How would someone measure the rate of a reaction by using amylase as the enzyme and starch substrate? - amylase catalyses the breakdown of starch. So you time how long it takes for the starch to dissappear - to do this - regularly take a drop of the amylase and starch mixture - and put it into a drop of iodine solution on a spotting tile. Record the colour change - it will true blue-black if starch is present. Note the time when the iodine solution no longer turns blue-black - the starch has then been broken down by the amylase. You can use times to compare reaction rates under different conditions.