Question

Cyanobacteria are useful biofertilizers in fields of
(a) Wheat
(b) Maize
(c) Rice
(d) Sugarcane

Answer 1

Hint: China is the largest and India is the second- largest producer of this crop. Azolla is the smallest pteridophyte, it is an aquatic fern that is used as a biofertilizer which helps in increasing the yield. This is because of the association with nitrogen- fixing cyanobacteria in its leaves.

Complete answer:
Cyanobacteria are used as biofertilizers mostly in paddy fields or rice fields. They help in nitrogen fixation and thus help in increasing the yield of rice. They may be symbiotic or free- living nitrogen- fixing cyanobacteria.
- 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.
- Nitrogen fixation is the process of converting nitrogen to ammonia. It is of two types, abiological and biological.
- Natural biological fixation occurs naturally by facts such as UV radiation and lightning. Industrial abiological nitrogen fixation occurs in chemical industries.
- Biological nitrogen fixation is of two types: symbiotic and symbiotic.
- Asymbiotic bacteria involve free- living nitrogen- fixing microorganisms like  Azotobacter, Rhodospirrilium, , Clostridium, etc.
- 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.
- Biological nitrogen fixation was discovered by Winogradsky.
- 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,” Cyanobacteria are useful biofertilizers in fields of rice.”

Note: It should be kept in mind that nitrogen- fixing cyanobacteria may be free- living and or symbiotic. Examples of free- living nitrogen- fixing cyanobacteria are Nostoc, Anabaena, Aulosira, and Cylindrospermum. Anabaena can also fix nitrogen symbiotically. In leguminous plants root nodules are found which harbor nitrogen- fixing bacterias like Rhizobium which help in nitrogen fixation