Which statement about gastrulation is true?
A) In frogs, gastrulation begins in the vegetal hemisphere.
B) In sea urchins, gastrulation produces the notochord.
C) In birds, cells from the surface of the blastodisc move down through the primitive groove to form the hypoblast.
D) In mammals, gastrulation occurs in the hypoblast.
E) In sea urchins, gastrulation produces only two germ layers.

Question

Quizplus · Accepted Answer

In frogs, gastrulation begins in the vegetal hemisphere, where cells invaginate to form the blastopore and eventually the three germ layers.

Answer: E
 In sea urchins, gastrulation produces only two germ layers - the endoderm and ectoderm. The mesoderm is formed later through a process called ingression.

The other options are incorrect. In sea urchins, gastrulation does not produce the notochord (B) and in birds, cells from the surface of the blastodisc move down through the primitive streak to form the epiblast, not the hypoblast (C). In mammals, gastrulation begins in the epiblast, not the hypoblast (D).

Which Statement About Gastrulation Is True