Thallus

The following types of thallus differentiation are known in green algae:

1. monadic (for example, Chlamydomonas, Volvox, Gonium, Dictyosphaerium");
2. palmelloid or tetrasporal ( Tetraspora, Sphaerocystis);
3. coccoid ( Chlorella, Hydrodictyon);
4. sarcinoid ( Chlorosarcinopsis);
5. trichal, or filamentous ( Ulothrix, Spirogyra);
6. heterotrichal, or heterofilamentous ( Chara, Stigeoclonium);
7. pseudoparenchymatous ( Protoderma);
8. parenchymal ( Ulva, Ulvaria);
9. siphonal ( Caulerpa, Bryopsis);
10. siphonocladal ( Cladophora, Dictyospheria).

Cell structure

Flagellar apparatus

Monad cells and stages of green algae are isokont, rarely heterokont. The number of flagella per cell can be different - 1, 2, 4, 8, 16 or more (up to 120). In Oedogonians and some bryopsids, numerous flagella are collected in the form of a corolla at the anterior end of the cell; such cells are called stephanokontnymi. A characteristic feature of the transition zone of flagella of green algae is the presence of a stellate body in it. Flagella of green algae do not have mastigonemes (unlike heterokonts), but may have graceful hairs or scales.

Cell wall

In the classes Chlorophyaceae and Prasinophyceae there are algae in which the cells are naked and lack a cell wall. In mesostigmidae and many prasinophyceae, organic scales are deposited on top of the plasmalemma. They are found in motile cells of a number of ulva and charophyte algae. The presence of organic scales on motile cells is apparently a primitive feature. The appearance of theca in Prasinophyceae and then in Chlorophyceae is considered more progressive. The theca in Chlorophyaceae is composed of glycoproteins that are rich in hydroxyproline and associated with various oligosaccharides.

Ecology and significance

Green algae are widespread throughout the world. Most of them can be found in fresh water bodies (representatives of the charophytes and chlorophyceae), but there are many brackish-water and marine forms (most representatives of the class ulvophyceae). They are found in reservoirs of varying trophicity (from dystrophic to eutrophic) and with different contents of organic substances (from xeno- to polysaprobic), hydrogen ions (from alkaline to acidic), at different temperatures (thermo-, meso- and cryophilic species). Among them there are planktonic, periphyton and benthic forms. In the group of marine picoplanktonic representatives, the prasinophycean alga Ostreococcus tauri considered the smallest free-living eukaryotic cell. Eat green algae, which have adapted to life in soil and terrestrial habitats. They can be found on the bark of trees, rocks, various buildings, on the surface of the soil and in the air. Among them, representatives of the genera are especially common in these habitats Trentepohlia And Trebuxia. The massive development of microscopic green algae causes “blooming” of water, soil, snow, tree bark, etc. So, Chlamydomonas nivalis can be found high in the mountains on red-colored snow. In this species, chlorophyll is masked by carotenoid pigments.

A unique ecological group is represented by endolithophytic algae associated with calcareous substrate. Firstly, this is boring algae. For example, algae from the genus Gomontia They drill into the shells of pearl barley and toothless beetles and penetrate the calcareous substrate in fresh water bodies. They make the limestone substrate loose, easily susceptible to various influences of chemical and physical factors. Secondly, a number of algae in fresh and marine waters are capable of converting calcium salts dissolved in water into insoluble ones and depositing them on their thalli. A number of tropical green algae, e.g. Halimeda, deposits calcium carbonate in the thallus. They take an active part in building reefs. Giant deposits of remains Halimeda, sometimes reaching 50 m in height, are found in continental shelf waters associated with the Great Barrier Reef in Australia and other regions, at depths ranging from 12 to 100 m.

Green algae (class trebuxiophyceae), entering into a symbiotic relationship with fungi, are part of lichens. About 85% of lichens contain unicellular and filamentous green algae as phytobionts, 10% of lichens contain cyanobacterial partners, and 4% (or more) contain canobacteria and green algae. They exist as endosymbionts in the cells of protozoa, hydras, sponges and some flatworms. Even the chloroplasts of individual siphon algae, e.g. Codium, become symbionts for nudibranchs. These animals feed on algae, the chloroplasts of which remain viable in the cells of the respiratory cavity, and in the light they photosynthesize very efficiently. A number of green algae develop on the fur of mammals.

A number of green algae are of economic importance. They are used as indicator organisms in the monitoring system of aquatic ecosystems. For example, the US Environmental Protection Agency recommends the use of indicator organisms such as Selenastrum capricornutum And Scenedesmus subspicatus. Green algae are used for the purification and purification of polluted waters, as well as as food in fishery reservoirs. Some species are used by the population of a number of countries for food. For these purposes, for example, in Japan, they are specially cultivated Ulva And Enteromorpha. Certain types of green algae are used as producers of physiologically active substances. So, species of the genus Haematococcus cultivated on an industrial scale to produce the carotenoid astaxanthin, Botryococcus- to obtain lipids. At the same time, with the “blooming” of the water of one of the lakes in Taiwan, caused by Botryococcus, link the death of fish.

Types of childbirth Chlorella And Chlamydomonas- model objects for studying photosynthesis in plant cells. Giant multinucleated thalli Acetabularia, multicellular thalli Chara and unicellular representatives Dunaliella And Chlamydomonas in genetic engineering they are used as objects for transformation.

Phylogeny

The presence of chloroplasts, in which the shell consists of two membranes collected in stacks of thylakoids and chlorophylls a And b, carotenoids (lutein, β-carotene) and starch, which is deposited in the chloroplast, are the main synapomorphic characters that distinguish green algae and their sister group of streptophytes from other lineages of eukaryotes. Monophyletic origin of all green plants supports phylogenetic analysis based on comparison of 18S rRNA sequences in different eukaryotic lineages. This analysis showed the division of all green plants into two important groups - the division Chlorophyta s. str. Sluiman 1985 and Streptophyta Bremer 1985. Within the monophyletic group Chlorophyta s. str. there are four independent evolutionary lines - classes Chlorophyceae, Trebouxiophyceae, Ulvophyceae And Prasinophyceae. The latter class is a polyphyletic group that separated at the founding Chlorophyta. Within the group Streptophyta, two lineages are distinguished - higher plants and charophytes. Noteworthy position Mesostigma viride, which was previously classified as prasinophycean algae. Today, there are two points of view on its position: 1) it stood out at an early stage in the streptophyte branch; 2) the place of its origin is associated with the division of all green plants into two main groups.

Ecological groups and habitats

The department of green algae (Chlorophyta) unites 5,700 species. Green algae are one of the most common and diverse groups of algae. Unlike red or brown algae, Most green algae live in freshwater bodies and only some species are in the seas.

Some representatives have adapted to life on land - in the soil or in damp, shaded places with periodic moistening (on tree bark, boulders, fences).

