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Sept 16-08 - Fungi, Symbiosis, Decay and Ecosystems Notes

Sept 16-08 - Fungi, Symbiosis, Decay and Ecosystems Notes -...

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Josh Bovard Biology 111 – Tuesday, September 16 th , 2008 Professor Graham Bell F UNGI , S YMBIOSIS , D ECAY , & E COSYSTEMS – T EXTBOOK N OTES Chapter 30 – pp. 650-669, Chapter 56 – 1204-1225 How Do Fungi Thrive in Virtually Every Environment? Modern fungi are believed to have evolved from a unicellular protistan ancestor that had a flagellum Current evidence suggests that today’s choanoflagellates, fungi, and animals share a single common ancestor The three lineages are often grouped together as the opisthokonts Fungi live by absorptive nutrition They secrete digestive enzymes that break down large food molecules in the environment, then absorb the breakdown products through the plasma membranes of their cells This heterotrophy is successful in virtually every conceivable environment Saprobes are fungi that absorb nutrients from dead organic matter Parasites absorb nutrients from living hosts Mutualists live in intimate associations with other organisms that benefit both partners Structure: Generally multi-cellular, although there are some unicellular members (chytrids or yeasts) The body of a multi-cellular fungi is called a mycelium , composed of rapidly growing individual tubular filaments called hyphae Hyphae may be subdivided into cell-like units by incomplete cross-walls called septa Septa do not completely close off compartments in the hyphae, leaving pores allowing the intercellular movement of organelles Hyphae that lack septa are called coenocytic , while hyphae with septa are called septate Instead they contain hundreds of nuclei Modified hyphae, called rhizoids , anchor some fungi to their substratum (dead organism or other matter on which they feed) The hyphae may be widely dispersed to forage for nutrients or may clump together in a cottony mass to exploit a rich nutrient source The cells are greatly strengthened by microscopic gibrils of chitin Contact with their environment: 1
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Josh Bovard Biology 111 – Tuesday, September 16 th , 2008 Professor Graham Bell Fungal mycelium has an enormous surface area-to-volume ratio compared with that of most large multicellular organisms The downside of this is a tendency to lose lots of water in a dry environment For this reason, most fungi are found in moist environments They have a high tolerance for highly hypertonic environments They are more resistsnt than bacteria to damage in hypertonic surroundings Exploitation of Nutrient Sources Most fungi form mutualistic associations with other organisms Sugars are their favoured source of carbon Most obtain nitrogen from proteins or the products of protein breaken Some fungi can use nitrate or ammonium as their nitrogen source, although none can use N 2 Most fungi are unable to synthesize certain vitamins and must absorb them from their environment However, they can form vitamins that animals cannot They also require a source of mineral elements Parasitic Fungi
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