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🔬 Biology  ·  Biological Classification  ·  NEET

A student observes an organism with a peptidoglycan cell wall, no membrane-bound nucleus, and the ability to fix nitrogen using heterocysts. This organism most likely belongs to which group?

Answer: Cyanobacteria (Eubacteria).

  • A Archaebacteria (Archaea)
  • B Cyanobacteria (Eubacteria)
  • C Chrysophytes (golden algae and diatoms)
  • D Slime moulds (Myxomycota)

Correct answer: B. Cyanobacteria (Eubacteria)

Explanation: Cyanobacteria (blue-green algae), classified under eubacteria within Monera, are photosynthetic prokaryotes with chlorophyll a and a rigid cell wall; some filamentous forms like Nostoc and Anabaena fix nitrogen using heterocysts.

Whittaker's Five KingdomsMoneraprokaryotesProtistaunicell. eukaryotesFungichitin wallPlantaecellulose wallAnimaliano wallNOT in any kingdom: Viruses (non-cellular), Viroids (RNA, no coat), Lichens (alga+fungus symbiosis)Classification criteria: cell structure, nutrition mode, body organisation, reproduction, phylogeny

Whittaker's five-kingdom system (1969) groups all cellular life by cell structure and nutrition; viruses, viroids, and lichens fall outside this system entirely since they aren't independently classifiable as one of the five.

Concept context

Whittaker's five kingdom system covering Monera, Protista, Fungi, plus viruses, viroids, and lichens. A foundational NEET chapter on how living organisms are grouped.

Read the full Biological Classification notes →