Rhizobium bacteria and leguminous plant help each other in survival. What is this relationship known as?

Explanation

**Step-by-Step Solution:**

1. **Identify the Organisms Involved**: The question involves two key organisms: Rhizobium bacteria and leguminous plants.

2. **Understand Their Interaction**: Rhizobium bacteria are known for their ability to fix atmospheric nitrogen, which is essential for plant growth. They typically reside in the root nodules of leguminous plants.

3. **Recognize the Benefits**: In this relationship, the Rhizobium bacteria benefit the leguminous plants by converting atmospheric nitrogen into a form that the plants can use for growth. In return, the leguminous plants provide carbohydrates (food) to the Rhizobium bacteria.

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