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Answer the following. (Science 2024 31/3/1 Q35b)

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ScienceCBSE Class 10 · Board exam 2024, set 31/3/1 · 5 marks · Long answer

CBSE Class 10 Science 2024: question 35(b)

Set in the CBSE Class 10 board exam of 2024, paper 31/3/1, section D, question 35(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q35(b) · 5 marks · Long answerHow do Organisms Reproduce?

Answer the following.

  1. (i)

    Study the diagram given below and name the parts marked as A, B and C. What happens when B reaches C in the ovary ? Mention its significance.

    0 marks
  2. (ii)

    Write the post fertilisation changes that occur in a flower.

    0 marks

Figure in the paper: Longitudinal section of a flower showing the stigma at top, a long style, and an ovary at the base containing ovules. Arrows labelled A (pointing to the style just below the stigma), B (pointing to the pollen tube growing down the style) and C (pointing to the micropyle/egg region inside an ovule within the ovary). See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/3/1.

Hints

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

Hint 1

Follow the path of the pollen grain after it lands on the stigma. What grows down the style?

Hint 2

What does the pollen tube carry, and what does it meet in the ovule?

Hint 3

For (ii), think about what the ovule, the ovary and the petals each become after fertilisation.

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) Labels (as in NCERT's figure of pollen germinating on the stigma):

    • A – male germ cell (male gamete)
    • B – pollen tube
    • C – female germ cell (female gamete, the egg inside the ovule)
    1½ marks

  2. (i) When B reaches C: The pollen tube (B) grows down through the style and enters the ovule. It carries the male germ cell (A) with it. The male germ cell fuses with the female germ cell (C). This fusion is fertilisation, and it forms a zygote.

    1 mark

  3. (i) Significance: The zygote develops into an embryo, which grows into a new plant. Because genetic material comes from two parents, the offspring also show variation.

    ½ mark

  4. (ii) Post-fertilisation change 1: The zygote divides many times to form an embryo inside the ovule.

    ½ mark

  5. (ii) Post-fertilisation change 2: The ovule develops a tough coat and becomes the seed.

    ½ mark

  6. (ii) Post-fertilisation change 3: The ovary grows rapidly and ripens into the fruit.

    ½ mark

  7. (ii) Post-fertilisation change 4: The petals, sepals, stamens, style and stigma shrivel and fall off.

    ½ mark

Answer: (i) A – male germ cell, B – pollen tube, C – female germ cell; male germ cell fuses with female germ cell (fertilisation) to form a zygote, which grows into a new plant. (ii) Zygote forms embryo, ovule becomes seed, ovary becomes fruit, other floral parts shrivel and fall

Where the marks are

  • Correctly names A, B and C (½ × 3 marks)
  • States that the pollen tube carries the male gamete, which fuses with the female gamete to form a zygote (1 mark)
  • Significance: the zygote grows into a new plant (½ mark)
  • Any four post-fertilisation changes (½ × 4 marks)

Revise the chapter

Practise this chapterBoard-style questions from How do Organisms Reproduce?, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 31/3/1: 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.