Which one of the following Statements IS correct?
Viroids are subviral pathogens composed solely of a short, circular, single-stranded RNA molecule. Unlike viruses, they lack a protein coat (capsid). They primarily infect plants, causing various diseases, and replicate within the host cell's machinery.
Prions are infectious proteinaceous particles devoid of nucleic acids. They are not cellular organisms and thus cannot be considered free-living cells. They are known to cause transmissible spongiform encephalopathies. Mycoplasma species are generally recognized as the smallest free-living cells.
Mycoplasma species are distinguished by the complete absence of a cell wall. This structural characteristic makes them resistant to antibiotics like penicillin, which target peptidoglycan synthesis in bacterial cell walls.
Rickettsias are obligate intracellular parasitic bacteria that possess a cell wall. While their cell wall structure may differ from typical Gram-negative bacteria, it is present and essential for their integrity.