They have a general formula (C₆H₁₀O₅)n where n represent any number. They are carbohydrates with high molecular weight. When conditions are favourable, monosaccharide and disaccharide link up with the help of glycosidic bonds to form a linear, branch or circular multi-sugar called polysaccharide. They can be polymers of pentoses called pentozanes, if they are all hexose sugar they are called hexozanes and if only glucose molecules are present, they are called glucozanes.

Polysaccharides include starch which is the storage form of carbohydrates in plants, glycogen in animals, cellulose which form the cell wall of plants, chitin which form the hexose skeleton of arthropods. They are formed from the condensation of numerous monosaccharide such as glucose

1. STARCH

It is a polymer of alpha-glucose molecules and two types exist namely amylose and amylopectin.

1. Amylose

This is a straight chain polymer made up of several thousand of alpha glucose molecules. It can be called or compact.

1. Amylopectin

These are starch molecules with the presence of many branches.  These branches are formed by 1,6 glycosidic bonds. It has almost 2 times as many glucose molecules as amylose.

Fig:

2. GLYCOGEN

This is the storage form of carbohydrate in animals. It occurs in great quantity in the liver and muscles. They are lony chain polymers of glucose molecules. Glycogen is similar to amylopectin but for the fact it shows more branches. Hence it is known to be more stable than starch.

3. CELLULOSE

This is the most important structural polysaccharide. It is found the plant cell. It is made up of a linear chain or linear polymer consisting of beta-glucose units; which form a diasaccharide units known as callubroses. This linear chain presences many OH groups that projects outward from each chains and in all directions. These feature enable them to form hydrogen bords zith neighbouring parallel chains. These account for the stability of cellulose and also enable it to save as a structural molecule.

When two molecules of B-glucose line up. The OH group on carbon atom 1 can only line up alongside the OH group on carbon atom 4 if one of the molecule rotates at 180⁰ to the other this is because. The OH group on carbon atom 1 projects above the ring and the OH group on carbon atom, 4 project below the ring. Hence, there is a rotation of successive residue for condensation to take place.