A cell wall is an additional layer found in specific organism's cells. Among its major functions is the ability to regulate the water and materials that enter and leave a cell. Depending on the organism, a cell wall may be composed of different materials or possess additional features.
A cell wall surrounds every cell of a plant, fungi, algae and bacteria. Animal cells, including those of humans, do not contain cell walls. The cell wall is a rigid extracellular layer that rests outside of the cell membrane. The materials that comprise a cell wall vary between species. Cellulose, for example, makes up most of the cell wall in plants, while algae cell walls are mostly made of glycoproteins and polysaccharides.
A cell wall provides addition strength to its cell. It limits the entry of larger molecules into the cell, which would otherwise cause significant damage. The cell is also able to retain water that it would have lost with just a membrane. An organism can hold and maintain its physical shape due to the cell wall. In plants and multicellular organisms with multiple plant cells join to each other by their cell walls.
A cell wall safely transports materials between cells. In multicellular organisms, cells connect to one another by using the cell wall. Through small pores in cell walls called "Plasmodesmata," the cytoplasm of one cell is connected to another cell adjacent to it. Once connected, materials in the cytoplasm such as ctyosol, organelles, vesicles and the cytoskeleton can transfer between cells. Additionally, key nutrients such as water and carbon dioxide are distributed throughout an organism through cell wall transfers.
Secondary Cell Wall
A secondary cell wall is in some plants, algae and single cell protists. The wall is essentially a thicker layer of cellulose or other material such as lignin or suberin. The cell wall forms inside the primary cell wall after the cell grows fully. The wall provides added rigidity to the cell, and is waterproof. In plant cells, an additional layer exists outside the primary and secondary cell wall. Called the middle lamella, the layer contains pectin, which is a gelling agent. The middle lamella connects multiple cells.