NCERT Solutions Class 7 Science Chapter 10 Life Processes in Plants

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 10: Life Processes in
Plants

NCERT Textbook — Curiosity

BOOK PAGES SECTIONS QUESTIONS MEDIUM

137 – 152 22 54 English

Solutions, notes, sample papers & more at 46 pages

Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

CLASS 7 · SCIENCE · CURIOSITY

NCERT Solutions — Chapter 10: Life Processes in Plants
Complete NCERT Solutions for Class 7 Science Chapter 10 Life Processes in Plants from the NCERT textbook
Curiosity. Every question is answered — Activities 10.1 to 10.8 with Tables 10.1, 10.2 and 10.3 filled in, the
Dive Deeper and Know a Scientist boxes, every in-text question from pages 137 to 149, all ten Let Us
Enhance Our Learning exercises and the three Exploratory Projects — with labelled diagrams of
photosynthesis, stomata and the xylem–phloem transport system.

TEXTBOOK BOOK PAGES

Curiosity (Class 7) 137 – 152

SECTIONS QUESTIONS

22 54

MEDIUM

English

In-text Questions — Page 137
Chapter opener

Q1 Have you ever seen plants eating food like animals do?

No. Nobody has ever seen a plant eat. Animals take in ready-made food through a mouth;
plants have no mouth and no digestive system, and they do not swallow anything.
Plants are green and stay in one place — and that is the clue. Instead of eating, they make their
own food inside their leaves, using sunlight, water and a gas from the air. Only the raw
materials enter the plant: water and minerals through the roots, and carbon dioxide through
tiny pores in the leaves.

Why it matters: because plants make food and animals cannot, every animal —
including us — depends on plants either directly (eating chapati, rice, vegetables) or
indirectly (eating milk, eggs or meat from animals that ate plants).

Q2 What changes do you notice in plants when they grow?

When a plant grows, you can see these changes:

Page 1 of 46

Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

New leaves and branches emerge from the buds.
The height increases — a sapling becomes a tall plant.
The stem thickens and becomes stronger, so the plant can hold itself up.
The root system spreads deeper and wider in the soil.
After some time flowers and then fruits and seeds appear.
The plant's weight increases, just as it does in a growing animal.

Check it yourself: tie a thread loosely around the stem of a young tomato or chilli
plant and mark its height on a stick. Look again after two weeks — the thread will
have become tight and the mark will be well below the top.

In-text Questions — Page 138
10.1 How Do Plants Grow?

Q1 Look around your neighbourhood. Have you observed any changes in a plant during
its life span?

Yes. A plant changes continuously through its life span. A neem or a money plant that you pass
every day looks quite different after a few months.

A tiny seedling with two small leaves becomes a leafy plant.
The number of leaves and branches keeps increasing.
The height increases and the stem becomes thick and woody in trees.
Old leaves turn yellow and fall; new green leaves take their place.
In the right season the plant flowers, then bears fruits and seeds.

Try This: pick one plant near your home and photograph or sketch it on the first day
of every month for a year. Your own record will show its whole life span in twelve
pictures.

Q2 What do you think causes these changes? Discuss with your friends and provide
your explanation as well.

These changes happen because the plant is making food and using it to build new parts. Four
things supply what is needed:

Page 2 of 46

Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Sunlight — the energy source for making food.
Water — taken up by the roots; used in food-making and to keep the plant firm.
Air — supplies carbon dioxide, the raw material that becomes the plant's food.
Minerals from the soil — important nutrients that the roots absorb along with water.

The four explanations the children in the book give — water, sunlight, food from the soil
through the roots, and 'something else' — are all sensible hypotheses. Two of them (water and
sunlight) are tested in Activity 10.1. The third one needs correction: roots do not take food
from the soil; they take water and minerals. The plant makes its own food in the leaves.

Why a discussion is asked for: in science, an explanation is only a starting point. It
becomes knowledge when an experiment is designed to test it — which is exactly
what Activity 10.1 does.

Q3 I think, maybe, ________ plays some role!

The blank can be filled in several correct ways. The strongest answers, and how you could test
each one, are:

FILL THE BLANK WHY IT IS A GOOD GUESS HOW YOU COULD TEST IT
WITH

Air (carbon dioxide) Plants are surrounded by air all Enclose one leaf with caustic soda, which absorbs
the time carbon dioxide — Activity 10.4

Minerals in the soil Plants in rich garden soil grow Grow similar saplings in garden soil and in
better than in sand washed sand, water both equally

Warmth / temperature Plants grow faster in some Keep identical potted plants in a warm and a
seasons than others cool place, both in light

Green colour of Almost all growing plants are Do the iodine test on green and non-green
leaves green patches of the same leaf — Activity 10.3

Sample answer: "I think, maybe, air plays some role!" — and the book proves this right in
Activity 10.4, where the part of the leaf kept away from carbon dioxide makes no starch.

Activity 10.1: Let us test some explanations — Pages 138 & 139

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Class 7 Science Chapter 10 Life Processes in Plants
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10.1 How Do Plants Grow?
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ACTIVITY

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Observe
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leaves, and any other changes that may appear. Record your observations in Table 10.1

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Fig. 10.1, page 138 — experimental set-up to understand the role of sunlight and water in pla

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POTS KEPT AVAILABILITY OF HEIGHT OF NUMBER OF COLOUR
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UNDER PLANT (CM) LEAVES LEAVES
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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Table 10.1, page 139 — the blank recording table to be filled in with your own observati

Three identical pots of garden soil, each with a similar chilli or tomato sapling, are kept as
shown in Fig. 10.1 — A in direct sunlight with water, B in direct sunlight without water, C in the
dark with water. Here is Table 10.1 with the readings a class usually gets after two weeks.

TABLE 10.1: EFFECT OF SUNLIGHT AND WATER ON PLANT GROWTH

POTS KEPT AVAILABILITY OF HEIGHT OF NUMBER OF COLOUR OF
UNDER PLANT (CM) LEAVES LEAVES
DIFFERENT (GREEN/YELLOW)
CONDITIONS SUNLIGHT WATER DAY AFTER DAY AFTER
1 2 1 2
WEEKS WEEKS

Pot A: In direct Yes Yes 10 17 6 13 Green (healthy,
sunlight, with upright)
water

Pot B: In direct Yes No 10 10 6 2 (rest Yellow to brown, dry
sunlight, without (drooped, fell off)
water then
dried)

Pot C: In the No Yes 10 13 (thin, 6 8 Pale yellow-green
dark, with water weak, (small)
leaning)

Other changes worth recording: the stem of Pot A becomes thicker and sturdy; the plant in Pot
C becomes thin and spindly and bends towards any crack of light; the soil in Pot B becomes
hard and cracked.

Check it yourself: write down the height and leaf count on Day 1 before you
separate the pots. Numbers taken only at the end cannot show growth.

Q2 What differences did you observe between the plants in the three pots?

The three plants started alike but ended up completely different.

Pot A (sunlight + water): tallest, most leaves, dark green leaves, thick upright stem — a
healthy plant.

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Pot B (sunlight, no water): the leaves first drooped, then turned yellow and dry and fell off.
There was almost no increase in height. The plant wilted and may have died.
Pot C (dark + water): the plant stayed alive and even grew a little taller, but it was thin,
weak and pale yellow-green, with small leaves. It leaned towards any light that entered.

