Question

The extraembryonic membrane that involve in the formation of the placenta in human is
a) Chorion
b) Allantois
c) Yolk sac
d) Amnion

Answer 1

Hint: For the survival of life inside the womb, it needs nutrition as well as safety. Fetus develops from the successive division of zygote after fertilization of gametes. The fetal membranes are present around the fetus from the gestational period. It ensures the maintenance of pregnancy to delivery.

Complete answer:
Fetus is present in four fetal membranes. Fetus is attached to the wall of the uterus through the placenta which arises from one of the fetal membranes.
Placenta is a structure that helps in the attachment of fetus with mother via umbilical cord. This structure is responsible for all the nutrition which is necessary for fetal development and also removes all waste material which is created by the fetus.
The total four fetal membranes collectively called as extra-embryonic membrane:
Chorion: this is made up of trophoblast from outside and from inside it is made up of extra-embryonic mesoderm. It is responsible for the formation of placenta.
Amnion: the space between embryo and amnion is known as amniotic cavity which has fluid in it which acts as a shock absorber.
Allantois: it is made up of endoderm inside. It appears as a sac that arises from the gut of an embryo near the yolk sac.
Yolk sac: it is non-functional in humans but acts as a site for early blood cell formation.

Hence, the correct answer is option (a).

Note:
In reptiles, birds etc, chorion is known as Serosa. The chorion is the outer shell of the insect egg in insects. Placenta also acts as a temporary endocrine gland that means during pregnancy it releases many hormones like hcG, Hpl, Progesterone etc. The allantois and yolk sac together forms the umbilical cord which helps in attachment of placenta with the uterus.