Answer: They are the smallest living cells and lack a cell wall.
- A They possess an unusually thick peptidoglycan cell wall structure
- B They are the smallest living cells and lack a cell wall
- C They are obligate photosynthetic autotrophs lacking any cell wall
- D They belong specifically to kingdom Protista among microorganisms
Correct answer: B. They are the smallest living cells and lack a cell wall
Explanation: Mycoplasma (PPLO, pleuropneumonia-like organisms) are the smallest known living cells, lacking a cell wall, and can survive without oxygen. They belong to kingdom Monera.
Whittaker's five-kingdom system (1969) groups all cellular life by cell structure and nutrition; viruses, viroids, and lichens fall outside this system entirely since they aren't independently classifiable as one of the five.
Concept context
Whittaker's five kingdom system covering Monera, Protista, Fungi, plus viruses, viroids, and lichens. A foundational NEET chapter on how living organisms are grouped.