IGCSE Biology Paper-1: Specimen Questions with Answers 195 - 195 of 208

Question 195



Lichens grow on tree trunks and buildings. The diagrams show the number of lichens and the amount of Sulphur dioxide in the air for two areas, R and S.

Lichens and Sulphur Dioxide Graph

Which conclusion can be made from these diagrams?


Choice (4)


Lichens produce Sulphur dioxide and clean the atmosphere.


Lichens need Sulphur dioxide for their growth.


An increase in the amount of Sulphur dioxide results in a decrease in the number of lichens.


Area R is more heavily polluted by Sulphur dioxide than area S.




Lichens are well known as sensitive indicators of air pollution, particularly for Sulphur dioxide. Acid precipitation effects are closely related to SO2 effects. The extreme sensitivity of lichens to SO2 is partially related to their ability to absorb more SO2 for a given concentration than typical vascular plants. Air pollutants adversely impact not only growth, reproductive potential, and morphology, but also a wide variety of physiological processes, which also becomes reflected in ultrastructural changes. What Sulphur dioxide do is that it removes Mg ion from chlorophyll molecule which results information of a chemical molecule called phaeophytin. This phaeophytin does not absorb light and results in poor growth of algae and lichen may even die.