Biochemical tests

• Who is the instructor for the A-level biology lesson?

  1. Ik
• What is the focus of the lesson?

  Biochemical tests for biological molecules
• What types of biological molecules are tested in this lesson?

  Carbohydrates, proteins, and lipids
• Which polysaccharide test is covered in this lesson?

  Starch test
• What reagent is used to test for starch?

  Iodine
• What color change indicates the presence of starch?

  Brown-orange to blue-black
• What is the reagent used for the reducing sugars test?

  Benedict's solution
• What color indicates a positive result for reducing sugars?

  Blue to orange
• What does a negative result for reducing sugars look like?

  Remains blue
• What does the color change in the reducing sugars test indicate?

  Concentration of reducing sugar
• Why does the reaction occur first at the top of the solution?

  Due to convection currents
• What is the only non-reducing sugar mentioned?

  Sucrose
• What is the first step in testing for non-reducing sugars?

  Perform the Benedict's test
• What must be done to sucrose before retesting with Benedict's solution?

  Perform acid hydrolysis
• What happens during acid hydrolysis of sucrose?

  It breaks glycosidic bonds
• What is the result of boiling sucrose in acid?

  It converts to glucose and fructose
• What color change indicates a positive result for non-reducing sugars after hydrolysis?

  Blue to brick red
• What reagent is used to test for proteins?

  Biuret reagent
• What color indicates a positive result for proteins?

  Purple-lilac color
• What is the first step in testing for lipids?

  Dissolve lipid in ethanol
• What indicates a positive result for lipids?

  White emulsion
• What are the steps for testing reducing sugars?

  1. Add Benedict's reagent.
  2. Heat the mixture.
  3. Observe color change.
  4. Interpret results based on color.
• What are the steps for testing non-reducing sugars?

  1. Perform Benedict's test.
  2. If negative, boil with acid.
  3. Neutralize with alkaline.
  4. Retest with Benedict's reagent.
  5. Observe color change.
• What are the steps for testing proteins?

  1. Add Biuret reagent.
  2. Observe color change.
  3. Interpret results based on color.
• What are the steps for testing lipids?

  1. Dissolve lipid in ethanol.
  2. Add distilled water.
  3. Observe for white emulsion.
• What are the positive test results for each biomolecule?

  • Lipids: White emulsion
  • Proteins: Purple-lilac color
  • Starch: Blue-black color
  • Reducing sugars: Color varies (green to brick red)