NCERT Solutions Class 7 Science Chapter 9 Life Processes in Animals

F R E E S T U D Y M AT E R I A L F O R E V E R Y S T U D E N T

CLASS 7 · SCIENCE

NCERT Solutions

Chapter 9: Life Processes in
Animals

NCERT Textbook — Curiosity

BOOK PAGES SECTIONS QUESTIONS MEDIUM

121 – 136 16 39 English

Solutions, notes, sample papers & more at 44 pages

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

CLASS 7 · SCIENCE · CURIOSITY

NCERT Solutions — Chapter 9: Life Processes in Animals
Complete NCERT Solutions for Class 7 Science Chapter 9 Life Processes in Animals from the NCERT textbook
Curiosity. Every question is answered — the in-text questions on the journey of food and on breathing,
Activities 9.1, 9.2 and 9.3 with Table 9.1 filled in, the Science and Society box, all ten questions of Let Us
Enhance Our Learning and all six Exploratory Projects.

TEXTBOOK BOOK PAGES

Curiosity (Class 7) 121 – 136

SECTIONS QUESTIONS

16 39

MEDIUM

English

In-text Questions — Page 122
9.1 Nutrition in Animals

Q1 How do the complex food components get broken down into simpler forms and
used by the body in various animals? Is this process the same in all animals or does
it vary?

The complex components of food — carbohydrate, protein and fat — are broken down inside a
long tube called the alimentary canal. It begins at the mouth and ends at the anus. As food is
pushed along this tube, digestive juices secreted at different parts break it down into
simpler forms. These simpler forms are then absorbed into the blood and carried to every part
of the body.

Page 1 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

PART OF JUICE / SECRETION IT WHAT IT DOES TO THE FOOD
THE CANAL RECEIVES

Mouth Saliva Teeth crush and chew (mechanical digestion);
saliva starts changing starch into sugar

Stomach Digestive juice, acid and mucus Proteins are broken into simpler components; acid
kills harmful bacteria; mucus protects the stomach
lining

Small intestine Bile from the liver, pancreatic juice Fat, protein and the remaining carbohydrate are
from the pancreas, and juice from broken into the simplest forms, and the nutrients
its own wall are absorbed into the blood

Large intestine — Absorbs water and some salts, leaving semi-solid
stool

No, the process is not exactly the same in all animals. The plan is similar, but the canal is built
differently to suit the food an animal eats.

Cows and buffaloes (ruminants) swallow grass after chewing it only partly, and later bring
it back to the mouth for thorough chewing — this is rumination.
Birds have no teeth at all. They grind food in a muscular chamber called the gizzard, often
with the help of grit they swallow.

Why it happens: the body cannot use a big molecule of starch or protein as it is. It
has to be cut into small, soluble pieces that can pass through the wall of the
intestine into the blood. Digestive juices are the tools that do this cutting.

Q2 Think about your favourite food. Does your mouth feel watery?

Yes. Just thinking about a favourite food — hot samosas, a bowl of rasgulla, mango pickle —
makes the mouth feel watery. This happens because more saliva is released in the mouth
when you recall your favourite food.

Why it happens: saliva is the first digestive juice food meets. The body prepares in
advance — the smell, the sight, or even the memory of food is enough to start the
flow of saliva, so that the food can be moistened and its starch can begin to be
digested as soon as it arrives.

Page 2 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Did you know? Saliva does two jobs at once — it moistens the food so it is soft and
easy to swallow, and it carries a digestive juice that begins to change starch into
sugar.

In-text Questions — Page 123
9.1.1 Digestion in human beings — Beginning with the mouth cavity

Q1 What do you think is the role of saliva in your mouth? What do you feel when you
eat other types of food, such as chapati?

Saliva has two roles in the mouth:

1. It moistens the food. The tongue mixes chewed food with saliva, making it soft and slippery
so that it is easy to swallow and can slide down the food pipe.
2. It begins digestion. Saliva contains a digestive juice that breaks down starch into sugar.

When you eat a chapati, at first it tastes like an ordinary chapati. But if you keep it in the mouth
and chew it for 30–60 seconds, it begins to taste sweet.

Why it happens: chapati contains starch, a type of carbohydrate. Starch itself has no
sweet taste. The digestive juice in saliva breaks the starch into sugar, and sugar
tastes sweet — so the longer you chew, the sweeter the chapati tastes.

Q2 Take a small piece of chapati or a bite-sized portion of boiled rice and chew it
properly for 30–60 seconds. At first, the chapati or rice has its usual taste, but as
you continue chewing, do you notice a change in taste? The food begins to taste
sweet! Have you ever wondered why this happens?

Yes — the taste changes. The chapati or rice slowly begins to taste sweet as you keep chewing.

Chapati / boiled rice → contains starch (a carbohydrate) — not sweet

Starch + digestive juice of saliva → sugar — sweet

So: longer chewing → more starch changed to sugar → sweeter taste

Page 3 of 44

as e
Class 7 Science Chapter 9 Life Processes in Animals
a g l AglaSem · NCERT Solutions

co m
m.
Why it happens: saliva is not just water. It carries a digestive juice that acts on

m l a se
starch and breaks it into simple sugar. Digestion of starch therefore begins in the
o
.c not in the stomach. a g
m
mouth itself,

l a se
g
aTry This: chew a piece of chapati for only 5 seconds and note the taste, then chew a

co m
ag
fresh piece for a full minute. The difference is easy to notice, and it is proof that
m .
saliva is working.
as e
a g l

co m
m.
Science and Society — Page 123
m as e
.co l
9.1.1 Digestion in human beings — Beginning with the mouth cavity

a g
se m
a
SCIENCE AND SOCIETY

a g l
s
Find out the ways our elders were maintaining oral hygiene.
a
Q1
m
m .co agl
l a se
g

a
Ask your grandparents and older neighbours, and note down what they used before toothpaste
and brushes became common. Almost every part of India had its own method.

co m
.
a s em
com
TRADITIONAL WHAT WAS USED WHY IT WORKED

m .
PRACTICE
agl
aseDatun (chewing stick)
agl
Fresh twig of neem, babool (kikar), The fibres clean the teeth like bristles;

m
banyan or mango, chewed at one end neem and babool have a bitter juice that

a se
com
into a brush checks germs

. a g l
e m
asmustard oil, rubbed with
Manjan (tooth powder) Charcoal, burnt rice husk, salt, or salt Mildly gritty, so it rubs away food film;

a g l
mixed with
a finger
salt keeps the gums firm

co m
.
Tongue cleaning A U-shaped copper or brass tongue Removes the coating on the tongue that
scraper (jibhi)
se m
causes bad smell

com (kulla) l a
.Rinsing ag away food bits before they can
sem
Plain water, or lukewarm salt water, Washes

a
agl
after every meal decay between the teeth

.c
e m
Oil pulling (gandusha / Swishing sesame or coconut oil in the An old Ayurvedic practice believed to

m a s
.co gl
kaval) mouth keep the gums and mouth clean

m a
Chewing after meals
l a se
Fennel (saunf), clove, cardamom Freshens the breath and increases the

a g flow of saliva

com
m .
m ase
.co


a g l Page 4 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Sample answer: "My grandfather says that till he was about twenty he never used a
toothbrush. Every morning he broke a fresh neem twig, chewed one end till it opened into a soft
brush, and cleaned his teeth with it for several minutes. He scraped his tongue with a copper
jibhi and rinsed his mouth with water after every meal. He still has most of his teeth at seventy."

