The organism having the smallest cell is:

Correct option is A

Correct Answer: (a)
Explanation:
PPLOs / Mycoplasmas are the smallest known free-living cells — extremely small bacteria lacking cell walls (size ~0.1–0.3 µm), smaller than typical bacteria and much smaller than yeast or cyanobacteria.
Information Booster:
Mycoplasma species penetrate filter membranes and require special culture conditions.
Yeast (e.g., S. cerevisiae) are eukaryotic and much larger (~5–10 µm).
Cyanobacteria are prokaryotic but larger than mycoplasmas.
PPLOs are medically significant (respiratory, urogenital infections).
Their lack of cell wall makes them resistant to β-lactam antibiotics.
Additional Information (Incorrect Options):
(b) Yeast are eukaryotes with much larger cell size.
(c) Cyanobacteria are multicellular/filamentous or larger unicells.
(d) “Bacteria” as a group includes many sizes, but PPLOs are the smallest among those listed.