Diversity in Living Organisms

Five Kingdom Classification

Scientists have been trying to classify living organisms in various ways for centuries. In fact, even Aristotle classified living organisms on the basis whether they lived on land, water or air. But biologists wanted a broader system of classifying living organisms. Hence came the five kingdom classification. Let us look at it in detail.

Five Kingdom of Classification

Very early on, scientists began grouping the living organisms under different categories. Some biologists classified organisms into plants and animals. Ernst Haeckel, Robert Whittaker, and Carl Woese are some biologists who attempted a broader system of classification. Amongst these, the Five Kingdom Classification proposed by Robert Whittaker stood out and is widely used.

Whitaker proposed that organisms should be broadly divided into kingdoms, based on certain characters like the structure of the cell, mode of nutrition, the source of nutrition, interrelationship, body organization, and reproduction. According to this system, there are five main kingdoms. They are:

Kingdoms are divided into subgroups at various levels. The following flowchart shows the hierarchy of classification.

Kingdom → Phylum  →  Class  →   Order  →   Family →   Genus  →   Species

Five Kingdom Classification

(Source: Wikipedia)

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Distinguishing Features of the Five Kingdoms

Kingdom Monera

These organisms are prokaryotic and unicellular. They do not have a well-defined nucleus and also lack cell organelles.  Some organisms show the presence of cell wall while there are others without a cell wall. Consequently, some organisms are autotrophic and others are heterotrophic. Examples include Bacteria, Cyanobacteria, and Mycoplasma.

Features of Monerans

  1. They are typically unicellular organisms (but one group is mycelial).
  2. Sap vacuoles do not occur. Instead, a gas vacuole may be present.
  3. The predominant mode of nutrition is absorptive but some groups are photosynthetic (holophytic) and chemosynthetic.
  4. The organisms are non-motile or move by the beating of simple flagella or by gliding.
  5. The genetic material in these organisms is the naked circular DNA.
  6. A nuclear envelope is absent. Both, ribosomes and simple chromatophores, are the only subcellular organelles in the cytoplasm.

Types of Monerans

Kingdom Monera is classified into three sub-kingdoms-

  • Archaebacteria
  • Eubacteria
  • Cyanobacteria

Kingdom Protista

Organisms grouped under Kingdom Protista are all unicellular, but eukaryotic organisms. These are the simplest forms of eukaryotes that exhibit either autotrophic or heterotrophic mode of nutrition. Some organisms have appendages such as cilia or flagella or pseudopodia to move around. Some examples are Diatoms, Protozoans like Amoeba, Paramoecium

Five Kingdom Classification

(Source: Wikipedia)

 Features of Kingdom Protista:

  1. They are primarily aquatic.
  2. They form a link with the others dealing with plants, animals and fungi.
  3. Also, they have a well-defined nucleus and other membrane-bound organelles.
  4. Some have flagella or cilia.
  5. They can reproduce asexually and sexually.

Sub-groups of Protista:

  • Chrysophytes
  • Dinoflagellates
  • Euglenoids
  • Slime Moulds
  • Protozoans

Kingdom Fungi

Heterotrophic, Multicellular and Eukaryotic organisms are grouped under Kingdom Fungi. Their mode of nutrition is saprophytic as they use decaying organic matter as food. They have cell walls, which are made up of a substance called Chitin. Fungi also form a symbiotic association with some blue-green algae. Yeast, Mushroom, Aspergillus are examples of Fungi.

Features of Fungi:

  1. The plant body of true fungi is a thallus. It may be non-mycelial or mycelial.
  2. The cell wall of fungi is mainly made up of chitin and cellulose.
  3. The fungi are achlorophyllous organisms. Hence, they cannot prepare their food. They live as heterotrophs i.e., as parasites and saprophytes. Some forms live symbiotically with other green forms.
  4. The fungi either reproduce vegetatively, asexually or sexually.

Kingdom Plantae

These are Eukaryotic, Multicellular organisms with a cell wall that is made up of cellulose. They are autotrophs and synthesize their own food through the process of photosynthesis. This kingdom includes all plants.

