Question

Pollution indicator is
(a)Agrobacterium
(b)Lichen
(c)Pteridium
(d)Both A and B

Answer 1

Hint: These represent a symbiotic relationship between two microorganisms out of which one is algae. These are very sensitive to sulfur dioxide contamination in the air.

Complete answer:
The symbiotic association between the algae and the fungi is known as the lichen. They will absorb mineral nutrition mostly from the moisture-laden air rather than from the soil. Hence the air contamination will severely impair their growth and is very sensitive to the high sulfur concentrations. The lichen became extinct in the lowland Britain area because of the sulfur dioxide pollution. Lichens are very sensitive to sulfur dioxide because they have an efficient absorption system that results in the rapid accumulation of sulfur when exposed to high sulfur dioxide pollution. The alga will be most affected by the sulfur dioxide, the chlorophyll will be destroyed and photosynthesis will be inhibited. Lichens will also absorb sulfur dioxide present in the dissolved water.
Bio-indicators
Lichens are used widely as an environmental indicator/ bio-indicator. If air is getting badly polluted by the sulfur dioxide then there will be no lichens, only the green algae will be found. If the air is not polluted then the lichens will become abundant. Some lichen species have the ability to tolerate high levels of pollution and are commonly observed on the pavements, walls, and tree bark in urban areas. Some lichen species are most sensitive and appear to be shrubby leafy while the tolerant lichens will be crusty in appearance.

So, the correct answer is, ‘Lichen’.

Note: -Usnic acid is found in several species of lichen and it is used as an anti-inflammatory substance.
-Lichen is also used as an acid-base indicator and has the ability to show the pH of a substance, similar to that of the litmus paper. Furthermore, ancient Egyptians had used lichens to fill the body cavities of the mummies.