Answer: Frankia.
- A Frankia
- B Rhizobium
- C Azotobacter
- D Clostridium
Correct answer: A. Frankia
Explanation: The actinomycete Frankia fixes nitrogen in root nodules of some non-leguminous plants like Alnus and Casuarina.
Atmospheric N₂ is fixed into ammonia by nitrogen-fixing bacteria (protected from oxygen by leghaemoglobin in root nodules), converted to nitrate via nitrification for plant uptake, and eventually returned to the atmosphere as N₂ via denitrification, completing the cycle.
Concept context
Essential mineral elements, their roles and deficiency symptoms. Nitrogen fixation and soil nutrition.