Question

Blue green algae fix ........... directly from air to enhance fertility of soil.

• A. Atmospheric oxygen
• B. Atmospheric nitrogen
• C. Atmospheric sulfur
• D. None of the above

Answer 1

The correct option is B Atmospheric nitrogen

Blue-green algae can fix the atmospheric nitrogen because they contain an O${}_2$ sensitive enzyme nitrogenase. They live in close association with the leaves of the Azolla plant and fix the atmospheric nitrogen into the soluble form which is utilised by the plant. This nitrogen helps in increasing the fertility of the soil and can be used for the growth of the paddy crops.

Thus, the correct answer is option B.