Tip: old and new methods agree on the same three rules — clean the teeth twice a
day, clean the tongue, and rinse the mouth after every meal.

Activity 9.1: Let us investigate — Page 123
9.1.1 Digestion in human beings — Beginning with the mouth cavity

ACTIVITY

Q1 Add 3–4 drops of iodine solution into each test tube with the help of a dropper. Mix
the content of each test tube separately and observe. Record your observations in
Table 9.1.

TABLE 9.1: ACTION OF SALIVA ON STARCH

TEST INITIAL COLOUR FINAL COLOUR POSSIBLE REASON FOR
TUBE BEFORE ADDING AFTER ADDING THE CHANGE IN
IODINE IODINE COLOUR, IF ANY

A: Boiled
rice

B: Chewed
boiled rice

Table 9.1 as printed on page 123 — fill it in yourself.

Iodine is the test for starch: it turns blue-black where starch is present, and stays its own
brownish-orange colour where starch is absent.

Page 5 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

TABLE 9.1: ACTION OF SALIVA ON STARCH

TEST INITIAL FINAL COLOUR POSSIBLE REASON FOR THE
TUBE COLOUR AFTER ADDING CHANGE IN COLOUR, IF ANY
BEFORE IODINE
ADDING
IODINE

A: Boiled Milky white (rice + Blue-black The rice was not chewed, so no saliva
rice water) acted on it. Starch is still present, and
iodine gives a blue-black colour with
starch.

B: Chewed Milky white (rice + No change — stays While chewing, the digestive juice in saliva
boiled rice water) brownish-orange; or broke the starch into simple sugars. Little
only a very light blue- or no starch is left, so iodine cannot give
black its blue-black colour.

Why it happens: the two test tubes differ in only one thing — whether saliva was
mixed with the rice. So whatever difference appears in the colour must be caused by
saliva. That is what makes this a fair test.

Check it yourself: if tube B still turns fairly dark, you did not chew long enough.
Repeat with 60–90 seconds of chewing and the colour will fade further.

In-text Questions — Page 124
9.1.1 Digestion in human beings — Food pipe (Oesophagus)

Q1 What causes the change of colour in test tube A?

The starch of the boiled rice causes it. In Grade 6 we learnt that iodine gives a blue-black
colour when it reacts with starch. The rice in test tube A was never chewed, so no saliva ever
touched it and its starch is still whole. Iodine finds that starch and turns blue-black.

Test tube A: boiled rice (starch present) + iodine → blue-black

Test tube B: chewed rice (starch broken to sugar) + iodine → no change / very light colour

Page 6 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Why it happens: saliva acts only on the food it is mixed with. Tube A is the control —
it shows what the rice looks like when saliva has not acted. Comparing it with tube B
is what proves that saliva digested the starch.

Q2 If the colour still appears in test tube B, what changes would you make in the
activity to explore it further? Would the colour change if chewing time is increased?

If tube B still shows a blue-black colour, some starch is left undigested. Change one thing at a
time and repeat:

Chew for longer — 90 seconds or 2 minutes instead of 30–60 seconds, so saliva gets more
time to act.
Chew more thoroughly, so that the rice is broken into finer pieces and more of it is exposed
to saliva.
Take a smaller amount of rice in the mouth, so that the saliva available is enough for it.
Keep the mixture standing for some minutes before adding iodine, giving the saliva
already mixed in more time to work.
Add fewer, counted drops of iodine (the same number in both tubes) so that the
comparison is fair.

Yes — increasing the chewing time does change the colour. The longer you chew, the more
starch is turned into sugar, so the blue-black colour becomes lighter and lighter and finally does
not appear at all.

Check it yourself: take four tubes with rice chewed for 15 s, 30 s, 60 s and 120 s.
Line them up after adding iodine — you will see a clear ladder of colour from dark to
almost none.

Q3 But how does the food move down?

The food does not fall down by its own weight — it is pushed. The walls of the food pipe gently
contract and relax in a wave-like motion, and this travelling wave squeezes the food forward
into the stomach.

Page 7 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

contraction relaxation

food to stomach

Fig. 9.2 in the book: the wall squeezes behind the food and relaxes in front of it, so the food is pushed
towards the stomach.

Why it happens: the food pipe has muscles in its wall. When the muscle behind the
lump of food tightens and the muscle in front of it loosens, the food has only one
way to go — forward. This same wave-like movement takes place throughout the
alimentary canal, which is why food keeps moving even when you lie down, and
why an astronaut can swallow in space.

In-text Question — Page 125

Page 8 of 44

as e
Class 7 Science Chapter 9 Life Processes in Animals
a g l AglaSem · NCERT Solutions

9.1.1 Digestion in human beings — Small Intestine
co m
e m.
m l as
Q1
.co a
Look at Fig. 9.4. It is a sketch of a stretched-out alimentary canal. Guess how long it
m
g
l a se
is.

a g

o m
e m .
Mouth c ag
a s
agl
Food pipe
(Oesophagus)

co m
em.
m l as
m .co a g
l a se
a g Stomach

m a s
.co agl
sem
gla
Liver Pancreas
a

co m
m .
m as e
.co
Small
a g l
se m intestine
g l a
a
se m
com g l a
m . a
ase
agl Large
intestine

co m
m .
m e
as
l
Anus
m .co a g
l a se
ag Fig. 9.4, page 125 — the alimentary canal drawn stretched out.
.c
s e m
m a
m . co agl
l a se
ag a metre or two — the answer is far bigger. The small intestine alone
Most students guess about
is almost 6 metres long, which is nearly twice the height of your classroom. Add the other

co m
m .
m ase
.co


a g l Page 9 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

parts and the whole canal is longer still.

PART OF THE APPROXIMATE HOW TO PICTURE IT
ALIMENTARY CANAL LENGTH

Small intestine about 6 m Twice the height of a classroom; the
longest part of the canal

Large intestine about 1.5 m Shorter than the small intestine, but wider

Why it happens: such a long tube is folded and coiled to fit inside the abdomen.
Length is useful — the longer the food stays in contact with the digestive juices and
the absorbing wall, the more completely it is digested and absorbed.

Try This: mark 6 metres on the ground with a measuring tape or a piece of rope and
stand beside it. That single length of rope is the small intestine, coiled up inside you.

In-text Questions — Page 126
9.1.1 Digestion in human beings — Large intestine

Q1 How are these nutrients absorbed from the small intestine?

The inner lining of the small intestine is thin and carries thousands of finger-like projections
(Fig. 9.5). These projections greatly increase the surface area of the lining. Digested nutrients
pass through this thin wall into the blood present in the blood vessels of the wall, and the blood
carries them to every part of the body. This passing of nutrients into the blood is called
absorption.

Page 10 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

More surface = more nutrients absorbed

flat wall wall with projections
small area much larger area

The finger-like projections of the small intestine work the way a folded towel soaks up much more
water than a flat sheet of paper.

Why it happens: absorption can happen only where the food touches the wall. A
smooth tube 6 m long would touch very little food. Thousands of tiny fingers turn
the same 6 m into an absorbing surface many times bigger, so almost nothing useful
is wasted.

Did you know? This is exactly why celiac disease is so serious. It damages this inner
lining, the absorbing surface is lost, and the person stays weak even after eating
well.

Q2 After most of the nutrients are digested and absorbed in the small intestine, what
happens to the undigested food?

