Which one among the following kinds of organisms resides in the roots of pulse plants to do nitrogen fixation ?

Nitrogen fixation in pulse plants (legumes) is primarily carried out by bacteria, specifically the genus Rhizobium. These bacteria establish a symbiotic relationship with the host plant, residing within specialized structures called root nodules [c2][c3]. In this mutualistic association, the bacteria utilize the enzyme nitrogenase to convert atmospheric gaseous nitrogen into chemical forms like ammonia and nitrates, which the plant can readily assimilate for growth [c3][t3][t7]. In exchange, the plant provides the bacteria with carbohydrates and a protected anaerobic environment necessary for nitrogenase activity [t3][t6]. While other organisms like blue-green algae (cyanobacteria) and certain fungi exist in soil, the specific organisms that form nodules in pulse plant roots to fix nitrogen are classified as bacteria [c1][t2][t5]. This biological nitrogen fixation is vital for soil fertility and reduces the need for synthetic fertilizers [t6][t8].

Sources

1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > s r n r u l z N ,- / & f . -. : : u ' , \ S ACADEMY * d 6 # . , r '' t u f Y l ' ' J * w { d ) / u Y . / > p. 20
2. [2] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
3. [3] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > The Nitrogen Cycle > p. 20
4. [4] https://pmc.ncbi.nlm.nih.gov/articles/PMC4074912/