Which feature of some species of blue-green algae helps promote them as bio-fertilizers?

1. They convert atmospheric methane into ammonia which the crop plants can absorb readily
2. They induce the crop plants to produce the enzymes which help convert atmospheric nitrogen to nitrates
3. They have the mechanism to convert atmospheric nitrogen into a form that the crop plants can absorb readily
4. They induce the roots of the crop plants to absorb the soil nitrates in larger quantities

Explanation

Option (c) is correct

• Blue-green algae, also known as cyanobacteria, such as Anabaena and Nostoc, have the ability to fix atmospheric nitrogen. They possess specialised cells called heterocysts which convert atmospheric nitrogen into ammonia and other nitrogenous compounds. These nitrogen compounds enrich soil fertility and are readily available for absorption by crop plants.

Answer: (c) They have the mechanism to convert atmospheric nitrogen into a form that the crop plants can absorb readily