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(i) Draw a diagrammatic… (Class 12 Biology 2024, Q31b)

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

CBSE Class 12 Biology 2024: question 31(b)

Set in the CBSE Class 12 board exam of 2024, paper 57/1/1, section E, question 31(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q31(b) · 5 marks · Long answerHuman Reproduction

(i) Draw a diagrammatic sectional view of ovary of human female and label the following : (2)
(1) Blood vessels
(2) Primary follicle
(3) Tertiary follicle
(4) Ovum
(ii) At which stage of life are primary follicles formed in a human female ? (½)
(iii) Explain the events (both hormonal and structural) that occur at the time of ovulation till the onset of the next menstrual cycle. (2½)

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

Place the follicles in order of maturity around the ovary's margin, and show blood vessels in the medulla.

Hint 2

Oogenesis starts long before birth.

Hint 3

Follow the hormones: LH surge → ovulation → corpus luteum → progesterone → what happens when it degenerates?

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) Diagram (described): an oval section of the ovary with stroma, showing stages of follicle development around the periphery. Label 1: blood vessels, entering at the hilum and running through the medulla.

    ½ mark

  2. (i) Label 2: primary follicle, a primary oocyte surrounded by a single layer of granulosa cells, near the surface.

    ½ mark

  3. (i) Label 3: tertiary follicle, a larger follicle with a fluid-filled cavity (antrum) and theca layers.

    ½ mark

  4. (i) Label 4: ovum, the secondary oocyte released from the ruptured Graafian follicle.

    ½ mark

  5. (ii) Primary follicles are formed at the embryonic (foetal) stage. Oogonia formed in the foetal ovary enter meiosis I and are arrested as primary oocytes surrounded by granulosa cells.

    ½ mark

  6. (iii) Both LH and FSH reach their peak in the middle of the cycle, around day 14.

    ½ mark

  7. (iii) The rapid secretion of LH to its maximum level, the LH surge, induces rupture of the Graafian follicle and release of the ovum. This is ovulation.

    ½ mark

  8. (iii) Ovulation is followed by the luteal phase, in which the remaining parts of the Graafian follicle transform into the corpus luteum.

    ½ mark

  9. (iii) The corpus luteum secretes large amounts of progesterone, which is essential for maintaining the endometrium for implantation.

    ½ mark

  10. (iii) If fertilisation does not occur, the corpus luteum degenerates and progesterone falls. The endometrium then disintegrates, leading to menstruation and the start of a new cycle.

    ½ mark

Answer: (i) Labelled ovary section showing blood vessels, primary follicle, tertiary follicle, ovum; (ii) embryonic (foetal) stage; (iii) LH and FSH peak; LH surge ruptures Graafian follicle (ovulation); corpus luteum forms and secretes progesterone; without fertilisation it degenerates, endometrium breaks down and menstruation begins

Where the marks are

  • Four correct labels (½ × 4 marks)
  • Embryonic stage (½ mark)
  • LH and FSH peak mid-cycle (½ mark)
  • LH surge causes rupture of Graafian follicle / ovulation (½ mark)
  • Corpus luteum forms in luteal phase (½ mark)
  • Progesterone maintains endometrium (½ mark)
  • Corpus luteum degenerates without fertilisation, leading to menstruation (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 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.