Ncert Solutions For Class 12 Biology Chapter 3 | Download Free PDF

 

NCERT Solutions for Class 12 Biology Chapter 3 – Human Reproduction

 

The Ncert Solutions for class 12 biology chapter 3 provides information about Human Reproduction. The events of sexual reproduction in human beings are- Gametogenesis- the process of formation of gametes is called as gametogenesis. Insemination- the process of transfer of sperms into the ovum is called insemination. Fertilization- the process of fusion of male and female gamete to form a single celled zygote is called fertilization. Implantation- the process of attachment of embryo to the endometrial wall of uterus of female is called implantation. Gestation- the period of embryonic development is called gestation. Parturition- the process of delivery of the baby is called parturition.

 

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Features of the NCERT Solutions Class 12th Biology Chapter 3 – Human reproduction

 

NCERT Solutions of class 12 have been answered based on the important information on the question.

• The columns are used wherever necessary.
• Solutions are solved point-wise and accurately answered point to point.

 

Important Questions of NCERT Solutions Class 12th Biology Chapter 3- Human Reproduction

 

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 _____________which is implanted in uterus.

(k) The structure which provides vascular connection between foetus and uterus is called _______

 

Answer:  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 Leutinizing hormone.
(h) The fusion of male and female gametes is called fertilization.
(i) Fertilisation takes place in oviduct.
(j) Zygote divides to form blastula which is implanted in uterus.
(k) The structure which provides vascular connection between fetus and uterus is called umbilical cord.

 

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

 

Answer:

(i) Functions of testis:

(a) Formation of sperms by the process of spermatogenesis.

(b) Secretion of testosterone hormone.

 

(ii) Functions of ovary:

(a) Formation of ova by the process of oogenesis.

(b) Secretion of female hormones like estrogens, progesterone and relaxin.

 

Question 5. 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. The Leydig’s cells secrete androgens.

 

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

 

Answer:  Spermatogenesis

The process of formation of sperms is called spermatogenesis. It involves 3 phases- multiplication phase, growth phase, maturation phase.

In multiplication phase, male germ cells also called as spermatogonia undergo mitotic divisions to form large number of spermatogonia.

In growth phase, spermatogonia increases their size by accumulation of nutrition in the cytoplasm and are ready for meitoic division and the spermatocytes are called as primary spermatocytes with 46 chromosomes.

In maturation phase- A primary spermatocyte completes the first meiotic division leading formation of two equal, haploid cells called secondary spermatocytes, which have only 23 chromosomes each and the secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids

Spermiogenesis-

The spermatids are transformed into sperms, also called as spermatozoa by the process called spermiogenesis.

After spermiogenesis, sperm heads become embedded in the Sertoli cells and are released from the seminiferous tubules by the process called spermiation.

 

Hormonal control of spermatogenesis

Spermatogenesis starts at the age of puberty due to significant increase in the secretion of gonadotropin releasing hormone (GnRH) from hypothalamus.

The increases level of gonadotropin releasing hormone stimulates the anterior pituitary to

secrete luteinizing hormone(LH) and follicle stimulating hormone(FSH).

LH acts at the Leydig cells and stimulates synthesis and secretion of androgens.

Androgens stimulate the process of spermatogenesis.

FSH acts on the Sertoli cells and secrete two factors- androgen binding protein (ABP) and inhibin which helps in spermiogenesis.

 

Question 7.  Name the hormones involved in regulation of spermatogenesis.

 

Answer:  Spermatogenesis starts at the age of puberty due to significant increase in the secretion of gonadotropin releasing hormone (GnRH) from hypothalamus.

The increases level of gonadotropin releasing hormone stimulates the anterior pituitary to secrete luteinizing hormone(LH) and follicle stimulating hormone(FSH).

LH acts at the Leydig cells and stimulates synthesis and secretion of androgens.

Androgens stimulate the process of spermatogenesis.

FSH acts on the Sertoli cells and secrete two factors- androgen binding protein (ABP) and inhibin which helps in spermiogenesis.

 

Question 8. Define spermiogenesis and spermiation.

 

Answer:  Spermiogenesis – is a process in which spermatids are transformed into mature sperms/spermatozo

Spermiation – is a process in which the mature spermatozoa are released into the lumen of seminiferous

tubules from the sertoli cells.

 

Question 9. Draw a labelled diagram of sperm.

 

Answer:  Spermatozoon is a mature male gamete or reproductive cell. A sperm cell comprises of a round or cylindrical nucleated cell. a short neck, and a thin motile tail. The structure of sperm is very important for its motility and function in sexual reproduction. The nucleus contains half of the genetic information and fuses with the ovum (female gamete) to form a zygote. A sperm cell determines the sex of its offspring in mammals, if it bears Y chromosome, then male offspring will be the result and if X chromosome the female offspring.