It moves on into the large intestine. There:

1. The large intestine absorbs water and some salts from it, so the watery waste becomes
semi-solid.
2. This semi-solid waste is called stool.
3. The stool is stored in the rectum, the lower part of the large intestine, until the body is
ready to get rid of it.
4. Finally it is expelled through the anus — a process known as egestion.

Page 11 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Undigested food → large intestine (water + salts absorbed)

→ semi-solid stool → stored in rectum

→ expelled through anus = egestion

Tip: eating fibre-rich food — fruits, vegetables and whole grains — helps the large
intestine work properly and makes the stool easier to pass.

Q3 It is shorter than the small intestine. Then why is it called the large intestine?

Because it is named for its width, not its length. The large intestine is only about 1.5 m long
against the small intestine's 6 m, but it is much wider than the small intestine — and that is why
it is called "large".

FEATURE SMALL INTESTINE LARGE INTESTINE

Length about 6 m — the longest part of the about 1.5 m
canal

Width Narrow Wider

Main job Digestion is completed; nutrients are Water and some salts are absorbed; stool is
absorbed formed and stored

Why it happens: the two names describe the bore of the tube, the way we speak of
a "large" pipe and a "small" pipe in a house even when the small one runs further.

In-text Question — Page 127
9.1.2 Do all animals digest food the same way as humans do?

Q1 I have seen cows keep chewing the food even when they are not actively grazing or
eating anything. Why?

Because the cow is ruminating — chewing food it had swallowed earlier.

Page 12 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

1. A cow, like a buffalo, partially chews the grass and swallows it quickly into the stomach.
Grazing is done fast, in the open.
2. In the stomach, the grass is partially digested.
3. Later, when the animal is resting, the partially digested food is brought back to the mouth
and chewed slowly and thoroughly.
4. This process is called rumination, and such animals are called ruminants. A cow spends
about 8 hours a day just chewing.
5. The thoroughly chewed food then passes down the alimentary canal again for further
digestion.

Why it happens: grass is tough and full of fibre, and cannot be broken down in one
round of chewing. Swallowing first and chewing later lets the animal collect a lot of
grass quickly in the field — where it is exposed to danger — and then do the slow
work of grinding it in a safe place.

Did you know? The large first chamber of a ruminant's stomach is called the rumen
(labelled in Fig. 9.6). The word "ruminate" in English also means "to think something
over slowly" — borrowed from exactly this habit of the cow.

In-text Questions — Page 129
9.2.1 Respiration in humans

Q1 How is this oxygen used in the body? Are breathing and respiration different?

The oxygen we inhale is used to break down glucose and release energy. Food is first
digested into simple substances like sugar (glucose); oxygen then helps break this glucose down
inside the body. That process is called respiration.

Glucose + Oxygen → Carbon dioxide + Water + Energy

Yes, breathing and respiration are different.

Page 13 of 44

as e
Class 7 Science Chapter 9 Life Processes in Animals
a g l AglaSem · NCERT Solutions

co m
m.
POINT BREATHING RESPIRATION

mInhaling and exhaling air as e
What it is
.co a g l
Breaking down glucose with oxygen to release

m
ase
energy

gl of
aType A physical process A chemical process
process

co m
Where it In the respiratory system — nose,
e m . Inside the body, in all its parts ag
happens windpipe, lungs
g l as
What it gives
a
Brings oxygen in, removes carbon Releases the energy that lets us walk, run,
dioxide play and think
co m
e m.
m l as
.co
Why it happens: breathing only delivers the oxygen and carries away the waste gas.
a g
a s emuseful work — getting energy out of food — is done by respiration. Breathing is
gl the transport; respiration is the purpose. Both are essential for survival.
The
a
m a s
m .co agl
l a se
g
It is difficult to live without food for a week; without water for a day or two, but
a
Q2
without breathing, we usually cannot survive more than a few minutes. Why is

m
that?

. co
se m
o m l a
m .c the body can store food and water, but it cannot storeagoxygen.
se
Because

g l a
a Food is stored in the body, so energy can be drawn from those stores for days.
Water is held in the body and is lost slowly, so a person can manage a day or two.
se m
com g l a
.
Oxygen, however, is used up every single second by every part of the body to release energy
m a
ase
from glucose, and there is no store of it anywhere.

agl
The moment breathing stops, the supply of oxygen stops. Respiration in the body slows down at
once, energy is no longer released, and delicate organs such as the brain begin to fail within
minutes.
co m
m .
m as e
.co
Why it happens: respiration is not something the body does now and then — it
a g l
se m goes on non-stop in every part of the body, awake or asleep. A process that never
g l a
a pauses needs a supply that never pauses.
c
m .
m a s e
e m . co agl
g l as
a

co m
m .
m as e
.co


a g l Page 14 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Q3 Have you noticed tiny hair inside your nostrils?

Yes. There are tiny hair inside the nostrils. These hair, along with mucus, trap dust and dirt
from the air we breathe in, so that clean air goes down to the lungs.

Dusty air enters nostrils

↓ tiny hair + sticky mucus catch the dust

Cleaner air → nasal passages → windpipe → lungs

Why it happens: the delicate alveoli deep inside the lungs have no way of cleaning
themselves. So the air must be filtered before it gets there, and the nose is the filter.
This is why we should breathe through the nose and not through the mouth —
the mouth has no such filter.

Did you know? The nose also warms and moistens the air on the way in, so cold dry
air does not shock the lungs.

Activity 9.2: Let us make a model — Page 130

Page 15 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

9.2.1 Respiration in humans — How do we breathe?

ACTIVITY

Q1 Pull the rubber sheet from the centre of the base downwards and watch the
balloons (Fig. 9.9a). What do you observe? Now, release the rubber sheet upwards
and observe the balloons (Fig. 9.9b). What changes do you see in the balloons?

(a) Inhalation (b) Exhalation

Fig. 9.9, page 130 — model made in Activity 9.2 to show the mechanism of breathing.

When you pull the rubber sheet downwards, the balloons inflate (blow up). When you
release the rubber sheet upwards, the balloons deflate (go flat again).

Page 16 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

WHAT YOU DO WHAT HAPPENS TO WHAT THE BALLOONS WHAT IT STANDS
THE SPACE IN THE DO FOR IN THE BODY
BOTTLE

Pull the rubber Space inside the bottle Balloons inflate — air Inhalation
sheet down [Fig. increases rushes in through the tube
9.9(a)]

Release the rubber Space inside the bottle Balloons deflate — air is Exhalation
sheet up [Fig. decreases pushed out through the tube
9.9(b)]

Why it happens: the bottle is sealed, so the only way air can get in or out is through
the tube. Pulling the sheet down makes more room inside the bottle, and air enters
through the tube to fill that room — the balloons swell. Letting the sheet snap back
reduces the room, and the same air is squeezed out — the balloons collapse. Your
chest works in exactly this way.

Check it yourself: if a balloon does not inflate, the seal has leaked. Press the clay
round the lid again and check the rubber band at the base — the model works only
if the bottle is airtight.

In-text Question — Page 131

Page 17 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

9.2.1 Respiration in humans — How do we breathe?

Q1 What do the balloons in the model mentioned in Fig. 9.9 represent? What does the
rubber sheet represent?

(a) Inhalation (b) Exhalation

Fig. 9.9, page 130 — model made in Activity 9.2 to show the mechanism of breathing.

In this model, the balloons represent the lungs and the rubber sheet represents the diaphragm.

