NCERT Solutions Class 12 Biology Chapter 3

NCERT Solutions Class 12 Biology Chapter 3: Human Reproduction

NCERT Solutions Class 12 Biology Chapter 3 is about reproduction in humans. Reproduction is a biological practice in which an organism gives rise to young ones similar to itself. The offspring grow, mature and in turn produce new offspring. Thus, there is a cycle of birth, growth and death. 

Reproduction facilitates the continuation of the species, generation after generation, which you can study in NCERT Solutions Class 12 Biology Chapter 3. 

This chapter deals with the study of sexual reproduction consisting of a set of events and can be divided into three stages: 

• Pre-fertilization
• Fertilization
• Post-fertilization. 

By referring to Extramarks’s NCERT Solutions Class 12 Biology Chapter 3, students will gain good knowledge and write precise answers in the examination. These notes have been designed by teachers with several years of experience in teaching this subject. 

Extramarks’ objective is to assist students of Class 12 by offering all the knowledge about the examinations, important questions, and the CBSE syllabus, including NCERT Solutions Class 12 Biology Chapter 3. The notes prepared by the Extramarks will give you an understanding of the critical concepts and smoothen your learning process.

Key Topics Covered In NCERT Solutions Class 12 Biology Chapter 3

Basic Steps in Human Reproduction:

1. Gametogenesis.
2. Insemination.
3. Fertilization.
4. Blastocyst development.
5. Implantation.
6. Embryo development.
7. Parturition.

1.Male Reproductive System:

There are four primary parts of the male reproductive system:

1. Testes.
2. Accessory ducts.
3. Glands
4. External Genitalia.

Testes (Singular Testis):

• The scrotum is located in the pelvic region outside the abdominal cavity within a pouch.
• A tiny muscular sac is called a Scrotum that contains and protects the testes. The scrotum is situated behind the penis and is treated as a part of the outer male genitalia.
• The testes are positioned outside the abdominal cavity to defend the moderate temperature of the testes, nearly 2-2.5◦C, lesser than the average human body temperature. This condition is essential for the synthesis of sperms.
• The shallow temperature in testes is necessary for spermatogenesis as the standard human body temperature can lead to mutation in the sperm.
• The testis is oval with a length of 4-5cm and 2-3cm wide.
• The testis consists of about 250 compartments called Testicular lobules.
• Each lobule generally constitutes 1-3 highly coiled seminiferous tubules that play a crucial role in sperm production.
• Seminiferous tubules are the place that creates spermatozoa by the method of meiosis.
• Each seminiferous tubule has two types of cells, i.e., Sertoli cells and spermatogonia in their inner lining.
• These spermatogonia are diploid in the environment and called the immature germ cells, and they shape the sperm by the procedure of meiosis. They hold 46 chromosomes in their cells.
• Sertoli cells in seminiferous tubules offer nutrition to the spermatogonia.
• Interstitial spaces are the region outside the seminiferous tubule that carries the narrow Leydig cells, blood vessels, and some immunocompetent cells.
• Leydig cells synthesize and emit the testicular hormones known as androgens.

Accessory Ducts:

The accessory ducts facilitate the movement of the sperm from the testes to the urethra for their discharge outside the physique. The male reproductive system includes four accessory ducts:

• Rete Testis: 

These are the duct points where the seminiferous tubules start into a sequence of channels.

• Vasa Efferentia: 

These ducts make a pathway to shift the sperm from the rete testis to the Epididymis, which is located on the posterior surface of every testis.

Epididymis: 

It is a long, coiled tube that joins a testicle to a vas deferens. The Epididymis is placed on the backside of every testicle.

Vas Deferens: 

Vas deferens is a muscular duct that mounts into the abdominal cavity and constructs a loop above the urinary bladder. It transmits the sperm from the Epididymis to the ejaculatory duct.

