Which organisms are primarily responsible for transforming atmospheric nitrogen (\(N_2\)) into a form that is usable by plants?

• A. Bacteria
• B. Animals
• C. Fungi
• D. Humans

Answer: (A)

Verified step by step guidance

1. Understand the concept of nitrogen fixation: Nitrogen fixation is the process by which atmospheric nitrogen (\(N_2\)), which is inert and unusable by most organisms, is converted into ammonia (\(NH_3\)) or other nitrogenous compounds that can be utilized by plants.
2. Identify the organisms capable of nitrogen fixation: Certain bacteria, including free-living bacteria like Azotobacter and symbiotic bacteria like Rhizobium, are primarily responsible for nitrogen fixation. These bacteria possess the enzyme nitrogenase, which facilitates the conversion of \(N_2\) into ammonia.
3. Recognize the role of symbiotic relationships: Symbiotic bacteria, such as Rhizobium, form mutualistic relationships with leguminous plants. They reside in root nodules and provide the plant with usable nitrogen while receiving carbohydrates and a suitable environment in return.
4. Eliminate incorrect options: Animals, fungi, and humans do not possess the ability to fix atmospheric nitrogen. While humans can industrially fix nitrogen through processes like the Haber-Bosch method, this is not a biological process.
5. Conclude that bacteria are the correct answer: Based on the biological process of nitrogen fixation and the organisms involved, bacteria are the primary agents responsible for transforming atmospheric nitrogen into a form usable by plants.