Biology Paper 1 - Required Practical - Food Tests

Question 1

Methodology

Answer 1

• Take food sample and grind this with distilled water using a mortar and pestle - in order to make a paste.
• Transfer the paste to the beaker and add more distilled water. Stir so the chemicals in the food dissolve in water.
• Filter solution to remove suspended food particles.

Question 2

Testing For Starch

Answer 2

• Place 5cm^3 food solution into a test tube and add a few drops of Iodine solution.
• If starch is present the iodine will go from
  Orange - Blue-black.
• If no starch = stays Orange.

Question 3

Testing For Sugars

Answer 3

• Place 5cm^3 of food solution into a test tube and add 10 drops of Benedict’s solution to the test tube.
• Place the test tube into a beaker half-filled with hot water (75 degrees) from a kettle.
• Leave for 5 mins
• Blue - Green = small amount of sugar
• Blue - Yellow = More sugar present
• Blue - Brick-red = Lots of sugar present.

Benedict’s solution only works for reducing sugars like glucose - will not work for non-reducing sugars like sucrose.

Question 4

Testing For Protein

Answer 4

• Place 2cm^3 of food solution into a test tube and add 2cm^3 of Biuret solution.
• If protein is present, the solution goes :
  Blue - Purple or Lilac

Question 5

Testing For Lipids

Answer 5

You do NOT filter the solution when testing for lipids (this is ONLY for lipids) because lipid molecules can stick to filter paper

• 2cm^3 Food solution into a test tube and add a few drops of distilled water and a few drops of ethanol (same volume)
• Gently shake the solution.
• If lipids are present :
  A white cloudy emulsion forms

Ethanol is flammable - make sure no naked flames are present