o Glycocalyx: Outer layer. It differs in composition and thickness among different bacteria. It may be a slime layer (loose sheath) or capsule (thick & tough).
o Cell wall: Middle layer. Seen in all prokaryotes. It gives shape to the cell and provides a structural support to prevent the bacterium from bursting or collapsing.
o Plasma membrane: Inner layer. It is semi-permeable in nature and interacts with the outside. This is structurally similar to that of the eukaryotes.
Based on the types of the cell envelopes and response to Gram staining (developed by Gram), bacteria are 2 types:
o Gram positive: They take up and retain the gram stain.
o Gram negative: They do not retain the gram stain.
