Kingdom Protista: Classification, Types, Significance

Kingdom Protista: Kingdom Protista consists of living organisms which are mostly unicellular and less complex in nature. The kingdom is very diverse as the organisms in this group have a wide variety of characteristics. These organisms are eukaryotes, which are organisms in which the genetic material is DNA in the form of chromosomes within a single nucleus. This group is distinct because it does not include any animal, plant or fungus.

Protists are found almost everywhere in every form and shape. Some are microscopic while some are clearly visible. It is difficult to categorise the organisms falling under Protista and hence they have been grouped under a separate kingdom. This article has information about the salient features, types and characteristics of Kingdom Protista. Continue reading.

Definition of Protista

Protista is aquatic small unicellular, i.e., single-celled, eukaryotic microorganisms with a well-defined nucleus.

History of Kingdom Protista

Coming to the history of this kingdom, according to the evolution, this Protista acts as a connecting link between the prokaryotic kingdom Monera and other multicellular kingdoms like Fungi, Animalia and Plantae. The term ‘Protista’ was given by German biologist Ernst Haeckel in the year 1866. The kingdom Protista classification was included in the third kingdom classification.

Characteristics of Protista Kingdom

The group Protista shows the following characteristics in common:

1. Protista is a unicellular eukaryotic organism.
2. The members of the kingdom Monera are mostly aquatic in habitat.
3. The cell wall is present in some protists and absent in some other forms.
4. The eukaryotic cell of protists possesses a well-defined nucleus, and membrane-bound organelles are also present.
5. Nutrition may be autotrophic and heterotrophic.
6. The organisms show locomotion with the help of cilia, flagella or pseudopodia.
7. Reproduction is by both sexual and asexual reproduction.

Kingdom Protista Flow Chart

The Kingdom of Protista includes three broad groups, as shown in the following flow chart:

Fig: A Flowchart of the Kingdom Protista

Kingdom Protista Classification

The kingdom of Protista is divided into three groups, namely, Plant-like Protists, Fungi-like Protists and Animal-like Protists.

Plant-like Protists

These are organisms that show plant-like characteristics and are also photosynthetic organisms. It is of three sub-types namely, Dinoflagellates, Chrysophytes and Euglenoids.

1. Dinoflagellates

The group of around 1000 species of photosynthetic protists belongs to the division – Pyrrophyta and class – Dinophyceae.

The members show the following characteristics:

1. These are photosynthetic, i.e., autotrophic in nutrition.
2. These are motile, biflagellate and mostly marine forms.
3. They contain green, yellow, brown, red or blue pigments.
4. These form the important components of phytoplankton.
5. Their macronuclei possess condensed chromosomes, even in interphase, called mesokaryon.
6. Some dinoflagellates emit light and glow in the dark. This refers to the phenomenon of bioluminescence.
7. They also emit toxins, and toxins released that make the sea appear red, and they even kill marine organisms. This red tide is also caused by the colouration of the dinoflagellates, and this phenomenon of red tide is seen during the rapid multiplication of the organism.
8. Reproduction is by both asexual and sexual methods.
9. Examples: Gonyaulax, Noctiluca, etc.

Fig: Dinoflagellates

2. Chrysophytes

These are called jewels of the plant world. The members show the following characteristics:

1. These are unicellular-floating fresh or marine water forms.
2. Most of them are photosynthetic, and their cell wall is made up of silica and pectin.
3. Reproduction is done by both sexual and asexual methods.
4. The accumulation of a large amount of cell wall deposit of Diatoms is referred to as diatomaceous earth (which can be used as fuel after mining).
5. In Diatoms, the cell wall form two thin overlapping shells, that fit together as in a soapbox.
6. Example: Diatoms, Desmids, golden algae, etc.

Fig: Diatoms With Different Shapes

3. Euglenoids

These are unicellular and share the characteristics of both plants and animals. The members show the following characteristics:

1. These are green and autotrophic in nutrition (plant character).
2. These are Euglena like unicellular flagellates (animal character) found mostly in stagnant fresh water.
3. They have two types of flagella – Long Whiplash and Short Tinsel.
4. Instead of a cell wall, they have a protein-rich layer called pellicle, which makes their body flexible.
5. The food is stored in proteinaceous granules known as pyrenoids.
6. Reproduction is only by the asexual method.
7. Photosynthetic euglenoids behave like heterotrophs in the dark, this mode of nutrition is known as mixotrophic.
8. Example: Euglena – The chief member of this group and regarded as the connecting link between animals and plants.

