Hint: There is no mention of some acellular organisms like viroid and lichens in Whittaker’s five kingdom classification. So, this microbe is highly infectious, with sample, acellular organisation.
Viruses: are highly infectious agents, with sample, acellular organisation. They are an exception to the cell theory. The study of viruses is called virology. Viruses are a connecting link between living and living microbes or organisms because they have properties of both. Viruses can reproduce only within living cells and obligatory intracellular parasites.
Non-living nature of virus: Lacking protoplast, ability to get crystalized that is TMV, poliomyelitis virus, absence of energy storing system, Inability to live independent of living cell, Absence of respiration, High specific gravity which is in non-living objects and absence of growth and division.
The Living nature of virus: being formed of organic macromolecules, presence of genetic material, Ability to multiply, Occurrence of mutations, infectivity and host specificity, Viruses can be killed by autoclaving and ultraviolet rays, Viruses are responsible for a number of infectious disease like common cold, Occurrence of certain enzymes like, neuraminidase, transcriptase and lysozyme in certain viruses, They take over biosynthetic machinery of the host cell and produce chemicals required for their multiplication, epidemic influenzas, chicken pox, mumps, poliomyelitis, rabies, herpes, Aids, SARs etc.
Term virus was coined by Pasteur (1880). DJ Ivanowsky recognised certain microbes as causal organisms of the mosaic disease of tobacco. These could pass through bacteria proof filters, hence are smaller than bacteria.