Chapter 31 - Fungi - Chapter 31 Fungi more related to...

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Chapter 31 Fungi Eukaryotes, most multicellular Differ in nutritional mode, structural organization, growth & reproduction Once grouped with plants - molecular studies indicate that animals are closest relatives Heterotrophs - acquire nutrients by absorption Digest food outside body by secreting powerful hydrolytic enzymes (exoenzymes )
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Fungi function as: (1) decomposers (saprobes) - absorb nutrients from non-living organic material (2) parasites - absorb nutrients from cells of living hosts (3) Mutualistic symbionts - absorb nutrients from living host but reciprocate Extensive surface area and rapid growth adapt fungi for absorptive nutrition. Vegetative bodies diffusely organized around and within food source
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Except for yeasts & microsporidia, fungi constructed of tiny filaments called hyphae Composed of tubular walls that surround plasma membranes & cytoplasm Hyphae form interwoven mat = mycelium Mycelia can be huge (maximizes surface area). Armillaria ostoyae : 3.4 miles in diameter, 2200 acres of forest, 2600 years old and weighs hundreds of tons
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Most fungi multicellular with hyphae divided into cells by septa Large enough holes in septa to allow cellular organelles to flow from cell to cell Cell walls of fungi built mainly of chitin Some fungi are aseptate - hyphae not divided called coenocytic fungi -continuous cyto- plasmic mass - hundereds or thousnads of nuclei
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Parasitic fungi - hyphae modified as haustoria absorbing hyphal tips that penetrate host tissue
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Filamentous structure of mycelium - extensive surface area for rapid growth kilometer of hyphae each day Fungi disperse and reproduce by releasing spores that are produced sexually or asexually Output is enormous - trillions of spores Distributed by air - spores have been found 100 miles above Earth
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Nuclei of fungal hyphae & spores of most species are haploid except for transient diploid stages that form during sexual life cycle Some mycelia have become genetically heterogeneous through the fusion of 2 hyphae with genetically different nuclei - heterokaryon
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In many fungi with sexual life cycles union occurs in two distinct stages called (1) plasmogamy = fusion of 2 parents cytoplasm (2) karyogamy = fusion of haploid nuclei May be separated by hours to centuries Meiosis restores haploid condition before spores are produced.
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