Which of the following is the best indicator of SO2 pollution ?

Question

Accepted Answer

Lichens are considered the best indicators of sulfur dioxide (SO2) pollution for several reasons. Lichens are symbiotic associations between fungi and algae or cyanobacteria, and they are highly sensitive to air quality, particularly to sulfur dioxide. This sensitivity arises because lichens absorb water and nutrients directly from the atmosphere over their entire surface area. When SO2 is present in the air, it can be absorbed by lichens, leading to physiological stress or damage, which can be observed as changes in their growth, color, or even death. This makes lichens excellent bioindicators of SO2 pollution, as their presence or absence, as well as their health, can provide valuable information about air quality.

Now, let's examine why the other options are not as suitable as indicators of SO2 pollution:

1. **Bryophyte**: While bryophytes (such as mosses) can also be sensitive to air pollution, they are generally less sensitive to SO2 compared to lichens. Bryophytes have a different structure and physiology, which makes them less effective as specific indicators of sulfur dioxide pollution.

2. **Pteridophyte**: Pteridophytes, or ferns, are vascular plants that are not as sensitive to air pollutants as lichens. They have a more complex structure and are less directly exposed to atmospheric conditions compared to lichens, making them less reliable indicators of SO2 pollution.

3. **Algae**: Algae, particularly those living in aquatic environments, are not directly exposed to atmospheric SO2 in the same way lichens are. While some algae can be affected by pollution, they are not as effective as lichens in indicating SO2 levels in the air.

In conclusion, lichens are the best indicators of SO2 pollution due to their high sensitivity to atmospheric conditions and their ability to reflect changes in air quality through observable changes in their health and presence. This makes Option 3, Lichen, the correct choice.