Lichens indicate SO2 pollution because they

Explanation

Lichens are composite organisms formed through a mutualistic association between a fungus and an alga or a cyanobacterium. The alga or cyanobacterium provides food through photosynthesis, while the fungus provides a protective structure and absorbs water and nutrients.Lichens are highly sensitive to air pollution, especially sulfur dioxide (SO2) pollution. When SO2 is present in the air, it can be absorbed by the lichens along with other pollutants. The high sensitivity of lichens to SO2 makes them excellent bioindicators of air quality.As SO2 levels increase in the environment due to pollution, lichens become stressed and can even die off. So, the presence or absence of certain lichen species in an area can indicate the level of SO2 pollution. If lichens are thriving and diverse in an area, it suggests a cleaner, less polluted environment. On the other hand, if lichens are absent or limited in their diversity, it indicates higher levels of SO2 pollution in that region.