Q.Give a detailed, labelled account of the structure of a generalised prokaryotic (bacterial) cell, describing the cell envelope and its modifications (glycocalyx, cell wall, plasma membrane, mesosomes) and the cytoplasmic components (nucleoid, plasmids, ribosomes, inclusion bodies, and surface structures such as flagella, pili and fimbriae where present).

[!TLDR]

A generalised bacterial cell has a shape-giving cell envelope (glycocalyx-cell wall-plasma membrane, sometimes with mesosomes), and a cytoplasm holding a nucleoid, plasmids, ribosomes, inclusion bodies, and surface structures like flagella/pili/fimbriae.

[!ANSWER]

Cell envelope: glycocalyx, cell wall, plasma membrane (± mesosomes). Cytoplasm: nucleoid (main DNA), plasmids (extra DNA), 70S ribosomes, unbound inclusion bodies. Surface: flagella (locomotion), pili (conjugation), fimbriae (attachment).

A generalised prokaryotic (bacterial) cell has a definite shape (coccus, bacillus, vibrio or spirillum) maintained chiefly by its cell envelope, a three-layered protective structure. The outermost layer, the glycocalyx, built mainly of polysaccharides, may form a thick, well-organised capsule, a loose slime layer, or only a minimal layer. The middle layer, the cell wall, gives the cell its shape and its resistance to osmotic bursting, and in most bacteria is built from peptidoglycan. The innermost layer, the plasma membrane, is the selectively permeable interface with the environment; in many bacteria it also extends inward as mesosomes -- vesicular, tubular or lamellar infoldings that increase membrane surface area and assist cell-wall formation, DNA replication and distribution, respiration, secretion and sporulation.

Within the cytoplasm (protoplasm) enclosed by this envelope, the most important structure is the genetic material: a single, circular, double-stranded DNA molecule, negatively supercoiled and held in a compact but membrane-less mass called the nucleoid, lying in direct contact with the surrounding cytoplasm. Many bacteria additionally carry one or more small, separate circular plasmids, which often confer specific advantages such as antibiotic resistance and are important tools in genetic engineering. Scattered through the cytoplasm are numerous 70S ribosomes (50S + 30S subunits), the sites of protein synthesis, and unbound inclusion bodies -- deposits of reserve material such as glycogen granules, lipid droplets, cyanophycean granules, or polyphosphate granules, none enclosed by any membrane of their own.

Finally, many bacterial cells bear specialised surface structures. Flagella are long, whip-like appendages (filament, hook and basal body) that rotate to drive locomotion. Pili are protein tubes that, among other roles, allow genetic material transfer between two bacterial cells during conjugation. Fimbriae are shorter, more numerous, bristle-like fibres used purely for attachment to surfaces, host tissues or other cells, with no role in locomotion.

[!ANSWER]

Cell envelope: glycocalyx, cell wall, plasma membrane (± mesosomes). Cytoplasm: nucleoid (main DNA), plasmids (extra DNA), 70S ribosomes, unbound inclusion bodies. Surface: flagella (locomotion), pili (conjugation), fimbriae (attachment).

Work outward-in for the envelope (glycocalyx -> cell wall -> plasma membrane, noting mesosomes), then cover cytoplasmic contents (nucleoid, plasmid, ribosomes, inclusion bodies), then external structures (flagella/pili/fimbriae) with their distinct roles.

Treating inclusion bodies as membrane-bound organelles (they are not -- prokaryotes entirely lack membrane-bound organelles), or confusing the roles of pili (conjugation) and fimbriae (attachment only).