Answer the following question given this paragraph: Like other catalysts, enzymes are not reactants in the reactions they control. They help the reactants interact but are not used up in the reactions. Instead, they may be used over and over again. Unlike other catalysts, enzymes are usually highly specific for particular chemical reactions. They generally catalyze only one or a few types of reactions. Q: Enzymes are a type of what, and as such, they are not reactants in the reactions they control? A:
Choices:
I. hormone.
II. metabolite.
III. neurotransmitter.
IV. catalyst.
IV.