You observe an animal embryo that is spherical in shape. Transverse sections through the embryo show that the outer wall consists of three layers of cells, and that there is a single axis of symmetry. The interior of the embryo is a fluid-filled cavity. The most recent developmental process to affect this embryo directly was
A) organogenesis.
B) gastrulation.
C) cleavage.
D) morphogenesis.
E) neurulation.

Question

Quizplus · Accepted Answer

The description of the embryo having three layers of cells (triploblastic) and a single axis of symmetry, along with a fluid-filled cavity, suggests that gastrulation has recently occurred. Gastrulation is the process that forms the three primary germ layers (ectoderm, mesoderm, and endoderm) and establishes the basic body plan.

You Observe an Animal Embryo That Is Spherical in Shape