Starches are biologically significant because they are insoluble in water and can therefore serve as storage areas for glucose. Plants convert excess glucose into starch for storage. As starch is a common storage compound in plants, it is the main carbohydrate in human diet.
Animals store excess glucose by polymerising it to form glycogen. The structure of glycogen is similar to that of amylopectin, although the branches in glycogen tend to be shorter and occur more frequently.
Glycogen is biologically significant as we eat relatively small amounts of it and it is used as our main carbohydrate storage compound - we store small amounts in our liver and muscles. Glycogen is broken back down into glucose when energy is needed in a process called glycogenolysis.
Research has shown that intense exercise and a high-carbohydrate diet can increase the reserves of glycogen in the muscles and thus may help people exercising work their muscles somewhat longer and harder than normal. But in most cases, a high-carbohydrate diet without much exercise leads to increased deposits of fat.
Cellulose is biologically significant as it is the major structural material of which plants are made. Wood is largely cellulose while cotton and paper are almost pure cellulose. Cellulose forms the bulk of the fibre in a human diet that is necessary to maintain a healthy colon and bowel.
Like starch, cellulose is a polysaccharide with glucose as its monomer. However, cellulose differs greatly from starch in its properties.
There are other polysaccharides which effect related compounds and organisms- they are: Callose which is another polymer of glucose found in plants; Inulin which is found in some plants and acts as a storage carbohydrate; Pectins which are found in plant cellulose cell walls; Chitin is similar to the structure of cellulose and is found in fungal hyphae and forms the exoskeleton in arthropods; Murein which is found in the cell walls of bacteria and Mucopolysaccharides found in bone and cartilage.
Hence, Polysaccharides are extremely important in plants and animals because they help the organisms to function properly and survive.