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If the cells in the leaves of… (Class 12 Biology 2024, Q25)

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BiologyCBSE Class 12 · Board exam 2024, set 57/5/1 · 3 marks · Short answer

CBSE Class 12 Biology 2024: question 25

Set in the CBSE Class 12 board exam of 2024, paper 57/5/1, section C, question 25, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q25 · 3 marks · Short answerSexual Reproduction in Flowering Plants

If the cells in the leaves of a maize plant contain 10 chromosomes each, write the number of chromosomes in its endosperm and zygote. Name and explain the process by which an endosperm and a zygote are formed in maize.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 57/5/1.

Hints

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

Hint 1

Leaf cells are diploid. Work out n first.

Hint 2

The endosperm is triploid and the zygote is diploid.

Hint 3

Double fertilisation has two fusions. Which cells take part in each?

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. Leaf cells are diploid (2n = 10), so n = 5. The endosperm is triploid (3n), so it has 15 chromosomes.

    ½ mark

  2. The zygote is diploid (2n), so it has 10 chromosomes.

    ½ mark

  3. The endosperm is formed by triple fusion.

    ½ mark

  4. In triple fusion, the second male gamete fuses with the two polar nuclei (or the secondary nucleus) of the central cell to form the triploid primary endosperm nucleus.

    ½ mark

  5. The zygote is formed by syngamy.

    ½ mark

  6. In syngamy, one male gamete fuses with the egg cell to form the diploid zygote. Syngamy together with triple fusion makes up double fertilisation.

    ½ mark

Answer: Endosperm: 15 chromosomes (triple fusion of a male gamete with two polar nuclei). Zygote: 10 chromosomes (syngamy of a male gamete with the egg).

Where the marks are

  • Endosperm has 15 chromosomes (½ mark)
  • Zygote has 10 chromosomes (½ mark)
  • Names triple fusion (½ mark) and explains it as the fusion of a male gamete with two polar nuclei (½ mark)
  • Names syngamy (½ mark) and explains it as the fusion of a male gamete with the egg (½ mark)

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 paper2024 board paper, set 57/5/1: 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.