Which of the following is the best indicator of SO₂ pollution?

Question

Accepted Answer

Lichens are considered the best indicator of SO₂ pollution for several reasons. Lichens are symbiotic associations between fungi and algae or cyanobacteria. They are highly sensitive to air pollution, particularly sulfur dioxide (SO₂), because they absorb water and nutrients directly from the air over their entire surface. This makes them excellent bioindicators of air quality.

1. **Why Option 2 is Correct (Lichen):**
   - **Sensitivity to SO₂:** Lichens are extremely sensitive to sulfur dioxide pollution. SO₂ can damage the photosynthetic partner in the lichen, leading to a decline in lichen populations in polluted areas. This sensitivity makes them reliable indicators of SO₂ levels in the environment.
   - **Absence in Polluted Areas:** In areas with high levels of SO₂ pollution, lichens are often absent or show reduced diversity and abundance. This absence or reduction is a clear indicator of air quality issues related to sulfur dioxide.
   - **Long-term Indicators:** Lichens can provide information about long-term air quality trends because they have a slow growth rate and can live for many years, accumulating pollutants over time.

2. **Why Other Options are Incorrect:**
   - **Option 1 (Algae):** Algae are not as sensitive to SO₂ pollution as lichens. They primarily live in aquatic environments and are more affected by water quality than air quality. While some algae can be affected by air pollution, they are not as reliable indicators of SO₂ as lichens.
   - **Option 3 (Bryophyte):** Bryophytes, such as mosses, can be affected by air pollution, but they are generally more tolerant of SO₂ compared to lichens. They do not provide as clear or sensitive an indication of SO₂ pollution levels.
   - **Option 4 (Pteridophyte):** Pteridophytes, which include ferns, are not particularly sensitive to SO₂ pollution. They are more robust and can tolerate a wider range of environmental conditions, making them less effective as indicators of SO₂ pollution compared to lichens.

In conclusion, lichens are the best indicators of SO₂ pollution due to their high sensitivity and direct absorption of air pollutants, making them reliable bioindicators for assessing air quality related to sulfur dioxide.