NCERT Solution Class 12 Chapter 3 Human Reproduction -

NCERT Solution Class 12 Chapter 3 Human Reproduction

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 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 _____________

Answers :

(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 luteinizing hormone (LH). (h) The fusion of male and female gametes is called fertilisation. (i) Fertilisation takes place in the 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.

Ans : As Given in the NCERT book
3. Draw a labelled diagram of female reproductive system.

Ans : As Given in the NCERT book

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

Testis and ovary are the primary reproductive organs in males and females respectively. They play crucial roles in the production of gametes and the secretion of hormones necessary for the proper functioning of the reproductive system. The following are the two major functions of testis and ovary:

Functions of Testis:

Production of sperm: Testes are responsible for the production of male gametes or sperm. Sperm production occurs in the seminiferous tubules of the testes. The mature sperm is then transported to the epididymis where it is stored until ejaculation.
Secretion of testosterone: Testes are also responsible for the production of testosterone, the male sex hormone. Testosterone plays a significant role in the development of secondary sexual characteristics in males such as the growth of facial hair, deepening of the voice, and the development of muscles and bone mass.

Functions of Ovary:

Production of ova: The primary function of the ovary is to produce female gametes or ova. The ova develop within the ovarian follicles and are released during the menstrual cycle.
Secretion of estrogen and progesterone: The ovary secretes two essential hormones, estrogen and progesterone. These hormones regulate the menstrual cycle and are responsible for the development of secondary sexual characteristics in females, such as the growth of breasts and the widening of hips. They also play a significant role in the preparation of the uterus for pregnancy..

5. Describe the structure of a seminiferous tubule.

Seminiferous tubules are the coiled structures located within the testes where the process of spermatogenesis takes place. They are lined with two types of cells, namely Sertoli cells and spermatogenic cells. The spermatogenic cells are responsible for the production of sperm cells, while Sertoli cells provide support and nourishment to the developing sperm cells.

The seminiferous tubules are surrounded by a thin layer of smooth muscle cells known as myoid cells. The tubules are arranged in a network that is connected to the epididymis through a series of ducts. Blood vessels and lymphatic vessels also run through the tubules, providing nutrients and oxygen to the developing sperm cells.

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

Spermatogenesis is the process by which spermatogonia, the diploid germ cells in the seminiferous tubules of the testes, undergo meiosis to produce haploid sperm cells. It is the process of sperm cell development in the male reproductive system.

The process of spermatogenesis can be divided into three stages:

The mitotic stage: During this stage, spermatogonia undergo mitosis to produce two daughter cells, one of which is a stem cell that remains in the tubule, while the other is a primary spermatocyte that undergoes meiosis.
The meiotic stage: During this stage, the primary spermatocyte undergoes two rounds of meiosis to produce four haploid spermatids.
The spermiogenesis stage: During this stage, the spermatids undergo a series of changes that transform them into mature sperm cells or spermatozoa. The spermatids grow a tail and the head reduces in size and becomes compact, containing the genetic material. The midpiece develops with organelles called mitochondria that provide energy for movement.

Once the sperm cells are fully developed, they are released from the seminiferous tubules into the epididymis, where they are stored until ejaculation. The mature sperm cells consist of three parts, namely the head, midpiece, and tail. The head contains the genetic material, the midpiece contains mitochondria that provide energy for movement, and the tail is responsible for the movement of the sperm. During ejaculation, the sperm is propelled out of the epididymis and through the vas deferens to the urethra for ejaculation.

7. Name the hormones involved in regulation of spermatogenesis.

The regulation of spermatogenesis is controlled by a complex interplay of hormones. The two main hormones involved in the regulation of spermatogenesis are testosterone and follicle-stimulating hormone (FSH).

Testosterone is produced by the Leydig cells in the testes and is responsible for promoting the development and maintenance of the male reproductive system, including the production of sperm cells. It also helps to regulate the maturation and differentiation of sperm cells during spermatogenesis.

FSH is produced by the pituitary gland in the brain and acts on the Sertoli cells in the seminiferous tubules of the testes. FSH stimulates the Sertoli cells to produce and secrete factors that are required for the development and maturation of sperm cells during spermatogenesis.

