of same temperature are kept in contact.
2. People living on the top floor paint the terrace with white cement during summers because
white colour absorbs the least amount of heat energy.
3. We cannot measure the temperature of boiling water using a clinical thermometer because it
has a range of 35°C – 45°C while water boils at 100°C.
E. Link and Learn (Page 55)
Students will do it on their own.
(Hint: They can take help from the Internet to precisely draw monsoon winds on the given dates.)
F. Mind Map (Page 55)

Modes of Transfer of Heat

Conduction Convection Radiation

• Transfer of heat • Transfer of heat by • Heat travels in a

from hotter end to actual movement of straight line from the
colder end of an hot particles object which radiates it
object • Requires medium • Does not require a
• Requires medium • Happens only in medium
• Fastest in solids liquids and gases • Takes place in solids,
liquids and gases

22
G. Integrating ICT (Page 55)
Students will do it on their own.
H. Case Study (Page 56)
1. 37°C
2. 3 am
3. Between 12pm to 3 pm.
4. 37.5°C
5. Clinical thermometer
6. After eating meals there is a slight increase in the temperature of the body.

Exercises
Stop and Reflect (Page 57)
A. 1. (a) 2. (c) 3. (b) 4. (b) 5. (b)
B. 1. True
2. False (Dark coloured clothes are more comfortable in winter season.)
3. False (The bottom of some cooking utensils has a black coating to absorb heat faster.)
4. True
5. False (Clinical thermometers are used to measure the temperature of the body.)
C. 1. (d) 2. (e) 3. (b) 4. (c) 5. (a)
D. 1. Temperature
2. Radiant heat
3. Copper
4. Clinical thermometer
5. Fahrenheit temperature scale
E. 1. Convection
2. Radiation
3. Convection
4. Conduction
5. Convection and radiation
F. 1. Copper, aluminium
2. Wood, plastic
3. Sea breeze, land breeze
4. Convection, conduction
5. Clinical thermometer, laboratory thermometer
Crisp and Accurate (Page 58)
A. 1. The materials which allow heat to pass through them are called conductors.
2. Substances that do not allow heat to flow through them easily are called insulators.
3. The process by which heat is transferred from the hotter end of an object to its colder end is
known as conduction.

23
 4. The process by which transfer of heat takes place from the hotter part of a substance to its
colder part by the actual movement of hot particles is called convection.
5. The mode of transfer of heat from a hot body to a cold body that does not require a medium
is called radiation.
B. 1. Heat is important to all forms of life which includes both plants and animals. Plants require
heat to survive. We require heat for activities like cooking, heating, drying as well as for
generating electricity. Life would not be possible on earth without heat.
2. Handles of cooking utensils are made up of bakelite or wood because they are insulators of
heat and prevent our hands from burning.
3. Ventilators are placed near the ceiling of a room because warm air being lighter moves up
and escapes through the ventilators while fresh air enters the room through the doors and
windows.
4. Wool fibres trap air which is a poor conductor of heat. Hence, woollen clothes help in retaining
body heat in winter.
5. Clinical thermometer has a kink to prevent the mercury from falling down on its own after it
has expanded in the capillary tube.
Think and Explain (Page 58)
1. The following activity would help us to understand that the sense of touch is not a reliable
technique to measure temperature.
For this, we need three vessels, ice-cold water, warm water (ensure that the water is only warm
such that your hand does not burn) and tap water. Now, we will follow the steps given below.
• Take three vessels.
• Fill the first vessel with ice-cold water, the second with normal tap water and the third vessel
with warm water.
• Dip your right hand in ice-cold water and your left hand in warm water for a minute.
• Then, dip both the hands together in normal water.
We can observe that our right hand will feel warm and our left hand will feel cold. This shows
that our body cannot measure temperature correctly.
2. The precautions that should be taken care of while measuring the body temperature using a
clinical thermometer are given below.
• Ensure that the mercury level is below 35°C. It is set by giving a few jerks to the thermometer
so that the mercury level falls down.
• Place the thermometer bulb properly under your tongue or under your arm such that the
bulb is in contact with your armpit for at least a minute.
• Remove the thermometer and read the temperature. Ensure that it is held horizontally at your
eye level.
• Do not touch the bulb of the thermometer. Note down the value till which the mercury has
expanded.
3. In coastal areas, the direction of breeze is different during the day and at night. Breeze blows from
the sea to the land during the day. This is because during the day, land warms up faster than the
sea. The air over the land becomes hot and rises up. The cool air from the sea moves towards the
land to occupy the space. This results in blowing of air from sea to land and it is known as sea
breeze. At night, the land cools down faster than the sea. So, cool breeze blows from land to the
sea. This is known as land breeze.

24
 4. We can perform the following activity to show that black surfaces are better absorbers and
radiators of heat.
We will need two identical cold drink cans, black paint, white paint, two thermometers and water.
Now, we will follow the steps given below.
• Take two cold drink cans.
• Paint the outer surface of one can black and the other white.
• Fill them with equal amounts of water.
• Now place both the cans in the mid-day sun for half an hour.
• Note the temperature of water in both the cans using separate thermometers.
• Leave these cans undisturbed at room temperature for 10 minutes.
• Place the thermometers in the cans with the bulb of the thermometer dipped in water. Ensure
that it does not touch the bottom or the sides of the can.
• Note the temperature again.
It can be observed that the temperature reading in the thermometer placed in the black
can is higher than that of the thermometer placed in the white can when both the cans are
placed in the sun. It can also be observed that the reading in the thermometer placed in
the black can falls more rapidly than that of the thermometer placed in the white can when
both the cans are kept at room temperature. Hence, it is proved that black surfaces are better
absorbers and radiators of heat than white surfaces.
5. Following are some practical applications of radiation.
• In summer, white and light-coloured clothes are more comfortable as they absorb less heat
and reflect most of the sun’s heat that falls on them.
• In winter, black and dark-coloured clothes are worn as they absorb most of the radiant heat
of the sun.
• The bottom of some cooking utensils has a black coating so that they absorb most of the heat
energy provided and help to cook food faster.
• Electric room heaters have a polished metal surface behind the heating element as this
surface reflects the radiant heat in front of the heater making it more effective.

25
 5. Acids, Bases and Salts

Answer Key

In-text Questions
Sort the Categories (Page 59)
Sweet Chocolate, cream
Sour Vinegar, Indian gooseberry (amla), lemon, tamarind
Bitter Baking soda
Salty Popcorn

Think and Answer (Page 60)

We cannot taste all acids because some acids are strong and cause severe burns on coming in contact
with the skin.
Food Acid Check (Page 61)

Malic acid Lactic acid Citric acid

Tartaric acid Oxalic acid Ascorbic acid

Think and Answer (Page 61)

A base that is soluble in water is called an alkali. However, all bases are not soluble in water. Thus, all
alkalis are bases but all bases are not alkalis.
Think and Answer (Page 63)
A stain of turmeric on a white cloth turns reddish-brown when washed with soap because soap is a
base which reacts with the turmeric stain and turns it reddish-brown in colour.

26
In the Lab (Pages 63 to 64)
Effect on Red Effect on Blue Effect on China Solution: Acidic/
Test Solution
Litmus Paper Litmus Paper Rose Solution Basic
Lemon juice No change Red Dark pink Acidic

Washing soda Blue No change Green Basic

Milk of magnesia Blue No change Green Basic

Vinegar No change Red Dark pink Acidic

Common salt No change No change No change Neutral

Shampoo No change Red Dark pink Acidic

Milk No change Red Dark pink Acidic

Baking soda Blue No change Green Basic

Colour Change Recap (Page 64)

Indicator Colour in Acidic Medium Colour in Basic Medium
Blue litmus Red No change
Red litmus No change Blue
Turmeric Yellow Reddish-brown
China rose Dark pink (magenta) Green
Methyl orange Red Yellow
Phenolphthalein Colourless Pink

In the Lab (Page 65)

Effect Effect
Effect on Effect on Effect on
on Red on Blue Effect on
Sample China Phenolph- Methyl
Litmus Litmus Turmeric
Rose thalein Orange
Paper Paper

Dilute sulphuric acid No change Red Dark pink Yellow Colourless Red
Dilute sodium Reddish-
Blue No change Green Pink Yellow
hydroxide brown
Dilute hydrochloric
No change Red Dark pink Yellow Colourless Red
acid
Dilute potassium Reddish-
Blue No change Green Pink Yellow
hydroxide brown

27
 Dilute nitric acid No change Red Dark pink Yellow Colourless Red
Dilute ammonium Reddish-
Blue No change Green Pink Yellow
hydroxide brown
Dilute calcium Reddish-
Blue No change Green Pink Yellow
hydroxide brown

Quick Check (Page 65)

1. concentrated, water
2. turmeric
3. China rose
4. alkalis
Think and Answer (Page 66)
The reactions that evolve heat are known as exothermic reactions.
Daily Life Chemicals (Page 68)

A. Window cleaning solution B. Soap C. Milk of magnesia D. Turmeric

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

Apply Your Learning

A. Colour Change (Page 69)

Substance Phenolphthalein Blue litmus Methyl orange Red litmus

Nitric acid Colourless Red Red No change

Sodium hydroxide Pink No change Yellow Blue

Sodium bicarbonate Pink No change Yellow Blue

Hydrochloric acid Colourless Red Red No change

Acids: Nitric acid; Hydrochloric acid

28
 Bases: Sodium hydroxide; Sodium bicarbonate
B. Neutralise It (Page 69)
A. We can neutralise indigestion and acidity by consuming milk of magnesia (antacid) which is
a base that will neutralise the acid present in the stomach.
B. We can use moist baking soda or calamine solution to neutralise the acid present in the bee
sting.
C. We will add quicklime or slaked lime which are bases to neutralise acidic soil.
C. Life Skills (Page 70)
Basic substances are added to factory wastes before releasing them into the water bodies because
these wastes are acidic in nature. If they are released directly into the water bodies, the aquatic
organisms are harmed.
D. Reason Out (HOTS) (Page 70)
1. He did not get relief on applying acetic acid because the bee sting is acidic in nature. He
should rub some basic substance like moist baking soda on the stung area to get relief.
2. Indigestion occurs due to the excess of hydrochloric acid produced by the stomach. Antacid
syrups or tablets such as milk of magnesia (magnesium hydroxide) are prescribed by doctors
as they are basic in nature. This neutralises the presence of excess acid in stomach to give
relief from acidity.
E. Link and Learn (Page 70)
1. Acid rain makes the water bodies acidic, thereby harming the aquatic life.
2. Acids present in acid rain are sulphuric acid, nitric acid and carbonic acid.
3. Taj Mahal has turned yellow due to acid rain.
4. Colosseum in Rome
F. Mind Map (Page 70)
Indicators

Natural Synthetic

Colour Colour Colour Colour

Name in Acidic in Basic Name in Acidic in Basic
Medium Medium Medium Medium
Litmus Red Blue Methyl orange Red Yellow

Turmeric Yellow Reddish-

brown
Phenolphthalein Colourless Pink
China Dark pink/ Green
rose Magenta

29
G. Integrating ICT (Page 70)
Students will do it on their own.
H. Case Study (Page 71)
1. Bitter orange
2. Mandarin orange
3. Lemon
4. Vitamin C is obtained from citrus fruits. It is very beneficial for the body and skin.
5. Grapefruit and tangerine
6.
Levels of ascorbic acid in citrus fruits
30

25

20

15

10

0
lemon mandarin orange sweet orange bitter orange
ripe unripe

Exercises
Stop and Reflect (Page 72)
A. 1. (d)
2. (c)
3. (a)
4. (b)
5. (d)
B. 1. False (An acid that has more amount of water is said to be diluted.)
2. True
3. False (Strong acid and weak base react to form acidic salt.)
4. False (Quicklime is added to soil if it is too acidic.)
5. True
C. 1. (b)
2. (d)

30
 3. (e)
4. (c)
5. (a)
D. 1. Moist baking soda/calamine lotion
2. Milk of magnesia
3. Vinegar
4. Toothpaste
5. Quicklime/Slaked lime
E. 1. Yellow
2. Reddish-brown
3. Green
4. Red
5. Colourless
F. 1. Sulphuric acid, Nitric acid
2. Sodium hydroxide, Calcium hydroxide
3. China rose, Turmeric
4. Methyl orange, Phenolphthalein
5. Ascorbic acid, Citric acid
Crisp and Accurate (Page 73)
A. 1. The chemical substances that are sour in taste and corrosive in nature are called acids.
2. The chemical substances that taste bitter and feel soapy to touch are called bases.
3. Indicators are substances that indicate whether a given substance is an acid or a base. The
indicators that occur naturally are called natural indicators.
4. The reaction between an acid and a base to form salt and water along with the evolution of
heat is called neutralisation reaction.
5. A salt is a substance formed by the reaction of an acid with a base. It can be acidic, basic or
neutral in nature.
B. 1. The colour of litmus solution in distilled water is purple. It turns red when added to an acid,
and blue when added to a base.
2. HCl + NaOH → NaCl + H2O
(Hydrochloric acid) (Sodium hydroxide) (Sodium chloride) (Water)
3. Antacids give relief during indigestion as they are basic in nature. When the tablet is ingested,
the chemicals in it dissolve to make an alkaline solution. In this way they neutralise the
presence of excess hydrochloric acid in the stomach to provide relief from acidity.
4. Acid present in ant sting is formic acid. To provide relief, the affected area is rubbed with
moist baking soda or calamine solution as they are basic in nature. They neutralise the effect
of acid and reduce itching.
5. Toothpastes contain alkaline substances that neutralise the action of acids and helps to
prevent damage to teeth by tooth decay.

31
Think and Explain (Page 73)
1. Acids have the following properties.
• They are corrosive in nature.
• They conduct electricity.
• They are water-soluble. Based on the amount of water present in acids, they can be dilute or
concentrated.
Bases have the following properties.
• Bases are bitter in taste and soapy to touch.
• They are corrosive.
• They conduct electricity.
• They may or may not be soluble in water.
2. Indicators are substances that indicate whether a given substance is an acid or a base.
The indicators that occur naturally are called natural indicators. For example, turmeric is a natural
indicator that is a common kitchen ingredient. In acidic and neutral medium it is yellow, and in
basic medium, it turns reddish-brown.
Synthetic indicators are prepared in the laboratory. For example, methyl orange is a synthetic
indicator. It is red in acidic solution and yellow in alkaline solution.
3. We can perform the following activity to explain the neutralisation reaction between a strong
acid and a strong base.
We would need dilute hydrochloric acid, phenolphthalein, dilute sodium hydroxide, dropper and
test tube. Now, we will follow the given steps.
• Take 5 mL of dilute hydrochloric acid in a test tube.
• Add 2–3 drops of phenolphthalein indicator to it.
• Shake the test tube. The solution remains colourless.
• Now, add dilute sodium hydroxide dropwise till pink colour just appears.
• Touch the test tube immediately and check whether it is warm or not.
• Again add a drop of dilute hydrochloric acid. The pink colour disappears.
• Now add a drop of dilute sodium hydroxide. The pink colour will appear again.
When acid and base are mixed, they neutralise each other and the solution formed is neither
acidic nor basic. It can be checked by adding a single drop of base to the neutralised solution
which turns pink. Similarly, adding a single drop of acid to the same solution turns it colourless.
4. Acid rain contains unusually high amounts of acids. Harmful gases such as sulphur dioxide, nitrogen
dioxide and carbon dioxide that are released from the industries or vehicles mix with rainwater
and form sulphuric acid, nitric acid and carbonic acid, respectively. These acids make rainwater
acidic and cause huge damage to buildings, crops, marine life and historical monuments.
5. Following are the uses of neutralisation reaction in everyday life.
 Indigestion: An excess of hydrochloric acid produced by the stomach causes indigestion and
acidity. Antacid syrups or tablets such as milk of magnesia (magnesium hydroxide) are prescribed
by doctors as they are basic in nature. When the tablet is ingested, the chemicals in it dissolve to
make an alkaline solution. This neutralises the presence of excess hydro­chloric acid in stomach to
provide relief from acidity.

32
 Ant and bee sting: Formic acid is present in ant and bee stings. The sting causes itching. To provide

relief, the affected area is rubbed with moist baking soda or calamine solution as they are basic in
nature. They neutralise the effect of acid and reduce itching.
Tooth decay: Bacteria in our mouth accumulate and feed on food particles that get stuck in between

our teeth. This releases acids that cause tooth decay. Toothpastes contain alkaline substances that
neutralise the action of acids and helps to prevent damage to teeth.

33
 6. Changes around Us

Answer Key

In-text Questions
Reversible or Irreversible Change (Page 74)

R I I

I R R
1. A reversible change is a change that can be undone or reversed.
2. When a substance cannot be brought back to its original state after a change in conditions, it is
said to be an irreversible change.
Changes around You (Page 75)
Students will do it on their own. (Hint: They can add sharpening of pencil, cooking of food, melting of
ice, burning of matchstick, along with other things.)
Think and Answer (Page 76)
Yes, boiling of water is a physical change because it simply changes the state of water from liquid to
gas.
Quick Check (Page 77)
1. F 2. T 3. F 4. F
Think and Answer (Page 78)
A magnesium ribbon is cleaned before burning to remove the layer of magnesium oxide formed on
the ribbon due to the reaction of magnesium with air.

