Q.Which of the following lack cell wall?

Among Monera, only Mycoplasma lack a cell wall entirely.

Monera includes eubacteria (true bacteria), archaebacteria, cyanobacteria (blue-green algae), and mycoplasma. Bacteria, archaebacteria, and cyanobacteria all have a rigid cell wall (though of different chemical composition -- e.g., archaebacterial walls lack peptidoglycan). Mycoplasma, however, are unique: they are the smallest known living cells that can survive without a cell wall, bounded only by a plasma membrane. This absence of a wall makes them pleomorphic (variable in shape) and resistant to antibi …

PPLO stands for Pleuro Pneumonia Like Organism.

PPLO, now formally classified in the genus Mycoplasma, are the smallest known free-living organisms, lacking a cell wall entirely (unlike bacteria, which is why they can be pleomorphic in shape and pass through bacterial filters). They were originally discovered in association with a pleuropneumonia-like respiratory disease in cattle, which is the origin of their common name. Mycoplasm …

Mycoplasma is the only organism among the four options that has no cell wall at all.

A cell wall is present in Archaebacteria (built of pseudomurein, chemically distinct from the murein/peptidoglycan of true bacteria), in Dinoflagellates (which have rigid cellulose plates called thecae forming an armour), and in Chrysophytes such as diatoms (which have a two-piece silica shell). Mycoplasma, by contrast, are the smallest known free-living cells and lack a cell wall entirely — they are bounded only by a plasma membrane that is stabilised by sterols, which is why Mycoplasma cells can be irregular in shape (pleomorphic) and can even pas …