<P> An S - layer (surface layer) is a cell surface protein layer found in many different bacteria and in some archaea, where it serves as the cell wall . All S - layers are made up of a two - dimensional array of proteins and have a crystalline appearance, the symmetry of which differs between species . The exact function of S - layers is unknown, but it has been suggested that they act as a partial permeability barrier for large substrates . For example, an S - layer could conceivably keep extracellular proteins near the cell membrane by preventing their diffusion away from the cell . In some pathogenic species, an S - layer may help to facilitate survival within the host by conferring protection against host defence mechanisms . </P> <P> Many bacteria secrete extracellular polymers outside of their cell walls called glycocalyx . These polymers are usually composed of polysaccharides and sometimes protein . Capsules are relatively impermeable structures that cannot be stained with dyes such as India ink . They are structures that help protect bacteria from phagocytosis and desiccation . Slime layer is involved in attachment of bacteria to other cells or inanimate surfaces to form biofilms . Slime layers can also be used as a food reserve for the cell . </P> <P> Perhaps the most recognizable extracellular bacterial cell structures are flagella . Flagella are whip - like structures protruding from the bacterial cell wall and are responsible for bacterial motility (i.e. movement). The arrangement of flagella about the bacterial cell is unique to the species observed . Common forms include: </P> <Ul> <Li> Monotrichous--Single flagellum </Li> <Li> Lophotrichous--A tuft of flagella found at one of the cell pole </Li> <Li> Amphitrichous--Single flagellum found at each of two opposite poles </Li> <Li> Peritrichous--Multiple flagella found at several locations about the cell </Li> </Ul>

Briefly outline the general features of a bacterial spore cycle