NCERT Solutions for class 12th Biology Chapter 3 Human Reproduction


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 ofrelease of ovum from a mature follicle is called_____ .

(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 vascular connection between foetus and uterus is called____

(a) sexually
(b) viviparous
(c) internal
(d) haploid
(e) diploid
(f) ovulation
(g) LH (luteinising hormone)
(h) fertilisation
(i) ampullary-isthmic junction (fallopian tube)
(j) blastocyst
(k) placenta (umbilical cord)

Question 2. Draw a labelled diagram of male reproductive system.

Sol. Male reproductive system produces, maintain, and transport sperm (the male reproductive cells) and protective fluid (semen) within the female reproductive tract during sex.
Labelled diagram of male reproductive system is given below:

Question 3. Draw a labelled diagram of female reproductive system.

Sol. Female reproductive system produces eggs, sex hormones like oestrogen, progesterone and maintains reproduction and pregnancy.
Labelled diagram offemale reproductive system is given below:

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

Sol. • Testes – Testes are the primary sexual organs in male. Two major functions of testes are :
(i) Testosterone production from Leydig cells of seminiferous tubule.
(ii) Production of sperm cells in seminiferous tubules through spermatogenesis.
Ovary – Ovaries are the primary female sex organs. Two main functions of ovaries are :
(i) Productions of female germ cells called eggs or oocytes through oogenesis.
(ii) Production of hormones – oestrogens & progesterone which affect many of the female secondary sexual characters & reproductive functions.

Question 5. Describe the structure of a seminiferous tubule.

Sol. The seminiferous tubule is a structural unit located within the testis. These tubules are enclosed by a thick basal lamina and surrounded by 3-4 layers of smooth muscle cells (or myoid cells). The insides of the tubules are lined with seminiferous epithelium, which consists of two general types of cells: Sertoli or supporting cells & spermatogenic cells.

Sertoli cells, are elongated and pyramidal & partially envelop the spermatogenic cells. Sertoli cells have pale nuclei and dense nucleoli. These cells provide nourishment to the developing spermatogenic cells.
Spermatogenic cells are stacked in 4-8 layers. These cells divide several times & differentiate to produce spermatozoa.
Between seminiferous tubules lie the interstitial cells or Leydig cells which produces testosterone hormone.

The seminiferous tubules function to produce sperm, maintain sperm, and store the sperm. During the process of meiosis the Sertoli cells that line the seminiferous tubules undergo the process of differentiation to be converted into sperm.

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

Sol. Spermatogenesis is the process of producing sperms from primordial germ cells with half the number of chromosomes (haploid) as somatic cells. It takes place in seminiferous tubules

Process of spermatogenesis : Sperm production begins at puberty continues throughout life with several hundred million sperms being produced each day. Once sperm are formed they move into the epididymis, where they mature and are stored.
Spermatogenesis starts due to significant increase in the secretion of gonadotropin releasing hormone (GnRH) from hypothalamus.

During spermatogenesis one spermatogonium produces 4 sperms. Spermatogenesis completes through the following phases multiplicative phase, growth phase, maturation phase & spermiogenesis.

  1. In multiplicative phase, the sperm mother cells divide by mitosis & produce spermatogonia.
  2. The spermatogonia grow in size to form large primary spermatocytes by getting nourishment from sertoli cells in growth phase.
  3. Maturation phase involves meiosis I in which primary spermatocytes divide to produce secondary spermatocyte and meiosis II which produces spermatids. Thus, each primary spermatocyte gives rise to four haploid spermatids.
  4. Spermiogenesis or spermateliosis is process of formation of flagellated spermatozoa from spermatids. Spermiogenesis begins in the seminiferous tubules but usually completed in epididymis. During spermiogenesis, the acrosome forms, the flagellar apparatus forms, and most excess cytoplasm (the residual body) is separated and left in the Sertoli cell. Spermatozoa are released into the lumen of the seminiferous tubule. A small amount of excess cytoplasm (the cytoplasmic droplet) is shed later in the epididymis

Question 7. Name the hormones involved in regulation of spermatogenesis.

