Answer:
Zymase is acting as a catalyst
Explanation:
Zymase is an enzyme that is naturally produced in yeast. Enzymes are biological catalysts that speed up the rates of reactions in living things.
Zymase catalyses the breakdown of glucose into ethanol and carbon dioxide, which causes the bread to rise.
Zymase speeds up this reaction, but is not physically changed itself. Therefore, it is a catalyst.
Actually, zymase represents a collection of enzymes in yeast, not just one!