Green algae presented unicellular, multicellular And colonial forms. Some green algae have noncellular thallus. Among multicellular forms, filamentous algae are especially common, which form mud in ponds and rivers.

Evolutionary significance of green algae

Green algae are considered ancestors land plants. They have the same set of photosynthetic pigments: main photo synthetic pigment - chlorophyll A, auxiliary pigments - chlorophyll b and carotenoids. Cell membrane green algae contains cellulose and pectin, which is a characteristic feature not only of green algae, but also of terrestrial plants; reserve substance- just like terrestrial plants - starch(sometimes fat). Spare substances accumulate green algae not in the cytoplasm (as in representatives of other divisions of algae), but in plastids, which also indicates the relationship between green algae and land plants.

Rice. The structure of green algae. Above is Euglena. From below Chlamydomonas

The bright green color of algae in this department is due to the presence of chlorophylls, but in some species it can be masked by a red pigment - hematochrome, so there are types of green algae that cause red “blooming” of water or snow.

Using the example of individual representatives, two directions of evolution of the thallus of green algae can be traced:

• from a unicellular mononuclear thallus to a noncellular multinucleate one, which is one giant supercell (for example, in caulerpa);
• from a unicellular motile thallus equipped with flagella through immobile unicellular forms to a multicellular filamentous thallus, the development of which leads to the emergence of complex organisms with differentiation of organs and tissues - charophyte algae and land plants.

In general, the evolution of the thallus of green algae can be reflected by the diagram presented in Fig. 1.

Rice. 1. Evolution of the thallus of green algae

The green algae department includes 5 classes:

• volvoxaceae;
• protococcal;
• ulotrix;
• siphon;
• conjugates, or couplings.

We present brief description the most characteristic representatives of each class.

Volvox class

To the class volvox(Volvocophyceae) are the most primitive representatives of the department of green algae, having a monadic thallus shape, i.e. a unicellular, mobile thallus with 2 (less often 4) identical flagella at the end of the body (for example, representatives of the genus Chlamydomonas). The cells of some Volvoxidae form colonies.

Volvoxaceae are typical planktonic algae that live in shallow, often drying up water bodies. Active cleaners of polluted and wastewater, in which they multiply very quickly, causing green “blooming” of the water.

Typical representatives of Volvoxidae

Genus Chlamydomonas(Chlamydomonas) - from Greek. "Chlamydomonas" is a single organism covered with the ancient Greek loose clothing - chlamys. The genus includes over 500 species of microscopic algae (length 5-44 microns, width 3-28 microns) - Fig. 2.

Representatives of the genus Chlamydomonas are unicellular, motile algae with flagella (this form of thallus is called monadic). On the outside, the Chlamydomonas cell is covered with a transparent pectin-cellulose cell wall. At the anterior end of the body are located 2 flagella, and in the center of the cell - core and a light-sensitive peephole - stigma, which allows Chlamydomonas to move towards the light. Photosynthesis occurs in a large chloroplast - chromatophore shaped like a bowl. In the center of the chromatophore there is a rather large protein body - pyrenoid, around which starch granules are deposited. Thus, starch in green algae, unlike algae of other divisions, accumulates not in the cytoplasm, but in plastids, which indicates their relationship with green plants. At the base of the flagella there are 2 pulsating vacuoles, which remove excess water and harmful metabolic products from the cell.

Rice. 2. Chlamydomonas: 1 - cytoplasm; 2 - flagella; 3 - core; 4 - pulsating vacuole; 5 - photosensitive eye; 6 - chromatophore; 7 photosynthetic membranes; 8 - pyrenoid

In addition to nutrition through photosynthesis, Chlamydomonas is able to absorb and assimilate organic substances dissolved in water. Thanks to mixed type nutrition chlamydomonas is an active sanitary worker of polluted and waste waters, rapidly multiplying in sedimentation basins. Some types of Chlamydomonas can develop on the surface of snow and ice. They cause red “blooming” of water and snow (for example, Chlamydomonas snow).

Most species of Chlamydomonas are characterized by an isogamous sexual process, but in some species heterogamy and oogamy occur. Chlamydomonas is cultivated in laboratories as an object of research in the fields of genetics, photosynthesis, developmental biology and to determine the toxicity of polluted waters.

Genus Volvox(Volvox) has about 20 species of colonial flagellates. A typical representative is Volvox globulus(Volvox globator), the colony of which has the shape of a ball with a diameter of 2-3 mm, consisting of 50-75,000 Chlamydomonas-like cells (Fig. 3). All cells are connected by cytoplasmic bridges, so they act as a single unit. The inside of the ball is filled with mucus.

During vegetative propagation, 8-15 daughter colonies are formed within the mother colony. When they mature, the walls of the ball rupture and the young colonies come out, and the mother colony dies, which is why it is sometimes said that Volvox is the first organism that “invented” inevitable (rather than random) death.

Rice. 3. Colonies of green algae: a) pandorina (round colony); b) gonium (flat colony); c) Volvox

Volvox can also reproduce sexually, and both monoecious and dioecious species are found. In monoecious species, each colony produces both female and male gametes; in dioecious species, each colony is either male or female and produces, respectively, only male or only female gametes.

The Volvox class also includes other colonial flagellates, for example the gonium, which has a flat colony. When moving, it looks like a small flying carpet. Colonies of Eudorina and Pandorina have a round shape. The cells of all these colonial flagellates are immersed in a common mucus wrapper.

Thus, the most primitive representatives of Volvoxidae- These are single-celled, motile organisms with flagella. They have a mixed diet- they can feed both like plants (through photosynthesis) and like animals (by assimilating organic substances from the environment), which indicates their origin from ancient flagellates, which combined the characteristics of plants and animals.

From primitive mobile unicellular algae (Chlamydomonas mucus) arise colonial forms(such as Volvox). However, for plants this is a dead-end branch of evolution. Further evolutionary progress is associated with the loss of motility, which is typical for representatives of the protococcal class.

Class protococcal

Protococcal(Protococcophyceae) are unicellular or colonial algae, deprived of mobility in adulthood(only zoospores and gametes are motile). They live in freshwater bodies and soil. There are species living in air environment, for example, on the bark of trees and inside plants growing on water (for example, duckweed). Typical representatives of this class are chlorococcus, chlorella and water net.

Genus Chlorococcus(Chlorococcum) includes unicellular algae, the cells of which are round in shape and lack flagella (see Fig. 4 a). Representatives of the genus Chlorococcus are found on tree bark, fences, flower pots, accumulate in significant quantities in soils (up to 140 kg per 1 ha). Sometimes they are a component of lichens.

