Development of Embryo

Question 1 What is fertilisation?

Question 2 How does the development of an embryo takes place?

Question 3 What is implantation?

Question 4 How does the fertilisation of a human egg by a sperm take place to form a zygote?

Question 5 Define foetus? After how many weeks of development, a human embryo is said to become a foetus?

Question 6 Give a difference between embryo and foetus?

The process of reproduction in human take place in 2 steps:

(1) Fertilisation

(2) Development of embryo

Fertilisation

(1) The sperms made in the testes of man are introduced by penis into the woman’s body through vagina. The sperms enter into vagina, pass through the uterus and then go into the oviducts.

(2) The tail of sperms help in moving and reach the oviducts. If at the same time, the ovary of woman releases an egg, then this egg also goes into the oviduct.

(3) One of the sperms enter the egg. The fusion of sperm with egg is called fertilisation. During fertilisation, the nucleus of sperm fuses with the nucleus of egg cell to form a single nucleus. This results in the formation of a fertilised egg called zygote.

Development of Embryo

(1) The zygote divides repeatedly to make a ball of hundreds of cells. This is called an embryo. The embryo moves down the oviduct into the uterus. The embryo gets embedded in the soft and thick lining of the uterus. This is called implantation.

(2) When the embryo settles down in the uterus, the woman is said to have become pregnant. The embryo starts growing into a baby. The embryo gets food and oxygen from the blood vessels in the lining of the uterus.

(3) The cells of embryo begin to form specialised groups that develop into different tissues and organ of the baby.

An unborn baby at an early stage of development in uterus is called an embryo. The unborn baby remains an embryo in the first eight weeks of pregnancy.

(4) The embryo continues to grow and develop in the uterus to form a baby. The embryo gradually develops body part such as hands, legs, head, eyes and ears.

(5) An unborn baby in the uterus at the stage when all the body parts can be identified is called foetus.

(6) A human embryo becomes a foetus after about eight weeks of pregnancy.

(7) It takes 38 weeks from the fertilisation of eggs to the formation of fully developed baby. When the development of foetus into a baby is complete, the mother gives birth to the baby. The fully formed baby comes out of mother’s body through vagina.