Question

Nitrogen fixing cyanobacteria Anabaena is found in the root pockets of -

• A. Azolla
• B. Pistia
• C. Marsilea
• D. Salvinia

Hint:

The {Azolla}-{Anabaena} combination is a very important biofertilizer, especially in rice cultivation. This unique and powerful symbiotic relationship is a frequently tested topic.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The question asks to identify the plant that hosts the nitrogen-fixing cyanobacterium Anabaena in a symbiotic relationship.
Step 2: Detailed Explanation:
The symbiosis between the aquatic fern {Azolla} and the cyanobacterium {Anabaena azollae} is a classic example of a mutualistic relationship.
The Anabaena lives within specialized cavities in the dorsal lobes of Azolla's leaves, not in its roots. (The question uses the term "root pockets," which is biologically inaccurate, but points towards the known symbiotic pair). The cyanobacterium fixes atmospheric nitrogen, providing this essential nutrient to the fern. In return, the fern provides a protected environment and carbohydrates to the Anabaena.
The other plants listed (Pistia, Marsilea, Salvinia) are also aquatic ferns or floating plants but are not known for this specific symbiosis with Anabaena.
Step 3: Final Answer:
Despite the inaccuracy of "root pockets" (it should be leaf cavities), Azolla is the correct answer as it is the well-known symbiotic partner of Anabaena.