Lichen as an example of a symbiosis of fungus and alga
fungi are a group of heterotrophic organisms that form one of the five kingdoms;
fungi include edible, inedible and poisonous species.
to describe lichens;
to present the significance of fungi and lichens.
Lichen as an example of a symbiosis of fungus and alga
Lichens occur all over the Earth. They are found behind the Arctic Circle as well as in sun‑burned deserts and steppes. They also grow on the tops of high mountains. As pioneer organismspioneer organisms they can grow in areas devoid of plants. They can be found on rocks and stones, tree bark and soil, on roofs, plaster and metal elements of buildings. Lichens take different forms and shapes. This diversity depends on their habitat and place of occurrence.
Lichens are organisms made of fungal and algae cells, classified as the thallophytes.
Description of the diversity of lichen thalli.
lichen specimens of different thallus shapes,
magnifying glass.
During your visit to the park or forest, observe the lichen thalli, take note of their shape and classify them as bushy, leafy or crusty lichens.
Specify the colour of lichens.
Determine the surface which the observed lichens grow on.
Lichens’ thalli take on various shapes, from flat and discoid to raised and bushy. They are also diversified in terms of colour. They can be yellow, grey‑green, orange, and even brown.
Lichen’s thallus is built of individual cells of algae entwined with hyphae of the fungus. The hyphae form a compact outer structure, impermeable to water and resistant to frost. In addition, they produce haptera that fix the lichen to the substrate. Inside the thallus, a loose layer of algae cells occurs.
Fungi and algae of lichen cooperate with each other. The fungus's function is to protect the delicate algae against environmental factors as well as to provide water and mineral salts. The algae nourish the lichen, producing organic compounds in the process of photosynthesis. Such a close relationship between organisms is called symbiosis. It makes lichens completely self‑sustaining organisms which may inhabit areas devoid of life, where harsh conditions prevail. They only need light, carbon dioxide, water and mineral salts to survive.
Lichens reproduce asexually by random division of the thallus and by soredia. Soredia are small fragments of a lichen containing algae cells and fungal hyphae that spread carried by the wind. When they fall on a suitable substrate, they grow, creating a new thallus.
Significance of lichens
Lichens inhabit extremely infertile grounds, even naked stones. They give off to the environment the so‑called lichen acids that cause weathering of rocks. Dead thalli enrich gravel and sand with organic substances. They participate in soil formation in this way. Thanks to them and other pioneer organisms, plant habitats are created. The resistance of lichens to unfavourable environmental conditions is evidenced by the fact that they are the main component of the tundra. They are the basic food of a reindeer and musk muskoxen.
Lichens cannot excrete absorbed toxic compounds which cause the death of their thallus. The most sensitive to air contamination are bushy lichens and leafy lichens, and they are the ones that die the fastest. This feature of lichens is used to assess the degree of air pollution in which they play the role of bioindicatorsbioindicators – indicators of air purity. When comparing lichens occurring in a given area with a lichen scale, it is possible to determine the degree of sulfur oxide contamination of the environment.
Lichens are used for the production of medications: Infusions and powdered thallus of the Iceland moss and tree lungwort (Lobaria pulmonaria) have been used for centuries in the treatment of colds, cough and tuberculosis. Some are used to produce organic dyes used in chemical research. Dishes from lichens are valued delicacies, for example in Japan. To this day, in many areas of Lapland, the ground thallus of the Icelandic moss is added to the flour from which bread is baked.
Look for lichens on the tree bark during the walk. Take photographs of them and recognise their forms. Using the lichen scale, determine the state of air pollution.
Match the pairs: English words with Polish definition.
organizmy wskaźnikowe, gatunki organizmów wykazujące dużą wrażliwość i charakterystyczne reakcje na działanie określonych czynników środowiska, grupa organizmów o małych wymaganiach środowiskowych, odporna na niekorzystne czynniki środowiska; należą do nich głównie porosty i mchy; organizmy te jako pierwsze zasiedlają nowe środowiska
| bioindicators | |
| pioneer organisms |
Conclusion
Lichens are symbiotic organisms formed by fungi and algae, they are classified into the kingdom of fungi.
Keywords
lichens, fungi, algae, bioindicators, pioneer organisms, acid rains
Glossary
bioindykatory – organizmy wskaźnikowe, gatunki organizmów wykazujące dużą wrażliwość i charakterystyczne reakcje na działanie określonych czynników środowiska
organizmy pionierskie – grupa organizmów o małych wymaganiach środowiskowych, odporna na niekorzystne czynniki środowiska; należą do nich głównie porosty i mchy; organizmy te jako pierwsze zasiedlają nowe środowiska