Mycoplasma is the smallest living cell, only about 0.3 µm long. It is the only prokaryote that has NO cell wall, so it is called a "wall-less" organism. Memory hook: "My-coplasma = My cell has no wall" — small, wall-less, and the tiniest living thing you must know for NEET.
Mycoplasma has only a plasma membrane, cytoplasm, ribosomes and genetic material — but no cell wall. At about 0.3 µm it is the smallest living cell and can pass through filters smaller than 1 micron.
Your doubts, answered
Is Mycoplasma really the smallest living cell?
Yes. NCERT clearly states Mycoplasma is the smallest cell, about 0.3 µm (micrometre) in length. This makes it smaller than normal bacteria. For NEET, remember the exact number 0.3 µm — it is asked directly. (For contrast, the largest cell is an ostrich egg, and the longest human cell is a nerve cell.)
Why does Mycoplasma have no cell wall?
All prokaryotes normally have a cell wall around the cell membrane. Mycoplasma is the ONE exception — it naturally lacks a cell wall. Because of this, it does not have a fixed shape (it is pleomorphic, meaning its shape can change). No cell wall also means antibiotics like penicillin, which attack the cell wall, do NOT work on Mycoplasma.
What does PPLO mean?
PPLO stands for Pleuro-Pneumonia-Like Organism. Mycoplasma was first found causing a lung disease (pleuropneumonia) in cattle, so early scientists called this group PPLO. Today PPLO and Mycoplasma mean the same thing. NEET may use either name, so learn both.
Is Mycoplasma a prokaryote or a eukaryote?
Mycoplasma is a PROKARYOTE. It has no nucleus and no membrane-bound organelles, just like bacteria. It only differs from other prokaryotes by having no cell wall. Do not get confused — being tiny and wall-less does not make it a eukaryote.
Why can Mycoplasma pass through a filter?
Because it is so small (~0.3 µm), Mycoplasma can pass through filters with pores less than 1 micron in size, which trap normal bacteria. This is a favourite NEET point. It can also survive without oxygen (anaerobically) and can cause disease in both plants and animals.
How is Mycoplasma different from a virus?
A virus is NOT a living cell — it has no cell membrane, no cytoplasm, and cannot live on its own. Mycoplasma IS a living cell — it has a plasma membrane, cytoplasm, ribosomes and genetic material, and it can grow and divide by itself. So Mycoplasma, not a virus, is the smallest LIVING cell.
⚠️ The NEET trap ✗ Mycoplasma is a bacterium that has a very thin cell wall. ✓ Mycoplasma has NO cell wall at all — it is the only prokaryote without one. It can also pass through filters smaller than 1 micron. 🧠 NEET 2022 tested exactly this: 'Mycoplasma are bacteria with a cell wall' is FALSE. If a statement gives Mycoplasma any cell wall, mark it wrong.
Real NEET questions
NEET 2017
Which among the following are the smallest living cells, known without a definite cell wall, pathogenic to plants as well as animals and can survive without oxygen?
A · Bacillus
B · Pseudomonas
C · Mycoplasma ✓
D · Nostoc
Solution: Mycoplasmas are the smallest cells, only about 0.3 µm in length, and are the only prokaryotes that lack a cell wall. They are pathogenic to both plants and animals and can survive anaerobically (without oxygen). Bacillus, Pseudomonas and Nostoc all have cell walls, so they are ruled out. Answer: (C) Mycoplasma.
NEET 2022
Statement I: Mycoplasma can pass through less than 1 micron filter size. Statement II: Mycoplasma are bacteria with a cell wall. In the light of the above statements, choose the most appropriate answer.
A · Both Statement I and Statement II are correct
B · Both Statement I and Statement II are incorrect
C · Statement I is correct but Statement II is incorrect ✓
D · Statement I is incorrect but Statement II is correct
Solution: Statement I is correct: because Mycoplasma is only ~0.3 µm, it can pass through filters with pores smaller than 1 micron. Statement II is incorrect: Mycoplasma is the one prokaryote that has NO cell wall. So Statement I is correct but Statement II is incorrect. Answer: (C).
NEET 2016 · NEET 2018
Select the wrong statement.
A · Bacterial cell wall is made up of peptidoglycan
B · Pili and fimbriae are mainly involved in motility of bacterial cells ✓
C · Cyanobacteria lack flagellated cells
D · Mycoplasma is a wall-less microorganism
Solution: The wrong statement is (B): pili and fimbriae are surface structures but do NOT cause motility — bacterial movement is due to flagella. Option (D) is a correct fact: Mycoplasma is indeed wall-less. This shows NEET treats 'Mycoplasma is wall-less' as a true statement. Answer: (B).
Solved Cell: The Unit of Life NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Mycoplasma is about 0.3 µm (micrometre) in length, making it the smallest living cell. Learn this exact figure for NEET.
Which is the smallest living cell known?
Mycoplasma (also called PPLO) is the smallest living cell. It is a living prokaryote, unlike a virus which is not a true cell.
Does Mycoplasma have a cell membrane?
Yes. Mycoplasma has a plasma (cell) membrane, cytoplasm, ribosomes and genetic material. It only lacks the cell WALL, not the membrane.
Why is Mycoplasma resistant to penicillin?
Penicillin kills bacteria by damaging their cell wall. Mycoplasma has no cell wall, so penicillin cannot harm it. This is why it is naturally resistant.
Is Mycoplasma harmful?
Yes. Mycoplasma is pathogenic to both plants and animals and can cause diseases such as pleuropneumonia in cattle. It can also grow without oxygen.
