2. describe an experiment that could test the hypothesis that an enzyme binds to a substrate when it acts. an experiment that could test the hypothesis that an enzyme binds to a substrate when it acts would be

A possible experiment to test an enzyme binding to the substrate to convert in to product(s), could be this one:

STARCH amylase> MALTOSE + MALTOSE

 Amylase is an enzyme, that exists in the saliva, which catalyzes the hydrolysis of the polysaccharide starch to the disaccharide maltose (which is the product).
 If amylase is added to starch (substrate), the starch will be digested by the enzyme, becoming maltose. 

While the experiment happens we see one disappearing and the other appearing (product).

The reaction will happen faster if its at body temperature(37º).