In the studies on the atmospheric pollution, lichens are important as they

The correct option is "are very sensitive to pollutants".

Lichens are complex organisms that arise from a symbiotic relationship between a fungus (the mycobiont) and an alga or cyanobacterium (the photobiont). In environmental studies, particularly those focusing on air quality, lichens serve as excellent bioindicators of atmospheric pollution.

Here is a step-by-step breakdown of why lichens are important in studying atmospheric pollution:

1. Absence of a Cuticle and Roots: Unlike vascular plants, lichens do not have a protective outer cuticle or a root system. This means they absorb water, nutrients, and gases directly from the atmosphere across their entire surface. Consequently, they also readily absorb airborne pollutants.

2. High Sensitivity to Pollutants: Lichens are particularly sensitive to sulfur dioxide (SO₂), nitrogen oxides, and heavy metals. When exposed to elevated levels of these pollutants, their metabolic processes—such as photosynthesis and respiration—are severely disrupted, leading to chlorosis, structural damage, or death.

3. Indicators of Air Quality: Because of their high sensitivity, the health, diversity, and abundance of lichen populations in a specific area directly reflect the quality of the local air. A complete absence of lichens, often referred to as a "lichen desert," is a strong indicator of high atmospheric pollution, particularly from sulfur dioxide.