Provide information about the structure of the prokaryotic cell envelope and its specific functions.

(N/A) $\Rightarrow$ Prokaryotic cells possess a chemically complex cell envelope.
$\Rightarrow$ The cell envelope consists of a tightly bound three-layered structure: $(i)$ the outermost glycocalyx,$(ii)$ the cell wall,and $(iii)$ the plasma membrane.
$\Rightarrow$ Although each layer of the envelope performs a distinct function,they act together as a single protective unit.
$\Rightarrow$ Bacteria are classified into two groups based on differences in their cell envelopes and their response to the Gram staining procedure:
$(i)$ Gram-positive bacteria: Those that take up the Gram stain.
$(ii)$ Gram-negative bacteria: Those that do not take up the Gram stain.
$(i)$ Glycocalyx: The outermost layer. It varies in composition and thickness among different bacteria. It can be a loose sheath called the slime layer or a thick,tough layer called the capsule.
$(ii)$ Cell wall: It determines the shape of the cell and provides strong structural support to prevent the bacterium from bursting or collapsing.
$(iii)$ Plasma membrane: It is semi-permeable and interacts with the external environment. Structurally,it is similar to that of eukaryotes.
$\Rightarrow$ Mesosomes: Special membranous structures formed by the extensions of the plasma membrane into the cell in the form of vesicles,tubules,and lamellae. They assist in cell wall formation,$DNA$ replication,distribution to daughter cells,respiration,secretion,and increasing the surface area of the plasma membrane and enzymatic content.
$\Rightarrow$ Chromatophores: In some prokaryotes like cyanobacteria,there are other membranous extensions into the cytoplasm containing pigments.