Given below is the diagram of a human ovum surrounded by a few sperms. Observe the diagram and answer the following questions:
(a) Compare the fate of sperms shown in the diagram.
(b) What is the role of zona pellucida in this process?
(c) Analyze the changes occurring in the ovum during the process.
(d) How is the entry of sperm into the ovum facilitated?
(e) Specify the region of female reproductive system where the event represented in the diagram takes place.
OR
The graph given below shows the variation in the levels of ovarian hormones during various phases of the menstrual cycle:
(a) Identify ‘A’ and ‘B’.
(b) Specify the source of the hormone marked in the diagram.
(c) Reason out why A peaks before B.
(d) Compare the role of A and B.
(e) Under which condition will the level of B continue to remain high on the 28thday?
(a) The sperm A will enter the ovum while sperms B and C won’t be able to enter the ovum. The sperms A will secrete certain enzymes which will block the entry of other sperms.
(b) The zona pellucida undergoes changes when encountered with a sperm. There occur some changes in the membrane of ovum which blocks the entry of other sperms.
(c) The changes that occur in the ovum during the process are the membrane composition changes and the nature of zona pellucida changes which blocks the entry of other sperms.
(d) The acrosomal region of sperms contain certain enzymes which help them to penetrate through zona pellucida. These enzymes alter the composition of ovum membranes and bring about changes in the zona pellucida due to which the entry of other sperms is blocked.
(e) The above event of fertilisation occurs in the ampullary region of fallopian tube.
OR
(a) In the above diagram, A refers to Estrogen level, and B refers to Progesterone levels during menstruation.
(b) The source of hormones estrogen and progesterone is an ovary.
(c) The level of estrogen rises during the follicular phase. Estrogen helps in the regeneration of endometrium and maturation of primary follicles to Graafian follicles. The LH(luteinizing hormone) and FSH (follicle stimulating hormone) levels also rise. The growing and developing follicles keep secreting estrogen. Hence A which is estrogen peaks before B which is progesterone.
(d) The function of estrogen is prominent during the follicular phase. It helps in the regeneration of endometrial wall and helps the primary follicles to mature to Graafian follicles.
The function of progesterone is prominent in the luteal phase or secretory phase. In this phase corpus luteum produced in the ovulatory phase, secretes a large amount of progesterone. It is essential for maintaining the endometrium and prepares it for implantation of the embryo.
(e) The level of B that is progesterone will continue to remain high on the 28th day in case if pregnancy occurs. As progesterone is responsible for maintenance of endometrium so if pregnancy has occurred, the level of progesterone will remain high.