Starch, Glycogen And Cellulose



  • A polysaccharide found in many parts of a plant in the form of small grains.
  • Forms an important component of food and is the major energy source in most diets.
  • Made up of chains of alpha-glucose monosaccharides linked by glycosidic bonds that are formed by condensation reactions.
  • The chains may be branched or unbranched.
  • The unbranched chain is wound into a tight coil that makes the molecule very compact.
  • Structure related to function:
    • It is insoluble and therefore doesn't affect water potential, so water is not drawn into the cells by osmosis.
    • Being large and insoluble, it does not diffuse out of cells.
    • It is compact, so a lot of it can be stored in a small space.
    • When hydrolysed it forms alpha-glucose, which is both easily transported and readily used in respiration.
    • The branched form has many ends, each of which can be acted on by enzymes simultaneously meaning that glucose monomers are released very rapidly.


  • Found in animals and bacteria but never in plant cells.
  • Very similar in structure to starch but has shorter chains and is more highly branched.
  • Sometimes called animal starch because it is the major carbohydrate storage product of animals.
  • In animals it is stored as small granules mainly in the muscles and the liver.
  • The mass of carbohydrate that is stored is relatively small because fat