Question

Modern farmers can increase the yield of paddy up to 50% by the use of
A. Cyanobacteria
B. Rhizobium
C. Cyanobacteria in Azolla pinnata
D. Farm yard manure

Answer 1

Hint: The substance that contains living or latent cells of microorganism is called biofertilizers. Biofertilizers help to increase the nutrients of host plants. The cost of biofertilizers is very less in comparison to chemical fertilizers, biofertilizers are used in organic farming.

Complete answer:
- Azolla is a biofertilizer because its leaves have cyanobacteria called anabaena. This algae has the enzyme nitrogenase in the heterocyst.
- In algae heterocyst are specialized cells. These cells fix the nitrogen with the help of enzymes. These paddy fields use this fixed oxygen. Azolla pinnata is a species of fern which is also known as feather mosquito fern and water velvet.
- It is a free floating freshwater fern that has symbiotic association with blue green algae. It leaves in the leaf cavity of the fern. It has nitrogenase enzymes that fix nitrogen of the atmosphere. Nitrogen is one of the main essential elements which is needed by the plants for their growth. The presence of azolla content makes it an ideal biofertilizer for plants.
- Azolla gives the ability to the fern to grow in those habitats which are low in nitrogen. This plant is used by farmers in paddy fields because it generates valuable nitrogen through its symbiotic cyanobacteria.

So option C is correct.

Note: Blue-green algae are photoautotrophic, prokaryotic algae. They are nitrogen fixing free living microorganisms. It fixes the atmospheric oxygen in the moist soil. Because of that BGA is considered as the best biofertilizer for paddy fields.