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Explain the mode of action of… (Class 12 Biology 2024, Q22)

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

CBSE Class 12 Biology 2024: question 22

Set in the CBSE Class 12 board exam of 2024, paper 57/1/1, section C, question 22, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q22 · 3 marks · Short answerReproductive Health

Explain the mode of action of contraceptive pills taken by human females. Mention the schedule to be followed for effective outcome.

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

Hints

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

Hint 1

Which hormones do the pills mimic?

Hint 2

Think about three barriers: release of the egg, entry of sperm, and attachment of the embryo.

Hint 3

The schedule has two numbers: days on pills and days off.

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. Oral contraceptive pills contain progestogens alone, or a progestogen–estrogen combination, in small doses.

    ½ mark

  2. Mode of action 1: they inhibit ovulation.

    ½ mark

  3. Mode of action 2: they inhibit implantation.

    ½ mark

  4. Mode of action 3: they alter the quality of cervical mucus, which prevents or retards the entry of sperms.

    ½ mark

  5. Schedule: the pills are taken daily for 21 days, starting preferably within the first five days of the menstrual cycle.

    ½ mark

  6. After a gap of 7 days (during which menstruation occurs), the course is repeated in the same pattern for as long as the female wishes to prevent conception. (Saheli, a non-steroidal pill, is taken once a week.)

    ½ mark

Answer: Progestogen/progestogen–estrogen pills inhibit ovulation and implantation and alter cervical mucus; taken daily for 21 days from within the first 5 days of the cycle, then a 7-day gap, repeated.

Where the marks are

  • Composition: progestogens or progestogen–estrogen combination (½ mark)
  • Inhibit ovulation, inhibit implantation, alter cervical mucus (½ × 3 marks)
  • Daily for 21 days starting within first five days of cycle (½ mark)
  • 7-day gap, then repeated in the same pattern (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Reproductive Health, one at a time, marked against the answer key and marking points.Back to the full paper2024 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.