Biology Question on human reproduction

Question

Which layer develops first during embryonic development?

Answer 1

Solution

Gastrulation results in the formation of three germ layers. In all triploblastic animals three germ layers are ectoderm, mesoderm and endoderm. (i) Formation of Endoderm. The blastocyst (blastodermic vesicle) grows in size by absorbing food from the uterus. Some cells detach from the inner cell mass to form endoderm in the blastocoel. Endoderm differentiates into the primitive gut. The primitive gut differentiates into two portions at a later stage. One portion forms the gut tract and the other portion communicates with the gut of the embryo and is called the yolk sac. (ii) Formation of Embryonic Disc. Just after the formation of endoderm, the remaining mass of cells of the inner cell mass is called embryonic disc. (iii)Formation of Mesoderm. It starts after the formation of endoderm. Formation of mesoderm starts from the caudal margin of the embryonic disc by rapid proliferation of cells. The proliferated cells detach from the embryonic disc and form mesoderm. (iv)Formation of ectoderm. After the formation of mesoderm, the remaining cells of the embryonic disc form a layer, the ectoderm.