Fig: Euglena

Fungi-Like Protists (Slime Moulds)

They possess the characteristics of both animals and fungi, therefore, combinedly called fungus-animals. The members show the following characteristics:

1. They occur in moist terrestrial habitats and are seen moving along the decaying twigs and leaves.
2. They reproduce by both sexual and asexual methods.
3. These show saprophytic nutrition.
4. Under suitable conditions, they form Plasmodium. On the basis of occurrence of Plasmodium, these are of two types:
   a. Acellular/Plasmodial slime moulds, E.g., Fuligo septica, Physarum, etc.
   b. Cellular slime moulds, E.g., Dictyostelium, Polysphondylium, etc.

Fig: Slime moulds

Animal-Like Protists (Protozoans)

These are the most primitive relatives of animals and these protozoans are heterotrophic organisms.
They are divided into four major groups, namely,

Amoeboid Protozoans

1. They live in freshwater, moist soil and saltwater.
2. They move with the help of pseudopodia, as in Amoeba.
3. Other members of this group are Entamoeba histolytica and E. gingivalis which cause various digestive and oral diseases or infections when engulfed in contaminated water.

Fig: Amoeba

Flagellated Protozoans

1. These are either-living or parasitic in nature.
2. Chief members of this group are as follows:
   (a). Trypanosoma sp. – carried by the tsetse fly and causes African sleeping sickness.
   (b). Leishmania sp. – carried by sand flies and causes kala-azar or dum-dum fever.
   (c). Giardia sp. – causes giardiasis.
   (d). Trichomonas vaginalis – cause leucorrhoea.

Fig: Trichomonas vaginalis

Ciliated Protozoans

1. They are aquatic, and locomotion is due to the presence of cilia.
2. They show nuclear dimorphism (macro and micronucleus), E.g., Paramecium, etc.
   (a). Macronucleus/Vegetative nucleus – This helps in controlling the metabolic activities and growth.
   (b). Micronucleus/Reproductive nucleus – This helps in controlling the reproduction process.

Fig: Paramecium

Sporozoans

1. These Sporozoans process an infectious, spore-like stage in their life cycle.
   2. All are endoparasites.
   3. These move with the help of the locomotory organs called cilia, flagella and pseudopodia.
   4. Example: Plasmodium, Monocystis, etc.

Fig: Plasmodium

Economic Importance

The economic importance of Protista is as follows:

1. The protists play a very important role in the aquatic food chain.
2. Certain types of seaweed may be consumed as food in some countries.
3. Diatomaceous earth can be used as fuel after mining (Most of the oils and gasoline supply comes from diatoms fossil beds).
4. Some of the protists may be used for the production of cosmetics, drugs and vitamins.
5. Deposits of these diatoms’ sheets are used as car polishes, cleansers, paints and also used in toothpaste.
6. Red algae contain carrageenan, algin that is used in the preparation of ice creams, cereals, candies, marshmallows, jams and jellies, chocolates, etc.
7. Environmental indicators of pollution.

Summary

Protista is unicellular eukaryotic microorganisms. The only Protista that shows both plant and animal characters is Euglena. These Protists reproduce both asexually and sexually. Through this article, we have understood many interesting facts about the members of the kingdom. Some protists are useful, but some are dangerous as they are disease-causing and cause deadly diseases in human beings.

Frequently Asked Questions (FAQs) on the Protista Kingdom

Q.1: What does the Protista kingdom classification contain?
Ans: The Protista kingdom contains unicellular eukaryotic microorganisms, which are not plants or animals. They are eukaryotic organisms.

Q.2: Enlist the characteristics of Kingdom Protista.
Ans: The characteristics of protists are as follows:
1. Protista is a unicellular eukaryotic organism.
2. The eukaryotic cell of protists possesses a well-defined nucleus, and membrane-bound organelles are also present.
3. Nutrition may be autotrophic and heterotrophic.
4. The organisms show locomotion with the help of cilia, flagella or pseudopodia.

Q.3: How is the kingdom Protista classified?
Ans: The kingdom Protista is classified into three groups namely, Plant-like Protists, Fungi-like Protists and Animal-like Protists.

Q.4: What are three examples of protists?
Ans: The three examples of protists are Euglena, Paramecium and Amoeba.

Q.5: What are the 5 major groups in the kingdom Protista?
Ans: The five major groups in the kingdom Protista are Dianoflagellates, Chryophyta, Euglenoids, Slime moulds and Protozoans.

Q.6: Are Protists unicellular or multicellular?
Ans: The members of the Protista kingdom can be both unicellular and multicellular. For instance, algae and moulds are multicellular Protists whereas Amoeba, Euglena and Paramecium are examples of Unicellular Protists.

Q.7: What are some of the examples of Chrysophytes?
Ans: Diatoms and Golden Algae are examples of Chrysophytes.

Q.8? Name some protists that take part in Photosynthesis?
Ans: Dinoflagellates are photosynthetic in nature. Euglenoids participate in the process of Photosynthesis as well. 

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