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.
In which of the following pairs do the females show a menstrual cycle?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Apes and human beings
The reproductive cycle of the female is called the menstrual cycle only in primates, such as monkeys, apes and human beings. In these animals the cycle ends with menstrual flow, the breakdown of the endometrium. In human females it repeats about every 28/29 days.
Option (1) Monkeys and cows — Incorrect. Monkeys are primates and do show a menstrual cycle, but cows are not primates. One wrong member makes the pair wrong.
Option (2) Apes and human beings — Correct. Apes and human beings are both primates, and the book names both of them as examples of females with a menstrual cycle.
Option (3) Sheep and human beings — Incorrect. Human beings show a menstrual cycle, but sheep are not primates, so the pair does not fit.
Option (4) Rats and dogs — Incorrect. Rats and dogs are mammals but not primates. Neither is named by the book as showing a menstrual cycle.
NCERT Extract:
Menstrual Cycle – “The reproductive cycle in the female primates (e.g. monkeys, apes and human beings) is called menstrual cycle. The first menstruation begins at puberty and is called menarche. In human females, menstruation is repeated at an average interval of about 28/29 days, and the cycle of events starting from one menstruation till the next one is called the menstrual cycle.”