AQA AS Biology

Revision Notes

1.1.3 Monosaccharides

Monosaccharides: Common Examples

  • 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 Benedict’s test as they reduce the soluble copper sulphate to insoluble brick-red copper oxide
  •  Examples of reducing sugars include: glucose, fructose and galactose
    • Fructose and galactose have the same molecular formula as glucose however they have a different structural formula
    • The different arrangement of atoms in these monosaccharides gives them slightly different properties
  • 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

Exam 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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