AQA GCSE Combined Science: Biology

• Testing for carbohydrates, lipids and proteins

  1. Grind up the food and add distilled water to dissolve some of the food
  2. Test for starch by adding iodine solution (turns blue-black if present)
  3. Test for sugar by adding Benedict's reagent and heating (turns green, yellow or red depending on concentration)
  4. Test for proteins by adding Biuret solution (turns mauve or purple if present)
  5. Test for lipids by adding Sudan Ill (red-stained oil layer floats on water surface if present)