Based on the body differentiation and presence or absence of specialized vascular tissue, Kingdom Plantae is divided into different divisions, namely Thallophyta, Bryophyta, Pteridophyta, Gymnosperms, and Angiosperms. Examples are Spirogyra, Ferns, Pines, and Mango Plant etc.

Features of Plantae:

  1. They have special organelles called chloroplasts.
  2. They are autotrophic.
  3. Reproduction can be asexual and sexual.
  4. They show alternation of generation.

Kingdom Animalia

This Kingdom includes organisms that are Multicellular, Eukaryotic, without the presence of cell wall. They have a heterotrophic mode of nutrition. They also exhibit great diversity. Some organisms are simple while others have a complex body with specialized tissue differentiation and body organs.

The Animal Kingdom is divided into many phyla and classes. Some of the phyla are Porifera, Coelenterata, Arthropoda, Echinodermata, Chordata etc. Examples – Hydra, Starfish, Earthworms, Monkeys, Birds etc.

Features of Animalia:

  1. They are multicellular organisms that do not possess chlorophyll.
  2. The mode of nutrition is heterotrophic i.e. they depend on other organisms for food.
  3. They have muscle cells due to which they have the capability to contract and relax the body parts.
  4. Reproduction is sexual. However, asexual reproduction is also found in lower forms.
  5. During development, the multicellular embryo is formed from the zygote.
  6. They require oxygen for aerobic respiration.

Solved Questions For You

Q. Pick the correct statement from the following:

  1. Fungi are unicellular.
  2. Monerans are eukaryotic.
  3. Protistans are eukaryotic.
  4. Plants and animals are not multicellular.

Ans. Protistans are Eukaryotic is the correct option. Fungi are microorganisms but are multicellular. Monerans are prokaryotes. And we all know that plants and animals are definitely multi-cellular.

FAQ’s on Five Kingdom Classification

Q1. Who proposed a five-kingdom classification and named kingdoms as Monera, Protista, Fungi, Plantae and Animalia?

Answer: R.H. Whittaker in 1969 introduced a Five Kingdom Classification. The kingdoms characterize by him were titled Monera, Protista, Fungi, Plantae, and Animalia.
The main principle for analysis used by him include complexity of cell structure (it may be eukaryotic or prokaryotic), complexity of organisms (unicellular or multicellular), thallus organisation, mode of nutrition (autotrophs or heterotrophs or acrophobic), reproduction (sexual or asexual) and phylogenetic relationships (prokaryotes to eukaryotes, unicellular to multicellular organism).

Q2. In Whittaker’s five kingdom classification, eukaryotes were assigned to
A. All five
B. Only Four
C. Only Three
D. Only One

Answer: The five-kingdom classification was proposed by R. H. Whittaker in the year 1969.
The kingdom Monera is comprised of unicellular prokaryotic organisms. The other four kingdoms, Protista, Fungi, Plantae, and Animalia are composed of all the eukaryotic organisms.

Thus, the correct answer is option B.

Q3. In the five-kingdom system of classification developed by R. H. Whittaker, members of the kingdom Animalia are heterotrophic, eukaryotic and
A. Multicellular
B. Motile
C. Unicellular or Multicellular
D. Both A and B

Answer: R. H. Whittaker proposed the five kingdom classification. The five kingdom classification are- Monera, Protista, Fungi, Plantae and Animalia. 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. These are multicellular organisms which are composed of many cells and can perform activities like locomotion.
Thus, the correct answer is option D.

Q4. Who proposed the five-kingdom system of classification and on what basis?

Answers: Five kingdoms of classification was proposed by RH Whittaker in 1969. He divided all living organisms into five kingdoms based on the following features:

  • The complexity of cell structures
  • The complexity of body structures
  • Mode of obtaining nutrition
  • Ecological lifestyle
  • Phylogenetic relationship
  • The five kingdoms proposed by him were:
  • Kingdom Monera which includes prokaryotes.
  • Kingdom Protista which includes unicellular eukaryotes.
  • Kingdom Fungi which includes fungi.
  • Kingdom Plantae which includes multicellular eukaryotic plants.
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