Final answer:
By the end of the second week, the embryonic disk consists of a bilaminar structure of epiblast and hypoblast, which will soon form the three germ layers: ectoderm, mesoderm, and endoderm, essential for further organ and tissue development.
Step-by-step explanation:
At the end of the second week of development (day 14), the composition of the embryonic disk comprises a two-layered (bilaminar) structure with the differentiation of the embryoblast into two groups of cells, the epiblast and the hypoblast. This transformation is a precursor to gastrulation, which is the process where these layers further develop into the three germ layers: the ectoderm, mesoderm, and endoderm. The ectoderm, forming the outer layer, will give rise to skin and nervous system cells, the mesoderm, the middle layer, will develop into organs such as bones, muscles, and the heart, and the endoderm, the innermost layer, will evolve into cells of internal glands and organs.
At the end of the second week of development (day 14), the embryonic disk is composed of three layers called the ectoderm, mesoderm, and endoderm. The ectoderm develops into the skin and nervous system cells, the mesoderm develops into organs like bones and muscles, and the endoderm develops into internal glands and organs. These germ layers are formed through the process of gastrulation, where cells migrate and differentiate to form the different cell layers.