Mycoplasma: The Smallest Living Cells Without a Cell Wall
Biology · Biological Classification · NEET
Mycoplasma are the smallest living cells known, only about 0.3 micrometre (µm) long. They are the only prokaryotes that completely lack a cell wall, they can survive without oxygen, and many cause disease in both plants and animals. Memory hook: "My-co-plasma = My-co-NO-wall" — the tiniest cell that forgot its wall.
Mycoplasma is far smaller than a normal bacterium and, unlike every other prokaryote, has only a cell membrane with NO cell wall. Both have DNA and ribosomes.
Your doubts, answered
Does Mycoplasma have a cell wall? This confuses me.
No. Mycoplasma completely LACK a cell wall. This is the most important fact for NEET. Every other prokaryote (all bacteria, cyanobacteria) has a cell wall around the cell membrane, but Mycoplasma is the one exception. Because it has no rigid wall, its shape is not fixed — it can change shape (pleomorphic). If any NEET option says 'Mycoplasma has a cell wall', that option is WRONG.
Why is Mycoplasma called the smallest living cell?
Mycoplasma is only about 0.3 micrometre (µm) in length. A normal bacterium is much bigger (a few µm). Because it is so tiny AND has no cell wall, it can pass through filters with pore size less than 1 micron — filters that normally stop bacteria. NCERT directly says Mycoplasma are 'the smallest living cells known'. Remember 0.3 µm as the exam number.
Is Mycoplasma a bacteria or something separate?
Mycoplasma is a prokaryote and is placed in Kingdom Monera, like bacteria. It has DNA and ribosomes like other prokaryotes. But it is NOT a normal bacterium because it has no cell wall. So it is safest to call it a wall-less prokaryote / wall-less microorganism, not 'a bacterium with a cell wall'. In NEET, 'Mycoplasma is a prokaryote' is correct.
What is PPLO? Is it the same as Mycoplasma?
Yes. PPLO stands for Pleuro-Pneumonia-Like Organism. It is another name for Mycoplasma. It got this name because it causes a lung disease (pleuropneumonia) in cattle. So if NEET writes PPLO, it means Mycoplasma.
Can Mycoplasma live without oxygen?
Yes. Mycoplasma can survive without oxygen (anaerobically). This is a common NEET matching point. So the full NCERT description is: smallest living cell + no cell wall + survives without oxygen + pathogenic to plants and animals.
Why does Mycoplasma matter for NEET?
It is a guaranteed one-mark question. NEET repeatedly asks 'which is the smallest cell / which lacks a cell wall / which is not a normal bacterium'. The answer is almost always Mycoplasma. Options like Bacillus, Pseudomonas and Nostoc all HAVE a cell wall, so they are wrong — only Mycoplasma fits the 'no wall, smallest' description.
⚠️ The NEET trap ✗ Mycoplasma is a bacterium that has a cell wall made of peptidoglycan. ✓ Mycoplasma completely LACKS a cell wall. It is a wall-less prokaryote (PPLO), the smallest living cell (~0.3 µm), and can survive without oxygen. 🧠 NEET loves the statement 'Mycoplasma has a cell wall' — it is ALWAYS false. No wall = the whole point of Mycoplasma.
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: Mycoplasma completely lack a cell wall, are the smallest living cells known (~0.3 µm), can survive without oxygen (anaerobic) and many are pathogenic to both plants and animals. Bacillus, Pseudomonas and Nostoc all possess a definite cell wall, so they do not fit the description. Answer: Mycoplasma (C).
NEET 2022
Statement I: Mycoplasma can pass through less than 1 micron filter size. Statement II: Mycoplasma are bacteria with a cell wall. 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: Mycoplasma are the smallest living cells and pass through fine (<1 micron) filters. Statement II is WRONG: Mycoplasma completely lack a cell wall, so they cannot be called 'bacteria with a cell wall'. Hence Statement I correct, Statement II incorrect (C).
NEET 2019 · NEET 2022
Which of the following is a correct statement?
A · Cyanobacteria are autotrophic organisms classified under Kingdom Monera ✓
B · Bacteria are exclusively heterotrophic organisms
C · Slime moulds are saprophytic organisms classified under Kingdom Monera
D · Mycoplasma have DNA, Ribosome and cell wall
Solution: Cyanobacteria are prokaryotic photosynthetic autotrophs in Kingdom Monera (A correct). Bacteria are metabolically diverse, not only heterotrophic (B wrong). Slime moulds are protists, not Monera (C wrong). Mycoplasma have DNA and ribosomes but NO cell wall, so 'have DNA, Ribosome and cell wall' is wrong (D wrong).
Solved Biological Classification NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
