Here's a breakdown:

* Enzymes: Biological catalysts that speed up chemical reactions within living organisms. They are highly specific in their actions.

* Substrate: The molecule or molecules that an enzyme binds to and acts upon.

* Active site: The specific region on an enzyme where the substrate binds.

Think of it like this: an enzyme is a lock, and the substrate is the key that fits into the lock. The enzyme then "unlocks" the substrate, causing a chemical change to occur.