Why Pot C turns pale: in the dark, the leaves cannot make food and do not develop
their full green colour, because chlorophyll needs light. The plant lives for a while on
the food already stored in it — that is why it can stretch upward but cannot become
strong.

Q3 Which pot has the plant with the maximum growth?

Pot A — the pot kept in direct sunlight with an adequate amount of water every day.
It is the only pot in which both the things being tested are available at the same time. The plant
gets sunlight to make food and water both as a raw material and to stay firm, so it grows tallest,
produces the most leaves and keeps them dark green.

Q4 Which pot has the plant with the least growth?

Pot B — the pot kept in direct sunlight without any water.
Water is needed to keep the plant firm, to carry minerals up from the roots and as a raw
material for food-making. Without it the plant wilts, its leaves dry and fall, and it may die — so
its growth is the least, even though it received plenty of sunlight.

Tip: do not confuse "least growth" with "looks weakest in colour". Pot C looks pale
but still gains height; Pot B gains almost nothing at all.

Q5 What do you infer from the observations made in this activity?

Plants require both sunlight and water for their growth.

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Sunlight + water (Pot A) → best growth

Water but no sunlight (Pot C) → poor, pale, weak growth

Sunlight but no water (Pot B) → wilting and death

Removing either one damages the plant, so neither can replace the other. This is why the
experiment uses three pots: pot A is the comparison (control), and pots B and C each remove
one factor.

Why the pots must be identical otherwise: same size pots, same garden soil,
saplings of the same kind and similar size. If the pots differed in more than one way,
we could not say which change caused the difference in growth.

Activity 10.2: Let us check (demonstration activity) — Pages 140 & 141

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

10.2.1 Leaves: the 'food factories' of plants

ACTIVITY

Q1 Keep a leaf in boiling water for five minutes to soften it. Dip this leaf in a test tube
containing alcohol. Place the test tube in a beaker containing boiling water. Wait
until the leaf becomes colourless (Fig. 10.2a). Take out the leaf and place it on a
plate. Now, put a few drops of diluted iodine solution with the help of a dropper on
the decolourised leaf (Fig. 10.2b). Wait for a few minutes and observe.

Test tube

Water

Alcohol

Leaf

Wire gauze

Iodine
solution

Spirit lamp

(a) Boiling set-up (b) Iodine test

Fig. 10.2, page 140 — starch test in a leaf: (a) the boiling set-up, (b) adding iodine to the
decolourised leaf.

Observation: the leaf, which was pale cream after decolourisation, turns blue-black where
iodine touches it. This indicates the presence of starch in the leaf.
What each step is for:

STEP WHAT IT DOES

Boiling water for five minutes Softens the leaf and kills it, so that alcohol and iodine can enter easily

Alcohol in a test tube, tube kept in boiling Hot alcohol dissolves out the green chlorophyll — the leaf becomes
water colourless

Dilute iodine solution on the leaf Iodine gives a blue-black colour with starch — the test for food stored
in the leaf

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Class 7 Science Chapter 10 Life Processes in Plants
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Caution: alcohol should never be placed near a heat source directly, as it is highly

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flammable and can easily lead to fire and burns. That is why the test tube of alcohol
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inside a beaker of boiling water, and why the

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Why this matters: a blue-black leaf is direct evidence that the leaf itself made and
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photosynthesis needs.

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Dive Deeper — Page 141
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10.2.1 Leaves:

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Q1 Did you wonder why we decolourise the leaf in the beginning of this activity?

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Because the leaf's own green colour would hide the result.

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Iodine turns starch blue-black. On a dark green leaf, blue-black on green simply looks like "dark

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green" — you cannot tell whether the colour changed. Once the chlorophyll has been dissolved
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out by.chot alcohol, the leaf is pale cream, and even a faint blue-black
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sethe book's words: decolourisation of a leaf enables us to easily observe colour change
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and, thus, the presence of starch.

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Tip: this also explains Activity 10.3.

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

10.2.1 Leaves: the 'food factories' of plants

Q1 How does sunlight contribute in the production of starch in plants?

Sunlight supplies the energy for making food. Chlorophyll in the leaf captures this light energy
and uses it to combine carbon dioxide and water into glucose, which is then converted into
starch for storage.

Sunlight

Carbon dioxide + Water → Glucose + Oxygen

Chlorophyll

Bhaskar's question is answered by Activity 10.3: a leaf from a plant kept in sunlight gives a
blue-black colour on its green patches, while a leaf from an identical plant kept in the dark for
36 hours gives no blue-black colour at all. No sunlight means no starch.

Activity 10.3: Let us check — Pages 141 to 143
10.2.1 Leaves: the 'food factories' of plants

ACTIVITY

Q1 Non-green patches of the leaf obtained from the plant placed in sunlight do not
turn blue-black. Does it indicate that there is no chlorophyll present in those
patches?

Not necessarily. The correct conclusion is more careful: the non-green patches may not have
sufficient chlorophyll to prepare enough starch for the iodine test to detect.
This is what Bhaskar recorded:

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

TABLE 10.2: PRESENCE OF STARCH IN GREEN AND NON-GREEN PARTS OF THE LEAVES OF
PLANTS

S.NO. LIGHT CONDITIONS INITIAL COLOURS FINAL COLOURS AFTER
FOR POTTED PLANT BEFORE IODINE TEST IODINE TEST

1. Plant kept in sunlight Green and non-green Green patches of leaf turned blue-
patches on the leaf black (non-green patches
unchanged)

2. Plant kept in the dark Green and non-green No change in colour
patches on the leaf

Why we must be careful: the iodine test detects starch, not chlorophyll. "No blue-
black" only tells us that too little starch was made there to be detected. A small
amount of chlorophyll may still be present in those patches — some coloured leaves
even contain other pigments that hide the green.

Did you know? Some leaves look red, violet or brown because they contain more of
these coloured pigments than green chlorophyll, which hides the green. Some of
those pigments also help in photosynthesis — an iodine test on such a leaf can still
turn blue-black.

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Q2 What do we infer from the observations listed in Table 10.2?

TABLE 10.2: PRESENCE OF STARCH IN GREEN AND NON-GREEN PARTS OF THE
LEAVES OF PLANTS

S.NO. LIGHT CONDITIONS INITIAL COLOURS FINAL COLOURS
FOR POTTED PLANT BEFORE IODINE AFTER IODINE TEST
TEST

1. Plant kept in sunlight Green and non-green Green patches of leaf
patches on the leaf turned blue-black

2. Plant kept in the dark Green and non-green No change in colour
patches on the leaf

Table 10.2, page 142 — the observations Bhaskar recorded in Activity 10.3. The leaves are
redrawn sketches of the ones printed in the table.

Two clear inferences:

Page 12 of 46

Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

1. Chlorophyll is essential for making starch. In the leaf from the sunlit plant, only the green
patches turned blue-black. Starch was produced exactly where chlorophyll was present.
2. Sunlight is essential for making starch. The leaf from the plant kept in the dark for 36
hours showed no blue-black colour even on its green patches — chlorophyll alone,
without light, made no starch.

Putting them together: chlorophyll helps in preparing starch in the presence of sunlight. Since
starch is made in the leaves, leaves are called the 'food factories' of plants.

