Starch is a polymer of glucose. It exists in two forms amylose and amylopectin. Amylose is formed by linkage of glucose by $\alpha-1,4$ glucose unit. It is a linear polymer. Amylopectin is a branched polymer of glucose where two polymeric chains of glucose of alpha 1,4 glucose unit are linked by $\alpha-1,6$ linkage.

Cellulose is linear homopolysaccharide of $\beta$ - glucose units, which are linked together by $\beta-1,4$ glycosidic bonds.