State an important function performed by blue - green algae.

Explanation

**Step-by-Step Solution:**

1. **Identify the Organism**: The question asks about blue-green algae, which are scientifically known as cyanobacteria.

2. **Understand Their Habitat**: Blue-green algae are commonly found in various environments, including soil and water bodies.

3. **Recognize Their Role**: One of the significant functions of blue-green algae is their ability to fix nitrogen from the atmosphere.

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