We continue with our unit about macromolecules and turn our focus on carbohydrates. All carbohydrates are formed from simple sugar monomers also called monosaccharides, examples include glucose, fructose, and galactose. Through the process of dehydration synthesis two monosaccharides become a disaccharide like sucrose made of one glucose and one fructose molecule. Start stinging more together and you get polysaccharides such as glycogen made by animals for glucose storage, cellulose by plants as a building material for sturdy cell walls (think the crunchiness of celery), and lastly starch also produced by plants for glucose storage and eaten by animals (including us) for energy (got to love those mashed potatoes).
Starch will react with an iodine solution to turn black. The iodine will react with the coil structure of starch but not with simple sugars or even carbohydrate food sources high in fiber. In the photo below you can see a sample of carbohydrates that we tested for the presence of starch. As a control I have the students start with a known sample of corn starch. Test items included: white potato, wheat bread, saltine cracker, apple, banana, table sugar, white flour, celery, lettuce, Chinese yam, macaroni, flaxseed meal, and a piece of notebook paper. Note that we give the students a wax coated paper plate to work on. Can you guess why? That's one of the post lab questions.
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