Transport systems in plants: xylem and transpiration

Water and mineral ions are transported from the roots, up the stem, to the leaves, in vessels made of xylem. Xylem is made of dead, empty cells with no cytoplasm, that form a tube with a tough wall made of lignin. Water is continually lost from the surface of a plant when water molecules diffuse into the air through open stomata. Water is pulled up through xylem tubes to replace the water lost through open stomata; this process is transpiration. The water that is pulled through xylem tubes has mineral ions dissolved in it, including nitrate ions.