PART OF LEAF TESTED CHLOROPHYLL SUNLIGHT RESULT OF IODINE TEST

Green patch, plant in sunlight Yes Yes Blue-black — starch present

Non-green patch, plant in Insufficient Yes No colour change — starch not
sunlight detected

Green patch, plant in the dark Yes No No colour change — no starch

Non-green patch, plant in the Insufficient No No colour change — no starch
dark

Tip: the tracing-paper sketch Bhaskar made before the test is the key to this activity.
Without a record of where the green patches were, you could not match the blue-
black areas to them afterwards.

In-text Questions — Page 143
10.2.2 Role of air in the preparation of food

Q1 What else is essential for the preparation of food in plants? Let us find out.

So far the chapter has established water, sunlight and chlorophyll. The one raw material still
missing is a gas from the air — carbon dioxide.
The complete list of requirements for photosynthesis is therefore:

Carbon dioxide — from the air, entering through the stomata
Water — absorbed by the roots and carried up by the xylem
Sunlight — the energy source
Chlorophyll — the green pigment that captures that energy

Activity 10.4 is designed to test the fourth item on this list.

Page 13 of 46

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Class 7 Science Chapter 10 Life Processes in Plants
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Which gas from the air is essential in the process of food preparation in plants?
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Carbon
Air is a mixture of gases — mainly nitrogen and oxygen, with a very small amount of carbon

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dioxide. Of these, it is carbon dioxide that the plant uses as a raw material and builds into
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glucose. It enters the leaf through the tiny pores
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How we know: in Activity 10.4, caustic soda inside the bottle absorbs the carbon
dioxide around the enclosed half of a leaf. That half makes no starch, while the half
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outside — in the same sunlight, on the same plant, with the same chlorophyll and
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water — turns blue-black. The only difference between the two halves is carbon
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Activity 10.4: Let us experiment (demonstration activity) — Pages 143 &
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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

10.2.2 Role of air in the preparation of food

ACTIVITY

Q1 Observe and record the availability of water, sunlight, chlorophyll, and carbon
dioxide in Table 10.3. Remove the leaf and test it for starch using the iodine test, as
was done in Activity 10.2. Record your observations in Table 10.3.

Destarched
plant

Sodium
hydroxide
solution

(a) The set-up

Fig. 10.3(a), page 143 — the set-up for Activity 10.4.

TABLE 10.3: ROLE OF AIR IN THE PREPARATION OF STARCH BY PLANTS

PART AVAILABILITY OF STARCH
OF THE PRESENT
LEAF WATER SUNLIGHT CHLOROPHYLL CARBON (YES/NO)
DIOXIDE

Part of
the leaf
inside the
bottle

Part of
the leaf
outside
the bottle

Table 10.3, page 144 — the blank recording table for Activity 10.4.

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Half of a destarched leaf is sealed inside a wide-mouthed bottle containing caustic soda through
a split cork; the other half stays outside in the air (Fig. 10.3a). The whole set-up is kept in
sunlight for a few hours. Here is Table 10.3 completed.

TABLE 10.3: ROLE OF AIR IN THE PREPARATION OF STARCH BY PLANTS

PART OF AVAILABILITY OF STARCH
THE LEAF PRESENT
WATER SUNLIGHT CHLOROPHYLL CARBON (YES/NO)
DIOXIDE

Part of the leaf Yes Yes Yes No (absorbed by No
inside the caustic soda)
bottle

Part of the leaf Yes Yes Yes Yes Yes
outside the
bottle

After the iodine test (Fig. 10.3b), the half that was outside the bottle turns blue-black; the half
that was inside shows no colour change.

Caution: caustic soda is a strong chemical that can cause skin burns; only teachers
should handle it.

Why the plant is destarched first: if the plant already had stored starch, both
halves of the leaf would turn blue-black and the experiment would prove nothing.
Keeping the plant in the dark for two to three days empties this store, so any starch
found afterwards must have been made during the experiment.

Q2 What does this experiment show?

This experiment shows that carbon dioxide present in the air is essential for plants to
prepare starch.
The two halves are part of the same leaf on the same plant, in the same sunlight, with the same
water and the same chlorophyll. Only one factor differs — the air around the inside half has had
its carbon dioxide removed by the caustic soda. That half makes no starch; the other half does.

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Why one leaf, and not two plants: using two halves of one leaf makes every other
condition automatically identical. It is the cleanest possible way to test a single
factor — a good example of a fair test.

Q3 Based on Activities 10.3 and 10.4, what do you conclude?

Together, the two activities identify all four requirements for making food in plants.

ACTIVITY FACTOR REMOVED STARCH CONCLUSION
FORMED?

10.3 — plant kept in the dark Sunlight No Sunlight is essential

10.3 — non-green patches of Chlorophyll No Chlorophyll is essential
leaf (insufficient)

10.4 — leaf-half inside the Carbon dioxide No Carbon dioxide is
bottle essential

10.1 — pot without water Water Plant wilts and dies Water is essential

Conclusion: sunlight, water, chlorophyll and carbon dioxide are all essential for the synthesis of
food in plants. This process, by which plants prepare food in the presence of sunlight and
chlorophyll, is called photosynthesis.

Sunlight (energy)

Carbon dioxide Glucose
from the air
PHOTOSYNTHESIS stored as starch
in the green leaf
Water (chlorophyll + sunlight) Oxygen
from the roots released into the air

Remove any one input and no starch is formed.

What goes into photosynthesis and what comes out of it. Activities 10.1, 10.3 and 10.4 each remove
one input and show that starch is then not formed.

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Q4 Which part of the plant is involved in the synthesis of starch?

Mainly the leaf. A leaf is the primary site for photosynthesis — that is why leaves are called the
'food factories' of plants.
Leaves are suited to the job because they are:

broad and flat — a large surface to catch sunlight;
green — full of chlorophyll to capture that light;
dotted with stomata — pores through which carbon dioxide enters;
supplied by xylem — thin tubes bringing water from the roots.

Q5 Do other green parts of the plant also perform photosynthesis?

Yes. Other parts of the plant which have chlorophyll also perform photosynthesis.

Green stems of young plants, and of cactus, where the stem does the work because the
leaves are reduced to spines.
Green sepals of a flower and the green skin of unripe fruits such as raw mango or lauki.
Green parts of leaf stalks and tendrils.

Check it yourself: destarch a money plant, keep it in sunlight for a day, and do the
iodine test on a piece of its green stem. It too turns blue-black.

In-text Questions — Pages 144 & 145
10.2.2 Role of air in the preparation of food

Q1 Do plants only take in substances from their surroundings, or do they also release
something?

Plants both take in and give out. During photosynthesis they take in carbon dioxide and
water, and they release oxygen into the air.

Carbon dioxide + Water → Glucose + Oxygen

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Class 7 Science Chapter 10 Life Processes in Plants
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Water vapour also escapes from the leaves. Separately, plants respire all the time — taking in
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oxygen and giving out carbon dioxide.
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Activity 10.5 is the experiment that shows the release of oxygen: bubbles of gas collect in an

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inverted test tube above a water plant kept in sunlight.

