Questions: Where is the active site located? On both the enzyme and the substrate On the substrate On the enzyme

The answer is the third one: On the enzyme.

Explanation for each option:

1. On both the enzyme and the substrate: This is incorrect because the active site is a specific region on the enzyme where the substrate binds. The substrate has a complementary shape to the active site but does not have an active site itself.
2. On the substrate: This is incorrect because the substrate is the molecule upon which the enzyme acts. The substrate binds to the active site of the enzyme, but it does not contain the active site.
3. On the enzyme: This is correct. The active site is a specific region on the enzyme where the substrate binds and the chemical reaction takes place. The active site is typically a pocket or groove on the surface of the enzyme.

Summary: The active site is located on the enzyme.