Exercises

1. Fill in the blanks:

• (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 LH (Luteinising Hormone).
• (h) The fusion of male and female gametes is called fertilisation.
• (i) Fertilisation takes place in ampullary region (Fallopian tube).
• (j) Zygote divides to form blastocyst which is implanted in uterus.
• (k) The structure which provides vascular connection between foetus and uterus is called placenta.

2. Draw a labelled diagram of male reproductive system. (Answer based on Fig 2.1 in the textbook)

3. Draw a labelled diagram of female reproductive system. (Answer based on Fig 2.3 in the textbook)

4. Write two major functions each of testis and ovary.

• Testis:
  1. Production of sperms (spermatogenesis).
  2. Secretion of the male sex hormone, testosterone (by Leydig cells).
• Ovary:
  1. Production of the female gamete (ovum).
  2. Secretion of female sex hormones like estrogen and progesterone.

5. Describe the structure of a seminiferous tubule.

• Each seminiferous tubule is lined on its inside by two types of cells: male germ cells (spermatogonia) and Sertoli cells.
• The male germ cells undergo meiotic divisions leading to sperm formation.
• Sertoli cells provide nutrition to the germ cells.
• The regions outside the tubules are called interstitial spaces, which contain small blood vessels and Leydig cells, which synthesize and secrete androgens.

6. What is spermatogenesis? Briefly describe the process of spermatogenesis.

• Spermatogenesis is the process of formation of sperms in the testes.
• It begins at puberty when GnRH stimulates the secretion of LH and FSH.
• Spermatogonia multiply by mitosis to form diploid cells. Some of these, the primary spermatocytes, undergo meiosis.
• The first meiotic division produces two equal haploid secondary spermatocytes.
• The second meiotic division produces four equal haploid spermatids.
• Spermatids are transformed into spermatozoa (sperms) by spermiogenesis.

7. Name the hormones involved in regulation of spermatogenesis.

• Gonadotropin Releasing Hormone (GnRH)
• Luteinising Hormone (LH)
• Follicle Stimulating Hormone (FSH)
• Androgens (e.g., Testosterone)

8. Define spermiogenesis and spermiation.

• Spermiogenesis: The process of transformation of spermatids into spermatozoa (sperms).
• Spermiation: The release of mature sperms from the seminiferous tubules into the lumen.

9. Draw a labelled diagram of sperm. (Answer based on Fig 2.6 in the textbook)

10. What are the major components of seminal plasma?

• Seminal plasma is rich in fructose, calcium, and certain enzymes. It is formed from the secretions of the seminal vesicles, prostate, and bulbourethral glands.

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

• Accessory Ducts (rete testis, vasa efferentia, epididymis, vas deferens): Store and transport sperms from the testis to the outside through the urethra.
• Accessory Glands (seminal vesicles, prostate, bulbourethral glands): Their secretions constitute the seminal plasma, which provides nutrition, motility, and lubrication (by bulbourethral glands) for the sperms.

12. What is oogenesis? Give a brief account of oogenesis.

• Oogenesis is the process of formation of a mature female gamete (ovum).
• It is initiated during the embryonic stage when millions of oogonia are formed.
• These cells start division and are arrested at Prophase-I as primary oocytes.
• At puberty, primary oocytes are surrounded by granulosa cells, forming primary, secondary, and then tertiary follicles.
• In the tertiary follicle, the primary oocyte completes its first meiotic division (unequal) to form a large secondary oocyte and a tiny first polar body.
• Upon ovulation, the secondary oocyte is released from the Graafian follicle.

13. Draw a labelled diagram of a section through ovary. (Answer based on Fig 2.7 in the textbook)

14. Draw a labelled diagram of a Graafian follicle? (Answer based on Fig 2.7 or specialized diagrams in the textbook)

15. Name the functions of the following:

• (a) Corpus luteum: Secretes large amounts of progesterone essential for maintaining the endometrium.
• (b) Endometrium: Necessary for implantation of the fertilized ovum and support during pregnancy.
• (c) Acrosome: Contains enzymes (like hyaluronidase) that help the sperm penetrate the zona pellucida of the ovum.
• (d) Sperm tail: Provides motility to the sperm, facilitating its movement to the site of fertilization.
• (e) Fimbriae: Help in the collection of the ovum from the ovary after ovulation.

16. Identify True/False statements. Correct each false statement to make it true.

• (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 testes).
• (d) Leydig cells synthesise androgens. - True.
• (e) Oogenesis takes place in corpus luteum. - False. (Oogenesis takes place in the ovary; corpus luteum is formed after ovulation).
• (f) Menstrual cycle ceases during pregnancy. - True.
• (g) Presence or absence of hymen is not a reliable indicator of virginity or sexual experience. - True.

17. What is menstrual cycle? Which hormones regulate menstrual cycle?

• The reproductive cycle in female primates (including humans) is called the menstrual cycle. It involves periodic changes in the ovary and uterus approximately every 28/29 days.
• Regulatory Hormones: LH, FSH, Estrogen, and Progesterone.

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

• Parturition is the process of delivery of the foetus (childbirth) at the end of the gestation period.
• Hormones: Oxytocin (primary), Cortisol, and Estrogens.

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

• Sex determination in humans depends on the chromosome provided by the father's sperm.
• The female (mother) only produces ova with X chromosomes. The male (father) produces sperms, 50% of which carry the X chromosome and 50% carry the Y chromosome.
• If an X-bearing sperm fertilizes the ovum, the child will be a girl (XX). If a Y-bearing sperm fertilizes the ovum, the child will be a boy (XY).
• Therefore, the sex of the child is genetically determined by the father.

20. 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?

• Usually, one egg is released by a human ovary in a month.
• Identical Twins: One egg was released; it was fertilized by one sperm, and the resulting zygote split into two embryos.
• Fraternal Twins: Two eggs were released (one from each ovary or both from one), and each was fertilized by a separate sperm.

21. How many eggs do you think were released by the ovary of a female dog which gave birth to 6 puppies?

• Six eggs were released, each fertilized by a separate sperm, as dogs are polytocous (producing many offspring at one birth).