Rice. 4. Protococcal (s. Protococcales): a) chlorococcus (s. Chlorococcum); 6) chlorella (p. Chlorella); 1 - unicellular thallus; 2- formation of zoospores; 3 - zoospore; 4 - young individuals; 5 - formation of autospors

Genus Chlorella(Chlorella) - rice. 4b. - includes unicellular immobile algae with a diameter of about 15 microns, with one large cup-shaped chloroplast, one nucleus and one pyrenoid (pyrenoids are protein bodies around which carbohydrates are deposited). Chlorella reproduces using immobile, flagellated spores ( aplanospore). There is no sexual process. These are mainly planktonic organisms. They are widespread both in the seas and in freshwater bodies. Some species live in the soil and on tree bark. Chlorella absorbs and uses solar energy much more efficiently than ordinary terrestrial plants (the latter use about 1% of the solar energy falling on them for photosynthesis, and chlorella - more than 10%). It multiplies very quickly, as a result of which it is artificially cultivated, and the resulting biomass, containing about 50% complete proteins and about 20% fats and carbohydrates, is used as a feed additive. In terms of protein and fat content, chlorella is not inferior to soybean. Chlorella biomass also contains vitamins A, B, C, K(and it contains 2 times more vitamin C than lemon juice).

Due to the high rate of photosynthesis, chlorella intensively absorbs carbon dioxide and releases oxygen, which is why it is used to purify the air in submarines and spacecraft.

Rod water mesh(Hidrodiction) is represented by colonial forms. Water net colonies have the shape of a mesh bag ranging in length from a few centimeters to 5 m (Fig. 5).

From the immobile unicellular forms characteristic of representatives of the protococcal class, in the process of evolution filamentous and then lamellar forms of algae arise, characteristic of representatives of the ulothrix class.

Rice. 5. Water mesh (Hidrodiction reticulum)

Ulothrix class

Ulotrix(Ulotrichophyceae) are multicellular organisms with a filamentous or plate-like structure of the thallus, the cells of which have one nucleus and usually one chloroplast.

The most famous representatives of this class are Ulotrix and Ulva.

Genus Ulothrix(Ulothrix). This is a genus of filamentous algae that lives in fresh water bodies. Their thallus is an unbranched thread of one row of cells (Fig. 6).

Rice. 6. Life cycle of Ulothrix: a) asexual reproduction; 6) sexual reproduction; 1 - main life form; 2 - formation of zoospores; 3 — release of zoospores; 4 - empty cell; 5 - zoospores; 6 - formation of gametes; 7- yield of gametes; 8 - isgamy; 9-10 - zygote; 11 - germination of the zygote; 12 - zoospore

They reproduce mainly asexually (by 4-flagellated zoospores). Sexual process - classic example isogamy.

An important lateral evolutionary line in the development of green algae associated with the transition from the filamentous form of the thallus, characteristic of ulothrix, to the lamellar one. It is this form of thallus that is characteristic of representatives of the genus Ulva.

Genus Ulva(Ulva) or sea salad. Externally, the ulva resembles a thin, bright green sheet of cellophane. The lamellar thallus is whole, dissected or branched, 30-150 cm high, consists of two layers of cells. Ulvacaceae evolved directly from Ulothrixaceae. In the initial stages of development, the ulva forms a single-row filament, reminiscent of ulotrix, and then a double-row filament, after which a tubular structure is formed. Subsequently, the walls of the tube close and it begins to grow like a two-layer plate. Ulva is characterized by an alternation of isomorphic generations, one of which reproduces asexually, and the other sexually.

Representatives of the genus Ulva can be found in the seas of all climatic zones, but they prefer the relatively warm seas of the temperate zone (they are widespread in such warm seas as the Black or Japanese). Residents of many coastal countries eat ulva, hence its second name - “sea salad”.

Siphon class

Siphon algae(Siphonophyceae) (about 300 species) is one of the oldest groups of green algae, which is a dead-end branch of their evolutionary development.

Siphonaceae differ from other green algae in that their thallus is one giant multinucleate cell. However, externally the thallus is complexly dissected and often imitates a terrestrial plant with a rhizome, adventitious roots and large feathery leaves. An example of such a structure is seaweed caulerpa(Сaulerra) - fig. 7.

Over 90% of siphonids are marine organisms that live in tropical seas, covering large areas of the seabed.

One of the most numerous genera of the class Siphonaceae - genus of Cladophora(Cladophora). A typical representative of the genus - Cladophora sauter(C. zauterii) (Fig. 8), which is widespread in freshwater bodies of temperate and cold zones. It has a branching filamentous thallus of large multinucleated cells. The threads form large spherical clusters that float to the surface of the reservoir. Such balls with a diameter of up to 25 cm contain a lot of cellulose. They are used to make paper. The initial stages of development of Cladophora show that it is close not to filamentous algae of the Ulotrix type, but to siphon algae, which have a non-cellular structure, since at first the thallus of Cladophora develops as one giant multinucleated cell, and partitions imitating individual cells appear later.

Fig 7. Caulerpa (Caulerpa sertularioides): a) general form; b) a section of the thallus on a cross section

Rice. 8. Cladophora (p. Cladophora): a) filamentous thallus; b) a cell with a chloroplast; c) cell with zoospores: 1 - reticulate chloroplast

Class conjugates, or couplings

Class conjugates, or couplings(Conjusatophyceae), unites about 4,500 species of multicellular and unicellular algae. The sexual process is conjugation. Flagellar stages of development are absent.

Conjugation is a side branch of the evolution of the sexual process. During conjugation, it is not the nuclei of cells that merge, but their entire protoplasts.

A classic example of conjugation is the reproduction of the freshwater filamentous alga Spirogyra ( Spirogyra).

In heterothallic Spirogyra species, so-called ladder conjugation occurs. Between the cells of the (+) - and (-) - threads, channels are formed through which the protoplasts of the (-) - thread cells pass into the cells of the (+) - thread. Externally, a series of conjugating cells connected by copulation channels resembles a ladder.

In homothallic Spirogyra species, lateral conjugation occurs, in which a conulation channel connects two adjacent cells. Outwardly, such a channel resembles a loop. After the fusion of protoplasts, a diploid zygote is formed.

The main life form of Spirogyra is haploid. Only the zygote is diploid. After a period of rest, the zygote divides twice, forming four haploid cells. Three of them, the smaller ones, degenerate, and the fourth, the largest, germinates and gives rise to a new individual.

Green algae department. general characteristics.

• 
  This is the most extensive department among all algae, numbering over 13 thousand species.
• 
  Green algae are varied in appearance: unicellular, siphonal, multicellular, filamentous, lamellar, colonial.
• 
  Representatives of the department mostly live in fresh waters, although there are marine and terrestrial species.
• 
  Their hallmark- the green color of the thalli, similar to the color of higher plants, caused by the predominance of chlorophyll over other pigments. Among the assimilation pigments, the pigments a, b, α- and β-carotenes were found in them.
• 
  Chromatophores are surrounded by a shell of two membranes. Pyrenoid absent or present. The cells are mononuclear or multinucleate, mostly covered with a cellulose or pectin membrane, less often naked. The reserve product is starch, deposited inside chloroplasts, and rarely oil.
• 
  Iso- and heteromorphic generational changes are observed.

Asexual and sexual reproduction of algae.

