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

Part 1: 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 Your Next Topic 👇

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