Human Reproduction ncert solutions: Class 12th biology chapter 2 ncert solutions
Textbook | NCERT |
Class | Class 12 |
Subject | Biology |
Chapter | Chapter 2 |
Chapter Name | Human Reproduction class 12 ncert solutions |
Category | Ncert Solutions |
Medium | English |
Are you looking for Ncert Solutions for Class 12 Biology Chapter 2 Human Reproduction? Now you can download Ncert class 12 biology chapter 2 questions and answers pdf from here.
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 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 a ……..which is implanted in the uterus.
- (k) The structure which provides a vascular connection between the foetus and uterus is called the ………
Solution 1:
- (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 luteinising hormone (LH).
- (h) The fusion of male and female gametes is called fertilisation.
- (i) Fertilisation takes place in the ampullary-isthmic junction (fallopian tube).
- (j) Zygote divides to form a blastocyst, which is implanted in the uterus.
- (k) The structure which provides a vascular connection between the foetus and the uterus is called the placenta.
Question 2: Draw a labelled diagram of male reproductive system.
Solution 2: The diagram of the male reproductive system is as follows:
Question 3: Draw a labelled diagram of female reproductive system.
Solution 3: The diagram of the female reproductive system is as follows:
Question 4: Write two major functions each of testis and ovary.
Solution 4: The testis and ovary are primary reproductive organs in males and females, respectively. Each has distinct functions essential for reproduction.
Functions of the Testis:
1. Sperm Production (Spermatogenesis): The primary function of the testis is to produce sperm cells through a process called spermatogenesis. This occurs in the seminiferous tubules of the testis and is crucial for male fertility, as sperm are the male gametes that fertilize the female egg.
2. Hormone Production (Testosterone): The testis produces the hormone testosterone, which is essential for the development of male secondary sexual characteristics (such as facial hair, deep voice, and muscle mass), maintenance of the male reproductive system, and regulation of libido (sex drive). This occurs in the Leydig cells of the testis.
Functions of the Ovary:
1. Egg Production (Oogenesis): The ovary is responsible for the production of eggs (ova) through a process called oogenesis. Eggs are the female gametes and are released during ovulation, which is essential for reproduction when they are fertilized by sperm.
2. Hormone Production (Estrogen and Progesterone): The ovary produces the hormones estrogen and progesterone, which regulate the menstrual cycle, support pregnancy, and contribute to the development of female secondary sexual characteristics (such as breast development, fat distribution, and regulation of the menstrual cycle). Estrogen is mainly produced by follicular cells, while progesterone is produced by the corpus luteum after ovulation.
Both organs play vital roles in the reproductive system and in maintaining overall hormonal balance.
Question 5: Describe the structure of a seminiferous tubule.
Solution 5: The production of sperms in the testes takes place in a highly coiled structure called the seminiferous tubules. These tubules are located in the testicular lobules. Each seminiferous tubule is lined by germinal epithelium. It is lined on its inner side by two types of cells namely spermatogonia and sertoli cells respectively. Spermatogonia are male germ cells which produce primary spermatocytes by meiotic divisions.
Primary spermatocytes undergo further meiotic division to form secondary spermatocytes and finally, spermatids. Spermatids later metamorphoses into male gametes called spermatozoa. Sertoli cells are known as nurse cells of the testes as they provide nourishment to the germ cells. There are large polygonal cells known as interstitial cells or leydig cells just adjacent to seminiferous tubules. These cells secrete the male hormone called testosterone.
Question 6: What is spermatogenesis? Briefly describe the process of spermatogenesis.
Solution 6: Spermatogenesis is the process by which sperm cells (spermatozoa) are produced in the testes. It occurs in the seminiferous tubules and is essential for male fertility. This complex process involves the formation of mature, haploid sperm cells from diploid stem cells called spermatogonia. Spermatogenesis begins at puberty and continues throughout a male’s life.
Stages of Spermatogenesis:
Sperm production begins at puberty continues throughout life with several hundred million sperms be ing produced each day. Once sperm are formed they move into the epididymis, where they mature and are stored. During spermatogenesis one spermatogonium produces 4 sperms. Spermatogenesis completes through the following phases – multiplicative phase, growth phase, maturation phase & spermiogenesis. In multiplicative phase the sperm mother cells divide by mitosis & produce spermatogonia. The spermatogonia grow in size to form large primary spermatocytes by getting nourishment from sertoli cells in growth phase. 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. Spermiogenesis or spermateliosis is process of formation of flagellated spermatozoa from spermatids. Spermiogenesis begins in the seminiferous tubules but usually completed in epididymis.
Summary of Key Stages:
- Spermatogonia (2n) undergo mitosis → Primary spermatocytes (2n).
- Primary spermatocytes (2n) undergo Meiosis I → Secondary spermatocytes (n).
- Secondary spermatocytes (n) undergo Meiosis II → Spermatids (n).
