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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