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Q.
Which layer develops first during embryonic development?
UP CPMTUP CPMT 2009
Solution:
Gastrulation results in the formation of three germ layers. In all triploblastic animals three germ layers are ectoderm, mesoderm and endoderm. The blastocyst 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. Just after the formation of endoderm, the remaining mass of cells of the inner cell mass is called embryonic disc. Formation of mesoderm starts after the formation of endoderm from the embryonic disc by rapid proliferation of cells. After the formation of mesoderm, the remaining cells of the embryonic disc form a layer, the ectoderm.