starch a constituent of plants, is the most important form of carbohydrate in our food, and supplies most of the energy in the diet of most peoples. Pure starch, when cooked, is easily and almost completely digestible, turning to sugar. Actual plant starches contain a certain amount of cellulose, another carbohydrate which is not digested by humans but supplies essential dietary fibre.
In plants starch acts as a food reserve. It is stored in various places: seeds, as in cereals; tubers, as in potatoes and yams; or stems, as in sago.