Question

$SO_2$ pollution is indicated by
A) Deschampsia (grasses)
B) Sphagnum (mosses)
C) Usnea (lichens)
D) _Cucurbita/i> (Climbers)

Answer 1

Pollution is defined as any undesirable changes in our surroundings that adversely affects plants, animals and human beings and the substances that cause pollution are called pollutants.

Complete answer:

Sulphur dioxide is released majorly from the emission when sulphur containing coal is burnt. The other sources that release significant amounts of sulphur dioxide are ore smelters and oil refineries.
The increased concentration of sulphur dioxide in air causes various health problems like severe respiratory problems- asthma, bronchitis, emphysema in human beings. The irritation to the eyes, resulting in tears and redness is another effect of this.
Sulphur dioxide pollution is indicated by Usnea which is an example of lichens. Lichens is a complex organism consisting of algae and fungi growing together in symbiosis.
The algae partner in the lichen prepares the food and the fungi absorb the water and mineral salts and offer protection to the algae.
Lichen is found as a thin, greenish patch on the tree trunks or walls. They absorb mineral nutrients from the air and if the air is polluted they are not able to absorb minerals and die. This is why lichens are the best indicators of sulphur dioxide pollution and many species of lichens got extinct during the industrialization era because of sulphur dioxide pollution.

Hence the correct answer is option ‘C’.

Note: Lichens are the best examples of symbiotic association. Symbiotic association is the relationship of two organisms in such a way that they help each other and are mutually dependent on each other for their survival. The organisms that show such relationships are called the symbionts.