Main types of asexual reproduction:

• 
  Vegetative propagation. In some colonial forms, colonies can split into separate fragments, which give rise to smaller colonies. In large algae, for example, fucus, additional thalli can form on the main thallus, which break off and give rise to a new organism.
• 
  Fragmentation. This phenomenon is observed in filamentous algae. The thread splits in a strictly defined way lengthwise, forming two new threads.
• 
  Binary fission. In this case, a single-celled organism divides into two equal halves, with the nucleus dividing mitotically. Longitudinal division of this type is observed in euglena.
• 
  Zoospores. These are motile spores with flagella. They are formed in many algae, for example in Chlamydomonas.
• 
  Aplanospores. These are non-motile spores formed in brown algae.

Sexual reproduction of algae

During sexual reproduction they unite genetic material two separate individuals of the same species. Its essence is the fusion of germ cells - gametes, formed in special mother cells gametangia, resulting in zygote . Sometimes, in some green algae, the contents of two vegetative undifferentiated cells, physiologically performing the functions of gametes, merge. This sexual process is called conjugation . The simplest method of sexual reproduction in algae is the fusion of two structurally identical gametes. This process is called isogamy , and gametes - isogametes. Spirogyra and Chlamydomonas are isogamous.

If one of the gametes is less mobile and larger than the other, then this process is called anisogamy . When one gamete is large and immobile, and the second is small and mobile, then the gametes are considered female and male, respectively, and the process is called oogamy . Female gametes are larger because they contain a reserve nutrients, necessary for the development of the zygote after fertilization. Some Chlamydomonas and representatives of the genus Fucus are oogamous.

In algae, in the development cycle, the alternation of asexual and sexual generations first appeared and became established, i.e. sporophyte and gametophyte. Sporophyte asexual and diploid, gametophyte - haploid, sexual. Both generations may not differ in structure (isomorphic), as in marine green algae. Heteromorphic alternation of generations is characteristic of brown algae.

Unicellular algae: Chlamydomonas, Chlorella. Structure and features of life.

Large genus of green algae chlamydomonas includes about 320 species of unicellular organisms. Species of this genus live in puddles, ditches and other fresh water bodies, especially if the water is also enriched with soluble nitrogen compounds, such as runoff from livestock yards. When they develop en masse, the water often acquires a green color. Some species live in seawater or brackish estuaries.

Chlamydomonas cells have an ellipsoidal shape, with a small colorless “spout” at the anterior end, from which two equal in length extend undulipodium (flagellum), thanks to which the algae moves. The Chlamydomonas cell moves by screwing into the water like a corkscrew, rotating around its longitudinal axis. The shell adheres tightly to the protoplast. The protoplast contains a single nucleus, usually a cup-shaped chloroplast, which contains a pyrenoid, a pigment eye, and pulsating vacuoles located at the front of the cell. Pyrenoid - This is a protein formation, consisting mainly of an enzyme that helps fix carbon dioxide; it stores starch. Red eye senses changes in light intensity and the cell either moves to where the light intensity is optimal for photosynthesis or remains in place if the intensity is sufficient. This response to light is called phototaxis . The photopigment of the eye is homologous to rhodopsin, the visual pigment of multicellular animals.

IN



The adult Chlamydomonas is haploid. Asexual reproduction carried out using zoospore . When the reservoir dries out, chlamydomonas lose their undulipodia, their walls become slimy, and in this immobile state they multiply. Mitotic division of the nucleus occurs, the chloroplast divides, and the cell protoplast divides into four daughter protoplasts. The daughter protoplasts form cell walls and new eyes. The walls of the daughter cells also mucus, and thus a system of mucous membranes nested within each other is obtained, in which immobile cells are located in groups. When transferred to water, the daughter cells - zoospores - again produce undulipodia and return to the monadic state.

At sexual reproduction In most species of Chlamydomonas, identical gametes (isogametes) are formed in the cells, similar to zoospores, but smaller in size and in greater number. Some species are characterized by heterogamy or oogamy. During germination, the zygote nucleus divides meiotically for the first time, and the haploid state is restored.

Representatives of the genus chlorella also widespread in fresh water bodies, seas, damp soil, and tree bark. Their spherical cells are covered with a smooth shell and usually contain a cup-shaped chloroplast and one nucleus. During asexual reproduction, the contents of the cells break up into four or more parts - autospores, which, while still inside the shell of the mother cell, are covered with their own membranes. Autospores are released after the mother cell wall ruptures. There is no sexual process. Chlorella is characterized by a very rapid rate of reproduction and is often the object of study of photosynthesis. It is capable of using from 10 to 12% of light energy (versus 1-2% for terrestrial plants). During photosynthesis, chlorella is capable of releasing a volume of oxygen 200 times greater than its own volume. Has a wide practical use. It is one of the most useful algae, since in dry matter it contains up to 50 complete proteins, fatty oils, vitamins B, C and K. There are industrial installations for breeding chlorella to obtain cheap feed. The Japanese have learned to process chlorella into a colorless powder that can be mixed with flour to make baked goods. The use of chlorella for energy has recently been studied; in these experiments, it is grown together with a bacterium that converts the starch synthesized by the algae into lipids. Such systems can be used on barges or platforms in the open ocean or even in space.

Volvox- colonial algae, spherical in shape (2-3 mm in diameter). A Volvox colony consists of many (500-60,000 cells) located along the periphery of the ball in one layer. The internal cavity of the ball is occupied by mucus. Each cell is equipped with two flagella directed outside the ball, and in its structure resembles Chlamydomonas. These are vegetative cells that perform the functions of nutrition and movement, but are not capable of reproduction. The movement of a Volvox colony is completely coordinated, since the cells are not isolated from each other, but are connected by cytoplasmic strands passing through the cell walls. In addition to vegetative cells, there are specialized cells characterized by larger sizes and the absence of flagella. They perform the functions of sexual reproduction. Small, motile spermatozoa with two flagella are formed only by special organs - antheridia (this term is used to refer to organs of higher

Plants that produce sperm). A single large immobile egg cell is formed inside a special organ - the oogonia. The motile sperm swims up to the egg and fuses with it. A diploid zygote is formed, around which a thick cell wall is formed. During germination, the zygote divides meiotically to form haploid cells, giving rise to a new colony. Some species of Volvox have antheridia and oogonia in the same colony, while others have only antheridia or only oogonia, i.e. differentiation of the sexes is observed.

Vegetative propagation of Volvox is carried out with the help of daughter colonies formed in the mother colonies through successive longitudinal divisions of cell protoplasts.

Chlamydomonas Chlorella Volvox

Filamentous algae.

Numerous species spirogyra live in fresh water bodies with stagnant, but clean water and are notable for the sexual process such as conjugation. Their filamentous thallus, floating on the surface of the water, consists of large cells, the threads are slimy and slippery.

