In humans, the three germ layers are established when the:
A)blastula forms.
B)inner cell mass of the blastula forms.
C)blastula implants into the uterine wall.
D)cells of the inner cell mass reorganize themselves into the gastrula.
E)gastrula implants into the uterine wall.

Question

Quizplus · Accepted Answer

The three germ layers are established during gastrulation, when cells of the inner cell mass reorganize themselves into the three germ layers (ectoderm, mesoderm, and endoderm) within the gastrula. Choice A is incorrect because the blastula only contains one layer of cells. Choice B is incorrect because the inner cell mass gives rise to the embryo, but does not establish the germ layers. Choices C and E are incorrect because implantation occurs after gastrulation, and does not contribute to the establishment of the germ layers.

In Humans, the Three Germ Layers Are Established When The