Previous Year Question

Statement 1 is correct. Lichens are important biological indicators (Bioindicators) of air pollution. They are formed through a Symbiotic Association between a Fungus and an Alga or Cyanobacterium. The algal component is called the Phycobiont or Photobiont, while the fungal component is known as the Mycobiont. The photosynthetic component produces food, whereas the fungus provides structural protection and assists in the absorption of water and mineral nutrients. Lichens are good pollution indicators because they generally do not grow well in polluted areas.

Statement 2 is incorrect. Lichens are particularly sensitive to Sulphur Dioxide (SO₂) and certain other atmospheric pollutants. Unlike higher plants, they lack well-developed Roots and Stomata that regulate gaseous exchange. They directly absorb atmospheric moisture and nutrients through their body surfaces, allowing pollutants to enter their tissues. High concentrations of SO₂ can interfere with Photosynthesis, Respiration, and other metabolic processes. In heavily polluted areas, the growth, abundance, and diversity of pollution-sensitive lichen species may decline. However, some Pollution-Tolerant Species can survive under moderately polluted conditions.

Pollution Sensitivity of Lichens varies according to their structure and species. Lichens are generally classified into three major morphological types—Crustose, which remain firmly attached to surfaces; Foliose, which have leaf-like structures; and Fruticose, which are shrubby or branched. Generally, Fruticose lichens may be more sensitive to SO₂ pollution, whereas many Crustose species are relatively more tolerant. Pollution can cause chlorophyll damage, reduced photosynthetic rates, and changes in tissue structure in lichens. Therefore, the presence and absence of different lichen species are used to assess air quality.

In Biomonitoring, the Species Diversity, Abundance, and accumulated pollutants within lichen tissues are studied. Lichens are useful for investigating environmental deposition of sulphur compounds, nitrogen pollutants, and heavy metals such as Lead. Generally, areas with cleaner air may support greater diversity of pollution-sensitive lichen species, whereas their numbers may decline in severely polluted environments. However, lichen occurrence is also influenced by Humidity, Light, Temperature, and Substrate. Therefore, scientists examine other environmental conditions alongside lichens when assessing air pollution.