In this activity, you fill a dialysis bag with a sugar/starch solution and immerse the bag in a dilute iodine solution. Water, sugar, starch, and iodine molecules will all be in motion, and each molecule will move to a region of its lower concentration, unless the molecule is too large to pass through the membrane. Your task is to determine relative size of the various molecules and gather evidence of molecular movement.

Hint: One piece of information that will help you is to recall that when iodine comes in contact with starch, it changes from an orange-brown color to blue-black.

For more information, review the section on Concentration Gradient.

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