Seaweed- these are multicellular, predominantly aquatic, eukaryotic photosynthetic organisms that do not have tissues or whose body is not differentiated into vegetative organs (i.e., belonging to the subkingdom of lower plants).
❖ Systematic divisions of algae(they differ in the structure of the thallus, the set of photosynthetic pigments and reserve nutrients, the characteristics of reproduction and development cycles, habitat, etc.):
■ Golden;
■ Green (examples: spirogyra, ulotrix);
■ Red (examples: porphyry, phyllophora);
■ Brown (examples: lessonia, fucus);
■ Chara (examples: hara, nitella);
■ Diatoms (example: lymophora), etc.
The number of species of algae is more than 40 thousand.
❖Algae Habitat: fresh and salt water, wet soil, tree bark, hot springs, glaciers, etc.
❖ Ecological groups of algae: planktonic, benthic (), terrestrial, soil, etc.
Planktonic forms are represented by green, golden and yellow-green algae, which have special devices to facilitate water transfer: reducing the density of organisms (gas vacuoles, lipid inclusions, gelatinous consistency) and increasing their surface (branched outgrowths, flattened or elongated body shape, etc.).
benthic forms live at the bottom of reservoirs or envelop objects in the water; attached to the substrate by rhizoids, basal discs and suckers. In the seas and oceans, they are represented mainly by brown and red algae, and in fresh water bodies - by all divisions of algae, except Brown. Benthic algae contain large chloroplasts with a high content of chlorophyll.
Ground, or air, algae (usually Green or Yellow-green algae) form raids and films of various colors on the bark of trees, wet stones and rocks, fences, roofs of houses, on the surface of snow and ice, etc. With a lack of moisture, terrestrial algae are impregnated with organic and inorganic substances.
Soil algae (mainly yellow-green, golden and diatoms) live in the thickness of the soil layer at a depth of up to 1-2 m.
Features of the structure of algae
The body of algae is not divided into vegetative organs and is represented by strong and elastic thallus (thallus) . The structure of the thallus is filamentous (examples: ulotrix, spirogyra), lamellar (example: kelp), branched or bushy (example: hara). Dimensions - from 0.1 mm to several tens of meters (for some brown and red algae). The thallus of branched and bushy algae is dissected and has a linear-segmented structure; in it one can distinguish the main axis, "leaves" and rhizoids.
Some algae have special air bubbles , which hold the thallus at the surface of the water, where there is the possibility of maximum light capture for photosynthesis.
The thallus of many algae secretes mucus, which fills their internal cavities and is partially excreted to the outside, helping to better retain water and preventing dehydration.
Algae thallus cells are not differentiated and have a permeable cell wall, the inner layer of which consists of cellulose, and the outer layer of pectin and (in many species) a number of additional components: lime, lignin, cutin (which retains ultraviolet rays and protects cells from excessive loss of water during low tide ), etc. The shell performs protective and supporting functions, while providing the possibility of growth. With a lack of moisture, the shells thicken significantly.
The cytoplasm of the cell in most algae forms a thin layer between the large central vacuole and the cell wall. The cytoplasm contains organelles: chromatophores , endoplasmic reticulum, mitochondria, Golgi apparatus, ribosomes, one or more nuclei.
Chromatophores are algae organelles containing photosynthetic pigments, ribosomes, DNA, lipid granules and pyrenoids . In contrast to the chloroplasts of higher plants, chromatophores are more diverse in shape (can be cup-shaped, ribbon-shaped, lamellar, stellate, disc-shaped, etc.), size, number, structure, location, and set of photosynthetic pigments.
In shallow water ( green ) algae photosynthetic pigments are mainly chlorophylls a and b, which absorb red and yellow light. At brown algae living at medium depths, where green and blue light penetrates, photosynthetic pigments are chlorophylls a and c, as well as k arotin and fucoxanthin having a brown color. In red algae living at depths up to 270 m, photosynthetic pigments are chlorophyll d (characteristic only for this group of plants) and have a reddish color. phycobilins- phycoerythrin, phycocyanin and allophycocyanin, which absorb blue and violet rays well.
Pyrenoids- special inclusions that are part of the chromatophore matrix and are a zone of synthesis and accumulation of reserve nutrients.
