Tag: botany

In lithosere (xerosere or xerarch), the pioneer community is usually constituted by crustose lichens(e.g., Graphis, Rhizocarpon). Foliose lichens(e.g., Dermatocarpon, Parmelia) kill the crustose lichens by shading them, cause deeper depressions and accumulate more soil particles and organic matter. Foliose lichens make the conditions favourable for the growth of hardy mosses(e.g., Tortula, Grimmia).

Lichen forms a crust over bare rocks and starts forming soil from their organic remains by secreting carbonic acid which results in the chemical breakdown of rocks. 

Litmus is a natural dye with a water-soluble mixture extracted from lichens, it is used as a pH indicator.

Lichens are association (mutually beneficial) between fungus and alga. The fungal partner is mycobiont and algal partner is phycobion. The mycobiont is usually an ascomycete and phycobiont is usually green algae Lichens can grow in extremely inhospitable conditions In many ecosystems they are the pioneer species. The role of mycobiont is providing body structure and anchorage and absorption of minerals and water. The role of phycobiont is mainly in providing food through photosynthesis. So, the correct answer is 'Fungus and algae'.

Symbiosis in lichens is the mutually helpful symbiotic relationship of green algae and/or blue-green algae (cyanobacteria) living among filaments of a fungus. The fungus benefits from the algae or cyanobacteria, because they produce food by photosynthesis. The algae or cyanobacteria benefit by being protected from the environment by the filaments of the fungus, which also gather moisture and nutrients from the environment, and provide an anchor to it.

Lichen is a symbiotic partnership between fungus and alga. It has algal and fungal partners in its thallus. In this, the fungus is a dominant partner. Hence, lichen has majority of characteristics of fungus. It absorbs sulphur dioxide from the atmosphere. Hence, it is widely used as indicator of air pollution. It grows very slowly.  It is eaten by snails, squirrels and some species of monkeys and reindeers during winter. They grow at 1 mm per day.

 According to Crombic, the relation between an algae and a fungi is helotism. Which is a kind of master-slave relationship, where the algal partner acts as a slave to the fungal partner, because, algae is an autotroph  however, the fungal partner may hinder the reproduction and nutrition of the algae.

Lichens are the symbiotic association of algae and fungi. Lichens are autotrophic, they can make their own food with the help of sunlight and provide food to the fungi and in return fungi provide protection to the lichen. Lichens always reproduce asexually. It is the most controversial organism, it possesses the characters of algae and fungi both. It is placed in ascomycetes.

Fruticose lichen ususally round in cross secetion (terete), and most are branched. They can be like little shrubs growing upward, or they can hang down in long strands. The fruticose lichens have much branched cylindrical, ribbon-like, flattened or sometimes filamentous thalli. 

• A lichen is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.
  
• If air is very badly polluted with sulfur dioxide($SO _2$) there may be no lichens present, just green algae may be found. If the air is clean, shrubby, hairy and leafy lichens become abundant
  
• Hence Lichens are important in the studies on atmospheric pollution because they are very sensitive to pollutants like sulfur dioxide. 
• So, the correct answer is ' Are very sensitive to pollutants like $SO _2$.