Read the given passage and answer the following questions:
The menstrual cycle starts with the menstrual phase, when menstrual flow occurs and it lasts for 3-5 days. The menstrual flow results due to breakdown of endometrial lining of the uterus and its blood vessels which forms liquid that comes out through vagina. Menstruation only occurs if the released ovum is not fertilised. Lack of menstruation may be indicative of pregnancy. However, it may also be caused due to some other underlying causes like stress, poor health etc. The menstrual phase is followed by the follicular phase. During this phase, the primary follicles in the ovary grow to become a fully mature Graafian follicle and simultaneously the endometrium of uterus regenerates through proliferation. These changes in the ovary and the uterus are induced by changes in the levels of pituitary and ovarian hormones. The secretion of gonadotropins (LH and FSH) increases gradually during the follicular phase, and stimulates follicular development as well as secretion of estrogens by the growing follicles. Both LH and FSH attain a peak level in the middle of cycle (about 14th day). Rapid secretion of LH leading to its maximum level during the mid-cycle called LH surge induces rupture of Graafian follicle and thereby the release of ovum (ovulation). The ovulation (ovulatory phase) is followed by the luteal phase during which the remaining parts of the Graafian follicle transform as the corpus luteum . The corpus luteum secretes large amounts of progesterone which is essential for maintenance of the endometrium.
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): In the absence of fertilisation, the endometrium disintegrates, leading to menstruation.
Reason (R): During the follicular phase, the endometrium of the uterus regenerates through proliferation.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
The endometrium is the inner lining of the uterus. It grows during the follicular phase, is kept up by progesterone from the corpus luteum during the luteal phase, and breaks down if no fertilisation takes place.
Assertion (A): In the absence of fertilisation, the endometrium disintegrates, leading to menstruation. — True. When the ovum is not fertilised, the corpus luteum degenerates. Progesterone falls, the endometrium breaks down, and menstruation marks a new cycle.
Reason (R): During the follicular phase, the endometrium of the uterus regenerates through proliferation. — True. After menstruation the follicles grow in the ovary, and at the same time the endometrium regenerates by proliferation.
Why R does not explain A? A is about the breakdown of the endometrium at the end of a cycle. R is about its rebuilding in the next follicular phase, which comes after menstruation. The cause of the breakdown is the degeneration of the corpus luteum, which R does not mention. So both statements are correct, but R is not the explanation of A.
NCERT Extract:
Menstrual Cycle – “… The menstrual phase is followed by the follicular phase. During this phase, the primary follicles in the ovary grow to become a fully mature Graafian follicle and simultaneously the endometrium of uterus regenerates through proliferation. … The corpus luteum secretes large amounts of progesterone which is essential for maintenance of the endometrium. … In the absence of fertilisation, the corpus luteum degenerates. This causes disintegration of the endometrium leading to menstruation, marking a new cycle.”