Answer:
The open area where the substrate is attached to an enzyme is called the active site.
Step-by-step explanation:
The active site of an enzyme corresponds to the place where the tertiary structure of this molecule leaves a free space to couple the substrate and be able to catalyze a chemical reaction.
Since the enzyme-substrate complex functions as a key lock system, the active site has a three-dimensional configuration that only admits certain molecules as substrate, which determines its specificity.