34
Picture Study (Page 79)
1. Yes 2. No
3. Chemical change 4. Irreversible
Think and Answer (Page 81)
Hydrogen gas burns with a pop sound.
Think and Answer (Page 82)
The part of ship that remains underwater rusts faster because it comes in continuous contact with air,
water and salts in seawater.
Think and Answer (Page 83)
Amalgam is the name of the alloy of mercury and other metals.
Quick Check (Page 83)
1. exothermic
2. precipitate
3. rusting
4. zinc

Apply Your Learning

A. Corrosion (Page 84)
1. Rust
2. Presence of oxygen and water is necessary for the formation of this brown substance called
rust.
3. Iron + Oxygen + Water → Rust (Hydrated iron oxide)
  Fe O2 H2O Fe2O3.xH2O
4. It is not formed immediately on a new car because the car is coated with paint which prevents
rusting.
5. Following are the methods to prevent rusting.
• Applying grease or oil on the exposed part of the article
• Galvanising the surface of the articles
B. Kitchen Chemistry (Page 84)
1. sodium bicarbonate
2. gas; evolved
3. carbon dioxide; CO2
4. air
5. Vinegar + Baking soda → Carbon dioxide + Other substances
C. Life Skills (Page 84)
1. Chemical change
2. Glucose and oxygen are formed during photosynthesis.
3. Following reaction takes place in the presence of sunlight during photosynthesis.

35
 light energy
Carbon dioxide + Water Glucose + Oxygen
4. If photosynthesis doesn’t take place in plants then they will die and it will also result in food
scarcity for all the living beings which depend on plants for their food.
D. Reason Out (HOTS) (Page 85)
1. When slices of potato and apple are left in the open for some time, a colour change is observed
due to a chemical change. This is because exposure to air and moisture causes a chemical
reaction that changes the composition of potato and apple slices, which results in noticeable
colour change.
2. It is because the coastal areas have air rich in moisture and suspended salt particles which
speeds up the process of rusting.
3. Crystallisation is involved in the preparation of salt from seawater.
E. Link and Learn (Page 85)
1. Zinc is coated on iron during galvanisation.
2. The chemical formula of rust is Fe2O3.xH2O.
3. It is necessary to prevent rusting as it destroys the entire iron object.
4. Nickel and chromium can be electroplated on iron articles to prevent rusting.
F. Mind Map (Page 85)

Characteristics of Chemical Reaction

Evolution of heat (Exothermic reaction)

Calcium oxide + Water → Calcium hydroxide + Heat

Absorption of heat (Endothermic reaction)

Water + Ammonium chloride → Ammonium hydroxide + Hydrochloric acid
(Beaker feels cold)

Change in colour and formation of precipitate

Copper sulphate + Iron → Iron sulphate + Copper
(Colour changes from blue to green; copper is precipitated)

Evolution of gas and production of sound

Vinegar + Baking soda → Carbon dioxide↑ + Other substances

G. Integrating ICT (Page 85)

Students will do it on their own.
H. Case Study (Page 86)
1. An alloy is a homogeneous mixture that is composed of two or more elements, out of which
at least one is a metal.

36
 2. 22 karat gold is mostly used to make jewellery.
3. 24 karat gold
4. Yellow gold
5. Rose gold
6. Pure gold will not rust because gold is a noble metal and has the least reactivity.

Exercises
Stop and Reflect (Page 87)
A. 1. (c)
2. (b)
3. (a)
4. (d)
5. (d)
B. 1. True
2. False (Heat is released in exothermic reactions.)
3. False (Carbon dioxide gas reacts with lime water to form a milky solution.)
4. True
5. False (Magnesium hydroxide turns red litmus blue.)
C. 1. (e)
2. (a)
3. (b)
4. (c)
5. (d)
D. 1. Magnesium oxide + Water → Magnesium hydroxide
2. Calcium oxide + Water → Calcium hydroxide + Heat
3. Copper sulphate + Iron → Iron sulphate + Copper
4. Carbon dioxide + Lime water → Calcium carbonate + Water
5. Iron + Oxygen + Water → Hydrated iron oxide
E. 1. White
2. Blue
3. Brown
4. Green
5. Reddish-brown
F. 1. Cutting of paper, melting of ice
2. Burning of wood, curdling of milk
3. Salt, sugar
4. Iron, copper
5. Galvanisation, painting

37
Crisp and Accurate (Page 88)
A. 1. A change in any of the physical properties i.e. its size, shape, colour and state of a substance
is known as a physical change.
2. A change in which two or more substances react and form one or more new substances is
called a chemical change.
3. A reaction in which heat is released or evolved is called exothermic reaction.
4. A reaction in which heat is absorbed is called an endothermic reaction.
5. Crystallisation is the process by which pure crystals of a substance are obtained from the
solution of that substance in water.
B. 1. Cutting of paper is considered a physical change because even though the process is
irreversible, no new substance is formed here. The composition of paper remains the same.
2. Magnesium ribbon burns in the presence of oxygen to give magnesium oxide, in the form of
ash.
2Mg + O2 → 2MgO
3. Following is a reaction which involves evolution of gas.
Vinegar  +  Baking soda  →  Carbon dioxide   +  Other substances
CH3COOH NaHCO3 CO2
4. Copper deposits on an iron nail when it is placed in copper sulphate solution.
CuSO4 + Fe → FeSO4 + Cu
5. The process of improving the properties of a metal by mixing with another metal or non-
metal is called alloying.
Think and Explain (Page 88)
1. We can perform the following activity to demonstrate the process of crystallisation of copper
sulphate.
For this, we need beakers, copper sulphate powder, dilute sulphuric acid, distilled water, filter
paper, funnel and burner. We will follow the steps given below.
• Take 50 mL of distilled water in a 100 mL beaker.
• Add 2–3 drops of dilute sulphuric acid to it and heat it over a burner.
• Add a small amount of copper sulphate powder when the water starts boiling. Stir the
solution continuously and keep adding copper sulphate powder till no more powder can be
dissolved.
• Filter the solution carefully into another beaker and leave it overnight.
Blue crystals of copper sulphate would be formed at the bottom of the beaker. These crystals are
formed by the process of crystallisation.
2. Physical change: A change in any of the physical properties of a substance i.e. its size, shape,
colour and state is known as a physical change. Such a change is temporary and is generally
reversible in nature. It may be irreversible in some cases. No new substance is formed during a
physical change. Some examples of physical changes include melting of ice, freezing of water,
melting of wax and solidification of wax.
Chemical change: During a chemical change, two or more substances react and form one or
more new substances. This is also called a chemical reaction. As a chemical change involves the
formation of new substances with different properties, it is generally a permanent and irreversible

38
 change. A large amount of heat is either evolved or absorbed during the process. Examples of
chemical changes include germination of seeds, digestion of food, ripening of fruit and rusting of
iron.
3. Following are the characteristics of a chemical reaction.
• It involves absorption or evolution of heat, light or any other radiation.
• It can result in change in colour of the solution.
• These changes are also accompanied by evolution of gas and production of sound.
• Sometimes, formation of precipitate can also take place.
4. The formation of product during a chemical reaction may be accompanied by deposition of
certain insoluble substances known as precipitate. Precipitate is denoted by a downward ( ) arrow
in a chemical reaction.
We can perform the following activity to observe the formation of precipitate.
For this, we need copper sulphate crystals, dilute sulphuric acid, beaker, iron nail and water. Now,
we will follow the steps given below.
• Dissolve a few crystals of copper sulphate in water in a beaker.
• Add a few drops of dilute sulphuric acid to it. A blue-coloured solution will be formed.
• Divide this solution into two equal parts. Drop a clean iron nail in one part.
• Leave it for half an hour and observe the changes.
It can be observed that the solution turns green and there is a brownish precipitate on the iron
nail. The change in colour of the solution is due to the formation of iron sulphate.
5. Following are the ways to prevent rusting of iron.
• Applying grease or oil on the exposed part of the article
• Painting the surface of iron articles
• Galvanising the surface of the articles
• Electroplating the surface of iron articles with metals resistant to corrosion, such as nickel and
chromium
• Alloying iron with corrosion-resistant metals and non-metals
bottle C so that it forms a film on its surface. Put the bottles away for a few days. Take out nails from
each bottle and observe them. Explain the observations.

39
 7. Weather, Climate and Adaptations in Animals

Answer Key

In-text Questions
Desert Vegetation (Page 89)

Leaves are reduced to

spines.

Green stem performs

photosynthesis.

Long roots go deep

into the soil.

1. Xerophytes
2. In a cactus, leaves are reduced to spines. This adaptation is important as it helps to prevent water
loss from the plant.
3. Stems of a cactus plant perform photosynthesis.
4. A cactus has long roots to absorb water which is deep inside the soil.
Think and Answer (Page 90)
A person who studies the weather is known as meteorologist.
Think and Answer (Page 91)
The amount of rainfall is measured through a rain gauge in millimetres (mm).
Weather Data for a Month (Page 93)
Students will do it on their own.
Quick Check (Page 93)
1. weather 2. hygrometer 3. forecast 4. humidity

40
Think and Answer (Page 96)
Antarctica is the continent in which most of the penguins in the world live.
Quick Check (Page 96)
1. T 2. F 3. F 4. F
Map Time (Page 96)
Students will do it on their own.
(Hint: Students can take help from the atlas and the Internet to precisely mark the required areas.)
Think and Answer (Page 97)
There is intense competition between animals for food, water and shelter in tropical rainforests due to
the high levels of biodiversity and the limited resources available. Many species live in close proximity
and hence, there is intense competition for resources that are essential for survival.
Terrestrial Animals (Page 98)
1. Trunk
2. Tusk
3. The incisors of elephants are modified into tusks that help them to tear the bark of trees. The
elephants, thus do not face problems regarding availability of food.
4. Elephants have large fan-shaped ears that enable them to hear even the softest sounds. The ears
also help the elephant to remain cool in the hot and humid climate of the rainforest.

Apply Your Learning

A. Knowing Birds (Page 99)
1. Siberian crane 2. migratory
3. Rajasthan, Haryana 4. Siberia
B. How’s the Weather Today? (Page 99)
1. Sunny 2. 29°C
3. 16°C 4. The wind speed is 8 km/h and humidity is 55%.
5. No, one doesn’t need to carry umbrella while going out this week.
C. Life Skills (Page 100)
1. Global warming is caused due to the excessive emission of greenhouse gases.
2. It is important to save animals from becoming extinct because every species plays a vital role
in the ecosystem. Animals help to maintain a balance in nature and help to keep ecosystems
functioning properly. The loss of a single species affects other species in the ecosystem and
even humans.
3. Polar bears have thick fur to keep them warm. They have flat and board paws to help them
walk on ice and swim in water.
4. Penguin and reindeer are the other animals that live in polar region.
D. Reason Out (HOTS) (Page 100)
1. If Delhi was near the sea, then it would have moderate climate i.e. neither too hot nor too
cold.

41
 2. The loss of trees and other vegetation of the tropical rainforest can result in climate change,
desertification, soil erosion, fewer crops, flooding and increased greenhouse gases in the
atmosphere.
3. The climate of Kerala and Kashmir are different. A moderate climate exists at places close
to the sea, i.e. the climate is neither too hot nor too cold. However, the places that are away
from the sea face extreme climatic conditions, i.e. these places are either too hot or too cold.
Therefore, Kerala has moderate climate while Kashmir has extremely cold climate.
4. The thick white fur covers the body of a polar bear and keeps it warm. Its colour blends with
the snow and protects the polar bear from predators. It also helps the polar bear in catching
the prey.
5. Winds blowing from the sea bring rainfall, while winds blowing from the land are dry.
Therefore, places near the sea will receive more rainfall as compared to those places that are
away from the sea.
E. Link and Learn (Page 100)
1. Students will do it on their own.
(Hint: Students can take help from the atlas and the Internet to precisely mark the required
regions.)
2. Students will do it on their own.
(Hint: Students can take help from the atlas and the Internet to precisely mark the required
regions.)
3. Following are the three animals that live in
(a) Tropical rainforests : Elephant, apes, lions
(b) Polar regions : Polar bear, penguins, reindeer
F. Mind Map (Page 100)

Adaptation of Animals

Polar region Desert Tropical rainforest

Example: Example: Example:

Polar bear Camel Toucan

• Thick layer of fat called • Long eye lashes • 

Sleek and shiny
blubber feathers
• Hump to store fat
• Flat and broad paws; • Big and long beak
• Wide-padded foot
long curved sharp claws
• Camouflaging
• Small ears

G. Integrating ICT (Page 101)

Students will do it on their own.

42
H. Case Study (Page 101)
1. August is the most humid month in Delhi.
2. April is the least humid month in Delhi.
3. February
4. July, August and September
5. 42%

Exercises
Stop and Reflect (Page 102)
A. 1. (d) 2. (a) 3. (c) 4. (c) 5. (a)
B. 1. True
2. False (The maximum temperature is recorded in the afternoon.)
3. False (Monkeys use their long hands and tail to grasp branches of trees.)
4. True
5. False (The incisors of an elephant are modified into tusk. )
C. 1. (e) 2. (c) 3. (d) 4. (b) 5. (a)
D. 1. Polar bear
2. Red-eyed frog
3. Penguin
4. Toucan
5. Lion-tailed macaque
E. 1. Hygrometer
2. Climate
3. Maximum-minimum thermometer
4. Meteorological department
5. Rain gauge
F. 1. Polar bear, penguin
2. Elephant, jaguar
3. Humidity, rainfall
4. Monkey, birds
5. Camel, ground squirrel
Crisp and Accurate (Page 103)
A. 1. Weather forecasting refers to predicting weather conditions of a place over a short period of
time.
2. The amount of water vapour present in air at a specific temperature as compared to the
maximum amount of water vapour that air can hold at that temperature is called relative
humidity.
3. The seasonal movement of animals from one place to another place to avoid harsh climatic
conditions is known as migration.

43
 4. Humidity is the amount of moisture present in the air.
5. Blubber is the thick layer of fat, present under the skin of animals like polar bear, penguin and
seal.
B. 1. Weather refers to the day-to-day conditions of the atmosphere at a certain place with respect
to temperature, speed of wind, humidity, rainfall, sunshine and clouds.
On the other hand, climate refers to the average weather conditions prevailing at a place over
a long period of time (say 25–30 years). The climate varies from region to region.
2. Weather forecasting helps us to plan our day-to-day activities. When a rainy day is predicted,
we can carry an umbrella or a raincoat while going out. We can plan a picnic when a cool and
pleasant day is predicted. Weather forecasting helps us to prepare well in advance for bad
weather conditions.
3. Birds migrate from one place to other to avoid harsh climatic conditions at home environment.
These birds are known as migratory birds. For example, Siberian crane.
4. Animals in polar regions have a thick layer of fat under their skin called blubber. It helps to
keep the body warm by providing insulation.
5. Lion-tailed macaques spend most of their lives on trees because they get almost all their food
from trees and thus rarely come on to the land.
Think and Explain (Page 103)
1. Following are the different elements of weather.
• Temperature: The heat of the sun is transferred to the earth by the process of radiation. The
maximum and minimum temperatures of a day are recorded with the help of a maximum-
minimum thermometer.
• Humidity and rainfall: Moisture is always present in the atmosphere in the form of water
vapour. This amount of moisture in the air is called humidity. It is measured in terms of relative
humidity using an instrument called hygrometer. The chances of rainfall are high when the
humidity is high.
• Wind: The movement of air parallel to the earth’s surface is called wind. The wind carries
moisture with it when it blows from one place to another, thereby resulting in the fluctuating
temperatures.
2. Following are the factors that affect the climate of a place.
• The distance of the earth from the sun determines the temperature of a place and hence its
climate. The temperature falls as the distance of a place from the equator increases.
• The distance from the sea also affects the climate. A moderate climate exists at places close to
the sea, whereas places that are away from the sea face extreme climatic conditions.
• The amount of rainfall that a place receives also influences the climate of that place. The
amount of rainfall depends on factors like wind, proximity to the sea and the presence of
mountains. Thus, places near sea receive more rainfall.
3. The adaptations in a polar bear are as follows.
• A thick white fur covers the body of a polar bear. Its colour blends with the snow and protects
the polar bear from predators.
• A thick layer of fat called blubber is present under the skin of polar bears. It helps to keep its
body warm by providing insulation.
• Their paws are flat and broad which helps them to walk on ice and swim in water.
• They have small ears that help them to retain as much heat as possible.

44
 The adaptations in penguins are as follows.
• Their body is white on the underside that merges well with the white background of snow.
• Their feathers are densely packed with no gaps between them. These features protect
penguins from severe cold.
• They have webbed feet and streamlined body. Their wings are shaped like flippers. These
features make them good swimmers.
• Penguins live in groups and stay huddled together. This helps them to stay warm and fight
enemies.
4. The climate of tropical rainforests is hot and humid. These regions are located near the equator
and have suitable climatic conditions to support a rich variety of plants and animals. Tropical
rainforests occupy 1/12th of the earth’s surface and possess more than half of the earth’s total
number of living organisms.
There are animals that have adapted to live on trees as the living area is quite less as compared to
the number of animals. For example, the red-eyed frog has sticky pads on its feet to help it climb
trees on which it lives. Monkeys have long tails for grasping branches. Their hands and feet help
them to swing across branches of trees.
5. The adaptations of camels that help them to survive in deserts are as follows.
• They have long eyelashes that protect their eyes during sandstorms.
• They can close their nostrils to prevent sand from entering the nasal cavity.
• The hump stores fat and helps the camel to survive during food shortage.
• They can drink a large quantity of water at a time. It is stored for later use.
• They have well-padded wide feet that help them to walk on hot sand.

