Five Kingdom Classification: In the beginning, all living organisms were classified as either plants or animals. Due to the disputed position of organisms like Euglena, fungi and bacteria, and the discovery of viruses, a better system of classification called Five Kingdom Classification was proposed by Whittaker in \(1969.\) This classification is based on cell structure, mode of nutrition and body organisation.

The five kingdoms classification involves Kingdom Monera, Protista, Fungi, Plantae, and Animalia. Furthermore, the five kingdom classification is now considered as one of the most common ways to classify living beings based on their features such as cell structure, mode of nutrition, reproduction, etc. In this article, we will study about the Five Kingdom of Classification in detail. Continue reading to find out more!

Five Kingdom Classification: Overview

Whittaker in \(1969\) proposed the Five Kingdom System of Classification. The Five Kingdom classification is simply defined as the placing of organisms with respect to their cell structure, mode of nutrition and body composition. The Five-kingdoms are as follows:
1. Monera
2. Protista
3. Fungi
4. Plantae
5. Animalia

Fig: Five Kingdom Classification

History of Classification

Very early on, scientists began grouping living organisms under different categories. Some biologists classified organisms into plants and animals. Many kingdoms came into existence later. The following table gives the correct figure of classifications.

Kingdom Systems of Classification	Proposed by
1.  Two Kingdom System	Carolus Linnaeus (Kingdom Plantae and Kingdom Animalia)
2. Three Kingdom System	Ernst Haeckel (Kingdom Plantae, Kingdom Animalia, Kingdom Protista)
3. Four Kingdom System	Copeland (Kingdom Metaphyta (= Plantae), Kingdom Metazoa (= Animalia), Kingdom Protozoa (= Protista), Kingdom Monera)

Five Kingdom Classification Diagram

Below we have provided the diagram of five kingdom classification for your reference:

Bases for Five Kingdom System of Classification

This Five System of Classification takes into account the following:

1. Complexity of cell structure: There are two main types, Prokaryotes and Eukaryotes. The only kingdom encompassing all prokaryotes is Monera.
2. Complexity of body organisation: There are two main types, Unicellular and Multicellular. The only kingdom encompassing all unicellular organisms is Protista.
3. Mode of nutrition: There are two main modes, Autotrophic and Heterotrophic. The kingdom primarily comprising all autotrophs is Plantae.
4. Ecological role: There are two main roles played by the heterotrophs, Decomposers and Consumers. Kingdom Animalia encompasses the consumers and kingdom Fungi encompasses all decomposers.
5. Phylogenetic relationship: Evolution has been one of the backbones of the Five Kingdom System of classification. 

Kingdom Monera

Characteristics of Monerans:
1. The bacteria are categorized underneath the Kingdom Monera.
2. Kingdom Monera includes Eubacteria, Cyanobacteria or blue-green algae, Mycoplasma, Spirochaete, Actinomycetes, etc.
3. These organisms are prokaryotic, i.e, they do not have a defined nucleus and lack cell organelles.
4. They are unicellular. Some may be colonial, filamentous. 
5. There are no membrane-bound cellular organelles.
6. Some of the organisms have cell walls (like bacteria and blue-green algae), while others lack cell walls (as in Mycoplasma).
7. Respiration may be aerobic or anaerobic.
(a) Obligate aerobes are those which cannot survive without oxygen. Rhodospirillum, Bacillus subtilis.
(b) Obligate anaerobes are those which cannot survive in oxygen. Clostridium botulinum. 
8. The mode of nutrition is either autotrophic (as in blue-green algae and some bacteria) or heterotrophic (Mycoplasma and most bacteria). They may be saprophytic and parasitic as well.
9. General mode of reproduction is asexual.
(a) Binary fission is the most common multiplication mode.
(b) Some bacteria like Clostridium, Bacillus form thick-walled endospores which are highly resistant, under certain conditions.
10. Few examples of kingdom monera are Anabaena (Blue-green algae), Oscillatoria, Nostoc colony, Mycoplasma, Bacterium, etc.

