Lichens have an important difference from all other living things. In the body of a lichen, two organisms always coexist - a fungus and an algae.
Lichen structure
The body of a lichen is called a thallus or thallus. According to the external structure of the thallus, lichens are divided into three groups:
- scale;
- leafy;
- bushy.
Rice. 1. Types of lichen thalli.
The thallus of any organisms of the kingdom of fungi and lichens is formed by filaments of mycelium, which are called hyphae. Between the hyphae in the lichen are algae cells. More often these are unicellular green algae, but in some lichens they are filamentous multicellular, those that form mud in water bodies in a free form.
Rice. 2. The internal structure of the lichen.
Symbiosis
Symbiosis is the joint activity of organisms of different species, in which each organism receives benefits from the other.
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In lichen, symbiosis proceeds as follows. The algae produces organic matter that the fungus consumes. With the help of hyphae, the fungus absorbs water with substances dissolved in it from the environment and creates a humid environment for the algae.
This symbiosis is more beneficial for the fungus. The fungus cannot live without the algae, but the algae can and, if separated from the fungus, develops faster.
reproduction
Lichens most often reproduce in two ways:
- pieces of thallus that accidentally break off and then germinate, forming a new organism;
- special particles in which algae cells are surrounded by hyphae.
Such particles can be located on the surface of the lichen or inside the thallus. Over time, the thallus bursts and the particles fly apart. When germinating, they form new thalli.
Rice. 3. Vegetative propagation of lichens.
In addition, the lichen fungus reproduces by spores. Spores are small cells of the fungus that, after maturation, fly out of the cracks of the lichen. Having met the corresponding type of algae, the spores germinate and form a new lichen with it.
What is "reindeer moss"?
"Deer moss", or reindeer moss, is not a separate type of moss or lichen. Yagel is the name of a whole group of lichen species growing in the tundra.
Spreading
Lichens are found all over the Earth, and in Antarctica, and in deserts, and in the mountains. There are more of them in forests than in steppes and deserts.
Mandatory conditions for the life of lichens are sufficient light and humidity. Illumination is important for algae, since in it the formation of organic substances occurs only in the light.
The meaning of lichens
Tundra lichens are the main food for reindeer. Reindeer roam the tundra in search of the best pastures. Pigs, sheep and cows can also eat reindeer moss.
Some types of snails feed on lichens. Some species are edible for humans. Paints and some medicines are also obtained from lichens.
Interesting facts about the use of lichens by humans:
- as diapers;
- to preserve products (due to the suppression of bacteria by them);
- to obtain glucose (the method was developed in the USSR in wartime);
- as a source of vitamin C.
Cetraria lichen is included in the recipes of many dishes of Icelandic traditional cuisine. It is added to cereals, soups, sausages, cottage cheese, bread, and also to lollipops used for sore throats.
What have we learned?
When preparing a report or homework in biology in grade 5 on the topic “Lichens”, you need to pay attention to the following: lichens are a fungus and algae living together. Their relationship is called symbiosis, but for the fungus they are more beneficial. Lichens are unpretentious and widespread. The nutritional value of lichens for humans is small, but in the northern regions, lichens are indispensable for animal husbandry.
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General characteristics. Lichens are a peculiar group of living organisms, the body (thallus) of which is formed by two organisms - a fungus (mycobiont) and an algae or cyanobacterium (phycobiont), which are in symbiosis. About 20 thousand species of fungi and about 26 genera of phototrophic organisms were found in the composition of lichens. The most common are green algae of the genera trebuxia, trentepolia, and cyanobacterium nostoc, which are autotrophic components in approximately 90% of all lichen species.
The symbiotic (mutualistic) relationship between the components of lichens boils down to the fact that the phycobiont supplies the fungus with organic substances created by it during photosynthesis, and receives water from it with dissolved mineral salts. In addition, the fungus protects the phycobiont from drying out. Such a complex nature of lichens allows them to receive nutrition from the air, precipitation, dew and fog moisture, dust particles deposited on the thallus, from the soil. Therefore, lichens have a unique ability to exist in extremely unfavorable conditions, often completely unsuitable for other organisms - on bare rocks and stones, roofs of houses, fences, tree bark, etc.
The mycobiont is specific, i.e., it is part of only one type of lichen.
The structure of lichens. The lichen thallus is usually gray, light or dark brown in color. In appearance, lichen thalli are divided into scale, leafy and bushy (Fig. 6.3).
Most common scale, or cortical, lichens (about 80%), having thallus in the form of a thin crust, firmly growing together with the substrate and not separable from it. More highly organized leafy lichens have the form of scales or plates attached to the substrate by bundles of hyphae called rhizins. They grow on rocks and tree bark. So, for example, on the trunks and branches of aspen, a golden-colored lichen, xanthoria, is often found. bushy lichens are bushes formed by thin branching filaments or stems attached to the substrate only at the base.
