Author: Jan Scholten
The kingdoms give a very good differential diagnosis. Often this can be straightforward but in many cases the differentiation is less clear. Patients often have aspects of more than one kingdom.
In general one can see that near the poles the Mineral kingdom is the most promiment and near the equator the Animal kingdom, with the Plant kingdom in between.
In recent classifications changes have been made according to the kingdoms. In the past things were clear.
The ancient classification was in 2 kingdoms: Plants and Animals.
The kingdom of the Bacteria was discovered after the invention of the microscope. Bacteria, also named Monera or Prokaryota, are sometimes divided in two kingdoms: Eubacteria and Archaebacteria.
Later 2 new kingdoms were defined. One the fungi, as a split-off from the Plant kingdom.
The second is the Protoctista or Protista, unicellular organisms. This clade turned out to be not a single group in cladistic analysis. So it was split into two kingdoms:
- Protozoa: including the Amoebozoa, Choanozoa, Excavata.
- Chromista, including Alveolata, Cryptophytes, Heterokonta (stramenopiles), Haptophyta, Rhizaria.
Life can be divided in Prokaryota and Eukaryota. Prokaryotes, also called Bacteria or Monera, are single-celled microorganisms. They have been split into Bacteria and Archaea, also called Eubacteria and Archaebacteria. For 2 billion years only Prokaryota lived on earth. Prokaryotes have no nucleus and are very small compared to the Eukaryota.
Eukaryotic cells are typically much larger than those of prokaryotes. They have a variety of internal membranes and structures called organelles and a cytoskeleton composed of microtubules, microfilaments and intermediate filaments which play an important role in defining the cell's organization and shape. Eukaryotic DNA is divided into cellular and mitochondrial DNA.
Eukaryota have probably developed out of co-operation of many bacteria, forming a cell about 100 times as big as most bacteria.
- Animalia, Animals
- Rhizaria: various amoebae, flagellates and amoeboids like plankton.
- Excavata: unicellular eukaryotes, like Giardia lamblia.
Alternative division of Eukaryota is
Apusozoa: several genera of flagellate protozoa.
Archaeplastidae: plants, broadly defined.
Chromalveolata; like Fucus
The plants are in the new classifications part of the Archaeplastidae. The Archaeplastidae are sometimes all seen as plants, broadly defined. Plants more narrowly defined are the Viridaeplantae, the green plants, plants containing chlorophyll.