PART OF THE MODEL PART OF THE BODY IT REPRESENTS

Two balloons The two lungs

Thin rubber sheet at the base The diaphragm

Y-shaped hollow tube The windpipe and its two branches

Wide plastic bottle The chest cavity, enclosed by the rib cage

Page 18 of 44

as e
Class 7 Science Chapter 9 Life Processes in Animals
a g l AglaSem · NCERT Solutions

co m
m.
Why it happens: pulling the sheet down copies the diaphragm moving downwards

m l a se
during inhalation, which increases the space inside the chest so that air enters the
o
.c a gexhalation, which
m
lungs. Releasing it copies the diaphragm moving upwards during

l a se the space and pushes air out.
ag
reduces

o m
c ag
Tip: the model has one limitation — the bottle is rigid, so it cannot show the ribs
.
m the ribs move as well as the diaphragm.
s e
moving up and outwards. In the real chest,
a
agl

co m
m.
Activity 9.3: Let us explore — Page 131
m as e
.co l
9.2.1 Respiration in humans — What do we breathe out?

a g
se m
a
ACTIVITY

ag l
s
Do you observe any changes in the colour of the lime water?
a
Q1
m
m.co agl
l a se
g

a
Yes — but only in one of the two test tubes.

co m
TEST AIR PASSED INTO THE LIME WATER
.
CHANGE OBSERVED
m
TUBE
m as e
.co a g l
a s em A Surrounding air, pushed in with a syringe or pichkari — the Lime water stays clear — no

agl same air we inhale change

Air blown out from the mouth through a straw — exhaled
se m
com a
B Lime water turns milky
air
.
(cloudy)
a g l
m
ase
agl
Tip: take an equal amount of freshly prepared lime water in both tubes. Old lime
water has already reacted with the carbon dioxide of the air and may be cloudy

co m
before the activity even begins.
m .
m as e
.co a g l
a s em
agl Q2 The lime water in test tube B turns milky (or cloudy), but the lime water in test tube

.c
m
A does not. What does this indicate?

m a s e
e m . co agl
as

a g l
It indicates that the air we breathe out contains more carbon dioxide than the air we breathe
in.

co m
m .
m ase
.co


a g l Page 19 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Lime water turns milky only when it reacts with carbon dioxide

Tube B (exhaled air) → milky → a lot of carbon dioxide

Tube A (inhaled air) → clear → very little carbon dioxide
∴ exhaled air is richer in carbon dioxide than inhaled air

Why it happens: carbon dioxide is a waste product of respiration. It is produced all
over the body when glucose is broken down, is carried by the blood to the alveoli,
and is released into the air we exhale. So the returning air must carry more of it than
the air that went in.

Check it yourself: tube A is the control. Without it, someone could argue that lime
water turns milky on its own. Because A stays clear under exactly the same
treatment, the milkiness of B can only be due to the exhaled air.

In-text Question — Page 132
9.2.1 Respiration in humans — How does the exchange of gases happen?

Q1 Have you ever wondered how the food you eat gives you energy?

The key is not only the food but also the oxygen we breathe. Food alone cannot give energy,
and oxygen alone has nothing to act on — the two must meet inside the body.

1. Food is digested and broken down into simple substances like sugar (glucose).
2. The glucose is absorbed into the blood and carried to every part of the body.
3. Oxygen from the inhaled air passes from the alveoli into the blood and is also carried
everywhere.
4. Oxygen helps break down the glucose, and energy is released. This is respiration.
5. Carbon dioxide and water are formed as waste; the blood carries the carbon dioxide back to
the alveoli, and we breathe it out.

Glucose + Oxygen → Carbon dioxide + Water + Energy

Page 20 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Why it happens: the energy is locked inside the glucose molecule. Oxygen is what
unlocks it. This is why you feel breathless after running — your muscles want more
energy, so they want more glucose broken down, so they want more oxygen, so you
breathe faster.

Did you know? This is the same energy that lets you walk, run, play — and even
think. The brain uses a large share of the body's energy while sitting perfectly still.

In-text Question — Page 133
9.2.2 Do other animals breathe the same way as humans do?

Q1 You may have observed birds flying and fish swimming. How do they breathe?

Birds breathe through lungs, like humans. Fish breathe through gills. Different animals have
different breathing organs to suit the habitat they live in.

ANIMAL BREATHING HOW IT WORKS
ORGAN

Birds, elephants, lions, Lungs All have lungs, but the structure of the lungs is quite
cows, goats, lizards, different in each of them
snakes

Most aquatic animals, Gills Gills are richly supplied with blood vessels; oxygen and
such as fish carbon dioxide are exchanged between the blood and
the gases dissolved in the water

Frog — tadpole stage Gills The young tadpole lives entirely in water

Frog — adult Lungs on land, skin An amphibian uses different body parts at different
in water stages and in different places

Earthworm Moist skin Oxygen and carbon dioxide are exchanged straight
through the damp body surface

Page 21 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Why it happens: in every case the gas has to pass through a thin, moist surface that
is well supplied with blood. Lungs keep that surface inside the body, safe from
drying; gills spread it out in water, where oxygen is dissolved; the earthworm simply
keeps its whole skin moist. Each design suits its habitat — which is why an
earthworm dries up and dies on hot ground, and a fish out of water cannot breathe
even though there is plenty of oxygen around it.

Let Us Enhance Our Learning — Pages 135 & 136
Chapter exercises

LET US ENHANCE OUR LEARNING

Q1 Complete the journey of food through the alimentary canal by filling up the boxes
with appropriate parts— Food → Mouth → ____ → Stomach → ____ → ____ → Anus

The three empty boxes are the food pipe (oesophagus), the small intestine and the large
intestine.

Food → Mouth → Food pipe (Oesophagus) → Stomach → Small intestine → Large

intestine → Anus

Food pipe
Food Mouth Stomach
(Oesophagus)

Small Large
Anus egestion
intestine intestine

Orange boxes are the three parts you had to fill in.

The complete journey of food through the alimentary canal.

Page 22 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

BOX PART WHAT HAPPENS THERE

1st Food pipe Wave-like contraction and relaxation of the walls pushes the food
blank (Oesophagus) down into the stomach

2nd Small intestine Bile, pancreatic juice and its own juice complete the digestion;
blank nutrients are absorbed into the blood

3rd Large intestine Water and some salts are absorbed; stool is formed and stored in the
blank rectum

Tip: the liver and the pancreas do not go into any box. Food never passes through
them — they only pour their juices into the small intestine, so they are called
associated parts of the alimentary canal.

Q2 Sahil placed some pieces of chapati in test tube A. Neha placed chewed chapati in
test tube B, and Santushti took boiled and mashed potato in test tube C. All of them
added a few drops of iodine solution to their test tubes—A, B, and C, respectively.
What would be their observations? Give reasons.

Iodine turns blue-black wherever starch is present, and keeps its own brownish-orange colour
where starch is absent.

