Question

Members of which of the nitrogen fixing genera form symbiotic associations with aquatic fern {Azolla

• A. Nostoc
• B. Anabaena
• C. Azotobacter
• D. Calothrix

Hint:

Azolla is often called a "green manure factory" in rice cultivation because of its rapid growth and high nitrogen-fixing capacity.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks to identify the specific cyanobacterium that lives symbiotically within the cavities of the aquatic fern Azolla.
Detailed Explanation:

• Azolla-Anabaena Association: Azolla is a small, free-floating aquatic fern. It has a unique symbiotic relationship with a nitrogen-fixing cyanobacterium (blue-green algae) known as {Anabaena azollae.

• Location: The Anabaena filaments reside in specialized cavities found on the dorsal leaf lobes of the Azolla fern.

• Function: The cyanobacterium fixes atmospheric nitrogen and provides it to the fern. In return, the fern provides a protected environment and carbohydrates to the cyanobacterium. This association is extremely efficient and is used as a biofertilizer in rice paddies.

• Other Options: While Nostoc and Calothrix are nitrogen fixers, they are not the primary symbionts of Azolla. Azotobacter is a free-living, non-symbiotic nitrogen-fixing bacterium.
Final Answer:
The symbiotic nitrogen-fixing partner of Azolla is the genus Anabaena.