Spare substances of algae: starch, glycogen, oils, polysaccharides, etc.
Algae breeding
Algae reproduce asexually and sexually.
❖ Organs of reproduction of algae (single-celled):
■ sporangia (organs of asexual reproduction);
■ gametangia (organs of sexual reproduction).
❖ Ways of asexual reproduction of algae: vegetative (thallus fragments) or unicellular zoospores.
❖ Forms of the sexual process in algae:
■ isogamy
- fusion of mobile gametes identical in structure and size,
■ heterogamy
- fusion of mobile gametes of different sizes (the larger one is considered female),
■ oogamy
- the fusion of a large immobile egg with a spermatozoon,
■ conjugation- fusion of the contents of two non-specialized cells.
The sexual process ends with the formation of a diploid zygote, from which a new individual is formed or mobile flagella are formed. zoospores , serving for the resettlement of algae.
❖ Peculiarities of algae reproduction:
■ in some species of algae, each individual is able to form (depending on the season or environmental conditions) both spores and gametes;
■ in certain species of algae, the functions of asexual and sexual reproduction are performed by different individuals - sporophytes
(they form spores) and gametophytes (they form gametes);
■ in the development cycle of many types of algae (red, brown, some green) there is a strict alternation of generations - sporophyte and gametophyte
;
■ algae gametes, as a rule, have taxises that determine the direction of their movement depending on the intensity of light, temperature, etc.;
■ non-flagellated spores make amoeboid movement;
■ in seaweeds, the release of spores or gametes coincides with the tide; there is no rest period in the development of the zygote (i.e., the zygote begins to develop immediately after fertilization, so as not to be carried away to the sea).
The value of algae
❖ Algae Meaning:
■ they produce organic matter through photosynthesis;
■ saturate water with oxygen and absorb carbon dioxide from it;
■ are food for aquatic animals;
■ are the ancestors of plants that inhabited the land;
■ participated in the formation of mountain limestone and chalk rocks, some types of coal and oil shale;
■ green algae clean up water bodies polluted with organic waste;
■ are used by humans as organic fertilizers and feed additives in the diet of animals;
■ are used in the biochemical, food and perfume industries to produce proteins, vitamins, alcohols, organic acids, acetone, iodine, bromine, agar-agar (required for the manufacture of marmalade, marshmallow, soufflé, etc.), varnishes, dyes, glue ;
■ many species are used for human food (kelp, some green and red algae);
■ some species are used in the treatment of rickets, goiter, gastrointestinal and other diseases;
■ silt from dead algae (sapropel) is used in mud therapy;
■ may cause water to bloom.
green algae
❖ Spirogyra
■ Habitat: fresh stagnant and slowly flowing reservoirs, where it forms bright green mud; common in Belarus.
■ Body Shape: thin filiform; cells are arranged in a row.
■ Structural features cells are cylindrical in shape with a well-defined cell wall; covered with a pectin shell and a mucous membrane. The chromatophore is ribbon-shaped, spirally twisted. The vacuole occupies most of the cell. The nucleus is located in the center and is connected by strands to the parietal cytoplasm; contains a haploid set of chromosomes.
■ Reproduction: asexual carried out by breaking the thread into short sections; spore formation is absent. sexual process - conjugation. In this case, two strands of algae are usually located parallel to each other and grow together with the help of copulatory outgrowths or bridges. Then the cell membranes at the points of contact of the threads dissolve, forming a through channel through which the contents of one of the cells move into the cell of the other thread and merge with its protoplast, forming a zygote with a dense shell. The zygote divides into meiosis; 4 nuclei are formed, three of them die; from the remaining cell after a dormant period, an adult develops.
❖ Ulotrix
■ Habitat: fresh, less often marine and brackish water bodies, soil;
Department of green algae. General characteristics.
This is the most extensive department among all algae, numbering over 13 thousand species.
Green algae are diverse 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 distinguishing feature is the green color of the thalli, similar to the color of higher plants, caused by the predominance of chlorophyll over other pigments. Of the assimilation pigments, pigments a, b, α- and β-carotenes were found in them.
