Question

Nitrogen fixation by Rhizobium is increased in the presence of

• A. Potassium
• B. Nitrogen
• C. Phosphorus
• D. None of the above

Answer 1

Answer: (C)

Phosphorus

Biological nitrogen fixation (BNF) is the process, whereby atmospheric nitrogen is reduced to ammonia in the presence of nitrogenase. Phosphorus is needed for plant growth, nodule formation and development, and ATP synthesis, each process being vital for nitrogen fixation. Nitrogen fixation, which involves the chemical reduction of N${}_2$ to NH${}_3$ or NH${}_4$, requires a source of electrons. Sources of electrons for the nitrogenase activity vary with the organism. They are all small proteins and highly reductive molecules such as flavodoxin, ferredoxin, nicotinamide, or adenine dinucleotide (phosphate). Thus, option C is correct.