in cell biology, a cell wall is an organelle found immediately inside the cell membrane primarily providing the cell with structural support
the cell wall also helps the cell withstand osmotic pressure
a cell wall can be tough, flexible or rigid
composition
the composition of cell walls varies across taxonomy
in land plants, the primary cell wall comprises of polysaccharides like cellulose, hemicelluloses and pectin
other polymers such as lignin, suberin or cutin are often anchored to or embedded in plant cell walls
algae have cell walls composed of glycoproteins and polysaccharides such as carrageenan and agar
wood and bark cells of trees have secondary cell walls, a thicker additional layer of cellulose used to increase cell wall rigidity