Mutualistic Fungi: Lichens and Mycorrhizae:

Symbiosis refers to species that live in close association. If both partners benefit, the relationship is called mutualism. Lichens and mycorrhiza are examples of mutualists.

Lichens

A lichen consists of a fungus and a photosynthetic organism (e.g. algae). Lichens can absorb mineral ions, extract nitrogen from the air, and colonize new habitats. They also are good indicators of deteriorating environmental conditions.

Lichens are mutualistic associations between fungi and cyanobacteria, or green algae, or both. The fungal component usually is an ascomycete. The fungus parasitizes the photosynthetic alga upon which it depends entirely for its food. The algae in turn get a protected place to survive.

Lichens live in inhospitable places such as bare rock and tree trunks. By their metabolic activities, lichens can change the composition of their substrate. They are unusually sensitive to air pollution.

Mycorrhizae

Mycorrhiza form when fungi enter into mutualistic interactions with tree roots, which benefit greatly from the fungi's ability to absorb needed nutrients.

A mycorrhiza is a symbiotic relationship in which fungal hyphae surround roots of shrubs and trees. The hyphae of ectomycorrhizae do not penetrate the cells of the root. The hyphae form a net around roots. They are common in temperate forests. The hyphae of endomycorrhizae do penetrate the cells of the root. Because of its extensive surface area, the fungus can absorb mineral ions and facilitate their entry into the plant. Zygomycetes are the fungal partner.

Well, that's the end of today's lecture. The next time your visiting the grocery store, look for foods derived from the organisms studied in this lecture and the previous one: fungi, bacteria and algae. Don't neglect the Asian food section, the frozen food section, and the dairy section.

REVIEW: Despite their tolerance for harsh climates, lichens are particularly intolerant of

REVIEW: A lichen is a composite organism made up of

REVIEW: A mycorrhiza is a _____ .

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