Since plants do not have bones like we do to hold them up, they need to have another means of support. What plants use for structure is a polysaccharide known as cellulose. Cellulose is found in the rigid cell walls and is actually the most abundant organic compound on Earth! Similar to starch, cellulose is a polymer of glucose. In cellulose, the glucose molecules are in the beta position. This means that every glucose molecule is upside-down in comparison to the neighboring glucose molecules. Cellulose resembles a rod in that it is straight and never branched. Two neighboring and parallel cellulose molecules can bond their hydroxyl groups to form microfibrils. Microfibrils are a strong building material for plants and are even useful for humans. Cellulose is one of the main components of paper and the only ingredient in cotton.
Although cellulose is such a vital part in plants, and plays an important roles in humans’ lives also, animals (including humans) cannot digest it. Cellulose, instead, acts as fiber to help food pass through the digestive tract. Cellulose, just like other foods, is eliminated from our system with the feces. On food packages, insoluble fiber is mainly referring to cellulose.