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Activity 10.5: Let us explore — Page 145
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10.2.2 Role of air in the preparation of food sem

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ACTIVITY

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In Fig. 10.4, set-up A is placed in sunlight, and set-up B is placed in the dark. What
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difference do you observe in the two set-ups?
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Air bubbles

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Beaker

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test tube

Funnel

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Water plant

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Both set-ups are identical — a water plant under an inverted funnel in a beaker of water, with an
inverted test tube full of water over the funnel stem. Only the light is different.

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SET- KEPT WHAT YOU SEE

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Sunlight A steady stream of air bubbles rises from the water plant, passes up the funnel stem and

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collects as gas in the inverted test tube, pushing the water level down

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B The dark No bubbles. The test tube stays full of water; no gas collects

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Why the funnel and the inverted test tube: the funnel gathers every bubble rising
from the plant and channels it into one narrow stream, and the water-filled inverted
test tube traps that gas so it can be collected and tested later.

Q2 Do you observe air bubbles emerging in the inverted test tube in set-up A?

Yes. In set-up A, kept in sunlight, bubbles rise continuously from the leaves of the water plant,
travel up through the funnel and gather in the inverted test tube.
They appear only in A. In set-up B, kept in the dark, no bubbles form — because photosynthesis
occurs in the presence of sunlight, and no gas is being produced.

Try This: use a fresh sprig of hydrilla and place set-up A near a sunny window. Count
the bubbles per minute, then shade the beaker partly with cardboard and count
again. The rate falls as the light falls.

Q3 The gas produced in this set-up caused bubbles to emerge and get accumulated in
the inverted test tube. Which gas is this?

It is oxygen.
Barkha didi proved it. When enough gas had collected, she closed the mouth of the inverted
test tube with her thumb, lifted it off the set-up, and quickly inserted a lit matchstick into it.
The matchstick produced an intense flame.

Why the flame flares up: oxygen supports burning. A glowing or small flame
becomes bright and intense in gas rich in oxygen. That is the standard test for
oxygen — and it also rules out carbon dioxide, which would have put the flame out.

Conclusion: oxygen is released during photosynthesis, and photosynthesis takes place in the
presence of sunlight.

Know a Scientist — Page 146

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

10.2.3 Photosynthesis: in a nutshell

KNOW A SCIENTIST

Q1 Who was Rustom Hormusji Dastur, and what did he contribute to our
understanding of photosynthesis?

Many scientists across the world contributed to develop an understanding of photosynthesis. In
India, Rustom Hormusji Dastur (1896–1961) studied the process.

He was a plant scientist (botanist).
He served as the head of the Botany Department at the Royal Institute of Science, Bombay
— now the Institute of Science, Mumbai — from 1921 to 1935.
He studied the effects of the amount of water and of temperature on photosynthesis.
He examined the importance of water, temperature and the colour of light in the process
of photosynthesis.

Did you know? His work on the colour of light connects directly to Activity 10.3 —
chlorophyll does not use every colour of sunlight equally, which is one reason leaves
look green.

In-text Question — Page 146
10.2.4 How do leaves exchange gases during photosynthesis?

Q1 Which part of the plant helps in the exchange of carbon dioxide and oxygen?

The leaves — more exactly, the tiny pores on their surface called stomata.
Carbon dioxide from the air enters the leaf through the stomata, and the oxygen produced
during photosynthesis leaves through them. During respiration the flow is the other way round:
oxygen in, carbon dioxide out. Activity 10.6 lets you see these pores under a microscope.

Activity 10.6: Let us examine (demonstration activity) — Page 147

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

10.2.4 How do leaves exchange gases during photosynthesis?

ACTIVITY

Q1 What do you observe? Do you notice tiny pores on the peel, as shown in Fig. 10.6?

Stomata

0.1 mm

Fig. 10.6, page 147 — stomata on the lower surface of a rhoeo leaf (redrawn sketch).

Yes. Under the microscope the thin peel from the lower surface of the leaf looks like a sheet of
closely fitted cells, and scattered among them are many tiny oval openings. Each opening is
bordered by a pair of curved, bean-shaped cells.
These pores are called stomata (one pore is a stoma). In the rhoeo leaf of Fig. 10.6 they are
about 0.1 mm across at the scale marked on the figure — far too small to see with the naked
eye.

Page 22 of 46

Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Guard cell

Carbon dioxide in Oxygen out
pore

Guard cell
Surrounding cells of the leaf peel are not shown.

One stoma as it appears in the peel: a pore between two guard cells. Gases pass in and out of the leaf
through thousands of such pores.

Why the ink and the lower surface: the ink does not stain the pores, so they stand
out clearly against the darkened cells around them. The lower surface is peeled
because most stomata of a broad leaf are on the shaded underside, where less
water is lost.

Q2 What are these pores called, and how do they help the plant?

They are called stomata. Stomata, present on the surface of leaves, help in the exchange of
gases.

PROCESS GAS ENTERING THROUGH GAS LEAVING THROUGH
STOMATA STOMATA

Photosynthesis (in Carbon dioxide Oxygen
sunlight)

Respiration (all the time) Oxygen Carbon dioxide

Did you know? Water vapour also escapes from the leaf through the stomata. That
is why a potted plant covered with a transparent polythene bag soon has drops of
water inside the bag.

Page 23 of 46

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Class 7 Science Chapter 10 Life Processes in Plants
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co m
m.
In-text Question — Page 147
m as e
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10.3.1 Transport of water and minerals
a g l
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aQ1gl How do water and minerals taken up by the roots move to all parts of the plant?

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Through thin tube-like structures called the xylem, which run continuously from the roots up

agthe leaves.
through the stem and branches into
Water and dissolved minerals absorbed by the roots enter these tubes and move upward,

co m
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reaching the leaves, flowers and every other part of the plant. Activity 10.7, with red ink, makes
this movement visible.
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Activity 10.7: Let us experiment — Page 148

m a s
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10.3.1 Transport of water and minerals

ACTIVITY
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Q1 What do you notice? Compare the plant stems placed in the tumblers. Do you

co m
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observe red colour in the stem, leaves, and flowers of the plant from Tumbler B?

e m
m l as
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emAfter one day, the twig standing in Tumbler B (water + a few drops of red ink) shows a clear

a s
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Yes.
a red tinge — fine red streaks run up the stem, red lines appear along the veins of the leaves, and
the white flowers turn pink or red (Fig. 10.7d).
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The twig in Tumbler A, standing in plain water,
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stem is green, the flowers still white.

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TUMBLER CONTENTS APPEARANCE OF THE TWIG AFTER ONE DAY

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Water only
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A No change — stem green, leaves green, flowers white

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B Water + a few drops of red Red colour visible in the stem, in the leaf veins and in the

l a s ink flowers

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Why Tumbler A is needed: A is the control. It proves the red colour came from the
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ink travelling up the plant and not from the twig drying or ageing.
e m agl
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a

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Q2 How did different parts of the plant acquire this red colour?

The twig absorbed the red-coloured water through its cut end and carried it upward inside
itself.
The coloured water travelled through the thin tubes of the xylem, which run from the base of
the stem into the branches, the leaf veins and the flowers. Wherever the water reached, the dye
it carried was left behind and made that part look red.

Tip: the stems are cut obliquely (at a slant) and while kept inside the water. A
slanting cut gives a larger surface for absorption, and cutting under water stops air
from entering the xylem tubes and blocking them.

