Plant cell walls are composed of complex carbohydrates, proteins, phenolic compounds, and inorganic ions, all of which play functional roles. Cellulose (1,4-fR-glucan) and callose (1,3-fR-glucan) are synthesized in the plasma membrane, while other polysaccharides are synthesized in the Golgi. Plant cell growth occurs with the loosening of the walls, which may be caused by several enzymatic actions. Plant development is related to the morphological changes of cells and tissue, which is caused by structural changes of the walls.