_________ associated with plants like Azolla and Cycas can be used as a biofertilizers.

Options

A. Anabaena
B. Nostoc
C. Plectonema
D. Oscillatoria

Answer

**Step-by-Step Solution:**

1. **Identify the Organisms**: The question asks for organisms associated with plants like Azolla and Cycas that can be used as biofertilizers. The key organisms mentioned in the transcript are Anabaena, Nostoc, Plectonema, and Oscillatoria.

2. **Focus on the Correct Organism**: From the transcript, it is highlighted that Anabaena is specifically associated with Azolla and is known for its nitrogen-fixing capabilities. This makes it a suitable candidate for a biofertilizer.

3. **Understanding Biofertilizers**: Biofertilizers are substances that contain living microorganisms which promote plant growth by increasing the supply or availability of primary nutrients to the host plant. In this case, Anabaena helps in nitrogen fixation, converting atmospheric nitrogen into a form that plants can use.

4. **Association with Plants**: Azolla is a water fern that has a symbiotic relationship with Anabaena, which resides in its leaves. Cycas, a gymnosperm, also has a symbiotic relationship with nitrogen-fixing cyanobacteria, but the transcript emphasizes Anabaena's association with Azolla.

5. **Conclusion**: Therefore, the blank in the question can be filled with "Anabaena," as it is the nitrogen-fixing cyanobacterium associated with Azolla and can be used as a biofertilizer.

**Final Answer**: Anabaena associated with plants like Azolla and Cycas can be used as biofertilizers.

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