Read the passage and answer the following questions:
The major events of the 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.
Assertion (A): Endometrium is necessary for implantation of blastocyst.
Reason (R): In the absence of fertilisation, the corpus luteum degenerates, which causes disintegration of endometrium.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both A and R are true but R is not the correct explanation of A.
Assertion (A): Endometrium is necessary for implantation of blastocyst. — True. A is about the role of the endometrium. In the luteal phase, the corpus luteum secretes progesterone, which keeps the endometrium ready, and such an endometrium is needed for the blastocyst to get implanted.
Reason (R): In the absence of fertilisation, the corpus luteum degenerates, which causes disintegration of endometrium. — True. R is about what happens when there is no fertilisation. The corpus luteum breaks down, progesterone falls, the endometrium disintegrates, and menstruation starts a new cycle.
Why R does not explain A? A asks why the endometrium matters for implantation: the blastocyst gets embedded in it, so it must be maintained. R describes the opposite case, where there is no fertilisation and the endometrium is lost. It tells what happens to the endometrium, not why the blastocyst needs it. So both statements are correct, but R is not the explanation of A.
NCERT Extract:
Menstrual Cycle – “… The ovulation (ovulatory phase) is followed by the luteal phase during which the remaining parts of the Graafian follicle transform as the corpus luteum (Figure 2.9). The corpus luteum secretes large amounts of progesterone which is essential for maintenance of the endometrium. Such an endometrium is necessary for implantation of the fertilised ovum and other events of pregnancy. During pregnancy all events of the menstrual cycle stop and there is no menstruation. In the absence of fertilisation, the corpus luteum degenerates. This causes disintegration of the endometrium leading to menstruation, marking a new cycle.”