Sol. Hormones involved in the regulation of spermatogenesis are GnRH, LH, FSH and inhibin.
After sexual maturity, spermatogenesis starts due to the secretion of gonadotropin releasing hormone (GnRH) from the hypothalamus of brain. GnRH acts on pituitary gland and stimulates secretion of luteinising hormone (LH) and follicle stimulating hormone (FSH).

A negative feedback system occurs in the male with rising levels of testosterone acting on the hypothalamus and anterior pituitary to inhibit the release of GnRH, FSH, and LH.
The Sertoli cells produce the hormone inhibin, which is released into the blood when the sperm count is too high.

Question 8. Define spermiogenesis and spermiation.

Sol. Spermiogenesis is the process of transformation of spermatids into mature flagellated spermatozoa (sperms).
Spermiation is the process of release of mature spermatozoa from the sertoli cells. In this spermatozoa are shed into the lumen of seminiferous tubule for transport.

Question 9. Draw a labelled diagram of sperm.

Sol. Sperm are the only human cells that contain flagella. They are made up of three basic parts- head, middle piece and tail.

Question 10. What are the major components of seminal plasma?

Sol. Semen, also called seminal fluid (produced in male), is composed of sperms and seminal plasma. Seminal plasma is the fluid in which sperm is ejaculated. Major components of seminal plasma are secretions from seminal vesicles, prostrate and bulbourethral gland; sperms from testis and mucus. Seminal plasma is rich in fructose and contains enzymes, citric acid, hormones like prostaglandins, calcium and clotting proteins. It provides nourishment and protection to sperms.

Note: Seminal vesicles are major contributors to the production of semen.

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


The male accessory ducts are vasa efferentia, epididymis, vas deferens, and rete testis. Major functions of male accessory ducts are as follows:

  • aid in sperm transport.
  • It acts as a temporary storage of spermatozoa.

Male accessory glands in humans are the seminal vesicles, prostate gland, and the bulbourethral glands (also called Cowper’s glands). The major function of these glands is to secrete fluids that enter the urethra. Secretions of these glands constitute the seminal plasma which are rich in fructose, ascorbic acid, citrate, calcium, certain enzymes and prostaglandins. These secretions lubricates the reproductive system and nourish and activate the spermatozoa to swim.

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

Sol. The process of formation of a mature female gamete (ovum) is called oogenesis. It occurs in the ovaries of female reproductive system. It is a discontinuous process as it begins before birth, stops in mid process & only resumes after menarch.

Process of oogenesis : It occurs in three phases :

  1. Multiplicative phase: The initial phase of oogenesis starts during foetal stage. The primordial germinal cells divide repeatedly to form the oogonia. The oogonia are known to divide again several times mitotically to produce a large number of cells called the primary oocytes. After the formation of primary oocytes there is no more division. The cells enter into the growth phase.
  2. Growth phase: In the growth phase, the size of the primary oocyte increases enormously.
  3. Maturation phase: During this phase, diploid primary oocyte transformed into mature through meiosis.

Maturation phase produces two haploid cells – Larger one called secondary oocyte & the smaller one called polar bodies (1st polar body). Meiosis II of secondary oocyte results in the formation of functional egg or ovum and a second polar body. The first polar body may also divide to form two polar bodies of equal sizes which do not take part in reproduction & ultimately degenerates. First maturation division may be completed in the ovaries just prior to ovulation but second one (final) is completed outside the ovary after fertilisation. The egg is released at secondary oocyte stage under the effect of LH.


  • The growth phase of oogenesis is longer and more complicated than in sper­ matogenesis.
  • The primary oocyte completes its first meiotic division producing a secondary oocyte and the first polar body. The secondary oocyte enters meiosis II and is arrested at metaphase II.

Question 13. Draw a Labelled diagram of a section through ovary.

Sol. Ovary is an female reproductive organ that produces an ovum and female sex hormones (like oestrogen).

