The organisms belonging to the first two kingdoms, Archaebacteria and Eubacteria, are Prokaryotes,
organisms whose cells do not have a nucleus and other internal structures.
(More information on Prokaryotes can be found here).
All of the other organisms, Protists, Fungi, Plants and Animals, are Eukaryotes.
The cells of Eukaryotes are highly organized, with a nucleus and other internal organelles
(More information on Eukaryotes can be found here).
All six kingdoms are well represented in the fossil record.
They are subdivided into several subordinate groups (taxonomic groups, or taxa)
and the study of what belongs to what group (taxon) and how they relate to each other is the object of taxonomy.
The kingdom is the highest-rank taxon (or taxonomic group).
Within a kingdom is the phylum
, within a phylum is the class, followed by the order,
the family, the genus and, last, the species.
For instance, these would be all the taxonomic groups a mountain lion (puma) would belong to:
A species is a group of individuals that can interbreed.
Names of taxa are capitalized, except for the species; genus (pl. genera) and species are italicized.
The name of the species is always associated with that of the genus:
Felis concolor
Homo sapiens
Evidence from morphology, biochemistry and gene sequencing strongly suggests
that all Earth organisms are genetically related.
The genealogical relationships between all living things can be represented by a diagram
resembling a branching tree, appropriately called the Tree of Life
The Tree of Life represents the Phylogeny of organisms,
or the history of their lineage as they change through time.
When classifying organisms in different taxa, one rule must be followed:
all of the species within each taxon must be traceable to a common ancestor.
A cluster of species that share such an ancestry is called a clade.
An illustration showing the different kinds of living organisms and their classification
from net.metadynamics.com
