Question 1

Fill in the blanks:(a) Humans reproduce .............. (asexually/sexually).(b) Humans are ............ (oviparous, viviparous, ovoviviparous).(c) Fertilisation is ............. in humans (external/internal)(d) Male and female gametes are ............. (diploid/haploid).(e) Zygote is ............. (diploid/haploid).(f) The process of release of ovum from a mature follicle is known as ..............(g) Ovulation is induced by a hormone called .............(h) The fusion of male and female gametes is called ..............(i) Fertilisation takes place in ..............(j) Zygote divides to form ............. which is implanted in uterus.(k) The structure which provides the vascular connection between fetus and uterus is called ............

Accepted Answer

a) Humans reproduce sexually.(b) Humans are viviparous.(c) Fertilisation is internal in humans. (d) Male and female gametes are haploid.(e) Zygote is diploid.(f) The process of release of ovum from a mature follicle is called ovulation.(g) Ovulation is induced by a hormone called Leutinizing hormone.(h) The fusion of male and female gametes is called fertilization.(i) Fertilisation takes place in oviduct.(j) Zygote divides to form blastula which is implanted in uterus.(k) The structure which provides vascular connection between fetus and uterus is called umbilical cord.

Question 2

Draw a labelled diagram of male reproductive system.

Accepted Answer

The given diagram represents the male reproductive system that regulates the formation and transportation of male gametes.

Question 3

Write two major functions each of testis and ovary.

Accepted Answer

Testes serve as the site of spermatogenesis for the production of sperm. The endocrine cells present in the space between seminiferous tubules are termed as interstitial cells. They serve to secrete androgen, testosterone, which is responsible for the development of male secondary sexual characters. Ovaries serve as the site of egg production by oogenesis and secrete female sex hormones namely estrogen and progesterone for development of female secondary sexual characteristics.

Question 4

Describe the structure of a seminiferous tubule.

Accepted Answer

Each testicular lobule has tightly coiled seminiferous tubules which are packed with cells undergoing spermatogenesis (spermatogonia) and Sertoli cells. A germinal epithelium of delicate connective tissue surrounds the seminiferous tubules. The large sustentacular cells that extend from the capsule to the lumen of the seminiferous tubule are called Sertoli cells. They serve to support, nourish and regulate the development of cells undergoing spermatogenesis. The endocrine cells present in the space between seminiferous tubules are termed as interstitial cells of Leydig. They serve to secrete androgen, testosterone.

Question 5

What is spermatogenesis? Briefly describe the process of spermatogenesis.

Accepted Answer

Spermatogenesis is the process of the production of sperms from the immature male germ cells. It starts at puberty and usually continues uninterrupted until death, although a slight decrease in the quantity of sperm is seen with increase in age.Process of Spermatogenesis:The spermatogonia (2N) present at the inner side of the seminiferous tubules multiply by mitotic divisions and increase in number. They stop undergoing mitosis, grow and become primary spermatocytes (2N). Each primary spermatocyte undergoes meiosis to form two equal haploid secondary spermatocytes (N). Each secondary spermatocyte then undergoes second meiotic division to form four equal haploid cells called spermatids (N). Spermatids receive nourishment to form sperms by the process called spermiogenesis.

Question 6

Name the hormones involved in regulation of spermatogenesis.

Accepted Answer

Gonadotropins FSH and LH are secreted by the anterior pituitary. FSH promotes spermatogenesis in the seminiferous tubules and LH promotes androgen production in the interstitial cells (androgens are required for attainment of reproductive maturity in males).

Question 7

Define spermiogenesis and spermiation.

Accepted Answer

Transformation of spermatids into sperm by morphological changes without involving cell division is called as spermiogenesis. The release of mature spermatozoa from the Sertoli cells into the lumen of seminiferous tubules is called as spermiation.

Question 8

What are the major components of seminal plasma?

Accepted Answer

Semen is a mixture of sperms and seminal plasma. Seminal vesicle secretion accounts for 60% of seminal plasma and adds alkaline pH (to counteract acidic pH of the vagina), fructose (a nutrient), mucus and coagulating and local acting enzymes. Prostate gland secretions account for 30% of plasma and add citrate (a nutrient for sperm mitochondria), calcium and a proteolytic enzyme termed as prostate specific antigen (to liquefy ejaculate just before release). Secretion from Cowper gland adds only small volume.

Question 9

What are the major functions of male accessory ducts and glands?

Accepted Answer

The male accessory ducts (vasa efferentia, epididymis, vas deferens, and rete testis) serve to store spermatozoa and to transport them outside urethra during ejaculation. Male accessory glands are seminal vesicles, prostate glands, and bulbourethral glands which contribute seminal plasma to semen. Seminal vesicle secretion accounts for 60% of seminal plasma and adds alkaline pH (to counteract acidic pH of the vagina), fructose (a nutrient), mucus and coagulating and local acting enzymes. Prostate gland secretions account for 30% of plasma and add citrate (a nutrient for sperm mitochondria), calcium and a proteolytic enzyme termed as prostate-specific antigen (to liquefy ejaculate just before release). Secretion from Cowper gland adds only small volume.

Question 10

What is oogenesis? Give a brief account of oogenesis.

Accepted Answer

Oogenesis is the production of egg cells inside the ovaries. During foetal development, few germinal cells in human ovary differentiate and divide mitotically to produce egg mother cell/oogonia. Further, oogonia become larger and divide to produce diploid primary oocyte. In follicular prenatal phase, the primary oocytes start first meiotic division but are transitionally suspended into prophase stage of meiosis I and are stored in the follicle. After puberty, primary oocyte resumes the division and completion of first meiotic division produce one secondary oocyte (egg cell) and one polar body (non-functional cell).

