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First exams 2025

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Reducing & Non-Reducing Sugars (CIE AS Biology)

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Cara Head

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Reducing & Non-Reducing Sugars

  • Sugars can be classified as reducing or non-reducing; this classification is dependent on their ability to donate electrons
  • Reducing sugars can donate electrons (the carbonyl group becomes oxidised), the sugars become the reducing agent
    • Thus reducing sugars can be detected using the Benedict’s test as they reduce the soluble copper sulphate to insoluble brick-red copper oxide
    • Examples: glucose, fructose, maltose
  • Non-reducing sugars cannot donate electrons, therefore they cannot be oxidised
    • To be detected non-reducing sugars must first be hydrolysed to break the disaccharide into its two monosaccharides before a Benedict’s test can be carried out
    • Example: sucrose

OILRIG, downloadable IGCSE & GCSE Biology revision notes

The mnemonic to remember the definitions for oxidation and reduction

Examiner Tip

Become familiar with the OILRIG mnemonic to remember what happens to a molecule when electrons are lost from it (oxidation) or gained by it (reduction). 

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Cara Head

Author: Cara Head

Expertise: Biology

Cara graduated from the University of Exeter in 2005 with a degree in Biological Sciences. She has fifteen years of experience teaching the Sciences at KS3 to KS5, and Psychology at A-Level. Cara has taught in a range of secondary schools across the South West of England before joining the team at SME. Cara is passionate about Biology and creating resources that bring the subject alive and deepen students' understanding