NCERT Solutions for Class 7 Science Chapter 10 Life Processes in Plants (PDF) – 2027

No. Plants do not eat food like animals do. Green plants make their own food in their leaves, using sunlight, water and carbon dioxide from the air.

When a plant grows, you can see these changes:

• 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.

Yes. A plant changes continuously through its life span.

• 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.

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

• 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.

“I think, maybe, air plays some role!”

Other good answers are minerals in the soil, warmth (temperature) or the green colour of leaves. The role of air is tested in Activity 10.4: the part of a leaf kept away from carbon dioxide makes no starch.

Table 10.1 with sample readings after two weeks (your own numbers will differ, but the pattern will be the same):

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.

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

Pot A — the pot kept in direct sunlight with an adequate amount of water every day.

Pot B — the pot kept in direct sunlight without any water.

Plants require both sunlight and water for their growth.

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.

To see the colour change clearly. Decolourisation of a leaf enables us to easily observe colour change and, thus, the presence of starch. On a green leaf, the blue-black colour would be hidden by the green.

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.

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.

1. Chlorophyll is essential for making starch — only the green patches of the leaf from the plant in sunlight turned blue-black.
2. Sunlight is essential for making starch — the leaf from the plant kept in the dark showed no blue-black colour, even on its green patches.

So, chlorophyll helps in preparing starch in the presence of sunlight. That is why leaves are called the ‘food factories’ of plants.

Carbon dioxide, a gas present in the air. We have already seen that water, sunlight and chlorophyll are essential; Activity 10.4 tests the role of air (carbon dioxide).

Carbon dioxide.

Air is a mixture of gases — mainly nitrogen and oxygen, with a very small amount of carbon dioxide. Of these, it is carbon dioxide that the plant uses as a raw material and builds into glucose. It enters the leaf through the tiny pores called stomata.

Completed Table 10.3:

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.

This experiment shows that carbon dioxide present in the air is essential for plants to prepare starch.

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.

Mainly the leaf. A leaf is the primary site for photosynthesis — that is why leaves are called the ‘food factories’ of plants.

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.

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

In set-up A (in sunlight), air bubbles rise from the water plant and collect in the inverted test tube. In set-up B (in the dark), no bubbles are seen.

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.

It is oxygen. A lit matchstick put into the collected gas burnt with an intense flame, and oxygen is the gas that supports burning.

Rustom Hormusji Dastur (1896–1961) was an Indian scientist who studied the process of photosynthesis.

• 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.

The leaves — more exactly, the tiny pores on their surface called stomata.

Yes. Many tiny pores are seen scattered among the cells of the leaf peel. Each pore lies between two bean-shaped cells. These pores are called stomata.

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

Through thin tube-like structures called the xylem, which run continuously from the roots up through the stem and branches into the leaves.

Water and dissolved minerals absorbed by the roots enter these tubes and move upward, reaching the leaves, flowers and every other part of the plant. Activity 10.7, with red ink, makes this movement visible.

Yes. After one day, red colour is seen in the stem, leaves and flowers of the twig in Tumbler B (water with red ink). The twig in Tumbler A (plain water) shows no change.

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.

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).

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.

Through another set of thin tube-like structures called the phloem. The phloem carries the food made in the leaves to all parts of the plant. Some of this food is stored in parts such as seeds and roots.

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.

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.

Because lime water turns milky due to the presence of more carbon dioxide in the flask.

From the germinating moong seeds in the flask. Carbon dioxide is naturally present in very small quantities in the air; in the flask, additional carbon dioxide is produced by the seeds as they respire.

During respiration, glucose is broken down in the presence of oxygen, releasing carbon dioxide, water and energy:

Living organisms could not survive. Organisms that carry out photosynthesis are the only ones that make food from simple substances, and they add oxygen to the air.

• No new food would be made. Plant-eating animals would starve first, then the animals that eat them, and finally all animals, including humans.
• Oxygen in the air would fall and carbon dioxide would build up, because nothing would replace the oxygen used up in respiration and burning.
• Food chains would break down and the balance of nature would be lost.

Where the starch comes from: from the food made by the potato plant in its leaves by photosynthesis — not from the soil.

Where food is synthesised: in the leaves, from carbon dioxide and water in the presence of sunlight and chlorophyll.

How it reaches the potato: the food is carried from the leaves down to the underground stem through the phloem. There it is stored as starch; this swollen underground stem is the potato.

Yes. The broad, flat shape makes leaves more efficient for photosynthesis because:

• a large surface catches more sunlight;
• the leaf is thin, so light reaches all the cells that have chlorophyll;
• many stomata are exposed to the air, so carbon dioxide enters easily and oxygen leaves;
• veins spread through the flat blade bring water to every part of the leaf and carry food away.

X = Glucose, Y = Oxygen, Z = Water. The equation is the word equation for respiration:

(i) She is testing whether sunlight is essential for plants to grow and to make food (starch).

(ii) The plant kept in sunlight has green, healthy, upright leaves. The plant kept in the dark has pale yellow, weak, drooping leaves.

(iii) Only the leaves of the plant kept in sunlight will turn blue-black in the iodine test, confirming starch. Leaves of the plant kept in the dark show no colour change, because without sunlight no photosynthesis took place.

(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).

What she wants to find out: how living things change the amount of carbon dioxide in water — the snail adds carbon dioxide by respiration, the water plant uses it up by photosynthesis (in light), and together they can balance each other. Test tube D is the control.

How she will know: by comparing the final colour of each tube with its initial colour and with D. If the indicator shows more carbon dioxide in A, less in B, little change in C and no change in D, her idea is correct.

Aim: to find out whether water moves up a plant faster in warm or in cold conditions.

1. Put the same amount of water and the same number of drops of red ink in two tumblers, W and C.
2. Cut two similar white-flowered twigs obliquely under water; put one in each tumbler.
3. Stand W in a bowl of warm water and C in a bowl of cold water, side by side in the same light.
4. Every hour, note how high the red colour has risen in each stem.

Result: the red colour rises faster in twig W, so water transport is quicker in warm conditions.

Photosynthesis and respiration are opposite processes — what one uses, the other produces.

• Gases: respiration uses oxygen and gives out carbon dioxide; photosynthesis uses carbon dioxide and gives out oxygen. So the amounts of these gases in the air stay roughly steady.
• Food and energy: photosynthesis stores the sun’s energy in food; respiration releases this energy for living things to use.

Together they keep the balance of oxygen, carbon dioxide and food in nature.

How to make it: put a layer of pebbles and then garden soil in a large transparent bottle, plant a small spider plant or jade plant, and water it lightly. Let it grow with the bottle open for some time, then seal the mouth and keep it in good light.

What it shows: if the plant keeps growing in the sealed bottle, it is maintaining the exchange of gases — carbon dioxide from its respiration is used in photosynthesis, and oxygen from photosynthesis is used in respiration.

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.

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.

What you are likely to find — how light, water and carbon dioxide are regulated in a greenhouse:

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

Kamala Sohonie (1911–1998) was an Indian woman scientist.

• She received a Ph.D. from Cambridge University for her work on respiration in plants.
• She worked at the Lady Hardinge Medical College, New Delhi, and the Nutrition Research Laboratory, Coonoor.
• She later became Director of the Royal Institute of Science, Bombay.
• Her work helped improve the nutritive value of plant foods. She also worked on Neera, a nutritive drink made from the sap of the coconut palm.