7th Chapter 10 Life Processes in Plants

Class 7 Science – Questions & Answers

1Complete the following table

S.No.	Feature	Photosynthesis	Respiration
1	Raw materials	Carbon dioxide and water	Glucose and oxygen
2	Products	Glucose and oxygen	Carbon dioxide and water
3	Word equation	CO₂ + H₂O → Glucose + O₂	Glucose + O₂ → CO₂ + H₂O
4	Importance	Makes food for plants	Releases energy for life processes

2 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?

Oxygen levels would plummet while carbon dioxide would skyrocket. With no breathable oxygen and no food production, animals and humans would ultimately perish.

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

Starch originates from glucose made in the green leaves during photosynthesis. The phloem then transports this food down to the underground potato tuber, where excess glucose is stored as starch.

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

Yes. A larger, flatter surface captures more sunlight and allows many stomata to absorb carbon dioxide, boosting photosynthetic efficiency.

5 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 same process. What do X, Y, and Z stand for?

X = Glucose (food)  •  Y = Oxygen  •  Z = Water —this represents aerobic respiration.

6 Krishna set-up an experiment with two potted plants of same size and placed one of them in sunlight and the other in a dark room, as shown in Fig. 10.10.

1. What idea might she be testing through this experiment?
2. What are the visible differences in plants in both the conditions?
3. According to you, leaves of which plants confirm the iodine test for the presence of starch?

(i) She is testing whether sunlight is necessary for photosynthesis.
(ii) The sunlit plant stays green and healthy; the dark-kept one turns pale and weak.
(iii) Only leaves from the sunlit plant turn blue-black with iodine, confirming starch presence.

7 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.

1. In which plant(s) in the above set-up(s) will starch be formed?
2. In which plant(s) in the above set-up(s) will starch not be formed?
3. In which plant(s) in the above set-up(s) will oxygen be generated?
4. In which plant(s) in the above set-up(s) will oxygen not be generated?

• Starch forms (and oxygen is generated) in plants (a) and (c) where CO₂ is available.
• Starch does not form (and oxygen is not released) in plants (b) and (d) lacking CO₂.

8 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 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?

She wants to discover how animals add CO₂ and plants remove CO₂ from water. The indicator’s colour shift will reveal CO₂ increase in the snail-only tube and CO₂ decrease in the plant-only tube, confirming her hypothesis.

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

Place two identical leafy shoots in coloured water—one in a warm location, one in a cool location. Measure the height the dye rises every 10 minutes; the faster ascent indicates quicker water transport under that temperature.

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

Photosynthesis locks atmospheric CO₂ into food and releases O₂, whereas respiration consumes O₂ and returns CO₂. These complementary cycles keep Earth’s oxygen and carbon dioxide levels in dynamic equilibrium, making life possible.