Biological Classification Overview

Biological Classification

• Biological classification organizes organisms based on significant features and relationships.
• Aristotle was the pioneer of biological classification, categorizing plants as trees, shrubs, and herbs, and animals based on specific characteristics.

Purpose of Biological Classification

• Facilitates the systematic study of a vast number of known plants and organisms.

Systems of Classification

• Two Kingdoms: Proposed by Carolus Linnaeus, classifies organisms into Plantae and Animalia.
• Three Kingdoms: Introduced by Ernst Haeckel and Copeland, including Plantae, Protista, and Animalia.
• Four Kingdoms: Proposed by R.H. Whittaker, adding Monera to the previous system.
• Five Kingdoms: Classification includes Plantae, Protista, Monera, Fungi, and Animalia.
• Six Kingdoms: Introduced by Carl Woese, further dividing Monera into Archaebacteria and Eubacteria.

Two Kingdom Classification System

• Kingdom Plantae: Comprises autotrophic, fixed organisms.
• Kingdom Animalia: Includes motile, heterotrophic organisms.

Limitations of the Two-Kingdom System

• Unicellular and multicellular organisms are grouped together despite differences.
• Prokaryotic organisms, such as bacteria and cyanobacteria, are included under plants.
• Puts lichens, which are symbiotic organisms, under plants.

Five Kingdom Classification System

• Proposed by R.H. Whittaker in 1969.
• Defined kingdoms: Monera, Fungi, Protista, Animalia, Plantae.

Criteria for Five Kingdom Classification

• Cell Structure: Differences between prokaryotic and eukaryotic cells.
• Thallus Organisation: Organization of the body structure.
• Reproduction: Methods of reproduction among organisms.
• Phylogenetic Relationships: Evolutionary relationships and lineage.

Key Points of Five Kingdom Classification

• Earlier systems grouped diverse organisms into 'Plants', leading to inaccuracies.
• Eukaryotic and prokaryotic organisms were mixed, failing to distinguish key differences.
• Kingdom Fungi was established separately due to differences in cell wall composition (chitin vs. cellulose).
• Kingdom Protista brought together unicellular organisms like Chlamydomonas and Amoeba, reflecting distinctions not previously considered.

Merits of Five Kingdom Classification

• Exhibits a phylogenetic perspective for better understanding evolutionary lineages of organisms.