Chapter 20
Objectives Identify the basic characteristics of
fungi Explain the role of fungi as
decomposers and how this role affects the flow of energy and nutrients through food chains
SCS:
Kingdom Fungi contains 80,000 spp
Mostly multicellular eukaryotes that share a common mode of nutrition• Heterotrophic
• Cells release digestive enzymes and then absorb resultant nutrient molecules
Some are parasitic
Several have mutualistic relationship
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Body (thallus) of most fungi is multicellular mycelium (yeasts are unicellular)• Consists of a vast network of thread-like hyphae
Septate fungi have hyphae with cross walls Nonseptate fungi are multinucleated Hyphae grow from tip
• Give the mycelium a large surface area per unit volume
Cell walls of chitin, like insect exoskeleton Excess food stored as glycogen as in animals Possibly evolved from red algae - both lack
flagella
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Both sexual (in most) and asexual reproduction
Three types of asexual reproduction:
• Fragmentation – piece breaks off
• Budding-mitosis produces a new individual which then pinches off
• Spores – reproductive cell
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Advantages of sporesSporangia protect sporesLarge number of spores produced increases survival rate
Small and light so they can easily dispersed
During sexual reproduction, hyphae from two different mating types fuse
Asexual reproduction usually involves the production of windblown spores
Unicellular yeasts reproduce by budding
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Identify the four major types of fungi Distinguish among the ways spores
are produced in zygomycotes, ascomycotes, and basidiomycotes
Summarize the ecological roles of lichens and mhycorrhizae
Zygospore Fungi
Phylum Zygomycota
•Mainly saprotrophs decomposing animal and plant remains
•Black bread mold - Rhizopus stolonifer
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Life cycle• Produce spores• Spores dispersed by air currents; germinate
into mycelia
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Phylum Ascomycota - about 60,000 species of sac fungi
Most are saprotrophs that digest resistant materials Most are composed of septate hyphaeUses of sac fungi vaccines Morels and truffles Many plant diseases:
• Powdery mildews; leaf curl fungi; ergot of rye; chestnut blight and Dutch elm disease
Aspergillus and Candida cause serious human infections
Talaromyces (formerly Penicillium) is source of penicillin
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Life cycle Asexual reproduction is the norm
• Yeasts usually reproduce by budding• The other ascomycetes produce spores called
conidia or conidiospores
Sexual reproduction• Mitosis and then meiosis produces 8
ascospores
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Term “yeasts” is loosely applied to unicellular fungi, many of which are ascomycetes
Budding is common form of asexual reproduction
• Sexual reproduction results in the formation of asci and ascospores
• When some yeasts ferment, they produce ethanol and carbon dioxide
Beer and wine making
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Phylum Basidomycota – 22,000 spp Familiar toadstools, mushrooms,
bracket fungi, puffballs, stinkhorns – some deadly poisonous
Also plant diseases such as the smuts and rusts
Mycelium composed of septate hyphae
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Usually reproduce sexually
Haploid hyphae fuse, forming a dikaryotic (n + n) mycelium
Dikaryotic mycelium forms fruiting bodies called basidiocarps
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Smuts and rusts are club fungi that parasitize cereal crops• Great economic importance because of
annual crop losses Do not form basidiocarps
Life cycle of rusts often requires two different plant host species
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Symbiotic association between a fungus and a cyanobacterium or green alga
• Specialized fungal hyphae penetrate photosynthetic symbiont
• Transfer nutrients directly to the fungus
Possibly mutualistic, but fungal symbiont probably a parasite of photosynthetic symbiont
• Photosynthetic symbiont independent
• Fungal symbiont usually can’t grow alone
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Three morphological types
• Compact crustose lichens - seen on bare rocks or on tree bark
• Fruticose lichens – shrub-like
• Foliose lichens - leaf-like
Can live in areas of extreme conditions and contribute to soil formation
Sensitive indicators of air pollution
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Mutualistic relationships between soil fungi and the roots of most familiar plants• Give plant greater absorptive surface
• Help plants acquire mineral nutrients in poor soil
Fungal symbiont usually a sac fungus• Hyphae may enter cortex of root, but not cytoplasm
Ectomycorrhizae form a mantle that is exterior to the root, and they grow between cell walls.
Endomycorrhizae penetrate only the cell walls
Earliest fossil plants have mycorrhizae associated with them
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