Cellulose

Cellulose is, like amylose, a linear plant polysaccharide made up solely of glucose sugars. Yet thanks to a minor difference in the way the sugars are linked to each other, the two compounds have very different properties: cooking dissolves starch granules but leaves cellulose fibers intact; most animals can digest starch, but not cellulose. Cellulose is a structural support that’s laid down in cell walls in the form of tiny fibers analogous to steel reinforcing bars, and it’s made to be durable. Few animals can digest cellulose, and hay-eating cattle and wood-eating termites can do so only because their guts are populated by cellulose-digesting bacteria. To other animals, including ourselves, cellulose is indigestible fiber (which has its own value).