Biology · Cell: The Unit of Life · NEET
A mesosome is a specialised membranous structure inside a prokaryotic (bacterial) cell. It is NOT a separate organelle brought in from outside. It forms when the plasma membrane (cell membrane) pushes inward, or folds into, the cell. These infoldings take the shape of vesicles (small sacs), tubules (tiny tubes) and lamellae (thin sheets). So the mesosome is just an extension of the plasma membrane into the cytoplasm.
NCERT lists these functions clearly. A mesosome helps in: (1) cell wall formation, (2) DNA replication and distribution of DNA to daughter cells during division, (3) respiration, and (4) secretion. It also increases the surface area of the plasma membrane and the enzymes on it. Remember all four for NEET: cell wall, DNA, respiration, secretion.
No. A mesosome is found only in prokaryotes (bacteria). Eukaryotic cells do NOT have mesosomes. This is a very common NEET trap: if a statement says the eukaryotic plasma membrane forms mesosomes, it is WRONG. In eukaryotes, jobs like respiration are done by mitochondria, not by a mesosome.
Both help in respiration, so students mix them up. Mesosome is a fold of the plasma membrane in prokaryotes (bacteria have no mitochondria). Mitochondria are double-membrane organelles found only in eukaryotes. So mesosomes carry out respiration in bacteria because bacteria have no mitochondria to do that job.
The mesosome is formed by the PLASMA MEMBRANE (cell membrane), not the cell wall. The plasma membrane extends (folds) inward to make it. Do not confuse this: cell wall is the outer rigid layer, plasma membrane is the inner living membrane, and only the plasma membrane makes the mesosome.
Yes. One key function of the mesosome is to help in DNA replication and then help distribute (separate) the copied DNA to the two daughter cells when the bacterium divides. This is exactly what NEET 2023 tested, and both the DNA-replication and cell-wall-formation statements were marked correct.
A specialised membranous structure in a prokaryotic cell which helps in cell wall formation, DNA replication and respiration is:
Statement I: In bacteria, the mesosomes are formed by the extensions of plasma membrane. Statement II: The mesosomes, in bacteria, help in DNA replication and cell wall formation. Choose the most appropriate answer.
Select the correct statements regarding cell membrane in eukaryotic cell. A. Membrane of human RBCs has approximately 52% protein. B. Major phospholipids are arranged in a bilayer. C. Extensions of the plasma membrane into the cell form mesosomes. D. Tails towards the inner part of lipids are hydrophobic and thus protected from aqueous medium. E. Glycocalyx is present on the outer surface of the plasma membrane.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Mesosomes are a characteristic feature of prokaryotes and are commonly described in bacteria. For NEET, treat the mesosome as a prokaryotic (bacterial) structure. It is not found in eukaryotic cells at all.
Bacteria are prokaryotes and have no membrane-bound organelles like mitochondria. So respiration and other tasks are handled by the mesosome, which is just a fold of the plasma membrane that increases surface area and enzyme space.
Remember: (1) cell wall formation, (2) DNA replication and distribution to daughter cells, (3) respiration, and (4) secretion. These four are the NCERT-listed functions and are directly asked in NEET.
According to NCERT, mesosomes are extensions of the plasma membrane in the form of vesicles (sacs), tubules (tubes) and lamellae (sheets).
Mesosome-based questions appeared in NEET 2023 and NEET 2025 directly, and a trap statement about mesosomes appeared in a NEET 2026 cell-membrane question. It is a repeatedly tested topic.
