Describe the developmental stages of human embryo after fertilization with the help of neatly labelled diagrams.

Explanation

(1) During fertilization, chromosomes of the ovum and the chromosomes of the sperm make up into pairs and the resulting cell is called zygote.
(2) Fertilization takes place in the oviduct or fallopian tube.
(3) The zygote which is diploid travels down the fallopian tube . As it moves it undergoes several mitotic divisions formating the embryonic stage called blastocyst. (4) Blastocyst moves towards the wall of the uterus and finally gets attched and embedded in the wall of the uterus . This is called implantation.
(5) The growing embryo forms two membrances chorion and Amnion.

(6) Chorion establishes connection with the walls of the uterus and helps in the supply of nutrients to the embryo and removal of wastes from the embryo.
(7) Amnion froms a sec like structure around the embryo . The space between the amnion and embryo is filled with a fluid called amniotic fluit .
(8) Amnion and amniotic fluid give orotection to the embryo against minor mechanical injury.
(9) Placenta is a tissue formed by the cells from the embryo and the mother. It is formed around 12 week of pregnancy.

(10) Plancenta nourishes the growing embryo.
(11) A tough cord called umbilical cord also formed by the embryo which is connected to the walls of the uterus through the placenta.
(12)From 3 months of pregnancy , the embryo is called foetus.
(13) Pregnancy lasts on an average 9 month or 280 days . This period is called gestation period .