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Write down three drawbacks of two-kingdom classification system

GeneralClass 12AllAnswered 27 Mar 2026
Answer

Solution: The two-kingdom classification (Plantae and Animalia) had several fundamental limitations:

Drawback 1: Failed to Distinguish Unicellular and Multicellular Organisms

  • Grouped bacteria (E. coli) with complex plants
  • No recognition of cellular complexity levels
  • Ignored fundamental organizational differences

Drawback 2: Did Not Differentiate Eukaryotes and Prokaryotes

  • Placed prokaryotic blue-green algae with eukaryotic plants
  • Overlooked crucial nuclear membrane presence/absence
  • Ignored differences in:
    • Ribosome size (70S vs 80S)
    • Genetic organization
    • Cellular compartmentalization

Drawback 3: Could Not Separate Photosynthetic and Non-Photosynthetic Organisms

  • Placed photosynthetic algae and non-photosynthetic fungi together
  • Ignored nutritional mode as classification criterion
  • Failed to recognize fundamental metabolic differences

Additional Limitations:

  • No provision for viruses (acellular)
  • Ignored phylogenetic relationships
  • Placed slime molds ambiguously
  • Could not accommodate fungi (heterotrophic but plant-like)

Pro Tip: Understanding these limitations helps explain why modern classification uses five or six kingdoms with molecular phylogeny.

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