The enzyme responsible for the breakdown of hydrogen peroxide is catalase.

Here's why:

* Hydrogen peroxide (H₂O₂) is a toxic byproduct of cellular metabolism. It can damage cells if allowed to accumulate.

* Catalase is an enzyme found in nearly all living organisms. It catalyzes the decomposition of hydrogen peroxide into water (H₂O) and oxygen (O₂).

* The reaction is very efficient: Catalase can break down millions of hydrogen peroxide molecules per second.

The reaction catalyzed by catalase is:

2 H₂O₂ → 2 H₂O + O₂