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Green Plants – The Food Producers
We know that all living things need food for growth and repair of their body
parts. But not all of them can produce food. Animals and human beings lack
this ability. Green plants are the only living things that can produce food. They
are able to do so because of the presence of a substance called chlorophyll in
their leaves. Chlorophyll is green in colour and is also responsible for imparting
green colour to the leaves.
In this chapter, we will discuss how a leaf prepares food in the presence of
chlorophyll.
Quick Recall
Identify the parts of the plant and discuss their main functions.
Structure and Function of a Leaf
We have already studied about the structure of a leaf. Let’s review it quickly.
Bingo’s Activity Time
Take any green leaf. Observe it carefully and answer the following
questions.
(a) Does it have a flat part called the leaf blade?
(b) Does it have a main vein and several side veins?
(c) Is the whole leaf green in colour?
Now observe a few different leaves and again answer these questions. Did you find any
similarity between the leaves you observed?
Request your teacher to show you the underside of a leaf
under a microscope. You will see that there are many tiny
openings called stomata (singular stoma) on it. Plants breathe
through these stomata.
Bingo’s Knowledge Bank
The main vein called the midrib, and the side veins
transport water from the stem to all parts of the leaf.
A green leaf performs the following tasks for the plant.
1. It prepares food for the plant in the presence of chlorophyll using sunlight,
water and carbon dioxide. That’s why it is called the food factory of a plant.
2. It helps the plant to breathe through stomata.
Bingo’s Teaser
3. Some leaves also store food prepared by the plant.
Name four leaves
that contain stored
food which you eat.
cabbage
spinach
fenugreek
The Process of Making Food – Photosynthesis
We generally call a leaf the food factory of a plant. Let’s understand the working
of this factory.
carbon dioxide
(from air)
sunlight
(from the sun)
chlorophyll
(in the leaf )
water
(from soil)
Plants take in carbon dioxide from the
atmosphere through stomata. Water is
absorbed from the soil through roots.
Chlorophyll traps the sunlight. All these are
used by the leaf to prepare food. This process
of making food by plants using sunlight,
water and carbon dioxide in the presence
of chlorophyll is known as photosynthesis.
This term comes from two words—‘photo’
meaning light and ‘synthesis’ meaning putting
together.
Bingo’s Challenge!
If chlorophyll is the machine of a leaf and carbon dioxide and water are
the raw materials that go into it, what would sunlight and food be?
(a) Fuel and product (b) Force and product
The food prepared by a plant is called sugar. This food is transported throughout
the plant by the stem and branches. A plant uses some amount of the prepared
food to carry out its life processes while the rest of the food is stored in fruits,
leaves, stem or roots. We consume such parts of a plant.
mango
spinach
carrot
Bingo’s Challenge!
Name the grain which we boil in
excess water and use its strained
water to starch our clothes.
sugarcane
Starch
Starch is the stored
form of sugar.
Apart from food, oxygen is also given out by plants during photosynthesis through
stomata. This gas is then used by animals and human beings for breathing. They,
in turn, give out carbon dioxide in the air.
Quick Recall
Fill in the blanks.
1. The process of making food by the plants using ____________, ____________
and carbon dioxide in the presence of ____________________ is known as
____________________.
2. A plant uses some amount of the prepared food to carry out its ____________
processes while the rest of the food is stored in the form of ____________ in
fruits, leaves, stem or roots.
Bingo’s Knowledge Bank
We can come to know whether a leaf has carried out photosynthesis or
not. Test the leaf with iodine solution. If it turns blue-black, then starch
is present in it. This confirms that it has carried out photosynthesis.
Bingo’s Activity Time
1. Take a well-watered potted plant (plant A) and keep it in a dark room for 2 days.
Water the plant regularly. Keep another plant (plant B) in the sunlight.
2. Now pluck a leaf each from both the plants. Go to the laboratory with your
teacher and carefully see her performing the following experiment.
3. Boil each leaf separately first in water and then in alcohol.
plant A
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plant B
A
B
4. Wash both of them separately with cold water. You
will find that the leaves get bleached (lose colour).
This is done so that you can see the results clearly.
5. Put a few drops of iodine solution on each leaf.
A
B
What do you observe?
You will observe that the leaf of plant A does not turn blue-black. This indicates that
starch was not formed in that leaf or in other words, photosynthesis was not carried out.
While the leaf of plant B turns blue-black showing the presence of starch. This means that
plant B carried out photosynthesis properly.
What do you think is the reason for the absence of starch in the leaf of plant A? Discuss
with your teacher.
Bingo’s Activity Time
1. Take a fresh green leaf and a fallen leaf which has turned completely yellow. Go
to the laboratory and see your teacher performing the following experiment.
2. Boil both the leaves separately first in water and then in alcohol. Then wash
them separately with cold water.
3. Pour a few drops of iodine solution on each leaf.
A
B
What do you observe?
You will notice that the green leaf turns blue-black showing the presence of starch. The
yellow leaf does not turn blue-black proving that there was no starch in it.
