Chapter 3

Human Reproduction

Humans reproduce sexually and are viviparous. The male reproductive system consists of two testes, male sex accessory ducts, accessory glands, and external genitalia. Each testis has around 250 sections known as testicular lobules. One to three strongly coiled seminiferous tubules are seen in each lobule. Every Spermatogonia and Sertoli cell line the interior of the seminiferous tubule. Learn about Human Reproduction class 12 NCERT with these study notes and exercise solutions. Spermatogonia undergo meiotic divisions, which result in the production of sperm. Sertoli cells, on the other hand, feed the dividing germ cells. Leydig's Testicular cells synthesise and produce testicular hormones outside the seminiferous tubules. Androgens are male hormones. The male external genitalia is referred to as the penis. The female reproductive system comprises two ovaries, two oviducts, a uterus, a vagina, external genitalia, and two mammary glands. The ovaries are responsible for producing the female gamete (ovum) and several steroid hormones (ovarian hormones). The stroma contains ovarian follicles at various phases of growth. Female accessory ducts include the oviducts, uterus, and vagina. The uterus comprises three layers: perimetrium, myometrium, and endometrium. Mons pubis, labia majora, labia minora, hymen, and clitoris are the female external genitalia. One of the female secondary sexual organs is the mammary glands. Given below are the exercises and class 12 Biology chapter 3 NCERT solutions.

Exercises for Human Reproduction Class 12 Ncert

  1. Fill in the blanks:
  2. Humans reproduce _____________ (asexually/sexually)
  3. Humans are _____________ (oviparous, viviparous, ovoviviparous)
  4. Fertilisation is _____________ in humans (external/internal)
  5. Male and female gametes are _____________ (diploid/haploid)
  6. Zygote is _____________ (diploid/haploid)
  7. The process of release of ovum from a mature follicle is called _____________
  8. Ovulation is induced by a hormone called _____________
  9. The fusion of male and female gametes is called _____________
  10. Fertilisation takes place in _____________
  11. Zygote divides to form _____________which is implanted in the uterus.
  12. The structure which provides vascular connection between foetus and uterus is called _____________
  13. Draw a labelled diagram of the male reproductive system.
  14. Draw a labelled diagram of the female reproductive system.
  15. Write two major functions, each of testis and ovary.
  16. Describe the structure of a seminiferous tubule.
  17. What is spermatogenesis? Briefly describe the process of spermatogenesis.
  18. Name the hormones involved in the regulation of spermatogenesis.
  19. Define spermiogenesis and spermiation.
  20. Draw a labelled diagram of sperm.
  21. What are the major components of seminal plasma?
  22. What are the major functions of male accessory ducts and glands?
  23. What is oogenesis? Give a brief account of oogenesis.
  24. Draw a labelled diagram of a section through the ovary.
  25. Draw a labelled diagram of a Graafian follicle?
  26. Name the functions of the following:
  27. Corpus luteum
  28. Endometrium
  29. Acrosome
  30. Sperm tail
  31. Fimbriae
  32. Identify True/False statements. Correct each false statement to make it true.
  33. Androgens are produced by Sertoli cells. (True/False)
  34. Spermatozoa get nutrition from Sertoli cells. (True/False)
  35. Leydig cells are found in the ovary. (True/False)
  36. Leydig cells synthesise androgens. (True/False)
  37. Oogenesis takes place in the corpus luteum. (True/False)
  38. Menstrual cycle ceases during pregnancy. (True/False)
  39. Presence or absence of a hymen is not a reliable indicator of virginity or sexual experience. (True/False)
  40. What is the menstrual cycle? Which hormones regulate the menstrual cycle?
  41. What is parturition? Which hormones are involved in the induction of parturition?
  42. In our society, women are often blamed for giving birth to daughters. Can you explain why this is not correct?
  43. 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?
  44. How many eggs do you think were released by the ovary of a female dog which gave birth to 6 puppies?

Here are the Human Reproduction class 12 Ncert solutions:

1. The answers to be filled in the blanks are as follows:

(a) sexually

(b) viviparous

(c) internal

(d) haploid

(e) diploid

(f) ovulation

(g) LH (Luteinizing hormone)

(h) fertilisation

(i) Fallopian tube

(j) blastocyst

(k) placenta (Umbilical cord)


4. Testes are a part of the reproductive system and the endocrine system. The testes have two functions. These functions are:

  • Generating sperm (spermatozoa) through spermatogenesis, and
  • Manufacturing male sex hormones, the most well-known of which is testosterone.


The ovaries serve two important functions, including:

  • The first is the generation of eggs or ova, and
  • The second is the generation of hormones or chemicals that manage menstruation and other elements of health and well-being, including sexual health. Oestrogen and progesterone are the two most significant hormones, serving a variety of roles.


5. Seminiferous tubules are strongly curled formations that may be seen in testicular lobules. Within the seminiferous tubules, two kinds of cells line them: spermatogonia and Sertoli cells. Sertoli cells supply nourishment to the germ cells, whereas spermatogonia are male germ cells that create sperms by meiotic divisions followed by mitotic divisions. The interstitial space is the area outside the seminiferous tubules that includes tiny blood arteries and Leydig cells. Androgen is secreted by Leydig's cells.


