A ligand produces a response in a cell if it finds the right kind of

receptor

Explanation:

Ligands are chemicals that exert their effects when they bind specifically to plasma membrane receptors. Some of the examples of ligands are neurotransmitters and the hormones produced by endocrine glands. Each ligand has specific receptors on the target cells. Some ligands have intracellular receptors.

Binding of a ligand to a receptor triggers structural changes in the receptor which in turn alters the cell proteins to produce the desired effect. For example, insulin is a hormone that promotes the uptake of glucose from the blood by liver and muscle cells. For the purpose, it binds to the plasma membrane receptors of these cells.