(a) What is a substrate? What is an active site? How are they related? (b) Why is an enzyme considered a biological catalyst?

(a) A substrate is a substance that is recognized and binds to an enzyme. An active site is the location on an enzyme where a substrate binds and is the location of the enzymatic reaction. (b) Enzymes are considered biological catalysts because they can be used repeatedly and are not wasted after they catalyze a reaction.