45
 8. Soil

Answer Key

In-text Questions
All about Soil (Page 104)
1. growth
2. earthworm, fertility
3. deforestation, erosion, wind, water
4. Terrace, conservation
Think and Answer (Page 107)
When living organisms die, they are decomposed by certain bacteria which decompose organic matter,
and release excess nutrients into the soil which increase its fertility.
Knowing the Soil Profile (Page 107)
Soil Features Topsoil Subsoil Parent rock
The colour of soil is the darkest in this layer. 3 7 7
This layer is rich in oxides of iron. 7 3 7
This layer is a home to many organisms. 3 7 7
This is the most fertile layer. 3 7 7
This layer consists of rocks with cracks and crevices. 7 7 3
Water retention of this soil layer is high. 3 7 7

Quick Check (Page 110)

1. weathering 2. topsoil, nutrients
3. atmospheric nitrogen, nitrogen fixation 4. sandy
Think and Answer (Page 113)
When plants are waterlogged, they wilt and die. This is because the plant does not get enough oxygen
as water occupies the spaces between soil particles. It can also cause root damage and nutrient
deficiencies.
Soil Type (Page 113)
1. True 2. False 3. True 4. True 5. False
Quick Check (Page 115)
1. percolation 2. Sandy 3. high; paddy 4. Afforestation; prevents

46
Apply Your Learning
A. Identifying Soil Types by Percolation Rates (Page 116)
Soil Type Time Taken by Water to Percolate Percolation Rate
X 5 min 150/5 = 30 mL/min
Y 17 min 150/17 = 8.8 mL/min
Z 8 min 150/8 = 18.75 mL/min

1. Percolation rate is the rate at which the water moves down in the soil.
Amount of water (mL)
2. Percolation rate (mL/min) =
Time taken (min)
3. Soil Y has lowest percolation rate.
4. Soil X has the highest percolation rate.
5. Soil X would be sandy soil.
6. Soil Y would be clayey soil.
B. Label and Learn (Page 116)

Topsoil

Subsoil

Parent rock

Bedrock

1. The picture shows soil profile.

2. Topsoil
3. Subsoil
4. Bedrock
5. Earthworms, bacteria and fungi are three living organisms present in the topmost layer of soil.
6. Topsoil and subsoil are the layers of soil that have humus.
C. Life Skills (Page 117)
1. Removal of forest cover loosens the soil and makes it easier for the soil to be carried away by
running water and wind.
2. Overgrazing and forest fires are some other causes of soil erosion.
3. We can prevent soil erosion by afforestation i.e. planting more trees and terrace farming.
4. Terrace farming is employed in hilly areas to prevent soil erosion.

47
D. Reason Out (HOTS) (Page 117)
1. In hilly regions, where the land is sloped, soil is frequently washed away and hence the soil is
thin. On the other hand, valleys are typically flatter and receive more water runoff from the
surrounding mountains. This water helps to deposit sediment and organic material in the
valley, gradually building up the thickness of soil.
2. Clayey soil absorbs rainwater quickly because it has high water retention capacity.
3. Due to the absence of vegetation in desert regions, the soil can be easily blown away by wind.
Thus, soil erosion is more severe in areas with little or no surface vegetation, such as deserts.
4. Earthworms burrow into the soil, mix the layers of soil and allow the dispersion of organic
matter present in it. Due to this, the nutrients present in organic matter are made available to
plants. As earthworms help to increase soil fertility, they are known as farmer’s friends.
E. Link and Learn (Page 117)
1. The three major types of rocks are igneous rocks, sedimentary rocks and metamorphic rocks.
2. Igneous rocks are also known as primary rocks because directly or indirectly all kinds of rocks
are made from them.
3. Sedimentary rocks are also called stratified rocks.
4. Quartzite is an example of metamorphic rock.
5. Rocks are used to make cement and in building monuments.
F. Mind Map (Page 118)

Types of Soil

Sandy soil Clayey soil Loamy soil

• Small-sized • High humus

• Light and dry
particles content
• Large-sized
• High water • Sufficient water
particles
retention retention
• Lacks humus
• Contains minerals • Well-aerated

G. Integrating ICT (Page 118)

Students will do it on their own.
H. Case Study (Page 118)
1. Eight types of soil are identified by the ICAR.
2. Black soil is present in the highest percentage, and saline and alkaline soil is present in the
lowest percentage.
3. Gujarat, Maharashtra and Karnataka
4. Wheat, rice and pulses
5. Maharashtra and Kerala

48
Exercises
Stop and Reflect (Page 119)
A. 1. (b) 2. (d) 3. (a) 4. (d) 5. (d)
B. 1. True
2. False (Sandy soil does not support the growth of crops.)
3. True
4. False (Sandy soil is composed of large-sized particles.)
5. False (Soil profile consists of four layers.)
C. 1. (d) 2. (a) 3. (e) 4. (b) 5. (c)
D. 1. Gravel 2. Clayey soil 3. Loamy soil 4. Humus 5. Terrace farming
E. 1. It has high humus content.
2. It has high water retention capacity.
3. This layer is soft, porous and fertile.
4. It has large-sized particles.
5. It is rich in minerals and oxides of iron.
F. 1. Deforestation, overgrazing
2. Use of manure, treatment of industrial wastes before disposal
3. Afforestation, construction of dams
4. Temperature, wind
5. High amount of humus, well-aerated soil
Crisp and Accurate (Page 120)
A. 1. Weathering is the process of formation of soil by the continuous breakdown of rocks.
2. Soil profile is a vertical section of the soil that shows its different layers or horizons.
3. Soil erosion is the removal of topsoil by the action of wind and water.
4. Percolation rate is the rate at which the water moves down in the soil.
5. Bedrock is the layer that lies below the parent rock. This layer is non-porous and hence
rainwater collects over the bedrock to form the water table.
B. 1. The two types of weathering are as follows.
• Physical weathering: It is the breakdown of rocks into smaller pieces caused by the
effect of change in temperature, wind, roots of plants that penetrate the rocks and
other natural forces.
• Chemical weathering: It is the breakdown of rocks caused as a result of change in
its chemical nature. In this process, the minerals present in rocks undergo chemical
reaction with water to form new minerals that make the rock brittle and thus lead to the
breakdown of rocks.
2. Temperature variations caused during day and night lead to weathering. During the day,
rocks expand due to the heat of the sun. At night, they contract due to low temperature. The
continuous expansion and contraction of rocks break them and cause weathering.
3. Yes, loamy soil is suitable for the growth of crops. Loamy soil is composed of sand, silt and clay
particles in equal amounts. It also has high amounts of humus which makes it perfect for the
growth of crops.

49
 4. The major causes of soil erosion are deforestation, overgrazing, floods and heavy rainfall,
forest fires and poor farming methods.
5. The normal composition of soil is altered due to the addition of poisonous substances that
may pose a health risk to living organisms like plants, animals and human beings. This is
known as soil pollution.
Think and Explain (Page 120)
1. Following are the different stages of weathering of rocks.
• Stage I: Parent rocks break down into smaller pieces as a result of physical and chemical
weathering.
• Stage II: Continuous weathering results in the formation of a very fine layer of rock particles
at the surface. Humus is formed by the action of bacteria and other microorganisms on dead
remains of plants and animals.
• Stage III: The formation of soil gets completed when minerals and salts seep deeper into the
ground.
2. There are three main layers of soil. They are described as follows.
• Topsoil: The topsoil is the uppermost layer of soil that consists of fine particles and humus. This
layer is soft, porous and can hold a lot of water. The topsoil is fertile and it provides nutrients
to the plants in the form of humus. Many living organisms like fungi, bacteria, rodents, insects
and worms live in the topsoil. This layer is the darkest in colour.
• Subsoil: The subsoil lies below the topsoil. It is more compact than the topsoil. It has very
little humus but it is rich in minerals and oxides of iron. The roots of only tall trees reach this
layer. Rainwater gets collected in this layer.
• Parent rock: The parent rock lies below the subsoil. It consists of small pieces of rocks with
cracks and crevices. Rainwater collects in this region also.
3. Following are the different types of soil.
• Sandy soil: Sandy soil is composed of a large amounts of sand particles, and a very small
amount of clay and silt particles. It is light and dry. As it is composed of large-sized particles,
it has many air spaces between the particles and the soil is highly porous. The water retention
of the soil is poor as water drains quickly through the spaces. The soil lacks humus making it
unsuitable for the growth of plants.
• Clayey soil: Clayey soil is mainly composed of clay particles, and a little amount of sand and
humus. As the clay particles are small, this soil is compact with little air spaces. The water
retention of the soil is high and it is sticky when wet. Due to the presence of minerals, plant
growth takes place in this soil.
• Loamy soil: Loamy soil is composed of sand, silt and clay particles in equal amounts. This soil
is the best soil for the growth of crops. The amount of humus in the soil is very high. It has
sufficient water-holding capacity. This soil is well-aerated. It can trap air that is required by the
roots of plants.
4. Soil is a valuable natural resource in the following ways.
• Soil supports the growth of plants. We get food, cloth (cotton and wool), fuel, medicine, wood
and paper from plants.
• Clay is used as a raw material for the manufacture of tiles, bricks and pottery items.

50
 • Rainwater that is absorbed into the soil is stored in the subsoil layer. This maintains water
table. This water is used for drinking and for other household activities.
5. Following methods can be used to prevent soil erosion.
• Afforestation: Planting more trees is called afforestation. Roots of trees hold the soil particles
firmly and thus control soil erosion.
• Terrace farming: This technique is practised in hilly areas. It reduces steepness of slopes and
controls soil erosion.
• Constructing dams: Flood control by construction of dams prevents soil erosion.
• Preventing overgrazing: Overgrazing by cattle should be prevented to control soil erosion.

Weight of moisture (g)

Percentage of moisture in soil = × 100
Original weight of soil sample (g)

51
 9. Respiration in Organisms

Answer Key

In-text Questions
Synthesis of Food by Plants (Page 121)
A. The names of the labelled things are as follows.
1. Sunlight
2. Carbon dioxide
3. Water
4. Oxygen
B. Tick the correct answer.
(a) 4
(b) 2
C. Photosynthesis
D. Transpiration
Products of Respiration (Page 123)
Carbon dioxide
In the presence of Water
oxygen in humans
Energy
Lactic acid
During deficiency of
Glucose oxygen in muscles Energy
Carbon dioxide
In yeast Alcohol

Energy

Quick Check (Page 124)

1. Energy, carbon dioxide
2. lactic
3. Inhalation, exhalation
4. Aerobic, anaerobic
5. increases
Quick Check (Page 127)
1. T 2. F 3. F
4. T 5. F

52
Picture Study (Page 128)

(a)
(b)

(c) (d)

Process A Process B

(a) – Movement of ribs outwards

(b) – Movement of ribs inwards
(c) – Movement of diaphragm downwards
(d) – Movement of diaphragm upwards
Process A – Inhalation
Process B – Exhalation

Apply Your Learning

A. Observe and Label (Page 129)

Nostrils
Nasal cavity
Windpipe
Windpipe which further
divides into bronchi

Alveoli
Bronchiole
Lung
Diaphragm

1. Windpipe is also known as trachea .

2. The ribcage protects the lungs in the chest cavity.
3. Breathing involves coordinated movement of the diaphragm and the ribs .

53
B. Complete the Table (Page 129)
Colour of lime water Milky
Gas present in exhaled air Carbon dioxide
Type of respiration in humans Aerobic respiration
Products formed during respiration in Energy, carbon dioxide, water
humans
Does anaerobic respiration take place Yes
in humans?
If yes, then where does it take place? In muscles
An organism in which anaerobic Yeast
respiration takes place
Products formed during respiration in Energy, carbon dioxide, alcohol
this organism
C. Life Skills (Page 130)
1. The two causes of air pollution are as follows.
• Release of toxic fumes from factories
• Burning of fossil fuels
2. Following are the measures to reduce air pollution.
• Using filters for chimneys
• Using public transport
3. Asthma and lung cancer are caused due to air pollution.
4. A passive smoker is someone who inhales smoke from tobacco products, such as cigarettes,
that are being smoked by others nearby. Passive smokers may be exposed to the same harmful
chemicals and toxins as active smokers, even though they do not smoke themselves. This can
lead to various negative health effects.
5. Smoking is very harmful to health as it damages lungs and airways. The breathing becomes
very difficult and the person may suffer from a persistent cough. It can even lead to lung
cancer and other diseases like chronic bronchitis. It can also increase the risk of heart disease
and weakens the immune system.
D. Reason Out (HOTS) (Page 130)
1. Yes, we sneeze when we inhale dust-laden air. It is to expel out these foreign particles. These
particles get past the hair in the nasal cavity and irritate the lining of the nasal cavity which
results in sneezing.
2. It is not correct to breathe through our mouth because most of the dust particles can enter our
body along with the air we breathe in. Breathing should be done through the nose because
the nose has hair and mucus present in the inner lining which traps the dust particles. Also, as
the air passes through the nasal passage, it gets moistened and warm which makes it easier
for the lungs to absorb oxygen. Breathing through the mouth can cause irritation and dryness
in the airways.

54
 3. Oxygen is replenished in air due to the balance set between plants and animals. Animals
exhale carbon dioxide which is taken by plants during photosynthesis. After this, plants give
out oxygen which is consumed by animals and other living beings.
E. Link and Learn (Page 130)
1. There are many factors that can trigger asthma, these range from allergic substances to viral
and bacterial infections.
2. Shortness of breath and chest pain are some of the symptoms of asthma.
3. Inhalers allows the medicine to reach the lungs directly and is readily absorbed by them.
Thus, resulting in effective relief.
4. Yes, smoking can cause asthma. Even passive smokers may also have asthma.
F. Mind Map (Page 130)

Types of Respiration

Aerobic respiration Anaerobic respiration

• Takes place in the presence • Takes place in the absence of

of oxygen oxygen
• Carbon dioxide, water and • Carbon dioxide, alcohol and
energy are produced energy are produced
• Example: Humans • Example: Yeast

G. Integrating ICT (Page 131)

Students will do it on their own.
H. Case Study (Page 131)
1. Breathing rate is the number of times a person breathes in one minute.
2. 10 min (rest)
3. 8 min
4. 30 times per minute
5. During exercise, the breathing rate increases while at rest, it decreases.

Exercises
Stop and Reflect (Page 132)
A. 1. (a) 2. (c) 3. (d) 4. (c) 5. (c)
B. 1. False (The windpipe is also known as trachea.)
2. True
3. False (Anaerobes are the organisms that respire in the absence of oxygen.)
4. False (Cellular respiration is chemical process.)
5. False (Respiration takes place in plants.)

55
C. 1. (d) 2. (b) 3. (a)
4. (e) 5. (c)
D. 1. Skin
2. Lungs
3. Both skin and lungs
4. Spiracles
5. Gills
E. 1. Human
2. Grasshopper
3. Fish
4. Earthworm
5. Neem plant
F. 1. Carbon dioxide
2. Lactic acid
3. Aerobic respiration
4. 15-18 times per minute
5. Diaphragm
Crisp and Accurate (Page 133)
A. 1. The process of breakdown of food in the cells along with the release of energy is known as
respiration or cellular respiration.
2. The physical process in which oxygen-rich air is taken in and carbon dioxide-rich air is given
out is known as breathing.
3. The breakdown of food (glucose) in the presence of oxygen to release a large amount of
energy is called aerobic respiration.
4. Breathing rate is the number of times a person breathes in one minute.
5. In anaerobic respiration, the breakdown of food takes place in the absence of oxygen.
B. 1. Living organisms respire to get energy from food. This energy is then utilised by the organisms
to carry out their basic life processes.
2. During vigorous muscular activity, the demand of energy in our body increases. However, the
supply of oxygen is limited. During this time, our muscles respire anaerobically.
3. Nostrils, nasal cavity, trachea, bronchi and lungs together forms the human respiratory
system.
4. Following reaction takes place during anaerobic respiration in humans.
Glucose → Lactic acid + Energy
(in muscles)
5. Frogs are able to breathe through their moist skin as well as through their lungs. In water,
frogs breathe through their moist skin. On the land, they breathe through their nostrils and
the air reaches the lungs.
Think and Explain (Page 133)
1. The two types of respiration are as follows.

56
 Aerobic respiration: The breakdown of food (glucose) in the presence of oxygen to release a
large amount of energy is called aerobic respiration. Human beings, green plants and most of the
animals respire aerobically. Aerobic respiration can be represented as follows.
Glucose + Oxygen → Carbon dioxide + Water + Energy
Anaerobic respiration: In anaerobic respiration, the breakdown of food takes place in the absence
of oxygen. This leads to the release of a small amount of energy, carbon dioxide and alcohol. Yeast
and some bacteria perform anaerobic respiration. Anaerobic respiration can be represented as
follows.
Glucose → Carbon dioxide + Alcohol + Energy
2. Our chest moves up and down while breathing. When we inhale, the ribs move up and outwards,
and the diaphragm moves down. Due to this, the space in our chest cavity increases and air rushes
into the lungs. The expansion of chest takes place as the lungs get filled with air. When we exhale,
the ribs move down and inwards, and the diaphragm moves up. Due to this, the size of the chest
cavity decreases and air is pushed out of the lungs.
3. We can perform the following experiment to show that carbon dioxide is released during
breathing.
We need two test tubes A and B, two corks each with two holes, four glass tubes, a syringe and
lime water. Now, we will follow the given steps.
• Fill test tubes A and B with freshly prepared lime water.
• Fit a cork in both the test tubes and fix glass tubes through the corks.
• Exhale air into test tube A through the glass tube and note your observations.
• Using a syringe, pass air into test tube B and note your observations.
It can be observed that lime water in test tube A turns very milky as exhaled air contains carbon
dioxide (CO2). The reaction of lime water with CO2 forms a milky solution. It can also be observed
that the lime water in test tube B turns only slightly milky as the surrounding air contains less
carbon dioxide as compared to exhaled air.
4. (a) Grasshoppers breathe through tiny openings called spiracles that are present on the sides
of their bodies. These spiracles are linked to air tubes called tracheae. Oxygen-rich air enters
through spiracles into the tracheal tubes and then diffuses into the body tissues to reach
every cell of the body. Similarly, carbon dioxide released by the cells moves out through the
spiracles.
(b) Fish breathe under water through organs called gills. Gills help fish to absorb the dissolved
oxygen in water. They are composed of tiny thread-like projections known as filaments which
are well-supplied with blood vessels. Water enters the mouth of a fish and flows through
the gills. Oxygen from the water diffuses into the blood in the gills. In the same way, carbon
dioxide is diffused out into the water from the gills.
5. Plants also respire like animals. They take in oxygen and give out carbon dioxide. In leaves, tiny
pores called stomata are present mostly on their under surface. The exchange of gases takes place
through stomata. Roots take in oxygen from the air spaces that are present in between the soil
particles. Farmers plough the soil so that sufficient oxygen is available for root respiration.
Respiration can take place through different parts of the plant such as roots, stems and leaves.