Now discuss with your teacher the reason for this.
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Bingo’s Activity Time
1. Take a potato and cut it into two parts.
2. Put a few drops of iodine on the cut side
of the potato.
What do you observe?
You will observe blue-black colour on the portion
where you have put iodine drops. This proves
that potato has starch.
Some Amazingly Different Plants
There are some plants that are different from the usual green plants. Let’s find
out more about them.
• The leaves of cactus plant are reduced to spines and
cannot perform photosynthesis. The food is prepared by
the green stem.
• Mushrooms and moulds do not contain chlorophyll and
are non-green. These plants lack the ability to make their
food and therefore, obtain it from dead and decaying
plants and animals.
Bingo’s Knowledge Bank
Mushrooms and moulds are known as ‘saprophytic
plants’ because they obtain nutrition from dead
and decaying plants and animals.
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• Money plant and croton plant have
variegated leaves, i.e., having patches of
different colours. Only the green part of
such leaves performs photosynthesis.
The Flow of Energy
Plants help to transfer energy from the sun to animals and human beings.
Plants trap energy
from the sun.
Herbivores
eat plants.
Omnivores eat
plants and animals.
Carnivores eat animals.
Dependency of Plants, Animals and Human Beings on Each Other
Plants, animals and human beings show
dependency on each other. Plants give food,
shelter and oxygen to us and animals. In
turn, we give out carbon dioxide which is
used by plants to carry out photosynthesis.
This way plants help to purify air. Impure air
that carries excess of carbon dioxide is not
good for us and animals. We also help in
spreading seeds of plants and therefore help
in increasing their number.
We need
each other.
Recall with Bingo
1. All living things need food for growth and repair of their body parts.
2. Animals and human beings lack the ability to prepare food. They depend on
plants for food.
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3. Green plants are the only living things that can make food. They are able to do
so because of the presence of a substance called ‘chlorophyll’ in their leaves.
4. Many tiny openings called stomata (singular stoma) present mostly on the
underside of a leaf help plants to breathe.
5. A green leaf prepares food for the plant and is known as its food factory.
6. The process of making food by the plants using sunlight, water and carbon
dioxide in the presence of chlorophyll is known as photosynthesis.
7. The food prepared by a plant is called sugar and is transported throughout the
plant by the stem and branches.
8. Apart from food, oxygen is also given out by plants during photosynthesis
through stomata.
9. Plants give animals and us food, oxygen, and shelter, while we give carbon
dioxide and help in spreading the seeds of plants. Therefore, plants, animals
and human beings are interdependent.
Exercise Time
A. Complete the following web chart.
Photosynthesis
green leaf having chlorophyll
B. Answer the following questions.
1. What is chlorophyll?
2. What are the functions performed by a leaf?
3. Explain the process of photosynthesis with the help of a diagram.
4. What happens to the food prepared by a leaf?
5. Write what happens in the following cases:
(a) If you put a few drops of iodine solution on a potato slice.
(b) If you put a few drops of iodine solution on a fresh green leaf which has
been bleached.
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6. Give examples of plants:
(a) having variegated leaves
(b) lacking chlorophyll
7. Write a short note on how plants and animals depend on each other.
C. State whether the following statements are true or false.
1. The green colour of leaves is due to the presence of stomata.
2. The food prepared by the plants is called starch.
3. Stomata help plants in breathing.
4. A yellow leaf turns blue-black when a few drops of iodine
solution are put on it.
__________
__________
__________
__________
D. Tick the correct answer.
1. Which of these traps the sunlight?
(a) Stomata
(b) Chlorophyll
(c) Both of these
2. Which of these cannot prepare food and obtain it from dead and decaying plants
and animals?
(a) Mould
(b) Cactus
(c) Croton
3. A green leaf turns blue-black when a few drops of iodine solution are put on it
showing the presence of
(a) sugar.
(b) chlorophyll.
(c) starch.
4. Which of these is known as the food factory of a plant?
(a) Roots
(b) Stem
(c) Leaves
5. Which of these plants has variegated leaves?
(a) Croton
(b) Mushroom
(c) Cactus
Leisure Time
Unscramble the given words.
1. AMTOSTA
2. LROPHYLCOHL
3. STHESISTOPHOYN
4. CHARTS
5. LUDMOS
___________________
___________________
___________________
___________________
___________________
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Project and Activities
Perform the given activity in pairs.
1. Take the given fruits and vegetables.
potato
banana
sweet potato
grapes
colocasia
cucumber
melon
orange
2. Cut each and feel it with your fingers. You will find that some of them have a
sticky feel, while others have a watery feel.
3. Name the ones that have a sticky feel.
________________________________________________________________
4. Now test them with iodine solution.
5. What do you observe?
They turn blue-black.
Their colour does not change.
6. What does it prove?
They contain proteins.
They contain starch.
Now discuss in class and make a list of at least ten more food items that contain a lot of
starch. Include grains in your list.
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