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First, let's get this straight, carbohydrates come in one of three forms:

  • Monosaccharide 
  • Diasaccharide 
  • Polysaccharide

Monosaccharides contain one sugar unit, Diasaccharides two sugar units and polysaccharides multiple sugar units. 


Monoaccharides are single sugar units with the general formula: (CH2O)n2. Monosaccharides have between three and seven carbon atoms, the most common number being six. Monosaccharides are a fast-acting energy source, and are often know as simple carbohydrates as few reactions - if any- are needed for them to be used in cellular respiration. Glucose and Fructose can be found naturally in fruits and honey, but are used extensively in foods such as cake and biscuits. 

The three monosaccharides you need to know are:

  • Glucose
  • Galactose
  • Fructose

Glucose is the main sugar used by cells in respiration. Starch and Glycogen are polymers made up of glucose subunits joined together. When starch or glycogen is digested gluscose is produced, this can be transported in the bloodstream to the cells. 

Galactose occurs in our diet mainly as part of the diasaccharide sugar lactose, found in milk.

Fructose occurs naturally in fruit, honey and some vegetables. This sweetness attracts animals to eat these foods and thus helps with food dipersal. 


Two monosaccharides may join together in a condensation reaction to form a diasaccharide. It is called a condensation reaction due to a water molecule veing released as the two units bind together. The bond that holds the teo molecules together is always a glycosidic bond or link.

Alternatively, this link can be broken through the process of hydrolysis, which is the opposite of a condensation reaction! Adding water! 

Diasaccharides are complex carbohydrates, meaning that your body has to work harder in order to use them. They must be first digested into monosaccharides before being absorbed. This is often considered positive, as although they don't


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