Question

Symbiotic nitrogen fixation involving Rhizobium bacteria occurs in

• A. Rice
• B. Groundnut
• C. Sorghum
• D. Wheat

Hint:

Rhizobium $\rightarrow$ Legumes (Groundnut, Pulses, Soybean).
Azospirillum $\rightarrow$ Cereal crops (Sorghum, Maize).
Azotobacter $\rightarrow$ Non-symbiotic aerobes (Wheat, Cotton).
Anabaena azollae $\rightarrow$ Lowland Rice.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Biological Nitrogen Fixation (BNF) occurs via symbiotic associations between host leguminous root nodules and diazotrophic Rhizobium bacteria.
Key Formula or Approach:
\[ \text{N}_2 + 8\text{H}^+ + 8e^- + 16\text{ATP} \xrightarrow{\text{Nitrogenase}} 2\text{NH}_3 + \text{H}_2 + 16\text{ADP} + 16\text{P}_i \]

Step 2: Detailed Explanation:
Groundnut (Arachis hypogaea) is a leguminous oilseed crop.
Its roots form a mutualistic symbiotic association with Bradyrhizobium Rhizobium bacteria, developing root nodules.
The bacterial nitrogenase enzyme reduces atmospheric dinitrogen ($\text{N}_2$) directly into plant-available ammonia ($\text{NH}_3$).
Rice, sorghum, and wheat are non-leguminous graminaceous cereals (which host free-living or associative bacteria like Azotobacter and Azospirillum, but not symbiotic nodulating Rhizobium).

Step 3: Final Answer:
Thus, symbiotic nitrogen fixation with Rhizobium occurs in Groundnut, corresponding to option (B).