Question

the spot on the enzyme where the substrate fits:
catalyst
enzyme
activation energy
active site

Explanation:

To solve this, we analyze each option:

• Catalyst: A substance that speeds up reactions, not the enzyme - substrate binding site.
• Enzyme: The biological catalyst itself, not the specific binding spot.
• Activation Energy: The energy needed to start a reaction, not related to the binding site.
• Active Site: By definition, the region on an enzyme where the substrate binds.

Answer:

D. Active Site