The Spirogyra filament is formed by cylindrical cells connected end to end. All cells are identical, and there is no separation of functions between them. Thin layer The cytoplasm lies along the periphery of the cell, and the large vacuole is, as it were, wrapped in strands of cytoplasm. Such strands hold the nucleus in the center of the cell. One or more spiral-shaped chloroplasts lie in a thin wall layer of cytoplasm.

Spirogyra grows due to the division of any of the cells that make up the filament; growth usually occurs at night. First the nucleus divides, then the whole cell is laced together. . Vegetative propagation carried out by breaking the threads into separate sections, sometimes even into individual cells ( fragmentation ).

At sexual reproduction Usually the two threads are parallel to each other.

A


. Opposite cells form projections directed towards each other and fused at their ends.

B. Their shells dissolve at the point of contact and form a through channel, through which the compressed contents of one cell move into another within a few minutes and merge with its protoplast, also compressed by that time.

B. The zygote formed as a result of the fusion of protoplasts of conjugating cells is rounded, a thick three-layer membrane is formed, and the entire cell enters a resting state. The resulting zygote is surrounded by a thick cell wall and survives the winter in this form. In the spring, the zygote divides meiotically and forms four haploid nuclei, of which three degenerate, and the fourth remains, breaks the cell wall, divides mitotically and gives rise to a new haploid thread. This process of reproduction is called conjugation. It involves unspecialized cells that are no different from each other (a variant of isogamy).

Thus, Spirogyra goes through its life cycle in the haploid phase; only the zygote is diploid.

WITH Among filamentous green algae, which also live in fresh water bodies, it is found ulothrix. Non-branching ulothrix filaments are attached by the basal rhizoid cell to underwater objects. In the center of the cell is the nucleus, the wall chromatophore. Due to cell division in the transverse direction, the filament grows in length. Under favorable conditions, ulothrix reproduces by zoospores, which bear four flagella. By autumn, individual cells of the filament turn into gametangia, within which biflagellate gametes are formed. When gametes fuse, a four-flagellate zygote is formed, then it sheds the strands and enters a resting state. Subsequently, the zygote divides meiotically and gives rise to four cells, from which new threads are formed. Thus, in Ulotrix, sexual reproduction is isogamous - it occurs by the fusion of two identical cells, but these cells are specialized and differ from ordinary vegetative cells.

In the most highly organized algae (and in all higher plants) there is a clearly defined alternation of generations - a generation that reproduces sexually (by gametes) and a generation that reproduces asexually (by spores). Yes, green seaweed ulva(or sea lettuce) is represented by plants of two genus, identical in size and structure. Some Ulva specimens have a shiny flat thallus, two layers of cells thick, and up to a meter or more long. The thallus is attached to the substrate by a basal cell. Each thallus cell contains a nucleus and a chromatophore. However, one of these plants is a diploid sporophyte, and the other is a haploid gametophyte. The sporophyte forms haploid spores (zoospores) through meiosis, from which the haploid gametophyte develops. The gametophyte produces gametes that fuse to form a diploid zygote, from which the diploid sporophyte develops. These algae are usually found along the sea coasts of all temperate regions globe. Used as a green for food.

WITH Among green algae, they have the most complex structure charophyte algae. They are separated into a separate department. They live in freshwater bodies of water and serve as the main food for waterfowl. Where charophyte algae grow, there are few mosquito larvae (these algae secrete substances harmful to them). Characeae are multicellular (look like miniature trees); they have formations resembling roots, stems, leaves and seeds, but anatomically they have nothing in common with these organs of higher plants. Some of the characeae species have heavily calcified cell walls, so they are well preserved in fossil form, and they also soften hard water. Their growth is apical, like higher plants; the body is differentiated into nodes and internodes. The sexual process is ovogamous. Gametangia have a more complex structure than other groups of algae. The zygote germinates after a period of dormancy.

Genus cladophora widely distributed in both fresh and sea water. This is a filamentous form with large multinucleated cells separated by septa. The filaments grow in dense clumps that are either free-floating or attached to rocks or plants; they are elongated, branching closer to the ends. Each cell contains a reticulate chromatophore with a large number of pyrenoids.

Department Brown algae. General characteristics.

• 
  Brown algae are common in seas and oceans all over the world, living mainly in shallow coastal waters, but also far from the coast, for example, in the Sargasso Sea. They are an important component benthos.
• 
  The brown color of the thallus is due to a mixture of different pigments: chlorophyll, carotenoids, fucoxanthin. The set of pigments enables photosynthetic processes, since chlorophyll does not capture those wavelengths of light that penetrate to depth.
• 
  In low-organized filamentous brown algae, the thallus consists of one row of cells, and in highly organized ones, the cells not only divide in different planes, but are partially differentiated, as if forming “petioles”, “leaves” and rhizoids, with the help of which the plant is fixed in the substrate.
• 
  The cells of brown algae are mononuclear, the chromatophores are granular, numerous. Spare products are contained in them in the form of polysaccharide and oil. Pectin-cellulose walls are easily mucused, growth is apical or intercalary.
• 
  Asexual reproduction (absent only in Fucus) is ensured by numerous biflagellate zoospores formed in unicellular, less often multicellular, zoosporangia.
• 
  Asexual vegetative reproduction is carried out by parts of the thallus.
• 
  Forms of the sexual process: isogamy, heterogamy and oogamy.
• 
  All brown algae, except fucus algae, have a pronounced change in developmental phases. Reduction division occurs in zoosporangia or sporangia; they give rise to a haploid gametophyte, which can be bisexual or dioecious. The zygote without a resting period grows into a diploid sporophyte. In some species, the sporophyte and gametophyte do not differ in appearance, while in others (for example, in kelp), the sporophyte is more powerful and more durable. In Fucus, a reduction of the gametophyte is observed, since the gametes fuse outside the mother plant, in water. The zygote, without a resting period, develops into a diploid sporophyte.

WITH Among brown algae there are both microscopic and macroalgae. The latter can reach gigantic sizes: for example, algae macrocystis can reach 30-50 m in length. This plant grows very quickly, producing a large amount of extracted biomass; in a day the algae thallus grows by 0.5 meters. In the course of evolution, sieve tubes similar to those found in vascular plants appeared in the thallus of Macrocystis. A special group of substances is extracted from macrocystis species - alginates - mucous intercellular substances. They are widely used as thickening agents or colloid stabilizers in the food, textile, cosmetics, pharmaceutical, pulp and paper, and welding industries. Macrocystis can produce several harvests per year. Attempts are now being made to cultivate it on an industrial scale. Hundreds of animal species find protection, food, and a place for reproduction in macrocystis thickets. Charles Darwin compared its thickets with terrestrial tropical forests: “If forests were destroyed in any country, I do not think that approximately the same number of species of animals would die as with the destruction of thickets of this algae.”

