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Mohan and Rohit… (Class 10 Science SQP 2024-25, Q38)

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ScienceCBSE Class 10 · Sample paper, session 2024-25 · 4 marks · Case-based

CBSE Class 10 Science sample paper 2024-25: question 38

From the official CBSE sample question paper for 2024-25, section E, question 38, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q38 · 4 marks · Case-basedCompetency-basedControl and Coordination

Mohan and Rohit observed that shoots of a plant growing in shade bend towards the sunlight. Whereas, leaves of 'Touch me not' plant fold and droop soon after touching. They were curious to know how these movements occur in plants.
In order to help them understand the movements in the plants, answer the following questions:

  1. A

    What causes the bending of shoots in the plants as shown in figure A? (2)

    2 marks

  2. OR

    B

    What causes the folding of the leaves in 'Touch me not' plant as shown in figure B? (2)

    2 marks
  3. C

    Compare the movement of growth of the pollen tube towards ovule with the movements shown in part A of the above figure.

    1 mark
  4. D

    Compare the movement shown in figure B with the movement of body parts in the animals.

    1 mark

Figure in the paper: Figure A: a potted plant whose shoots bend toward a window. Figure B: photographs of Touch me not leaves, open and folded when touched. See it in the official paper.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2024-25.

Hints

Open one hint at a time and try again before the next.

Hint 1

Which hormone made at the shoot tip makes cells grow longer, and where does it move when light comes from one side?

Hint 2

The touch-me-not leaf folds within seconds. Can growth be that fast? Think about water moving in and out of cells.

Hint 3

Name the stimulus in each case: chemicals for the pollen tube, light for the shoot.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. A. The bending of the shoot towards light is phototropism. It is a directional movement that depends on growth.

    ½ mark

  2. The plant hormone auxin is made at the shoot tip and helps cells grow longer.

    ½ mark

  3. When light falls from one side, auxin diffuses towards the shaded side of the shoot.

    ½ mark

  4. The cells on the shaded side therefore elongate more than those on the lit side. The shoot bends towards the light.

    ½ mark

  5. B. (Alternative to A) The folding of 'Touch me not' leaves is a growth-independent movement and happens quickly.

    ½ mark

  6. The touch stimulus is passed from cell to cell by electrical–chemical signals.

    ½ mark

  7. The movement occurs at a point different from the point of touch, showing that the information has travelled.

    ½ mark

  8. The cells there change shape by changing the amount of water in them. They swell or shrink, which makes the leaflets fold and droop.

    ½ mark

  9. C. Both are tropic movements, i.e. directional growth in response to a stimulus.

    • The pollen tube grows towards the ovule in response to chemicals: chemotropism.
    • The shoot in figure A bends towards light: phototropism.
    1 mark

  10. D. Plants and animals both pass information by electrical–chemical means, but they differ in two ways.

    • Signal conduction: Plants have no specialised tissue such as nerves for conducting information. Animals have nerve cells.
    • Change of shape: Plant cells move by changing their water content. Animal body parts move because special proteins in muscle cells change the shape of those cells.
    1 mark

Answer: A: phototropism, as auxin moves to the shaded side and those cells elongate more, so the shoot bends towards light; OR B: growth-independent movement, with electrical–chemical signals causing cells to lose or gain water and change shape, so leaves fold; C: pollen tube growth is chemotropism, while shoot bending is phototropism (both directional growth movements); D: plants have no nervous tissue and move by changing water content, while animals use nerves and contractile muscle proteins

Where the marks are

  • A: Phototropism as a directional, growth-related movement (0.5 mark)
  • A: Auxin is made at the shoot tip (0.5 mark)
  • A: Auxin diffuses to the shaded side (0.5 mark)
  • A: Greater elongation on the shaded side makes the shoot bend towards light (0.5 mark)
  • OR B: Growth-independent movement (0.5 mark)
  • OR B: Electrical–chemical signalling (0.5 mark)
  • OR B: Movement away from the point of touch (0.5 mark)
  • OR B: Change in water content changes cell shape (0.5 mark)
  • C: Chemotropism (pollen tube) versus phototropism (shoot) (1 mark)
  • D: No specialised conducting tissue in plants (0.5 mark)
  • D: Water-based shape change in plants versus muscle proteins in animals (0.5 mark)

Revise the chapter

Practise this chapterBoard-style questions from Control and Coordination, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2024-25: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.