TEST WHAT IT OBSERVATION REASON
TUBE CONTAINS

A — Sahil Plain pieces of Blue-black colour Chapati is rich in starch and no saliva has
chapati (not acted on it, so all the starch is intact
chewed)

B— Chewed chapati No change in colour, or While chewing, the digestive juice in
Neha only a very light blue- saliva broke the starch down into simple
black sugars, so little or no starch is left for the
iodine to react with

C— Boiled and Blue-black colour Potato is also rich in starch, and it was
Santushti mashed potato only boiled and mashed — no saliva was
mixed with it, so its starch is untouched

Page 23 of 44

as e
Class 7 Science Chapter 9 Life Processes in Animals
a g l AglaSem · NCERT Solutions

co m
m.
Why it happens: A and C are alike in the one thing that matters — starch that saliva

m l a se
has never touched — so both give the same blue-black result even though one is
o g
.cthe other a potato. Only B is different, and the only difference
a
m
wheat and is saliva.
a e comparison is what proves that saliva digests starch.
ssingle
ag l
That

o m
c ag
Check it yourself: if Neha's tube B still turns dark, she has not chewed long enough.
m .
s e
Chewing for a full minute makes the difference
a
clear.

agl
m
.co
What is the role of the diaphragm in breathing? (i) To filter the air (ii) To produce
m
Q3

m a se
sound (iii) To help in inhalation and exhalation (iv) To absorb oxygen
o l
.c a g
se m
l a
agThe correct answer is (iii) To help in inhalation and exhalation.

m a s
m .co agl
ase
Air is drawn in Air is forced out

agl

com
m .
m as e
.co a g l
se m
g l a
a
se m
com g l a
m . a
l ase
agdownward
Diaphragm moves Diaphragm moves upward
(a) Inhalation (b) Exhalation
co m
m .
m as e
.co l
Fig. 9.10 of the book: the diaphragm changes the space inside the chest, and air follows.

a g
se m
g l a
a c
m .
m a s e
e m . co agl
g l as
a

co m
m .
m ase
.co


a g l Page 24 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

INHALATION EXHALATION

Ribs Move up and outwards Move down and inwards

Diaphragm Moves downwards Moves upwards

Space inside the chest Increases Decreases

Air Enters the lungs Is pushed out of the lungs

Why the other options are wrong: (i) filtering the air is done by the tiny hair and
mucus in the nostrils, not by the diaphragm; (ii) sound is produced in the voice box
in the windpipe; (iv) oxygen is absorbed into the blood at the alveoli. The diaphragm
is a dome-shaped muscle below the lungs — its only job here is to change the size
of the chest cavity.

Q4 Match the following — (i) Nostrils (ii) Nasal passages (iii) Windpipe (iv) Alveoli (v)
Ribcage with (a) fresh air from outside enters (b) exchange of gases occurs (c)
protects lungs (d) tiny hair and mucus help to trap dust and dirt from the air we
breathe (e) air reaches our lungs through this part

NAME OF FUNCTION WHY
THE PART

(i) Nostrils (a) fresh air from outside enters The pair of nasal openings where the
respiratory system begins

(ii) Nasal (d) tiny hair and mucus help to trap dust The air is cleaned here before it goes any
passages and dirt from the air we breathe further

(iii) Windpipe (e) air reaches our lungs through this part It carries air down and divides into two
branches, one for each lung

(iv) Alveoli (b) exchange of gases occurs Balloon-like sacs with thin walls
surrounded by fine blood-carrying tubes

(v) Ribcage (c) protects lungs The bony cage around the chest that
guards the soft lungs

Page 25 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Nostrils

Windpipe

Alveoli

Right lung Left lung

Rib cage

Diaphragm

Air path: nostrils → nasal passages → windpipe → alveoli

The human respiratory system (Fig. 9.8 of the book), with the parts named in the question.

Tip: remember the order in which air travels — nostrils, nasal passages, windpipe,
its two branches, finer branches, alveoli. Four of the five matches simply follow that
order; the rib cage is the one part that does not carry air at all, so it takes the odd
option, "protects lungs".

Q5 Anil claims to his friend Sanvi that respiration and breathing are the same process.
What question(s) can Sanvi ask him to make him understand that he is not correct?

Sanvi should ask questions whose honest answers force Anil to admit that the two words stand
for two different things.

1. "If breathing and respiration are the same, then where does the energy in our body come
from? Does simply pulling air in and pushing it out release energy?"
2. "Write the word equation of respiration. Now write one for breathing. Why can you write
Glucose + Oxygen → Carbon dioxide + Water + Energy for one and not for the other?"

Page 26 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

3. "Breathing takes place in the nose, windpipe and lungs. In which part of the body does
respiration take place?"
4. "An earthworm has no lungs and a fish has no nose to breathe with — yet both are alive
and active. If breathing and respiration were the same word, how would you explain that?"
5. "Is a physical change the same as a chemical change? Breathing is a physical process;
respiration is a chemical one. Can two processes of different kinds be the same process?"
6. "When you hold your breath for half a minute, does respiration in your body also stop?"

BREATHING RESPIRATION

Taking air in and pushing it out Breaking down glucose with oxygen to release energy

A physical process A chemical process

Happens in the respiratory system Happens inside the body, in all its parts

No energy is released Energy is released

Only supplies oxygen and removes carbon dioxide Actually uses that oxygen to do useful work

Why it happens: breathing is the delivery; respiration is the use. Comparing them is
like comparing a milkman bringing milk to the house with the family drinking it —
related, needed one after the other, but not the same event.

Q6 Which of the following statements is correct and why? Anu: We inhale air. Shanu:
We inhale oxygen. Tanu: We inhale air rich in oxygen.

Tanu's statement is correct — "We inhale air rich in oxygen."

Page 27 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Inhaled air

Nitrogen and other gases 21% O₂

Exhaled air

Nitrogen and other gases 16–17% O₂

0.04% carbon dioxide (inhaled)
4–5% carbon dioxide (exhaled)

Air is a mixture — oxygen is only about a fifth of it.

Fig. 9.13 of the book, drawn as bars: inhaled air is rich in oxygen but is not oxygen.

STATEMENT VERDICT REASON

Anu: We inhale air. True, but We do inhale air, but this says nothing about the oxygen that
incomplete makes the air useful to us

Shanu: We inhale Incorrect We never inhale pure oxygen. Air is a mixture; only about 21%
oxygen. of it is oxygen, and even that is not fully used — exhaled air
still has 16–17% oxygen

Tanu: We inhale air Correct It says both things that matter — what we take in is air, and
rich in oxygen. that air is rich in oxygen compared with the air we breathe
out

Why it happens: the lungs simply take in whatever mixture is around them. Oxygen
is picked up from that mixture at the alveoli and carbon dioxide is added to it, so the
air that comes out has less oxygen and much more carbon dioxide — but it is still air,
not a single gas.

Q7 We often sneeze when we inhale a lot of dust-laden air. What can be possible
explanations for this?

Sneezing is the body's way of throwing the dust out again. Possible explanations:

Page 28 of 44

as e
Class 7 Science Chapter 9 Life Processes in Animals
a g l AglaSem · NCERT Solutions

co
1. The filter is overloaded. The tiny hair and the mucus in the nostrils can trap only a limited
m
se m.
amount of dust. When the air is very dusty, more particles get through than they can hold.

c o m g l a
it,.and this irritation sets off a sneeze automatically.
2. The lining is irritated. Dust particles settling on the delicate lining of the nasal passage
irritatem a
a se is a protective reflex. It is not something we decide to do. A sudden, forceful rush
3. Alsneeze
agof air is pushed out through the nose and mouth, and it carries the dust particles out with it.

co m
4. It keeps the lungs safe. If the dust travelled further down, it would reach the windpipe and

m . ag
se
the delicate alveoli, where there is no easy way to remove it. Sneezing stops the dust while it

l a
agwith the sneeze, so more dust is trapped and washed out;
is still near the entrance.
5. Extra mucus is produced along
this is why the nose runs in a dusty place.

com
se m.
m l a
Why it happens: the whole respiratory system is built to protect one thing — the
o
.c walls of the alveoli. Nose hair, mucus, coughing and
a gsneezing are all
m
thin, moist

l a se of the same defence.
g
layers
a
a s
comdroplets that can carry infection to people agl
Tip: always cover your nose and mouth with a handkerchief or your bent elbow

m .
a s ecover
while sneezing. A sneeze throws out tiny

agl
standing nearby. In a dusty place, your face with a cloth or a mask.