57
 10. Transportation of Materials

Answer Key

In-text Questions
Transportation through Stem (Page 134)
1. orange
2. water
3. minerals
4. It supports branches, leaves, flowers and fruits.
Think and Answer (Page 136)
Since the blood pumped from the heart into the arteries flows at higher pressure than the blood in
veins, hence arteries need to have thick elastic walls that can stretch and shrink when blood flows
through them rapidly.
Blood Circulation Recap (Page 139)
Pulmonary Aorta
Oxygenated vein
blood

Left auricle Left ventricle

All parts of body
Lungs Right ventricle Right auricle

Heart
Pulmonary
Deoxygenated
artery Vena cava blood

Think and Answer (Page 140)

A doctor often holds our wrist to check our pulse because the radial artery can be located here. Each
heartbeat generates one pulse in the arteries and the pulse rate indicates the rate of heartbeat.
Quick Check (Page 140)
1. Erythrocytes 2. Pulmonary vein 3. Capillary
4. Ventricles 5. Septum
Think and Answer (Page 141)
Sweating help to regulate the temperature of the body. As sweat evaporates, it cools the body. This
happens because the process of evaporation requires heat energy, which is taken from the surrounding
environment, including the body's skin.

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Observe and Match (Page 141)
A: Blood is filtered by this organ
B: It carries urine from the kidney to the urinary bladder
C: Urine is stored in this organ
D: It is the opening through which urine is excreted
Quick Check (Page 143)
1. nephrons 2. urinary bladder 3. dialysis
4. Phloem 5. transpiration

Apply Your Learning

A. Label and Answer (Page 145)

Aorta
Vena cava

Pulmonary artery

Left auricle

Right auricle
Pulmonary vein
Valves

Right ventricle

Septum Left ventricle

1. Septum
2. Aorta
3. Pulmonary artery
4. Pulmonary vein
B. Image Study (Page 145)
1. When both the kidneys of a person stop functioning due to an injury or an infection, the toxic
substances start accumulating in the blood.
2. The process shown in the image is dialysis.
3. The method of separating toxic substances from the blood using artificial kidneys or dialysis
machine in case of kidney failure is called dialysis.
4. The name of the machine is dialysis machine.

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C. Life Skills (Page 146)
1. Blood donation refers to the practice where people donate their blood to other people so it
helps them with their health problems.
2. Following are a few benefits of blood donation.
• Blood donation also enhances the health of the donor, as new blood cells form in
her/his body to replenish the lost blood.
• The donated blood helps save the lives of people who have lost a lot of blood due to
some illness or accident.
3. Temporary side effects of blood donation include fatigue and light-headedness. To help with
this, the donor should be kept hydrated and given some light snack to replenish energy.
D. Reason Out (HOTS) (Page 146)
1. The excretory system works together with the circulatory system because the blood of the
circulatory system is filtered through the excretory system. The main organ in the excretory
system is the kidney. Blood from the circulatory system passes through the kidneys where it
is filtered.
2. White blood cells are also called the soldiers of the body because they provide immunity to
our body. They help in fighting against diseases, infections, allergies and foreign particles.
These cells keep our body safe and healthy.
3. We sweat more in summer as it acts as a cooling mechanism. The body produces sweat which
evaporates and cools down the body.
4. No, a wound will not heal if there were no platelets. In the absence of platelets, the blood will
not clot and would result in excess blood loss.
E. Link and Learn (Page 146)
1. Coronary artery disease is one of the main causes of heart attacks.
2. Chest pain and pain or discomfort in one or both arms or shoulders are two symptoms of
heart attack.
3. Yes, heart attack can be prevented by leading a healthy lifestyle with proper food and exercise.
4. Yes, diabetic people are more prone to heart attacks.
F. Mind Map (Page 146)

Circulatory System in Human Beings

Heart Blood vessels Blood

• Transports blood from • Transports oxygen from

• Pumps blood to all lungs to different cells
heart to all parts of
parts of the body of the body
body and vice versa

G. Integrating ICT (Page 147)

Students will do it on their own.

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H. Case Study (Page 147)
1. Cigarette smoking
2. Approximately 49 Percentage
3. Approximately 19 percent
4. Approximately 35 percent
5. One can reduce the risk of occurrence of heart diseases by following a healthy lifestyle.

Exercises
Stop and Reflect (Page 148)
A. 1. (b) 2. (c) 3. (d) 4. (c) 5. (a)
B. 1. False (Xylem is a type of vascular tissue.)
2. True
3. False (The process by which plants lose water is called transpiration.)
4. False (Arteries carry oxygenated blood.)
5. False (Xylem transports water from roots to all parts of the plant.)
C. 1. (e) 2. (d) 3. (b) 4. (c) 5. (a)
D. 1. Excretory system 2. Circulatory system
3. Digestive system 4. Respiratory system
5. Excretory system
E. 1. Pumps blood to all parts of the body 2. Carry oxygen to all parts of the body
3. Used to measure heartbeat 4. Filters the blood
5. Transports food to all parts of the plant
F. 1. Veins, arteries 2. WBCs, RBCs
3. Kidney, urinary bladder 4. Xylem, phloem
5. Water, minerals
Crisp and Accurate (Page 149)
A. 1. The blood vessels that carry blood from the heart to other parts of the body are called arteries.
2. The blood vessels that carry blood from all the body parts to the heart are called veins.
3. The red pigment present in blood which transports oxygen to all the cells of the body is called
haemoglobin.
4. Excretion is the process by which waste products are removed from the body.
5. Transpiration is the process by which plants lose water from their leaves in the form of water
vapour.
B. 1. Water, minerals and food are the three materials that are transported in plants.
2. Blood, blood vessels and heart together forms the human circulatory system.
3. Right side of the heart is separated from the left side of the heart to prevent the mixing of
oxygenated and deoxygenated blood.
4. Skin acts as an excretory organ because the sweat glands present in the skin help to remove
urea, salt and excess water.

61
 5. White blood cells are useful because they help to destroy disease-causing microorganisms
that may have entered the body.
Think and Explain (Page 149)
1. The heart is divided vertically into two halves. The right side receives impure blood from the
body and pumps it to the lungs. The left side receives pure blood from the lungs and pumps
it to different parts of the body. The heart consists of four chambers. Each side of the heart has
two chambers. The two upper chambers are known as auricles or the atria, and the two lower
chambers are called ventricles. The left auricle opens into the left ventricle and the right auricle
opens into the right ventricle. Valves are located between the auricle and the ventricle on both
sides that prevent the backflow of blood. The left side and the right side of the heart are separated
by a muscular wall known as septum. It ensures that the deoxygenated blood does not mix with
the oxygenated blood.
2. Pulmonary vein brings oxygenated blood from the lungs to the left auricle of the heart. It then
pumps the blood into the left ventricle. Then the blood is distributed to different parts of the body
through the aorta. The aorta gets divided into arteries and then to capillaries. The deoxygenated
blood that is collected by the capillaries from various body parts now flows into the veins. The
deoxygenated blood is brought into the right auricle by the vena cava. From here it is pumped into
the right ventricle. The blood is then carried by the pulmonary artery to the lungs for oxygenation.
Then the oxygenated blood is again carried to the left auricle through the pulmonary vein. In this
way, the circulation of blood goes on.
3. The human excretory system is composed of a pair of kidneys, ureters, urinary bladder and
urethra. Kidneys are reddish-brown, bean-shaped organs that are located just above the waist.
Each kidney consists of a large number of coiled tubes known as nephrons. They act as filters and
help to remove waste products from the blood that reaches the kidneys. The useful substances
are absorbed into the blood, and the filtrate that contains the waste products forms the urine.
Ureters are the narrow tubes that arise from each kidney. They carry urine from the kidneys to the
urinary bladder, where it is stored. The urine gets excreted from the body through an opening
known as the urethra.
4. In plants, water and minerals are absorbed through the roots. Roots have many tiny root hairs
that increase the surface area for absorption of water and minerals present in between the soil
particles. The upward movement of water and minerals takes place through the vascular tissue
known as xylem. Similarly, the vascular tissue that transports food from the leaves to all parts of
the plants is called phloem.
5. Transpiration is the process by which plants lose water from their leaves in the form of water
vapour. Transpiration is useful for plants in the following ways.
• Transpiration creates a suction pull that helps to pull water up to great heights in tall trees. As
water is evaporated by transpiration, more water is absorbed through the roots. This helps in
the transport of water and minerals from the soil to the leaves.
• It helps to protect the plant cells from the heat of the sun by producing a cooling effect.
Otherwise, the leaves and flowers will droop.
• It provides rigidity to the soft parts of the plant body.

62
 11. Reproduction in Plants

Answer Key

In-text Questions
Reproductive Parts of a Flower (Page 150)
Stigma

Anther
Style

Ovary

Ovule
Filament

1. Stamen 2. Pistil

Picture 1 is the male reproductive part of a flower and picture 2 is the female reproductive part of a
flower.
Think and Answer (Page 153)
Yes, if we place a cutting of rose stem in the soil, it will grow into a new plant. This is due to vegetative
propagation of the stem.
Complete the Chart (Page 154)

Asexual Reproduction in Plants

Vegetative propagation Budding Spore formation Fragmentation

Root Stem Leaf

Potato Sugar cane Turmeric Ginger

63
Quick Check (Page 154)
1. T 2. F 3. T 4. F
Think and Answer (Page 156)
Plants produce a large number of seeds to be dispersed to increase the chances of successful
reproduction and survival of the species. Seed dispersal helps in avoiding competition for light, water
and minerals in the soil .
Quick Check (Page 157)
1. bisexual/complete
2. ovule
3. fertilisation
4. wind, water, animals, explosion
Picture Study (Page 158)

Pistil

Stamen

Petal

Sepal

1. flower 2. stamen 3. pistil

4. Bisexual 5. China rose

Apply Your Learning

A. Identify and Answer (Page 159)
1. Yeast (A) and Spirogyra (B)
2. Budding
3. Fragmentation
4. Asexual reproduction
5. Colony
B. Growing New Plants (Page 159)
1. Asexual reproduction
2. Vegetative propagation
3. A
4. Bryophyllum
5. Sweet potato, Asparagus

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C. Life Skills (Page 160)
1. The two types of pollination are self-pollination and cross-pollination.
2. Cross-pollination
3. Insects help in pollination. If there were no insects, pollination will not take place in plants.
4. Animals eat fruits and the small seeds present in the fruit. They are passed out in the faeces
without being damaged and thus get dispersed.
5. If seeds reach unfavourable conditions, then they will die.
D. Reason Out (HOTS) (Page 160)
1. Yes, we can grow a money plant by using its cutting. It involves selecting a healthy stem,
removing the lower leaves and rooting the stem in soil. Thus, money plant can grow via
vegetative propagation.
2. Insects are attracted to flowers because they have nectar which is a sweet liquid that is present
at the base of flowers.
3. If a plant does not produce nectar, then pollination takes place through other methods such
as wind, water, animals or by explosion of fruit.
E. Link and Learn (Page 160)
Cells in culture dish at present = 2
Cells in culture dish after 1.5 hours = 2 × 2 = 4
Cells in culture dish after 3 hours = 4 × 2 = 8
Cells in culture dish after 4.5 hours = 8 × 2 = 16
Cells in culture dish after six hours = 16 × 2 = 32
F. Mind Map (Page 161)

Asexual Reproduction in Plants

Vegetative propagation Budding Fragmentation Spore formation

Yeast Spirogyra Ferns

Roots:
Stem:
Sweet
Turmeric
potato

Leaves: Bryophyllum

G. Integrating ICT (Page 161)

Students will do it on their own.
H. Case Study (Page 161)
1. The growth of bread mould was highest in bag A because it was placed in favourable
conditions for the growth of mould.

65
 2. The growth of bread mould was the least in bag C because it was kept in completely
unfavourable conditions.
3. 70%
4. The mould would grow on bread when it is placed in moist and warm places.

Exercises
Stop and Reflect (Page 162)
A. 1. (b) 2. (d) 3. (a) 4. (d) 5. (d)
B. 1. False (Yeast reproduces by budding.)
2. False (Spirogyra reproduces through the process of fragmentation.)
3. True
4. False (The fusion of male and female gametes is known as fertilisation.)
5. False (After fertilisation, the ovules become seeds.)
C. 1. (d) 2. (a) 3. (e) 4. (b) 5. (c)
D. 1. Stem 2. Leaves 3. Stem 4. Roots 5. Stem
E. 1. Wind
2. Water
3. Animals
4. Explosion
5. Wind
F. 1. Animals, wind
2. Madar, dandelion
3. Coconut, lotus
4. Rose, sunflower
5. Cucumber, papaya
Crisp and Accurate (Page 163)
A. 1. The flowers that have both stamen and pistil are called bisexual flowers or complete flowers.
2. The flowers that have either the stamen or the pistil are known as unisexual flowers or
incomplete flowers.
3. The production of a new plant from the vegetative parts of a plant such as roots, stems, leaves
or buds is called vegetative propagation.
4. In self-pollination, the pollen grains are transferred from an anther to the stigma of the same
flower or another flower of the same plant.
5. The process of fusion of male and female gametes is known as fertilisation.
B. 1. Spirogyra reproduces by the process of fragmentation. In this process, the organism’s body
divides into two or more fragments under favourable conditions. Then each fragment grows
into a new individual.
2. Stems or branches of some plants are cut from the parent plant and then planted separately
in moist soil. Later on, they grow into new plants and this process is called stem cutting.

66
 3. Stamen is the male reproductive part of a flower and consists of two parts—anther and
filament. Pollen grains that are present in an anther produce the male gametes.
The pistil consists of ovary, style and stigma. The ovary contains one or more ovules that
produce female gametes (egg).
4. Pollination can take place via insects, wind or water. When insects visit flowers to collect
nectar, pollen grains stick to their bodies. Insects then visit the next flower and transfer these
pollens to them.
5. Following are the steps that take place in sexual reproduction of plants.
• Pollen grains are transferred from anther to stigma of a flower through agents like wind,
water or insects.
• After landing on the stigma, the pollen grains germinate and form pollen tubes.
• Only one pollen tube reaches the ovule and it carries the male gamete to the ovary.
• Inside the ovary, the male gamete fuses with the female gamete that is present inside
the ovule. This fusion produces a single cell known as zygote which divides rapidly to
form embryo.
• The embryo is enclosed by the seed which gives rise to a new plant.
Think and Explain (Page 163)
1. In asexual reproduction, new plants are produced without the production of seeds. Following are
the different types of asexual reproduction.
• Vegetative propagation: The production of a new plant from the vegetative parts of a plant
such as roots, stems, leaves or buds is called vegetative propagation. It can take place through
stems, roots and leaves.
• Budding: Budding takes place in yeast. In yeast, a small bulb-like projection is formed in the
body. This bulb is called bud. The nucleus of the parent cell divides into two and one nuclei
goes into the bud. The bud grows and then detaches itself from the parent body to form a
new yeast cell.
• Fragmentation: In this process, the organism’s body divides into two or more fragments
under favourable conditions. Then each fragment grows into a new individual.
• Spore formation: Ferns, mosses and many fungi (like bread mould) reproduce through the
process of spore formation. Spores are microscopic single-celled bodies that are covered
by a thick protective coat. The spores germinate to form new organisms under favourable
conditions.
2. The different methods of vegetative propagation are as follows.
• Vegetative propagation by stem: In this method, a modified swollen underground stem
forms in plants like ginger and onion. It can be grown by planting it in moist soil. Plants such
as grass and strawberry have runners which are horizontal stems that grow over the surface
of soil parallel to the ground. There is growth of new roots and shoots wherever the nodes
come in contact with the soil.
• Vegetative propagation by roots: Plants such as sweet potato, Dahlia and Asparagus possess
swollen roots. When these roots are buried in the soil, they grow into new plants.
• Vegetative propagation by leaves: In plants like Bryophyllum, we can observe buds present
on the margins of the leaves. Plantlets develop from these buds. When they detach from the
leaf and fall on the moist soil, they grow into new plants.

