| The kingdom protoctista summarizes all eukaryotic microorganisms which are not fungi, animals or plant. These divers group includes algae (autotroph) and protozoa (heterotroph). |
Characteristics of Protoctista |
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| Protoctista include all eukaryotic microorganisms and the organisms that directly evolved from them exclusive of fungi, plants and animals. In this group belong all algae, flagellated water molds, slime molds and slime nets, the traditional protozoa, and other even more obscure aquatic organism. It is a very divers group with remarkable variation in cell organisation, patterns of cell division and life cycle. All algae photosynthesise (= autotroph), the other forms need to eat organic material (= heterotroph), some are mixotroph (change between autotrophy and heterotrophy according to condition) and most are aerobes (have mitochondria = power plants of the cells). They all developed from symbiosis (= living together of two species to the advantage of both) between at least two different kinds of bacteria. As the symbionts integrated, a new level of individuality appeared. The protoctista can be grouped due to their organelle structure, e.g. the form of the membranous structures (= cristae) of the mitochondria. Similarly the differences in the pigments used for photosynthesis are used for classification. |
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Importance of Protoctista |
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| Protoctista are aquatic. They can be found in marine, freshwater habitats as well as in moist soil or parasitic or symbiontic in moist tissues of others. The number of protoctista species is unknown. At the moment around 10 000 live protoctists are described, but estimates of all extant protoctista lay as high as 250 000. Historically the members of this group has been studied by scientists of different organism groups, e.g. water moulds and plant parasites are described in the literature on fungi, parasitic protozoa in the medical literature, algae by botanists, and free-living protozoa by zoologists. This leads to difficulties in nomenclature. Another problem in the study of protoctista is that the highest diversity is in the tropical regions where scientists are rare. In addition the description of new species requires detailed life-cycle and ultrastructure studies. |
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