Fig: Types of Bacteria

In shape, bacteria are of three types:
(i) Rod shape called bacilli (singular Bacillus)
(ii) Spherical or cocci (singular Coccus)
(iii) Spiral or spirilla (singular Spirillum)
(iv) Vibrio or Comma shaped

Kingdom Protista

Characteristics of Protista:
1. Kingdom Protista includes unicellular algae, diatoms, fungi and protozoans.
2. The organisms in this kingdom are unicellular, eukaryotic organisms (as well defined nuclei and other cell organelles are present).
3. They have \({\rm{80S}}\) ribosomes in the cytoplasm. Organelles have \({\rm{70S}}\) ribosomes. 
4. They show zygotic meiosis and gametic meiosis.
5. Mode of nutrition is either autotrophic (as in algae and diatoms) or heterotrophic (as in protozoans). Some forms show mixotrophic nutrition (example, Euglena).
6. Some protists bear hair-like cilia or whip-like flagella for movement. In some protists like Amoeba movement takes place by pseudopodia (false feet).
7. Flagella is of \(9+2\) pattern of microtubular arrangement. 
8. These organisms show overlapping characters of plants and animals. The boundaries of this kingdom are not well defined.
a. There are Plant-like Protists, like Diatoms, Dinoflagellates, Euglenoids.
b. There are Fungus-like Protists, like Slime Moulds.
c. There are Animal-like Protists, like Sarcodina, Mastigophora members.

Fig: Examples of Kingdom Protista

Sub-groups of Protists:

1. Chrysophytes
2. Dinoflagellates
3. Euglenoids
4. Slime Moulds
5. Protozoans

Kingdom Fungi

Fungi, in the traditional two kingdom system of classification, were kept under plants because of the presence of a cell wall.

Characteristics of Fungi:
1. Fungi are non-green (lacking chlorophyll) eukaryotic organisms. 
2. The body is haploid and thalloid. Body is made up of thread-like elongated, tubular hyphae. 
3. The body of fungus is made up of microscopic threads, called hyphae (singular hypha). The mass of hyphae that form an individual is called the mycelium (plural mycelia).
4. Fungi are heterotrophic in nutrition, and the food is obtained either saprophytically (from dead organic matter) or parasitically (from living tissues of other organisms). Most fungi are saprophytes.
5. Cell wall consists of a tough complex sugar called chitin.
6. Reserve food material consists of glycogen.
7. Some fungi live in symbiotic relationship with green algae or blue green algae, as in lichens.
8. Many fungi cause diseases to both animals (like ringworm), plants (like black stem rust of wheat, white rust in mustard, late blight of potato).
9. Examples: Yeast, Rhizopus, mushrooms, Aspergillus, Penicillium.
10. Fungi are classified on the basis of reproduction into following four major classes:
(a) Phycomycetes
(b) Ascomycetes
(c) Basidiomycetes
(d) Deuteromycetes

Fig: Examples of Kingdom Fungi

Kingdom Plantae

Characteristics of Plantae:
1. Kingdom Plantae includes all organisms which are multicellular, eukaryotic and green autotrophs.
2. The kingdom which consists of green plants is further divided first on the basis of the differentiation of the plant body, whether well differentiated into different parts (like root, stem, leaf, etc.) or not.
3. The second level of classification is based on whether the differentiated plant body has vascular tissues or not. Further classification is based on 
(i) whether seeds are present or not, and 
(ii) whether seeds are enclosed within fruits or not.
4.Kingdom Plantae includes aquatic thallophytes (green, brown and red algae), and land plants consisting of Bryophytes, Pteridophytes, Gymnosperms and Angiosperms

Fig: Examples of Kingdom Plantae

5. The organisms of this kingdom are non-motile (in higher forms) and possess rigid cell walls and chlorophyll inside the plastids.
6.They are primarily photoautotrophic and evolve oxygen during photosynthesis.

Kingdom Animalia

Despite more than a million types of animals inhabiting the earth, the animal kingdom is characterized by the following common features:

Characteristics of Animalia:
1. Animals are multicellular, eukaryotic organisms.
2. Most animals have a high level of tissue differentiation and many have specialized body organs.
3. Most animals have a nervous system that is used to coordinate their body actions and responses.
4. Animal nutrition is heterotrophic. They lack photosynthetic pigments.
5. Animal cells lack cell walls.
6. Animals possess the power of locomotion.
7. In sexual reproduction, animals produce haploid male gametes (sperms) and female gametes (ova; singular ovum). After fertilization, the zygote after repeated divisions and differentiation produces the new individual. Kingdom Animalia includes sponges, corals, flatworms, roundworms, earthworms, insects, snails, starfish, fishes, frogs, toads, birds, snakes, tigers, elephants and humans.

