Post on 15-Dec-2015
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
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 31.11 Basidiomycetes (club fungi): Greville's bolete (top left), turkey tail (bottom left), stinkhorn (right)
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
Yeasts• Unicellular fungi • Inhabit liquid or moist habitats
• Reproduce asexually by budding
• Used commercially to raise bread and ferment alcohol
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
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)