Question 14. Draw a labelled diagram of a Graafian follicle.

Sol. Graafian follicle is a mature fluid filled cavity in the ovary that ruptures during ovulation to release an egg (secondary oocyte).

Question 15. Name the functions of the following:
(a) Corpus luteum
(b) Endometrium
(c) Acrosome
(d) Sperm tail
(e) Fimbriae

Question 16. 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)


  • (a) False. Androgens or male sex hormones (e.g. testosterone) are secreted by Leydig cells found in the seminiferous tubule of the testis.
  • (b) True. Sertoli cells are the somatic cells of the testis that are essential for testis formation and spermatogenesis. Its main function is to nourish the developing sperm cells through the stages of spermatogenesis, hence, also been called the “mother” or “nurse” cell. Sertoli cells also act as phagocytes, consuming the residual cytoplasm during spermatogenesis.
  • (c) False. Leydig cells are found in testis.
  • (d) True. Leydig cells, also known as interstitial cells of Leydig produce testosterone (androgen) in the presence of luteinising hormone (LH).
  • (e) False. Oogenesis takes place in ovary and lead to formation ofa single egg cell or ovum.
  • (f) True. Menstrual cycle ceases during pregnancy because if the woman gets pregnant around the mid-cycle, the foetus’s placenta starts secreting Human Chorionic Gonadotropin (HCG). HCG causes the remnant of the ruptured follicle to start growing (and make the yellow body, corpus luteum) and start secreting progesterone for maintaining the pregnancy.
  • (g) True. Presence or absence of the hymen is not a reliable indicator of virginity or sexual experience because hymen is a very thin membrane which exists at the opening of the vagina and it can easily be broken due to following reasons: during the first coitus (intercourse), sudden fall or jolt, insertion of a vaginal tampon, active participation in some sports like horseback riding, cycling, etc.

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


Menstrual cycle is the cyclic change in the reproductive tract of primate female. This period is marked by a characteristic event repeated almost every month (28 days with minor variation) in the form of a menstrual flow (i.e. shedding of the endometrium of the uterus with bleeding). It may be temporarily stopped only in pregnancy.

The hormones that regulates menstrual cycles are:

  • FSH (Follicle stimulating hormone) and LH (Luteinising hormone) (secreted from anterior pitutary gland)
  • Oestrogen (secreted from ovary)
  • Progesterone (secreted from corpus luteum).

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

Sol. Vigorous contraction of the uterus at the end of pregnancy causes expulsion/delivery of the foetus. This process of delivery of the foetus is called parturition (child birth).

Parturition is induced by hormone oxytocin which acts on the uterine muscle and causes stronger uterine contractions.

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

Sol. All human beings contain 23 pairs of chromosomes in which 22 pair of chromosomes are autosomes and one pair of sex chromosome.

The sex chromosome pattern in the human females is XX and that of male is XY. Therefore, all the haploid female gametes (ova) have the sex chromosome X, however, the haploid male gametes have either X or Y. Thus 50% of sperms carry the X-chromosome while the other 50% carry the Y-chromosome. After fusion of the male and female gametes, the zygote carries either XX or XY depending upon whether the sperm carrying X or Y fertilizes the ovum. The zygote carrying XX would be a female baby and XY would be a male baby. That is why it is correct to say that the sex of the baby is determined by the father.

Question 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

Sol. One egg is released by human ovary in a month.

Identical twins : Identical twins are formed when a single fertilised egg splits into two genetically identical parts. The twins share the same DNA set, thus they may share many similar attributes. However, since physical appearance is influenced by environmental factors and not just genetics, identical twins can actually look very different.

Fraternal twins : These twins are formed when two fertilised eggs are formed. The twins share the different DNA set, thus they may share different attributes (dizygotic embryo).

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

Sol. Dogs and rodents are polyovulatory species. In these species, more than one ovum is released from the ovary at the time of ovulation. Hence, six eggs are released by the ovary of a female dog to produce six puppies.

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