Why are root nodules useful for the leguminous plants?

Explanation

**Step-by-Step Solution:**

1. **Definition of Root Nodules**: Root nodules are spherical structures found on the roots of leguminous plants, such as peas. They are essential components of these plants.

2. **Presence of Nitrogen-Fixing Bacteria**: Inside these root nodules, there are specific bacteria known as Rhizobium. These bacteria play a crucial role in the nitrogen cycle.

3. **Nitrogen Fixation Process**: The primary function of Rhizobium bacteria is to convert atmospheric nitrogen (N₂), which plants cannot use directly, into ammonia (NH₃). This process is known as nitrogen fixation.

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