This about lichens is incorrect

The correct option is "They grow rapidly about 2cm every day".

Let's analyze why this statement is incorrect by evaluating the characteristics of lichens step-by-step:
1. Symbiotic Relationship: Lichens are complex life forms representing a symbiotic partnership between a fungus (the mycobiont) and an alga or cyanobacterium (the photobiont). Thus, the option stating they have a symbiotic relationship is correct.
2. Pollution Indicators: Lichens are highly sensitive to air pollution, particularly sulfur dioxide, because they absorb water and nutrients directly from the atmosphere rather than through roots. A lack of lichens in an area is a strong indicator of poor air quality. Thus, they are indeed indicators of pollution.
3. Food Source: Certain species of lichens, such as reindeer moss (Cladonia rangiferina), serve as a critical food source for reindeers and caribou, especially during winter months. Thus, this statement is also correct.
4. Growth Rate: Lichens are known for their extremely slow growth rates. Depending on the species and environmental conditions, they typically grow only a few millimeters (often less than 1 mm to 10 mm) per year, not centimeters per day. Therefore, the claim that they grow rapidly at a rate of 2 cm every day is completely incorrect.