Question

Study and identify the correct combinations.
(a) Amnion - Somatopleure - Protection
(b) Allantois - Splanchnopleure - Placenta formation
(c) Yolk sac - Midgut - Nutrition
(d) Chorion - Outer wall of amniotic folds - Excretion

A. a, b
B. b, d
C. a, c
D. b, c

Answer 1

Amnion, a membrane that forms a fluid-filled cavity (the amniotic sac) in reptiles, birds, and mammals that encloses the embryo. Often the amniotic sac and the fluid it contains is referred to as the water bag. Allantois is derived from splanchnopleure and is mainly involved in placenta formation.

Complete answer:
The amnion, lined with ectoderm and coated with mesoderm, contains a thin, translucent fluid that suspends the embryo and thus provides a mechanical injury cushion. The amnion also offers protection from the embryo's own fluid loss and against tissue adhesions. It extends considerably between two other membranes, the amnion and chorion, in reptiles and birds to act as a temporary respiratory organ while foetal excretions are deposited in its cavity. The allantois is closely related to the chorion in mammals other than marsupials, adding blood vessels to the structure as it forms in combination with the uterus endometrium or mucosal lining, the placenta.

- Amnion is generated from the somatopleure and is involved in the functions of defence.
- In supplying nutrients to the developing embryo, the yolk sac is involved and is produced by the hypoblast cells located adjacent to the embryonic disc and not by the midgut.
- Chorion is the exterior wall of the amniotic folds and is involved not in excretion but in the development of the placenta.

Hence, the correct answer is option (A).

Note: In reptiles, birds, and mammals, Chorion, also called Serosa, is the outermost membrane around the embryo. On the surface of the yolk sac, it emerges from an outer fold. The chorion is the outer shell of the insect egg in insects. The chorion is covered with mesoderm-lined ectoderm in vertebrates and is separated by an extraembryonic body cavity, the coelom, from other embryonic membranes. It merges with the Allantois in reptiles and birds.