A free living nitrogen-fixing cyanobacterium which can also form symbiotic association with the water fern Azolla is
- Tolypothrix
- Chlorella
- Nostoc
- Anabaena.
The Correct Option is D
Approach Solution - 1
Approach Solution -2
Anabaena is a free-living cyanobacterium that can also form a symbiotic relationship with the water fern Azolla. In this symbiotic relationship, Anabaena fixes nitrogen from the atmosphere and makes it available to the Azolla. The Azolla, in turn, provides Anabaena with a protected environment and fixed carbon.
Explanation of other options:
- Tolypothrix: Tolypothrix is a filamentous cyanobacterium that can be found in freshwater and marine environments. It is not known to form a symbiotic relationship with Azolla.
- Chlorella: Chlorella is a unicellular green alga. It does not fix nitrogen and cannot form a symbiotic relationship with Azolla.
- Nostoc: Nostoc is a filamentous cyanobacterium that can be found in freshwater and terrestrial environments. Some species of Nostoc can form symbiotic relationships with plants, but not with Azolla
Thus, the right answer to this question is Anabaena.
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