Question

Which nitrogen-fixing bacteria forms a symbiotic relationship with the water fern Azolla?

• A. Rhizobium
• B. Azotobacter
• C. Anabaena
• D. Clostridium

Hint:

Azolla + Anabaena → Symbiotic nitrogen fixation → Used as biofertilizer.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Biological nitrogen fixation involves converting atmospheric $N_2$ into ammonia. This is often done by bacteria living inside plant tissues.
Step 2: Detailed Explanation:
Azolla is a small, free-floating aquatic fern.
It has a symbiotic relationship with a cyanobacterium (blue-green alga) called Anabaena azollae.
The bacteria live in specialized cavities in the fern's leaves, where they fix nitrogen and provide it to the plant.
In exchange, the fern provides carbohydrates and a protected niche for the bacteria.
This association is highly valued in agriculture, especially in rice cultivation, as a natural nitrogen fertilizer.
Rhizobium is symbiotic with legumes (beans/peas).
Step 3: Final Answer:
The nitrogen-fixing bacteria symbiotic with Azolla is Anabaena.