Solution: For Rhizobium to fix nitrogen, the following conditions must be met.

1. The production of root nodules requires a symbiotic connection between Rhizobium and roots.
2. The requirement for a reduced environment
3. Nitrogenase enzyme – this enzyme produces ammonia.
4. Adenosine triphosphate (ATP) is necessary for ammonia production.
5. NAD(P) H2 or FMNH2 is a decreasing power source.
6. Ferredoxin – Ferredoxin functions as an electron donor.
7. Amino groups are picked up by keto acids.
8. Nitrate as a substrate — nitrate availability is lowered.

Rhizobium’s role in N2 fixation:

• Using the nitrogenase enzyme, they fix atmospheric nitrogen into a form that plants can use, namely ammonia.
• The plant, in turn, provides bacteria with proteins, carbohydrates, and enough oxygen to ensure that the fixation process is not disrupted.
• Leghaemoglobin is a plant protein that helps provide oxygen for the respiration process while keeping free oxygen levels low enough to keep nitrogenase activity from being hampered.