What is an instinctive behavior ?

An inborn pattern of behavior that is characteristic of a species and is often a response to specific environmental stimuli: the spawning instinct in salmon; altruistic instincts in social animals.

Explanation:

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products