Final answer:
The progress zone responds to growth factors such as Epidermal Growth Factor (EGF), which are signaling molecules that trigger cell division and growth through signaling pathways involving phosphorylation events.
Step-by-step explanation:
The progress zone in developmental biology is a region at the distal end of a developing limb in an embryo that responds to growth factors. These growth factors are signaling molecules that bind to cell-surface receptors, often receptor tyrosine kinases (RTKs), and initiate a signaling pathway crucial for cell division and growth. For instance, the Epidermal Growth Factor (EGF) is a signaling molecule that binds to its receptor, EGFR, and promotes cell growth and division. When EGF binds to EGFR, it leads to a cascade of phosphorylation events that signal the cell to grow and replicate. This is an example of how the progress zone can respond to specific signaling molecules like EGF, facilitating proper limb development.