Kingdom Protista- classification, characters, Examples

• The term ‘Protista’ wasgiven by German biologist Ernst Haeckel.

• Kingdom Protista consists of  unicellular and eukaryotic organisms.

• Protists have all cell organs like multicellular eukaryotes but the body of protistan is less complex than multicellular eukaryotes.

• This kingdom was constituted by Whittaker by including those  organisms that  do not fit into any of the other kingdoms.

• Some protists are photosynthetic,  some make symbiotic relationships, some are solitary and form colonies; some are microscopic, some have bioluminesce properties and some are pathogens in plants and animals. 

• They also are link between plant and animal.

General characters  of Kingdom Protista

• Protista are unicellular eukaryotic organisms and found in  mostly aquatic habitats.

• The cell wall is sometimes  present or sometimes  absent.

• Protists have well-defined nucleus and membrane-bound cell organelles.

• They have autotrophic nutrition  or  heterotrophic nutrition.

• The organisms show locomotion with the help of cilia, flagella or pseudopodia.

• They reproduce asexually and sexually by cell fusion and zygote formation. 

Example of Kingdom Protista

Dinoflagellates- 

• Dinoflagellates are  photosynthetic, motile, and live in  marine environments. 

• They are biflagellated having two flagella one longitudinally and one is located transversely .

• Both flagella are located between the furrow of wall plates.

• They contain green, yellow, brown, red or blue pigments. They make enormous groups of phytoplankton.

• They have condensed chromosomes, their nucleus called mesokaryon. 

• Some dinoflagellates emit light  in the dark. This is a phenomenon of bioluminescence.

• They release  toxins, and due to these  toxins . Their toxins also  kill marine organisms.                   

• The  red tide in sea  is caused by the colouration of the dinoflagellates like Gonyaulax. This phenomenon of red tide is seen during the rapid multiplication of the organism.

• Reproduction  take place  by both asexual and sexual methods.

• Cell wall of Dinoflagellates has cellulosic plate on outer surface.

Chrysophytes or  jewels of the plant world.

• Diatoms and Desmids are members of chrysophyta. Out of two, Desmids are called Golden algae.

• These are unicellular, photosynthetic, free-floating fresh or marine water forms.

• The cell wall is made up of silica and pectin.

• Reproduction is by both sexual and asexual methods.

• Diatoms  accumulate  large amounts of cell wall deposit where they present. This deposition of Diatoms is called diatomaceous earth. Formation of this earth takes millions of years.

• They are plankton because they float passively in water current.

• In Diatoms, The two layers of  the cell wall are fitted together and form a soapbox.Example: Diatoms, Desmids etc. 

Euglenoids

• These are unicellular, mixotrophic and have features    of both plants and animals.

• They  are green, autotrophic in nutrition and have chlorophyll similar to green plants.

• They are also regarded as a connecting link between plants and animals.

• They have two flagella, one is long and other is short.

• They are found mostly in stagnant freshwater.

• Their body is covered by  a protein-rich layer called pellicle, which makes their body flexible.

• The food is stored in the form of proteinaceous granules known as pyrenoids in their chlorophyll.

• Reproduction is only by the asexual method.

• Photosynthetic euglenoids behave like heterotrophs in the dark, this mode of nutrition is known as mixotrophic. Example: Euglena

Slime Moulds ( Fungus animals)

• They possess the characteristics of both animals and fungi.

• They are found   in moist places and may be found  moving along the decaying twigs and leaves hence they are saprotrophic.

• They reproduce by both sexual and asexual methods.

• Under favourable conditions, they aggregate and  form a stage called Plasmodium up to saveral freet. During the offset of favourable conditions ,

• Plasmodium is broken and forms fruiting bodies. Spores inside the fruiting bodies are liberated through the air. These spores have thick wall. Due to wall they may remain alive up to saveral years.

Protozoans

• These are the most primitive animals and  are heterotrophic in nature and live as predator or parasites.

• On the basis of locomotory organs, They are divided into four major groups.

Amoeboid Protozoans

• They are found  in freshwater  and saltwater or moist soil.

• They move with the help of pseudopodia. They capture and engulf the food also by the pseudopodia.

• Some marine form of amoebid protozoan have shell of silica. Amoeba, Entamoeba histolytica and Entamoeba gingivalis (parasites) etc are examples of amoeboid protozoans.

Flagellated Protozoans

• They are either free-living or parasitic in nature.They have flagella as a locomotory organ. Ex- Trypanosoma causes African sleeping sickness

• Leishmania is caused by kala-azar or dum-dum fever.

• Giardia causes giardiasis.

• Trichomonas vaginalis causes leucorrhoea.

Ciliated Protozoans

• They are aquatic, and locomotion is done by the presence of cilia.

• They exhibit  nuclear dimorphism or they have two nuclei - macro and micronucleus.

• They also have a cavity called gullet in which food and water are laden due to beating of cilia. Gullet is opened outside the cell surface. E.g., Paramecium, etc.

Sporozoans

• They have  less developed or no locomotory organs and members are parasites. Example: Plasmodium, Monocystis, etc.