Question

Lichens indicate $S{O_2}$ pollution because they-
A. Show association between algae and fungi
B. Grow faster than others
C. Are sensitive to $S{O_2}$
D. Flourish in $S{O_2}$ rich environment

Answer 1

Lichens are living organisms which originated from algae or blue green algae also known as cyanobacteria, which survives over the filaments present in various species of fungi. Lichens live in mutualistic relationships with both algae and fungi.

Complete answer:
Mutualistic relationship is a relationship among two or more different organisms which work together to gain benefit from this mutual relationship. Since lichens have association with both algae and fungi it shows properties of both of them. Lichens themselves are unable to obtain their nutrition and water from soil because of lack of roots. But due to algae-like properties it is capable of synthesizing its own food by photosynthesis.
Liches are present in very rare places where other living organisms find difficult to grow like arctic tundra. It is an inherent property of lichens to grow in a pollution free atmosphere. It is observed practically that population growth of lichens is much higher in pollution less environments as compared to polluted environments.
Due to this inherent property of lichens they are used widely as a biological indicator of pollution. Presence of sulphur dioxide in the atmosphere inhibits the growth of lichens. Therefore, they are used as an indicator to detect the presence of sulphur dioxide.
Presence of sulphur dioxide reduces the rate of growth of lichens because lichens are highly sensitive towards sulphur dioxide.
$\Rightarrow$ Lichens indicate $S{O_2}$pollution because they Are sensitive to $S{O_2}$.

Therefore, option $\left( C \right)$ is the correct option.

Note:
Lichens are non-edible for humans because they contain high amounts of vulpinic acid which is toxic for humans. Some varieties of lichens including tortured horsehair lichen and wolf lichen are poisonous lichens. Only a few varieties of lichens tolerate high levels of atmospheric pollution which are found usually in urban areas, bark of trees.