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Give reasons for the… (Class 12 Biology 2025, Q18b)

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BiologyCBSE Class 12 · Board exam 2025, set 57/7/1 · 2 marks · Very short answer

CBSE Class 12 Biology 2025: question 18(b)

Set in the CBSE Class 12 board exam of 2025, paper 57/7/1, section B, question 18(b), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q18(b) · 2 marks · Very short answerHuman Reproduction

Give reasons for the following :
(i) Why can a woman generally not conceive a child after 50 years of age ?
(ii) Polar bodies are formed during oogenesis and not during spermatogenesis.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 57/7/1.

Hints

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

Hint 1

(i) What happens to the menstrual cycle at about 50 years?

Hint 2

(ii) Compare how the cytoplasm is shared during the meiotic divisions in the two processes.

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) Around 50 years of age the menstrual cycle stops (menopause). Ovulation no longer occurs, so no ovum is available for fertilisation and conception is generally not possible.

    1 mark

  2. (ii) In oogenesis, meiosis I and meiosis II are unequal divisions. Each gives one large cell and a tiny polar body, so the ovum keeps most of the cytoplasm and nutrient reserve for the zygote.

    ½ mark

  3. In spermatogenesis, both meiotic divisions are equal. All four products become functional sperms, so no polar bodies are formed.

    ½ mark

Answer: (i) Menopause at about 50 years ends ovulation; (ii) the meiotic divisions are unequal in oogenesis (giving polar bodies) but equal in spermatogenesis.

Where the marks are

  • Menopause and cessation of the menstrual cycle at about 50 years (1 mark)
  • Unequal meiotic divisions in oogenesis give one large ovum and polar bodies (½ mark)
  • Equal divisions in spermatogenesis, so no polar bodies (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Human Reproduction, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 57/7/1: 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.