Read the given passage and answer the following questions:
Spermatogenesis results in the formation of sperms that are transported by the male sex accessory ducts. A normal human sperm is composed of a head, neck, a middle piece and tail. The process of formation of mature female gametes is called oogenesis. The reproductive cycle of female primates is called menstrual cycle. Menstrual cycle starts only after attaining sexual maturation (puberty). During ovulation only one ovum is released per menstrual cycle. The cyclical changes in the ovary and the uterus during menstrual cycle are induced by changes in the levels of pituitary and ovarian hormones. After coitus, sperms are transported to the ampulla, where the sperm fertilises the ovum leading to formation of a diploid zygote. The presence of X or Y chromosome in the sperm determines the sex of the embryo. The zygote undergoes repeated mitotic division to form a blastocyst, which is implanted in the uterus resulting in pregnancy. After nine months of pregnancy, the fully developed foetus is ready for delivery. The process of childbirth is called parturition which is induced by a complex neuroendocrine mechanism involving cortisol, estrogens and oxytocin. Mammary glands differentiate during pregnancy and secrete milk after child-birth. The new-born baby is fed milk by the mother (lactation) during the initial few months of growth.
Which of the following statements about the human menstrual cycle is incorrect?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → During the follicular phase, the primary follicles in the ovary grow to become a fully mature corpus luteum.
In the follicular phase the primary follicles grow into a fully mature Graafian follicle. The corpus luteum forms only later, in the luteal phase, from the parts of the Graafian follicle left after ovulation.
Option (1) Menstruation occurs if the released ovum is not fertilised. — A correct statement. Menstruation is the breakdown of the endometrium and its blood vessels. It happens only when the released ovum is not fertilised.
Option (2) Lack of menstruation may be indicative of pregnancy, but it may also be caused by stress or poor health. — A correct statement. Missed menstruation may point to pregnancy, but stress or poor health can also cause it.
Option (3) During the follicular phase, the primary follicles in the ovary grow to become a fully mature corpus luteum. — An incorrect statement. The follicles grow into a Graafian follicle, not a corpus luteum. The corpus luteum appears only in the luteal phase.
Option (4) The secretion of gonadotropins (LH and FSH) increases gradually during the follicular phase. — A correct statement. LH and FSH rise gradually through the follicular phase. They stimulate the growth of follicles and their secretion of estrogens.
NCERT Extract:
Menstrual Cycle – “… 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 (Figure 2.9). 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.”
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).”