Final answer:
Extracellular signals act via cell-surface receptors to change the behavior of the target cell. There are three main types of cell-surface receptors: enzyme-linked receptors, ion channel-linked receptors, and G-protein-linked receptors.
Step-by-step explanation:
Extracellular signals can act via cell-surface receptors to change the behavior of the target cell. Cell-surface receptors are membrane-anchored proteins that span the plasma membrane and perform signal transduction, converting extracellular signals into intracellular signals. There are three main types of cell-surface receptors: enzyme-linked receptors, ion channel-linked receptors, and G-protein-linked receptors. These receptors bind to external ligands and can initiate a chain of events within the target cell, ultimately leading to changes in cell behavior.