Question

the substance enzymes act upon
activation energy
enzyme
acid
substrate

Explanation:

To solve this, we recall the definition of the substance that enzymes act upon. Enzymes are biological catalysts, and the substance they act on is called a substrate. Activation energy is the energy needed for a reaction, an enzyme is the catalyst itself, and an acid is a different type of chemical substance. So the correct term for the substance enzymes act upon is substrate.

Answer:

D. Substrate (assuming the options are labeled A: Activation Energy, B: Enzyme, C: Acid, D: Substrate; if the original options have different labels, adjust accordingly, but based on the given choices, the correct one is Substrate)