Question

Which extraembryonic membrane in humans prevents desiccation of the embryo inside the uterus?
A) Chorion
B) Allantois
C) Yolk sac
D) Amnion

Answer 1

Hint:The extraembryonic membranes consist of the chorion (the combination of trophoblast plus underlying extraembryonic mesoderm), amnion, yolk sac, and allantois.

Complete Answer:
Firstly, we will know what are extraembryonic membranes-
They are the membranes which assist in the development of the embryo. They include the following membranes- Chorion (the combination of trophoblast plus underlying extraembryonic mesoderm), amnion, yolk sac, and allantois.
1) The chorion is one of the membranes that wholly surrounds the foetus during the course of its development. The foetus lies in the amniotic sac, which is formed by the chorion and the amnion. Both of these membranes separate the embryo from the mother’s endometrium. The embryo grows inside, and along with four extraembryonic membranes that protect and nurture it.
2) The amnion is an extraembryonic membrane that surrounds an amniote embryo. The amnion is made from two germ layers- the mesoderm and the ectoderm.Amnion surrounds the embryo creating the amniotic cavity that is filled with amniotic fluid. The amniotic fluid serves as a shock absorber for the foetus, regulates foetal body temperature and prevents desiccation.
3) The yolk sac is an early extra-embryonic membrane which is endoderm origin and covered with extra-embryonic mesoderm. It lies outside the embryo. The yolk sac is connected by a yolk to the midgut with which it forms a continuous connection.
4) The allantois is found near the posterior side of the embryo. It lies between two other extraembryonic membranes- the amnion and the chorion. Reptiles, birds, and mammals have the characteristic of allantois.
Hence, the correct option is D (Amnion).

Note: With these four membranes, the developing embryo is able to carry on essential metabolism while sealed within the egg and it is surrounded by amniotic fluid, the embryo is then kept as moist as a fish embryo in a pond.