Which of the following is true regarding gastrulation:

Which of the following is true regarding gastrulation:

A. Establishes all the three germ layers
B. Occurs at the caudal end of the embryo prior to its cephalic end
C. Involves the hypoblastic cells of the inner cell mass
D. Usually occurs at 4 weeks

Answer is A. Establishes all the three germ layers.

• Gastrulation is the process that establishes all the 3 germ layers in the embryo.
•  Gastrulation is the most characteristic event occurring during the 3rd week and not the 4th week
• The embryonic epiblast undergoes gastrulation. It does not involve the hypoblastic cells of the inner cell mass.
• Occurs at the cephalic end prior to the caudal end.

Gastrulation of a diploblast: Formation of Germ Layers from (1) a blastula to (2) a gastrula.

Some of the ectoderm cells (orange) move inward forming the endoderm (red).