How do the results of the iodine test indicate that hydrolysis of starch occurred?

Answer 1

Here is some more simple information with a clear explanation:

Starch agar is a simple nutritive medium with starch added. Since no color change occurs in the medium when organisms hydrolyze starch, we add iodine to the plate after incubation. Iodine turns blue, purple, or black (depending on the concentration of iodine) in the presence of starch. A clearing around the bacterial growth indicates that the organism has hydrolyzed starch.

Iodine has been added to this starch agar plate. The zone of clearing surrounding Bacillus megaterium and Bacillus subtilis indicate that both were able to hydrolyze starch.

Answer 2

Did you do the iodine test before and after some treatment that should have resulted in hydrolysis of starch? What were the colors of the two samples after adding iodine? What does iodine react with, and what color does it produce?

If you think a bit about what you did and what you observed in the experiment, you should be able to answer your own question.