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Observe the diagram given… (Class 12 Biology 2023, Q33b)

questionbuddy.in/q/cbse-12-biology-2023-57-1-1-q33b-observe-diagram-showing-menstrual-cycle

BiologyCBSE Class 12 · Board exam 2023, set 57/1/1 · 5 marks · Long answer

CBSE Class 12 Biology 2023: question 33(b)

Set in the CBSE Class 12 board exam of 2023, paper 57/1/1, section E, question 33(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q33(b) · 5 marks · Long answerCompetency-basedHuman Reproduction

Observe the diagram given below showing the menstrual cycle of a normal human female and answer the questions that follow :
(i) What are the suitable technical terms used for the following ?
(1) Days 1 – 7
(2) Days 8 – 12
(3) Days 16 – 28
(4) Days 13 – 15
(ii) Explain the role of ovarian and pituitary hormones during the following time periods :
(1) Days 8 – 12
(2) Days 13 – 15
(3) Days 16 – 28

Figure in the paper: Circular wheel divided into 28 numbered segments (days 1 to 28 of the menstrual cycle) with outer arcs bracketing days 1-7, 8-12, 13-15 and 16-28. Numbers indicate the days of the menstrual cycle. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 57/1/1.

Hints

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

Hint 1

Name each phase after what happens in the uterus or the ovary during those days: bleeding, follicle growth, egg release, or the yellow body.

Hint 2

FSH and LH come from the pituitary, while estrogen and progesterone come from the ovary. Decide which one dominates each period.

Hint 3

A sudden peak of one pituitary hormone mid-cycle triggers egg release. Ask yourself which hormone from the corpus luteum then keeps the uterine lining ready.

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)(1) Days 1–7: menstrual phase (menstruation).

    ½ mark

  2. (i)(2) Days 8–12: follicular phase, also called the proliferative phase.

    ½ mark

  3. (i)(3) Days 16–28: luteal phase, also called the secretory phase.

    ½ mark

  4. (i)(4) Days 13–15: ovulatory phase (ovulation occurs around day 14).

    ½ mark

  5. (ii)(1) Days 8–12 – pituitary: rising levels of FSH (and LH) from the anterior pituitary stimulate the development of ovarian follicles and the secretion of estrogen by the growing follicles.

    ½ mark

  6. Days 8–12 – ovarian: the estrogen secreted by the growing follicles causes proliferation (regeneration) of the endometrium.

    ½ mark

  7. (ii)(2) Days 13–15 – pituitary: LH and FSH reach their peak, and the LH surge induces rupture of the Graafian follicle, releasing the ovum (ovulation).

    ½ mark

  8. Days 13–15 – ovarian: high estrogen levels complete the maturation of the Graafian follicle and keep the endometrium thickened.

    ½ mark

  9. (ii)(3) Days 16–28 – pituitary: LH acts on the remains of the ruptured follicle and maintains it as the corpus luteum.

    ½ mark

  10. Days 16–28 – ovarian: the corpus luteum secretes large amounts of progesterone, which maintains the endometrium for implantation. If fertilisation does not occur, the corpus luteum degenerates, progesterone falls and the endometrium breaks down, leading to the next menstruation.

    ½ mark

Answer: (i) 1–7: Menstrual phase; 8–12: Follicular/proliferative phase; 16–28: Luteal/secretory phase; 13–15: Ovulatory phase. (ii) 8–12: FSH stimulates follicle growth, and estrogen proliferates the endometrium; 13–15: LH surge ruptures the Graafian follicle (ovulation), and high estrogen matures the follicle and thickens the endometrium; 16–28: LH maintains the corpus luteum, whose progesterone maintains the endometrium.

Where the marks are

  • Names the four phases correctly (½ × 4 = 2 marks)
  • Days 8–12: FSH stimulates follicular development/estrogen secretion, and estrogen proliferates the endometrium (½ + ½ mark)
  • Days 13–15: LH surge causes rupture of the Graafian follicle/ovulation, and estrogen matures the follicle/thickens the endometrium (½ + ½ mark)
  • Days 16–28: corpus luteum maintained by LH, and its progesterone maintains the endometrium (½ + 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 paper2023 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.