Is an entity set that contains the commonly shared characteristics of it entities or subtypes. it includes characteristics that are not common to all entities within the set and becomes the parent to one or more subtypes in the hierarchy.

A supertype entity

Explanation:

A supertype is a form of entity which has one or even more subgroups to relate to. A subtype is an entity type sub-group of entities that is relevant to the organisation and shares similar characteristics or relations which are different from certain sub-groups.

The entity supertype is a different form of entity type which has relationship with one or even more subtypes and includes subtypes '  of specific attributes.

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.