Final answer:
To respond to a signaling molecule, a target cell requires specific receptor proteins that bind the signaling molecule. These receptors can trigger second messengers that vary the response according to the cell type and signaling pathways involved.
Step-by-step explanation:
For a target cell to respond to a cell signaling molecule, it is necessary for the target cell to have specific receptor proteins that can recognize and bind to the signaling molecule or ligand. These receptors could be, for example, G-protein-linked receptors, ligand-gated ion channels, voltage-gated ion channels, or receptor tyrosine kinases. Once the ligand binds to the receptor, it may trigger the use of a second messenger inside the cell that propagates the signal. The uniqueness of the cell's response is because different cells contain different genes that code for different types of receptors. Additionally, the same second messenger can initiate different responses depending on the cell type's specific signaling pathways and components.