Q3 Cut the stem from the upper part of the plant that is not immersed in the red-
coloured water. Observe the cut stem using a magnifying glass. Do you spot the red
colour in the stem (Fig. 10.7e)?

Phloem

Xylem

Cut

(e) Enlarged view of cut end of the twig

Fig. 10.7(e), page 148 — enlarged view of the cut end of the twig.

Yes. In the freshly cut cross-section, the red colour is not spread all over. It appears as a ring of
small red dots or dashes arranged in a circle inside the stem (Fig. 10.7e).

Page 25 of 46

Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Each red dot is the cut end of one xylem tube filled with the coloured water. Just outside them
lies another set of tubes, the phloem, which stays uncoloured because it does not carry this
water.

Why this observation is important: it shows the water did not soak through the
whole stem. It travelled along a definite set of pipes — which is exactly what a
transport system means.

Q4 How does the red colour ink move upwards?

Through the xylem — thin tube-like structures present in the stem, branches and leaves of
plants. Just like red ink, minerals dissolved in water also move up the stem through the xylem.

Leaves — food is made here

Water transport Food transport
through xylem through phloem

soil level

Roots — water and minerals are absorbed here

Two separate sets of tubes run through the plant: xylem carries water and minerals upward from the
roots, phloem carries food away from the leaves in all directions.

Try This: split the lower half of a white gladiolus or sadabahar stem lengthwise and
dip one half in red ink and the other in blue ink. After a day the flower is half red and
half blue — proof that separate xylem tubes carry water along separate paths.

In-text Question — Page 148

Page 26 of 46

Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

10.3.2 Transport of food

Q1 How does food get transported to other parts of a plant?

Through another set of thin tube-like structures called the phloem.
Leaves are the primary site for photosynthesis, so food is made there. The phloem carries this
food from the leaves to all parts of the plant — upward to growing buds and flowers, and
downward to the stem and roots. The transported food may also be stored in other parts, such
as seeds and roots.

TISSUE WHAT IT CARRIES FROM TO

Xylem Water and dissolved minerals Roots Leaves and other parts (upward only)

Phloem Food (made in the leaves) Leaves All parts, including seeds, roots and tubers

In-text Question — Page 149
10.4 Do Plants Respire?

Q1 Do plants also respire like we do?

Yes. All living beings respire, and plants are no exception. Like us, plants take in oxygen, use it
to break down glucose, and release carbon dioxide, water and energy.
The difference is only in the arrangement, not in the process: we have lungs and a breathing
system, while a plant has no lungs. Gases simply diffuse in and out through the stomata of
leaves and through the surface of young stems and roots. All parts of a plant, green or non-
green, carry out respiration — by day and by night.

Why we do not notice it: in daylight a green leaf is also photosynthesising, and
photosynthesis uses up carbon dioxide much faster than respiration produces it.
That is why Activity 10.8 uses germinating seeds kept in the dark — no
photosynthesis is possible, so respiration alone can be detected.

Activity 10.8: Let us find out (demonstration activity) — Page 149

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

10.4 Do Plants Respire?

ACTIVITY

Q1 Compare both the test tubes for any change in colour. Does the lime water turn
milky in both the test tubes?

No. The lime water turns milky only in the test tube connected to the conical flask. In the other
test tube, kept open beside it, the lime water stays clear.

TEST TUBE CONNECTED TO THE FLASK OF LIME WATER AFTER 24
GERMINATING SEEDS? HOURS

Test tube joined by the Yes Turns milky
rubber pipe

The other test tube No — only ordinary air above it Stays clear
(control)

Why a second test tube at all: it is the control. Ordinary air contains a very small
amount of carbon dioxide, not enough to turn lime water milky in a day. The clear
control tube proves that the milkiness in the first tube is caused by something
coming from the flask.

Q2 Why does the lime water turn milky in the test tube connected to the flask?

Because lime water turns milky due to the presence of more carbon dioxide in the flask.
When air from the flask is pushed through the glass tube into the lime water, the carbon dioxide
it carries reacts with the lime water and forms a fine white insoluble solid, which makes the
clear liquid look milky. The more carbon dioxide, the quicker and denser the milkiness.

Check it yourself: blow gently through a straw into a little lime water in a glass. It
turns milky within seconds — the carbon dioxide of your own respiration doing
exactly what the seeds' carbon dioxide does.

Page 28 of 46

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Class 7 Science Chapter 10 Life Processes in Plants
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co m
m.
But where does this carbon dioxide come from?
e
Q3

m l as
.co a g
a
s em
a gl the germinating moong seeds in the flask. Carbon dioxide is naturally present in very
From
small quantities in the air; in the flask, additional carbon dioxide is produced by the seeds as

om ag
they respire.
During respiration, glucose is broken down m . c
a s e in the presence of oxygen, releasing carbon dioxide,

agl
water and energy:

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Glucose + Oxygen → Carbon dioxide + Water + Energy

o m l a se
g — which is why
.c produced is used by the plant for its growth and development
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The energy

l a
soakedse seeds sprout so vigorously.
ag
s
Why the set-up is kept in the dark for 24 hours: in the dark the seeds cannot
m a
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photosynthesise, so no carbon dioxide is used up. Everything collected in the flask is

se m
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the product of respiration alone — that is what makes this a fair test of respiration.

a g l

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Let Us Enhance Our Learning — Pages 150 to 152
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m a s e
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a

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Chapter exercises

LET US ENHANCE OUR LEARNING

Q1 Complete the following table — S.No. / Feature / Photosynthesis / Respiration: 1.
Raw materials, 2. Products, 3. Word equation, 4. Importance

S.NO. FEATURE PHOTOSYNTHESIS RESPIRATION

1. Raw materials

2. Products

3. Word equation

4. Importance

The table as printed on page 150, with the cells left blank for you to fill in.

S.NO. FEATURE PHOTOSYNTHESIS RESPIRATION

1. Raw Carbon dioxide and water (with sunlight as Glucose and oxygen
materials the energy source and chlorophyll as the
pigment)

2. Products Glucose and oxygen Carbon dioxide, water and energy

3. Word Carbon dioxide + Water → Glucose + Glucose + Oxygen → Carbon dioxide
equation Oxygen + Water + Energy
(in the presence of sunlight and chlorophyll)

4. Importance Makes food for the plant and for every Releases the energy stored in glucose,
organism that feeds on plants; stores energy which the plant uses for its growth
as glucose and starch; releases the oxygen and development; it goes on in all
that living beings need parts of the plant, day and night

Tip to remember: the two processes are almost mirror images. What
photosynthesis takes in, respiration gives out — and the other way round.

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Q2 Imagine a situation where all the organisms that carry out photosynthesis on the
earth have disappeared. What would be the impact of this on living organisms?

Life on the earth would collapse. Photosynthesising organisms — green plants, algae and some
bacteria — are the only ones that make food from simple substances. Everything else depends
on them.

Food would run out. No new food would be produced anywhere. Herbivores would starve
first; then the carnivores that eat herbivores; finally every animal, including human beings.
Oxygen would fall. Oxygen is added to the air mainly by photosynthesis. Respiration by all
living things, and burning, would keep using it up without any being replaced.
Carbon dioxide would build up in the air, because nothing would be removing it.
Food chains and food webs would break down, and with them the whole balance of
nature.
There would be no grains, fruits, vegetables, cotton, timber or fodder, so farming,
clothing and much of industry would end too.

