Here's why:

* Functional Proteins: These proteins perform specific tasks within a cell or organism. Enzymes are excellent examples because they catalyze (speed up) biochemical reactions. They are essential for a wide range of processes like digestion, metabolism, and DNA replication.

Let's differentiate from the other options:

* Hormones: These are chemical messengers produced by glands that travel through the bloodstream to target cells and tissues. While some hormones are proteins, not all enzymes are hormones.

* Structural Proteins: These proteins provide shape and support to cells and tissues. Examples include collagen and keratin. While some enzymes can have structural roles, their primary function is catalysis.

In summary, enzymes are functional proteins because their primary role is to facilitate biochemical reactions within living organisms.