Whittaker Five Kingdom Classification System

In this Whittaker five kingdom classification system post we have briefly explained about Whittaker classification of five kingdom, Monera, Protista, Fungi, Plantae and Animalia, merits and demerits.

Whittaker Five Kingdom Classification System

In order to suggest a better system of classification of living organisms, R.H. Whittaker (1969) an American Taxonomist divided all the organisms into five kingdoms based on their phylogenetic relationships commonly known as Whittaker classification of five kingdom. 

Whittaker classification of five kingdom are Monera, Protista, Fungi, Plantae and Animalia. Whittaker classification of five kingdom.  takes into account the following important criteria: Complexity of Cell structure, Mode of nutrition, Body organization, Phylogenetic or evolutionary relationship.

Kingdom Prokaryotes

This kingdom includes all prokaryotic organisms i.e. mycoplasma, bacteria, actinomycetes (filamentous bacteria) and cyanobacteria (blue green Algae). They show the following characters.

They are microscopic. They do not possess a true nucleus. They lack membrane bound organelles. Their mode of nutrition is autotrophic or heterotrophic. Some bacteria are autotrophic and are photosynthetic. i.e. they can synthesize their organic food in the presence of sunlight eg. Spirillum. Some bacteria are chemosynthetic i.e. they can synthesize their organic food by deriving energy from some chemical reactions. eg. Nitrosomonas and Nitrobacter.

Many other bacteria like Rhizobium, Azotobacter and Clostridium can fix atmospheric nitrogen into ammonia. This phenomenon is called Biological Nitrogen Fixation. The heterotrophic bacteria depend upon external organic materials for their food. These can be saprotrophs, parasites and symbionts.

Some monerans like Archaebacteria can live in extreme environmental conditions like absence of oxygen (anaerobic), high salt condition, high temperature like 80⁰C or above and highly acidic soils.

Kingdom Protista

This kingdom includes eukaryotic unicellular mostly aquatic cells. They show the following characters. Most protist species are unicellular organisms; however, there are a few multicellular protists such as kelp.

They often bear cilia or flagella for locomotion. Most of them are photosynthetic autotrophs. They form the chief producers of food in oceans and in fresh water. All unicellular plants are collectively called as phytoplanktons and unicellular animals as zooplanktons. Phytoplanktons are photosynthetically active and have cell wall.

Zooplanktons are mostly predatory. They lack cell wall and show holozoic mode of nutrition as in Amoeba. Some protists are parasitic. Many protist species are decomposers, meaning they feed on dead creatures to meet their nutritional needs.

Euglena, a protozoan has two modes of nutrition. In the presence of sunlight it is autotrophic and in the absence of sunlight it is heterotrophic. This mode of nutrition is known as myxotrophic and hence they form a border line between plants and animals and can be classified in both.

Kingdom Fungi

This kingdom includes moulds, mushrooms, toad stools, puffballs and bracket fungi. They have eukaryotic cell organization. They show the following characteristics. Fungi can be unicellular, multicellular, or dimorphic, which means that depending on the environment, the fungi can be unicellular or multicellular.

Their mode of nutrition is heterotrophic since they lack the green pigment chlorophyll. Some fungi like Puccinia are parasites while others like Rhizopus are saprotrophic and feed on dead organic matter.

The filaments are referred to as hyphae (singular, hypha). Each hypha is made up of one or more cells with a tubular cell wall. A mycelium is a mass of hyphae that makes up the body of a fungus (plural, mycelia). The fungal classes of Basidiomycetes, Ascomycetes, Zygomycetes, and Deuteromycetes are known to contain chitin and chitosan in their cell walls.

Kingdom Plantae

It includes all multi-cellular plants of land and water. Major groups of Algae, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms belong to this kingdom. It shows the following characteristics. Plant cell walls are primarily made of cellulose, which is the most abundant macromolecule on Earth.

They show various modes of nutrition. Most of them are autotrophs since they have chlorophyll. Some plants are heterotrophs. For eg. Cuscuta is a parasite. Nepenthes and Drosera are insectivorous plants.

Kingdom Animalia

This kingdom includes all multi-cellular eukaryotic organisms. They are also referred to as metazoans. They show the following characteristic features. All animals show heterotrophic mode of nutrition. They form the consumers of an ecosystem. They have contractibility of the muscle cells. They can transmit impulses due to the presence of nerve cells. Some groups of animals are parasites eg. tapeworms and roundworms.

Merits

Whittaker (1969) an American Taxonomist divided all the organisms into 5 kingdoms based on their phylogenetic relationships an major merit of Whittaker classification of five kingdom. 

The organisms which are placed under the kingdom Animalia are heterotrophic and depend on the other organisms for food. These are eukaryotic organisms with well-developed organelles.

The main criteria of the Whittaker classification of five kingdom. were cell structure, body organization, mode of nutrition and reproduction, and phylogenetic relationships.

The organisms which are placed under the kingdom Animalia are heterotrophic and depend on the other organisms for food.

Demerits

Chlamydomonas and Chlorella are included under the kingdom Plantae in Whittaker classification of five kingdom. They should have been included under kingdom Protista since they are unicellular in Whittaker classification of five kingdom.

five kingdom system of classification

Whittaker Five Kingdom Classification System, Image Source: https://ncert.nic.in/ncerts/l/kebo102.pdf

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