A complex carbohydrate made by plants is cellulose. Complex carbohydrates are sugars made up of smaller sugar molecules. Complex carbohydrates are also called polysaccharides. Cellulose is made up of subunits of a monosaccharide, or simple sugar, called glucose.
The cellulose in plants is found in plant cell walls. Cellulose gives plant cells a rigid structure. This complex carbohydrate cannot be broken down by the human digestive system. Animals like horses and cows can break down cellulose with the help of symbiotic bacteria living in their digestive systems. Cellulose is an important component of dietary fiber.
The other complex carbohydrate made by plants is starch. Starch is a storage form of glucose. Like cellulose, starch is made of glucose subunits, but unlike cellulose, starch can be broken down by enzymes in the human digestive system.