30.1 The fungi share several key characteristics.
Distinctive Fungal Features
• Recent analysis indicates that fungi are more closely related to animals than to plants. (p. 600)
• Fungi are very diverse, but share several characteristics: Fungi are heterotrophs; they have several cell types although they are primarily filamentous; some have a dikaryon stage; they have cell walls that include chitin; and they exhibit nuclear mitosis. (p. 600)
The Body of a Fungus
• Many fungi have slender filaments called hyphae that are continuous, composed of branching tubes, or made up of long chains of cells joined end-to-end and divided by septa. (p. 601)
• A mycelium is a mass of connected hyphae that grows into the material in which the fungus is feeding. (p. 601)
• Cell walls are formed of polysaccharides and chitin. (p. 601)
How Fungi Reproduce
• Fungi exhibit both sexual and asexual reproduction. (p. 602)
• Sexual reproduction occurs when the haploid hyphae of two individuals fuse. (p. 602)
• Most fungi use spores to reproduce. (p. 602)
How Fungi Obtain Nutrients
• All fungi secrete digestive enzymes into their surroundings and absorb the organic molecules produced via external digestion. (p. 603)
Metabolic Pathways
• Humans use the metabolic pathways of fungi for commercial products such as cheese, soy sauce, bread, beer, and wine. (p. 603)
• Fungi are also used in bioremediation to rid water or soils of environmental contamination. (p. 603)
Ecology of Fungi
• Fungi are the principal decomposers in the biosphere and are nearly the only organisms capable of breaking down lignin. (p. 604)
• Symbioses fall into many categories, including obligate and facultative. (p. 604)
• Fungal species are responsible for billions of dollars of agricultural losses annually, and cause many human and animal diseases, including ringworm and athlete's foot. (p. 604)
• Lichens are mutualistic associations between fungi and algae or cyanobacteria, while mycorrhizae are specialized mutualistic associations between plant roots and fungi. (p. 604)
30.2 There are four major groups of fungi.
Phylogenetic Relationships
• Although the phylogeny of fungi changes rapidly, currently they are divided into four groups (Chytridiomycota, Zygomycota, Basidiomycota and Ascomycota. (p. 605)
Chytridiomycota
• The chytrids are aquatic, flagellated fungi that are the closest living relatives to the first fungi. (p. 606)
Zygomycota
• The zygomycetes are a very diverse group that includes many of the common bread molds. (p. 607)
• Zygomycotes are named after a characteristic feature of their sexual phase, the zygosporangium. (p. 607)
• In zygomycetes, asexual reproduction occurs much more frequently than sexual reproduction. (p. 607)
Basidiomycota
• Basidiomycetes include mushrooms, toadstools, puffballs, and many plant pathogens, such as smuts and rusts. (p. 608)
• Basidiomycetes are named for their characteristic sexual reproductive structure, the basidium. (p. 608)
Ascomycota
• The ascomycetes contain about 75% of known fungi, including bread yeasts, common molds, morels and truffles, and many plant pathogens, such as chestnut blight. (p. 609)
• Ascomycetes are named for their characteristic reproductive structure, the ascus. (p. 609)
• In ascomycetes, asexual reproduction is very common and takes place by conidia produced at the ends of conidiophores. (p. 609)
30.3 Fungi participate in many symbioses.
Lichens
• Lichens are symbiotic relationships between a fungus and a photosynthetic partner that colonize even the harshest habitats on the planet. (p. 611)
• Lichens vary in their sensitivity to atmospheric pollutants, and some are used as air quality indicators. (p. 611)
Mycorrhizae
• Mycorrhizae are mutualistic relationships between plant roots and certain fungi. (p. 612)
• The fungi in mycorrhizal associations increase the amount of soil contact and the total absorption area. (p. 612)
• Two principal types of mycorrhizae are arbuscular and ectomycorrhizae. (p. 612)
Endophytes
• Endophytic fungi live in the intercellular spaces inside living plants. (p. 613)
Mutualistic Animal Symbioses
• A range of fungal-animal symbioses has been identified. These include ruminants and the fungi in their gut, and leaf-cutter ants and specific fungal species. (p. 613)
Fungal Parasites and Pathogens
• Candida can cause common oral or vaginal infections. (p. 614)
• A chytrid can cause chytridiomycosis in amphibians.
• Crop losses due to parasitic or pathogenic fungi are extensive throughout the world. (p. 614)
• Aflatoxins can cause kidney or nervous system damage. (p. 614)