The outer most boundary in most of the plant cells is cell wall. The cell wall of plant cell is different from that of prokaryotes. Both in structure and chemical composition. It is secreted by the protoplasm of the cell. Its thickness varies in different cells of the plant. It is composed of three main layers: primary wall, secondary wall and the middle lamella. The middle lamella is first to be formed in between the primary walls of the neighboring cells. The neighboring cells. The primary wall is composed of cellulose and some deposition of pectin and hemicelluloses. Cellulose molecules are arranged n a criss cross arrangement (fig. 4.6). the primary wall is a true wall and develops in newly growing cells. The secondary wall is formed on its inner surface and is comparatively thick and prokaryotic cell wall lacks cellulose: its strengthening material is peptidoglycan or murein. Fungal cell wall contains chtin.
Fig.4.6. Secret of the plant structure is revealed by electron microscope photographs of the cell walls. The cellulose fibers are arranged in layers, with the fibres of eack layer at right angle to those of other layers.
Cell wall is very important. It provides a definite shape to the cell and keeps it rigid. It does not act as a barrier to the materials passing through it.