Starch is a carbohydrate polymer made up of glucose units linked together by alpha-1,4 and alpha-1,6 bonds. It is the main storage form of carbohydrates in plants and can be deposited as tiny granules in the stems (pith), roots, seeds and fruits. The granules are small grain-like particles in which starch molecules are deposited and stored by plants. In the case of wheat, corn or rice, the starch granule is located in the endosperm of the seed. In general, starch is made up of two glucan fractions, amylose and amylopectin, that differ in proportion depending on the botanical source. Some starch sources contain approximately one hundred percent amylopectin such as those from waxy corn, wheat, barley, rice, potato or sorghum. Others contain fifty percent or more amylose as in high amylose corn or barley. Starch is a partially crystalline polymer that can be modified physically, chemically and enzymatically to alter its properties. Starches sold in commerce are principally derived from cereal grains (corn, wheat, rice), roots/tubers (potato, tapioca) and pulses (pea).