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💡 Classification keeps growing up
From Aristotle’s land-water-air to today’s five kingdoms, every new tool — especially the microscope — forced scientists to rethink how life is grouped.
How have classification systems changed over time?
- Aristotle (4th century BCE) grouped animals by habitat — land, water, air; the two kingdom system (1758) split life into Plantae and Animalia.
- A third kingdom Protista was added for unicellular microscopic organisms; then Monera was separated for prokaryotes like bacteria (four kingdom).
- Finally fungi were separated (heterotrophic, non-moving, absorb nutrients), giving the five kingdom system — Monera, Protista, Fungi, Plantae and Animalia (Fig. 12.4).
NCERT Question 7 — If all unicellular organisms were
If all unicellular organisms were grouped into a single kingdom, what problems would arise?
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🏛 India’s Scientific Contributions
The Rigveda and the Brihat Samhita classify animals on the basis of their habitat (terrestrial, aquatic and aerial), behaviour patterns and ecological roles — an early example of grouping life by observable characteristics.
✅ Test Yourself
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Who proposed the five kingdom classification, and in which year?
Show answer
Robert H. Whittaker, in 1969. -
Why was Protista added as a third kingdom?
Show answer
Because organisms like Amoeba and Paramecium move like animals but are unicellular and heterotrophic, while plants and animals are multicellular — the two kingdom system had no place for them.
Important Definitions
- Biodiversity — the enormous variety of living organisms on the Earth.
- Endemic species — species restricted to a particular region and found nowhere else naturally.
- Biodiversity hotspot — a region rich in endemic species that has undergone significant habitat loss.
- Biological classification — the scientific system of grouping organisms by similarities and differences.
- Autotroph — an organism that makes its own food, e.g. green plants.
- Heterotroph — an organism that depends on others for food.
- Prokaryote — a cell without a true, membrane-bound nucleus, e.g. bacteria.
- Eukaryote — a cell with a true, membrane-bound nucleus.
