Class 11 Biology Chapter 2 Biological Classification – Revision Notes

Whittaker’s five-kingdom system anchors this Class 11 Biology chapter, grouping organisms from Monera to Animalia while placing viruses, viroids, and lichens outside conventional classification altogether.

Last Updated: September 23, 2026

Five Kingdoms (Whittaker, 1969)

• Monera: prokaryotic.
• Protista: unicellular eukaryotic.
• Fungi: heterotrophic, chitin cell wall, hyphae/mycelium.
• Plantae: autotrophic, cellulose cell wall.
• Animalia: heterotrophic, no cell wall.

Non-Cellular Entities

• Viruses: nucleic acid + protein coat, obligate parasites.
• Viroids: free RNA only, no protein coat (Diener).
• Lichens: alga/cyanobacterium + fungus symbiosis.

One-Line Summary

Biological classification organizes life into five kingdoms based on cell structure, nutrition, and organization, while viruses, viroids, and lichens are treated as special non-cellular or symbiotic entities outside this scheme.

Frequently Asked Questions

Why did the five-kingdom classification replace the older two-kingdom system?
The two-kingdom system, based only on plants and animals, could not properly place organisms like bacteria, fungi, and single-celled organisms with mixed characteristics; the five-kingdom system classifies life more accurately using cell structure and nutrition.

What is the main criterion that separates the kingdom Monera from all other kingdoms?
Monera consists entirely of prokaryotic organisms, meaning they lack a defined nucleus and membrane-bound organelles, while all other kingdoms consist of eukaryotic organisms.

Written by Satish

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