A student set up an experiment to investigate the digestion of starch. They mixed a starch suspension with amylase and, every 2 minutes, removed a drop and tested it with iodine solution. They recorded the time taken for the iodine to stop turning blue-black.
Explain why the iodine solution eventually stopped turning blue-black.
[2]
The student wanted to check that it was the amylase, and not the water it was dissolved in, that caused the change.
Suggest a suitable control experiment and the result they would expect.
[2]
State one variable that should be kept constant in this investigation.
[1]