- Spermatids undergo spermiogenesis → Spermatozoa (n) (mature sperm cells).
This entire process takes approximately 64-72 days and ensures continuous sperm production in males after puberty.
Question 7: Name the hormones involved in regulation of spermatogenesis.
Solution 7: The hormones involved in the regulation of spermatogenesis are:
Gonadotropin-Releasing Hormone (GnRH): Produced by the hypothalamus, GnRH stimulates the anterior pituitary gland to release LH and FSH, which are crucial for spermatogenesis.
Follicle-Stimulating Hormone (FSH): Secreted by the anterior pituitary, FSH stimulates the Sertoli cells in the seminiferous tubules to support the development and maturation of sperm cells.
Luteinizing Hormone (LH): Also produced by the anterior pituitary, LH stimulates the Leydig cells in the testes to produce testosterone, which is essential for maintaining spermatogenesis.
Testosterone: Produced by the Leydig cells, testosterone is the key hormone driving the maturation of sperm cells and the overall process of spermatogenesis.
Inhibin: Produced by Sertoli cells, inhibin provides negative feedback to the pituitary gland, inhibiting the secretion of FSH to regulate spermatogenesis.
Question 8: Define spermiogenesis and spermiation.
Solution 8:
Spermiogenesis: Spermiogenesis is the final stage of spermatogenesis, during which immature spermatids transform into mature, motile spermatozoa (sperm cells).
Spermiation: Spermiation is the process by which mature spermatozoa are released from the Sertoli cells into the lumen of the seminiferous tubules. This is the final step before sperm are transported to the epididymis for further maturation and storage.
Question 9: Draw a labelled diagram of sperm.
Solution 9: The diagram of sperm is as below:
Question 10: What are the major components of seminal plasma?
Solution 10: Semen (produced in males) is composed of sperms and seminal plasma. The major components of the seminal plasma in the male reproductive system are mucus, spermatozoa, and various secretions of accessory glands. The seminal plasma is rich in fructose, calcium, ascorbic acid, and certain enzymes. It provides nourishment and protection to sperms.
Question 11: What are the major functions of male accessory ducts and glands?
Solution 11: The male accessory ducts and glands play essential roles in the production, maturation, storage, and transport of sperm, as well as in the formation of semen. Their major functions include:
Male Accessory Ducts:
1. Epididymis: Stores and facilitates the maturation of sperm. Sperm gain motility and the ability to fertilize an egg while in the epididymis.
2. Vas Deferens: Transports mature sperm from the epididymis to the ejaculatory duct during ejaculation. It also serves as a temporary storage site for sperm.
3. Ejaculatory Duct: Conducts sperm and seminal fluid (from the seminal vesicles) into the urethra during ejaculation.
4. Urethra: Serves as a common passage for semen and urine. It transports semen from the reproductive system to the outside during ejaculation.
Male Accessory Glands:
1. Seminal Vesicles: Produce a significant portion of seminal fluid, rich in fructose, which provides energy for sperm motility, and prostaglandins, which enhance sperm motility and facilitate sperm transport within the female reproductive tract.
2. Prostate Gland: Secretes a milky, alkaline fluid that constitutes part of the semen. This fluid helps neutralize the acidic environment of the vagina, ensuring sperm survival, and contains enzymes that liquefy semen after ejaculation, aiding sperm motility.
3. Bulbourethral Glands (Cowper’s Glands): Produce a lubricating mucus that cleanses and neutralizes the urethra before ejaculation, ensuring a smooth passage for sperm, and provides lubrication for sexual intercourse.
Question 12: What is oogenesis? Give a brief account of oogenesis.
Solution 12: Oogenesis is the process of the formation of a mature ovum from the oogonia in females. It takes place in the ovaries. During oogenesis, a diploid oogonium or egg mother cell increases in size and gets transformed into a diploid primary oocyte. This diploid primary oocyte undergoes first meiotic division i.e., meiosis I or reductional division to form two unequal haploid cells.
The smaller cell is known as the first polar body, while the larger cell is known as the secondary oocyte. This secondary oocyte undergoes second meiotic division i.e., meiosis II or equational division and gives rise to a second polar body and an ovum. Hence, in the process of oogenesis, a diploid oogonium produces a single haploid ovum while two or three polar bodies are produced.
Question 13: Draw a labelled diagram of a section through ovary.
Solution 13: The diagram of a section of an ovary is as follows:
Question 14: Draw a labelled diagram of a Graafian follicle?
Solution 14: The diagram of a Graafian follicle is as follows:
Question 15: Name the functions of the following:
(a) Corpus luteum (b) Endometrium
(c) Acrosome (d) Sperm tail
(e) Fimbriae
Solution 15: (a) Corpus luteum − Corpus luteum is formed from the ruptured Grafiaan follicle. It secretes progesterone hormone during the luteal phase of the menstrual cycle. A high level of progesterone inhibits the secretions of FSH and LH, thereby preventing ovulation. It also allows the endometrium of the uterus to proliferate and to prepare itself for implantation.
