lecture 6 - Today: Lichen What are lichens? 3 main growth...

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Today: Lichen What are lichens? 3 main growth forms of lichen Symbiosis vs. parasitism o Pros and cons Reproduction (sexual vs. asexual) Growth Biochemistry Bioindicators Lichen and people 1. What are lichens? Characteristics o Interaction between algae and fungi (composite organism). They are unique, unclassifiable. Mostly green algae or cyanobaceteria . Cyanobacteria sometimes involves as 3rd species o 14,000 species (conglomerate of algae and fungi) o Huge variety in size, form and color. They are diverse o Found everywhere, any environmental conditions even arctic o It has intricate symbiosis of algae and fungi . We might expect one evolution but rather, fungi has come across several independent origins. Multiple evolutionary origins but all the same mode of food acquisition o It is recognized of symbiosis of 2 or 3 organisms in late 19th century (1868) o Great example of symbiosis or is it parasitism of algae? Fungal side of algae (mycobiont ) o Dominant organism. It controls algal partner o Mostly ascomycetes 50% of Ascos are known only from lichens (14,000 species). Mycobionts need algae to grow and exist. o Interaction between fungus and algae has been described as "farming ": fungus maintains condition for existence of algae so that it can harvest carbohydrates produced by photosynthesis Algae side of Lichen (phycobioint ) o Mostly green algae 80% Trebouxia (also common is Trentepohlia ) o Few golden algae o One brown alga o Many cyanobacteria (i.e. Nostoc ) --> blue-green algae o In contrast to limited survival of mycobiont, phycobiont can live independently . Basic lichen morphology o The fungal partner lies in outer-layer of lichen. Algae is trapped inside. They are placed close to the light. o Cross-section (left picture) The upper cortex is made up of cortex. The red section shows individual alga protected. The medulla is where gas exchange occurs. This is only made up of fungus The lower cortex is only done by fungus.
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The growth form of algae and fungi together (myco- and phycobiont) is different from cultivating them independently. 2. 3 types of lichens Foliose lichens o Rhizines for attachment o Upper-surface and lower surface can be clearly distinguished . This is characteristic of foliose lichens (leaf-like ) o Cortex: gelatinous , often tough
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Fruticose lichens o Tree-like . They are nicely branched o In contrast to foliose, there is no distinction between upper and lower surface . This is because branches are all round and same
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This note was uploaded on 06/21/2011 for the course BIO BIO251 taught by Professor Busch during the Fall '11 term at University of Toronto- Toronto.

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lecture 6 - Today: Lichen What are lichens? 3 main growth...

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