Classification of Kingdom Protista: The categorization of protists is done on the basis of their nutritional habits, mobility and modes of reproduction. They can be broadly classified into three categories:
Photosynthetic protists or Protist algae
The origin of the word ‘protozoa’ lies in the Latin word for first animals. Protozoa come under the group of parasitic protists that feed on other organisms that are mostly dead, for nutrients. Moreover, they are heterotrophic unicellular organisms. Protozoa can be further classified on the basis of their motility. For example, protozoa that use cilia to move are called ciliates and those that use flagella are called flagellates. Amoebas are those protozoa that use pseudopodia to move and protozoa such as sporozoa are not capable of moving at all. Sporozoa are mostly parasitic as they make dead organisms their host. They are likely to inhabit areas that have continuous food supply as they are unable to collect food by themselves.
Classification of Kingdom Protista
The protozoans can be divided into four major groups:
- Amoeboid protozoans – Mostly found in water bodies, either fresh or saline. They have pseudopodia (false feet) which help to change their shape and to capture and engulf food. E.g. Amoeba.
- Flagellated protozoans – As the name suggests, the members of this group have flagella. They can be free-living as well as parasitic. E.g. Euglena.
- Ciliated protozoans – They have cilia all over their body which help in locomotion as well as nutrition. They are always aquatic. E.g. Paramecium.
- Sporozoans – These organisms are so-called because their life cycle has a spore-like stage. For example, the malarial parasite, Plasmodium.
Photosynthetic Protists or Protist Algae
They are the protists that form the foundation of the food chain. Most organisms are dependent on organisms like algae for food and oxygen either directly or indirectly. They mainly include dinoflagellates, chrysophytes and euglenoids. A special characteristic of algae is that it is a major photosynthesizer of organisms, which makes it the dominant supplier of oxygen. Even though algae are grouped under the category of plant-like protists, they lack those parts that would define them as a plant (e.g. roots, stems, and leaves). Moreover, they are incapable of preventing water loss, so they have to inhabit areas that have an abundance of water. However, the one dominant characteristic that portrays them as plant-like is the presence of chlorophyll. The presence of chlorophyll in them makes them distinguishable and classifiable on the basis of different colours.
Dinoflagellates are a crucial component of phytoplankton. Some of the examples of dinoflagellates are Glenodinium, Peridinium, Gymnodinium, Ceratium, etc.
Chrysophytes include diatoms and desmids. Some of the examples are Navicula, Cymbella, etc.
Euglenoids can be defined as Euglena-like organisms and they possess pellicle instead of cell walls. Some examples are Euglena, Phocus, etc.
They resemble fungal organisms and come in dazzling colours of multiple variants. Moreover, they are likely to inhabit places that are murky and damp. Such organisms derive their nutrients from decaying and decomposing organic material. Some examples of slime moulds are Fuligo, Dictydium, etc.
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