Litmus: Litmus is extracted from Lichens. Lichen is a composite organism. Lichens consist of fungi and algae living in symbiotic relationship.

Lichens are unique organisms that consist of a symbiotic association between a fungus and an alga or cyanobacterium. This partnership allows lichens to grow in various environments, including extreme ones such as deserts, tundras, and rocks. Lichens have been used as bioindicators, which are organisms or substances that provide information about the quality of the environment they inhabit. One indicator obtained from lichens is the presence or absence of certain species or groups of lichens, which can be used to assess environmental conditions.

Lichen Diversity and Pollution
The diversity and abundance of lichen species can indicate the level of pollution in an area. Some lichens are highly sensitive to air pollutants such as sulfur dioxide, nitrogen oxides, and heavy metals. These pollutants can affect the growth and survival of lichens, leading to a decrease in their diversity. Therefore, the absence or low abundance of certain lichen species in an area may suggest high pollution levels.

Lichen Growth Forms
Lichens exhibit different growth forms, including crustose, foliose, and fruticose. The growth form of lichens can provide information about the environmental conditions they are exposed to.

- Crustose lichens grow as a crust or a thin layer attached to the substrate. They are often found in areas with good air quality and undisturbed environments.
- Foliose lichens have leaf-like structures and are relatively larger than crustose lichens. They can tolerate moderate pollution levels and are commonly found in semi-polluted areas.
- Fruticose lichens have a shrubby or hair-like appearance. They are more tolerant of pollution and can be found in heavily polluted areas.

Lichen Biomonitoring
Lichens can be used for biomonitoring, which involves the assessment of pollutants in the environment based on the accumulation or exclusion of certain substances by lichens. Lichens can accumulate heavy metals and other pollutants from the air or substrate they grow on. By analyzing the concentration of these substances in lichens, scientists can determine the level of pollution in an area.

Environmental Factors Affecting Lichens
Various environmental factors can influence the distribution and growth of lichens. These factors include air quality, humidity, light availability, substrate composition, and pH. By studying the presence, abundance, and health of different lichen species, researchers can gain insights into the overall environmental condition of an area.

Conclusion
Lichens serve as valuable indicators of environmental quality due to their sensitivity to pollution and their ability to accumulate substances from the environment. The presence or absence of certain lichen species and their growth forms can provide valuable information about the pollution levels and overall environmental condition of an area. By studying lichens, scientists can gain insights into the impacts of human activities on the environment and work towards better conservation and management practices.

Litmus paper is obtained from lichens. it is used to identify whether the given solution is acid or bases. if the solution is acid the litmus paper changes from blue to red and if the solution is bases then it changes from red to blue and if it is neutral it will not change its colour.