Plant biochemistry examines the molecular mechanisms of plant life. One of the main topics is photosynthesis, which in bigger plants takes place mainly in the leaves. Photosynthesis utilizes the energy of the sun to synthesize carbohydrates and amino acids from water, carbon dioxide, nitrate and sulfate. Via the vascular system a major part of these products is transported from the leaves through the stem into other regions of the plant, where they are required, for example, to build up the roots and amount them with energy. Hence the leaves have been accustomed the name “source,” and the roots the name “sink.” The reservoirs in seeds are also an important group of the sink tissues, and, depending on the species, act as a store for many agricultural products such as carbohydrates, proteins and fat.