How does the presence of a receptor on the cell membrane influence the ligand’s behavior?

Receptors are often embedded within the cell membrane. When a receptor is located on the surface of the membrane, the ligand does not necessarily need to enter the cell to initiate a response. In fact, specific properties of the ligand may prevent it from crossing the lipid bilayer of the membrane. For instance, a hydrophilic ligand, due to its affinity for water and inability to easily interact with the hydrophobic core of the membrane, may find it challenging to penetrate the cell membrane. Thus, the receptor’s position on the cell surface enables signaling without the ligand needing to traverse the membrane barrier.