Fucus is a dichotomously branching brown algae with air bubbles at the ends of the plates. Thalluses reach 0.5-1.2 m in length and 1-5 cm in width. This algae thickly covers many rocky areas exposed at low tide. When algae are flooded with water, air-filled bubbles carry them toward the light. The photosynthetic rate of frequently exposed algae can be seven times greater in air than in water. Therefore, algae occupy the coastal zone. In fucus there is no alternation of generations, but only a change of nuclear phases: the entire algae is diploid, only the gametes are haploid. Reproduction by spores is absent.

Two species of the genus sargassum, which do not reproduce sexually, form huge, free-floating masses in Atlantic Ocean, this place is called the Sargasso Sea. Sargassums swim, forming continuous thickets at the surface of the water. These thickets stretch for many kilometers. Plants are kept afloat by air bubbles in the thallus.

L Aminariaceae ("kombu") are regularly used as vegetables in China and Japan; They are sometimes bred, but are mainly taken from natural populations. Sea kale (kelp) is of greatest economic importance; it is prescribed for sclerosis, dysfunction of the thyroid gland, as a mild laxative. Previously, it was burned, the ash was washed, the solution was evaporated, and soda was obtained in this way. The soda was used to make soap and glass. Back in the early 19th century, 100 thousand tons of dry algae were burned per year in Scotland. Since 1811, thanks to the French industrialist Bernard Courtois, iodine began to be obtained from kelp. In 1916, 300 tons of iodine were extracted from seaweed in Japan. Laminaria is a large brown algae 0.5-6 m long, consisting of leaf-like plates, a stalk (trunk) and a structure for attachment to the substrate (rhizoids). The meristem zone is located between the plate and the stalk, which is very important for industrial use. When fishermen cut off the regrown plates of this algae, its remaining deeper parts regenerate. The trunk and rhizoids are perennial, and the plate changes annually. This structure is characteristic of a mature sporophyte. Single-locular zoosporangia are formed on the plate, in which motile zoospores mature and germinate into gametophytes. They are represented by microscopic, filamentous growths consisting of several cells that bear the genitals. Thus, kelp has a heteromorphic cycle with obligatory alternation of generations.

Department Red algae. general characteristics

• 
  Red algae are common in the seas of tropical and subtropical countries and partly in temperate climates (the Black Sea coast and the coast of Norway). Some species are found in fresh waters and on soil.
• 
  The structure of the thallus of red algae is similar to the structure of the thalli of the most highly organized brown algae. The thallus has the appearance of bushes composed of multicellular branching threads, less often lamellar or leaf-shaped, up to 2 m in length.
• 
  Their color is due to pigments such as chlorophyll, phycoerythrin, phycocyan. They live in deeper waters than browns and require additional pigments to capture light. Due to the presence of phycoerythrin and phycocyanin, they got their name - red algae.
• 
  Chromatophores in red algae have the form of disks; there are no pyrenoids. They contain reserve products in the form of oil and purple starch, specific for red algae, which turns red from iodine. The pectin-cellulose cell walls of some species mucus so much that the entire thallus acquires a slimy consistency. Therefore, some types are used to produce agar-agar, which is widely used in the food industry for the preparation of nutrient media for the cultivation of bacteria and fungi. The cell walls of some red algae may be encrusted with calcium carbonate and magnesium carbonate, giving them the hardness of rock. Such algae are involved in the formation of coral reefs.
• 
  Red algae have no mobile stages in their development cycle. They are characterized by a very special structure of the organs of sexual reproduction and the form of the sexual process. Most scarlet plants are dioecious plants. Mature spermatozoa (one immobile gamete) emerge from the antheridia into aquatic environment and are transported by water currents to the carpogon (female organ of sexual reproduction). The contents of the sperm penetrate into the abdomen of the carpogon and merge there with the egg. The zygote, without a resting period, divides by mitosis and grows into filamentous thalli of different lengths. The thallus is diploid. At the top of these filaments, sexual reproductive spores (carpospores) are formed. During asexual reproduction, sporangia are formed on the thallus, which contain one spore - a monospore, or four - tetraspores. Before the formation of tetraspores, reduction division occurs. In monosporous algae, gametangia and sporangia are formed on the same monoploid plant; only the zygote is diploid. Tetraspores are characterized by an alternation of developmental phases: haploid tetraspores grow into a haploid gametophyte with gametangia; diploid carpospores germinate into diploid plants with sporangia (diploid sporophyte). Gametophyte and sporophyte are indistinguishable in appearance. In Porphyra and Porphyridium, asexual reproduction is carried out by monoploid monospores. They go through the entire development cycle in the haploid state; Only their zygote is diploid (like many algae).

Porphyra red algae serves as food for many people in the North Pacific and has been cultivated for centuries in Japan and China. The production of this species employs more than 30,000 people in Japan alone, and the resulting products are valued at approximately $20 million annually. Salads, seasonings, and soups are made from it. Eat dried or candied. A famous dish is “nori” - rice or fish wrapped in dried seaweed. In Norway, during low tide, sheep are released onto the coastal area, rich in red algae, as if out to pasture. This is one of the typical representatives of the purple ones. The leaf-shaped purple thallus of species of this genus is attached to the substrate by its base and reaches 0.5 m in length.

Lives in the Black Sea. Half of the agar produced in Russia is made from this scarlet plant.

Distribution of algae in water and on land. The importance of algae in nature and agriculture.

Most true algae live in freshwater bodies of water and seas. However, there are ecological groups of terrestrial, soil, snow and ice algae. Algae living in water are divided into two large ecological groups: planktonic and benthic. Plankton called a collection of small, mostly microscopic organisms freely floating in the water column. The plant part of plankton, formed by true algae and some purple algae, constitutes phytoplankton. The importance of phytoplankton for all inhabitants of water bodies is enormous, since plankton produces the bulk of organic substances, due to which, directly or indirectly (through food chains), the rest of the living world of water exists. They play an important role in the formation of phytoplankton. diatoms.

To benthic algae are macroscopic organisms attached to the bottom of water bodies or to objects and living organisms in the water. Most benthic algae live at depths of up to 30–50 m. Only a few species, predominantly related to scarlet algae, reach depths of 200 m or more. Benthic algae are an important food for freshwater and marine fish.

Terrestrial algae are also quite numerous, but are usually not noticed due to their microscopically small size. However, greening of sidewalks and powdery green deposits on the trunks of thick trees indicate accumulations of soil algae. These organisms are found in the soils of most climate zones. Many of them contribute to the accumulation of organic matter in soils.

Ice and snow algae are microscopically small and are detected only when a large number of individuals accumulate. The most famous phenomenon has long been the so-called “red snow”. The main organism that causes reddening of snow is one of the types of unicellular algae - Chlamydomonas snowy . In addition to free-living algae, algae - symbionts, which are the photosynthetic part of lichens, play an important role in nature.

