Fungi
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Contents |
Introduction
Fungi (when capitalized) is a kingdom of filamentous or unicellular eukaryotic organisms, which are characterized by heterotrophic growth and the production of extracellular enzymes. Mycologists estimate that there are 100,000 species of fungi, including yeasts, molds, mildews, rusts, smuts, and mushrooms. Recent phylogenetic analyses have placed fungi more closely with animals than with plants.
Ecology
Unlike plants, fungi lack chlorophyll and other photosynthetic pigments, leaves, and true stems and roots. The main characteristic that distinguishes fungi from plants, or algae, is that the fungal cell walls are composed of the polysaccharide chitin, rather than cellulose. Additionally, some fungi are anaerobic. A fungus feeds by secreting digestive enzymes that release organic molecules that the fungus then absorbs from the tree, soil, or organism it is in contact with.
Fungi reproduce via sporogenesis, which eventually leads to the production of fruiting bodies, either conidia, microscopic stalks that hold spores, or fruiting bodies proper, ala "mushrooms."
In food webs, fungi take on the role of parasites, saprobes, or detritivores. A few genera can be considered carnivorous, such as Arthrobotrys, a genus of soil fungi famous for ensnaring free-living soil nematodes. Some fungi have formed symbiotic relationships with algae to create lichens. Many fungi also engage in symbiotic associations with the roots of higher plants creating mycorrhizae. Other fungi are farmed by leaf-cutter ants, an example of agriculture outside of humans.
Fungi and Health
As many as 150 of fungi species have now been linked to animal or human diseases -- candidiasis (thrush or yeast infections, caused by Candida albicans), cryptococcal meningitis (caused by Cryptococcus neoformans), aspergillosis (caused by Aspergillus nidulans), and ringworm and athlete’s foot (caused by dermatophytic "imperfect" fungi).
Fungi and Humans
Although some fungi are parasites of humans, there are many mutually beneficial fungi-human relationships. The most common example is the cultivation of yeasts, which are used in bread-making, and in the manufacture of wine and other alcoholic beverages. Other cases include the use of specific species in fermentation in order to form a particular product, such as the use of the mold "kōji-kin," Aspergillus oryzae, to ferment soybean paste into miso. Fungi are also used as a food, especially mushrooms.
Other fungi occur naturally on human skin and mucus linings and serve an immune function, keeping parasitic organisms at bay.
Fungi can be detrimental to humans in ways other than direct parasitism. Fungi destroy foodstuffs and infect domestic plants and animals.