Ejaculatory Duct: 

This duct is placed on each side of the prostate gland. Ejaculatory ducts store and supply the sperm from the testis to the exterior via the urethra.

Urethra: 

The urethra is a thin muscular tube that derives from the urinary bladder and then passes the penis to its external opening called the urethral meatus.

Accessory Glands:

There are primarily three kinds of accessory glands. These glands secrete the seminal plasma that principally contains calcium, fructose, and certain enzymes. This secretion blends with the sperms to nourish and guard them.

Seminal Vesicles: 

The Seminal vesicles contribute an essential proportion of approximately 60-75% of the fluid in semen. This fluid is high in proteins, enzymes, vitamin C, prostaglandins, fructose, and phosphorylcholine. 

Prostate Gland: 

The prostate gland is a thick composition positioned just menial to the urinary bladder. The discharge of the prostate gland is slightly thin, alkaline, and milky-coloured. It helps in the stability of sperm in the acidic vaginal condition and also develops the motility of the sperm.

Bulbourethral Glands: 

The secretion of these glands assists in the lubrication of the penis and also neutralizes any residual acidity in the urethra. 

2. Female Reproductive System:

The human female reproducing system is specialized to carry out various functions like ovulation, gametogenesis, fertilization, birth, pregnancy, and child care. The female reproductive structure is made up of numerous parts:

1. Ovaries:

• The ovaries are mini and oval-shaped and are known as critical female sex organs.
• They generate the female gamete, an ovum, and produce ovarian hormones.
• The ovaries are about 2-4cm in length.
• They are linked to the pelvic wall and uterus with the assistance of ligaments.
• The ovaries are secured by a thin epithelium that encloses the ovarian stroma.

Ovarian stroma is the matrix of the ovary that is split into double regions:

1. Peripheral cortex.
2. Inner medulla.

Accessory Ducts: 

The accessory ducts of the female reproducing system consist of the oviducts, uterus, and vagina.  

Oviduct (Fallopian Tube):

• A fallopian tube usually is 10-12 cm in length.
• It shields from the periphery region of every ovary to the uterus.
• Infundibulum: It is a proximal element of the oviduct near to the ovary. It is funnel-shaped and possesses fimbriae.
• Fimbriae: They are the finger-like projections at the infundibulum’s edges. They assist in the compilation of the ovum after ovulation.
• Ampulla: This is the broad part of the oviduct that fixes with the infundibulum.
• Isthmus: This is the last segment of the oviduct that expands through the uterine walls and opens into a small lumen.

Uterus:

• The uterus has also been labelled as the womb.
• Ligaments are crafted like an inverted pear and attached to the pelvic wall.
• In the uterus, the embryo grows into the fetus.
• It opens into the vagina via a slim cervix.
• The uterine wall has three layers of tissues: 
• Perimetrium.
• Myometrium.
• Endometrium.

Cervix:

• It is a thin canal, usually 2 to 3 cm in length, that attaches the uterus to the vagina.
• Cervical Canal: The cervical canal bridges the cavity of the physique of the uterus with the lumen of the vaginae.
• Birth Canal: The cervical canal across the vagina shapes the birth canal, which aids during the baby’s delivery.

External Female Genitalia:

The primary external female genitalia of the female reproductive system is made up of the mons pubis, labia minora, labia majora, hymen, and clitoris.

Hymen: 

The hymen is a thin membrane that revolves around the opening of the vagina. It is often torn during the first coitus or intercourse, or it can also be broken by participation in some sports like cycling, horseback riding etc.

Clitoris: 

It is a sensitive, small, finger-like projection at the junction of the labia minora over the urethral opening. 

Mammary Glands:

All-female mammals own a couple of functional mammary glands. The breasts are a paired system of glandular tissue and a variable amount of fats. Each mammary gland has 15-20 mammary lobes.

3. Gametogenesis:

It is the system by which the fundamental male and female sex organs like the testes in males and the ovaries in the female form gametes.

