Question

Indicator plants which can be used to indicate atmospheric pollution by SO${}_2$ are

• A. Lichens like Usnea
• B. Grassland like Deschampsia
• C. Moss like Sphagnum
• D. Climbers like Cucurbita

Answer 1

The correct option is A Lichens like Usnea

Lichens are mutualistic associations of a fungus and an alga or cyanobacterium and occur as crusty patches or bushy growths on trees, rocks and bare ground. Lichens are very sensitive to sulphur dioxide pollution in the air. Their efficient absorption systems result in rapid accumulation of sulphur when exposed to high levels of sulphur dioxide pollution. The algal partner is most affected by the sulphur dioxide; chlorophyll is destroyed and photosynthesis is inhibited. Lichens are widely used as environmental indicators or bio-indicators. If air is very badly polluted with sulphur dioxide, there may be no lichens present, just green algae may be found. If the air is clean, shrubby, hairy and leafy lichens become abundant. Thus, the correct answer is option A.