Why plants are called producers: because they alone produce food out of carbon
dioxide and water using sunlight. Animals are consumers — they can only use what
has already been produced.

Q3 A potato slice shows the presence of starch with iodine solution. Where does the
starch in potatoes come from? Where is the food synthesised in the plant, and how
does it reach the potato?

Where the starch comes from: it comes from the food the potato plant made in its own leaves
by photosynthesis. It was not taken from the soil.
Where the food is synthesised: in the leaves, the primary site of photosynthesis. Carbon
dioxide from the air and water from the roots are combined, in the presence of sunlight and
chlorophyll, into glucose.
How it reaches the potato: the glucose is loaded into the phloem and carried down from the
leaves to the underground stems. There the extra food is converted into starch and stored, and
those swollen underground stems are the potatoes we eat.

Page 31 of 46

Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Leaf (photosynthesis) → glucose

Glucose → carried by phloem

Stored in the underground stem as starch → the potato

Did you know? A potato is a stem, not a root. The "eyes" on it are buds — which is
why a potato left in a corner sprouts new shoots.

Q4 Does the broad and flat structure of leaves make plants more efficient for
photosynthesis? Justify your answer.

Yes, it does. The broad, flat shape suits every requirement of photosynthesis at once.

Large surface for sunlight. A wide flat blade held out to the sky catches far more light than
a narrow or rolled leaf of the same amount of material.
Thin, so light reaches all the chlorophyll. In a thick leaf the deeper cells would be shaded
by the ones above them.
More stomata exposed to the air, so carbon dioxide can enter quickly and oxygen can
leave.
Short distance for gases inside the leaf. Because the blade is thin, carbon dioxide has only
a tiny distance to travel from a stoma to the cells that use it.
A branching network of veins spread across the flat blade brings water everywhere in the
leaf and carries food away.

The exception proves the rule: a cactus lives where water is scarce, so its leaves are
reduced to spines to save water — and its green stem takes over photosynthesis.
Where water is not a problem, the broad flat leaf is the better design.

Q5 X is broken down using Y to release carbon dioxide, Z, and energy. X + Y → Carbon
dioxide + Z + Energy. X, Y, and Z are three different components of the process. What
do X, Y, and Z stand for?

The equation is the word equation for respiration:

Page 32 of 46

Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Glucose + Oxygen → Carbon dioxide + Water + Energy

Comparing term by term:

SYMBOL STANDS FOR ITS ROLE

X Glucose The food that is broken down — it holds the stored energy

Y Oxygen Used to break the glucose down

Z Water Formed as a product along with carbon dioxide and energy

How to be sure: the question says X is "broken down" and energy is released — so X
must be the food, glucose. Only one product of respiration is left unnamed once
carbon dioxide and energy are written, and that is water.

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Class 7 Science Chapter 10 Life Processes in Plants
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co m
m.
Krishna set-up an experiment with two potted plants of same size and placed one of
se
Q6

o m l a
them in sunlight and the other in a dark room, as shown in Fig. 10.10. Answer the
g this experiment?
m .c questions — (i) What idea might she be testing through
following a
l a se What are the visible differences in plants in both the conditions? (iii) According
(ii)
a g to you, leaves of which plants confirm the iodine test for the presence of starch?

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g l as
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(a) Sunlight (b) Complete dark

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Fig. 10.10, page 151 — experimental pots (redrawn sketch).

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se m
o m g l a
m .c a
seThe idea she is testing: that sunlight is essential for plants to grow and to make food

g l a
a (i)

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(starch). Both pots are of the same size with similar plants and, we assume, the same water and

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soil; only the light is different. So whatever difference appears must be due to sunlight.
. a g
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(ii) The visible differences (as seen in Fig. 10.10):

FEATURE agl
(A) PLANT IN SUNLIGHT (B) PLANT IN COMPLETE DARK

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Colour of leaves Deep, healthy green Pale yellowish-green

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Leaves Broad, firm, well spread out Narrow, thin, drooping

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Sturdy, upright Thin and weak, stretched out
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Overall look Bushy and healthy Sickly and lifeless

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(iii) Which leaves confirm the iodine test: only the leaves of the plant kept in sunlight turn

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blue-black, confirming the presence of starch. The leaves of the plant kept in the dark show no
a
colour change, because with no sunlight no photosynthesis took place and no starch was

m
made.

. co
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m l as
.co a g
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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Why the dark plant still grows a little taller: it survives on the food already stored
in it and stretches upward "searching" for light. But it cannot make new food, so it
becomes pale and weak.

Q7 Vani believes that ‘carbon dioxide is essential for photosynthesis’. She puts an
experimental set-up, as shown in Fig. 10.11, to collect evidence to support or reject
her idea. Answer the following questions — (i) In which plant(s) in the above set-
up(s) will starch be formed? (ii) In which plant(s) in the above set-up(s) will starch
not be formed? (iii) In which plant(s) in the above set-up(s) will oxygen be
generated? (iv) In which plant(s) in the above set-up(s) will oxygen not be
generated?

(a) Sunlight with (b) Sunlight without (c) Dark with (d) Dark without
carbon dioxide carbon dioxide carbon dioxide carbon dioxide

Fig. 10.11, page 151 — a potted plant with sufficient water is placed under the
prescribed conditions.

Photosynthesis needs all four of sunlight, chlorophyll, water and carbon dioxide. Each plant in
Fig. 10.11 has enough water and is green, so only sunlight and carbon dioxide decide the result.

Page 35 of 46

Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

SET-UP SUNLIGHT CARBON PHOTOSYNTHESIS? STARCH OXYGEN
DIOXIDE

(a) Sunlight with Yes Yes Yes Formed Generated
carbon dioxide

(b) Sunlight Yes No No Not Not
without carbon formed generated
dioxide

(c) Dark with No Yes No Not Not
carbon dioxide formed generated

(d) Dark without No No No Not Not
carbon dioxide formed generated

(i) Starch will be formed — only in plant (a), kept in sunlight with carbon dioxide.
(ii) Starch will not be formed — in plants (b), (c) and (d).
(iii) Oxygen will be generated — only in plant (a), since oxygen is released only during
photosynthesis.
(iv) Oxygen will not be generated — in plants (b), (c) and (d).

Does the experiment support Vani's idea? Yes. Comparing (a) with (b) is the
crucial comparison: both are in sunlight, both have water and chlorophyll, and only
carbon dioxide differs. Starch appears in (a) and not in (b) — so carbon dioxide is
essential for photosynthesis.

Tip: plants (c) and (d) also make no starch, but that does not prove Vani's point —
they fail for want of light. Always compare two set-ups that differ in only one factor.

Page 36 of 46

Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Q8 Ananya took four test tubes and filled three-fourth of each test tube with water.
She labelled them A, B, C, and D (Fig. 10.12). In test tube A, she kept a snail; in test
tube B, she kept a water plant; in test tube C, she kept both a snail and a plant. In
test tube D, she kept only water. Ananya added a carbon dioxide indicator to all the
test tubes. She recorded the initial colour of water and observed if there are any
colour changes in the test tubes after 2–3 hours. What do you think she wants to
find out? How will she know if she is correct?