According to the anatomical structure, lichens are divided into homeo- and heteromeric (see Fig. 6.3). At homeomeric lichen thallus is a loose plexus of fungal hyphae, among which cells or filaments of a phycobiont are more or less evenly distributed.
Fig6.3.Lichen thallus forms: a - cortical (scale); b - leafy; v.g.d - bushy; e - section of a heteromeric thallus: I - upper bark, 2 - layer of algae, 3 - core, 4 - lower bark; well - soredia.
heteromeric the structure is characterized by the presence of differentiated layers in the thallus, each of which performs a specific function: the upper and lower cortex are protective, the photosynthetic layer is involved in the process of photosynthesis and accumulates assimilation products, and the core is in attaching the thallus to the substrate and providing aeration of the phycobiont. This morphological type of lichen is the most highly organized form of the thallus and is characteristic of most foliose and fruticose lichens.
Reproduction. Lichens reproduce mainly by vegetative means - parts of the thallus, as well as special specialized formations - soredia and isidia (Fig. 6.4).
Fig 6.4.Vegetative propagation of lichens: a - section of the thallus with soredia; b - section of thallus with isidia; one - soredia; 2 - isidium.
Soredia are formed under the upper cortex in the photosynthetic layer and consist of one or more phycobiont cells entwined with fungal hyphae. Under the pressure of the overgrown mass of numerous soredia, the cortical layer of the thallus breaks, and the soredia come to the surface, from where they are carried by wind and water and, under favorable conditions, grow into new lichen thalli.
Isidia are small outgrowths of the thallus in the form of sticks, tubercles, covered with bark on the outside. They consist of several phycobiont cells, braided with fungal hyphae. Isidia break off and form new thalli.
The value of lichens in the biosphere and the national economy. About 26 thousand species of lichens are known. They are widely distributed in nature, except for places where the air is saturated with harmful gases. Lichens are very sensitive to air pollution and therefore most of them quickly die in large cities, as well as near factories and plants. For this reason, they can serve as indicators of air pollution with harmful substances.
Being autoheterotrophic organisms, lichens accumulate solar energy and create organic matter in places inaccessible to other organisms, and also decompose organic matter, participating in the general circulation of substances in the biosphere. Lichens play a significant role in the soil-forming process, as they gradually dissolve and destroy the rocks on which they settle, and due to the decomposition of their thalli, soil humus is formed. Thus, lichens, together with bacteria, cyanobacteria, fungi and some algae, create conditions for other, more advanced organisms, including higher plants and animals.
In human economic activity, an important role is played primarily by fodder lichens, such as reindeer moss, or reindeer moss, Icelandic moss and others, which are eaten not only by reindeer, but also by deer, musk deer, roe deer, and elk. Some types of lichens (lichen manna, hygrophora) are used for food, they have also found application in the perfume industry - for obtaining aromatic substances, in the pharmaceutical industry - for the manufacture of drugs against tuberculosis, furunculosis, intestinal diseases, epilepsy, etc. Lichen acids are obtained from lichens ( about 250 are known) that have antibiotic properties.
Ferns:
FERN-like, department of higher seedless plants. Herbaceous or tree-like terrestrial and aquatic plants. On the leaves (mostly on the underside) there are groups of sporangia - sori. OK. 12 thousand species (300 genera), around the globe. Many are decorative, some are edible (for example, young shoots of the kochedyzhnik, one of the species of bracken), others are medicinal (for example, male fern), some are poisonous. Modern ferns have been known since the Carboniferous .
Ferns, or fern-like plants (lat. Polypodióphyta) - a department of vascular plants, which includes both modern ferns and one of the oldest higher plants that appeared about 400 million years ago in the Devonian period of the Paleozoic era. Giant plants from the group of tree ferns largely determined the appearance of the planet at the end of the Paleozoic - the beginning of the Mesozoic era.
Spreading.
The largest number of species is found in humid subtropical and tropical forests, where they are represented not only by herbaceous, but also by tree-like forms. Tropical tree ferns reach 25 m in height and 50 cm in diameter. Liana ferns are also found in the tropics. In temperate climates, ferns are represented only by herbaceous species; medium-sized ones have very small plants a few millimeters in size.
Morphology
Ferns include both herbaceous and arboreal forms of life.
The body of a fern consists of leaf blades, a petiole, a modified shoot and roots (vegetative and adnexal). Fern leaves are called fronds.