Due to their wide distribution, algae are of great importance in the life of individual biocenoses and in the cycle of substances in nature. The geochemical role of algae is associated primarily with the cycle of calcium and silicon. Making up the main part of the plant and aquatic environment and participating in photosynthesis, they serve as one of the main sources of organic matter in water bodies. In the World Ocean, algae annually create about 550 billion tons (about ¼) of all organic matter on the planet. Their productivity here is estimated at 1.3–2.0 tons of dry matter per 1 g of water surface per year. Their role is enormous in the nutrition of aquatic organisms, especially fish, as well as in enriching the hydrosphere and atmosphere of the Earth with oxygen.

Some algae, together with heterotrophic organisms, carry out the processes of natural self-purification of waste and polluted waters. They are especially useful in open "oxidation ponds" used in tropical and subtropical countries. Open ponds with a depth of 1 to 1.5 m are filled with untreated wastewater. During the process of photosynthesis, algae release oxygen and provide the vital activity of other aerobic microorganisms. Many of the algae are indicators of pollution and salinization of habitats. Soil algae actively participate in soil formation.

The economic importance of algae lies in their direct use as food products or as raw materials for the production of various substances valuable to humans. For this purpose, especially those species are used whose ash is rich in sodium and potassium salts. Some brown algae are used as fertilizers and for feeding domestic animals. Algae are not particularly nutritious, because... humans do not have enzymes that allow them to break down and digest cell wall substances, but they are rich in vitamins, iodine and bromine salts, and microelements.

Seaweed is a raw material for several industries. Most important products products obtained from them are agar-agar, algin and carrageen. Agar - a polysaccharide obtained from red algae. It forms gels and is widely used in food, paper, pharmaceutical, textile and other industries. Agar is indispensable in microbiological practice when cultivating microorganisms. It is used to make capsules for vitamins and medicines, and is used to obtain dental imprints and in cosmetics. In addition, it is introduced into baked goods to prevent them from becoming stale, in the formulations of quick-hardening jellies and confectionery products, and is also used as a temporary casing for meat and fish in tropical countries. Agar is obtained from ahnfeltia, mined in the White and Far Eastern seas. Algin and alginates , extracted from brown algae (kelp, macrocystis), have excellent adhesive properties, are non-toxic, and form gels. They are added to food products, into tablets in the manufacture of medicines, used in the tanning of leather, in the production of paper and fabrics. Alginates are also used to make soluble threads used in surgery. Carrageen similar to agar. It is preferred to agar when stabilizing emulsions, cosmetics and dairy products. The possibilities for the practical use of algae are far from exhausted.

Under certain conditions, algae “bloom”, i.e. accumulate in large quantities in water. “Blooming” is observed in fairly warm weather, when there is eutrophication , i.e. a lot of nutrients (industrial waste, fertilizers from fields). As a result, the primary producers, algae, begin to multiply explosively, and they begin to die off before they can be eaten. In turn, this causes intensive proliferation of aerobic bacteria, and the water is completely deprived of oxygen. Fish and other animals and plants are dying. Toxins formed during water blooms increase the death of animals; they can accumulate in the body of mollusks and crustaceans that feed on algae, and then, entering the human body, cause poisoning and paralysis.

You will learn from this article what the importance of green algae is.

The meaning of green algae

What is green algae?

Green algae belong to the department lower plants, which have different morphological structure and sizes. They contain carotenoids and chlorophyll plates. Green algae come in multicellular and unicellular forms. They have a reserve substance - starch, sometimes oils. It is noteworthy that unicellular green algae live not only in the aquatic environment, but also in soil or snow. But multicellular plants live in the upper layers of reservoirs, which is due to the implementation of the productive process of photosynthesis.

What is the significance of green algae in nature?

1. They are an important chain in the digestion of young fish and zooplankton.

2. Green algae in large quantities supply the aquatic environment with oxygen.

3. They play the role of a biological filter for water purification - green algae cells absorb organic substances dissolved in water through the cell membrane.

4. Some green algae enter into symbiosis with worms, ciliates and hydras. Thus, they supply their host with chloroplasts. And mollusks, feeding on such algae, enrich the cells of the respiratory cavity with chloroplasts, which, being in a foreign body, effectively photosynthesize.

Green algae meaning in human life

1. Green protococcal algae contains nutritional and other valuable compounds that have highly productive properties. Thanks to the minimal costs spent on their cultivation, this type algae is used as a raw material for the production of chlorophyll and vitamins. They are used as feed for farm animals.

2. Filamentous green algae are used in industry - high-grade durable paper is made from them, ethyl and wine alcohols, acetone and the like are obtained.

3. Some species are used by the population of a number of countries for food. For these purposes, for example, in Japan, Ulva and Enteromorpha are specially cultivated.

4. Certain types of green algae are used as producers of physiologically active substances. Species of the genus Haematococcus are cultivated on an industrial scale to obtain the carotenoids astaxanthin, and Botryococcus for the production of lipids.

We hope that from this article you learned what the importance of green algae is.

Green algae (lat. Chlorophyta) are a group of lower plants. In modern taxonomy, this group has the rank of department, including unicellular and colonial planktonic algae, unicellular and multicellular forms of benthic algae. All morphological types of thallus are found here, except for rhizopodial unicellular and large multicellular forms with a complex structure. Many filamentous green algae attach to the substrate only in the early stages of development, then they become free-living, forming mats or balls. Multicellular green algae [Electronic resource] - Access mode: http://www.town33.ru/statrasvod.html

All green algae are distinguished primarily by the pure green color of their thalli, similar to the color of higher plants and caused by the predominance of chlorophyll over other pigments. The chromatophores of cells contain the pigments chlorophyll, carotene and xanthophyll, and the green pigment quantitatively predominates over the yellow ones. Encyclopedia for children. T. 2. Biology. - 5th ed., revised. And add./Ch. Ed. M.D. Aksenov. - M.: Avanta+, 2001. - P. 305-308

Among the green macrophytes there are various forms: colonial, filamentous in the form of highly branched bushes, lamellar, siphonous and rather complex charophytes, which outwardly resemble higher plants - hornwort or horsetail. The thallus of charophyte algae consists of branching shoots (“stems”) and whorled branches of limited growth (“leaves”). The locations of the “leaves” are called nodes, and the sections of the stem between them are called internodes.

The reserve product of green algae is starch.

Green algae are inhabitants of fresh and salt waters.

The most common species found in Russia and living mainly in the sea belong to the genera: Chara - Chara Vaill; Ulva -- Ulva L; Caulerpa -- Caulerpa Lamour; Codium -- Codium Stackh; Cladophora - Cladophora Kutz.; Ulvaria -- Ulvaria Rupr and others.

Characteristics of the most common genera of marine green algae

Rod Chara -- Chara Vaill:

Representatives of this genus are very different from the rest in that their filamentous multicellular thalli have a complex morphological organization. On the main shoots growing at the top (“stems”), at some distance from each other there are whorls of identical short lateral segmented shoots (“leaves”) that have limited growth. The locations of the whorls are called nodes, and the sections of the thallus between them are called internodes.

