Question

What is required for nitrogen fixation by Rhizobium?

• A. Potassium
• B. Phosphorus
• C. Molybdate
• D. Sodium

Answer 1

The correct option is B Phosphorus

Phosphorus is an essential ingredient for Rhizobium bacteria to convert atmospheric nitrogen (N${}_2$) into an ammonium (NH${}_4$) form useable by plants. Rhizobium is able to synthesize the enzyme nitrogenase which catalyzes the conversion of N${}_2$ to two molecules of ammonia (NH${}_3$). Phosphorus becomes involved as an energy source when 16 molecules of adenosine triphosphate (ATP) are converted to adenosine diphosphate (ADP) as each molecule of N${}_2$ is reduced to NH${}_2$.

So, the correct answer is option B.