4°C

Prof. Wilson: Let's find out based on your results. Are you sure that such a low temperature is the optimal temperature for an enzyme found in the human body? What is happening to the colour change at this temperature? 

James: Oh.. at 4°C the dark-blue colour has remained throughout the experiment. So, this cannot be the optimal temperature!

You: I understand now, it makes sense. I would like to give it another try. 

                 Results: Optimal temperature for amylase activity

What is the optimal temperature for amylase?