noun

A structure which forms a layer external to the cytoplasmic membrane which is responsible for the shape of the cell and protects it from mechanical and osmotic damage. Cell walls occur in algae, plants, fungi, archaea, and bacteria. Both the structure and composition of  cell walls vary greatly depending on species. In bacteria, cell walls are composed of peptidoglycan and exist in two distinct types: Gram positive and Gram negative (see Gram-type-positive and Gram-type-negative).