Diagrammatic representation of a sperm:

 

Question 10. What are the major components of seminal plasma?

 

Answer:

1. The secretions of seminal vesicles, prostate gland, and Cowper’s glands.
2. Spermatozoa
3. About 70% of the seminal plasma is secreted by seminal vesicles. It is rich in fructose, citrate, prostaglandins and certain enzymes.

 

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

 

Answer:

The male accessory ducts are:

Rete testis- The seminiferous tubules are closed at one end and on the other end it is joined to a network of rete testis from where fine ciliated ductules, the vasa efferentia arise.

Vasa efferentia: They are the fine ciliated ductules, which transport the sperm to the epididymis.

Epididymis- It stores the sperm and secretes the fluid which is considered to nourish the sperms.

Vasa deferentia- A vasa deferens emerges from the cauda epididymis on each side of the scrotal sac and enters the abdominal cavity.

The accessory ducts are responsible for the storage and transportation of sperms from the testis to the outside through the urethra.

The male accessory glands are:

Seminal vesicles- The seminal vesicles are one pair of sac-like structure which joins vasa deferentia to form ejaculatory ducts. The secretions of the seminal vesicles contain fructose and hormones like prostaglandins. Fructose provides energy to the sperms. The prostaglandins stimulate the secretion of uterine contractions and help the movement of the sperms inside the female uterus.

Prostate gland: The secretion of this gland contains citric acid and enzymes which nourish and activate the spermatozoa to swim.

A pair of the bulbourethral gland- It is present on either side of the membranous urethra. They secrete an alkaline fluid. They also secrete mucus that lubricates the end of the penis and the lining of the urethra.

 

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

 

Answer:  The formation of ovum from oogonia in females takes place by a process called oogenesis, which occurs in the ovary. During the process a diploid oogonium or egg mother cells increases in size and transforms into a diploid primary oocyte, the later then undergoes meiosis I or reductional division to form two unequal haploid cells. The smaller cell is called “first polar body” and the larger cell is called “secondary oocyte”. The secondary oocyte undergoes meiosis II or equational division to form a secondary polar body and an ovum

 

Read More Article Related To This

Frequently Asked Questions on NCERT Solutions Class 12 Biology Chapter 3

 

What are the advantages of referring NCERT Solutions for class 12 Biology chapter 3?

Students referring the NCERT Solutions of class 12 by Adda 247 find the solutions helpful during the exams. The solutions are prepared by the experts in an interactive manner keeping in mind the students. The students’ perspective is kept in mind while preparing the solutions. It helps in completing the syllabus on time and also provides notes for the revision prior to the exam.

 

What are the advantages of referring NCERT in competitive exams like JEE and AIPMT? 

Most of the competitive exams like NEET, JEE etc. follow the basic NCERT books for designing their question papers. NCERT serves as the base for every book prepared for NEET and JEE. The competitive exams are based on the CBSE syllabus applied in XI and XII classes and NCERT books strictly follow CBSE syllabus. In addition to this, NCERT books play an important role in clearing out the theoretical concepts. Every topic given in NCERT books is explained in such a way to help students make their basics and fundamentals strong and clear.

 

How to read NCERT books more efficiently?

Given below are the important points which must be followed while reading the NCERT books in an efficient manner:

Go through each topic thoroughly by understanding the meaning and significance of each line mentioned in that particular topic.

Ask your teacher if any doubts.

Note down the important topics to revise at the time of examination.

Solve all the exercise questions given at the end of each chapter. These questions are important for understanding the concepts in a better way.

 

Is it mandatory to solve all the NCERT questions mentioned at the end of each chapter?

The questions and answers mentioned in NCERT textbooks at the end of each chapter are quite important not only for examination but also for understanding the concepts in a better way. These questions aim to test the students’ understanding and learning over the topics that they have learned in the chapter.

Solving the NCERT exercise problems will help to

• clear all the concepts and formulae you learned in a chapter
• get comfortable with different types of questions that might be asked in exams
• get enough practice which is key to succeed in Mathematics exam
• improve your accuracy and speed

 

What are the important concepts covered in the Chapter 3 of NCERT Solutions for Class 12 Biology?

The concepts involved in the chapter 3 of NCERT Solutions are –

3.1 – The Male Reproductive System
3.2 – The Female Reproductive System
3.3 – Gametogenesis
3.4 – Menstrual Cycle
3.5 – Fertilisation and Implantation
3.6 – Pregnancy and Embryonic Development
3.7 – Parturition and Lactation

 

These concepts are created by the faculty at Adda 247. The solutions are available at Adda 247 in the PDF format which can be downloaded by the students.

 

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