Question

Primary tissue layers first appear ______.

Options

• in the egg cortex

• in the gastrula

• during cleavage

• in primary organs

Answer 1

Primary tissue layers first appear in the gastrula.

Explanation:

• Primary tissue layers ectoderm, mesoderm, and endoderm first appear during the gastrula stage of embryonic development. 
• This stage transforms the blastula into a structure with three germ layers, which later develop into all organ systems.
• The egg cortex, cleavage, and primary organs do not show the formation of these primary tissue layers initially; they appear specifically in the gastrula stage.