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Polysaccharides are long chains of sugars containing monosachharides as building blocks. If it is composed of the same monosaccharide it is called a homopolymer like cellulose. Heteropolymers contains different monosaccharide units. For eg starch

Polysaccharides perform various functions -

(1) Source of energy - polysaccharides are broken down to produce energy in the cells. 

(2) Storage - The food is stored in the form of starch in plants and in the form of glycogen in animals.

(3)Structural support -  Cellulose is the structural material of plants.

(4) Protective covering - Exoskeleton of the arthropods are made of polysaccharide chitin.