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Human Reproduction NCERT notes for Class 12

Human Reproduction - Exercise solutions

1. Fill in the blanks:
(a)Humans reproduce————— (asexually/sexually).
(b)Humans are————— (oviparous, viviparous,ovoviviparous).
(c)Fertilization 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 called————— .
(g)Ovulation is induced by a hormone called—————
(h)The fusion of male and female gametes is called————— .
(i)Fertilization 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————— .
Ans: (a) sexually
(b) viviparous
(c) internal
(d)haploid
(e)diploid
(f)ovulation
(g)LH (Luteinizing hormone)
(h)fertilization
(i)ampullary-isthmic junction (fallopian tube)
(j)blastocyst
(k)placenta (Umbilical cord)

2. Draw a labelled diagram of male reproductive system.

ans- Refer NCERT book

3. Draw a labelled diagram of female reproductive system.

Ans- Refer NCERT book

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

Ans-  Two major functions of Testis are as follows:

  • The process of spermatogenesis produces sperms through the seminiferous tubules
  • Testosterone, the male sex hormone is secreted by the Leydig cell.

Two major functions of ovary are as follows:

  • In the process of oogenesis, ovaries produces ova
  • Progesterone and oestrogen, the female sex hormones are secreted

5. Describe the structure of a seminiferous tubule.

Ans- The seminiferous tubules are situated in testicular lobules. Seminiferous tubule consists of two types of cells – Sertoli or supporting cells & spermatogenic cellsl Sertoli cells, are elongated and pyramidal & partially envelop the spermatogenic cells. The 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.

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

Ans- The process of formation of male gametes (sperms) is called spermatogenesis.

The process occurs in the seminiferous tubules located inside the testes. In this process, a diploid male germ cell or spermatogonium enlarges (in size) for the formation of a diploid primary spermatocyte which inturn goes through the first meiotic division or meiosis I. This division is a reductional division for the formation of two equal haploid secondary spermatocytes, each of which further undergoes second meiotic division or meiosis II for the formation of two equal haploid spermatids.

After that, four haploid spermatids are formed from a diploid spermatogonium. The spermatids hence produced alter to form spermatozoa(sperm) through the process of spermiogenesis.

7. Name the hormones involved in regulation of spermatogenesis.

Ans- 

Lutenising hormone (LH) – serves as Leydig cells triggering synthesis & secretion of androgens

  • Gonadotrophin-releasing hormone (GnRH) – it is a hypothalamic hormone that is secreted at the age of puberty, acting at the anterior pituitary gland and stimulating the secretion of LH & FSH
  • Follicle stimulating hormone (FSH) – acts on sertoli cells, stimulating the secretion of factors which aid in spermiogenesis process
  • Androgens – triggers inhibin production regulating the spermatogenesis process
  • Inhibin

8. Define spermiogenesis and spermiation.
Ans: Spermiogenesis is the process of transformation of spermatids into mature flagellated spermatozoa (sperms).Spermiation is the process of release of mature spermatozoa. In this spermatozoa are shed into the lumen of seminiferous tubule for transport.

9. Draw a labelled diagram of sperm.

Ans- Refer NCERT book.

10.What are the major components of seminal plasma?

Ans-

The major components of seminal plasma are:

  • Secretions of the accessory sex glands of males – prostate gland, seminal vesicles, bulbourethral glands.
  • Mainly composed of – calcium, fructose, and other enzymes.

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

Ans- Male accessory ducts include rete testis, vasa efferentia, epididymis and vas deferens. These ducts store and transport sperms from the testis to the outside through urethra. The male accessory glands include paired seminal vesicles, a prostate and paired bulbourethral glands. Secretions of these glands constitute the seminal plasma which is rich in fructose, calcium and certain enzymes. The secretions of bulbourethral glands also helps in the lubrication of the penis.

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

Ans- The process of formation of haploid female gametes (ova) from diploid oogonia in the ovary.

