Cells can respond to many different ligands. Some of these ligands may cause intracellular signaling cascades that converge on the same protein or enzyme. This phenomenon is called

Signal transduction

Explanation:

Ligand forms complexes with substance and a ligand protein binds to a target site on protein and produces a signals on binding to it.

Signal transduction is the process by which signals both physical and chemical are transmitted through a cell via a series of molecular events especially protein phosphorylation catalyzed by protein kinases that results in a cellular response.

Receptors are proteins that detect stimuli. The changes that comes from ligand binding a receptor give rise to a biochemical cascade.

i think it would be b. tissue because an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.

i think the answer would d