WAEC - Biology (2013 - No. 22)
Conduction of water and mineral salts through the xylem vessels is enhanced because the xylem cells are
thickened with lignin
long, narrow tubes placed end to end
close to the endodermis
centrally placed in the roots
설명
Xylem cells have no cytoplasm or end walls, meaning they form a tube through which water can pass freely to allow water transport. Lignin strengthens the cell walls, helping to support the plant, OR The xylem always includes specialized cells modified for water conduction. These are called Tracheary Elements. These are genetically programmed to die and their empty cell walls then act as a conduit through which water moves up the plant.