Lichens
லைக்கன்கள்
Lichens are not single organisms; they are a masterclass in biological cooperation. Do not mistake them for plants. They are a symbiotic association between two distinct kingdoms.
The idea
Lichens represent a symbiotic association between algae and fungi. The algal component is termed phycobiont, which is autotrophic. The fungal component is the mycobiont, which is heterotrophic. The fungus provides protection, anchorage, and absorption, while the alga prepares food.
Why it matters
This mutualistic relationship allows organisms to survive in harsh environments where neither could survive alone by sharing nutrients and shelter.
NEET lens
NEET focuses on the roles of phycobiont and mycobiont. Remember: Algae = Food, Fungi = Shelter. The 'pollution indicator' fact is a high-frequency question; never miss it.
Clinical significance
Lichens are primary colonizers on bare rocks, initiating soil formation for ecological succession. They are sensitive to sulfur dioxide, making them biological indicators of air pollution. Their absence in an area confirms high levels of atmospheric toxicity.
Introduction
A lichen growing on bare rock is performing a slow miracle. It secretes acids that dissolve the rock surface, extracting minerals. The algal partner photosynthesises and feeds the fungus. The fungal partner holds moisture and provides structure. Together, they colonise environments where neither could survive alone — exposed rock faces, Arctic tundra, tree bark. Lichens are the pioneers: the first organisms to inhabit bare surfaces.
Core concept
Lichens: symbiotic associations between a fungal partner (mycobiont, usually Ascomycete) and a photosynthetic partner (photobiont — alga or cyanobacterium).Roles: Fungus provides structure, protection, moisture retention, mineral absorption. Alga/cyanobacterium provides carbohydrates through photosynthesis.Ecological significance: Pioneer organisms on bare rocks — begin soil formation. Bioindicators — sensitive to air pollution (sulphur dioxide); absence indicates poor air quality.Growth forms: crustose (crust-like), foliose (leaf-like), fruticose (shrub-like).
Go deeper
Lichens reproduce primarily by soredia — small clusters of algal cells wrapped in fungal hyphae that break off and disperse. This ensures both partners remain together in the new propagule.Classification formally places lichens in Kingdom Fungi (the mycobiont determines classification).
From Class 10
In Class 10, you may have seen lichens as grey-green crusts on rocks or bark — neither plant nor animal. In Class 11, you learn exactly what they are: a symbiotic partnership between a fungus and an alga (or cyanobacterium), so tightly integrated that they look and function as one.