Organs and tissues in plants can be divided into sources and sinks. A source is a part where organic molecules are produced, whereas a sink is a part where the molecules are used and stored. In particular, plant leaves perform photosynthesis associated with the production of glucose and other organic molecules. These compounds are then transported to other plant tissues and organs. However, very often, the produced molecules are stored in leaves and are also used directly by the tissues of leaves. For example, developing leaves can be involved in the photosynthesis process, but also require multiple bioorganic compounds to grow. As a result, in this case, a growing leaf is a source and a sink at the same time as it synthesizes and uses various organic molecules. Another example is that starch produced from synthesized glucose can be accumulated in the leaf cells. This starch can be further used during the stressful seasons when photosynthesis is suppressed.