In a frog embryo, gastrulation A) is impossible because of the large amount of yolk in the ovum. B) occurs along the primitive streak in the animal hemisphere. C) produces a blastocoel displaced into the animal hemisphere. D) occurs within the inner cell mass that is embedded in the large amount of yolk. E) proceeds by involution as cells roll over the dorsal lip of the blastopore.

In a frog embryo, gastrulation E) proceeds by involution as cells roll over the dorsal lip of the blastopore.

Explanation:

Gastrulation is key because during it, cell movements result in a massive reorganization of the embryo from a simple spherical ball of cells, the blastula, into a multi-layered organism. Also many of the cells at or near the surface of the embryo move to a new, more interior location. It involves changes in cell motility, cell shape, and cell adhesion.