2.1 - Digestion

• Test for glucose

  • Add benedicts solution to a food sample
  • Heat the test tube
  • Change from blue to brick red if sugar is present
• Test for starch

  • Add iodine solution to a food sample
  • Will change from yellow / orange to a blue / black colour if starch is present
• Test for protein

  • Add biuret reagent to a food sample
  • Will change from blue to lilac if protein is present
• Test for lipids(fat)

  • Add ethanol to a food sample and shake
  • Add water
  • Colour will change to a white emulsion if fat is present
• Name the three parts of the human digestive system that produce amylase.

  • salivary gland in the mouth
  • small intestine
  • pancreas
• Explain how amylase breaks down starch.

  Answer in terms of the ‘lock and key theory’.

  1. starch / substrate binds to active site
  2. because the shape of active site and substrate are complementary
  3. a chemical reaction occurs to produce smaller molecules
• Starch has to be digested because large insoluble molecules can't be absorbed and starch is too large and is insoluble