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Question:medium

Which of the following organisms cannot fix nitrogen? A. Azotobacter
B. Oscillatoria
C. Anabaena
D. Volvox
E. Nostoc
Choose the correct answer from the options given below:

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Many cyanobacteria, like Anabaena and Nostoc, have specialized cells called heterocysts that help them fix nitrogen. Organisms like Volvox do not possess this ability.
Updated On: Nov 26, 2025
  • D only
  • B only
  • E only
  • A only
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The Correct Option is A

Solution and Explanation

Analysis of organisms: A. Azotobacter: Nitrogen-fixing bacterium. B. Oscillatoria: Cyanobacteria (blue-green algae); nitrogen-fixing. C. Anabaena: Nitrogen-fixing cyanobacterium. D. Volvox: Green alga; does not fix nitrogen; relies on environmental nitrogen. E. Nostoc: Nitrogen-fixing cyanobacterium. Conclusion: Only D does not fix nitrogen.
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