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

2. BIOLOGICAL CLASSIFICATION

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 (Bacteria, cyanobacteria) and eukaryotes (fungi, mosses, ferns, gymnosperms & angiosperms) were included under ‘Plants’ based on the presence of cell wall. But they are widely differed in other characteristics.
• It included the unicellular and the multicellular organisms in same group. E.g. Chlamydomonas and Spirogyra were placed under algae.
• It did not differentiate between the heterotrophic fungi and the autotrophic green plants. Fungi have chitinous cell wall while the green plants have cellulosic cell wall.

Five Kingdom Classification

-    It is proposed by R.H. Whittaker (1969).

-    It includes Monera, Protista, Fungi, Plantae & Animalia.

-    This is based on cell structure, thallus organization, mode of nutrition, reproduction and phylogenetic relationships.

Three-domain system: It divides Kingdom Monera into two domains. Eukaryotic kingdoms are included in third domain.  Thus it is 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 (poly-saccharide + amino acid)	Present in some	Present (Chitin & polysaccharides)	Present (Cellulose)	Absent
Nuclear membrane	Absent	Present	Present	Present	Present
Body organisation	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.)

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👇 Select Your Topic Here 👇

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