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Protista
This
is a kingdom comprised of simple, unicellular 'animals' that do
not fall easily into the plant and animal kingdoms.
Protists
exhibit an enormous range of body form, even though they are largely
microscopic. They may occur singly or in colonies. They may swim
freely, travel along a surface, or be fixed to a surface. They may
be housed in a shell, clothed in scales or other adhering matter,
or be naked. They may or may not be coloured. They may be parasites;
or they may live, apparently harmlessly, attached to or within plants
or animals.
Protists
were traditionally (for the last 150 years) subdivided into several
groups based on similarities to the higher kingdoms: the animal-like
protozoa
and the plant-like algae
and the fungi-like slime
moulds. These traditional groups often overlap. The traditional
classification is fundamentally flawed and new systems are proposed
and likely to be adopted. In some newer schemes, most algae are
classified in the kingdoms Plantae
and Chromista,
and in such cases the remaining forms may be classified as a kingdom
Protozoa. The name is misleading, since they are not truly 'animals'.
Protozoa
(in Greek proto = first and zoa = animal) are single-celled
eukaryotes
(organisms whose cells have nuclei)
that show some characteristics usually associated with animals,
most notably mobility
and heterotrophy.
Protozoa have traditionally been divided on the basis of locomotion,
as below, although this is no longer believed to represent genuine
relationships:
Most
protozoans are too small to be seen with the naked eye - most are
around 0.01-0.05 mm, although forms up to 0.5 mm are still fairly
common - but can easily be found under a microscope. Protozoa are
ubiquitous throughout aqueous
environments and the soil, and play an important role in their ecology.
Protozoa occupy a range of trophic
levels. As predators upon unicellular or filamentous algae,
bacteria,
and microfungi, protozoa play a role both as herbivores
and as consumers in the decomposer link of the food chain. Protozoa
also play a vital role in controlling bacteria population and biomass.
As components of the micro- and meiofauna, protozoa are an important
food source for microinvertebrates. Thus, the ecological role of
protozoa in the transfer of bacterial and algal production to successive
trophic levels is important. Protozoa are also important as parasites
and symbionts
of multicellular
animals.
Much
of whats above is taken from Wikipedia, the free encyclopedia -
see http://en.wikipedia.org.
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