Final answer:
A signaling cell releases signal molecules, which are received by the target cell. The signal molecules are called extracellular signal molecules or ligands, and they bind to specific receptors on the target cell.
Step-by-step explanation:
A signaling cell is a cell that releases signal molecules to communicate with other cells. An extracellular signal molecule, also known as a ligand, is a small molecule that is released by the signaling cell and binds to a specific receptor on the target cell. The target cell is a cell that has receptors for the signal molecule and responds to the signal by initiating a chain of events within the cell.