In photosynthesis, plants use light energy to produce glucose from carbon dioxide. The glucose is stored mainly in the form of starch granules, in plastids such as chloroplasts and especially amyloplasts.
Toward the end of the growing season, starch accumulates in twigs of trees near the buds. Fruit, seeds, Rhizomes, and tubers store starch to prepare for the next growing season.
Glucose is soluble in water, hydrophilic, binds with water and then takes up much space and is osmotically active; glucose in the form of starch, on the other hand, is not soluble, therefore osmotically inactive and can be stored much more compactly.