Cell (biology) made up of cellulose, fungi cell walls are made up of chitin and bacteria cell walls are made up of peptidoglycan. A gelatinous capsule is present in some bacteria outside the cell membrane and cell wall. The capsule may be polysaccharide as in pneumococci, meningococci or polypeptide as "Bacillus anthracis" or hyaluronic acid as in streptococci. Capsules are not marked by normal staining protocols and can be detected by India ink or methyl blue; which allows for higher contrast between the cells for observation. Flagella are organelles for cellular mobility. The bacterial flagellum stretches from cytoplasm through the cell membrane(s)
Natural killer cell memory, fundamental for responding to secondary infections with the same antigen. The role of NK cells in both the innate and adaptive immune responses is becoming increasingly important in research using NK cell activity as a potential cancer therapy. NK cell receptors can also be differentiated based on function. NK Cells are not a subset of the T lymphocyte family. Natural cytotoxicity receptors directly induce apoptosis after binding to Fas ligand that directly indicate infection of a cell. The MHC-dependent receptors (described above) use an alternate pathway to induce apoptosis in infected cells. Natural killer cell activation is determined by