Question

Assertion: Crustose lichens, in a lithosere, secrete organic acids causing the weathring of rocks so that minerals essential for proper growth of lichens are released.
Reason: Early colonists in a primary suceession are usually lichens, which suggests that colonisation is easier when an organism has a mutualistic association.

Answer 1

Correct Answer - B
The pioneer community in a lithosere (biotic succession on bare rock ) is constituted by lichens. The pioneer lichens are usually crustose lichens such as Graphis, Rhizocarpon, etc. Lichens can tolerate desiccation. They produce organic acids which cause weathering of rocks so that minerals essential for proper growth of lichens are released. Lichens hold the fine particles of rock and initiate soil formation. It paves the way for growth of next seral community. Lichens are dual organisms which contain a permanent symbiotic association of a fungus and an alga. Early colonisation by lichens suggests that colonisation is easier when the organism has mutulistic association.