A monosaccharide is a simple sugar made up of carbon oxygen and hydrogen, usually in the form of CnHnOn ( the n being the number of each type of element.) The most common monosaccharide is glucose which the equation is C6H12O6.
Glucose is commonly used in the human body as an energy source as a by product of respiration. The Glucose can be stored as glycogen and when the body needs it, it can be converted easily back into glucose for use at the muscles etc.
The structure of these monosaccharides are simple, hence why they are simple molecules.
Each glucose unit is known as a monomer and is capable of linking to others by glycocidic bonds. This is a bond where 2 alpha glucose molecules have bound together at the OH parts of their structure.
The reaction that binds them is called a condensation reaction. This type of reaction is called this because when reacted, the 2 molecules of glucose that have bound together, join and give off H2O (water). Hence the meaning of the condensation.
To seperate these molecules it would take hydrolisis. This is where a Water molecule is added, to replace the one lost during the condensation reaction. The seperated glucose molecules are monomers again.
This is almost the same as disaccharides apart from the fact that the polysaccharide can have as many glucose molecules as "it" wants, hence being called polysaccharide, as poly means many.
Starch is a polysaccharide of alpha glucose.
Uses of polysaccharides
Starch- this is stored in organisms as a future energy source, it is a very complex molecule and therefore is not soluble allowing for the easy storage of energy for later.
Glycogen- This is stored in the liver and can be converted into glucose at a moments notice to send around the body providing energy for the muscles etc. This is also a highly complex molecule made up of a lot of Glucose molecules. It is also ,like starch, insoluble and therefore will not dissolve in water.
Cellulose- has long chains and branches which allow for tough protection of the outside of a plant cell, thhis forms the basis of the cell wall.
Pectins- These polysaccharides are used alongside the cellulose in the cell wall. They are bound by a calcium pectate and are used to bind cells together.