Prokaryotic Cell

Bacterial cells lack the membrane-bound organelles seen in eukaryotes, so several of their functions are carried out by specialised extensions of the plasma membrane. The mesosome is formed by the inward folding of the plasma membrane in the form of vesicles, tubules and lamellae, and as described in NCERT Class 11, Chapter 8 (Cell: The Unit of Life), it helps in cell wall formation, DNA replication and its distribution to daughter cells, respiration, secretion and increasing the surface area of the membrane for enzymatic activity. The nucleoid is incorrect because it is the region containing the bacterial genomic DNA, not a membrane infolding. Glycocalyx refers to the outer protective coat, present either as a loose slime layer or a tight capsule, and does not perform respiratory functions. A pilus is a surface appendage used mainly for attachment and conjugation, not for internal enzyme distribution. Because prokaryotes have no mitochondria, the respiratory machinery must reside on the plasma membrane itself, and the mesosome conveniently multiplies that membrane surface so that more enzyme molecules can be accommodated. The same folds also keep the replicating DNA anchored, ensuring that each daughter cell receives an identical copy of the genome. Checking biological consistency, only a membrane-derived structure could host respiratory enzymes, which confirms the mesosome as the correct internal organelle-equivalent in prokaryotes.