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The image below shows… (Class 12 Biology SQP 2024-25, Q22)

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BiologyCBSE Class 12 · Sample paper, session 2024-25 · 3 marks · Short answer

CBSE Class 12 Biology sample paper 2024-25: question 22

From the official CBSE sample question paper for 2024-25, section C, question 22, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q22 · 3 marks · Short answerCompetency-basedSexual Reproduction in Flowering Plants

The image below shows two germinated seeds X and Y which belong to the same species. Seed X is produced by apomixis whereas seed Y is a product of sexual reproduction.

A. Write the number of embryo(s), embryo sac(s) and ovules in the ovary of seed X.
B. How multiples embryos are formed in citrus fruits?
C. What advantage will plants developed from seed Y have over seed X?

Figure in the paper: Two germinated seeds. Seed X (left) has three seedlings labelled PLANT 1, PLANT 2, PLANT 3 growing from the one seed. Seed Y (right) has a single seedling labelled PLANT 1. 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

One seed always develops from how many ovules?

Hint 2

In citrus, extra embryos arise from cells around the embryo sac.

Hint 3

Compare sexual and asexual offspring in terms of variation.

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. Seed X has 3 embryos (three seedlings), 1 embryo sac and 1 ovule, because one seed develops from one ovule containing one embryo sac.

    1½ marks

  2. B. In citrus, some nucellar cells surrounding the embryo sac divide mitotically, protrude into the embryo sac and develop into embryos. These are formed by asexual means without fertilisation, so one seed contains several embryos (polyembryony).

    ½ mark

  3. C. The plant from seed Y comes from fertilisation, so it shows genetic variation and greater adaptability to changing environmental conditions. Plants from seed X are clones, lack variation and may succumb to stress. Also, the single plant in seed Y uses the entire endosperm, whereas the three embryos of seed X must share it and may be undernourished.

    1 mark

Answer: A. 3 embryos, 1 embryo sac, 1 ovule; B. Nucellar cells divide mitotically to form extra embryos; C. Seed Y plant has genetic variation (adaptability) and uses the whole endosperm.

Where the marks are

  • States 3 embryos, 1 embryo sac and 1 ovule (0.5 × 3 = 1.5 marks)
  • Explains that nucellar cells divide mitotically to form embryos asexually (0.5 mark)
  • Gives an advantage of seed Y: genetic variation/adaptability or no sharing of endosperm (1 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 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.