The process of Oogenesis takes place in three phases:

Multiplicative phase –

  • Follicle cells are differentiated from the germinal epithelium of the ovary due to repeated mitosis division. Few follicle cells enlarge and are termed as egg mother cells and undergo mitosis to multiply which are referred to as oogonia.
  • Growth phase – one of the oogonium of the egg nest differentiates while the rest change into surrounding nutritive follicular epithelium. There is an increase in the size of the differentiated isolated oogonium as it gets nourished from the girdling follicle cells thereby transforming into a diploid primary oocyte.
  • Maturation phase – The diploid primary oocyte in this phase passes through two maturation divisions. Meiosis I – the first meiotic division splits the diploid primary oocyte into two haploid cells wherein the larger one is the secondary oocyte and the minor one is the polar body (polocyte). In meiosis II or the second meiotic division, the secondary oocyte splits to form one large ootid and a tiny second polar body. Furthermore, the first polar body splits through mitosis to form two polar bodies. The ootid matures into a functional haploid ovum. Therefore, one primary oocyte produces one large ovum and three polar bodies which inturn degenerate. They degenerate as they do no participate in reproduction, thus leaving behind one functional ovum.

13. Draw a labelled diagram of a section through ovary.

Ans- Refer NCERT book

14. Draw a labelled diagram of a Graafian follicle.

Ans- refer NCERT book

15. Name the functions of the following:
(a) Corpus luteum
(b) Endometrium

(c) Acrosome
(d) Sperm tail

(e) Fimbriae
Ans: (a) Corpus luteum : The corpus luteum secretes large amounts of progesterone which is essential for maintenance of the endometriuip.
(b) Endometrium is necessary for implantation of the fertilized ovum and other events of pregnancy.
(c) The acrosome is filled with enzymes that help during fertilization of the ovum.
(d) Sperm tail: Tail facilitates sperm motility which is essential for fertilization.
(e) Fimbriae: Fimbriae help in collection of the ovum after ovulation.

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 synthesize androgens. (True/ False)
(e) Oogenesis takes place in corpus luteum. (True/False)
(i) 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)
Ans: (a) False, Androgens or male sex hormones (e.g, testosterone) are secreted by Leydig cells.
(b) True.
(c) False, Leydig cells are found in testis.
(d) True.
(e) False, Oogenesis takes place in ovary.
(f) True.
(g) True.

17. What is menstrual cycle? Which hormones regulate menstrual cycle?
Ans: Menstrual cycle is the cyclic change( itf’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
(i) FSH (Follicle stimulating hormone),
(ii) LH (Luteinizing hormone),
(iii) Oestrogens,
(iv) Progesterone

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

Ans-

Parturution is the process wherein a fully developed foetus, from the mother’s womb, is expelled out after the completion of the gestation period.

There are two critical hormones that are involved in the induction of parturition, they are:

  • Oxytocin – It directs the full-term foetus towards the birth canal, as it causes the contraction of the smooth muscles of the myometrium of the uterus, leading the baby to be expelled out
  • Relaxin – It relaxes the pelvic ligaments, widening the pelvis to assist in an easier childbirth

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

Ans- 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.  So 50% of sperms are x- chromosomes and the other 50% are y-chromosomes .

Hence, if the sperm carrying ‘X’ fertilizes the ovum (zygote XX), then it would develop into a female baby and if the sperm carrying ‘Y’ fertilizes the ovum (zygote XY), then it would develop into a male baby. Both of these cases are attributed to the sperm that carries the chromosome fertilizing the ovum. Hence, we say that the sex of the child is determined by the father and not the mother. This is why it is incorrect to blame women for the gender of the child.

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?

Ans- Only one egg is released by female human in a month.

 Identical twins are formed when a single fertilized 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.

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

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

Ans- Since dogs have multiple births, several eggs mature and are released at the same time. If fertilised, the egg will implant on the uterine wall. Dogs bear their litters roughly 9 weeks after fertilisation, although the length of gestation can vary from 56 to 72 days. An average litter consists of about six puppies, though this number may vary widely based on the breed of dog. On this basis 6 eggs were released by the ovary of a female dog which gave birth to 6 puppies.

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