Chromatophores are surrounded by a sheath of two membranes. The pyrenoid is absent or present. Cells are mononuclear or multinuclear, mostly covered with a cellulose or pectin membrane, rarely naked. The reserve product is starch, deposited inside chloroplasts, rarely oil.
Iso- and heteromorphic alternation of generations is observed.
Asexual and sexual reproduction of algae.
The main types of asexual reproduction are:
vegetative reproduction. In some colonial forms, colonies can break up into separate fragments, which give rise to smaller colonies. In large algae, such as 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 along, forming two new threads.
binary division. In this case, a unicellular organism divides into two identical halves, while the nucleus divides mitotically. A longitudinal division of this type is observed in euglena.
Zoospores. These are motile spores with flagella. They are formed in many algae, such as Chlamydomonas.
Aplanospores. These are non-motile spores produced by brown algae.
sexual reproduction of algae
Sexual reproduction combines the genetic material of two separate individuals of the same species. Its essence is the fusion of germ cells - gametes formed in special mother cells gametangia, which results in zygote . Sometimes, in some green algae, the contents of two vegetative undifferentiated cells that physiologically perform 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. Such a process is called isogamy , and the 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 respectively female and male, and the process is called oogamy . Female gametes are larger because they contain a supply of 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, for the first time, the alternation of asexual and sexual generations arose and became fixed, 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. The 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 still enriched with nitrogenous soluble compounds, such as runoff from stockyards. With their mass development, water often acquires a green color. Some species live in sea water or brackish estuaries.
Chlamydomonas cells have an ellipsoidal shape, with a small colorless "nose" at the front end, from which two equal-length undulipodium (flagellum), through which the algae moves. The chlamydomonas cell moves by screwing into the water like a corkscrew, rotating around the longitudinal axis. The shell adheres tightly to the protoplast. The protoplast contains a single nucleus, usually a cup-shaped chloroplast, in which the pyrenoid, pigmented "eye" and pulsating vacuoles are immersed in the anterior part of the cell. pyrenoid - This is a protein formation, consisting mainly of an enzyme that helps fix carbon dioxide, starch is stored in it. red eye perceives 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.
AT 
The adult Chlamydomonas is haploid. asexual reproduction
carried out through zoospore
. When the reservoir dries up, chlamydomonas lose undulipodia, their walls become mucilaginous, in such a motionless state they multiply. Mitotic division of the nucleus occurs, the chloroplast divides, the protoplast of the cell divides into four daughter protoplasts. In daughter protoplasts, cell walls and new eyes are formed. The walls of the daughter cells are also mucilaginous, and thus a system of mucous membranes nested in each other is obtained, in which immobile cells are located in groups. When transferred to water, 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 numbers. Some species are characterized by heterogamy or oogamy. During germination, the nucleus of the zygote divides meiotically for the first time, and the haploid state is restored.
Representatives of the genus chlorella also widespread in fresh water, seas, on damp ground, tree bark. Their spherical cells are dressed in a smooth shell, usually containing a cup-shaped chloroplast and one nucleus. During asexual reproduction, the contents of the cells break up into four or more parts - autospores, which, even inside the shell of the mother cell, dress with their own shells. Autospores are released after rupture of the mother cell wall. The sexual process is absent. Chlorella is characterized by a very fast rate of reproduction and often serves as an object of study of photosynthesis. It is able to use from 10 to 12% of light energy (against 1-2% in land plants). In the process of photosynthesis, chlorella is able to release a volume of oxygen that is 200 times its own volume. Has wide practical application. It is one of the most useful algae, as it contains up to 50 complete proteins, fatty oils, vitamins B, C and K in dry matter. There are industrial plants for breeding chlorella to obtain cheap feed. The Japanese learned how to process chlorella into a colorless powder that can be mixed with flour in the manufacture of bakery products. Recently studied the possibility of using chlorella for energy; 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 and platforms in the open ocean or even space.
