Which one is the smallest cell?
(a) Bacteria
(b) Parenchyma
(c) PPLO
(d) Virus

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Hint: It is a genus of bacteria that lack a cell membrane around their cell membranes. This characteristic makes them naturally immune to antibiotics that focus on cell membrane synthesis (like the beta-lactam antibiotics). they will be parasitic or saprotrophic.

Complete answer:
The cell is the structural unit of life with various shapes and sizes. the dimensions of the cell range from 0.5 micrometers to 100 micrometers. The Mycoplasma gallicepticum is the parasitic bacterium that is thought to be the smallest known organism and its size from $0.2\mu m to 0.4\mu m$ and it equipped for autonomous development and proliferation. Afterward, the name for mycoplasma was pleuropneumonia- like organism or PPLO.

Additional information: Over 100 species are included within the genus Mycoplasma. Microbes of the category Mollicutes, to which Mycoplasma belongs, are parasites or commensals of humans, animals, and plants. The variety of Mycoplasma utilizes vertebrate and arthropod hosts. Dietary nitrogen accessibility has appeared to change codon inclination and genome advancement in Mycoplasma and Phytoplasma.
Mycoplasma bacteria also are referred to as mollicutes. they're the only and therefore the smallest free- living prokaryotes.
Mycoplasma bacteria are found within the pleural cavities of cattle affected by pleuropneumonia.
So the correct answer is ‘(c) PPLO’.

Note: Important characteristics of mycoplasma bacteria
- Cell wall is absent and therefore the cell wall forms the periphery of the cell.
- Due to the absence of a cell membrane these organisms can change their shape and are pleomorphic.
- Lack of nucleus and other membrane- bound organelles.
- Genetic material may be a single DNA duplex and is naked.
- Ribosomes are 70S type.
- Possess a replicating disc at one end which assists the replication process and also the separation of the genetic materials.
- Heterotrophic nutrition. Some live as saprophytes but the bulk is parasites of plants and animals. The parasitic nature is thanks to the lack of mycoplasmal bacteria to synthesize the specified protein.
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