NCERT Class 12 Biology: Chapter – 3 Human Reproduction Part 7 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 3:

The zygote passes through several developmental stages till implantation, Describe each stage briefly with suitable diagrams.


The Zygote Passes through Several Developmental Stages Till

The various stages of the zygote before implantation are:

In the stage ‘a’ as shown in the diagram, a zygote is formed after the fusion of male and female gametes. In stage ‘b’ as shown in the diagram, zygote enters the isthmus.

CLEAVAGE STAGE: Within the isthmus, the zygote formed by the fusion of the male and female gamete, enters the two-cell stage known as cleavage.

BLASTOMERE: The cleavage formed, undergoes mitosis. At first, to form a 2 then 4, then 8 and finally 16 cells stage. These daughter cells are called as blastomere.

MORULA: The 8 - 16 cell blastomere are known as Morula. This Morula divides continuously to form a blastocyst and moves into the uterus.

The blastomere present within the blastocyst are arranged into a layer known as trophoblast. There are cluster of interior cells attached to the trophoblast known as interior cell mass.

The trophoblast layer gets attached to the endometrium lining of the uterus, the inner cells than forms an embryo after differentiation.

After the attachment the uterine cells divide to cover the blastocyst.

This blastocyst then, gets embedded in the endometrium of the uterus known as implantation.

Question 4:

Draw a neat diagram of the female reproductive system and label the parts associated with the following (a) production of gamete, (b) site of fertilisation (c) site of implantation and, (d) birth canal.


Female Reproductive System

(a) Site for Production of gametes: Ovary

(b) Site of fertilisation: Isthmus-ampullary junction.

(c) Site of implantation: Uterine endometrium

(d) Birth canal: Cervix and vagina

The female reproductive system includes:

1. Uterus: It is a muscular pear-shaped organ and is also known as the womb. It is the part where the zygote develops into an embryo and then grows into the foetus.

2. Fallopian tubes: These are funnel shaped muscular tubes that extends from both right and left side of the uterus extended to the edge of the ovaries. These tubes have finger-like projections called fimbriae. These fimbriae extend to the ovary and pick up ova that is produced by ovary into the infundibulum and finally reaches the uterus.

3. Vagina: It is an elastic and muscular tube that acts as a receptor for sperms during sexual intercourse and delivers the sperm to the fallopian tube as well as to the uterus.

Question 5:

With a suitable diagram, describe the organisation of mammary gland.


The Organisation of Mammary Gland

1. Mammary glands or breasts are paired structure that have undeveloped duct system and adipose tissue.

2. When a woman gets pregnant, the secretion of oestrogen and progesterone increases. This develops a glandular system in the mammary glands which leads to the production of milk.

3. The glandular tissue of each breast, forms mammary lobes consisting of clusters of cells known as alveoli.

4. These alveoli cells start secreting milk that is stored within the cavities of the alveoli.

5. These cells further open into mammary tubules and join to form a mammary duct.

6. A number of mammary ducts join together in order to form a mammary ampulla from which the milk is sucked out.