Nitrogen-fixing bacteria ……………..

Options

A. Reduce nitrogen to `NH_(4)^(+)`
B. Can break the triple bond in `N_(2)`
C. Form mutualistic relationships with legumes
D. All of the above

Answer

**Step-by-Step Solution:**

1. **Understanding Nitrogen-Fixing Bacteria**: Nitrogen-fixing bacteria are microorganisms that can convert atmospheric nitrogen (N₂) into a form that plants can use, such as ammonium (NH₄⁺).

2. **Reducing Nitrogen to Ammonium Ion**: One of the primary functions of nitrogen-fixing bacteria is to reduce nitrogen gas (N₂) to ammonium ions (NH₄⁺). This process is essential for making nitrogen available to plants.

3. **Breaking the Triple Bond in Nitrogen**: Nitrogen gas (N₂) has a very strong triple bond between the two nitrogen atoms. Nitrogen-fixing bacteria possess the necessary enzymes to break this bond, allowing them to convert N₂ into usable forms like ammonium.

4. **Mutualistic Relationship with Legumes**: Many nitrogen-fixing bacteria, such as Rhizobium, form mutualistic relationships with leguminous plants. In this relationship, the bacteria provide the plants with fixed nitrogen, while the plants supply the bacteria with carbohydrates and a suitable environment.

5. **Nodule Formation in Leguminous Plant Roots**: The relationship between nitrogen-fixing bacteria and legumes leads to the formation of root nodules. These nodules are specialized structures where the bacteria reside and carry out nitrogen fixation.

6. **Conclusion**: Given the functions of nitrogen-fixing bacteria, the correct answer to the question is **Option 5: All of the above**. This option encompasses all the roles that nitrogen-fixing bacteria play in the ecosystem.