6. Spermatogenesis is when spermatozoa are formed from spermatogonia in the testes during adolescence. The spermatogonia on the seminiferous tubules' inner side grows and increases in quantity throughout this phase. There are 46 chromosomes in each spermatogonium. Spermatogonia produces a spermatocyte, which divides meiotically to generate secondary spermatocytes with 23 chromosomes. The secondary spermatocyte divides for the second time to create spermatids. Spermiogenesis is the process through which spermatids are converted into spermatozoa. The sperm heads stay attached to the Sertoli cells and are discharged into the seminiferous tubules during the spermiation process.


7. Gonadotropin-releasing hormone (GnRH), Luteinizing hormone (LH), Follicle-stimulating hormone (FSH), androgens are hormones that regulate spermatogenesis.


8. The process by which spermatids are turned into spermatozoa is known as spermiogenesis.

Spermiation is when sperms are released from Sertoli cells into the seminiferous tubules.


10. Mucous, fructose, calcium, ascorbic acid, some enzymes, and various accessory gland secretions are the primary components of seminal plasma.


11. The vasa efferentia, epididymis, vas deferens, and rete testis are all-male accessory ducts. They carry and preserve spermatozoa for a short period.

Seminal vesicles, the bulbourethral gland, and the prostate gland are examples of male accessory glands. Fluids secreted by these glands act as lubricants for the female reproductive system and sperms.


12. Oogenesis is the process through which mature female gametes are formed. During the embryonic stage, millions of oogonia arise in each foetal ovary. Then, the gamete mother cells begin to divide and enter prophase-I of meiotic division, briefly stopping them. They are referred to as primary oocytes at this stage. When a layer of granulosa cells surrounds a primary oocyte, it is a primary follicle. The primary follicle is surrounded by additional layers of granulosa cells called secondary follicles, which convert into tertiary follicles with a fluid-filled cavity known as the antrum. Tertiary follicles develop into the mature Graafian follicle, which ruptures to release secondary oocytes (ovum) from the ovary during the ovulation process.


15. The corpus luteum secretes progesterone. Progesterone is required for endometrial maintenance.


Endometrium- The endometrium is where the fertilised ovum implants and many other pregnancy processes occur.


Acrosome- It contains enzymes that hydrolyse egg membranes, allowing sperm to penetrate the ovum during fertilisation.


Sperm tail- It is responsible for sperm motility.


Fimbriae- Fimbriae aids in collecting the ovum after ovulation.


16. (a) False, Androgens or male sex hormones are secreted by Leydig cells.

(b) True.

(c) False, Leydig cells are found in testis.

(d) True.

(e) False, Oogenesis takes place in the ovary.

(f) True.

(g) True.


17. The menstrual period refers to the reproductive cycle of female primates. Menstruation occurs on cycle days 3-5 of a 28-day menstrual cycle. The menstrual cycle is divided into four phases: menstrual, follicular, ovulatory, and luteal.

Menstrual cycle phases:

  • LH production from the pituitary gland's anterior lobe is diminished.
  • Elimination of this hormone induces corpus luteum degeneration, which reduces progesterone synthesis.
  • Oestrogen production is also lowered during this era.
  • The uterine endometrium degrades, and menstruation starts.
  • The menstrual flow comprises endometrial fluids, blood, and unfertilised ovum cells.

Hormonal regulation of the menstrual cycle: 

  • FSH increases the production of oestrogens by the ovarian follicles.
  • LH promotes progesterone secretion in the corpus luteum.
  • A rise in oestrogen production triggers the menstrual phase.
  • LH causes ovulation.
  • A rise in oestrogen production triggers the proliferative phase.
  • An increase in progesterone production drives the secretory phase.


18. Childbirth is referred to as parturition or labour. Parturition refers to the process through which a baby and the afterbirth (placenta) are evacuated from the uterus after delivery. The process normally begins naturally around 280 days following conception; however, it can also be initiated artificially.


Parturition is triggered by a complicated neuroendocrine system that includes cortisol, oestrogen, and oxytocin.


19. The female sex chromosome pattern is XX, while the male sex chromosome pattern is XY. As a result, all haploid female gametes (ova) have sex chromosome X, whereas haploid male gametes have either X or Y. Thus, 50 percent of sperms have the X-chromosome, whereas the other 50 percent have the Y-chromosome. After the male and female gametes fuse, the zygote contains either XX or XY depending on whether the sperm carries X or Y and fertilises the ovum. The zygote containing XX would be a female kid, whereas the zygote carrying XY would be a male baby. As a result, it is true to claim that the father determines the sex of the infant.


20. A human ovary produces one egg every month. From a single egg, identical twins are produced. As a result, whenever the mother gives birth to identical twins, just one egg is released. If the twins are fraternal, they result from the development of two eggs.


21. The female dog lays six eggs, which would result in the birth of six puppies.

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