67
3. After the process of pollination, male and female gametes unite and form a zygote. The process of
fusion of male and female gametes is known as fertilisation. The zygote formed develops into an
embryo. The following events take place during fertilisation.
• After landing on the stigma, the pollen grains germinate and form pollen tubes.
• Only one pollen tube reaches the ovule and it carries the male gamete to the ovary.
• Inside the ovary, the male gamete fuses with the female gamete that is present inside the
ovule. This fusion produces a single cell known as zygote.
• After fertilisation, the size of the ovary increases and becomes a fruit. Ovules become seeds,
and petals and sepals along with other parts of the flower fall off.
4. Following are the advantages and disadvantages of vegetative propagation.
Advantages
• The plants that are reproduced through vegetative propagation grow in less time, and bear
flowers and fruits earlier than those produced through seeds.
• Plants that do not produce seeds can reproduce by this method.
• The new plant formed is identical to the parent plant. This helps to preserve characteristic
features of the parent plant.
• New characteristics can be introduced in plants.
Disadvantages
• All the undesirable characteristics of the parent plant will be present in the new plant.
• All the plants are prone to the same diseases as that of the parent plant.
• The parent plant can pass the germs to the offspring plant.
5. The different methods of seed dispersal in plants are as follows.
• Dispersal by wind: Some seeds are winged (maple and drumstick), some are hairy (madar
and dandelion) and some are very light (grasses). Such seeds are blown away by wind to
distant places.
• Dispersal by water: Fruits like coconut have a fibrous outer coat. Due to this, they can float on
water. Water carries the fruit away from the parent plant. Other examples of plants in which
seeds are dispersed by water are lotus and water lily.
• Dispersal by animals: Animals eat fruits and the small seeds present in the fruit. They are
passed out in the faeces without being damaged and thus get dispersed. Large seeds, such
as that of apricots, are not eaten and are thrown away. New plants are produced from these
seeds.
• Dispersal by explosion: Fruits of balsam, castor, peas and beans burst open with a sudden
jerk. This leads to scattering of seeds and new plants grow from them.

68
 12. Motion and Time

Answer Key

In-text Questions
Types of Motion (Page 164)
Following types of motion takes place in each fun activity.
A. Linear or rectilinear
B. Curvilinear or random motion
C. Circular motion
Following are the life examples of the type of motion exhibited in each of the fun activities mentioned
above.
A. Riding a cycle in a straight lane
B. A butterfly flying in a garden
C. Movement of spinning top
(Hint: Students can add a variety of examples.)
Quick Check (Page 166)
1. T
2. F
3. F
4. T
Think and Answer (Page 168)
The moon takes 27.3 days to revolve around the earth.
Speed Up! (Page 169)
Speed of the car = 150/2.5 = 60 km/h
Initial reading of the odometer = 280210 km
Distance covered in 1 hour = 60 km
Distance covered in 5 hours = 5 × 60 = 300 km
Present reading of the odometer = 280210 + 300 = 280510 km
Quick Check (Page 171)
1. time 2. time period
3. 8760 4. Speedometer

69
Apply Your Learning
A. Race Time! (Page 172)
Student Name Time (s) Distance (m) Speed (m/s)
Jasmine 60 240 4
Ritu 45 110 2.4
Arun 50 150 3
Atif 55 250 4.5
1. Ritu
2. Jasmine
3. Atif > Jasmine > Arun > Ritu
4. Arun
B. Picture Study (Page 172)
1. Time
2. It is based on the principle that as the sun’s position in the sky changes, the position and
length of the shadow cast by an object also changes.
3. Its disadvantage is that it cannot be used after sunset or on a cloudy day.
4. Students will do it on their own.
5. 'A' (digital watch) shows the most accurate time.
C. Life Skills (Page 173)
1. When the person does not follow the speed limit, then there are chances of her/him to meet
with an accident.
2. The speed that limit for motorcycles is 50-60 km/h and that for cars is 60-70 km/h in Delhi.
3. While riding a motorcycle, a person must wear helmet.
D. Reason Out (HOTS) (Page 173)
1. To decrease the time period of a pendulum, we need to decrease the length of the string.
2. Let’s assume that the car is moving with a uniform speed.
Speed = 50 km/h
Time = 2.5 h
Distance = Speed × Time
• = 50 × 2.5
• = 125 km
3. A sundial is based on the principle that as the sun’s position in the sky changes, the position
and length of the shadow cast by an object also changes. However, on a cloudy day, the sun
gets hidden by clouds. Therefore, we cannot use a sundial to measure time on a cloudy day.
4. A is the fastest.
E. Link and Learn (Page 173)
1. Delhi, Rajasthan and Madhya Pradesh
2. Maharaja Jai Singh II (1724)

70
 3. 13 architectural astronomy instruments are present in Jantar Mantar of Delhi.
4. Jaya Prakash Yantra, Rama Yantra and Misra Yantra
F. Mind Map (Page 174)

Units

Time Distance Speed

It is the measure of the It is the length of the It is the rate at which

duration between two path travelled by an an object moves or
events. object. covers a distance.

• SI unit = second

• Other units = • SI unit = m • SI unit = m/s
minutes, hour, day, • Other unit = km • Other unit = km/h
year

G. Integrating ICT (Page 174)

Students will do it on their own.
H. Case Study (Page 174)
1. 200 s
2. 1750 m
3. Yes, the person stopped for 50 s.
4. Speed = Distance/Time
• = 500/50 = 10 m/s
5. Non-uniform motion

Exercises
Stop and Reflect (Page 175)
A. 1. (d) 2. (a) 3. (d) 4. (d) 5. (c)
B. 1. True
2. False (Electronic clocks are used to measure time nowadays.)
3. False (The time between one new moon and the next new moon is called lunar month.)
4. True
5. False (The distance-time graph of an object moving in uniform motion is a straight line.)
C. 1. (d) 2. (e) 3. (b) 4. (a) 5. (c)
D. 1. 1 day = 24 h
2. 1 h = 60 min
3. 1 year = 365 days

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 4. 1 min = 60 s
5. 1 day = 86400 s
E. 1. Periodic motion
2. Uniform motion
3. Distance-time graph
4. Fast motion
5. Non-uniform motion
F. 1. A car moving with a constant speed of 50 km/h
2. Sundial
3. Second
4. Car
5. Electronic clocks
Crisp and Accurate (Page 176)
A. 1. An object is said to be in non-uniform motion if it covers unequal distances in equal intervals
of time.
2. Odometer is an instrument which is used to measure the distance covered by a vehicle like
car.
3. The time period is the time taken by the pendulum to complete one oscillation.
4. An object is said to be in uniform motion if it moves in a straight line and covers equal distances
in equal intervals of time.
5. Speed of a body is the distance covered by it in unit time.
B. 1. If the position of a body changes with respect to time and its surroundings, it is said to be in
motion. However, if the body does not change its position with time, then it is said to be at
rest.
2. If distance and time are given, then speed can be calculated by the formula given below.
Speed = Distance/Time
3. The time period between one new moon and the next was called a month.
4. Sundial and sand clock were the devices used in earlier days to measure time.
5. Speedometer is fitted in a vehicle to measure its speed.
Think and Explain (Page 176)
1. An object is said to be in uniform motion if it moves in a straight line and covers equal distances
in equal intervals of time. For example, if a car moves on a straight road at the same speed, then it
is said to be in uniform motion.
An object is said to be in non-uniform motion if it covers unequal distances in equal intervals
of time. For example, a car moving on a road may slow down or speed up depending upon the
traffic. At that time, it covers unequal distances in equal intervals of time.
2. A simple pendulum is composed of a small metallic ball called bob that is suspended from a
rigid stand with the help of a string. The bob is said to be in its mean position when it is at rest.
The pendulum moves to and fro about its mean position O when the bob is displaced slightly.
The pendulum completes one oscillation when the bob moves from the mean position O to one
end A and then from A to another end B and back from B to O. It can also be considered that

72
 the pendulum completes one oscillation when the bob moves from one extreme position (A)
to the other (B) and then back to the initial position (A). The time period is the time taken by the
pendulum to complete one oscillation. The time period of a pendulum of a given length of string
is always the same.
3. The motion of a moving body is represented by a line graph known as the distance-time graph.
The distance-time graph helps us to find the distance covered by an object at any instant of time.
The distance-time graph of a body that is moving in uniform motion is always a straight line.
Whereas, the distance-time graph of a body moving in non-uniform motion is not a straight line.
4. In earlier times, people observed the periodically occurring natural events to measure time. For
example, the time period between one sunrise and the next was a unit of time called a day. The
time period between one new moon and the next was called a month. A year is the time taken by
the earth to complete one revolution around the sun.
An object called sundial was used in ancient times to measure the time of the day. It was based on
the principle that as the sun’s position in the sky changes, the position and length of the shadow
cast by an object also changes. It was made by fixing a rod upright on a dial that is made on the
ground or carved from a stone. As the sun’s position changed across the sky, the shadow of the
rod aligned with the hours marked on the dial and indicated the time of the day.
The names of other devices that were used to measure time in earlier days were sand clocks, water
clocks and candle clocks.
5. We can perform the following experiment to show that the time period of a pendulum is constant.
For this we need a string, a small weight (a lock), a support (a hook or doorknob) and a stopwatch.
Now, we will follow the steps given below.
• Take a 1 m long string and tie a weight (lock) at one of its ends.
• Tie the other end of the string to a rigid support (hook or doorknob).
• Wait for the simple pendulum to come to rest at its mean position.
• Displace the bob to the left or right side and release it.
• Using a stopwatch, note the time taken by the bob to complete 20 oscillations. Calculate the
time period of the pendulum by dividing the time taken by the number of oscillations, i.e. 20.
• Perform the activity five times with the same apparatus and calculate the values of time
period.
• It can be observed that the value of time period is the same.
This shows that the time period of a pendulum is constant.

73
 13. Electric Current and Its Effects

Answer Key

In-text Questions
Conductor or Insulator? (Page 177)

Conductors ✓
Insulators ✓ ✓ ✓
Name an insulator that is coated on wires to protect us from electric shocks. _____Plastics______
Is human body a conductor of electricity? Yes ✓    No
Think and Answer (Page 179)
The electric wires used in circuits are covered with plastic or rubber because they are insulators and
protect us from getting electric shock.
Quick Check (Page 180)
1. electric circuit
2. positive, negative
3. OFF
4. cars/inverters
Recalling Circuit Symbols (Page 180)
Component Name Symbol

Cell

Switch in 'OFF' position or

74
 Wire

Switch in 'ON' position or

Bulb

Think and Answer (Page 181)

If air is filled in an electric bulb, then the extremely hot tungsten filament would burn up quickly in
the oxygen of air. So, the electric bulb is filled with a chemically unreactive gas like argon or nitrogen.
Quick Check (Page 185)
1. T
2. F
3. F
4. T
Picture Study (Page 186)
1. Crane
2. Separating magnetic materials in scrapyards
3. Yes
4. Magnetic effect

Apply Your Learning

A. Observe and Draw (Page 187)
Bulb

Switch

Cell

1. Cell 2. OFF 3. No

75
B. Image Study (Page 187)

Microwave oven Electromagnet Bulb Fuse

1. Electromagnet
2. Bulb
3. Microwave oven
4. Fuse
5. CFL
C. Life Skills (Page 188)
1. We can save electricity at home by the following ways.
• Switch off electrical appliances when not in use.
• Use LEDs or CFLs as they are energy efficient.
2. Fuse
3. Refrigerator; iron
4. Solar energy
D. Reason Out (HOTS) (Page 188)
1. Tungsten is used to make filament of electric bulb because it offers a high resistance. It gets
heated to a high temperature and starts glowing. It also has a high melting point.
2. When a copper wire is connected to a battery for some time, it becomes hot due to the heating
effect of electric current. The copper wire offers a little resistance, due to which a portion of
the electrical energy is changed to heat energy.
3. A fuse works on the principle of heating effect of current. The metal that is used to make
the wire of an electric fuse has high resistance and melts when the current flowing through
it exceeds a certain limit. When excess current flows through the fuse wire, it melts and
snaps. This breaks the circuit and the flow of current stops thereby, preventing fires due to
overloading.
E. Link and Learn (Page 188)
Per day electricity consumption in Watt = 14000 W
14000
Units of electricity consumed in a day = = 14 units
1000
Total units of electricity consumed in the month of April = 30 × 14 = 420 units
Total cost of electricity = 7 × 420
= 2940

76
F. Mind Map (Page 188)

Components of Electric Circuit

Electric Component Description

The electric cell is the power source that

Electric cell
provides electrical energy to the circuit.

The battery contains one or more cells that

Battery
convert chemical energy into electrical energy.

The wire is a conductor that connects the

Wire different components of the circuit and allows
the flow of electric current between them.

An electric bulb contains a filament that glows

Electric bulb when current passes through it. The M-shaped
current wire denotes the filament.

The switch is a component that can turn the

• Switch in ON position circuit on or off. When the switch is turned on,
it completes the circuit and allows electricity
• Switch in OFF position to flow from the battery to the bulb. When the
switch is turned off, it breaks the circuit and
stops the flow of electricity.

G. Integrating ICT (Page 189)

Students will do it on their own.
H. Case Study (Page 189)
1. No
2. Electric stove
3. Food processor
4. Coffee machine, frying pan, hotplate (small), microwave oven, toaster, sandwich maker, food
processor
5. Approximately 6800 J

77
Exercises
Stop and Reflect (Page 190)
A. 1. (d) 2. (d) 3. (c) 4. (d) 5. (a)
B. 1. False (A closed path in which electric current flows is called electric circuit.)
2. True
3. False (An oven works on the principle of heating effect of electric current.)
4. False (An electric bell works on the principle of magnetic effect of electric current.)
5. True
C. 1. (d) 2. (e) 3. (a) 4. (c) 5. (b)
D. 1. Tungsten 2. Battery 3. Toaster 4. LED/CFL 5. Fuse
E. 1. Battery
2. Bulb
3. Switch in 'ON' position
4. Wire
5. Switch in 'OFF' position
F. 1. Magnetic effect
2. Heating effect
3. Heating effect
4. Magnetic effect
5. Heating effect
Crisp and Accurate (Page 191)
A. 1. An electric circuit is a closed path, consisting of cell, bulb, switch and connecting wires, along
which electric current flows.
2. Fuse is a safety device in an electric circuit that prevents overloading of current. A fuse works
on the principle of heating effect of current.
3. When a wire is coiled into a series of loops around a metal and electric current is passed
through it, the magnetic field produced is concentrated within the core of the loops. This coil
is called an electromagnet.
4. A diagram that shows the arrangement of different components of an electric circuit with the
help of their respective symbols is called a circuit diagram.
5. A combination of two or more cells is called a battery. In a battery, the positive terminal of one
cell is connected to the negative terminal of the next cell.
B. 1. An MCB is better than a fuse because they are sensitive to the amount of current flowing
through them. The switches in MCBs automatically switch off when the current is too large or
there is a short circuit. Once the problem has been rectified, they can be reset unlike the fuse
that needs to be replaced after a single use.
2. The following factors determine the amount of heat produced in a wire.
• Material of the wire
• Thickness of the wire
• Length of the wire

78
 • Strength of the electric current
3. The strength of an electromagnet depends upon the factors given below.
• The amount of electric current passing through it.
• The number of turns of the wire around the core (an increase in the number of turns
increases the strength of the electromagnet).
4. The two uses of electromagnets are as follows.
• They are used for magnetic separation of iron ore.
• They are used in cranes to pick up magnetic material from scrapyards.
5. An electric bulb is used for light but it also gives heating effect. This is a waste of electrical
energy. Nowadays, wastage of electrical energy is reduced by the use of compact fluorescent
lamps (CFLs) which reduce the heat produced due to lighting.
Think and Explain (Page 191)
1. An electric circuit is a closed path along which electric current flows. It consists of a cell, a bulb and
connecting wires. The different components of an electrical circuit are described as follows.
• Electric cell or battery: The electric cell or battery is the power source that provides electrical
energy to the circuit. The battery contains one or more cells that convert chemical energy into
electrical energy.
• Wire: The wire is a conductor that connects the different components of the circuit and allows
the flow of electric current between them. Wires are typically made of copper or aluminum.
• Electric bulb: The electric bulb is the load that uses the electrical energy provided by the
battery to produce light. When electricity flows through the filament in the bulb, it heats up
and emits light.
• Switch: The switch is a component that can turn the circuit on or off. When the switch is
turned on, it completes the circuit and allows electricity to flow from the battery to the bulb.
When the switch is turned off, it breaks the circuit and stops the flow of electricity.
2. When electric current flows through a wire, a portion of the electrical energy is changed to heat
energy. This causes heating of the wire. This is known as heating effect of current. We can explain
the heating effect of electric current with the help of the following activity.
We need copper wires, knife and a cell. Now, we will follow the steps given below.
• Take a knife and remove the insulation at the ends of a copper wire.
• Connect a cell to the ends of the wire.
• After a few minutes, disconnect the wire from the cell.
• Touch the two ends of the wire
It can be observed that the two ends of the wire become hot. This shows that electric current
produces heat.
3. Fuse is a safety device in an electric circuit that prevents overloading of current. A fuse works on
the principle of heating effect of current. The metal that is used to make the wire of an electric
fuse has high resistance and melts when the current flowing through it exceeds a certain limit.
The metal used to make fuse wire has a melting point lower than the melting point of metals that
are used to make conducting wires. When excess current flows through the fuse wire, it melts and
snaps. This breaks the circuit and the flow of current stops.

79
 4. The magnetic effect of electric current can be explained with the help of the following activity.
We need a piece of cardboard, connecting wires, a cell and a magnetic compass. Now, we will
follow the steps given below.
• Take a rectangular piece of cardboard and make two holes at its two ends.
• Pass a wire through the holes.
• Place a compass between the wire and the cardboard.
• Connect the two ends of the wire to a cell. (Don’t keep the cell connected for more than a few
seconds.)
It can be observed that the compass needle gets deflected. If the wire is disconnected, the
needle comes back to its original position. This shows that when electric current passes through
a conducting wire, it behaves like a magnet. This is the magnetic effect of current.
5. An electric bell is the most common application of electromagnets. It consists of an electromagnet,
a strip of iron, a hammer, a screw, a gong, two switches and connecting wires. The iron strip is in
contact with the screw.
When the bell is rung, the current passes through the circuit and the electromagnet attracts the
iron strip. Then the hammer attached to the strip hits the gong making it ring. The iron strip now
no longer touches the screw. This breaks the circuit. Now, the electromagnet does not attract
the iron strip so it returns back to its original position, i.e. it comes in contact with the screw. This
completes the circuit again and the process repeats. This forward and backward movement of the
iron strip takes place many times in a second producing sound.
Compare the strengths of the four electromagnets and make a report.

