How are carbohydrates classified?

1 Answer


There are several methods of classification, but the most common method is based on the number of sugar units they contain.


Number of Sugar Units

  • Monosaccharides — 1 unit, e.g. glucose
  • Oligosaccharides —2 to 9 units
    o Disaccharides — 2 units, e.g. sucrose
  • Polysaccharides — ≥ 10 units, e.g., starch

Other methods of classification include:

Number of Carbon Atoms

  • 5 = pentose, e.g. ribose
  • 6 = hexose, e.g., glucose

Functional Groups

  • Aldoses — contain an aldehyde group, e.g. glucose
  • Ketoses — contain a ketone group, e.g. fructose

Chemical Properties

  • Reducing — react with Fehling's solution or Tollens' reagent, e.g. glucose, lactose
  • Non-reducing — no reaction with Fehling's solution or Tollens' reagent, e.g. sucrose, all polysaccharides

Polysaccharides have other classifications.


  • Linear chains, e.g. amylose
  • Branched chains, e.g. glycogen


  • Storage, e.g. starch, glycogen
  • Structural, e.g. starch


  • Homopolysaccharides — contain only single monosaccharide units, e.g. starch
  • Heteropolysaccharides — contain different kinds of monosaccharides, e.g. hyaluronic acid (N-acetylglucosamine and glucuronic acid)