In cellular metabolism, organic catalysts that increase the rate of biochemical reactions without being consumed or permanently changed are called:

Introduction / Context:
Cells rely on catalysts to speed up vital reactions at physiological temperatures. The precise term for these biological catalysts helps distinguish them from small helper molecules and from the substances they act upon.

Given Data / Assumptions:

• The catalysts are organic and biological in origin.
• They increase reaction rates without being consumed or permanently altered.
• The context is general cellular metabolism.

Concept / Approach:
An enzyme is a biological macromolecule (usually a protein; sometimes RNA in the case of ribozymes) that accelerates reaction rates by lowering activation energy while emerging unchanged after each catalytic cycle. Enzymes bind substrates at active sites and often require cofactors or coenzymes, but the defining property is catalysis without permanent change to the catalyst itself.

Step-by-Step Solution:

Verification / Alternative check:
Classic enzyme kinetics (Michaelis–Menten) demonstrates turnover where the enzyme participates in intermediate complexes but is regenerated each cycle.

Why Other Options Are Wrong:
Coenzymes: Small organic cofactors that assist enzymes but are not themselves the catalytic protein scaffold. Substrates/Reactants: The molecules transformed during the reaction; they are consumed or changed.

Common Pitfalls:
Confusing coenzymes (e.g., NAD+, FAD, CoA) with enzymes. Coenzymes can be altered during a cycle but are ultimately recycled; however, the catalyst proper is the enzyme macromolecule.

Final Answer:
enzymes