Life cycle
In the life cycle of a fern, asexual and sexual generations alternate - sporophyte and gametophyte. The sporophyte phase predominates. In the most primitive ferns (zhovnikovye) sporangia have a multi-layered wall and do not carry special devices for opening. In more advanced ones, the sporangium has a single-layer wall and adaptations for active opening. This device is in the form of a ring. Even among primitive ferns, heterosporation can be traced. Modern ones have a small number of isosporous species. The gametophyte of isospores is usually bisexual. In primitives, it is underground and always in symbiosis with fungi. In advanced gametophytes, above ground, green and rapidly maturing. They usually look like a green heart-shaped plate. The gametophytes of heterosporous ferns differ from isosporous ferns (in addition to their dioecious nature) by a strong reduction, especially of the male gametophyte. The female gametophyte, which consumes reserve nutrients from megaspores, is more developed and has nutritional tissue for the future sporophyte embryo. At the same time, the development of such gametophytes occurs inside the shells of mega- and microspores.
Lichens are a special group of organisms consisting of two completely different species. One part of a lichen is green algae (belongs to plants) or blue-green algae (belongs to bacteria). The other part of a lichen is a fungus.
Lichens are studied by science lichenology which is considered a branch of botany.
There are more than 25 thousand species of lichens.
Lichens are unpretentious and therefore widespread. They can be found even in permafrost conditions or on bare rocks. They can grow on tree trunks and the ground. Lichens living in the tundra spread along the ground in a continuous carpet.
The color of lichens varies from yellow and gray to brown and black.
According to the shape of the thallus, three types of lichens are distinguished.
fruticose lichens connected to the surface on which they grow, only at their base. Bearded lichen grows in spruce forests, where it hangs from tree branches. Reindeer moss (reindeer moss) grows on the soil. If you step on it in dry weather, you will hear a characteristic crack.
foliose lichens found on tree trunks. They look like plates of different colors and shapes. So golden-yellow xanthoria grows on aspen. Leafy lichens are connected to the substrate by rhizoid-like outgrowths. They are easily removed from the surface.
scale lichens(crustal lichens) appear as brownish and greyish crusts on stones and rocks. They adhere tightly to the surface, as a result of which it is difficult to tear them off from it.
Lichens are most often considered an example of symbiosis, in which cohabitation is beneficial for two different organisms.
The body of a lichen is called thallus. It consists of fungal hyphae, between which are single-celled green algae or blue-green algae.
Such cohabitation allows lichens to live where neither fungi nor algae can live separately. The hyphae of the fungus provide the algae with water and minerals. Algae provides the fungus with organic substances that it synthesizes in the process of photosynthesis.
Since algae have to feed not only themselves, but also the fungus, lichens grow very slowly. Also, often, growing in places with permafrost, lichens do not receive enough water. So the growth of bushy lichens can be several millimeters per year, and scale - in general, fractions of a millimeter. However, lichens live long enough (up to 100 years).
Lichens reproduce asexually. Algae cells divide into two, and the fungus forms spores. Also, special groups of cells can form in the lichen thallus. These groups leave the parent lichen and give rise to a new organism in a new place.
The meaning of lichens
Lichens are the first to colonize places where there is no soil. Gradually dying off, they form humus. Also, lichens secrete acids, which leads to the destruction of rocks. As a result of mixing destroyed rocks and humus, soil is formed on which plants can grow.
Yagel serves as food for deer in the tundra. It is also used as pet food.
Icelandic moss is eaten by humans.
From a number of lichen species, litmus (a chemical indicator) and antibiotics are obtained.
Oak moss is used in perfumery. It gives strength to spirits.
Lichens are ecological indicators. They die in polluted air. Therefore, by the absence or presence of lichens in a certain area, one can judge the ecological situation.
The structure and activity of lichens
Lichens are a group of very peculiar organisms, the body of which consists of two components - a fungus (mycobiont) and an algae (phycobiont).
Remark 1
The science that studies lichens is called lichenology.
The vegetative body of the lichen - thallus, or thallus - is formed by intertwining the hyphae of the fungus, and among them there are cells or filaments of algae - evenly (thallus of the homeomeric type), or only in the upper layer (thallus of the heteromeric type).
In most lichens, the phycobiont is the unicellular green alga trebuxia, but algae of 28 genera can also be part of lichens. Among them there are blue - green, green, yellow - green and brown.
For a long time, the relationship between fungus and algae in the body of a lichen was considered as a mutually beneficial existence for both organisms (symbiosis), since as a result, its heterotrophic fungal organism received organic substances from autotrophic algae, and the algae organism from the fungus received mineral compounds dissolved in water, as well as drying protection.
The algae that enter the body of lichens are extremely resilient. They can withstand prolonged drying and significant temperature fluctuations.
A characteristic feature of lichens is the absence of green color and leaves. The lichen thallus is mostly grayish, brown, yellow or almost black in color. Color depends on specific pigments, iron salts, content and concentration of various acids.
Lichens grow very slowly, the annual growth of the thallus in various species ranges from 0.25 - 1 to 36 mm per year.