Water Water +
+ Water
Snail plant

A B

Water +
Snail +
Water
Water
plant

C D

Fig. 10.12, page 151 — experimental set-up.

What she wants to find out: how living things change the amount of carbon dioxide in the
water around them — that is, that an animal (the snail) adds carbon dioxide by respiring, a
green plant uses up carbon dioxide by photosynthesising, and the two together can balance
each other. Test tube D, with water only, is her control.

Page 37 of 46

Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

TEST CONTENTS WHAT HAPPENS IN 2–3 HOURS IN CARBON DIOXIDE
TUBE LIGHT INDICATOR

A Water + snail The snail respires and gives out carbon Shows a clear increase in
dioxide carbon dioxide

B Water + water The plant photosynthesises and uses up Shows a decrease in
plant carbon dioxide faster than it respires carbon dioxide

C Water + snail + The carbon dioxide the snail gives out is Shows little or no change
water plant largely used by the plant

D Water only Nothing living inside No change — the control

How she will know she is correct: by comparing the colours after 2–3 hours with the initial
colour she recorded, and with test tube D.

If D shows no change, then any change in A, B or C was caused by the living organism inside
and not by the water or the indicator itself.
If A shows more carbon dioxide, B shows less, and C shows almost none of either change,
her idea is supported.
To be surer still, she can repeat the whole set in the dark. Then B should also show an
increase, because the plant can only respire — showing that the fall in B was really due to
photosynthesis.

Tip: all four tubes must get the same light, the same temperature and the same
amount of water, and be observed for the same time. Otherwise the comparison is
not fair.

Q9 Design an experiment to observe if water transportation in plants is quicker in
warm or cold conditions.

Question being tested: does water move up a plant faster in warm conditions than in cold
ones?
Materials: two similar tender twigs with white flowers (white sadabahar or balsam), two
identical glass tumblers, water, red ink, a marker pen, a scale, a clock, and a warm place and a
cool place (or a bowl of warm water and a bowl of cold water to stand the tumblers in).
Method:

1. Label the tumblers W (warm) and C (cold) and fill each one-third with water.
2. Add the same number of drops of red ink to both, and mark the starting water level on
each tumbler.

Page 38 of 46

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Class 7 Science Chapter 10 Life Processes in Plants
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3. Cut both twigs obliquely at the base while keeping them under water, and put one twig
co m
in each tumbler at once.
se m.
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g Everything else
c tumbler C in a cool, shaded place (or standing in cold water).
.and
4. Keep tumbler W in a warm place (in sunlight, or standing in a bowl of warm water at about
m a
sebe the same — same twigs, same ink, same amount of water, same light if possible.
35–40 °C)
l a
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must
5. After 1 hour, 2 hours and 3 hours, note in each twig: how far up the stem the red colour has

m
risen (measure with the scale), and whether the leaf veins and flowers have begun to turn
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pink.

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6. Also note how much the water level in each tumbler has fallen.
a
Observation table:

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TIME HEIGHT OF RED COLOUR IN TWIG W HEIGHT OF RED COLOUR IN TWIG C

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(WARM) (COLD)

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After 1 … …

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After 2 … …
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After 3 … …
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Expected result: the red colour rises higher and faster in the warm tumbler, its flowers turn
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pink sooner, and more water disappears from it. So water transportation in plants is quicker in
warm.c
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conditions.

a s
agl Why warmth speeds it up: in warm, dry air more water evaporates from the leaves
through the stomata. As water leaves the top, more is pulled up the xylem from
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Fair-test check: change
the other in a cupboard, or you will be testing light and temperature at the same
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The two processes are opposite
balance. What one uses, the other produces.

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

PHOTOSYNTHESIS RESPIRATION

Takes in Carbon dioxide and water Glucose and oxygen

Gives out Glucose and oxygen Carbon dioxide, water and energy

Energy Stores the sun's energy in food Releases that stored energy for use

When Only in the presence of sunlight All the time, day and night

oxygen + food

Photosynthesis Respiration
green plants, in sunlight all living things, always

carbon dioxide + water
Each process supplies exactly what the other one needs.

The oxygen–carbon dioxide cycle. Photosynthesis puts oxygen and food into the world; respiration
returns carbon dioxide and water, which photosynthesis uses again.

How the balance works

Balance of gases: respiration (and burning) removes oxygen and adds carbon dioxide to the
air; photosynthesis removes carbon dioxide and adds oxygen. So the proportion of these
gases in the air stays roughly steady.
Balance of food and energy: photosynthesis locks the sun's energy into glucose; respiration
unlocks it wherever it is needed. Without photosynthesis there would be no food to respire;
without respiration the food could not be used.
Balance of matter: the carbon dioxide breathed out by a cow feeds the grass, and the grass
feeds the cow. Carbon and water keep going round and round.

What happens if the balance is upset: cutting down forests reduces photosynthesis while
respiration and the burning of fuels go on, so carbon dioxide in the air rises and oxygen falls.
Planting trees restores the balance — which is why forests are called the lungs of the earth.

Did you know? The bottle garden in the Exploratory Projects is this balance in
miniature — sealed inside a bottle, the plant's own respiration and photosynthesis
keep supplying each other.

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Exploratory Projects — Page 152
Interdisciplinary projects

EXPLORATORY PROJECTS

Q1 Develop a bottle garden by planting a growing plant like spider plant or jade plant
in a large transparent bottle (Fig. 10.13). After growing the plant properly for some
time, seal the mouth of the bottle. Observe the growth of the plant.

Fig. 10.13, page 152 — bottle garden (redrawn sketch).

How to make it

1. Take a large transparent glass jar or bottle with a wide mouth and a lid. Wash and dry it.
2. Put a layer of small pebbles at the bottom (about 2 cm) for drainage, then a thin layer of
charcoal pieces, then 6–8 cm of garden soil mixed with a little compost.
3. Plant a small spider plant or jade plant in the soil with a spoon and a stick. Firm the soil
gently around the roots.
4. Sprinkle just enough water to moisten the soil — not so much that water collects at the
bottom.
5. Keep the bottle open in bright indirect light for some time so that the plant establishes itself
and grows properly.
6. Now seal the mouth of the bottle. Keep it in a place with good light but not in harsh direct
sunlight, and watch it for several weeks.

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

What to observe and record: new leaves and shoots; the colour of the leaves; mist or water
droplets that appear on the inside of the glass in the morning and disappear later; whether the
soil stays moist without any watering.
What it shows: if the plant is growing well, the plant is maintaining the exchange of gases
inside the sealed bottle — the carbon dioxide produced in respiration is used for
photosynthesis, and the oxygen generated in photosynthesis is used in respiration by the same
plant.

Why the droplets appear: water vapour given out by the leaves condenses on the
cool glass, runs back into the soil and is absorbed again by the roots. Gases and
water both keep cycling — a tiny, self-sufficient world.

Tip: if the glass stays permanently fogged and the leaves rot, there is too much
water. Open the lid for a day to let the extra moisture escape, then seal it again.

Q2 How are plant processes like photosynthesis, respiration, and water and food
transportation crucial for crop production?

A crop is simply a plant grown for the food it stores. Everything a farmer does is meant to keep
these four processes working well.

