The cell wall is the layer of material secreted by the plant cell outside its plasma membrane. All plants have cell walls that are generally very similar in chemical composition, organization, and development. The walls of the Chlorophyta (green algae) show characteristics virtually identical to those of flowering plants, another indication that flowering plants are derived evolutionarily from this division of algae. The wall serves as the first point of entry of materials into cells, functions in the movement of water throughout the plant, and is one of the major mechanical strengthening factors. In addition, the wall must be sufficiently flexible and plastic to withstand mechanical stresses while still permitting the growth of the cell.