Cellulose is a polysaccharide (a form of carbohydrate) that has a structural role in animals and plants. In plants, cellulose is the compound that gives rigidity to the cells. The bonds between each cellulose molecule are very strong, which makes cellulose very hard to break down.
Because there are so many plants in the world (think of all the flowers, trees, weeds, grasses, vines, and bushes), cellulose, which is found in every cell of every plant, is the most abundant organic compound on earth.
Most animals can’t digest cellulose because it is so hard to break down. Animals that eat only plants (herbivores) have special sacs in their digestive system to help break down cellulose.
Humans can’t digest cellulose either. (The proof is in the toilet the day after you eat corn, for example.) Because cellulose passes through your digestive tract virtually untouched, it helps maintain the health of your intestines. One way cellulose helps the intestines is that it clears materials from the intestinal walls, keeping them clear, which may help to prevent colon cancer. Cellulose is the fiber (or roughage) of which your cereal box says you need more.
Animals have only membranes surrounding their cells. Plants have walls surrounding theirs. Cell walls contain cellulose, and cellulose with its rigid structure gives “crunch” to vegetables when you cut or bite into them. Think celery. There are some other structural forms of carbohydrates, but usually they are combined with proteins.
