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Answer the following. (Class 12 Biology 2025, Q32A)

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BiologyCBSE Class 12 · Board exam 2025, set 57/1/1 · 5 marks · Long answer

CBSE Class 12 Biology 2025: question 32(A)

Set in the CBSE Class 12 board exam of 2025, paper 57/1/1, section E, question 32(A), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q32(A) · 5 marks · Long answerCompetency-basedSexual Reproduction in Flowering Plants

Answer the following.

  1. (a)

    Distinguish between the two cells enclosed in a mature male gametophyte of an angiosperm.

    0 marks
  2. (b)

    Study the diagram given below showing the modes of pollination. Answer the questions that follow.
    (i) The given diagram shows three methods of pollen transfer in plants. Examine them carefully and write the technical terms used for pollen transfer methods '1', '2' and '3'.
    (ii) How do the following plants achieve pollination successfully ?
    (a) Water lily
    (b) Vallisneria
    (iii) Write advantages of pollen transfer in method '3'.

    0 marks

Figure in the paper: Three flowers showing pollen transfer: arrow 1 within the same flower (self); arrow 2 between two flowers on the same plant; arrow 3 from a flower of one plant to a flower of another plant. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 57/1/1.

Hints

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

Hint 1

A mature pollen grain at the 2-celled stage contains one large cell and one small cell. Which one makes the gametes?

Hint 2

Name the pollination types by where the pollen comes from: same flower, same plant, or a different plant.

Hint 3

Do the flowers of water lily rise above the water? Where do the flowers of Vallisneria meet?

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 two cells are the vegetative cell and the generative cell.

    ½ mark
  2. Vegetative cellGenerative cell
    Large, with abundant food reserve and a large, irregularly shaped nucleusSmall, spindle-shaped, with dense cytoplasm; floats in the cytoplasm of the vegetative cell
    Forms the pollen tubeDivides mitotically to form two male gametes
    1 mark

  3. (b)(i) 1 = Autogamy (within the same flower)

    ½ mark

  4. 2 = Geitonogamy (between flowers of the same plant)

    ½ mark

  5. 3 = Xenogamy (between flowers of different plants)

    ½ mark

  6. (ii)(a) Water lily: the flowers emerge above the water surface and are pollinated by insects or wind.

    ½ mark

  7. (b) Vallisneria: pollination is by water. The female flower reaches the surface on a long stalk. Male flowers or pollen grains released onto the water surface are carried passively by water currents and reach the stigma.

    ½ mark

  8. (iii) Advantages of xenogamy (any two):

    • it brings genetically different pollen, giving genetic variation
    • it produces healthier, more vigorous offspring (heterosis) and avoids inbreeding depression
    • it improves disease resistance and helps evolution
    1 mark

Answer: (a) Vegetative cell is large with food reserve and forms the pollen tube; generative cell is small and forms two male gametes. (b)(i) 1 = autogamy, 2 = geitonogamy, 3 = xenogamy; (ii) water lily by insects/wind, Vallisneria by water; (iii) genetic variation, vigour/no inbreeding depression.

Where the marks are

  • Names the vegetative and generative cells (½ mark)
  • One correct difference between them (1 mark)
  • Autogamy, geitonogamy, xenogamy (½ mark each)
  • Water lily by insects/wind (½ mark); Vallisneria by water (½ mark)
  • Any two advantages of xenogamy (½ + ½ marks)

Revise the chapter

Practise this chapterBoard-style questions from Sexual Reproduction in Flowering Plants, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 57/1/1: 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.