One of the most characteristic biological features of lichens is their unpretentiousness to the conditions of existence. They can exist on rocks, on soil, on tree trunks and branches, on fences, and even on metal and glass.
Lichen reproduction
Lichens reproduce vegetatively, sexually and asexually.
Vegetatively: particles of the thallus or specially adapted formations - isidia and soredia.
Isidia - outgrowths of various shapes and sizes on the surface of the thallus, containing both components of the lichen. They can break off from the lichen and be spread by wind, water or animals.
Soredia are small dust particles that consist of one, two or more single-celled algae, braided with fungal hyphae. Formed in the middle of the thallus. They are released after its rupture and carried by the wind. Each component of a lichen is able to reproduce individually: algae - by division, fungi - by spores.
Lichen classification
By the appearance of the thallus, three types of lichens are distinguished:
cumulative, or cortical, - in the form of a crust, which is tightly grown together with the substrate (lecanora, aspicillia). It can reach a thickness of 0.5 cm, and in diameter it can be from a few millimeters to 20 - 30 cm. Sometimes several lichens grow together and form large spots.
Remark 2
There are so-called nomadic lichens, which have a spherical thallus shape. They are not attached to the substrate and can be carried by the wind.
leafy - have the appearance of a flattened leaf-shaped plate, horizontally attached to the substrate with bunches of hyphae (rhizoids, rhizins, or gomfs). Usually the shape of the thallus is round, with a diameter of 10 - 20 cm. Representatives are parmelia, xanthoria. In the mountains of Siberia and Chukotka, nomadic foliose lichens are found - one of the most beautiful lichens.
bushy - have the appearance of a bush or a hanging beard (cladonia, sleeping). They are attached to the substrate by a small lower part of the thallus or thin thread-like rhizoids. The largest bushy lichens reach a height of 50 cm.
These amazing plants are an example of the mutually beneficial living of fungi and algae, less often fungi and cyanobacteria. It even happens that the three of us cohabit: mushrooms (mandatory) and algae + cyanobacteria. Such cohabitation is called obligate symbiosis.
Lichen species for different characteristics
There are two-component lichens and three-component. Depending on the number of components in them.
Based on the appearance of the thallus (thallus), lichens can be divided into the following groups:
- scale lichens. The smallest and longest-lived, grow mainly on stones, rocks, concrete walls, trees, old fences. They are difficult to separate from the subject on which they grow;
- foliose lichens - these associates can no longer be attached to the substrate with their whole body, but only with one edge (outgrowths - rhizoids), they are easily separated, they look like a leaf. Grow on stones, stumps, long lying objects such as rusty iron, glass, slate;
- fruticose lichens the most developed. They grow upwards (unlike the first two) and have a bushy appearance. Attached mainly to the ground or trees. They are in the form of twigs or threads. They can grow up to 6 - 7 meters.
Behind the internal structure, this symbiosis can be grouped as follows:
- heteromeric - the body of the lichen on the cut is clearly divided into layers of fungus and algae;
- homeomeric - the components are randomly mixed inside the thallus.
After the place of growth, lichens are divided:
- epigeic (grow on the ground);
- epilithic (grow on stones);
- epiphytic (grow on tree trunks).
Mutual benefit of mushrooms and algae
So why live together, in the same body, fungi and algae? But why: algae need water (moisture) for normal life, and the fungus needs ready-made food - he himself will not cook anything from water and light (as almost all plants do), so he, a heterotroph, feeds on the products of photosynthesis of algae ( autotrophs) to which it provides moisture. He accumulates it in himself like a sponge.
Where do lichens grow
Probably everyone knows that lichens are the pioneers of the area. Often, in areas that have not yet been inhabited, due to some circumstances (fires, land reclamation, volcanic eruptions, drainage of territories), lichens appear first. Moreover, they serve as excellent fertilizer and food for other organisms.
These plants can survive in extreme conditions. Their scale ranges from -47 degrees Celsius to plus 80 ºC. They can withstand both acidic and alkaline influences, and even strong ultraviolet radiation. Which is not typical for other plants. The habitat is also large: from the far north to Antarctica.
The role of lichens in the life of animals and humans
Although these organisms are inconspicuous, their significance is important for other living beings, in particular for the inhabitants of the northern territories. In the harsh Siberian winters, Yagel lichens or reindeer moss, Icelandic moss are the main food for deer, and also elk and roe deer look for them under the snow. Many birds use it as nest litter.
There are edible lichens for humans as well. This is Bryoria Fremont, an edible aspicilia. Especially love them in China, Japan. For medicinal purposes, Icelandic cetraria, Lobaria are used. For the manufacture of dyes, the litmus indicator, the odor fixative, in perfumery, lichens are used everywhere.
