How are protozoa useful to us?

Explanation

**Step-by-Step Solution:**

1. **Understanding Protozoa**: Protozoa are single-celled microorganisms that play various roles in the ecosystem. They are often found in water bodies and soil.

2. **Role as Decomposers**: Protozoa act as decomposers by feeding on bacteria and fungi. This helps in breaking down organic matter, which is essential for nutrient cycling in the environment.

3. **Sewage Treatment**: Due to their decomposing abilities, protozoa are utilized in sewage treatment processes. They help in breaking down waste materials, thus improving water quality.

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