Download - Fungi
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Fungi
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Overview• Fungi are eukaryotes• Most are multicellular• Differ from other eukaryotess in nutritional mode, structural organization, growth & reproduction
• Molecular studies show they are more closely related to animals than to plants
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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
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Interface of Nutrition & Ecology
• Absorptive nutrition allows fungi to serve as decomposers (saprobes), parasites, or mutualistic symbionts
• Saprobic fungi absorb nutrients from non-living organic material (animal waste, dead plants & animals)
• Parasitic fungi absorb nutrients from cells of living hosts– Cause about 80% of plant diseases
• Mutualistic fungi absorb nutrients from the host but also benefit the host, such as aiding in uptake of nutrients
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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– Usually subterranean
• Fungi have cell walls, most made of chitin– Same material as exoskeleton of insects and arthropods
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Figure 31.1 Fungal mycelia
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Figure 31.2 Examples of fungal hyphae
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Figure 31.2x Septate hyphae (left) and nonseptate hyphae (right)
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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
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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
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Stages of The Sexual Life Cycle
• Two distinct stages in the union of partners during sexual reproduction
• Plasmogamy– The fusion of the parents’ cytoplasm when their mycelia come together
• Karyogamy – Fusion of the haploid nuclei of the 2 parents
• The two stages may be separated in time by hours, days, or years
• During the interim, the hybrid is a heterokaryon
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Figure 31.3 Generalized life cycle of fungi (Layer 1)
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Figure 31.3 Generalized life cycle of fungi (Layer 2)
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Figure 31.3 Generalized life cycle of fungi (Layer 3)
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Diversity of Fungi
• More than 100,000 species are known
• Four phyla– Chytridiomycota– Zygomycota– Ascomycota– Basidiomycota
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Figure 31.4 Phylogeny of fungi
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Chytridiomycota: The Chytrids
• Mainly aquatic• Form flagellated spores, so were once considered protists
• The most primitive fungi– Diverged first from protists
• Chitin cell walls• Absorptive nutrition
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Figure 31.5 Chytridiomycota (chytrids)
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Zygomycota: Zygote Fungi
• Live mostly in soil or on decaying plant or animal material
• One group forms mycorrhizae– mutualistic assiciation with the roots of plants
• Plasmogamy produces a resistant structure called a zygosporangium in which karyogamy, then meiosis occurs– The zygosporangium is multi-nucleated– Zygosporangium are resistant to freezing & drying and metabolically inactive
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Figure 31.6 The common mold Rhizopus decomposing strawberries
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Figure 31.7 The life cycle of the zygomycete Rhizopus (black bread mold)
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Figure 31.7x1 Young zygosporangium
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Figure 31.7x2 Mature zygosporangium
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Figure 31.8 Pilobolus aiming its sporangia
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Ascomycota: Sac Fungi• Over 60,000 species• Wide range of habitats, size, & complexity
• Many are important saprobes• Others cause devastating plant diseases• About half live in a mutualistic association with algae, forming lichens
• All produce sexual spore in sac-like asci
• The sexual stage is a fruiting body called an ascocarp
• Reproduce asexually by producing asexual spores: conidia
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Figure 31.9 Ascomycetes (sac fungi): Scarlet cup (top left), truffles (bottom left), morel (right)
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Figure 31.9x1 Carbon fungus
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Figure 31.9x2 Aspergillus
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Figure 31.10 The life cycle of an ascomycete
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Figure 31.10x1 Life cycle of an ascomycete
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Figure 31.10x2 Apothecium
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Ascomycota: The Club Fungi
• Approximately 25,000 species• Includes mushrooms, shelf fungi, puffballs, & rusts
• Important plant decomposers• Also includes mycorrhiza-forming mutualists and plant parasites
• Reproduce sexually by producing complex fruiting bodies called basidiocarps
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Figure 31.11 Basidiomycetes (club fungi): Greville's bolete (top left), turkey tail (bottom left), stinkhorn (right)
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Figure 31.11x1 Coprinus comatus, Shaggy Mane
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Figure 31.11x2 Geastrum triplex
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Figure 31.11x3 Tremella messenterica, Witch’s Butter
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Figure 31.11x4 Stinkhorn
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Figure 31.11x5 Amanita
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Figure 31.12 The life cycle of a mushroom-forming basidiomycete
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Figure 31.12x Gills
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Figure 31.13 A fairy ring
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Table 31.1 Review of Fungal Phyla
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Specialized Lifestyles
• Four types of fungi have developed highly specialized ways of life:
• Molds• Yeasts• Lichens• Mycorrhizae
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Molds• A rapidly growing, asexually reproducing fungus
• Mold applies only to the asexual stage
• Many are destructive, but some are commercially important– penicillin
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Figure 31.14 A moldy orange (left), Penicillium (right)
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Figure 31.21 Fungal production of an antibiotic
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Yeasts• Unicellular fungi • Inhabit liquid or moist habitats• Reproduce asexually by budding• Used commercially to raise bread and ferment alcohol
• One species is a normal inhabitant of moist human epithelial tissue
• May become pathogenic
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Figure 31.15 Budding yeast
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Lichens• A symbiotic association of millions of photosynthetic microorganisms held in a mesh of fungal hyphae
• The photosynthetic organisms are usually unicellular or filamentous green algae or cyanobacteria
• The lichen symbiosis is highly complex– The alga provides the fungus with food– The cyanobacteria in lichens fix nitrogen & provide organic nitrogen
– The fungus provides a physical structure for growth
– Hypahe reatin water & minerals and allow gas exchange
• Appear similar to mosses or simple plants
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Figure 31.16 Lichens
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Figure 31.17 Anatomy of a lichen
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Figure 31.17x Anatomy of a lichen
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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
• Fungi are in permanent association with their plant host
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Figure 31.18 Mycorrhizae
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Figure 31.19 An experimental test of the benefits of mycorrhizae
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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
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Fungal Pathogens• About 30% of fungi are parasites, mostly of plants– Wheat rust– Dutch Elm disease
• Some secrete toxins harmful to humans– Aspergillus secretes carcinogenic aflatoxins on improperly stored grain or peanuts
– Claviceps purpurea secretes ergot on rye; can cause gangrene, hallucinations, etc (LSD; Salem witch trials)
• Human diseases– Skin diseases: athlete’s foot, rimg worm– Respiratory illnesses from inhaled spores: coccidiomycosis, histoplasmosis
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Figure 31.20 Examples of fungal diseases of plants: Black stem rust on wheat (left), ergots on rye (right)
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Figure 31.20x1 Strawberries with Botrytis mold, a plant parasitic fungus
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Figure 31.20x2 Pink ear rot of corn
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Evolution of Fungi• Fungi colonized the land with plants• Oldest fungi fossils are 460 million years old
• Fossils of the first vascular plants have mycorrhizae
• Plants probably moved onto land with fungi– The four phyla may have diverged from a common ancestor during the transition from water to land
• Fungi and animals evolved from a common protistan ancestor– Proteins & rRNA demonstrate that fungi are more closely related to animals than to plants