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NCERT Solutions for Class 12 Biology

NCERT Solutions for Class 12 Biology -You will find intriguing problems from various themes in NCERT solutions for class 12 biology chapter 3 human reproduction, for which you must study the general principles of reproductive processes in living creatures and their explanation in full with related and relevant instances. NCERT solutions for biology chapter 3 human reproduction in class 12 will also assist you in comprehending the concepts and themes. If you need answers for any other class from 6 to 12, NCERT solutions are the most convenient way to receive all of the NCERT solutions for Class 12 Biology Chapter 3 PDF download.

Solution:

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

Answer:

Functions of testis

1. Testis produces spermatozoa which are male gametes.

2. In testis, the male sex hormone testosterone is developed.

Functions of ovary

1. The ovary produces ovum by the process oogenesis.

2. Graffian follicles in ovary produce female sex hormone called estrogen.

2. Describe the structure of a seminiferous tubule.

Answer:

Seminiferous tubules are highly coiled structures present in testicular lobules. The seminiferous tubules are lined by two types of cells i.e. spermatogonia and sertoli cells from inside. Spermatogonia are the male germ cells that form sperms through meiotic divisions followed by mitotic division, while Sertoli cells provide nutrition to the germ cells. The regions outside the seminiferous tubules called is called the interstitial space and it contains small blood vessels and Leydig cells. TheLeydig's cells secrete androgens.

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

Answer:

Spermatogenesis- It is the process of formation of spermatozoa from spermatogonia in testes at the time of puberty is called spermatogenesis. In this process, the spermatogonia present at the inner side of seminiferous tubules multiply by mitotic division and increase in number. Each spermatogonium contains 46 chromosomes. Spermatogonia forms spermatocyte that undergoes meiotic division to produce secondary spermatocytes having 23 chromosomes. The secondary spermatocytes undergo 2nd meiotic division to form spermatids. The spermatids are transformed into spermatozoa by the process called spermiogenesis . The sperm heads remain embedded in the Sertoli cells and are released from seminiferous tubules by the process of spermiation

4. Name the hormones involved in regulation of spermatogenesis.

Answer:

Spermatogenesis initiated due to an increase in the secretion of gonadotropin-releasing hormone by the hypothalamus. Increase in GnRH act on anterior pituitary and stimulate secretion of two gonadotropins, LH (luteinizing hormone) and FSH (follicular stimulating hormone). Among these, LH acts on Leydig cells and stimulates them to secrete androgens whereas FSH acts on Sertoli cells and stimulates the secretion of some factors which help in spermiogenesis.

5. Define spermiogenesis and spermiation.

Answer:

Spermiogenesis- The spermatids are transformed into spermatozoa by the process called spermiogenesis .

Spermiation- The release of sperms from the seminiferous tubules occurs through a process called spermiation.

6. What are the major components of seminal plasma?

Answer:

The major components of seminal plasma are mucous, fructose, calcium, ascorbic acid, certain enzymes and some secretions of accessory glands.

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

Answer:

Male accessory ducts include vasa efferentia, epididymis. vas deferens and rete testis. THey transport and temporarily store spermatozoa. Male accessory glands include seminal vesicle, bulbourethral gland and prostate gland. These glands secrete fluids that lubricate the female reproductive system and sperms.

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

Answer:

The process of formation of mature female gametes is called oogenesis. It starts during embryonic development stage when millions of oogonia (gamete mother cells) are formed in each fetal ovary. The gamete mother cells start division and enter into prophase-I of meiotic division and get temporally arrested. At this stage, they are called primary oocytes . Each primary oocyte gets surrounded by a layer of granulosa cell than it is called the primary follicle . The primary follicle gets surrounded by more layers of granulosa cells called secondary follicle that transform into tertiary follicle that contains a fluid filled cavity called antrum. The tertiary follicles further change into the mature follicle called Graafian follicle , which rapture to release secondary oocytes (ovum) from the ovary by the process of ovulation.

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

Answer:

The process of delivery of the foetus is called parturition. Oxytocin hormone causes a strong contraction of uterine. Contraction of uterine becomes stronger and stronger by the stimulatory reflex between uterine contraction and oxytocin secretion. This leads to the expulsion of the baby out of the uterus through the birth canal.

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

Answer:

The sex chromosome in human female is XX while in a male it is XY. Thus, female produces haploid gametes having all X chromosomes but male produces two types of gametes with either X or Y. The sex of the child will be dependent on which sperm whether the one with X chromosomes or the one with Y chromosome fertilises the ovum with X chromosome. Therefore, the sex of the baby is determined by the father's chromosomes not mother's.

11. 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 werefraternal?

Answer:

One ovum is released by a human ovary in a month. Identical twins are developed from a single egg. Hence, only one egg would have been released when the mother gave birth to identical twins. If the twins are fraternal twins then they must have been developed from two eggs.

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

Answer:

Dogs are polyovulatory animals and they release more than one egg at a particular time. So, a female dog with 6 puppies in one generation, releases 6 eggs.

Important topics of Class 12 Biology Chapter 3

• The Male Reproductive System

• The Female Reproductive System

• Gametogenesis

• Menstrual Cycle

• Fertilization and Implantation

• Pregnancy and Embryonic Development

• Parturition and Lactation