A system for all living organisms

Linnaeus divided the organisms into two realms. ”Plantae” was composed of land plants, fungi and algae and ”Animalia” contained the animals. As time went by the scientists realised that the organisms could not be divided into two parts, if a natural system was to be reached.

In 1969 the following system of realms that can be found in many textbooks was suggested:

	Monera (bacteria)
	Protista (unicellular organisms)
	Plantae (plants)
	Fungi (fungi)
	Animalia (animals)

However, quite soon it was realised that also these groups were unnatural. Especially Protista, which was composed of a number of different, unrelated groups of organisms, did not fit in any of the other realms. Scientists have reached the conclusion that the most natural division of the organisms must be to group them after the way their cells are composed. One of the most recent suggestions how to divide the organisms looks like this:

	Archaea (archae bacteria)
	Bacteria (common bacteria)
	Eucaryota (animals, plants, fungi and higher organisms)

Archae bacteria are some of the strangest organisms in the world. They can, for example, live in wells with a sulphur concentration and in submarine volcanoes. They differ much from the common bacteria, the Eubacteria, but both of these groups are characterised by having one simple cell lacking a nucleus. The rest of the world's organisms, Eucarya, have complicated cells with a nucleus and different cell organelles. To divide the Eucarya into natural groups is a great challenge to contemporary scientists, and this work is a continuing process.