NCERT Solutions for Class 12 Biology Chapter 3
Human Reproduction Class 12
Chapter 3 Human Reproduction Exercise Solutions
Exercise : Solutions of Questions on Page Number : 55
Q1 :
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 the ovum from a mature follicle is called .
(g) Ovulation is induced by a hormone called the .
(h) The fusion of the male and the female gametes is called .
(i) Fertilization takes place in the .
(j) The zygote divides to form , which is implanted in uterus.
(k) The structure which provides vascular connection between the fetus and uterus is called .
Answer :
(a) Humans reproduce .
(b) Humans are .
(c) Fertilization is in humans.
(d) Male and female gametes are .
(e) Zygote is .
(f) The process of release of the ovum from a mature follicle is called .
(g) Ovulation is induced by a hormone called the .
(h) The fusion of the male and the female gametes is called .
(i) Fertilization takes place in the .
(j) The zygote divides to form , which is implanted in uterus.
(k)
Q2 :
Draw a labeled diagram of male reproductive system.
Q3 :
Draw a labeled diagram of female reproductive system.
Q4 :
Write two major functions each of testis and ovary.
Answer :
Functions of the Testis:
(a) They produce male gametes called spermatozoa by the process of spermatogenesis.
(b) The leydig cells of the seminiferous tubules secrete the male sex hormone called testosterone. Testosterone aids the development of secondary sex characteristics in males.
Functions of the ovary:
(a) They produce female gametes called ova by the process of oogenesis.
(b)
Q5 :
Describe the structure of a seminiferous tubule.
Answer :
Q6 :
What is spermatogenesis? Briefly describe the process of spermatogenesis.
Answer :
Spermatogenesis is the process of the production of sperms from the immature germ cells in males. It takes place in seminiferous tubules present inside the testes. During spermatogenesis, a diploid spermatogonium (male germ cell)
Q7 :
Name the hormones involved in regulation of spermatogenesis.
Answer :
Q8 :
Define spermiogenesis and spermiation.
Answer :
Spermiogenesis: It is the process of transforming spermatids into matured spermatozoa or sperms.
Q9 :
Draw a labeled diagram of sperm.
Q10 :
What are the major components of seminal plasma?
Answer :
Q11 :
What are the major functions of male accessory ducts and glands?
Answer :
The male accessory ducts are vasa efferentia, epididymis, vas deferens, and rete testis. They play an important role in the transport and temporary storage of sperms. On the contrary, male accessory glands are seminal vesicles, prostate glands, and bulbourethral glands. These glands secrete fluids that lubricate the reproductive system and
Q12 :
What is oogenesis? Give a brief account of oogenesis.
Answer :
Q13 :
Draw a labeled diagram of a section through ovary.
Answer :
Q14 :
Draw a labeled diagram of a Graafian Follicle?
Q15 :
Name the functions of the following.
(a) Corpus luteum
(b) Endometrium
(c) Acrosome
(d) Sperm tail
(e) Fimbriae
Answer :
(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)
Q16 :
Name the functions of the following.
(a) Corpus luteum
(b) Endometrium
(c) Acrosome
(d) Sperm tail
(e) Fimbriae
Answer :
(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)
Q17 :
What is menstrual cycle? Which hormones regulate menstrual cycle?
Answer :
The menstrual cycle is a series of cyclic physiologic changes that take place inside the female reproductive tract in primates. The whole cycle takes around 28 days to complete. The end of the cycle is accompanied by the breakdown of uterine endothelium, which gets released in the form of blood and mucous through the vagina. This is known as menses.
Q18 :
What is parturition? Which hormones are involved in induction of parturition?
Answer :
Q19 :
In our society the women are often blamed for giving birth to daughters. Can you explain why this is not correct?
Answer :
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.
Q20 :
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?
Answer :
An ovary releases an egg every month. When two babies are produced in succession, they are called twins. Generally, twins are produced from a single egg by the separation of early blastomeres resulting from the first zygotic cleavage. As a result, the young ones formed will have the same genetic make- up and are thus, called identical twins.
Q21 :
How many eggs do you think were released by the ovary of a female dog which gave birth to 6 puppies?
Answer :
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.