CARBOHYDRATE LAB Objective: To establish test protocols for the detection of starch and sugar, and to understand the limitations of each test. Materials: Iodine solution ** avoid eye/skin contact, stains skin and clothing (it stains) ** Benedict’s solution ** avoid eye/skin contact Small beakers (100 - 250 ml) Test tubes Test tube rack Test tube holder Hot plate - Beaker of water (about 90o C) Starch solution (positive control for starch) Glucose solution (positive for reducing sugars) Solutions of fructose, sucrose, lactose, maltose, methyl cellulose, etc... Plant tissues (potato, carrot, radish, apple, orange, etc... Other materials to be tested PREPARE A SIMPLE TABLE FOR RECORDING YOUR RESULTS TEST FOR STARCH Put several drops of iodine solution into a small test tube containing a small amount of starch solution.....describe the results of this positive control. (Note: Use white paper for a background for better color detection.) Repeat with a test tube containing a small amount of water....describe the results of this negative control. Test for the presence or absence of starch in a variety of materials in a Petri dish. Note: Fresh food will not show results immediately as does the starch solution. Give unknowns time for the starch solution to diffuse into cells/tissues. Prepare a table for your data (“Iodine test for starch”) TEST FOR SUGARS - Note: Benedict’s test will be positive only for ‘reducing’ sugars (simple aldehyde sugars). Reducing sugars are able to donate free electrons to the copper compound in the test reagent, resulting in a color change. Glucose is a reducing sugar. Put about 10 drops each of sugar solution and a few drops of Benedicts solution into a test tube. Place the tube into hot (almost boiling) water for 3-5 minutes. ** Glucose is positive; water is negative ** Test other sugars, starch solution, soft drinks, etc... Try diluted solutions of known positives. Prepare a table for your data (“Benedict’s test for sugar”) QUESTIONS What are the limitations of the iodine test? What are the limitations of the Benedict’s test?