Biological Classification - Notes | Class 11 | Part 1: Classification systems

Classification Systems

Aristotle's Classification

• Aristotle was the earliest to attempt a more scientific basis for classification of organisms.
• He classified plants to trees, shrubs & herbs and animals into 2 groups: those with red blood & without red blood.

Linnaeus's Two-Kingdom Classification

• Linnaeus (1758) classified organisms into Two Kingdoms: Kingdom Plantae & Kingdom Animalia.

Drawbacks of 2-Kingdom Classification

• Prokaryotes and eukaryotes were both included under 'Plants'.
• Unicellular and multicellular organisms were grouped together.
• Didn't differentiate between heterotrophic fungi and autotrophic green plants.

Five Kingdom Classification

• Proposed by R.H. Whittaker (1969)
• Includes Monera, Protista, Fungi, Plantae & Animalia
• Based on cell structure, thallus organization, mode of nutrition, reproduction and phylogenetic relationships
• Three-domain system: Divides Kingdom Monera into two domains. Eukaryotic kingdoms are included in third domain (six-kingdom classification).

Characteristics of the Five Kingdoms
Characters	Monera	Protista	Fungi	Plantae	Animalia
Cell type	Prokaryotic	Eukaryotic	Eukaryotic	Eukaryotic	Eukaryotic
Cell wall	Non-cellulosic (polysaccharide + amino acid)	Present in some	Present (Chitin & polysaccharides)	Present (Cellulose)	Absent
Nuclear membrane	Absent	Present	Present	Present	Present
Body organization	Cellular	Cellular	Multicellular, loose tissue	Tissue/organ	Tissue/organ/organ system
Mode of nutrition	Autotrophic (photosynthetic & chemosynthetic) and heterotrophic (saprophyte/parasite)	Autotrophic (photosynthetic) and heterotrophic	Heterotrophic (saprophytic or parasitic)	Autotrophic (photosynthetic)	Heterotrophic (holozoic, saprophytic etc.)

Select Next Topic

Topic 1: Classification
Topic 2: Kingdom Monera
Topic 3: Kingdom Protista
Topic 4: Kingdom Fungi
Topic 5: Plantae, Animalia, Viruses, Lichens, etc.

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