Final answer:
Catalase is the exoenzyme that breaks down hydrogen peroxide (H₂O₂) produced by phagocytes into water and oxygen, preventing the digestion of the engulfed bacterium.
Step-by-step explanation:
The enzyme that is an exoenzyme and breaks down H2O2 produced by phagocytes into water and oxygen, preventing digestion of the engulfed bacterium, is catalase. When phagocytes, such as macrophages of the immune system, engage in phagocytosis to engulf pathogens, they produce reactive oxygen species like hydrogen peroxide. Catalase is crucial because it protects the bacteria from the harmful effects of H2O2 by breaking it down before it can be used by the phagocyte to kill the bacterium.
In contrast, enzymes like lipase and protease have different functions. Lipase initiates the breakdown of fats in the mouth, while proteases are involved in the digestion of proteins into smaller peptides.