<prompt> Porin present in ?Cell wall of gram positive bacteriaCell membrane of gram positive bacteriaCell wall of gram negative bacteriaOuter membrane of gram negative bacteria  <response>: Ans. is d i.e., Outer membrane of gram negative bacteria Cell envelop of bacteria comprises? An outer membrane only in gram negative bacteria. A cell wall composed of peptidoglycan. Periplasm only in gram negative bacteria. Cell membrane cytoplasmic membrane, which encloses cytoplasm. Outer membranes, which are present only in gram negative bacteria, function as the cells initial barrier to the environment. The membrane is a bilayered structure composed of lipopolysaccharide. Scattered throughout the lipopolysaccharide macromolecules are protein structures called porins. These control the passage of nutrients and other solutes, including antibiotics, through outer membrane. 