Biological Classification: 5 Kingdom & 6 Kingdom System

Botany Sir Himansu

BIOLOGICAL CLASSIFICATION

A. Classification

Arrangement of different organisms into groups and subgroups on the basis of similarities and differences is called classification.

KINGDOM SYSTEM OF CLASSIFICATION

1. Two Kingdom System

Proposed by Linnaeus.

The divided living organisms into 2 kingdoms:

  1. Plantae
  2. Animalia

Characters

Character Plantae Animalia
1. Type of organism Autotrophic Heterotrophic
2. Chlorophyll Present Absent
3. Mode of nutrition Holophytic / Photosynthetic Holozoic / Ingestive
4. Locomotion Absent Present
5. Consciousness Low High
6. Cell wall Present Absent
7. Cell organization Unicellular & multicellular Multicellular

Note: Most included in Plantae and Animalia.

Demerits

  • No differentiation between prokaryotes and eukaryotes.
  • No differentiation between autotrophic and heterotrophic organisms.
  • No differentiation between unicellular and multicellular organisms.
  • Fungi were included in kingdom Plantae.
  • Euglena has chlorophyll but was included in kingdom Animalia.
  • Slime mould has cell wall and chlorophyll but was included in Plantae.
  • Monera was not properly separated.

2. Three Kingdom System

Proposed by Ernst Haeckel.

He included Kingdom Monera.

Monera originally used term Mychota for kingdom Monera.

Kingdom Protista

It mainly includes unicellular organisms.

It includes unicellular autotrophic and heterotrophic organisms.

Demerits

It mainly includes unicellular organisms.

3. Four Kingdom System

Proposed by Copeland.

He included Kingdom Monera.

Copeland originally used the term Mychota for Kingdom Monera.

Monera

  • Prokaryotic
  • Includes unicellular & prokaryotic organisms
  • Example: Bacteria, Cyanobacteria, Mycoplasma, Spirogyra (as written in the notes)

Demerits

No differentiation between prokaryotes and eukaryotes.

Position of Fungi was controversial.

Both autotrophic and heterotrophic organisms are included.

4. Five Kingdom System

Proposed by R. H. Whittaker.

Widely accepted system of classification.

Phylogenetic System of Classification

Important criteria for 5-kingdom system:

  1. Complexity of cellular organisation
    • Multicellular
    • Unicellular
  2. Presence of nuclear membrane
    • Prokaryotic
    • Eukaryotic
  3. Mode of nutrition — 3 types
    • Photosynthetic / Autotrophic
    • Ingestive
    • Absorptive / Saprobic
  4. Reproduction
  5. Phylogeny / Evolutionary history

Five Kingdoms

  1. Monera
  2. Protista
  3. Fungi
  4. Plantae
  5. Animalia

5. Six Kingdom System

Proposed by Carl Woese.

The six-kingdom system divides the organisms into:

  1. Archaea
  2. Eubacteria
  3. Protista
  4. Fungi
  5. Plantae
  6. Animalia

Three Domains

Based on 16S rRNA:

  1. Bacteria
  2. Archaea
  3. Eukarya

Archaea

Archaea differ from Eubacteria mainly in:

  1. Absence of murein / peptidoglycan in the cell wall.
  2. Presence of branched-chain monolayer lipid in the cell membrane.
  3. Presence of introns in DNA of some archaea.
  4. Ribosomal proteins and RNA show similarities with eukaryotes.

Diagram

Three Domains

  • Bacteria → Bacterial Kingdom
  • Archaea → Archaeal Kingdom
  • Eukarya → Eukaryotic Kingdom

Note

Reproduction is not considered as a criterion for classification.

Most important criteria: Mode of nutrition.