Monosaccharides (AQA A Level Biology): Revision Note

Monosaccharides: common examples

Carbohydrates

• Carbohydrates are one of the main carbon-based compounds in living organisms

• All molecules in this group contain carbon, hydrogen and oxygen

• The three types of carbohydrates are:

  • monosaccharides

  • disaccharides

  • polysaccharides

Monosaccarides

• Monosaccharides are simple sugars

• These single units of sugars are monomers which join together to form more complex carbohydrates, such as disaccharides and polysaccharides. 

• 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), and the sugars become the reducing agent

  • Thus, reducing sugars can be detected using Benedict’s reagent 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

• 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 using Benedict’s reagent

  • Example: sucrose