Glucose is osmotically active substance. If glucose is stored inside our cell, it will draw a large amount of water inside the cell. Similarly when glucose is used up in reactions, a large amount of water will drawn out of the cell. Thus, osmotic concentration of cell will get disturbed if glucose is stored inside cell. On the other hand, starch and cellulose are osmotically inactive substances. These do not disturb the osmotic concentration inside the cell. Hence, starch and cellulose are used for storage instead of glucose.