__________ are used as indicato rs of sulpur dioxide cytoplasm and are called pollutants.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for a specific organism that serves as an indicator of sulfur dioxide in the environment and is also classified as a pollutant.

2. **Identifying the Organism**: The organism that fits this description is lichen. Lichens are sensitive to air quality and can indicate the presence of pollutants, particularly sulfur dioxide.

3. **Role of Lichens**: Lichens are known to thrive in clean air environments. When sulfur dioxide levels increase in the atmosphere, it negatively affects lichen growth. Therefore, a decrease in lichen populations can indicate higher levels of sulfur dioxide pollution.

...