Previous Year Question

Lichens are well-known Bioindicators of air pollution. Bioindicators are living organisms whose presence, absence, abundance, or physiological condition helps assess environmental quality. Lichens generally consist of a Symbiotic Association between a Fungus and an Alga or Cyanobacterium. The fungus provides protection and structural support, while the photosynthetic partner produces food.

Lichens are particularly sensitive to Sulfur Dioxide (SO₂) and certain other atmospheric pollutants. They lack true roots and obtain water and mineral nutrients primarily through Atmospheric Deposition. Their tissues can accumulate SO₂-related compounds, nitrogen compounds, and Heavy Metals. Excessive exposure to these pollutants can interfere with Photosynthesis, slow growth, and cause the disappearance of sensitive lichen species.

In Air Quality Monitoring, scientists examine the presence, diversity, and health of different lichen species. Areas with relatively low pollution may support more pollution-sensitive lichens, whereas polluted areas may experience a decline in these species and an increase in Pollution-tolerant Species. However, the absence of lichens does not necessarily indicate pollution, because temperature, moisture, tree-bark characteristics, and habitat conditions also influence their distribution.

Among the other options, Methylmercury (CH₃Hg⁺) is a toxic organic form of mercury that can undergo Bioaccumulation and Biomagnification in aquatic food chains. Rose and Sunflower are common flowering plants. Although certain plants can be used to study the effects of pollution, Lichens are particularly well known as biological indicators of air pollution. They are used to monitor pollution associated with sulfur, nitrogen, and certain heavy metals.