The balance between testosterone and FSH is critical for the regulation of spermatogenesis. Low levels of testosterone can lead to a decrease in sperm production, while low levels of FSH can impair the maturation and differentiation of sperm cells. Imbalances in these hormones can result in male infertility or other reproductive disorders.

8. Define spermiogenesis and spermiation.

Spermiogenesis and spermiation are two important processes that occur during the final stages of sperm cell development in the male reproductive system.

Spermiogenesis is the process by which spermatids, which are the immature male sex cells produced during spermatogenesis, differentiate into fully mature and functional sperm cells, or spermatozoa. During spermiogenesis, the spermatids undergo a series of structural changes that involve the development of the acrosome, the formation of the tail, and the elimination of excess cytoplasm. Once the spermatids have undergone spermiogenesis, they are fully developed and capable of fertilizing an egg cell.

Spermiation, on the other hand, is the process by which the fully developed sperm cells are released from the Sertoli cells that support and nourish them within the seminiferous tubules of the testes. Spermiation occurs as a result of a complex interplay of hormonal and physical factors, which cause the Sertoli cells to release the mature sperm cells into the lumen of the tubules. Once the sperm cells have been released, they move through the epididymis and into the vas deferens, where they are stored until they are ejaculated during sexual intercourse.

9. Draw a labelled diagram of sperm.

Ans : Draw as given in the NCERT book
10. What are the major components of seminal plasma?

Seminal plasma is the fluid component of semen that is produced by the accessory glands of the male reproductive system. It contains a variety of substances that are essential for the survival, motility, and fertilizing ability of sperm cells. Some of the major components of seminal plasma include:

Fructose: This is a type of sugar that provides energy to sperm cells for their motility.
Prostaglandins: These are hormone-like substances that play a role in the contraction of the female reproductive tract and can help to facilitate the movement of sperm cells towards the egg.
Enzymes: Seminal plasma contains a variety of enzymes, such as acid phosphatase and fibrinolysin, which help to break down substances that might inhibit the movement of sperm cells.
Citric acid: This is a compound that helps to neutralize the acidic environment of the male urethra and female reproductive tract, creating a more favorable environment for sperm cells.
Zinc: This mineral is essential for the development and maturation of sperm cells and is found in high concentrations in seminal plasma.
Immunoglobulins: Seminal plasma contains antibodies that help to protect sperm cells from immune attack and other harmful substances.
Water: Seminal plasma is mostly made up of water, which provides a medium for the movement and transport of sperm cells.

The components of seminal plasma play a critical role in the function and survival of sperm cells, and their absence or disruption can lead to male infertility or other reproductive disorders.

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

The male accessory ducts and glands are a collection of structures in the male reproductive system that play important roles in the production, storage, and transport of sperm cells. The major functions of these structures can be summarized as follows:

Epididymis: This is a long, coiled tube that lies along the surface of each testis. Its main function is to store and mature sperm cells that have been produced in the testes. During their stay in the epididymis, sperm cells undergo a process of maturation that is necessary for their fertilizing ability.
Vas Deferens: This is a muscular tube that carries sperm cells from the epididymis to the ejaculatory duct. Its main function is to transport sperm cells towards the urethra during ejaculation.
Seminal Vesicles: These are paired glands that secrete a fluid component of semen known as seminal plasma. The seminal plasma contains a variety of substances, such as fructose, prostaglandins, and enzymes, that are essential for the survival, motility, and fertilizing ability of sperm cells.
Prostate Gland: This is a gland located at the base of the bladder that secretes a milky fluid that makes up a significant portion of the seminal plasma. The prostatic fluid contains enzymes, citric acid, and zinc, among other substances, that help to protect and nourish sperm cells during ejaculation.
Bulbourethral Glands: These are small glands located near the base of the penis that secrete a clear, viscous fluid that is released during sexual arousal. The fluid helps to lubricate the urethra and prepare it for the passage of sperm cells during ejaculation.

The male accessory ducts and glands play critical roles in the production, storage, and transport of sperm cells, as well as in the composition and function of semen. Dysfunction or disease of these structures can lead to male infertility, sexual dysfunction, and other reproductive disorders.

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

Oogenesis is the process of formation and development of female gametes or egg cells in the ovaries of a female. The process begins during embryonic development and continues throughout the reproductive life of a female.

