Given the importance of this topic from competitive examinations like SSC CGL, UPSC in this article, we would look at kingdom Protista and its characteristics.
1. Protista: Discovered by Ernst Haeckel in 1866, this class includes both unicellular and multicellular organisms.
a. Cell type: Eukaryotic
b. Cell wall: Present in some
c. Nuclear membrane: Present
d. Mode of nutrition: Autotrophic and heterotrophic
2. All single-celled eukaryotes are placed under this class, most of which are aquatic in nature.
3. Protists reproduce asexually (cell fusion) as well as sexually (zygote formation).
4. Chrysophyta (golden algae): This group includes diatoms and golden algae (desmids) found in both fresh and marine environments. Fishes feed on diatoms as are the chief producers (phytoplanktons) in the ocean. These floating diatoms accumulate gradually over billions of years at the bottom of the water table to form diatomaceous earth (type of soil).
5. Diatomaceous earth is used for polishing, filtration of oils and syrups.
6. Dinoflagellates: Unicellular protists, dinoflagellates are mostly photosynthetic and found abundantly in marine waters. Their cell wall has stiff cellular plates on its outer surface. They appear yellow, green, brown, blue or red depending on the main pigments present in their cells.
7. Red dinoflagellates rapidly multiply during summers causing algal blooms. This phenomenon is known as red tide (water covered with these organisms make it appear red). It also releases toxins, which harms marine fauna.
8. Euglenoids: They are fresh water organisms found mostly in stagnant water. Instead of a cell wall, their outer surface is a protein-rich layer called pellicle (responsible for flexibility). They are autotrophic in the presence of sunlight, however, they behave as heterotrophs.
9. Slime moulds: Eukaryotic protists have a saprophytic mode of nutrition (feed on dead and decaying matter). They are generally single-celled but under suitable conditions, they fuse to form an aggregate called plasmodium, which can be several feet long. During unfavourable conditions, the plasmodium differentiates and forms fruiting bodies that have spores at their tips. These spores are dispersed by air currents.
10. Protozoans: Unicellular eukaryotic organisms, all protozoans are heterotrophic and live as predators or parasites. Four major groups of protozoans are Amoeboid (eg. Entamoeba), Ciliated (eg. Paramoecium), flagellated (eg. Trypanosoma) and Sporozoans (eg. Plasmodium – causal agent of malaria).
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Link to Classification of organisms capsule 1:
Link to Classification of organisms capsule 2:
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