Question

The bacteria ______ supply natural manure to paddy fields.
A. Azolla
B. Anabaena
C. Azotobacter
D. Nostoc

Answer 1

Hint: It is a bacteria associated with the leaves of a pteridophyte.

Complete answer:
Azolla is the smallest pteridophyte, it is an aquatic fern that is used as a biofertilizer, this is because of the association with nitrogen-fixing cyanobacteria Anabaena in its leaves. Therefore Anabaena help in the supply of manures to paddy fields.

Additional Information:
1. Azolla is grown in paddy fields as it requires an aquatic environment. It is known by several names like Carolina fern, duck fern, duckweed fern, fairy fern, fairy moss, feathered water fern, mosquito fern, pacific mosquito fern, water velvet, and water fern.
2. Nitrogen fixation is the process of converting nitrogen to ammonia. It is of two types, abiological and biological.
3. Natural abiological fixation occurs naturally by facts such as UV radiation and lightning. Industrial abiological nitrogen fixation occurs in chemical industries.
4. Biological nitrogen fixation is of two types: symbiotic and symbiotic.
5. Asymbiotic bacteria involve free-living nitrogen-fixing microorganisms like Azotobacter, Rhodospirillum, Beijerinckia, Clostridium, etc.
6. Symbiotic bacteria involve Anabaena azollae in Azolla pinnata fern. Rhizobium in root nodules of leguminous plants, Frankia in root nodules of Alnus and Casuarina, Aerorhizobium in stem nodules of Sesbania, Xanthomonas and Mycobacterium in leaves of Ardisia, etc are also symbiotic bacteria.
7. Biological nitrogen fixation was discovered by Winogradsky.
8. Nitrogen is required by plants in the greatest amount, it is absorbed as nitrate and ammonia. It forms a major part of proteins, nucleic acids, cytochromes, chlorophyll, ATP, etc.

So, the correct answer is, The bacteria Anabaena supplies natural manure to paddy fields.

Note: It should be remembered that the cyanobacteria are Anabaena and it is symbiotically associated with the leaves of Azolla, which is a Pteridophyte. Growing of Azolla along paddy fields increases the yield by an enormous amount.