Assertion :Azolla pinnata is used as a biofertiliser in rice fields.
Reason: Azolla pinnata is a nitrogen fixing cyanobacteria and can coexist with rice plants.

Assertion is true but reason is false.

The correct answer is Option (3)- Assertion is true but reason is false.

Azolla pinnata is indeed used as a biofertilizer in rice fields. Azolla is a small aquatic fern that forms a symbiotic relationship with the nitrogen-fixing cyanobacterium Anabaena azollae. Azolla and Anabaena have a fascinating symbiotic relationship that benefits both organisms and plays a crucial role in nitrogen fixation.

• Azolla: A tiny aquatic fern that lacks the ability to fix nitrogen from the air on its own.
• Anabaena: A nitrogen-fixing cyanobacterium (often referred to as a blue-green alga) that lives inside specialized cavities in the Azolla's leaves.

The Benefit for Azolla:

• Anabaena fixes atmospheric nitrogen (N2) and converts it into a usable form (e.g., ammonia) that Azolla can readily absorb. This provides Azolla with the essential nitrogen it needs for growth and development, even in environments devoid of combined nitrogen sources (like nitrates).

The Benefit for Anabaena:

• Azolla provides a safe haven for Anabaena within its leaf cavities. The fern protects the cyanobacterium from harsh environmental conditions like UV radiation and predation. Additionally, Azolla supplies Anabaena with fixed carbon compounds (sugars) produced through photosynthesis.