Cell walls are located around the plasma membranes of certain types of cells. Cell membranes protect the cell, but cell walls have many extra functions, including providing an extra layer of protection and giving cells a more rigid structure.
Bacteria, algae, fungi and plants have cell walls surrounding their cells while animal and protist cells do not. Cell walls are generally made up of carbohydrates. They give shape to cells, causing plants to be able to stand up straight. These walls also regulate how large cells can grow. In addition to the protection provided by the cell membrane, the cell wall also prevents the entry of pathogens and other harmful substances.