parama9000 | Student

A lichen is an associated organism: two beings, an alga and a fungus, live together in symbiosis, producing lichen thallus.

Much of the lichen body is hyphae which clasps alga. The fungus collects water and provides structure and protection for the alga, and may extract minerals in some cases. The alga uses its chloroplasts to carry out photosynthesis, providing carbohydrates for both itself and the fungus.

lichens are basically a combination of fungus and a type of algae (usually green algae and cyanobacteria). They are typically in a mutual symbiosis with other organisms. They are also the first colonists in barren environments. They usually come in 3 main body forms:

Fruticose: typically flat finger-like extensions

Foiliose: leaf- like extensions

Crustose: matted thick fungus on rocks

lichens are excellent indicators of air quality and play a role in turning rocks into soil.  

kezze | Student

A composite organism consisting of a fungus and a photosynthetic partner growing together in a symbiotic relationship.

fact-finder | Student

Lichens are organisms that grow on rocks, tree branches, or bare ground. They do not have roots, stems, flowers, or leaves. Lichens are composed of a green alga (singular form of algae) and a colorless fungus which co-exist for their mutual benefit. The alga, which has chlorophyll, manufactures its own food through photosynthesis (the process that uses sunlight as an energy source to convert water, carbon dioxide, and inorganic salts into oxygen and carbohydrates). The fungus, which has no chlorophyll, absorbs food from the alga. The fungus helps the alga by covering it and preventing it from drying out.

There is some question as to whether the fungus and alga derive equal benefit from their relationship. Some studies in which the fungus and alga of a lichen have been separated indicate that fungus is more dependent on the alga than vice-versa. While the alga is able to survive on its own, the isolated fungus has trouble growing and reproducing.

Sources: Hale, Mason E., Jr. The Biology of Lichens, 2nd ed., p. 69; Lawrence, Eleanor. Henderson's Dictionary of Biological Terms, 10th ed., p. 314; The Wise Garden Encyclopedia, p. 581.

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