Food tests

• What is the aim of the food test for starch?

  To find out if starch is present in the given types of food.
• What apparatus and chemicals are needed for the starch test?

  • Ten medium-sized test tubes or a test plate
  • Scalpel or razor blade
  • Dropper
  • Small amounts of different foodstuffs (e.g., carrot, rice, grapes, onion, potato, tomato, sweet potato, peanut, pumpkin, egg white)
  • Freshly prepared iodine solution
• How is the iodine solution prepared for the starch test?

  By mixing equal amounts of iodine crystals and potassium iodide, then dissolving in 20ml of water.
• What should be done with the food samples during the starch test?


  Cut a small piece from each food sample and place each in a separate cell of the test plate or test tube.
• What is the control used in the starch test?

  A half spatula-full of starch powder in one of the cells of the test plate/test tube.
• How long should the experiment for the starch test be left undisturbed?

  For 30 seconds.
• What color change indicates the presence of starch in the food test?

  The color changes from brown to blue-black.
• What is the aim of the food test for glucose?


  To demonstrate the presence of glucose.
• What apparatus and chemicals are needed for the glucose test?

  • 2 test tubes
  • 1 beaker
  • A burner
  • Glucose solution
  • Sucrose solution
  • Benedict's solution
• What does a positive result look like in the glucose test using Benedict's solution?


  A change of color from blue to green to yellow and orange/brick red indicates the presence of glucose.
• How should the test tubes be prepared for the glucose test?


  Quarter fill test tube A with glucose solution and test tube B with sucrose solution.
• What is the purpose of boiling the test tubes in the glucose test?

  To facilitate the reaction between the glucose and Benedict's solution.
• What is the aim of the food test for lipids?


  • To determine whether or not fats and oils are present.
• What apparatus and chemicals are needed for the lipid test?

  • Ethanol (or ether)
  • Cooking oil
  • 2 small test tubes
  • Filter paper (or blotting paper/brown paper/news paper)
• What indicates the presence of fats and oils in the lipid test?

  A grease spot stain left on filter paper indicates the presence of fats and oils.
• What is the aim of the food test for proteins using the Biuret test?

  To show if proteins are present or absent in a biological compound.
• What apparatus and chemicals are needed for the protein test?

  • Two test tubes
  • Two beakers
  • Water
  • Spatula
  • Medicine droppers
  • Egg white
  • Starch
  • Biuret solution (10% sodium hydroxide and 1% copper sulfate)
• What color change occurs in the Biuret test when proteins are present?

  The solution changes from blue to purple.
• What does a pink color indicate in the Biuret test?

  A pink color indicates the presence of short chains of polypeptides.
• What is the role of enzymes in digestion?

  • Enzymes break down larger food molecules into smaller units for energy.
  • Each enzyme is specific to the type of molecule it digests (e.g., protein-digesting enzymes vs. starch-digesting enzymes).
• What is the aim of the "hole in the jelly" activity?

  To see how an enzyme can break down proteins and test the claims of washing powders.
• What apparatus is needed for the "hole in the jelly" activity?

  • Two small plastic dishes
  • Gelatine
  • Agar
  • Ordinary washing powder
  • Biological washing powder
• What should be observed in the jelly after applying the biological washing powder?

  A hole should form in the gelatine if the biological washing powder contains enzymes that break down proteins.
• How can the results of the "hole in the jelly" activity validate the claims of biological washing powders?

  If a hole forms in the gelatine under the biological washing powder but not under the ordinary washing powder, the claims are validated.
• What are the expected results for the agar in the "hole in the jelly" activity?

  • The agar should not dissolve under either washing powder.
  • This indicates that agar is not a protein and should not be affected by the biological washing powder.
• What is the focus of the introductory lesson discussed in the material?

  Biochemistry
• What are the two main types of substances in biochemistry?

  Organic and inorganic substances
• What elements do organic substances contain?

  Carbon, oxygen, and hydrogen
• When is a substance considered organic?

  When the carbon molecule is attached to a hydrogen
• Name three examples of organic substances.

  DNA, table sugar, and ethanol
• Why is carbon dioxide considered inorganic despite containing carbon?

  Because it does not have a carbon-hydrogen bond
• What is the key difference between organic and inorganic substances?

  It depends on how the elements are arranged and attached
• What is the most important inorganic compound mentioned?

  Water
• How many hydrogen atoms are in a water molecule?

  Two hydrogen atoms
• What does it mean for water to be a polar molecule?

  It has one side that is slightly negative and another that is slightly positive
• What are hydrogen bonds responsible for in water molecules?

  Cohesion forces between the molecules
• What is the difference between adhesive and cohesive forces in water?

  Adhesive forces allow water to stick to other substances, while cohesive forces allow water molecules to stick to each other
• What is water often referred to as?

  The universal solvent
• Why is water important for chemical reactions in cells?

  It serves as the main medium for these reactions
• What is hydrolysis?

  A process where water is added to break down bonds between molecules