The polysaccharide (lat. amylum, multiple sugar; see under saccharides) is formed in the form of white to yellowish grains in green plants during photosynthesis from carbon dioxide and water and serves as a storage substance in roots, tubers, pith and seeds. The starch grains are built up during the day by sunlight. At night they are processed to obtain the sugar needed for respiration. Grapes contain relatively little starch, which is why they do not ripen after the grape harvest. Starch is particularly abundant in cereal grains, potatoes and bananas. It is one of the most important human foods (bread and flour) and can also be fermented into alcohol.