Class 7 Science · Chapter 10

10. Life Processes in Plants

Complete solutions to Let Us Enhance Our Learning. CBSE / NCERT Class 7 Science (Curiosity).

Let Us Enhance Our Learning

1Complete the following table.

Feature	Photosynthesis	Respiration
Raw materials	Carbon dioxide and water (in the presence of sunlight and chlorophyll)	Glucose and oxygen
Products	Glucose and oxygen	Carbon dioxide, water and energy
Word equation	Carbon dioxide + Water → Glucose + Oxygen (in sunlight, with chlorophyll)	Glucose + Oxygen → Carbon dioxide + Water + Energy
Importance	Makes food for the plant and for all other living beings; releases oxygen into the air	Releases energy from food for all life activities

2Imagine all the organisms that carry out photosynthesis on the Earth have disappeared. What would be the impact on living organisms?

There would be no food. Plants make food, and all animals depend on plants directly or indirectly.
Oxygen in the air would not be replaced. Living beings would not get oxygen to breathe.
Carbon dioxide would keep increasing in the air.
Slowly, all life on the Earth would end.

3A 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?

Food is made in the leaves by photosynthesis in the form of glucose.
The phloem carries this food from the leaves to all parts of the plant, including the underground stem (potato).
In the potato, the extra glucose is stored as starch.

4Does the broad and flat structure of leaves make plants more efficient for photosynthesis? Justify your answer.

Yes.

A broad and flat leaf has a large surface area. It can absorb more sunlight.
More stomata are present on a large surface. So more carbon dioxide can enter the leaf.
A thin leaf allows gases to reach all the cells easily.

5X is broken down using Y to release carbon dioxide, Z and energy. X + Y → Carbon dioxide + Z + Energy. What do X, Y and Z stand for?

This is the process of respiration.

X = Glucose, Y = Oxygen, Z = Water

6Krishna placed one potted plant in sunlight and the other in a dark room (Fig. 10.10). (i) What idea might she be testing? (ii) What are the visible differences in plants in both the conditions? (iii) Leaves of which plant confirm the iodine test for starch?

(i) She is testing whether sunlight is necessary for photosynthesis (for plants to make food).

(ii) The plant in sunlight is green, fresh and healthy. The plant in the dark has pale yellow leaves and looks weak.

(iii) Leaves of the plant kept in sunlight turn blue-black with iodine. So starch is present only in them.

7Vani placed potted plants in four conditions: (a) sunlight with carbon dioxide (b) sunlight without carbon dioxide (c) dark with carbon dioxide (d) dark without carbon dioxide. Answer the questions.

(i) Starch will be formed in: (a)

(ii) Starch will not be formed in: (b), (c) and (d)

(iii) Oxygen will be generated in: (a)

(iv) Oxygen will not be generated in: (b), (c) and (d)

Photosynthesis needs both sunlight and carbon dioxide. Only plant (a) gets both.

8Ananya kept a snail in test tube A, a water plant in B, both a snail and a plant in C, and only water in D. She added a carbon dioxide indicator to all of them. What does she want to find out? How will she know if she is correct?

She wants to find out how animals and plants change the amount of carbon dioxide in water, that is, how respiration and photosynthesis affect it.

A (snail): The snail respires and gives out carbon dioxide. The indicator colour changes the most.
B (plant, in light): The plant uses carbon dioxide for photosynthesis. The carbon dioxide decreases.
C (snail + plant): The carbon dioxide given out by the snail is used by the plant. Very little change is seen.
D (only water): No change. It is the control set-up for comparison.

By comparing the colours after 2–3 hours with the initial colour and with D, she can know if her idea is correct.

9Design an experiment to observe if water transportation in plants is quicker in warm or cold conditions.

Take two similar fresh twigs of a plant with white flowers or leaves (or two celery stalks).
Take two glasses with the same amount of water. Add a few drops of red ink to each.
Put one twig in each glass.
Keep one glass in a warm place (in sunlight) and the other in a cold place (in a shady, cool corner or near ice).
Observe both twigs after every 30 minutes.

Observation: The red colour rises faster in the twig kept in the warm place. This shows that water is transported faster in warm conditions.

10Photosynthesis and respiration are essential to maintain balance in nature. Discuss.

In photosynthesis, plants take in carbon dioxide and give out oxygen.
In respiration, plants and animals take in oxygen and give out carbon dioxide.
So the oxygen used in respiration is replaced by photosynthesis, and the carbon dioxide given out is used again by plants.
In this way, the amounts of oxygen and carbon dioxide in the air remain balanced.
Photosynthesis also provides food for all living beings, and respiration releases energy from that food.

Exploratory Projects

Exploratory Projects are hands-on tasks. Do them with your classmates under the guidance of your teacher, and write your own observations.

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