Enzymes are proteins that function as biological catalysts

Steps:

• Recall that enzymes speed up chemical reactions in cells by lowering activation energy.
• Note that enzymes are mostly proteins folded into specific shapes for binding substrates.
• Eliminate options that misidentify enzyme composition or function.
• Select the option matching the precise biological definition.

Why C is correct:

• By biological definition, enzymes are proteins that catalyze reactions in living organisms, increasing reaction rates without being consumed.

Why the others are wrong:

• A: Fats are lipids used for energy storage, not catalytic proteins with shapes for reactions.
• B: This duplicates C exactly, making it non-unique, but the question specifies C as the answer.
• D: Enzymes are proteins but highly sensitive to temperature, which can denature and inactivate them.

Final answer: C