Spermatogenesis:

This is the technique by which the immature male germ cells, also called spermatogonia, bring out mature sperm cells in the testis.

Oogenesis: 

Oogenesis is the practice by which the immature oogonia in the ovaries generates a mature ovum.

Spermatogenesis: 

The spermatogenesis process starts at puberty.

Spermatogonia:

They are the incomplete male germ cells that experience meiotic divisions to configure sperm. Spermatogonium (singular) is diploid in mother nature and contains 46 chromosomes.

Primary Spermatocytes: 

These are the spermatogonia that live through the meiosis procedure to create two equal haploid cells called secondary spermatocytes. They accommodate 46 chromosomes in every cell.

Secondary Spermatocytes: 

They are haploid and derive from the main spermatocytes due to meiosis . They encompass 23 chromosomes.

Spermatids: 

These cells arise from the subordinate spermatocytes as an action of meiosis II. Spermatids are haploid cells that incorporate 23 chromosomes.

Spermiogenesis: 

It is the method by which spermatids mature to create spermatozoa or sperms.

Spermiation: 

This is the system by which sperms are delivered from the seminiferous tubules. 

4. Menstrual Cycle:

This is the reproductive pattern that initiates from one menstruation to the next. It primarily takes place in female primates like apes, monkeys, and human beings. The rhythm repeats at 28-35 days intervals and usually releases one egg per cycle. This rotation is essential for the production of oocytes and the devising of the uterus for pregnancy. 

Menstruation: 

In this routine, the blood and mucosal tissue are discharged periodically. It happens due to the breakage of the inner lining of the uterus. This mechanism occurs once a month and is known as period.

Menarche: 

Menarche is the initial menstruation of a human female that starts at puberty. 

Menopause: 

Menopause is explained as the permanent end of the menstrual cycle in females.

 Phases of the Menstrual Cycle:

The menstrual cycle follows four phases:

1. Menstrual phase.
2. Follicular phase.
3. Ovulation.
4. Luteal Phase.
5. Fertilization and Implantation:

Insemination: 

It is how semen is released into the vagina by the penis during coitus or copulation.

Fertilization:

It mixes the haploid male gamete or sperm and the haploid female egg.

Morula: 

The embryo with 8-16 blastomeres is referred to as a morula. It continues its division as it transfers further along into the uterus. The blastomeres are assembled into double layers. The outer layer is termed the trophoblast, and the other is the inner cell mass which is attached to the trophoblast.

NCERT Solutions Class 12 Biology Chapter 3: Exercises and Answer Solutions

Extramarks offers updates on NCERT Class 12 Biology Chapter 3 as per CBSE regulations. Extramarks also has a syllabus of all the other subjects of the Class 12 Board examination. Students can clarify their questions and practice for the upcoming Biology Board examinations by clicking on the links below.

An elaborate Solution for all the exercise questions is listed below:

NCERT Solutions Class 12 Biology Chapter 3 Ex 3.1

NCERT Solutions Class 12 Biology Chapter 3 Ex 3.2

NCERT Solutions Class 12 Biology Chapter 3 Ex 3.3

To study more about the subject, go through the Extramarks’ website and access NCERT Solutions Class 12 Biology Chapter 3. Students can avail all the content anytime from anywhere. Students can also learn more about the NCERT Solutions for different Classes by clicking on the relevant links below.

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NCERT Exemplar Class 12 Biology

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NCERT Exemplar and Chapter 3 Biology Class 12 notes at Extramarks are excellent combo study material for thorough revision.

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Key Features of NCERT Solutions Class 12 Biology Chapter 3

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• NCERT Solutions Class 12 Biology Chapter 3 will guide students in formulating their answers effectively in the examination. 
• The theory described in these notes is detailed so students can compose crisp and clear Solutions based on the content available on the Extramarks.
• Knowledgeable professors write the notes with decades of experience in their respective Scientific fields.