Which among the following is a nitrogen-fixing organism?

All of these

The correct answer is Option (4) – All of these

Cyanobacteria, also known as blue-green algae, are a group of photosynthetic bacteria that are commonly found in various aquatic and terrestrial environments, including paddy fields. These microbes play a crucial role in enhancing soil fertility and promoting plant growth through their ability to fix atmospheric nitrogen.

Cyanobacteria are autotrophic organisms, meaning they can produce their own food through photosynthesis. During photosynthesis, they utilize sunlight to convert carbon dioxide and water into organic compounds, while releasing oxygen as a byproduct. One of the unique abilities of cyanobacteria is their nitrogen-fixing capability.

Certain species of cyanobacteria, such as Anabaena, Nostoc, and Oscillatoria, can fix atmospheric nitrogen into ammonia. " For example, Azolla, a small aquatic fern, hosts the cyanobacterium Anabaena in its leaf cavities. This association enables Azolla to fix nitrogen, benefiting the growth of rice plants when grown together in paddy fields.