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The amylase in starch forms helices where iodine molecules assemble forming a black colour. When starch is broken down into smaller carbohydrate units, the black colour is not produced. Whereas for the milk, cheese celery and apple does not change its colour when adding the iodine solution because there are no starch in it.
Then after I finished testing for the Iodine solution, I had to throw the foods and clean the white tile and test tubes and bring in the new foods again for the Sodium Hydroxide and Copper Sulphate solution. It contained protein in milk and in cheese these is because both of them are from a dairy product resulting that when you add the above solutions it changes its colour to purple. For the apple,celery, biscuit and bread they do not change colour as they stay the same because they do not contain any sorts of fat. Further to that they do not react with those
Then after I finished testing for the Iodine solution, I had to throw the foods and clean the white tile and test tubes and bring in the new foods again for the Sodium Hydroxide and Copper Sulphate solution. It contained protein in milk and in cheese these is because both of them are from a dairy product resulting that when you add the above solutions it changes its colour to purple. For the apple,celery, biscuit and bread they do not change colour as they stay the same because they do not contain any sorts of fat. Further to that they do not react with those