Which among the following is a useful biological indicator of sulphur dioxide pollution

Q. Which among the following is a useful biological indicator of sulphur dioxide pollution:

1. Bryophytes
2. Algal blooms
3. Pseudomonas
4. Lichens

Answer: Lichens

Lichens is a useful biological indicator of sulphur dioxide pollution

Lichens are a complex life form that is a symbiotic partnership of two separate organisms, a fungus and an alga. The dominant partner is the fungus, which gives the lichen the majority of its characteristics, from its thallus shape to its fruiting bodies.

Lichens can be used as air pollution indicators, especially of the concentration of sulfur dioxide since they derive their water and essential nutrients mainly from the atmosphere rather than from the soil. 

Lichens are plants that grow in exposed places such as rocks or tree bark. Air pollutants dissolved in rainwater, especially sulfur dioxide, can damage lichens and prevent them from growing.

This interaction between lichens and air pollution has been used as a means of monitoring air quality since 1859, with more systematic methods developed by William Nylander in 1866.