In appearance, many of the charophyte algae are very reminiscent of horsetails, although the similarity is, of course, purely external. Each internode on their thallus represents one multinucleate, giant (up to several centimeters long), often covered with bark, cell, incapable of division. And the nodes consist of several small mononuclear cells collected in a disk, which, in the process of their division, form the lateral branches of the “stem” and whorls of “leaves”. The shoots of characeae are attached to the bottom with the help of numerous thin rhizoids. These algae reach very large sizes - from 20-30 cm to 1-2 m.

There is no asexual reproduction in characeae; the sexual process is oogamy. The organs that produce gametes - multicellular oogonia and antheridia - are formed on the segments of the thallus, in the nodes. In the oogonia, up to 1 mm in size, one egg develops, in the antheridium (its diameter is about 0.5 mm) - many male germ cells. In most characeae species, oogonia and antheridia develop on the same plant, but there are also dioecious species.

About 300 species of charophyte algae are known. They are common in fresh water bodies, especially with hard calcareous water, where they often form continuous thickets at the bottom. Some species are also found in sea bays.

In most species, the thalli are heavily encrusted with lime, which makes them brittle and easy to break. Annuals.

The genus contains 117 species. There are 15 species in Russia. The most common type is

Rod Ulva -- Ulva:

The thallus of seaweed of the genus Ulva is a bright green, two-layer plate with corrugated edges, about 10-12 cm in size, attached to the substrate with a base narrowed into a short petiole. Ulva cells are mononuclear with a wall chromatophore and a large central vacuole. The most common method of vegetative propagation of Ulva is the germination of base cells to form young plants. Unlike the algae listed above, in the life cycle of which the haploid stage predominates, in Ulva there is an alternation of generations: a diploid sporophyte and a haploid gametophyte. The nuclei of sporophyte cells contain a double set of chromosomes, and during reduction division haploid zoospores are formed. When they germinate, they form haploid plants - gametophytes, capable of forming gametes. When gametes fuse, a zygote is formed, containing a diploid nucleus and germinating into a sporophyte without a dormant period. Ulva is characterized by an isomorphic change of generations - its sporophyte and gametophyte look exactly the same in appearance.

Ulva is found in the seas of all climate zones, although it prefers warm waters. Found in almost all seas of Russia. For example, in the shallow waters of the Black Sea this is one of the most abundant types of algae. Many Ulva species tolerate desalination; they can often be found in river mouths.

Ulva: A - appearance thallus; B - cross section of the thallus

The genus contains approximately 30 species. There are 3 species in Russia. The most common types:

Genus Caulerpa -- Caulerpa Lamour:

The genus Caulerpa includes about 60 species of seaweed, the creeping parts of the thallus spread on the ground look like branching cylinders, reaching a length of several tens of centimeters. At certain intervals, abundantly branching rhizoids extend down from them, anchoring the plant in the soil, and flat, leaf-shaped vertical shoots, in which chloroplasts are concentrated, extend upward.

The caulerpa thallus, despite its large size, does not have a cellular structure - it completely lacks transverse partitions, and formally it represents one giant cell. This structure of the thallus is called siphon. Inside the caulerpa thallus there is a central vacuole surrounded by a layer of cytoplasm containing numerous nuclei and chloroplasts. Various parts of the thallus grow at their tips, where the cytoplasm accumulates. The central cavity in all parts of the thallus is crossed by cylindrical skeletal strands - cellulose beams, which give the algae body mechanical strength.

Caulerpa: A - appearance of the thallus; B - section of thallus with cellulose beams

Caulerpa easily reproduces vegetatively: when older parts of the thallus die off, its individual sections with vertical shoots become independent plants.

Species of this genus live mainly in tropical seas, and only a few enter subtropical latitudes, for example, Caulerpa prolifera, widespread in the Mediterranean Sea. Caulerpa prefers shallow water with calm water, for example, lagoons protected from the action of constant surf by coral reefs, and settles both on various hard substrates - stones, reefs, rocks, and on sandy and muddy soil. Green algae [Electronic resource] - Access mode: http://bio.1september.ru/articlef.php?ID=200201003

Genus Codium -- Codium Stackh:

The thallus is of various shapes - compressed-cylindrical, cord-shaped or cushion-shaped, but not articulated and not calcified. Branching is dichotomous or polychotomous. Attached to the substrate by rhizoids.

The inner tissue is a loose plexus of threads, the outer layer is formed by dark green swollen close ends of the branches. The threads that make up the thallus are not separated by septa and are giant cells with many nuclei.

Marine plants found only in warm waters.

The genus contains 50 species. There are 3 species in Russia. The most common type:

Genus Ulvaria -- Ulvaria Rupr:

The thallus is lamellar, single-layered, on a cylindrical stalk, tubular in the initial stage of development. There are sometimes microscopic growths on the surface of the plate. Attaches with a small sole.

Characterized by the presence of brown pigment.

Annuals.

Found exclusively in the seas.

There are 2 types in Russia. The most common type is

Genus Enteromorpha -- Enteromorpha Link:

The thallus is tubular, sometimes strongly compressed, simple or branched, single-layered, with a cavity or with its remains due to the adhesion of the walls of the thallus.

Annuals.

It grows on stones, algae, shells in all seas of Russia and in fresh water bodies.

The genus contains about 40 species. There are approximately 10 species in Russia. The most common type is

Enteromorpha intestinal -- Enteromorpha intestinalis

Genus Bryopsis -- Bryopsis Lamour:

The thallus is quite large, unicellular, in the form of a highly branched tubular bush, having a more or less clearly defined main axis and pinnately lateral branches extending from it. Branching in one plane or along the entire axis. The lateral branches can in turn branch like the main axis, resembling a feather. The thallus is attached with the help of rhizoidal processes that extend from the base of the thallus and from the main branches and at the same time spread along the main axis.

It can reproduce by separate branches breaking off from the mother plant.

Annuals.

Grows on rocky soils, on algae and shells in warm seas.

The genus contains 30 species. There are 5 species in Russia. The most common type:

Bryopsis plumosa

Genus Ulothrix:

It lives in sea and fresh waters, forming green mud on underwater objects. Filamentous type of thallus differentiation. Chloroplast wall in the form of a belt, closed or open, with several pyrenoids. There is only one core, but without painting it is not visible.

It reproduces primarily vegetatively by four-flagellated zoospores. The sexual process is isogamy (gametes of the same size). Some species are characterized by heterothallism. Biflagellate gametes are formed in cells in the same way as zoospores. They come out and merge. After a period of rest, the zygote germinates into the codiolum stage, where its nucleus passes. After some time, meiosis occurs, after which there may be more mitoses. As a result, 4-8 zoospores are formed, germinating into new ulotrix filaments. All stages except the zygote are haploid.

The most widespread species is Ulothrix zonata. Belyakova G.A. Botany: in 4 volumes. T. 2. Algae and mushrooms: a textbook for students. higher textbook manager -- M: Publishing Center "Academy", 2006. -- P. 221.