The primary oocyte, which is the precursor to the mature egg cell, is formed during fetal development. The primary oocytes remain arrested in the first stage of meiosis until puberty, when they begin to mature and are released in a cyclical manner during the menstrual cycle.

During oogenesis, the primary oocyte undergoes two meiotic divisions to form a single haploid egg cell and two polar bodies. The first meiotic division occurs during follicular development, when the primary oocyte is stimulated by follicle-stimulating hormone (FSH) and begins to divide. However, the process is arrested at metaphase I until ovulation.

At ovulation, the secondary oocyte is released from the ovary and is taken up by the fimbriae of the fallopian tube. If the egg is fertilized by a sperm, the secondary oocyte undergoes the second meiotic division, producing a haploid egg cell and a second polar body. The egg cell then fuses with the sperm to form a diploid zygote.

If fertilization does not occur, the egg cell and the polar body are eventually shed during menstruation. The remaining primary oocytes in the ovary undergo a gradual decline in number and quality as a female ages, leading to menopause.

Oogenesis is the process of formation and development of female gametes, or egg cells, which occurs in the ovaries of females. It involves two meiotic divisions that produce a haploid egg cell and two polar bodies, with the mature egg cell being released during ovulation for potential fertilization.

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

Ans : Draw as given in the NCERT book
14. Draw a labelled diagram of a Graafian follicle?

Ans : Draw as given in the NCERT book
15. Name the functions of the following:
(a) Corpus luteum (b) Endometrium
(c) Acrosome (d) Sperm tail
(e) Fimbriae

Answer :

(a) Corpus luteum: The main function of the corpus luteum is to produce progesterone, which helps to maintain the thickened endometrium and prepare the uterus for implantation of a fertilized egg. If fertilization does not occur, the corpus luteum degenerates and stops producing progesterone, leading to the shedding of the endometrium and the start of a new menstrual cycle.

(b) Endometrium: The endometrium is the inner lining of the uterus, which thickens and prepares for implantation of a fertilized egg. If fertilization does not occur, the endometrium is shed during menstruation.

(c) Acrosome: The acrosome is a structure on the head of a sperm cell that contains enzymes needed to penetrate and fertilize an egg. The enzymes in the acrosome help to break down the outer layers of the egg so that the sperm can enter and fuse with the egg.

(d) Sperm tail: The tail of a sperm cell, also known as the flagellum, is responsible for propelling the sperm forward towards the egg. It is made up of a series of microtubules and is powered by a complex system of molecular motors.

(e) Fimbriae: The fimbriae are finger-like projections at the end of the fallopian tubes that help to capture the egg released from the ovary during ovulation. The fimbriae create a gentle current that draws the egg into the fallopian tube, where it may be fertilized by sperm.

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)

Answers :

(a) False. Androgens are produced by Leydig cells. (b) False. Spermatozoa do not get nutrition from Sertoli cells. They obtain nutrition from fructose present in seminal plasma. (c) False. Leydig cells are found in the testes. (d) True. (e) False. Oogenesis takes place in the ovary but not in the corpus luteum. (f) True. (g) True. The presence or absence of hymen is not a reliable indicator of virginity or sexual experience.

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

The menstrual cycle refers to the monthly physiological process that occurs in females of reproductive age, where the lining of the uterus is shed in the form of menstrual bleeding. The menstrual cycle is regulated by several hormones that work together in a complex system.

The primary hormones that regulate the menstrual cycle are estrogen and progesterone, which are produced by the ovaries. These hormones are responsible for stimulating the growth and development of the uterine lining in preparation for pregnancy.

The menstrual cycle is controlled by a complex interplay of hormones that are produced by the hypothalamus, pituitary gland, and ovaries. The hypothalamus produces gonadotropin-releasing hormone (GnRH), which stimulates the pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

FSH stimulates the development of follicles in the ovaries, which contain the eggs that will be released during ovulation. LH triggers the release of the mature egg from the ovary, which then travels down the fallopian tube and towards the uterus.

If the egg is fertilized by sperm, it will implant in the uterus and the menstrual cycle will stop. If fertilization does not occur, the levels of estrogen and progesterone will decrease, causing the shedding of the uterine lining and the start of a new menstrual cycle.