80
 14. Light

Answer Key

In-text Questions
Transparency of Objects (Page 192)
Object How Light Passes through the Object Classification
Bag Doesn’t pass Opaque
Glass tumbler Passes completely Transparent
Steel scale Doesn’t pass Opaque
Plastic ruler Passes partially Translucent
Frosted glass door Passes partially Translucent
Wood Doesn’t pass Opaque

Try Indoors (Page 195)

Light gets reflected on the following objects:
Steel plate, mobile phone, mirror
Light does not get reflected on the remaining objects.
We can conclude from this activity that smooth and shiny surfaces reflect light better than rough
surfaces.
Think and Answer (Page 196)
These 11 letters do not show lateral inversion: A, H, I, M, O, T, U, V, W, X, Y.
Quick Check (Page 197)
1. lateral inversion/reflection
2. real
3. absorbed, reflected
4. virtual, erect
Nature of Image (Page 202)
Type of Lens Position of Object Nature of Image
Concave lens Far from the lens Erect, virtual and diminished
Concave lens Near the lens Erect, virtual and diminished
Concave lens Very close to the lens Erect, virtual and diminished
Convex lens Far from the lens Real, inverted and diminished

81
 Convex lens Near the lens Real, inverted and magnified
Convex lens Very close to the lens Virtual, erect and magnified

Think and Answer (Page 203)

When light falls on a soap bubble, some part of it gets reflected and some part gets refracted. The
bubbles appear colourful due to interference between the waves reflected from the top and bottom.
Quick Check (Page 204)
A. 1. Spherical mirrors
2. Plane mirror
3. Convex lens
4. Spectrum
B. 1. Spherical mirrors are called so because of their spherical reflective surfaces.
2. Concave mirrors are used by dentists because they form a magnified image, which helps the
dentists to see the teeth clearly.
3. A converging lens is a convex lens while a diverging lens is a concave lens. Both are different
on the basis of images formed when the object is placed at varied distances from them.
4. The set of colours formed by the splitting of white light is known as spectrum.
5. Lens are used as magnifying glass in camera, spectacles, microscopes and telescopes.

Apply Your Learning

A. Observe and Label (Page 205)
Normal

Angle of Angle of
incidence reflection

Incident ray Reflected ray

Point of incidence

1. Plane mirror
2. No
3. Yes
4. Virtual
5. Both angles are equal.
B. Image Study (Page 205)
1. concave, magnified/enlarged
2. headlights, concave
3. side view mirror, convex, large

82
C. Life Skills (Page 206)
1. We should help them by buying them spectacles that can correct their eye defects.
2. Presbyopia
3. Convex lens is used to correct presbyopia.
D. Reason Out (HOTS) (Page 206)
1. Nothing will happen to the size of the image, if the size of the plane mirror is changed.
2. No, we cannot use a concave mirror as a rear view mirror because it forms a real and inverted
image and it would be difficult for the driver to judge the correct position of the vehicle
coming from behind.
3. Following are the types of mirrors.
(a) Plane mirror
(b) Concave mirror
(c) Convex mirror
4. When sunlight is focused on a paper through a convex lens, a real image of the sun forms and
the paper burns. This is because the sun's heat is concentrated at a point on the paper, which
is also the principal focus of the lens.
E. Link and Learn (Page 206)
1. Obsidian 2. Copper 3. Aranmula Kannadi
F. Mind Map (Page 206)

Types of Mirrors

Plane mirror Convex mirror Concave mirror

Reflecting surface is Reflecting surface is Reflecting surface is

plane curved outwards curved inwards

Used to make Used to make rear Used by dentists to

periscopes view mirrors examine teeth

G. Integrating ICT (Page 207)

Students will do it on their own.
H. Case Study (Page 207)
1. 15 cm
2. 15 cm
3. At point C, i.e. at 20 cm
4. From the graph it can be observed that the image distance decreases as the object distance
increases.

83
Exercises
Stop and Reflect (Page 208)
A. 1. (b)
2. (d)
3. (d)
4. (c)
5. (d)
B. 1. True
2. False (Light travels in straight lines.)
3. False (Convex lens is called converging lens.)
4. False (White light is composed of seven colours.)
5. True
C. 1. (e) 2. (d) 3. (a) 4. (b) 5. (c)
D. 1. Concave mirror
2. Concave/Convex lens
3. Convex mirror
4. Plane mirror
5. Concave mirror
E. 1. Mirrors have a reflecting surface while lens do not have reflecting surfaces.
2. Convex mirror forms virtual images while concave mirror generally forms real images.
3. Concave lens is a diverging lens while convex lens is a converging lens.
4. Plane mirror always forms a virtual image while concave mirror generally forms a real image.
5. Prism disperses light to form spectrum while plane mirror reflects light to form image.
F. 1. Used in torches 2. Used in binoculars
3. Used in side view mirror 4. Used in magnifying glass
5. Used in making periscope
Crisp and Accurate (Page 209)
A. 1. The bouncing back of light from the surface of an object is called reflection.
2. A real image is the image that can be taken on a screen.
3. A lens is a piece of transparent material (like plastic or glass) that has one or both the surfaces
spherical.
4. The phenomenon of splitting of white light into different colours is known as dispersion of
light.
5. The set of colours formed by the splitting of white light is known as spectrum.
B. 1. Convex mirrors are used as side view mirrors because they form a virtual, erect and diminished
image. This helps the driver to see a wide area in the side view mirror.
2. A real image can be taken on a screen. An example of a real image is the image formed on a
screen by a projector in a theatre. On the other hand, a virtual image cannot be taken on a
screen. An example of a virtual image is the image formed by a plane mirror.

84
 3. AMBULANCE is written in inverted letters on an ambulance van. This is because when the
driver of a vehicle in front of the ambulance looks in the rear view mirror, it will appear laterally
inverted as AMBULANCE and he can make way for it.
4. Convex lens is known as converging lens and concave lens is known as diverging lens.
5. A rainbow appears in the sky after rain in the morning or evening when the sun is low in the
sky. When sunlight passes through the water droplets, it splits into seven different colours
forming a rainbow.
Think and Explain (Page 209)
1. To show that light travels in a straight line, we need to roll a chart paper to form a pipe. Now, light
a candle and look at its flame through the pipe. Now, bend the tube and look again. It can be
observed that we were not able to see the flame of the candle through the bent pipe. This shows
that light travels in a straight line.
2. Mirrors that have a curved surface are known as spherical mirrors. They are called so as they are a
part of a complete sphere. There are two types of spherical mirrors—concave mirror and convex
mirror. A concave mirror generally forms a real, inverted and diminished image. The nature of
image formed is virtual, erect and magnified when the object is placed very close to the mirror.
On the other hand, a convex mirror always forms a virtual, erect and diminished image.
3. Following are some of the uses of spherical mirrors.
• Concave mirrors are used by dentists to see enlarged images of the teeth.
• Concave mirrors are used in make-up and shaving mirrors.
• Convex mirrors are used as rear view or side view mirrors in cars and scooters.
• Concave mirrors are used as reflectors in the torches and headlights of automobiles.
4. The difference between concave lenses and convex lenses are as follows.
Convex Lens Concave Lens
It is thicker in the middle and tapering at the It is thicker at the edges and thinner in the
edges. middle.
It converges the rays of light. It diverges the rays of light.
It generally forms real and inverted image. It always forms virtual and erect image,
However, it forms a virtual, erect and smaller in size than the object.
magnified image when the object is placed
very close to the lens.
5. To explain the splitting of white light through a prism, we need a source of narrow beam of light
(like a small hole in the window), a prism and a white screen or white wall. Now, we will follow the
steps given below.
• Place a prism in a dark room such that a narrow beam of light through a small hole in the
window falls on it.
• Place a white screen on the other side of the prism.
• Allow the beam of light to pass through the prism and fall on the white screen.
• Observe the pattern of the light coming out of the prism.
It can be observed that the light splits to form a spectrum that can be seen on the white screen.

85
 15. Winds, Storms and Cyclones

Answer Key

In-text Questions
Air and Its Composition (Page 210)

Carbon dioxide, water vapour

and other gases

Oxygen

Nitrogen

1. The atmosphere consists of 78% nitrogen, 21% oxygen and 1% other gases and water vapour.
2. Oxygen
3. Carbon dioxide
4. Oxygen
Think and Answer (Page 213)
During winters, the pressure of the air left inside the jar falls and the metal on the lid pops downwards.
The higher atmospheric pressure outside the jar keeps the metal lid depressed and makes it more
difficult to open the jar.
Try Indoors (Page 214)
1. No
2. The balloon does not get inflated due to high pressure of air inside the bottle.
3. Yes
4. The air pressure inside the bottle gets reduced due to the hole which allows air to pass through it
during inflation of the balloon.
Quick Check (Page 214)
1. pressure 2. decreases
3. increases 4. heating

86
Think and Answer (Page 215)
In winter, wind blows from land to the sea at the equator because in winter, the air pressure above the
sea is less than the air pressure above land. So, wind from land comes to fill the low pressure area above
the sea.
Quick Check (Page 218)
1. F 2. T 3. T
4. The answer can be true or false depending upon the speed of wind in a tornado. Most of the
tornadoes are weak and have speeds less than 100 m/h. However, tornadoes can also be strong
and cause huge damage.
Picture Study (Page 219)
A: Thunderstorm; B: Cyclone
1. A 2. B
3. Eye of the storm 4. Hurricane

Apply Your Learning

A. Cyclones and Destruction (Page 220)
1. A storm that develops over the sea and has high-speed winds revolving around a low pressure
centre, called the eye of the storm, is called a cyclone.
2. Cyclones are created due to the differences in air pressure. A cyclone is formed when a system
of winds moving in circular motion closes in towards an area of the sea with low atmospheric
pressure.
3. Hurricanes and typhoon
4. India Meteorological Department predicts cyclones in India.
B. Activity Corner (Page 220)
hot; cold; P; Q; increased; decreased; expands; heating
C. Life Skills (Page 221)
1. Tamil Nadu and West Bengal
2. Following precautions should be taken in case of a cyclone.
• Warnings issued by the meteorological department through TV, radio or newspapers
should not be ignored.
• People who live in cyclone prone areas should make arrangements to shift necessary
household goods, domestic animals and vehicles to safer places.
• One must not touch wet electrical switches or electric wires.
• People must not drive on roads that are submerged in water.
3. School children can help cyclone-affected people by donating food and other items such as
blankets and medicines.
D. Reason Out (HOTS) (Page 221)
1. Holes are made in hoardings in order to tackle the air pressure due to the wind. The air flows
through these holes made on the hoardings and reduces the pressure on them. In this way
the hoardings do not get blown away or torn apart due to air pressure.

87
 2. Ventilators are made near the ceiling to let out the hot air from a room. Hot air being light,
rises and escapes through the ventilators while fresh air enters through the windows and
doors of the room.
E. Link and Learn (Page 221)
1. Three types of winds
S. No. Types of Wind Other Names
1 Primary wind Planetary wind
2 Secondary wind Periodic wind
3 Tertiary wind Local wind
2. Polar winds
3. Seasonal/periodic winds
F. Mind Map (Page 222)

Natural Disasters Caused by Winds

Thunderstorm Cyclone Tornado

• V  iolent and
short period of • Develops over sea
• Violently rotating
disturbance • High-speed winds dark column of air
• Speedy winds revolving around a
low pressure centre • Extends from sky to
• Heavy rainfall the surface of the
• Cause a lot of earth
• Thunder and destruction
lightning

Precautions Precautions Precautions

• Stay indoors • Take warnings • Close the doors and
• Do not lie on seriously windows
ground • Stay away from wet • Sit under a bed/
• Do not sit near the electrical switches/ table
window wires • Bow down on
• Do not use • Do not drink knees to protect
umbrella with contaminated head and neck
metallic handle water • Must take shelter
• Must cooperate in room without
with rescue force windows or in
basement

88
G. Integrating ICT (Page 222)
Students will do it on their own.
H. Case Study (Page 222)
1. Eastern coast
2. November
3. January, February and March
4. June
5. Tamil Nadu, West Bengal, Andhra Pradesh, Odisha and Gujarat

Exercises
Stop and Reflect (Page 223)
A. 1. (b) 2. (b) 3. (d) 4. (c) 5. (a)
B. 1. True
2. False (We should not sit near a window during a thunderstorm.)
3. True
4. False (Tornadoes are not very frequent in India.)
5. True
C. 1. (d) 2. (a) 3. (e) 4. (c) 5. (b)
D. 1. Eastern coast
2. Buildings
3. Waterspout
4. 10-30 km
5. Typhoon
E. 1. Hot air rises up
2. Air exerts pressure
3. Air pressure decreases when wind speed increases
4. Air expands on heating
F. 1. cyclone
2. weather
3. Meteorological
4. thunderstorm
Crisp and Accurate (Page 224)
A. 1. Tornado is a violently rotating, dark column of air that extends from the sky to the surface of
the earth.
2. A storm that develops over the sea and has high-speed winds revolving around a low pressure
centre, called the eye of the storm, is called a cyclone.
3. Weather vane or wind vane is an instrument that is used to detect the direction of the winds.
4. Anemometer is an instrument that is used to measure the speed of wind.
5. A violent, short period disturbance in weather conditions that is characterised by speedy
winds, heavy rainfall, thunder and lightning is known as thunderstorm.

89
B. 1. The factors responsible for the generation of wind are uneven heating of the poles and the
equator, and uneven heating of land and water.
2. Following are the two precautions that are to be taken during a tornado.
• We must close the doors and windows of the house, and sit under a bed or table.
• We must bow down on our knees so as to protect our head and neck.
3. Cyclones occur worldwide and are known by different names in different regions. They are
known as hurricane in America, and typhoon over the Western Pacific regions like Japan and
Philippines.
4. When we blow air between two balloons that are tied at a distance of 10 cm from each other,
the air pressure between the balloons decreases. The higher pressure that lies outside the
two balloons pushes them close to each other.
5. Eye of the cyclone refers to the low pressure centre around which the high-speed winds
revolves in a cyclone.
Think and Explain (Page 224)
1. We can perform the following experiment to show that air pressure reduces when wind speed
increases.
We need a wide-mouthed bottle and a paper ball smaller than the mouth of the bottle. Now, hold
the bottle horizontally and place the paper ball inside the mouth of the bottle. Blow on the paper
ball so that it moves into the bottle. You will not be able to do so.
When you blow air inside the bottle, the air near the ball has higher speed which decreases the air
pressure in this area. The pressure inside the bottle is higher and it pushes the paper ball out, thus
preventing it from entering the bottle.
2. With the help of following experiment, we can show that air expands on heating.
We need a balloon, a cellotape, a test tube, a beaker, hot water and ice cubes. Now, we will follow
the steps given below.
• Stretch a balloon tightly over the mouth of a test tube and secure it with the help of cellotape.
• Keep the test tube in a beaker containing hot water.
• Observe the size of the balloon. It can be observed that the size of the balloon increases when
the test tube was kept in the hot water beaker. This is because the air expands on heating and
hence occupies more space filling up the balloon.
• Now, place the test tube in a beaker containing ice cubes. Observe the size of the balloon
again. The size decreases when it was kept in the cold water beaker. This is because the air
contracts upon cooling, thus decreasing the size of the balloon.
3. Thunderstorms develop quite frequently in hot and humid tropical areas like India. Due to the
high temperatures, air near the land heats up and generates strong upward rising winds. The
water vapour that gets carried upwards by these winds gets condensed rapidly and forms tiny
droplets of water which freeze at higher altitudes. The ice crystals and water droplets fall down.
On their way, they collide with the rising hot air. This leads to lightning accompanied by thunder
and heavy rainfall. The upward motion of hot air and the downward motion of cold air leads to
stormy winds.
4. Following are the precautions that are to be taken during a thunderstorm.
• We must stay indoors and close all the doors and windows.
• We must not take shelter under an isolated tree or a metal shed. We must not lie down on the
ground.
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 • We must not use an umbrella with a metallic handle.
• We must not sit near a window.
• If we are in a swimming pool, we must get out immediately and take shelter in a nearby
building.
• A car or a bus is a safe place to take shelter with its windows closed.
5. Following are the safety measures that are to be taken by the people before a cyclone.
• Warnings issued by the meteorological department through TV, radio or newspapers should
not be ignored.
• People who live in cyclone prone areas should make arrangements to shift necessary
household goods, domestic animals and vehicles to safer places.
• Phone numbers of all emergency services like police, fire brigade, ambulance and hospitals
should be kept handy.

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 16. Water—A Precious Resource

Answer Key

In-text Questions
Natural Disasters (Page 225)
1. Picture A: Drought caused due to scarcity of water
Picture B: Flood caused due to excess of rain
2. A
3. B
4. A
Think and Answer (Page 226)
Earth is called blue planet because nearly 71 Percentage of the planet is covered with water.
Think and Answer (Page 227)
Water is called a renewable natural resource because it replenishes itself through water cycle.
Observe and Answer (Page 228)
1. Water cycle
2. Rainwater
3. Yes
4. This process keeps the amount of water on the earth constant.
5. Evaporation
Quick Check (Page 229)
1. T 2. F 3. F 4. T
Quick Check (Page 232)
1. rainfall 2. groundwater 3. drip irrigation 4. bawaris
Water Pollution (Page 231)
1. The contamination of water bodies due to human activities is called water pollution.
2. Rivers and oceans
3. When polluting substances, like sewage, are dumped into the oceans, the aquatic animals that
depend on the ocean to survive, such as fish, die. This is because the animals get exposed to
toxic chemicals which can damage the organs of the animals. Water pollution can also lead to a
decrease in oxygen levels in the water, which can suffocate aquatic animals.
4. Following are the ways to reduce water pollution.
• Waste materials should be disposed of properly.
• Use biodegradable detergents and cleaners that do not contain harmful chemicals.

