Symbiosis is a term that means "at table together" and denotes a feeding relationship. Fungi are heterotrophs and must consume pre-formed organic compounds as food, unlike plants which can produce their own food. Some fungi are saphrophytes and consume the remains of dead organic matter. One symbiotic relationship involving fungi is called parasitism. The parasite benefits at the expense of a host organism. Athlete's foot fungi grow on the skin of the foot and cause itchy, painful symptoms. The fungi derive their nutrition from the foot cells of the host. A yeast infection is another example of parasitism. When yeast live inside a host(human) and overgrow, this produces a yeast infection. Another symbiotic relationship is called mutualism--both organisms in the feeding relationship benefit. This is shown in lichens- a combination of a fungus and an algae that live together. The algae can produce food by photosynthesis, some of which can be shared with the fungus. The fungus provides a moist home for the algae to grow. Both organisms need eachother to thrive. Commensalism is another example of symbiosis. In commensalism, one organism benefits while the other is unaffected. Symbiotic relationships involve two separate organisms and always involve feeding.