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Question: Answered & Verified by Expert
A free living nitrogen-fixing cyanobacterium which can also form symbiotic association with the water fern Azolla is:
BiologyMineral NutritionNEETNEET 2004
Options:
  • A Tolypothrix
  • B Chlorella
  • C Nostoc
  • D Anabaena.
Solution:
2794 Upvotes Verified Answer
The correct answer is: Anabaena.
Azolla (water fern) and the blue-green alga Anabaena azollae maintain a symbiotic relationship where the alga provides nitrogen to the fern, and the fern provides a habitat for the alga.
Related Theory
Frankia show nitrogen fixation in both symbiotic association with actinorhizal plants, Casuarina and free-living aerobic conditions, while most Rhizobia fixes nitrogen in symbiotic form only.

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