Final answer:
Ectoderm cells determine whether to form neural or epidermal cells through signals from growth factors and cell signaling pathways during organogenesis. These signals are vital for proper gene expression and cellular differentiation. Disruption in these signals can lead to incorrect differentiation of the ectodermal cells.
Step-by-step explanation:
During organogenesis, the ectoderm in vertebrates differentiates into neural cells and epidermal cells. This process is guided by growth factors which signal some of the cells to become epidermal cells, while the rest go on to form the neural plate, which is the precursor to the central nervous system. Environmental factors, such as the location-specific chemical signals from the cell's embryonic environment, play a key role in this process. Furthermore, cell signaling pathways, including proteins involved in the Wnt signaling pathway, help regulate this differentiation.
These growth factors and signaling pathways are crucial because they regulate the gene expression necessary for cellular differentiation. If these signals are disrupted, ectodermal cells may not properly differentiate, leading to a default pathway where the entire ectoderm could develop into neural tissue. Therefore, the answer to how ectoderm cells determine their fate is that it is regulated by cellular signaling cascades, including but not limited to environmental factors, growth factors, and genetic pathways linked to the mesoderm, such as signals from the notochord.