AQA GCSE Biology

Revision Notes

2.2.5 Required Practical: Food Tests

Food Tests

  • Aim: To use qualitative reagents to test for a range of carbohydrates, lipids and proteins. To include: Benedict’s test for sugars, Iodine test for starch, the emulsion test for lipids and the Biuret reagent for protein
  • You will:
    • Use qualitative reagents to test for the presence of key biological molecules in a range of foods
    • Safely use appropriate heating devices and techniques including the use of a Bunsen burden and a water bath
  • A qualitative food test indicates if a substance is present or absent in a sample (although it doesn’t tell you how much is present)
  • Observations are essential in this practical; you are looking for colour changes in particular which can indicate if a substance is present or absent:

Food test colour changes table

Food test colour changes table, downloadable IGCSE & GCSE Biology revision notes

Preparing a sample

  • Before you can carry out any of the food tests described below, you may need to prepare a food sample first (especially for solid foods to be tested)
  • To do this:
    • Break up the food using a pestle and mortar
    • Transfer to a test tube and add distilled water
    • Mix the food with the water by stirring with a glass rod
    • Filter the mixture using a funnel and filter paper, collecting the solution
    • Proceed with the food tests

Food Tests Method_1, downloadable IGCSE & GCSE Biology revision notes

Food Tests Method_2, downloadable IGCSE & GCSE Biology revision notes

Food Tests Method_3, downloadable IGCSE & GCSE Biology revision notes

Food Tests Method_4, downloadable IGCSE & GCSE Biology revision notes

It is important that you carry out the tests methodically, recording your observations carefully

Important hazards

  • Whilst carrying out this practical you should try to identify the main hazards and be thinking of ways to reduce harm:
    • Biuret solution contains copper (II) sulfate which is dangerous particularly if it gets in the eyes, so always wear goggles
    • Iodine is also an irritant to eyes (wear goggles)
    • Sodium hydroxide in biuret solution is corrosive, if any chemicals get onto your skin wash hands immediately
    • Ethanol is highly flammable; keep it away from the Bunsen burner used in the Benedict’s test (you should turn the Bunsen off completely)
    • And of course, the Bunsen itself is a hazard!

Food Tests Analysis, downloadable IGCSE & GCSE Biology revision notes

Be prepared to explain what molecules are or are not present in a food sample – make sure you know the positive and negative results for each test

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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