Diversity: Protists
Structure
Protists consist of all the eukaryotic organisms that do not fit easily into plants, animals or fungi. Thus it contains algae, amoebae, Oomycota, the ciliates and diatoms. While these organisms tend to be small and single celled, some are enormous and multicellular. The group is artificial, and divisions within the group tend to be artificial. In reality, diversity at the molecular level is greater than the diversity found among all remaining eukaryotic organisms.
Importance
Photosynthetic protists produce around a third of the planet's oxygen, most of it in the oceans. With a few important minor exceptions, all algae are photosynthetic. Some members of Chrysophyta are heterotrophic, including the Oomycetes, which includes some important plant and animal pathogens. All appear to require oxygen for respiration. Heterotrophic protists are important links in food webs and a small number are parasites involved in plant and animal pathology.
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