The sugar made by plants is glucose . Glucose is a simple molecule made up of six carbon, twelve hydrogen and six oxygen atoms. Simple sugar molecules can be joined together to form larger molecules. Starch is an example of a large molecule made by joining lots of glucose molecules together. Carbohydrates are important sources of energy for living things because they have been made by plants using the energy of light photons.
Plants make glucose predominantly in their leaf cells.
They either pass the glucose to other cells or join together the glucose molecules they have made from starch. Starch is a more compact way of storing sugar in a cell. Also, it is too large to escape from the cell. The starch molecules are stored in little storage sacs in the cell that are called starch grains. When the cell needs glucose, it breaks up the starch it has stored in the starch grains into glucose molecules.