Concept: Nitrogen fixation is the process by which atmospheric nitrogen ( ) is converted into ammonia ( ) or other nitrogenous compounds that can be used by plants. Some bacteria are capable of this process, and they often form symbiotic relationships with certain types of plants. Step 1: Symbiotic Nitrogen Fixation and Root Nodules
A well-known example of symbiotic nitrogen fixation occurs in leguminous plants (members of the Fabaceae or Leguminosae family). Bacteria, typically of the genus {Rhizobium}, infect the roots of these plants and induce the formation of specialized structures called root nodules.
Inside these nodules, the bacteria live and convert atmospheric nitrogen into ammonia, which the plant can then assimilate to produce proteins and other essential nitrogen-containing compounds. In return, the plant provides the bacteria with carbohydrates (energy) and a protected environment. Step 2: Identifying Leguminous Plants among the options
(1) Mustard (Brassica species): Belongs to the Brassicaceae family. Not a legume.
(2) Gram (Cicer arietinum - Chickpea): Gram is a type of pulse and belongs to the Fabaceae (legume) family. Leguminous plants like gram are known for forming root nodules with nitrogen-fixing bacteria.
(3) Wheat (Triticum species): Belongs to the Poaceae family (grasses). Not a legume.
(4) Cotton (Gossypium species): Belongs to the Malvaceae family. Not a legume. Step 3: Conclusion
Since Gram (chickpea) is a leguminous plant, it is the one among the options that would have root nodules containing nitrogen-fixing bacteria.