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 3

 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 4

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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 6

 Advantages of spores  Sporangia protect spores  Large 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 8

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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 11

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 Life cycle Produce spores Spores dispersed by air currents; germinate into mycelia 13

 Phylum Ascomycota - about 60,000 species of sac fungi  Most are saprotrophs that digest resistant materials  Most are composed of septate hyphae Uses 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 14

 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 15

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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 20

 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 21

 Usually reproduce sexually  Haploid hyphae fuse, forming a dikaryotic (n + n) mycelium  Dikaryotic mycelium forms fruiting bodies called basidiocarps 22

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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 25

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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 27

 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 28

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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 30