Explain how the signaling molecules released by an embryonic cell can induce changes in a neighboring cell without entering the cell. (See Figures 11.15 and 11.16.)

Signaling molecules that are released by cells are very small and soluble molecules that are called ligands. These can trigger a signal transduction pathway in the neighboring cells by binding the receptors present on their membranes. A specific signal binds with a specific receptor.

Cells can receive and process the signals released by other cells or the outer environment. For this purpose, they have receptors that are generally found as transmembrane proteins and transmit the message through a sequence of molecules to the internal signaling pathway.

Signals released by embryonic cells can initiate a signal transduction pathway that regulates the activity of genes in the nucleus of neighboring cells.

The signals make a phosphorylation cascade in the molecule switches and transcription factors that affect the gene expression of neighboring cells, thereby altering their activity.