PROCESS WHY THE CROP NEEDS IT WHAT THE FARMER DOES ABOUT
IT

Photosynthesis Makes all the food that ends up in Sows at the right spacing and season so
grains, fruits and tubers every plant gets sunlight; removes weeds
that shade the crop

Respiration Releases the energy the plant needs to Ploughs the field so the soil stays loose and
grow, flower and fill its grain; roots airy; drains waterlogged fields so roots do
respire too not suffocate

Transport of water and Carries water for photosynthesis and Irrigates at the right times; adds manure
minerals (xylem) minerals for growth to every leaf and fertilisers that supply minerals

Transport of food Moves the food from the leaves into the Protects the leaves and stem from pests
(phloem) parts we harvest — grain, potato, and diseases so the pathway stays intact
sugarcane stem

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

In short: a healthy leaf area, enough water, loose airy soil and undamaged stems together
decide the yield. Damage any one process — leaves eaten by pests, a field left dry, or roots
standing in water — and production falls.

Find out: ask a farmer near you why fields are ploughed before sowing, and why
paddy is drained before harvest. Match the answers to the table above.

Q3 Visit a greenhouse, if there is one near your place. Observe how people grow plants
in a green house. Find out how they regulate the amount of light, water, and carbon
dioxide used to grow plants.

What to observe on the visit

What the covering is made of — transparent polythene sheet, fibreglass or glass — and why
it must let light through.
Whether it feels warmer and more humid inside than outside, and at what time of day.
Which crops are grown there (usually tomato, capsicum, cucumber, strawberry, gerbera,
rose, orchids and nursery saplings).

What to ask, and the kind of answers you will get

FACTOR HOW IT IS REGULATED IN A GREENHOUSE WHICH PROCESS IT
SERVES

Light Shade nets or whitewash on the roof cut harsh summer light; the Photosynthesis
sheet is kept clean in winter; artificial lamps are used in some
greenhouses to extend day length

Water Drip irrigation delivers measured water to each plant's roots; Transport of water and
sprinklers and foggers raise humidity; the floor is drained so minerals; root respiration
roots never stand in water

Carbon Vents and exhaust fans bring in fresh air; large commercial Photosynthesis
dioxide greenhouses even release extra carbon dioxide to raise its level
around the plants

Temperature Vents, fans and pad-cooling in summer; the closed cover traps All processes work best in
warmth on cold nights a suitable range

Minerals Nutrients are dissolved in the irrigation water (fertigation) in Growth and food-making
measured amounts

Page 43 of 46

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Class 7 Science Chapter 10 Life Processes in Plants
a g l AglaSem · NCERT Solutions

Sample conclusion for your report: "A greenhouse works by controlling every factor that
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photosynthesis and respiration need. Because light, water, carbon dioxide, temperature and
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minerals are all kept near their best values, crops grow faster, give a higher yield, and can be

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season."

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even a seed tray covered with a transparent sheet at home shows the same idea.
Compare a covered tray with an uncovered one for a week.
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Know a Scientist — Page 152

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End of chapter

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KNOW A SCIENTIST

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Who was Kamala Sohonie, and what was her contribution to the study of plants?
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later

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Much of her work helped improve the nutritive values of plant foods.

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minerals. Her work showed how it could be used to improve the diet of poor children

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Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Chapter at a glance
Plants need sunlight and water to grow. Activity 10.1 shows this: the pot kept in sunlight
with water grows best, the pot kept in the dark with water grows poorly and turns pale, and
the pot kept in sunlight without water dries up and may die.
Plants make their own food. Photosynthesis is the process by which plants prepare food in
the presence of sunlight and chlorophyll, using carbon dioxide and water as raw
materials. The word equation is: Carbon dioxide + Water → Glucose + Oxygen.
Leaves are the 'food factories' of plants. They are broad and flat, and green because of
the pigment chlorophyll, which captures sunlight efficiently. Food is first made as glucose
and later stored as starch.
Starch is detected with the iodine test — a decolourised leaf containing starch turns blue-
black. Activity 10.3 shows starch only in the green patches of a leaf from a plant kept in
sunlight; Activity 10.4 shows no starch in the leaf-half enclosed with caustic soda, proving
carbon dioxide is essential.
Oxygen is released during photosynthesis. In Activity 10.5, bubbles collect in the inverted
test tube only in the set-up kept in sunlight, and a lit matchstick inserted into the collected
gas burns with an intense flame.
Tiny pores on the surface of leaves, called stomata, help in the exchange of gases —
carbon dioxide in and oxygen out during photosynthesis, and the reverse during
respiration.
Xylem carries water and dissolved minerals upward from the roots to all parts of the plant.
Phloem carries the food made in the leaves to every other part, including storage organs
such as seeds, roots and tubers.
Plants also respire. During respiration, glucose is broken down in the presence of oxygen,
releasing carbon dioxide, water and energy: Glucose + Oxygen → Carbon dioxide + Water +
Energy. All parts of a plant, green or non-green, respire, day and night.

Page 45 of 46

Class 7 Science Chapter 10 Life Processes in Plants AglaSem · NCERT Solutions

Quick revision

TERM WHAT IT MEANS WHERE IT POINT TO REMEMBER
APPEARS IN THE
CHAPTER

Photosynthesis The process by which plants prepare Section 10.2.3, Fig. Raw materials: carbon dioxide
food in the presence of sunlight and 10.5, page 146 and water. Products: glucose
chlorophyll and oxygen

Chlorophyll The green pigment in leaves that Section 10.2.1, page Only the green patches of a
captures sunlight efficiently 140; Activity 10.3 leaf make starch

Starch A type of carbohydrate in which Section 10.2.1; A leaf with starch turns blue-
plants store food iodine test in Activity black with iodine
10.2

Glucose The simple carbohydrate actually Section 10.2.3, page Instant energy; later converted
produced during photosynthesis 146 to starch for storage

Iodine test Test for starch — a decolourised Activity 10.2, Fig. Blue-black colour = starch
leaf is treated with dilute iodine 10.2, pages 140–141 present
solution

Destarching Keeping a plant in the dark for 2–3 Activity 10.4, page Without it, old starch would
days so it loses its stored starch 143 spoil the result

Caustic soda Sodium hydroxide — it absorbs Activity 10.4, Fig. Only teachers should handle it;
carbon dioxide from the air 10.3, page 143 it burns the skin

Stomata Tiny pores on the surface of leaves Activity 10.6, Fig. Mostly on the lower surface of
that help in the exchange of gases 10.6, page 147 a leaf

Xylem Thin tube-like structures that carry Activity 10.7 and Fig. Red ink rises through the
water and minerals from the roots 10.8, page 148 xylem and colours stem, leaves
upward and flowers

Phloem Thin tube-like structures that carry Section 10.3.2, Fig. Food may be stored in seeds,
food from the leaves to all parts of 10.8, page 148 roots and tubers such as
the plant potato

Respiration Breakdown of glucose in the Section 10.4, Activity Glucose + Oxygen → Carbon
presence of oxygen to release 10.8, page 149 dioxide + Water + Energy
energy

Lime water Lime water turns milky in the Activity 10.8, Fig. Germinating seeds give out
test presence of carbon dioxide 10.9, page 149 carbon dioxide as they respire

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