- A Mesosome
- B Heterocyst
- C Pyrenoid
- D Plasmid
Correct answer: B. Heterocyst
Explanation: Heterocysts are specialized cells in certain filamentous cyanobacteria (e.g., Nostoc, Anabaena) that are the sites of nitrogen fixation.
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.