Biology AS revision


Biological molecules are organic molecules made up primarily of carbon, hydrogen, nitrogen and oxygen. There are 3 groups of molecules; Carbohydrates, proteins and lipids.


  • Carbohydrates contain carbon, hydrogen and oxygen.
  • There are 3 types of carbohydrates; monosaccharides, disaccharides and polysaccherides. 
  • Monosaccharide (monomers) and disaccharide (dimers) are simple sugars. Monosaccharides include glucose, fructose and ribose. Disaccharides include Maltose, sucrose and lactose.
  • Polysaccharides are complex sugars such as starch, glycogen and cellulose.
  • Their main functions are to act as a source of energy in both plants and animals, and to play a structural role in plant cell walls.


  • Monosaccharides are used for energy and building blocks for other carbohydrates.
  • (CH2O)n 
  • Triose = C3 H6 O3
  • Pentose = C5 H10 O5 (ribose)
  • Hexose = C6 H12 O6 (glucose + fructose)
  • Some compounds can have the same chemical formula but different structural formula.This is called structural isomerism. An example of this is glucose. in which it has alpha or beta structure.


  • This is when two monosaccharides are bonded together by a glycosidic bond, which is a condensation reaction due to the elimination of water. Hydrolysis is used to break this bond.
  • The 3 most…


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