Question

a student adds more enzyme to a solution with limited substrate. the reaction rate doesnt change. why didnt the rate increase?
the enzyme was denatured
the temperature was too high
the substrate was already used up
the ph was optimal

Explanation:

Enzymes speed up reactions by binding to substrates. If adding more enzyme doesn't increase the reaction rate, it suggests that the substrate is the limiting factor. When substrate is already used up, extra enzymes have nothing to act on, so the rate remains unchanged.

Answer:

The substrate was already used up.