Cellulose

Like starch, cellulose is composed of a long chain of at least 500 glucose molecules. Cellulose is thus a polysaccharide (Latin for "many sugars"). Several of these polysaccharide chains are arranged in parallel arrays to form cellulose microfibrils. The individual polysaccharide chains are bound together in the microfibrils by hydrogen bonds. The microfibrils, in turn, are bundled together to form macrofibrils (Figure 1).

The microfibrils of cellulose are extremely tough and inflexible due to the presence of hydrogen bonds. In fact, when describing the structure of cellulose microfibrils, chemists call their arrangement "crystalline," meaning that the microfibrils have crystal-like properties. Although starch has the same basic structure as cellulose—it is also a polysaccharide—the glucose subunits are bonded in such a way that allows the starch molecule to twist. In other words, the starch molecule is flexible, while the cellulose molecule is rigid.