Fungi. Overview Fungi are eukaryotes Most are multicellular Differ from other eukaryotes in...
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Transcript of Fungi. Overview Fungi are eukaryotes Most are multicellular Differ from other eukaryotes in...
Overview• Fungi are eukaryotes• Most are multicellular• Differ from other eukaryotes in nutritional mode, structural organization, growth & reproduction
• Molecular studies show they are more closely related to animals than to plants
Nutrition
• Absorptive nutrition enables fungi to live as decomposers and symbionts
• Heterotrophs• Acquire nutrition through absorption
• Digest food outside of their body by secreting hydrolytic enzymes – Exoenzymes– Decompose complex molecules so fungus can absorb them
Structural Adaptations• Extensive surface area adapts fungi for absorptive nutrition
• Fungi are constructed of tiny filaments = hyphae– (yeast are an exception)– Hyphae have tubular walls which surround a membrane & cytoplasm
– Hyphae are divided into sepatarate cells by septa
• The hyphae form an interwoven mat = mycelium
• Fungi have cell walls, most made of chitin– Same material as exoskeleton of insects and arthropods
Reproduction• Reproduce by releasing spores• Spores are produced either sexually or asexually
• Trillions of spores can be produced by a single organism
• Dispersed by wind and water over many miles
• If they land in a receptive spot, grow to form a mycelium
The Heterokaryotic Stage
• Some mycelia become genetically heterogeneous through fusion of 2 hyphae with genetically different nuclei
• Such a mycelium = heterokaryon
• Has some of the advantages of diploidy
Diversity of Fungi
• More than 100,000 species are known
• Four phyla– Chytridiomycota– Zygomycota– Ascomycota– Basidiomycota
Zygomycota: Zygote Fungi
• Live mostly in soil or on decaying plant or animal material
• One group forms mycorrhizae– mutualistic association with the roots of plants
Figure 31.11 Basidiomycetes (club fungi): Greville's bolete (top left), turkey tail (bottom left), stinkhorn (right)
Specialized Lifestyles
• Four types of fungi have developed highly specialized ways of life:
• Molds• Yeasts• Lichens• Mycorrhizae
Molds• A rapidly growing, asexually reproducing fungus
• Mold applies only to the asexual stage
• Many are destructive, but some are commercially important– penicillin
Yeasts• Unicellular fungi • Inhabit liquid or moist habitats
• Reproduce asexually by budding
• Used commercially to raise bread and ferment alcohol
Mycorrhizae• Mutualistic associations of plant roots and fungi
• Extensions of the fungal mycelium increase the absorptive surface of the plant roots
• The plant derives minerals absorbed from the soil by the fungus
• The fungus derives organic nutrients synthesized by the plant
• Almost all vascular plants have mycorrhizae
Ecological Impacts
• Ecosystems depend on fungi as decomposers
• Provide ecosystems with inorganic nutrients essential to plant growth
• Recycle carbon, nitrogen, and other elements that otherwise would be tied in organic matter
• Structure suits function– Invasive hyphae enter tissues of dead organic matter
– Exoenzymes can hydrolyze polymers, including cellulose and lignin
Figure 31.20 Examples of fungal diseases of plants: Black stem rust on wheat (left), ergots on rye (right)