Final answer:
Placodes, thickened areas of ectoderm, are influenced by growth factors to differentiate into various tissues, with some forming the neural plate while others become epidermal cells, contributing to the patterning of tissues through reaction-diffusion.
Step-by-step explanation:
Placodes and Patterning Through Reaction-Diffusion
During embryogenesis, the structure known as the primitive streak forms along the dorsal surface of the epiblast, which is a key event during gastrulation. This leads to the formation of multiple germ layers including endoderm, mesoderm, and ectoderm. Growth factors play a crucial role during organogenesis, particularly in the development of the neural system from the ectoderm. Certain ectodermal cells, influenced by signaling molecules or growth factors, differentiate into the neural plate, while others form epidermal cells. In this way, placodes, which are thickened regions of ectoderm, give rise to tissues and structures such as sensory organs through the process of reaction-diffusion, where patterns of differentiated tissues emerge in response to gradients of signaling molecules.