Infectiology
Taxonomy is the science of defining and naming groups of biological organisms on the basis of shared characteristics.
This is a highly complex academic field, which considers enormous amounts of information. Taxonomic consensus changes continously, as more research is completed and more evidence is gathered.
Etymology
From Ancient Greek τάξις (táxis) = order, arrangement
From Ancient Greek νόμος (nómos) = law, custom
Taxonomy = the science of arrangement
Non-cellular 'life'
These are obligate infectious agents which cannot replicate independently of living organisms.The three domains
All living organisms can be categorised into three groups called domains: eukaryota, bacteria and archaea. This system was proposed in 1990.Eukaryotes are unicellular or multicellular organisms. The cells contain a nucleus enclosed within membranes.
Prokaryotes are unicellular or multicellular organisms. The cells which lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelle.
The seven kingdoms
All living organisms can be grouped into kingdoms.This is a relatively simplistic taxonomic system, which is bothersome to taxonomists, but it is relatively accessible and popular. The 2015 system of 7 kingdoms, proposed by Ruggiero et al. follows below:
The kingdoms Chromista and Protozoa include organisms which have been called 'protists' (kingdom: Protoctista). Many sources still (inaccurately) refer to chromists as 'protozoa', 'fungi' or 'animals'.
