Fungi

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

Figure 31.1 Fungal mycelia

Figure 31.2 Examples of fungal hyphae

Figure 31.2x Septate hyphae (left) and nonseptate hyphae (right)

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 31.6 The common mold Rhizopus decomposing strawberries

Figure 31.7x1 Young zygosporangium

Figure 31.7x2 Mature zygosporangium

Figure 31.8 Pilobolus aiming its sporangia

Figure 31.9 Ascomycetes (sac fungi): Scarlet cup (top left), truffles (bottom left), morel (right)

Figure 31.9x1 Carbon fungus

Figure 31.9x2 Aspergillus

Figure 31.10x1 Life cycle of an ascomycete

Figure 31.10x2 Apothecium

Figure 31.11 Basidiomycetes (club fungi): Greville's bolete (top left), turkey tail (bottom left), stinkhorn (right)

Figure 31.11x1 Coprinus comatus, Shaggy Mane

Figure 31.11x2 Geastrum triplex

Figure 31.11x3 Tremella messenterica, Witch’s Butter

Figure 31.11x5 Amanita

Figure 31.12x Gills

Figure 31.13 A fairy ring

Table 31.1 Review of Fungal Phyla

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

Figure 31.14 A moldy orange (left), Penicillium (right)

Yeasts• Unicellular fungi • Inhabit liquid or moist habitats

• Reproduce asexually by budding

• Used commercially to raise bread and ferment alcohol

Figure 31.15 Budding yeast

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

Figure 31.18 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)

Figure 31.20x1 Strawberries with Botrytis mold, a plant parasitic fungus

Figure 31.20x2 Pink ear rot of corn