. c om
m a s em workout. After
Paridhi and Anusha of Grade 7 started running for their morning
o completed their running, they counted their breaths gl per minute. Anusha was
Q8

. cthey a
a s em breathing faster than Paridhi. Provide at least two possible explanations for why
agl Anusha was breathing faster than Paridhi.

se m
com g l a
. a

m
ase
Any two of the following are acceptable explanations.

agl
1. Anusha may have run faster or covered a longer distance. Harder work means her
muscles needed more energy, so more glucose had to be broken down, so more oxygen was

co m
.
needed and more carbon dioxide had to be thrown out — and the only way to do that is to
m
m
breathe faster.
as e
.co a g l
m stronger breathing muscles and takes in more air with each breath, so she needs fewer
2. Anusha may be less used to running than Paridhi. Someone who exercises regularly has

l a se
ag breaths for the same work. A person who runs rarely gets out of breath sooner.
.c
3. Their bodies are different. Chest size, lung capacity and body weight vary from person to
s e m
. c om
person. A smaller lung capacity means less air per breath, so more breaths per minute.
a g la
4. Anusha may have counted her
s e m breaths sooner after stopping. Breathing rate falls
a counting right away gives a higher number than counting three
gradually after exercise,lso
g
minutes later. a

com
m .
m ase
.co


a g l Page 29 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

5. Anusha may have been carrying a bag, running uphill, or running on soft sand, so the
same distance cost her more effort.
6. Anusha may not have been well — a cold or a blocked nose makes each breath shallow, so
more breaths are needed.

More muscle work → more glucose to be broken down

→ more oxygen needed and more carbon dioxide to remove

→ breathing rate goes up

Check it yourself: count your breaths for one minute while sitting quietly, then skip
for two minutes and count again. Note both numbers, and repeat it for a week —
you will see your resting rate slowly drop as you become fitter.

Page 30 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Q9 Yadu conducted an experiment to test his idea. He took two test tubes, A and B, and
added a pinch of rice flour to the test tubes, half-filled with water and stirred them
properly. To test tube B, he added a few drops of saliva. He left the two test tubes
for 35–45 min. After that, he added iodine solution into both the test tubes.
Experimental results are as shown in Fig. 9.15. What do you think he wants to test?

Iodine
solution

(A) (B)

Fig. 9.15, page 136 — the two test tubes just after iodine solution was added.

Yadu wants to test whether saliva breaks down starch — that is, whether the digestive juice in
saliva changes the starch of rice flour into something that is no longer starch.
In Fig. 9.15 the two tubes look completely different:

Page 31 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

TEST CONTENTS COLOUR AFTER WHAT IT MEANS
TUBE IODINE (FIG. 9.15)

A Rice flour + water only Dark blue-black Starch is still present — nothing
acted on it

B Rice flour + water + a Stays brownish-orange, The starch has been broken down;
few drops of saliva the colour of iodine itself there is nothing for iodine to react
with

Only one thing is different between A and B — the saliva. So the difference in colour can only be
the work of the saliva.

Why this design is good: tube A is the control. Without it, Yadu could not claim
anything, because someone might say the rice flour never had starch in the first
place. He also keeps everything else the same — the same pinch of flour, the same
amount of water, the same stirring, the same 35–45 minutes and the same iodine —
so that saliva is the only variable.

Did you know? This experiment also shows something extra: saliva goes on working
even outside the mouth, in a test tube. Digestion is a chemical action of the juice,
not a magic that needs the body.

Page 32 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Q10 Rakshita designed an experiment taking two clean test tubes, A and B and filled
them with lime water as shown in the figure. In test tube A, the surrounding air
that we inhale was passed on by sucking air from the pipe, and in test tube B, the
exhaled air was blown through the pipe (Fig. 9.16). What do you think she is trying
to investigate? How can she confirm her findings?

(A) (B)

Fig. 9.16, page 136 - the two set-ups Rakshita used.

Rakshita is trying to find out whether the air we breathe out contains more carbon dioxide
than the air we breathe in.

Lime water turns milky only with carbon dioxide

Tube A (inhaled air) → stays clear

Tube B (exhaled air) → turns milky

∴ exhaled air has more carbon dioxide than inhaled air

How she can confirm her findings:

Compare the two tubes side by side. Tube A is the control. Both tubes get the same freshly
prepared lime water, the same amount, and air is passed for the same length of time. If only
B turns milky, the difference must come from the exhaled air.
Repeat the experiment two or three times, and let two or three classmates blow into fresh
tubes. A result that comes back every time is trustworthy.

Page 33 of 44

as e
Class 7 Science Chapter 9 Life Processes in Animals
a g l AglaSem · NCERT Solutions

Blow for longer. The milkiness in tube B should become more and more marked as more
co m
se
exhaled air is passed — showing that the effect grows with the amount of carbon dioxide.
m.
o m l a
g for carbon dioxide.
.c turns milky. This proves that the milkiness really is the test
Test in the reverse direction. Pass carbon dioxide from a known source into fresh lime
water; m
e a
sfresh
it too
l a
ag
Use lime water each time. Lime water left standing in the open has already met the
carbon dioxide of the air and may be cloudy before the test begins.

co m
e m .
Why it happens: carbon dioxide is a waste product of respiration. It is made all over ag
g l as
the body when glucose is broken down, is carried by the blood to the alveoli, and is
a
released into the air we exhale. So the air coming out must carry far more of it than

m
the air going in — nearly 4–5% against nearly 0.04%.
co
em.
m l as
.co a g
sem Projects — Page 136
a
agl
Exploratory
Interdisciplinary projects

m a s
.co agl
EXPLORATORY PROJECTS

se m
g l a
a
Q1 What are the good practices for maintaining oral hygiene? Try to gather
information on the same from books/newspapers/conversation with elders.
Prepare a report.
co m
m .
m as e
.co a g l
a s em
How to do this project: collect information from three kinds of sources — a science or health

agl book, a newspaper or magazine article, and a conversation with elders at home. Note the
m
source of each point. Then arrange your report under headings: Why oral hygiene matters →

a se
comis enough. l
What to do daily → What to avoid → What our elders did → Conclusion. Two pages, with a small
. a g
emsix specific practices, one reason for each, at least one
labelled sketch of a tooth-brushing routine,
s
A good report must contain: ataleast
agla clear statement of where each fact came from.
point taken from an elder, and

m
Sample answer:
. co
em
m l as
m .co a g
l a se
ag
.c
s e m
m a
e m . co agl
g l as
a

co m
m .
m ase
.co


a g l Page 34 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

GOOD PRACTICE WHY IT HELPS

Brush teeth twice a day — morning and before Removes the sticky film of food in which germs grow and
sleeping cause tooth decay

Clean the tongue twice a day The coating on the tongue is a main cause of bad smell in
the mouth

Rinse the mouth with water after every meal Washes away food bits stuck between the teeth before they
can decay

Cut down on toffees, chocolates and sweet drinks, Sugar left on the teeth is exactly what decay-causing germs
especially at night feed on

Eat crunchy fruits and vegetables — guava, carrot, Chewing them cleans the teeth and increases the flow of
cucumber, apple saliva

Do not open bottle caps or bite hard nuts with the Prevents cracks and chipping
teeth

Change the toothbrush every 3 months Bent, worn bristles no longer clean the corners

Get the teeth checked once a year A small cavity can be filled easily; a neglected one becomes
painful and costly

From my grandmother: "Till I was married I used a neem datun every morning, cleaned my
tongue with a copper jibhi, and rinsed my mouth after every meal. We rarely ate sweets, and no
one in our house had a decayed tooth."