Advantages of Five Kingdom Classification

1. All prokaryotic organisms were included under Kingdom Monera.
2. The fungi were placed in a separate kingdom – (they are heterotrophs and the cell wall is made up of chitin).
3. All the unicellular eukaryotic organisms were placed in Kingdom Protista.
4. It considered the evolutionary relationship among organisms.

Five Kingdom Classification – At a Glance

Character	Monera	Protista	Fungi	Plantae	Animalia
Nucleus	Prokaryotic	Eukaryotic	Eukaryotic	Eukaryotic	Eukaryotic
Nuclear membrane	Absent	Present	Present	Present	Present
Mitochondria	Absent	Present	Present	Present	Present
Plastid	Absent	Present for some forms	Absent	Present	Absent
Motility	By flagella, gliding, or some non-motile	By flagella, cilia, pseudopodia, some are non-motile	Non-motile	Non-motile in higher forms	Present in various modes
Nutrition	Photoautotrophic, Chemoautotrophic, Heterotrophic, Saprobiotic,Parasitic	Photoautotrophic, Heterotrophic	Saprobiotic, Parasitic	Photoautotrophic	Heterotrophic
Multicellularity	Absent	Absent	Present	Present	Present

Summary

The Five Kingdom classification was proposed by Whittaker. The basic criteria used to classify five kingdoms include cell organization, life form, mode of nutrition, role in ecology and finally, evolutionary relationships. Monera is the only kingdom encompassing all prokaryotic organisms. Protista is the kingdom that shows a link between animals, fungi, and plants. Furthermore, Fungi are non-green eukaryotic organisms. Kingdom Plantae covers all organisms which are multicellular, eukaryotic and green autotrophs. Kingdom Animalia includes all organisms that are multicellular and eukaryotic.

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FAQs on Five Kingdom Classification

Q.1. What are the limitations of five-kingdom classification?
Ans: This system of classification cannot classify composite organisms like lichens and borderline forms like viruses. This also clubbed Archaebacteria and Eubacteria together, which, according to modern understanding is not very much scientific.

Q.2. Why can’t viruses be placed in five kingdom classification?
Ans: Viruses are sub-microscopic, intracellular, pathogenic infectious agents which are thought to be in the borderline between living and non-living. Outside the living cells, in which it can replicate, viruses show nonliving characters like they can be crystallised. They do not show metabolism outside the host cell. So, they could not be classified in the five kingdom system of classification.

Q.3. What are the 5 Kingdom of classification?
Ans: The Five Kingdom classification is simply defined as the placing of organisms with respect to their cell structure, mode of nutrition and body composition. The Five Kingdom Classification is as follows: 
a. Kingdom Monera
b. Kingdom Protista
c. Kingdom Fungi
d. Kingdom Plantae
e. Kingdom Animalia

Q.4. What are the merits of five kingdom classification?
Ans: This system of classification for the first time separated prokaryotes and eukaryotes. Besides that, it also classified unicellular organisms from multicellular forms. The separation of Kingdom Fungi is logical, as they cannot be classified with plants or other categories.

Q.5. How many eukaryotic kingdoms are present in the five-kingdom classification?
Ans: There are four eukaryotic kingdoms, Protista, Plantae, Fungi, and Animalia. Monera is the prokaryotic kingdom.

Q.6. Who proposed the five kingdom classification?
Ans: R.H. Whittaker in 1969 proposed the Five Kingdom System of Classification.

Q.7. What are the 5 kingdoms and examples of each?
Ans: The 5 Kingdoms are:
a. Kingdom Monera- e.g., Anabaena (Blue-green algae), Oscillatoria, Nostoc colony, Mycoplasma, Bacterium, etc.
b. Kingdom Protista- e.g., Amoeba, Paramoecium, Euglena, etc.
c. Kingdom Fungi- e.g., Yeast, Mushroom, Rhizopus, etc.
d. Kingdom Plantae- e.g., Algae, bryophytes, pteridophytes, gymnosperms and angiosperms.
e. Kingdom Animalia- e.g., flatworms, roundworms, earthworms, insects, snails, starfish, fishes, frogs, toads, birds, snakes, tigers, elephants and humans.

Other important Biology articles:

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Circulatory Disorders	Blood Groups
Blood	Double Circulation

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