2. The most abundant polysaccharide in nature , a rigid, colorless, unbranched, insoluble, long chain polymer forming the skeleton of most plant structures and of plant cells.
3. A carbohydrate polymer of the simple sugar glucose.
4. The chief constituent of the cell walls of plants and of wood, cotton, hemp, paper, etc.
It is found in the cell walls of plants and green algae, as well as dinoflagellates (any of numerous minute, chiefly marine protozoans). Cellulose is said to be the most abundant compound on earth that is manufactured by living things.
Research in biofuels is striving to refine plant cellulose in the form of corn husks instead of corn kernels, bagasse (dry dusty pulp that remains after juice is extracted from sugar cane) instead of cane sugar, and agricultural and industrial wastes of all kinds; such as, wood chips, the remains of paper mills, and fallen tree leaves.
Many creatures, including termites and cattle, use gut microbes to break down plant cellulose in their digestive systems where microbes do it by secreting enzymes called cellulases.