Tip: end the report with one line of your own — what you have decided to change in
your own routine after doing this project.

Q2 Find out different ways to maintain a healthy digestive system. Suggest some food
items that help to maintain good digestive health. Make a report and present it in
class.

How to do this project: gather your points from the chapter itself (fibre, fermented food, the
Charaka Samhita box), from a doctor or an elder, and from a health article. Then make two lists
— habits and foods — and turn them into a five-minute class presentation with one chart paper.
A good report must contain: habits as well as foods; a reason for each; at least two examples
from local Indian food; and one thing to avoid.
Sample answer — habits:

Page 35 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Eat meals at proper timings and do not skip them — modern nutrition science and the
Charaka Samhita agree on this.
Chew food well and eat slowly (mindful eating). Digestion begins in the mouth; food
swallowed in a hurry gives saliva no time to act.
Avoid overeating. A stomach filled too full cannot churn the food properly.
Drink enough water. The large intestine needs water to keep the stool soft.
Wash hands before eating and eat freshly cooked food, to keep out germs.
Be physically active — walking, cycling and play keep the gut moving.
Do not lie down straight after a heavy meal; take a short walk instead.

Sample answer — foods:

FOOD HOW IT HELPS

Fruits and vegetables — papaya, guava, banana, Rich in fibre and water; make the stool easier to pass
spinach, carrot

Whole grains and millets — jowar, bajra, ragi, Fibre-rich; millets are also naturally gluten-free
whole wheat, brown rice

Fermented foods — curd, buttermilk, shrikhand, Help the useful bacteria of the large intestine, which break
kanji, pickles, gundruk, poita bhat down fibre and make essential nutrients

Pulses and beans Provide protein along with fibre

Spices used sensibly — ginger, black pepper, cumin The Charaka Samhita notes their judicious use to enhance
digestion

Plenty of plain water Prevents hard stool and constipation

Tip: what to cut down on — too much fried food, packaged snacks, and cold drinks.
They carry very little fibre and slow the gut down.

Q3 Using coloured clay, prepare a 3-D model of the digestive system and label all parts
of the digestive system using black paper strips.

How to do this project: take a stiff cardboard sheet as the base and draw a faint human outline
on it. Roll and shape coloured clay for each organ, press it into place, then write the names on
black paper strips in white ink and pin them beside each organ with a thread leader.
A good model must contain every part of the alimentary canal in the correct order, the two
associated parts (liver and pancreas) shown pouring into the small intestine, and correct relative
sizes — the small intestine must be clearly the longest and the large intestine clearly the widest.

Page 36 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

PART TO SHAPE AND COLOUR OF CLAY LABEL ON THE BLACK STRIP
MAKE

Mouth Small open oval, pink Mouth — teeth chew; saliva starts starch
digestion

Oesophagus Long thin rope, light pink, straight Food pipe (Oesophagus) — pushes food to the
down stomach

Stomach J-shaped bag, deep pink or red Stomach — churns food; digestive juice, acid
and mucus

Liver Large flat wedge, dark brown, upper Liver — secretes bile
right

Pancreas Thin leaf shape, cream, tucked below Pancreas — secretes pancreatic juice
the stomach

Small intestine A very long thin rope, orange, coiled Small intestine — about 6 m; digestion
tightly in the middle completed and nutrients absorbed

Large intestine A thicker, shorter tube, purple, Large intestine — about 1.5 m; absorbs water
framing the coil like an arch and salts

Rectum Short straight piece at the lower end Rectum — stores the stool

Anus Small opening at the bottom Anus — egestion

Tip: roll the small intestine as one single long rope, not several short pieces. The
whole point of the model is to show a student how astonishingly long that one tube
is.

Q4 What is air quality and AQI? Find out the effect of air quality on the respiratory
systems of people working in various fields — farmers, factory workers, or street
vendors.

Air quality tells us how clean or polluted the air is. AQI stands for Air Quality Index — a single
number, published daily for Indian cities by the Central Pollution Control Board, that turns the
amounts of the main pollutants (fine dust PM2.5 and PM10, sulphur dioxide, nitrogen dioxide,
carbon monoxide and ozone) into one easy figure with a colour.

Page 37 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

AQI VALUE CATEGORY WHAT IT MEANS FOR BREATHING

0–50 Good Air causes little or no risk

51–100 Satisfactory Minor breathing discomfort to a few sensitive people

101–200 Moderate Discomfort for people with asthma or lung and heart disease

201–300 Poor Breathing discomfort to most people on long exposure

301–400 Very poor Respiratory illness on prolonged exposure

401–500 Severe Affects even healthy people; serious effect on those already ill

How to do this project: note your city's AQI from a newspaper or the SAMEER app every day for
a week and plot it as a bar graph. Then interview two or three working people and write down,
in their own words, what they notice about their breathing.
Sample findings:

Farmers — dust while ploughing and threshing, smoke from burning crop residue, and
spray from pesticides. Many report cough, sneezing, watery eyes and breathlessness during
the harvest and stubble-burning weeks.
Factory workers — fine dust from stone cutting, cement, cotton mills or grinding, and
chemical fumes. Long exposure damages the lungs and can lead to lasting lung disease; a
good factory therefore supplies masks and exhaust fans.
Street vendors and traffic police — spend the whole day beside vehicles, breathing
exhaust smoke and road dust. They commonly report a burning throat, frequent colds and
headache in winter, when smoke settles low near the ground.

Tip: end with practical suggestions — a proper mask (not a thin cloth), planting trees
along roads, not burning leaves or crop residue, watering dusty roads, and taking
short breaks in clean air. Recall from the chapter that the nose can filter only part of
the dust; the rest reaches the lungs.

Page 38 of 44

as e
Class 7 Science Chapter 9 Life Processes in Animals
a g l AglaSem · NCERT Solutions

co m
m.
Try to read about the box-breathing technique (Fig. 9.17). What are its benefits?
e
Q5

m l as
m .co a g
l a se
g
Hold
a

co m
e m . ag
g l as
Breathing in a Breathing out

co m
em.
m l as
m .co a g
l a se
a g Hold

m a s
.co agl
Fig. 9.17, page 136 — the box-breathing technique.

se m
g l a
a
m

. co
m
Box breathing (also called square breathing) is a simple, slow breathing exercise with four

as e
comof the square: l
equal steps — which is why the book draws it as a square (Fig. 9.17). Count four seconds for
. a g
em
each side

a s
agl
se m
com g l a
m . a
ase
agl

co m
m .
m as e
.co a g l
se m
g l a
a c
m .
m a s e
e m . co agl
g l as
a

co m
m .
m ase
.co


a g l Page 39 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Hold — 4 counts

Breathe in Breathe out
4 counts 4 counts

Hold — 4 counts
Repeat the square 4 to 6 times.