Question 11

Draw a labelled diagram of a Graafian follicle.

Accepted Answer

Graafian follicle is a fluid-filled structure in the mammalian ovary which carries ovum development.

Question 12

Name the functions of the following:(a) Corpus luteum       (b) Endometrium(c) Acrosome                (d) Sperm tail(e) Fimbriae

Accepted Answer

(a) Corpus luteum − Corpus luteum is formed from the ruptured Graafian follicle. It secretes progesterone hormone during the luteal phase of the menstrual cycle. A high level of progesterone inhibits the secretions of FSH and LH, thereby preventing ovulation. It also allows the endometrium of the uterus to proliferate and to prepare itself for implantation.(b) Endometrium − It is the innermost lining of the uterus. It is rich in glands and undergoes cyclic changes during various phases of the menstrual cycle to prepare itself for the implantation of the embryo.(c) Acrosome − It is a cap-like structure present in the anterior part of the head of the sperm. It contains hyaluronidase enzyme, which hydrolyzes the outer membrane of the egg, thereby helping the sperm to penetrate the egg at the time of fertilization.(d) Sperm tail − It is the longest region of the sperm that facilitates the movement of the sperm inside the female reproductive tract.(e) Fimbriae − They are finger-like projections at the ovarian end of the fallopian tube. They help in the collection of the ovum (after ovulation), which is facilitated by the beating of the cilia.

Question 13

Identify True/False statements. Correct each false statement to make it true.(a) Androgens are produced by Sertoli cells. (True/False)(b) Spermatozoa get nutrition from Sertoli cells. (True/False)(c) Leydig cells are found in ovary. (True/False)(d) Leydig cells synthesise androgens. (True/False)(e) Oogenesis takes place in corpus luteum. (True/False)(f) Menstrual cycle ceases during pregnancy. (True/False)(g) Presence or absence of hymen is not a reliable indicator of virginity or sexual experience. (True/False)

Accepted Answer

(a) Androgens are produced by Sertoli cells. (False) Androgens are produced by Leydig cells.(b) Spermatozoa get nutrition from Sertoli cells. (True)(c) Leydig cells are found in ovary. (False) Leydig cells are found in the seminiferous tubules of the testis.(d) Leydig cells synthesise 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)

Question 14

What is menstrual cycle? Which hormones regulate menstrual cycle?

Accepted Answer

The menstrual cycle is the female reproductive cycle characterized by cyclic changes in the uterine lining. Menstrual cycle is regulated by gonadotropins secreted by anterior pituitary (FSH and LH). FSH stimulates growth, development and hormonal secretion of Graafian follicle and ovum maturation. LH stimulates maturation of Graafian follicle and LH surge between 12 to 14 days of cycle stimulates rupture of Graafian follicle and release of ovum i.e. ovulation. Gonadotropins also stimulate developing follicles to secrete progesterone and estrogen which in turn prepare the uterus for implantation and exert negative feedback regulation on the secretion of gonadotropins after ovulation.

Question 15

What is parturition? Which hormones are involved in induction of parturition?

Accepted Answer

Parturition is the act of giving birth to the young; childbirth. Fully developed foetus and placenta send signals for parturition which in turn induces mild uterine contractions by stretching of cervix referred to as foetal ejection reflex. Stretching of cervix exerts positive feedback on the posterior pituitary to secrete oxytocin. Oxytocin exhibits both direct and indirect (via prostaglandins) effect on the uterus to facilitate uterine contractions to push the foetus downward which in turn stretches cervix more and leads to childbirth. Relaxin is secreted by corpus luteum at the end of pregnancy. It serves to relax the pelvic ligament and cervix to facilitate the birth of young one.

Question 16

In our society the women are often blamed for giving birth to daughters. Can you explain why this is not correct?

Accepted Answer

In our society women are always falsely accused for giving birth to daughters.First of all, it is incorrect in itself as both Boys and Girls are equal. Also, women do not have any role in deciding the sex of their child. It is actually the male whose sperm chromosome decides the fate of the sex of the child.Females have 23 pairs of chromosomes, 22 + XX (sex chromosome) and males have 23 pairs of chromosomes as well 22 + XY (sex Chromosome). While fertilization ova will be carrying one X chromosome while sperm would either be carrying X or Y chromosome. So if ova having X chromosome fertilizes with sperm having X chromosome, the child will be Girl (XX) and if ova having X chromosome fertilizes with sperm having a Y chromosome, the child will be a boy (XY). Thus mothers are wrongly blamed.In humans, this XX, XY type of determination occurs to determine the sex of children.

Question 17

How many eggs are released by a human ovary in a month? How many eggs do you think would have been released if the mother gave birth to identical twins? Would your answer change if the twins born were fraternal?

Accepted Answer

One egg is released per month from the ovary. The term “monozygous” represent being developed from a single zygote. The first division in zygote produce two identical cells that independently develop into two embryos; monozygotic/identical twins are produced. The term “multizygous/fraternal” represent being developed from individual zygotes. Fertilization of two eggs by two sperms produces two zygotes that independently develop into fraternal embryos. So, identical twins are born from a single egg while two or more eggs are fertilized in case of fraternal twins.

Chapter 3 : Human Reproduction