(b) Endometrium − It is the innermost lining of the uterus. It is rich in glands and undergoes cyclic changes during various phases of the menstrual cycle to prepare itself for the implantation of the embryo.
(c) Acrosome − It is a cap-like structure present in the anterior part of the head of the sperm. It contains hyaluronidase enzyme, which hydrolyses the outer membrane of the egg, thereby helping the sperm to penetrate the egg at the time of fertilization.
(d) Sperm tail − It is the longest region of the sperm that facilitates the movement of the sperm inside the female reproductive tract.
(e) Fimbriae − They are finger-like projections at the ovarian end of the fallopian tube. They help in the collection of the ovum (after ovulation), which is facilitated by the beating of the cilia.
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)
Solution 16:
(a) Androgens are produced by Sertoli cells. ( False )
Correction: Androgens are produced by Leydig cells, not Sertoli cells. Sertoli cells support sperm development but do not produce androgens.
(b) Spermatozoa get nutrition from Sertoli cells. ( True )
Sertoli cells provide essential nutrients and support to developing spermatozoa throughout spermatogenesis.
(c) Leydig cells are found in ovary. ( False )
Correction: Leydig cells are found in the testes, not the ovary. They are responsible for producing testosterone.
(d) Leydig cells synthesize androgens. ( True )
Leydig cells synthesize and secrete androgens, primarily testosterone, which is essential for male reproductive functions.
(e) Oogenesis takes place in corpus luteum. ( False )
Correction: Oogenesis takes place in the ovary, specifically in the ovarian follicles. The corpus luteum is involved in hormone production after ovulation.
(f) Menstrual cycle ceases during pregnancy. ( True )
During pregnancy, hormonal changes prevent the menstrual cycle from occurring.
(g) Presence or absence of hymen is not a reliable indicator of virginity or sexual experience. ( True )
The presence or absence of the hymen is not a reliable indicator of virginity or sexual experience, as it can vary significantly among individuals due to various factors.
Question 17: What is menstrual cycle? Which hormones regulate menstrual cycle?
Solution 17: The menstrual cycle is a monthly process that prepares a woman’s body for potential pregnancy. It typically lasts about 28 days, although it can vary from 21 to 35 days. The cycle includes several phases: the Menstrual Phase (Days 1-5)(shedding of the uterine lining), the Follicular Phase (Days 1-13) (development of ovarian follicles), Ovulation (Day 14) (release of an egg), and the Luteal Phase (preparation of the uterus for potential implantation).
Key hormones regulating the menstrual cycle include:
- Gonadotropin-Releasing Hormone (GnRH): Released by the hypothalamus, GnRH stimulates the anterior pituitary to produce FSH and LH.
- Follicle-Stimulating Hormone (FSH): Produced by the anterior pituitary, FSH promotes the growth and maturation of ovarian follicles and stimulates the production of estrogen.
- Luteinizing Hormone (LH): Triggers ovulation and the development of the corpus luteum.
- Estrogen: Promotes the growth of the uterine lining and regulates the menstrual cycle.
- Progesterone: Prepares the uterus for implantation of a fertilized egg and maintains the uterine lining during pregnancy.
Question 18: What is parturition? Which hormones are involved in induction of parturition?
Solution 18: Parturition is the process of giving birth to a baby as the development of the foetus gets completed in the mother’s womb. The hormones involved in this process are oxytocin and relaxin. Oxytocin leads to the contraction of smooth muscles of myometrium of the uterus, which directs the full term foetus towards the birth canal. On the other hand, relaxin hormone causes relaxation of the pelvic ligaments and prepares the uterus for child birth.
Question 19: In our society the women are often blamed for giving birth to daughters. Can you explain why this is not correct?
Solution 19: All human beings have 23 pairs of chromosomes. Human males have 22 pairs of autosomes and contain one or two types of sex chromosome. They are either X or Y. On the contrary, human females have 22 pairs of autosomes and contain only the X sex chromosome. The sex of an individual is determined by the type of the male gamete (X or Y), which fuses with the X chromosome of the female. If the fertilizing sperm is X,then the baby will be a girl and if it is Y, then the baby will be a boy. Hence, it is incorrect to blame a woman for the gender of the child.
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?
Solution 20: Typically in a month, human ovaries release only one egg, rarely two.
In the case of identical twins or monozygotic twins, one egg is released by the ovary, which splits into two post-fertilisation. This is why identical twins exhibit the same genetic features. On the other hand, in fraternal twins or dizygotic twins, two eggs are released, which are fertilised by two different sperms causing the fraternal twins to exhibit different genetic characteristics.
Question 21: How many eggs do you think were released by the ovary of a female dog which gave birth to 6 puppies?
Solution 21: 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 were released by the ovary of a female dog to produce six puppies.