AP BIOLOGY

Detailed explanation-1: -Signaling molecules are often called ligands, a general term for molecules that bind specifically to other molecules (such as receptors). The message carried by a ligand is often relayed through a chain of chemical messengers inside the cell.

Detailed explanation-2: -Receptor sites are proteins typically found on the surface of cells, which are able to recognize and bond to specific messenger molecules.

Detailed explanation-3: -Cell-Surface Receptors These receptors are also known as transmembrane receptors. These are proteins that are found on the surface of cells and span the plasma membrane. They bind to ligands that cannot themselves pass through the plasma membrane.