Box breathing: four equal steps of four counts each, done slowly through the nose.

Benefits reported for box breathing:

Calms the mind quickly — it slows a racing heart and settles nervousness before an exam,
a stage performance or a match.
Improves concentration, because counting gives the mind one simple thing to hold on to.
Makes breathing deep and regular instead of shallow and fast, so more air reaches the
lower parts of the lungs.
Strengthens the diaphragm and the breathing muscles with regular practice.
Helps with sleep when done for a few minutes at bedtime.
Needs nothing at all — no equipment, no space, and it can be done sitting in a classroom.

Tip: breathe through the nose, keep the back straight, and never strain. If four
counts feel long, start with three. This belongs to the same family as pranayama,
which Indian traditions have used for centuries for respiratory health, relaxation and
concentration.

Page 40 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Q6 Both birds and mammals have lungs for breathing, but birds can fly at high
altitudes where oxygen levels are low. How might their respiratory system be
adapted to help them survive in such conditions?

Flying is very hard work, and the air high above the ground is thin — a given breath there
carries far less oxygen. A bird's respiratory system is built to squeeze more oxygen out of less
air.

Air sacs. Besides lungs, a bird has thin-walled air sacs spread through its body. They act like
bellows, storing and pushing air, so the lungs are never left empty between breaths.
Fresh air flows through the lungs in one direction. In a mammal the air goes in and
comes back out of the same blind sacs, so each fresh breath mixes with stale air. In a bird the
air keeps moving forward, so the lung is bathed in fresh air both while breathing in and
while breathing out.
Oxygen is taken up even during exhalation. Because of this one-way flow, a bird does not
waste half of every breathing cycle.
Very fine, closely packed air tubes in the lung give a large surface in contact with blood, so
oxygen passes into the blood quickly.
Blood that holds oxygen tightly and a fast, powerful heart carry the oxygen quickly to the
flight muscles.
A high breathing rate during flight moves a large volume of air through the system.

Result: the chapter notes that "some other animals can use a larger fraction of the oxygen
during respiration". Birds are exactly such animals — they take a bigger share of the oxygen out
of each breath than we do. That is why bar-headed geese can fly over the Himalayas, at heights
where a human being would need an oxygen cylinder.

Why it happens: flight muscles work far harder than walking muscles, so they need
a great deal of energy, and energy comes from breaking down glucose with oxygen.
An animal that needs more oxygen where there is less of it can survive only by
improving the delivery system — which is exactly what a bird's respiratory system
does.

How to explore this: read about bar-headed geese and Rüppell's vulture, and draw
a simple comparison chart — mammal lung: air in and out of the same sac; bird lung:
air flows through in one direction with air sacs at both ends.

Page 41 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Chapter at a glance
Nutrition, respiration, circulation, excretion and reproduction are the life processes that
keep an animal alive. This chapter takes up nutrition and respiration in detail.
Complex food components — carbohydrate, protein and fat — are broken into simpler
forms inside a long tube called the alimentary canal, which runs from the mouth to the
anus.
Digestion begins in the mouth: teeth do mechanical digestion and saliva starts changing
starch into sugar. The stomach adds digestive juice, acid and mucus; the liver adds bile and
the pancreas adds pancreatic juice.
The small intestine (about 6 m) is the longest part of the canal. Its thin inner lining carries
thousands of finger-like projections that absorb the digested nutrients into the blood.
The large intestine (about 1.5 m) is shorter but wider. It absorbs water and some salts, the
semi-solid stool is stored in the rectum, and it leaves through the anus — a process called
egestion.
Animals differ: cows and buffaloes are ruminants that bring food back for rumination;
birds have no teeth but grind food in a gizzard with the help of grit.
Breathing is the physical movement of air in and out of the lungs. Ribs move up and out
and the diaphragm moves down during inhalation; both move back during exhalation.
Gases are exchanged in the balloon-like alveoli. Inhaled air has nearly 21% oxygen and
0.04% carbon dioxide; exhaled air has nearly 16–17% oxygen and 4–5% carbon dioxide.
Respiration is a chemical process: Glucose + Oxygen → Carbon dioxide + Water + Energy.
Breathing brings the oxygen in; respiration uses it to release energy.
Different animals breathe differently — lungs in birds and mammals, gills in fish, gills then
lungs and skin in frogs, and moist skin in earthworms.

Page 42 of 44

Class 7 Science Chapter 9 Life Processes in Animals AglaSem · NCERT Solutions

Quick revision

TERM WHAT IT MEANS EXAMPLE / DETAIL FROM POINT TO REMEMBER
THE CHAPTER

Alimentary The long tube in which Mouth → oesophagus → Liver and pancreas are
canal food is digested stomach → small intestine → associated parts, not part
large intestine → anus of the tube

Mechanical Breaking food into fine Crushing and chewing by the Happens mainly in the
digestion pieces without changing it teeth mouth
chemically

Saliva Watery fluid of the mouth Breaks starch of chapati or rice Iodine test: starch gives
that carries a digestive into sugar — that is why it tastes blue-black colour
juice sweet on long chewing

Oesophagus Flexible tube from mouth Its walls contract and relax in a This wave-like movement
(food pipe) to stomach wave-like motion occurs all along the canal

Stomach Muscular bag that churns Secretes digestive juice, acid and Acid kills bacteria; mucus
food mucus protects the stomach
lining

Bile Mildly basic secretion of Neutralises the acid coming from Liver is the largest gland
the liver the stomach and breaks fat into of the body
tiny droplets

Pancreatic juice Basic juice secreted by the Acts on carbohydrate, protein Also helps neutralise acid
pancreas and fat in the food

Absorption Passing of digested Through the finger-like The projections increase
nutrients into the blood projections of the small intestine the surface area

Egestion Removal of undigested Semi-solid stool stored in the Fibre-rich food makes
waste through the anus rectum stool easier to pass

Rumination Bringing partly digested Cow, buffalo, goat — the A cow chews for about 8
food back to the mouth for ruminants hours a day
thorough chewing

Gizzard Muscular chamber in birds Works with grit (small stones) the Birds have no teeth
that grinds food bird swallows

Breathing Taking air in (inhalation) Ribs move up and out, A physical process
and pushing it out diaphragm moves down while
(exhalation) inhaling

Page 43 of 44

ase
Class 7 Science Chapter 9 Life Processes in Animals
a g l AglaSem · NCERT Solutions

co m
m.
TERM WHAT IT MEANS EXAMPLE / DETAIL FROM POINT TO REMEMBER

as e
com
THE CHAPTER

. a g l
m
ase
Alveoli Balloon-like sacs at the Thin walls surrounded by fine The actual site of gas

agl
ends of the finest branches blood-carrying tubes exchange
in the lungs

. co+ m ag
Respiration Breakdown of glucose Glucose + Oxygen → Carbon A chemical process,

e m
las
using oxygen to release dioxide Water + Energy happens inside the body

ag
energy

Gills Specialised breathing Fish, and tadpoles of frogs Richly supplied with
structures of most aquatic
co m
blood vessels

e m.
animals

m l as
m .co a g
l a se
a g
m a s
m.co agl
l a se
a g

co m
m .
m as e
.co a g l
se m
g l a
a
se m
com g l a
m . a
ase
agl

co m
m .
m as e
.co a g l
se m
g l a
a c
m .
m a s e
e m . co agl
g l as
a

co m
m .
m as e
.co


a g l Page 44 of 44