Biology

The correct answer is D. Enzymes.

Explanation:

Enzymes are a type of protein that act as biological catalysts. They speed up chemical reactions in the body by lowering the activation energy required for those reactions to occur. Enzymes are essential for processes like digestion, metabolism, and cellular functions.

Breakdown of other options:

A. Receptor proteins

Receptor proteins are involved in cell communication and signal transduction, not in catalyzing chemical reactions.