Which term best describes a protein that speeds up chemical reactions in living things?
a. structural protein
b. enzyme
c. amino acid
d. transport protein?

b. enzyme is the correct answer.

Explanation:

The chemical reactions require a catalyst termed as an enzyme to speed up the reaction in living things.

The enzyme speeds up the chemical reactions by giving another reaction pathway of reducing its activation energy.

Enzymes improve the efficiency of chemical reactions.

Enzymes decrease the activation energy of the chemical reaction which is required for a reaction to start.

Thus (b) enzyme is the correct answer.