A test tube contains starch and the enzyme amylase. after 30 minutes, the test for starch is negative and the test for sugar for positive. explain?

The enzyme amylase catalyzes the hydrolysis of starch into sugar. So what happens is the starch molecules are broken down by adding a water molecule between each simple sugar that comprised the original starch. And since no starch was detected, then there was enough time available for the chemical reaction to run to completion.