Question
Describe Whittaker’s five kingdom classification system. What criteria did he use, and what are the defining features and examples of each kingdom?
(NEET, CBSE Class 11 — Biological Classification)
Solution — Step by Step
R.H. Whittaker (1969) proposed five kingdoms based on: (1) Cell structure — prokaryotic vs eukaryotic, (2) Body organisation — unicellular vs multicellular, (3) Mode of nutrition — autotrophic, heterotrophic (absorptive or ingestive), and (4) Reproduction and phylogenetic relationships.
All prokaryotes. No membrane-bound organelles. Includes bacteria (eubacteria) and archaebacteria. Cell wall present (peptidoglycan in most). Nutrition: autotrophic (photosynthetic, chemosynthetic) or heterotrophic. Examples: E. coli, Nostoc (cyanobacteria), Mycobacterium.
Eukaryotic, mostly unicellular. Include protozoans (Amoeba, Paramecium), algae (diatoms, Euglena), and slime moulds. Link between prokaryotes and complex eukaryotes. Nutrition varies: autotrophic, heterotrophic, or mixotrophic.
Eukaryotic, mostly multicellular (except yeasts). Cell wall of chitin. Nutrition: heterotrophic by absorption (saprophytic, parasitic, or symbiotic). Body is made of hyphae forming mycelium. Examples: Mucor, Penicillium, Agaricus (mushroom), yeast.
Plantae: Multicellular eukaryotes, cell wall of cellulose, autotrophic (photosynthesis). Includes algae (in some classifications), bryophytes, pteridophytes, gymnosperms, angiosperms.
Animalia: Multicellular eukaryotes, no cell wall, heterotrophic by ingestion. Exhibit locomotion, nervous system. From sponges to mammals.
graph TD
A["Five Kingdoms<br/>(Whittaker 1969)"] --> B["Monera<br/>Prokaryotic<br/>Bacteria"]
A --> C["Protista<br/>Eukaryotic, Unicellular<br/>Amoeba, Euglena"]
A --> D["Fungi<br/>Eukaryotic, Absorptive<br/>Mushroom, Yeast"]
A --> E["Plantae<br/>Eukaryotic, Autotrophic<br/>Trees, Ferns"]
A --> F["Animalia<br/>Eukaryotic, Ingestive<br/>Insects, Mammals"]Why This Works
The five kingdom system improved upon the two-kingdom (plant/animal) system by giving separate kingdoms to prokaryotes (Monera), unicellular eukaryotes (Protista), and fungi. This resolved the problem of organisms like Euglena (photosynthetic but motile) and fungi (previously placed with plants despite being heterotrophic).
The main criterion that separates the three multicellular kingdoms: Plantae = autotrophic, Fungi = absorptive heterotrophy, Animalia = ingestive heterotrophy.
Alternative Method — Two Questions Approach
Ask two questions to classify any organism: (1) Prokaryotic or eukaryotic? If prokaryotic, it is Monera. (2) If eukaryotic: unicellular (Protista), multicellular autotroph (Plantae), multicellular absorptive heterotroph (Fungi), or multicellular ingestive heterotroph (Animalia).
NEET often asks about the limitations of Whittaker’s system. Key issue: viruses, viroids, and prions are NOT included in any kingdom. Also, some organisms like Euglena still do not fit neatly — it has chloroplasts (plant-like) but can also ingest food (animal-like).
Common Mistake
Students place fungi in Plantae because “they do not move.” But fungi are heterotrophs — they absorb nutrients from dead or living organic matter. The cell wall composition is also different: fungi have chitin, plants have cellulose. These two differences clearly separate fungi from plants.