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The growth movements of plant… (Class 10 Science 2025, Q38)

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ScienceCBSE Class 10 · Board exam 2025, set 31/6/1 · 4 marks · Case-based

CBSE Class 10 Science 2025: question 38

Set in the CBSE Class 10 board exam of 2025, paper 31/6/1, 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

The growth movements of plant parts in which the direction of the stimulus determines the direction of the response is known as tropic movements or tropism. Plants also have non-directional movements which may not be growth dependent.

  1. (I)

    Name the movement which causes 'X' and 'Y' to grow downwards and upwards respectively. (Refer above figure)

    1 mark
  2. (II)

    Write the name of a hormone that plays a major role in (i) falling of leaves (ii) rapid cell division

    1 mark
  3. (III)(a)

    Leaves of the sensitive plant move very quickly in response to 'touch'. How is this stimulus of touch communicated and explain how the movement takes place.

    2 marks

  4. OR

    (III)(b)

    Name the plant hormone which is synthesized at the shoot tip. How does this hormone helps the plant to bend towards light ?

    2 marks

Figure in the paper: A potted plant: a pot on the left with roots labelled X spreading downward-left out of the pot; a shoot labelled Y extending to the right and upward with leaves on branches. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/6/1.

Hints

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

Hint 1

Which stimulus always acts downwards on a plant, whichever way it is placed?

Hint 2

One hormone inhibits growth and causes wilting and leaf fall; another is found where cells divide fast, as in fruits.

Hint 3

The touch-me-not plant has no muscles. Think about how cells can change shape using water, and on which side of the shoot auxin collects.

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. (I) The roots 'X' grow downwards because of positive geotropism (they also show negative phototropism).

    ½ mark

  2. (I) The shoot 'Y' grows upwards because of negative geotropism (it also shows positive phototropism).

    ½ mark

  3. (II)(i) Falling of leaves is promoted by abscisic acid.

    ½ mark

  4. (II)(ii) Rapid cell division is promoted by cytokinin.

    ½ mark

  5. (III)(a) The touch is sensed at one spot. The information is passed from cell to cell by electrical–chemical means, since plants have no nervous tissue.

    1 mark

  6. (III)(a) The cells near the base of the leaflets then change shape by changing the amount of water in them. They swell or shrink, and this makes the leaves fold and droop quickly.

    1 mark

  7. (III)(b) The hormone synthesised at the shoot tip is auxin.

    1 mark

  8. (III)(b) When light falls on the shoot from one side, auxin diffuses towards the shady side. The higher auxin concentration there makes those cells grow longer, so the shady side grows faster. As a result, the shoot bends towards the light.

    1 mark

Answer: (I) X: positive geotropism; Y: negative geotropism. (II)(i) Abscisic acid; (ii) Cytokinin. (III)(a) Touch is conveyed by electrical–chemical signals; cells swell or shrink by changing their water content, so the leaves fold. (III)(b) Auxin; it moves to the shady side and makes those cells elongate, so the shoot bends towards light.

Where the marks are

  • (I) X – positive geotropism (½ mark); Y – negative geotropism (½ mark)
  • (II) Abscisic acid (½ mark); cytokinin (½ mark)
  • (III)(a) Electrical–chemical communication from cell to cell (1 mark); change in water content makes cells swell or shrink (1 mark)
  • (III)(b) Names auxin (1 mark); explains its diffusion to the shady side and cell elongation (1 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 paper2025 board paper, set 31/6/1: 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.