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In a human female, the… (Class 12 Biology 2024, Q29)

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BiologyCBSE Class 12 · Board exam 2024, set 57/5/1 · 4 marks · Case-based

CBSE Class 12 Biology 2024: question 29

Set in the CBSE Class 12 board exam of 2024, paper 57/5/1, section D, question 29, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q29 · 4 marks · Case-basedCompetency-basedHuman Reproduction

In a human female, the reproductive phase starts on the onset of puberty and ceases around middle age of the female. Study the graph given below regarding menstrual cycle and answer the questions that follow :

  1. (a)

    Name the hormones and their source organ, which are responsible for menstrual cycle at puberty.

    1 mark
  2. (b)

    For successful pregnancy, at what phase of the menstrual cycle an early embryo (upto 3 blastomeres) should be Implanted in the Uterus (IUT) of a human female who has opted for Assisted Reproductive Technology (ART) ? Support your answer with a reason.

    1 mark
  3. (c)

    Name the hormone and its source organ responsible for the events occurring during proliferative phase of menstrual cycle. Explain the event.

    2 marks

  4. OR

    (c)

    In a normal human female, why does menstruation only occurs if the released ovum is not fertilised ? Explain.

    2 marks

Figure in the paper: Graph of the 28-day menstrual cycle with four panels: pituitary hormone levels (FSH, LH with LH surge around day 14), ovarian events (developing follicle, mature follicle, ovulation at day ~14, developing corpus luteum, regressing corpus luteum), ovarian hormone levels (estrogen peaks before ovulation, progesterone peaks in luteal phase), and uterine events (menses, endometrium thickening). Days 1-29; phases: Menstruation, Follicular phase (Proliferative phase), Luteal phase (Secretory phase), Next cycle begins. See it in the official paper.

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

Look at the graph: which hormones come from the pituitary and which from the ovary?

Hint 2

In which phase is the uterine lining thickest and most vascular?

Hint 3

Follow progesterone: what happens to it when the corpus luteum regresses?

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) FSH and LH – source: anterior pituitary gland.

    ½ mark

  2. (a) Estrogen – source: ovary (Graafian follicle); progesterone – source: ovary (corpus luteum). Any two hormones with their correct sources earn the full mark.

    ½ mark

  3. (b) The embryo should be transferred during the luteal (secretory) phase.

    ½ mark

  4. (b) Reason: under progesterone, the endometrium is thick, well developed and vascular, so it is ready for implantation of the early embryo.

    ½ mark

  5. (c) [First alternative] Hormone: estrogen; source: ovary (growing or Graafian follicles).

    1 mark

  6. (c) [First alternative] Event: rising estrogen causes the endometrium of the uterus to regenerate through proliferation after menstruation.

    1 mark

  7. (c) [OR alternative] If the ovum is not fertilised, the corpus luteum degenerates.

    ½ mark

  8. (c) [OR alternative] As a result, the progesterone level falls.

    ½ mark

  9. (c) [OR alternative] Without progesterone, the endometrium and its blood vessels disintegrate.

    ½ mark

  10. (c) [OR alternative] The disintegrated endometrium is shed as the menstrual flow. If fertilisation occurs, the corpus luteum is maintained, so menstruation does not occur.

    ½ mark

Answer: (a) FSH and LH (pituitary); estrogen and progesterone (ovary). (b) Luteal/secretory phase, because the endometrium is thick and ready for implantation. (c) Estrogen from ovarian follicles, which regenerates the endometrium by proliferation; OR without fertilisation the corpus luteum degenerates, progesterone falls and the endometrium breaks down as menstrual flow.

Where the marks are

  • (a) Any two hormones with correct source organs (½ + ½)
  • (b) Luteal/secretory phase (½) with the reason that the endometrium is ready for implantation (½)
  • (c) Estrogen and ovary (½ + ½), and explains regeneration or proliferation of the endometrium (1)
  • (c) OR: corpus luteum degenerates, progesterone falls, endometrium disintegrates, menstrual flow (½ × 4)

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 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.