Symbiotic nitrogen-fixing bacteria and legumes: Which statements correctly describe Rhizobium–legume symbiosis and its benefits?

Introduction / Context:
Rhizobium–legume symbiosis is a cornerstone of sustainable agriculture. The partnership provides biologically fixed nitrogen to crops, reducing the need for synthetic fertilizers.

Given Data / Assumptions:

• Statements address nutrient exchange, the definition of symbiosis, and taxonomic identity.
• We must determine whether each statement is accurate.

Concept / Approach:
In nodules, rhizobia receive carbon compounds and minerals from the host plant. In return, bacterial nitrogenase converts N2 to ammonia, which is transferred to the plant as amino forms. The mutualistic relationship fits the definition of symbiosis. Classical taxonomy places these bacteria in Rhizobium/Bradyrhizobium and allied genera.

Step-by-Step Solution:
Evaluate (a): resource exchange is accurate; plants receive fixed nitrogen. Evaluate (b): definition and naming of symbiosis are correct. Evaluate (c): genus-level identification is correct (with related genera acknowledged). Since all statements are correct, choose “All of the above.”

Verification / Alternative check:
Plant physiology texts describe nitrogen transfer from bacteroids to host plant in exchange for photosynthate; inoculant labels list Rhizobium/Bradyrhizobium strains for specific legumes.

Why Other Options Are Wrong:

• Any single statement alone is incomplete because all three are true.
• “None of the above” contradicts established biology.

Common Pitfalls:
Forgetting that several genera (e.g., Bradyrhizobium, Sinorhizobium) participate; the concept remains valid.

Final Answer:
All of the above statements correctly describe symbiotic nitrogen fixation.