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 • Natural pest control methods should be used instead of chemical pesticides, which can be
harmful to aquatic life.
• Ensure that hazardous waste is disposed of correctly and not dumped into waterways.

Apply Your Learning

A. Identify and Answer (Page 233)

Hand pump Tube well Well

1. Village
2. Groundwater
3. Water table
4. Natural spring
B. Water Management (Page 233)
1. P
2. Drip irrigation
3. This technique is useful for water conservation because water is supplied to plants drop by
drop thereby avoiding wastage.
4. Q
5. Yes, hydroelectricity is generated through this construction i.e. dam.
C. Life Skills (Page 234)
1. It is important to save water because it is a precious resource necessary for the survival of all
living beings.
2. Yes, water scarcity affects plants as they need water to make food and to grow.
3. Rainwater harvesting
4. We can save water at home by using a bucket and a mug to bath instead of a shower, and
keeping the tap closed while brushing and shaving.
D. Reason Out (HOTS) (Page 234)
1. We should use a bucket and a mug while taking a bath instead of using a shower because
using shower results in wastage of water.
2. The temperature of groundwater does not change, however the temperature of the
atmosphere changes. In winter, the atmosphere becomes cold and hence the water from a
hand pump feels warm as its temperature is comparatively high.
E. Link and Learn (Page 234)
1. An ocean is a large body of saltwater that covers most of the earth's surface. It is a complex
and dynamic ecosystem that supports a wide variety of plant and animal life.

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 2. The five major oceans are Pacific ocean, Atlantic ocean, Indian ocean, Arctic ocean, and Southern
(Antarctic) ocean.
3. Indian ocean
4. Arctic ocean
5. Oceans are important due to the following reasons.
• Climate regulation: Oceans help regulate the earth's climate by absorbing and storing
heat, and distributing it around the globe through ocean currents.
• Biodiversity, food and resources: Oceans are home to a wide range of marine life,
which is the source of food and livelihood for many people. Oceans also provide oil,
minerals and other valuable resources.
F. Mind Map (Page 235)

Sources of Water

Rainwater Surface water Groundwater

Purest form of water • River and lake • Infiltration of rainwater

water: melting of  Infiltration: The process by
snow and rains which water seeps deep below
• Seas and oceans: the ground
contains salt Water table: The level of
groundwater
 Aquifer: Groundwater that
gets collected between the
layers of hard rocks below the
water table

G. Integrating ICT (Page 235)

Students will do it on their own.
H. Case Study (Page 235)
1. Depleting water resources due to increase in demand is majorly responsible for water crisis.
2. 21%
3. Water scarcity has the following effects on the quality of life.
• Food crops are destroyed and animals die, which leads to famines and droughts.
• People have to migrate to other places in search of water and food.
4. Uttar Pradesh and Rajasthan

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Exercises
Stop and Reflect (Page 236)
A. 1. (d) 2. (c) 3. (d) 4. (a) 5. (d)
B. 1. False (Water cycle keeps the amount of water on the earth constant.)
2. True
3. False (Water is a renewable natural resource.)
4. True
5. True
C. 1. (d) 2. (e) 3. (b) 4. (a) 5. (c)
D. 1. Rainwater
2. Saline water
3. Drip irrigation
4. Aquifer
5. Water table
E. 1. Saline
2. harvesting
3. interchanged
4. infiltration
F. 1. Lakes, rainwater
2. Wells, tube well
3. Cooking, bathing
4. Deforestation, increasing population
5. Prevent leakages, using a bucket and mug for bathing
Crisp and Accurate (Page 237)
A. 1. The level of groundwater is called water table.
2. Groundwater also gets collected between the layers of hard rocks below the water table. This
is known as an aquifer.
3. Groundwater may run along the surface of non-porous rocks and come out of the surface
with pressure in the form of a spring. This is known as natural spring.
4. The continuous circulation of water from the earth to the atmosphere and back to the earth
is known as water cycle.
5. Bawaris are deep wells dug in the soil. There are steps to access the collected water.
B. 1. Following are the four ways in which water is useful to us.
• It is necessary for the survival of living beings.
• It helps us to carry out daily life activities like cooking, bathing and washing.
• It is used in industries for manufacturing goods like textiles and in agriculture.
• It is used to generate hydroelectricity.
2. Water cycle keeps the amount of water constant on the earth.
3. Rainwater, surface water and groundwater are the different sources of water.

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 4. Yes, agricultural activities contribute to depletion of water table. Farmers use groundwater
for irrigation during the absence of regular rains and proper irrigation systems. This leads to a
decline in the level of water table.
5. In plants, water is required for photosynthesis and germination of seeds. It also helps to
transport nutrients to various parts of the plant body.
Think and Explain (Page 237)
1. In nature, water exists in the following forms.
• Solid state: Water exists as snow on high mountains and glaciers, and as ice caps at the poles.
• Liquid state: Water exists as liquid in rivers, lakes, seas, oceans and underground.
• Gaseous state: Water exists as vapour present in the atmosphere.
2. There is a scarcity of water in many parts of the world even though a major part of the earth is
covered with water. It is because 96.5% of the water found on the earth is saline water as it is
present in seas and oceans. Of the total water present on the earth, only 2.5% is freshwater. 98.8%
of this freshwater is in the form of ice. Less than 0.3% of the total freshwater is available to us, and
is found in rivers, lakes and as water vapour in air. Therefore, only a small amount is available for
human use. Hence, we should use water judiciously.
3. The main sources of water are rainwater, surface water and groundwater.
• Rainwater: The purest form of water is rainwater. However, when it falls on the earth, it
becomes polluted with gases and dust particles present in air.
• Surface water: Water in rivers, lakes, oceans and seas come under surface water.
➢ River and lake water: This water comes from the melting of snow on the mountains
and from rain.
➢ Seas and oceans: They cover 70% of the earth’s surface. The seawater is salty and is
known as saline water. This water is unfit for drinking, washing, irrigation and for
industrial purposes.
• Groundwater: Rainwater seeps through the soil into non-porous rocks and collects under the
ground. This water is known as groundwater or underground water. The level of groundwater
is called water table.
4. The factors responsible for the depletion of water table are as follows.
• Scanty rainfall: India largely depends on rainfall for water. The monsoon season lasts for only
a few months. There is unequal distribution of rainfall in India. There are floods and droughts
every year in some parts of the country.
• Increasing population: An increase in population has led to an increase in the demand of
water. Large amounts of water are required for the construction of houses, shops, offices and
roads. This decreases the seepage of rainwater into the ground. The water table has reduced
to alarmingly low levels in certain parts of our country.
• Increasing industries: All industries require water for different activities, for which generally
groundwater is used. With increase in the number of industries, the demand for underground
water has increased. This leads to the depletion of water table.
• Agricultural activities: Farmers use groundwater for irrigation during the absence of regular
rains and proper irrigation systems. This leads to a decline in the level of water table.
• Deforestation: This results in low seepage of rainwater and hence the replenishment of
groundwater becomes difficult.

96
5. Following steps should be taken to reduce wastage of water.
• Water is supplied through a network of pipes at some places. These pipe systems are managed
by civic authorities and it is their responsibility to ensure that there are no leakages in the
supply lines. In case of any leakage, they must be informed immediately.
• While brushing your teeth, shaving or washing clothes, do not leave the tap running. Leaking
taps must be repaired immediately. Mug and bucket should be used to take a bath or wash
vehicles.
• Farmers should use better methods of irrigation, like drip irrigation. In this type of irrigation,
water is supplied to plants drop by drop instead of filling the entire field with water.
• Polluted water should be recycled and used for irrigation.
• Rainwater harvesting is done by allowing rainwater that falls on roofs of buildings to flow into
a deep trench in the ground.
• Trees should be planted to slow down the flow of rainwater on land and to increase seepage
of water into the soil.

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 17. Forests

Answer Key

In-text Questions
Forests (Page 238)
equator; rainfall; forests; predator; tiger
Do and Learn (Page 240)
Students will do it on their own.
Quick Check (Page 242)
1. F 2. T 3. F 4. T
Observe and Rectify (Page 243)
Grass Rat Snake Eagle
Think and Answer (Page 243)
Plants depend on animals for pollination to prevent overcrowding and scarcity of resources necessary
for survival of the plants. Animals such as bees, butterflies and birds can transport pollen from one
flower to another allowing for cross-fertilisation between plants. This process is essential for the survival
and reproduction of many plant species.
Think and Answer (Page 244)
Afforestation can help prevent floods by increasing the amount of vegetation cover and reducing the
amount of water run-off during heavy rainfall. Trees and other vegetation can absorb and retain large
amounts of water, which can help to reduce the volume of water that flows downstream and cause
flooding.
Quick Check (Page 244)
1. plants 2. food web
3. global warming 4. overgrazing
Picture Study (Page 245)
1. City A has trees and plants while city B lacks them. Thereby, city A has a better environment and
has lesser pollution than city B.
2. B
3. A
4. A
5. A or B (Students will do it on their own.)

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Apply Your Learning
A. Observe and Answer (Page 246)
1. Picture A depicts deforestation and picture B depicts overgrazing by cattle.
2. Overgrazing and deforestation result in soil erosion.
3. Yes, deforestation causes natural calamities like flood.
4. We can conserve forests by afforestation and by preventing overgrazing.
B. Form a Food Web (Page 246)

1. A food web is a representation of interlinked food chains in an ecosystem.

2. Consumer
3. Yes, because plants are the producers. All the living beings are directly or indirectly dependent
on plants for their food. If the number of plants gets reduced then the consumers will die due
to shortage of food.
C. Life Skills (Page 247)
1. We obtain things like rubber, timbre and honey from forests.
2. During the process of photosynthesis, plants take in carbon doxide and release oxygen,
thereby purifying air. The released oxygen is used by both plants and animals for respiration
to release carbon dioxide gas. In this way, plants help to maintain the balance of oxygen and
carbon dioxide in the atmosphere.
3. During the process of transpiration, plants release water vapour into the air. This water
vapour rises in the atmosphere, cools down and forms clouds. The clouds eventually release
the condensed water back to the ground as precipitation, which can then be absorbed by the
soil and taken up by trees once again. This helps to maintain the water cycle.
4. Deforestation will lead to increased amounts of carbon dioxide in the atmosphere. This causes
a rise in the temperature of the earth and leads to global warming. Many species of plants
and animals cannot survive in such high temperatures and may die. It will also result in loss of
food and shelter for animals and other living organisms.

99
D. Reason Out (HOTS) (Page 247)
1. No, rabbits and wolfs do not occupy the same position in a food chain. This is because rabbit
is a herbivore i.e. a primary consumer while wolf is a carnivore i.e. a secondary consumer.
2. No, we will not be able to survive without forests. This is because we are dependent on forests
for food, oxygen and other resources like wood.
3. Decomposers are very importants as they help in the decomposition of dead and decaying
matter. If all the decomposers die then it will cause piling up of dead bodies of plants and
animals that could not be broken down and recycled. This leads to accumulation of toxic
substances in the environment which could lead to poisoning of plants, animals and ultimately
humans.
E. Link and Learn (Page 247)
1. Tropical evergreen forest, tropical deciduous forest and temperate forest
2. Monsoon forest is the other name of tropical deciduous forest.
3. These trees adapt themselves to dry summer with the help of their thick barks, broad leaves,
long roots and wax-coated leaves which help them to reduce transpiration.
4. Pine and oak trees are found in temperate deciduous forests.
F. Mind Map (Page 248)

Forests

Uses Deforestation Conservation

• Increases the amount of

• Acts as a food source • Afforestation
carbon dioxide
• Maintain water table • Prevention of overgrazing
• Lack of food and shelter for
• Purifies air by taking animals • Planned cultivation and
in carbon dioxide use of agricultural land
• Leads to natural calamities
and releasing • Encouraging conservation
like flood and landslides
oxygen programmes like Van
• Amount of rainfall would be
• Prevent soil erosion Mahotsav
affected

G. Integrating ICT (Page 248)

Students will do it on their own.
H. Case Study (Page 248)
1. 2001
2. 1997
3. 1999
4. Madhya Pradesh

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Exercises
Stop and Reflect (Page 249)
A. 1. (b) 2. (b) 3. (d) 4. (a) 5. (c)
B. 1. True
2. False (Animals depend on forests for food and shelter.)
3. True
4. False (Plants act as producers in a food chain.)
5. True
C. 1. (e) 2. (a) 3. (b) 4. (d) 5. (c)
D. 1. Crown
2. Oxygen
3. Understorey
4. Consumers
5. Scavengers
E. 1. Conservation
2. Destruction
3. Destruction
4. Conservation
5. Destruction
F. 1. Neem, mango
2. Owl, lizard
3. Beetles, ants
4. Monkey, sloth
5. Fungi, bacteria
Crisp and Accurate (Page 250)
A. 1. A canopy is formed when the branches of tall trees form a roof over the other plants. The
height of trees in this layer is about 100 feet.
2. Organisms, like bacteria and fungi, which feed on the dead remains of plants and animals are
known as decomposers.
3. Large-scale planting of trees is known as afforestation. It helps to prevent soil erosion, global
warming and reduction in rainfall.
4. Animals that feed on the dead bodies of other animals are called scavengers.
5. The plant layers found at different heights below the canopy are called understoreys.
B. 1. A food chain is a chain of organisms in which one organism eats another organism.
2. The rise in the temperature of the earth due to increase in carbon dioxide in the atmosphere
is called global warming.
3. The forest floor is covered with moist, warm, dead and decaying matter of leaves, twigs, fruits
and seeds. Hence, it is dark in colour.
4. Decomposers get food from the dead remains of plants and animals, and convert them into
nutrient-rich humus. These nutrients are released back into the soil and then utilised by the
plants. Therefore, decomposers are helpful for the environment.

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 5. Trees hold on to the particles of soil through their root system and prevent soil from being
carried away by agents like wind or water, thereby preventing soil erosion.
Think and Explain (Page 250)
1. Following are the ways in which forests are useful to us.
• Food source: All living organisms depend directly or indirectly on plants for their food.
• Source of many useful products: Forests give us timber, fibre, paper, firewood, honey, gum,
resins, dyes, medicines, spices, perfumes and fodder for animals.
• Prevention of soil erosion: Trees hold on to the particles of soil through their root system and
prevent soil from being carried away by agents like wind or water.
• Regulate climate and water cycle: During the process of transpiration, plants release water
vapour into the air. This helps to keep the air cool, and leads to cloud formation and rainfall.
This helps to maintain the water cycle.
• Provide food, shelter and protection: Forests provide a habitat to a large number of animals
like monkeys, lions, elephants, tigers, jackals, deers and squirrels. A wide variety of trees,
shrubs, herbs, creepers and climbers are also found in forests.
2. Following are the consequences of deforestation.
• There would be lack of food and shelter for animals.
• There will be natural calamities such as landslides and floods.
• We will not get valuable products like timber, fuel, wood and medicinal plants.
• The amount of rainfall would be affected.
• The amount of carbon dioxide in the air will increase, resulting in global warming.
3. Forests help to maintain gases in the atmosphere. During the process of photosynthesis, plants
take in carbon dioxide and release oxygen, thereby purifying air. The released oxygen is used
by both plants and animals for respiration to give out carbon dioxide. In this way, plants help to
maintain the balance of oxygen and carbon dioxide in the atmosphere.
4. Animals obtain nutrients from plants. Animals that feed on the dead bodies of other animals are
called scavengers. When animals die, scavengers like vultures, eagles, jackals and crows feed on
their dead bodies.
A number of bacteria and fungi feed on the dead remains of plants and animals. These organisms
are known as decomposers. They get food from the dead remains of plants and animals, and
convert them into nutrient-rich humus. Decomposers make sure that the nutrients are released
back into the soil. These nutrients are then utilised by the plants and this process goes on. This
cycle continues and the nutrients are recycled.
5. Following are the ways to conserve forests.
• Overgrazing by cattle must be prevented.
• Planned cultivation and wise use of agricultural land should be done.
• Illegal cutting of trees must be stopped.
• Conservation programmes such as Van Mahotsav must be encouraged.

