Enzymes as Biological Catalysts

Steps:

• Recall that enzymes are proteins that accelerate biochemical reactions without being consumed.
• Evaluate option A: Enzymes are not made of lipids; lipids form cell membranes.
• Evaluate option B: Matches the definition of enzymes as protein-based catalysts.
• Evaluate options C and D: Both incorrectly state enzymes are changed by reactions; catalysts remain unchanged.

Why B is correct:

• Enzymes are defined as protein molecules that act as biological catalysts, lowering activation energy to speed up reactions without altering themselves.

Why the others are wrong:

• A: Enzymes are composed of proteins, not lipids.
• C: Enzymes speed up, not slow down, reactions and remain unchanged.
• D: Enzymes speed up reactions but are not changed by them.

Final answer: B