Experiments

• Biological molecule tests (food tests)

  1. Obtain samples (fruit juice, egg whites, starch, cooking oil, distilled water)

  2. Add iodine solution drop-wise to samples

  3. Add biuret solution drop-wise to samples

  4. Add Benedict's reagent to samples, heat in water bath

  5. Add ethanol, shake, then add water to samples

  6. Add DCPIP to samples, observe color change
• Iodine test


  • Tests for presence of starch
  • Turns blue-black if starch is present
• Biuret test


  • Tests for presence of proteins
  • Turns purple/lilac if proteins are present
• Benedict's test


  • Tests for presence of reducing sugars (e.g. glucose)
  • Turns green, yellow, orange if reducing sugars are present
• Ethanol emulsion test


  • Tests for presence of fats
  • Forms a white emulsion if fats are present
• DCPIP test


  • Tests for presence of vitamin C
  • DCPIP turns colorless if vitamin C is present
• Distilled water used as a control
• The independent variable is the thing that changes during the experiment, while everything else stays the same.
• Benedict's reagent


  Can be used to test for the presence of reducing sugars, such as monosaccharides and some disaccharides (NOT sucrose)
• Positive reducing sugar test with Benedict's reagent


  1. Blue → green → orange → brick red once heated

  2. Semi-quantitative sugar concentration can be determined by final color

  
• Negative reducing sugar test with Benedict's reagent


  Solution remains blue

  
• Test protocol for a reducing sugar (e.g. glucose)

  1. Add Benedict's solution into sample solution in test tube

  2. Heat >80°C in water bath for 5 minutes

  3. Take test tube out of water bath and observe the color

  4. A positive test will show a color change from blue to orange or brick red

  
• Iodine solution


  May be added to samples/solutions to test for starch (plant polysaccharide)

  
• Starch test with iodine


  1. Add drops of iodine solution to the food sample

  2. A positive test will show a color change from orange-brown to blue-black

  
• Ethanol emulsion test


  • Can be used to test for fats
  • Fats are insoluble in water BUT soluble in ethanol
• Test for lipids with ethanol

  1. Food sample is mixed with 2cm3 of ethanol and shaken

  2. The ethanol is added to an equal volume of cold water

  3. A positive test will show a cloudy emulsion forming
• Biuret test


  • Can be used to test for the presence of proteins
  • Dilute copper sulfate and dilute potassium hydroxide are added to the sample

  
• Test for protein with Biuret


  1. Add drops of Biuret solution to the food sample

  2. A positive test will show a color change from blue to violet / purple

  
• Biological Bingo words


  • Monosaccharide
  • Lipid
  • Amino Acid
  • Disaccharide
  • Glucose
  • Maltose
  • Fatty acid
  • Polysaccharide
  • Proteins
  • Glycogen
  • Starch
  • Glycerol
  • Fats
  • Oils
  • glycerol
  • R group
  • Sucrose
  • Enzymes
  • Antibody
  • Carbon
  • Nitrogen
  • Insoluble
  • Energy
  • Cellulose