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 18. Wastewater Management

Answer Key

In-text Questions
Biodegradable or Not? (Page 251)
1. Paper is biodegradable while plastic bottle is non-biodegradable.
2. Paper
3. We can reuse and recycle plastic bottles instead of throwing them away.
Picture Study (Page 253)
1. Eutrophication is the process in which a water body becomes enriched with nutrients, leading to
plentiful growth of algae. The excessive growth (or bloom) of algae blocks sunlight from reaching
the deeper parts of water which can prevent the growth of other aquatic plants and can also
reduce oxygen levels in the water.
2. Algae
3. These algal blooms hinder the flow of sunlight to the bottom of the aquatic body and also reduce
the dissolved oxygen levels in the water. Due to this, many marine animals suffocate and die.
Quick Check (Page 255)
1. T 2. F 3. F 4. T
Quick Check (Page 257)
1. disposal
2. waterborne
3. chemical
4. vermicomposting

Apply Your Learning

A. Waste Separation (Page 258)
Waste Waste Bin Waste Waste Bin
Crushed plastic bottle Red Broken wine bottle Green
Old newspaper Blue Torn pages of book Blue
Tin can Yellow Broken copper jar Yellow
Plastic jar Red Empty soft drink glass bottle Green
B. Observe and Answer (Page 258)
1. septic 2. sewage 3. Anaerobic
4. sludge; lighter waste 5. 4-5 months

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C. Life Skills (Page 259)
1. Poor hygienic practices and inadequate sewage systems are two causes of poor sanitation.
2. Cholera and typhoid are waterborne diseases.
3. We can prevent waterborne diseases by implementing proper sanitation practices and
drinking clean water.
4. Chemical toilet
D. Reason Out (HOTS) (Page 259)
1. Yes, the contamination of drinking water can occur in this case also. This is because the joints
between the sewage lines may be leaky and can lead to the leakage of sewage thereby
contaminating nearby water bodies from where the pipes originate.
2. If we throw plastic bags on the roadside then they cause environmental pollution. They can
also get into drains and sewers which blocks them causing the dirty drain water to flow on
the roads.
3. When sewage gets collected in pits, it can seep into the surrounding soil and contaminate
nearby water sources such as lakes, rivers and groundwater. This can lead to the spread of
waterborne diseases and can also harm aquatic life.
E. Link and Learn (Page 259)
1. Prime Minister Narendra Modi launched the 'Swachh Bharat Abhiyan'.
2. 2 October 2014
3. The aim of Swachh Bharat Abhiyan is to improve the cleanliness and sanitation conditions
across India, with a focus on building toilets, promoting cleanliness in public areas, and
ending open defaecation.
F. Mind Map (Page 259)

Wastewater Management

Sources of Steps Involved in Alternate Methods of

Wastewater Treatment Sewage Disposal

• Wastewater passed through bar

screen
• Water passed to grit and sand
removal tank
• Water sent to water clarifier to
• Homes separate organic wastes
• Septic tanks
• Hotels • Digestion of sludge to produce
biogas • Chemical toilets
• Industries
• Air passed through clarified water • Vermicomposting
• Hospitals
toilets
• Offices • Upper layer of clean water
discharged into water bodies

104
G. Integrating ICT (Page 260)
Students will do it on their own.
H. Case Study (Page 260)
1. Odisha
2. Maharashtra
3. West Bengal, Madhya Pradesh and Tamil Nadu
4. Gujarat

Exercises
Stop and Reflect (Page 261)
A. 1. (a) 2. (c) 3. (c) 4. (d) 5. (c)
B. 1. True
2. False (Typhoid is a waterborne disease.)
3. True
4. False (Biogas contains methane and carbon dioxide.)
5. True
C. 1. (c) 2. (a) 3. (e) 4. (b) 5. (d)
D. 1. Contaminants
2. Sewer
3. Potable water
4. Biogas
5. Vermicomposting toilet
E. 1. A boy throwing a crushed plastic bottle in the dustbin ✓
2. A girl eating chips and throwing the packet on the road 7
3. A man spitting on a wall 7
4. A woman telling her child to keep the broken toy in his bag instead of throwing it on
the seat ✓
5. A boy spilling a cup of tea on a table 7
F. 1. Cholera, typhoid
2. Nitrates, phosphates
3. Plastic cans, sticks
4. Vermicomposting toilet, septic tank
Crisp and Accurate (Page 262)
A. 1. The dirty water that goes down the drains from the kitchen sinks and bathrooms is called
wastewater.
2. Sewage is the wastewater generated by a town.
3. The network of small pipes that carry wastewater from its point of production to its point of
disposal is known as sewer.
4. The clean water that we consume is known as potable water.

105
 5. The solid organic material such as faeces that settle at the bottom of the water clarifier tank is
known as sludge.
B. 1. Wastewater should be treated before it flows into rivers because wastewater contains a
number of contaminants that adversely affect the aquatic ecosystems as well as cause various
diseases in human beings.
2. Chemicals like cleaners, grease, paints, beauty products and medicines should not be poured
down the drains because they destroy the microorganisms that help in purifying water.
3. Bar screens help to remove large-sized objects such as sticks, rags, cans and plastic packets
when wastewater is passed through it.
4. Vermicomposting toilets are a new technique in which human excreta is transformed into
vermicakes by the action of redworms. Vermicakes or vermicompost can be used as manure
in fields. The amount of water required for processing is little. The operation is simple, safe
and hygienic.
5. Biogas is a mixture of gases mainly consisting of methane and carbon dioxide. It is obtained
by anaerobic decomposition of human and animal excreta.
Think and Explain (Page 262)
1. Wastewater is allowed to flow into a tank known as water clarifier. This tank is large and sloped
inwards so that solid organic materials such as faeces settle at the bottom of the tank. This settled
organic matter, also known as sludge, is removed by scrapers. Oil and grease that floats on top is
removed with the help of a skimmer. The cleared water thus obtained is known as clarified water.
2. The steps involved in the secondary treatment of wastewater are as follows.
• The sludge that was produced during primary treatment is transferred to a tank where
anaerobic bacteria convert it into biogas and humus-like material. This process is known as
digestion. Biogas can then be used as a fuel or to generate electricity. The digested sludge is
dried and used as fertiliser in agriculture.
• Air is passed through the clarified water. Aerobic bacteria grow in the presence of air and
consume the remaining wastes. The suspended microbes settle at the bottom of the tank as
activated sludge which is about 97% water. It is dried on sand beds and used as manure.
• The upper layer of clean water is then discharged into water bodies or into the ground to
recharge groundwater.
3. Septic tanks are low cost on-site sewage disposal system which are suitable for groups of 4–5
houses, hospitals and other isolated buildings. The household waste flows into the underground
septic tank that acts as a sedimentation-cum-digestion tank. The sludge settles at the bottom and
the lighter waste floats on top. Anaerobic bacteria present in the sludge help in decomposing the
waste. The septic tank needs to be cleaned every 4–5 months.
4. We can ensure proper disposal of wastes at home in the following manner.
• Cooking oil or other fats should not be disposed down the drains as they choke the pipes on
solidification. They should be thrown in dustbins only. If they are thrown in open drains, they
clog the soil pores and decrease its effectiveness to filter water.
• Solid wastes like used tea leaves and food remains should not be thrown down the drains as
they block them.
• Chemicals like cleaners, grease, paints, beauty products and medicines should not be poured
down the drains. They destroy the microorganisms that help in purifying water.

106
5. We can take the following steps to keep public places clean.
• Do not litter in public places.
• Do not throw waste on the roadside in case there is no dustbin nearby. Carry it with you and
throw it in a dustbin only.
• Do not spit or urinate in public places.
• Keep the home, school and areas around them neat and clean.

107
 Test Paper 1
(Chapters 1 to 9)
(Answer Key)
Choose the correct answer.
1. (a) 2. (b) 3. (c) 4. (d)
5. (c) 6. (b) 7. (a) 8. (d)
9. (d) 10. (a)
Fill in the blanks.
1. saprophytes 2. nitrogen 3. rumination 4. scouring
5. heat 6. natural 7. precipitate 8. humidity
9. soil profile 10. exhalation
State whether the given statements are True or False.
1. True 2. False 3. False 4. False
5. True 6. False 7. False 8. False
9. True 10. True
Answer the following questions briefly.
1. The process in which some bacteria convert atmospheric nitrogen into nitrogenous compounds
which can be used by plants is called nitrogen fixation.
2. Following are the functions of tongue.
• It helps us to sense taste with the help of taste buds.
• It helps in mixing the chewed food with saliva.
• It helps in swallowing the chewed food.
• It helps us to talk.
3. The inner wall of the small intestine has a number of finger-like projections called villi. These
increase the surface area for absorption of digested food. The villi have a network of very fine
blood vessels called capillaries. The food gets absorbed by the villi and then transported to
different organs of the body with the help of blood vessels.
4. Selective breeding involves choosing parents with particular characteristics to breed together
and produce offspring with more desirable characteristics.
5. Following are the differences between a clinical thermometer and a laboratory thermometer.
Clinical Thermometer Laboratory Thermometer
The temperature range is 35°C to 42°C. The temperature range is –10°C to 110°C.
It is used to measure human body It is used to measure temperature in the
temperature. laboratory.
It has kink, which prevents immediate It does not have a kink.
backflow of mercury.
6. A neutralisation reaction is the reaction between an acid and a base to form water and salt. For
example,
HCl + NaOH → NaCl + H2O

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 7. Following are the differences between a physical change and a chemical change.
Physical Change Chemical Change
It is reversible in nature. It is irreversible in nature.
No new substances are formed. New substances are formed.
8. Arboreal animals get almost all their food from trees. Hence they spend most of their lives on
trees and rarely come on to the land.
9. Soil consists of components like soil particles, humus (organic matter), water, air and organisms.
• Soil particles consist of fine, medium-sized and coarse pebbles, sand, clay and silt.
• Humus is the organic matter that is formed by the decomposition of remains of dead plants
and animals.
10. Following are the differences between aerobic respiration and anaerobic respiration.
Aerobic Respiration Anaerobic Respiration
This form of respiration takes place in the This form of respiration takes place in the
presence of oxygen. absence of oxygen.
Gases are exchanged in this form of Gases are not exchanged in this form of
respiration. respiration.
Glucose breaks down into carbon dioxide, Glucose breaks down into alcohol, carbon
energy and water. dioxide and energy.
Think carefully and answer the following questions.
1. Plants take up carbon dioxide from air and give out oxygen during photosynthesis. Animals take
up oxygen and release carbon dioxide during respiration. This maintains a balance between
oxygen and carbon dioxide in the atmosphere.
2. Oral hygiene is the practice of keeping one's mouth clean, and free from diseases and other
problems (like bad breath) by regular brushing of the teeth (dental hygiene). It is important to
follow good oral hygiene practices to prevent dental diseases and bad breath.
3. Amoeba does not have a mouth or a digestive system. It ingests its food with the help of its false
feet or pseudopodia. When it senses food, the pseudopodia surround the food particle and take
it inside the body forming a food vacuole. Digestive juices are secreted into the food vacuole,
which breaks down the food into simpler substances.
4. People working in the silk industry suffer from respiratory problems and skin disorders. Inhalation
of vapours arising from boiling, cooking and reeling cocoons causes asthma and other breathing
problems in workers of the sericulture industry.
5. Ventilators are provided near ceilings in the rooms of houses because the hot air is lighter and
rises out of the room through the ventilators. Cool air rushes into the room through the doors
and windows.
6. Formic acid is present in bee stings. The sting causes itching. To provide relief, the affected area is
rubbed with moist baking soda or calamine solution as they are basic in nature. They neutralise
the effect of acid and reduce itching.
7. When water (H2O) is added to calcium oxide (CaO), calcium hydroxide (Ca(OH)2) is formed along
with a lot of heat. It is an example of an exothermic reaction.
CaO + H2O → Ca(OH)2 + Heat

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 8. Some birds migrate from one place to another in search of food, to avoid extreme weather
conditions or to breed.
9. Soil is important to us due to the following reasons.
• It provides food through agriculture.
• It is the source of nutrients for many forms of life.
• Soil supports the growth of plants. We get food, cloth (cotton and wool), fuel, medicine,
wood and paper from plants.
• Clay is used as a raw material for the manufacture of tiles, bricks and pottery items.
• Rainwater that is absorbed into the soil is stored in the subsoil layer. This maintains water
table.
10. No, breathing and cellular respiration are not the same. Following are the differences between
them.
Breathing Cellular Respiration
It is a physical process in which exchange It is a chemical process which involves
of gases takes place. It does not involve oxidation of food.
any chemical reaction.
No energy is liberated in the process. Energy is liberated during the process.

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 Test Paper 2
(Chapters 10 to 18)
(Answer Key)
Choose the correct answer.
1. (d) 2. (a) 3. (c) 4. (b)
5. (d) 6. (b) 7. (a) 8. (c)
9. (b) 10. (d)
Fill in the blanks.
1. veins 2. cross-pollination 3. explosion
4. month 5. Nichrome 6. lens
7. anemometer 8. water cycle 9. canopy
10. contaminants
State whether the given statements are True or False.
1. True 2. False 3. True 4. False
5. False 6. True 7. False 8. True
9. True 10. False
Answer the following questions briefly.
1. Heartbeat is the regular rhythmic contraction and relaxation of the heart. In an adult human, the
average heartbeat is 70 to 72 beats per minute.
2. Each kidney consists of a large number of coiled tubes known as nephrons. They act as filters and
help to remove waste products from the blood that reaches the kidneys. The useful substances
are absorbed into the blood, and the filtrate that contains the waste products forms the urine.
3. In asexual reproduction, new plants are produced without the production of seeds. In sexual
reproduction, the fusion of male and female gametes gives rise to one or more seeds that grow
into new plants.
4. Sundial was used in ancient times to measure the time of the day. It was based on the principle
that as the sun’s position in the sky changes, the position and length of the shadow cast by an
object also changes. It was made by fixing a rod upright on a dial that is made on the ground or
carved from a stone. As the sun’s position changed across the sky, the shadow of the rod aligned
with the hours marked on the dial and indicated the time of the day.
5. A diagram that shows the arrangement of different components of an electric circuit with the
help of their respective symbols is called a circuit diagram.
6. Following are the characteristics of the image formed by a plane mirror.
• It is virtual and erect (upright).
• The size of the image is same as that of the object.
• The image formed is at the same distance as the object from the mirror.
• The image is laterally inverted.

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 7. Following precautions should be taken by people living in a cyclone-prone area.
• Store drinking water for each family member in airtight container.
• Keep first-aid box with you. Keep good quality torch, spare batteries and radio handy.
• Keep essential commodities like food items in case of emergency.
• Do not touch power lines and keep away from the loose hanging objects.
8. The factors responsible for the depletion of the water table are as follows.
• Increased population
• Increasing industries
• Scanty rainfall
• Agricultural activities
• Deforestation
9. Following are the main uses of forests.
• They act as food source.
• They maintain water table.
• They are sources of many useful products.
• They help to prevent soil erosion.
• They purify air.
• They regulate climate and water cycle.
• They provide food, shelter and protection to animals.
10. Potable water is the water which is suitable for drinking purposes. Hence, potable water is also
called drinking water.
Think carefully and answer the following questions.
1. If both the kidneys of a person stop functioning due to an injury or an infection, the toxic
substances start accumulating in the blood. These toxic substances are then removed from the
blood by using an artificial kidney known as dialysis machine. This process is known as dialysis.
In this process, blood from an artery of the arm is passed through the dialysis machine, where
waste materials are removed. The filtered blood is then led back to the patient’s body. Dialysis
needs to be carried out regularly.
2. When water gets evaporated from the surface of the leaves, in order to meet the requirements
of the plant, the water is sucked up from the soil by the roots of the plant and is transported
throughout the plant body. This process of sucking of water from the soil, by the roots of the
plant is called transpiration pull. It is a basic process needed for the maintenance and the growth
of the plant. This transports water and essential nutrients from the soil to the various parts of the
plant which are needed for its growth and maintenance.
3. Dispersal of seeds is important because if seeds germinate near parent plants, it will increase
competition for light, air, water and food. If competition increases, it will lead to the death of
many plants. Seed dispersal also leads to exposure of seeds to a new environment that helps in
adaptation and evolution.
4. The distance-time graph helps us to find the distance covered by an object at any instant of time.
It also helps to indicate the type of motion of the object, i.e. whether the object is at rest or at
uniform or non-uniform motion.

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 5. Miniature circuit breakers (MCBs) are being used nowadays in place of fuses. They are sensitive
to the amount of current flowing through them. The switches in MCBs automatically switch off
when the current is too large or there is a short circuit. Once the problem has been rectified, they
can be reset unlike the fuse that needs to be replaced after a single use.
6. AMBULANCE is written in inverted letters on an ambulance van. This is because when the driver
of a vehicle in front of the ambulance looks in the rear view mirror, it will appear laterally inverted
as AMBULANCE and the driver can make way for it.
7. Wind currents are generated due to uneven heating of the earth.
• Uneven heating between the poles and the equator: Equatorial regions of the earth receive
maximum heat from the sun. The air from this region rises and cooler air from the surrounding
regions (0–30° latitude belt on either side) rushes in. The direction of these winds is from
north and south towards the equator. The air at the poles is cooler as these regions receive
slanting rays of the sun. The warm air from the 30°–60° belt rises up and the cold air from the
poles moves in to fill this gap. Due to the rotation of the earth, the flow of wind is not exactly
vertical.
• Uneven heating of land and water: Wind currents are also caused by the uneven heating of
land and water. In summer season, the landmass of northern India gets heated and the air
rises. The wind from the ocean flows towards the land area. These are called monsoon winds
and cause rainfall in most parts of India. In winter season, the winds from the land blow
towards the oceans as the land is colder than the ocean.
8. Farmers should use better methods of irrigation like drip irrigation to manage wastage of water.
In this type of irrigation, water is supplied to plants drop by drop instead of filling the entire field
with water.
9. During the process of photosynthesis, plants release oxygen and thereby purify air. The released
oxygen is used by both plants and animals for respiration. Plants help to maintain the balance of
oxygen and carbon dioxide in the atmosphere. Therefore, forests are called green lungs.
10. We can ensure proper disposal of the wastes generated at homes in the following ways.
• Cooking oil or other fats should not be disposed down the drains as they choke the pipes on
solidification. They should be thrown in dustbins only. If they are thrown in open drains, they
clog the soil pores and decrease its effectiveness to filter water.
• Solid wastes like used tea leaves and food remains should not be thrown down the drains as
they block them.
• Chemicals like cleaners, grease, paints, beauty products and medicines should not be poured
down the drains. They destroy the microorganisms that help in purifying water.

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