Theory question 103
Food Substances and Enzymes(a) List five classes of food other than carbohydrates
(b) Explain why glucose is taken by an athlete ready for a race rather than corn meal
(c) Describe the test for starch
Show the model answer
(a) Proteins; fats and oils (lipids); vitamins; mineral salts; water; (roughage).
(b) Glucose is a simple sugar that needs no digestion; it is absorbed directly into the blood and quickly respired to release energy. Corn meal contains starch, which must first be digested to glucose, so its energy is released slowly.
(c) Put a little of the food (or a few cm3 of its solution) in a test tube or on a tile; add a few drops of iodine solution; a blue-black colour shows that starch is present (the iodine stays brown if starch is absent).
Glucose = quick energy because no digestion is needed.