The menstrual cycle is a complex process that is regulated by several hormones, including estrogen, progesterone, FSH, and LH. These hormones work together to prepare the uterus for pregnancy and trigger the release of an egg from the ovaries.

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

Parturition refers to the process of giving birth in mammals. It involves a series of physiological changes that prepare the mother’s body for delivery and culminate in the expulsion of the fetus from the uterus.

Several hormones play a critical role in the induction of parturition. The two primary hormones involved are oxytocin and prostaglandins.

Oxytocin is a hormone that is produced by the hypothalamus and released by the posterior pituitary gland. It plays a crucial role in uterine contractions during labor and delivery. Oxytocin stimulates the smooth muscle of the uterus, causing it to contract and push the fetus out of the birth canal.

Prostaglandins are a family of hormones that are involved in many physiological processes, including inflammation and smooth muscle contraction. In the context of parturition, prostaglandins help to soften and dilate the cervix, making it easier for the fetus to pass through the birth canal. Prostaglandins are also involved in stimulating uterine contractions, which further facilitate the delivery process.

The levels of these hormones increase towards the end of pregnancy, with oxytocin levels increasing significantly during labor. Additionally, prostaglandin levels increase as the cervix begins to ripen and prepare for delivery.

In conclusion, parturition is the process of giving birth in mammals. Oxytocin and prostaglandins are the two primary hormones involved in inducing parturition, with oxytocin stimulating uterine contractions and prostaglandins softening and dilating the cervix.

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

Blaming women for giving birth to daughters is not only incorrect but also unfair and discriminatory. This belief is rooted in patriarchal attitudes that prioritize male children and perpetuate gender inequality. However, it is important to understand that the sex of a child is determined by the father’s sperm and not by the mother.

The sex of a child is determined by whether the sperm that fertilizes the mother’s egg carries an X or Y chromosome. If the sperm carries an X chromosome, the child will be female, while a Y chromosome will result in a male child. Therefore, it is the father’s genetic contribution that determines the sex of the child, not the mother’s.

Furthermore, the notion of valuing male children over female children is not only unjust but also outdated. It is important to recognize and appreciate the inherent value of all individuals, regardless of their gender. Gender discrimination can have severe consequences, including the neglect and mistreatment of female children, leading to a number of social and health issues.

In conclusion, blaming women for giving birth to daughters is unfounded and discriminatory. The sex of a child is determined by the father’s sperm, and gender discrimination is harmful and unjust. It is essential to value all individuals equally, regardless of their gender, and work towards creating a more equitable and inclusive society.

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?

A human ovary typically releases only one egg per menstrual cycle, which occurs approximately every 28 days. This egg travels through the fallopian tube towards the uterus, where it may be fertilized by sperm.

If a mother gives birth to identical twins, it means that a single fertilized egg divided into two separate embryos during early development. In this case, only one egg would have been released from the ovary, which was fertilized by a single sperm. However, the resulting embryos split into two, resulting in two genetically identical individuals.

On the other hand, if the twins born were fraternal, it means that the mother released two eggs during ovulation, and both were fertilized by two different sperm. This would result in two genetically distinct individuals who are siblings.

Therefore, the number of eggs released by the ovary depends on whether the twins are identical or fraternal. In the case of identical twins, only one egg would have been released, while in the case of fraternal twins, two eggs would have been released.

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

In female dogs, the number of eggs released during ovulation can vary depending on the breed, age, and other factors. However, in general, dogs release multiple eggs during a single ovulation cycle, which can result in the birth of multiple puppies.

It is not always the case that each egg released during ovulation will result in the birth of a puppy, as some eggs may not be fertilized or may not develop properly. However, in general, the number of puppies born can provide an estimate of the number of eggs that were released during ovulation.

Assuming that all six puppies were from the same litter, it is likely that the female dog released at least six eggs during ovulation. However, it is possible that she released more than six eggs, and some of them did not develop into viable embryos.

It is important to note that the exact number of eggs released by a female dog during ovulation cannot be determined with certainty, as it is difficult to observe and track the entire process. However, the number of puppies born can provide an estimate of the number of eggs that were released during ovulation.