Required Practical: Food Tests (AQA GCSE Biology)

Revision Note

Lára Marie McIvor

Written by: Lára Marie McIvor

Reviewed by: Lucy Kirkham

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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

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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

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Food Tests Method_2, downloadable IGCSE & GCSE Biology revision notes

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Food Tests Method_3, downloadable IGCSE & GCSE Biology revision notes

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Food Tests Method_4, downloadable IGCSE & GCSE Biology revision notes

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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

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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

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Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Biology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

Lucy Kirkham

Author: Lucy Kirkham

Expertise: Head of STEM

Lucy has been a passionate Maths teacher for over 12 years, teaching maths across the UK and abroad helping to engage, interest and develop confidence in the subject at all levels.Working as a Head of Department and then Director of Maths, Lucy has advised schools and academy trusts in both Scotland and the East Midlands, where her role was to support and coach teachers to improve Maths teaching for all.