Chapter 2: Human Reproduction

Ans:

• Ans: The formation of eggs or ova in the ovary is called oogenesis. A diploid oogonium or egg mother cell size increases, transforming into a diploid primary oocyte. 

• After attaining full growth, the diploid primary oocyte undergoes the first meiotic division, i.e., meiosis I or reductional division, to form two unequal haploid daughter cells. 

• A very smaller cell is the first polar body or polocyte, while the larger cell is the secondary oocyte, which contains the nucleus and the entire cytoplasm of the yolk. 

• The secondary oocyte undergoes a second meiotic division, i.e., meiosis II or equational division, giving rise to a second polar body and an ovum. 

• Thus, a single haploid ovum is produced by a diploid oogonium, and two or three polar bodies are produced during the entire process of oogenesis.

Process of Oogenesis

Solution coming soon.

Solution coming soon.

Ans:

(a) Corpus luteum:

The ruptured Grafiaan follicle gives rise to a structure called the Corpus luteum. A hormone Progesterone hormone during the luteal phase of the menstrual cycle. The increased amount of progesterone inhibits the secretions of FSH and LH, thereby preventing ovulation. The proliferation of the endometrium of the uterus and the process of implantation is also allowed by the corpus luteum.

(b) Endometrium:

The innermost lining of the uterus is the endometrium. It is removed during menstrual discharge each month in the menstrual cycle and thus it prepares itself for the implantation of the embryo.

(c) Acrosome:

In the sperm, there is a cap-like structure present in the anterior part called the acrosome. There is a presence of an enzyme called hyaluronidase enzyme, which hydrolyses the outer membrane of the egg. The acrosome secretes enzymes that help in the penetration of sperm into the egg by dissolving the egg membrane during fertilization.

(d) Sperm tail:

It is the region of the sperm which is several times longer than the head. The locomotion of the sperm is determined inside the female reproductive tract by the tail of the sperm.

(e) Fimbriae:

The finger-like projections at the ovarian end of the fallopian tube are called fimbriae. After the process of ovulation, they help in the collection of the ovum which is facilitated by the beating of the cilia.

  Ans:

(a) Androgens are produced by Sertoli cells. (False)

Androgens are produced by Leydig cells found in seminiferous tubules of the testis.

(b) Spermatozoa get nutrition from Sertoli cells. (True)

(c) Leydig cells are found in the ovary. (False)

Leydig cells are found in the seminiferous tubules of the testis.

(d) Leydig cells synthesize androgens. (True)

(e) Oogenesis takes place in corpus luteum. (False)

Oogenesis takes place in the ovary.

(f) Menstrual cycle ceases during pregnancy. (True)

(g) Presence or absence of the hymen is not a reliable indicator of virginity or sexual experience. (True)

• Ans: The menstrual cycle is a rhythmic series of physiological changes in the sex organs that occur about  28 days throughout a woman's reproductive life. The end of the cycle is accompanied by the breakdown of the uterine endothelium, which gets released in the form of blood and mucus through the vagina. This is known as menses.

• The menstrual cycle is regulated by the follicle-stimulating hormone (FSH), luteinising hormone (LH), estrogen, and progesterone. The anterior pituitary gland secretes FSH and LH, which increase during the follicular phase. FSH converts A primary follicle into a Graafian follicle under the influence of RH (releasing hormone). 

• The secretion of LH increases gradually, which results in the growth of follicles and the secretion of estrogen. 

• The secretion of FSH is inhibited by estrogen, which stimulates the secretion of the luteinizing hormone. It also causes the thickening of the uterine endometrium. 

• The increased level of LH causes the rupturing of the Graafian follicle and releases the ovum into the fallopian tube. The ruptured Graafian follicle changes to the corpus luteum and starts secreting progesterone hormone during the luteal phase. 

• Progesterone hormone helps in the maintenance and preparation of the endometrium for the implantation of the embryo. High levels of progesterone hormone in the blood decrease LH and FSH secretion, inhibiting further ovulation. 

Ans: After the complete development of the foetus in the mother’s womb, the process of giving birth to a newborn baby is called Parturition. Oxytocin and Relaxin are the two hormones required in this entire process. Oxytocin results in the contraction of smooth muscles of the myometrium of the uterus, which pushes the fully formed foetus towards the birth canal. On the opposite hand, the relaxin hormone causes there is relaxation of the pelvic ligaments by a hormone called relaxin and it thus prepares the uterus for childbirth.

Ans: The number of chromosomes present in each individual is 23. 22 pairs of autosomes in and one or two types of sex chromosomes are present in males. They may be either X or Y. Whereas, 22 pairs of autosomes and only the X sex chromosome is found in females. The type of the male gamete (X or Y)during spermatogenesis A determines the sex of an individual, which further fuses with the X chromosome containing the female’s egg cell. If the fertilized sperm contains X, then the baby born will be a girl and if it contains Y, then the baby born will be a boy.

Thus, for the gender of the child, women should not be blamed.

Ans: Every coming month, a single egg is released by the ovary. Twins are produced when two babies are in a sequence. Generally, A single egg gives rise to twins which are produced by the separation of early blastomeres, emerging from the first zygotic cleavage. Thus, there will be the same genetic make-up in the developed young ones and so, they are called identical twins.

Sometimes, twins born are fraternal, which means they would have developed from two separate eggs. This happens when at the same time two eggs (one from each ovary) are released and fertilization takes place by two separate sperms. Thus, the developed young ones will have separate genes and are, therefore, called non-identical or fraternal twins.