A biological catalyst that speeds up the rate of a chemical reaction without being consumed in the process.

Here's why:

* Catalyst: Enzymes facilitate chemical reactions by lowering the activation energy required for the reaction to occur. They don't change the equilibrium of the reaction; they just make it happen faster.

* Biological: Enzymes are proteins (with a few exceptions, like ribozymes which are RNA molecules). They are produced by living organisms.

* Not consumed: Enzymes are not used up during the reaction. They can be reused over and over again to catalyze the same reaction.

Let me know if you'd like to know more about how enzymes work!