Home › MCQs › Agronomy › Question #2100
Back to Questions
Agronomy QUESTION #2100
Question 1
Biological nitrogen fixation (BNF) by soybean-Bradyrhizobium japonicum symbiosis requires which essential micronutrient as a component of the nitrogenase enzyme complex?
  • Zinc (Zn) — as a cofactor for auxin-mediated nodule initiation
  • Molybdenum (Mo) — as a component of the iron-molybdenum cofactor (FeMo-co) at the active site of nitrogenase that reduces \(N_2\) to \(NH_3\)✔️
  • Boron (B) — for nodule cell wall synthesis and longevity
  • Copper (Cu) — for leghemoglobin synthesis in nodule cortex
Correct Answer Explanation
Nitrogenase consists of two proteins: dinitrogenase (MoFe protein) containing the FeMo-co active site where \(N_2\) is reduced (\(N_2 + 8H^+ + 8e^- + 16ATP \rightarrow 2NH_3 + H_2 + 16ADP + 16P_i\)), and dinitrogenase reductase (Fe protein). Mo is irreplaceable at the active site — Mo deficiency severely impairs BNF. Fe is also essential (leghemoglobin, Fe-S clusters). Both Mo and Fe are required for full BNF activity.