Question

Give a general account on lichens.

Answer 1

1. Definition: A symbolic association of algae and Fungi helping each other & living together known as lichens.
2. Partners: Algal partner known as Phycobiont & Fungal partner known as Mycobiont
3. Role of Algal partner – Autotrophic prepare food – give nutrition to fungal partner also
4. Role of fungal partner – gives protection- helps in fixing to the substratum by rhizines.

Character	Phycobiont	Mycobiont
Asexual reproduction	Akinetes, hormogonia, Aplanospore, etc.	fragmentation soredia, and isidia
Sexual reproduction	absent	sexual reproduction by ascocarp & ascospores

 

Character	Classification of lichens
Habitat	Corticolous – growing on the bark Lichnicolous – growing on wood Saxicolous – growing on rock Terricolous – growing on the ground Marine – siliceous rock sea Freshwater – siliceous rocks (freshwater habitat).
Morphology of thallus	Leprose – distinct fungal layer absent Crustose – crust like Foliose – Leaf-like Fruticose-branched pendulous shrub-like
On the basis of the distribution of algae cells	Homoiomerous – Algae cells evenly distributed Heteromerous – A distinct layer of Algae and Fungi present
On the basis of the fungal partner	If it is Ascomycetes – Ascolichen If it is basidiomycetes-Basidiolichen

Economic importance:

Secretion of acids of lichens	Uses
Oxalic acid	Weathering of rocks Pioneers in xerosere
Usnic acid	Antibacterial

Pollution Indicators – Lichens sensitive to air pollutants- (pollution indicators)Rocella Montagne – Produces a dye used in litmus paper (acid-base indicator)
Cladonia rangiferina – Food for animals in tundra regions

Answer 2

The symbiotic association between algae and fungi is called lichens. The algal partner is called Phycobiont and the fungal partner is called Mycobiont. Algae provide nutrition for the fungal partners and also help in fixing the thallus to the substratum through rhizines. Asexual reproduction takes place through fragmentation, Soredia, and Isidia. Phycobionst reproduce by akinetes, hormogonia, aplanospore, etc. Mycobionts undergo sexual reproduction and produce ascocarps.
Classification:

1. Based on the habitat lichens are classified into the following types: Corticolous (on bark) Lignicolous (on wood) Saxicolous (on rocks) Terricolous (on ground) Marine (on siliceous rocks of the sea) and Freshwater (on the siliceous rock of freshwater).
2. On the basis of the morphology of the thallus they are divided into Leprose (a distinct fungal layer is absent) Crustose – crust-like; Foliose – leaf-like; Fruticose – branched pendulous shrub-like.
3. The distribution of algal cells distinguishes lichens into two forms namely Homoiomerous (Algal cells evenly distributed in the thallus) and Fleteromerous (a distinct layer of algae and fungi present).
4. If the fungal partner of lichen belongs to ascomycetes, it is called Ascolichen and if it is basidiomycetes it is called Basidiolichen.