Volvox- colonial algae, having a spherical shape (2-3 mm in diameter). The Volvox colony consists of many (500-60,000 cells) located along the periphery of the ball in one layer. The inner cavity of the ball is occupied by mucus. Each cell is equipped with two flagella directed outward of the ball, and in its structure resembles a chlamydomonas. These are vegetative cells that perform the functions of nutrition and movement, but are not capable of reproduction. The movement of the Volvox colony is quite coordinated, since the cells are not isolated from each other, but are connected using cytoplasmic strands passing through the cell walls. In addition to vegetative cells, there are specialized cells that are larger and lack flagella. They perform the functions of sexual reproduction. Small-sized motile spermatozoa with two flagella are formed only by special organs - antheridia (this term is used to refer to the organs of higher
plants that produce spermatozoa). The only large immobile egg is formed inside a special organ - the ogonium. 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 with the formation of haploid cells, giving rise to a new colony. Some Volvox species have antheridia and ovogonia in the same colony, while others have only antheridia or only ovogonia, i.e. gender differentiation is observed.
Vegetative propagation of Volvox is carried out with the help of daughter colonies formed in maternal colonies by successive longitudinal divisions of cell protoplasts.
Chlamydomonas Chlorella Volvox
Filamentous algae.
Numerous species spirogyre live in fresh water bodies with stagnant, but clean water and are remarkable for a sexual process such as conjugation. Their filamentous thallus, floating on the surface of the water, consists of large cells, the filaments are slimy and slippery.
The thread of spirogyra form cylindrical cells connected end to end. All cells are identical, and there is no separation of functions between them. A thin layer of cytoplasm lies along the periphery of the cell, and a large vacuole is, as it were, wrapped in strands of cytoplasm. These strands hold the nucleus in the center of the cell. One or more spiral chloroplasts lie in a thin parietal layer of the cytoplasm.
Spirogyra grows by dividing any of the cells that make up the thread, growth usually occurs at night. First, the nucleus divides, then, as it were, the entire cell is laced . Vegetative propagation carried out by breaking the threads into separate sections, sometimes even into separate cells ( fragmentation ).
At sexual reproduction usually two threads are parallel to each other.
BUT 
. Opposite cells form outgrowths directed towards each other and fused at the ends.
B. Their shells dissolve at the point of contact and form a through channel through which the compressed contents of one cell move to another within a few minutes and merge with its protoplast, which had also contracted by that time.
C. The zygote formed as a result of the fusion of the protoplasts of the conjugating cells rounds off, a thick three-layer membrane is formed, and the entire cell passes into a state of rest. The resulting zygote is surrounded by a thick cell wall and in this form survives the winter. In spring, the zygote divides meiotically and forms four haploid nuclei, of which three degenerate, and the fourth is preserved, breaks the cell wall, divides mitotically and gives rise to a new haploid thread. This process of reproduction is called conjugation. It involves non-specialized cells that do not differ from each other (isogamy variant).
Thus, spirogyra goes through the life cycle in the haploid phase, only the zygote is diploid.
With 
among filamentous green algae, also found in fresh water, is found ulotrix. Non-branching ulotrix filaments are attached by a basal rhizoid cell to underwater objects. In the center of the cell is the nucleus, the parietal chromatophore. Due to cell division in the transverse direction, the thread grows in length. Under favorable conditions, ulotrix reproduces by zoospores, which carry four flagella. By autumn, individual cells of the filament turn into gametangia, inside which biflagellated gametes are formed. When the gametes merge, a four-flagellated zygote is formed, then it sheds the bundles and goes into a state of rest. Subsequently, the zygote divides meiotically and gives rise to four cells, from which new threads are formed. Thus, in ulotrix, sexual reproduction is isogamous - 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), a pronounced alternation of generations is observed - a generation that reproduces sexually (by gametes) and a generation that reproduces asexually (spores). Yes, green seaweed. ulva(or sea lettuce) is represented by plants of two kinds, identical in size and structure. Individual Ulva individuals 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 produces haploid spores (zoospores) by meiosis, from which the haploid gametophyte develops. The gametophyte produces gametes that fuse to form a diploid zygote, from which a diploid sporophyte develops. These algae are usually found along the sea coasts of all temperate regions of the globe. Used for food as greens.
With 
among green algae, the most complex structure is charophytes. They are separated into a separate section. They live in freshwater reservoirs and serve as the main food for waterfowl. Where Chara algae grow, there are few mosquito larvae (these algae emit substances harmful to them). Chara algae are multicellular (similar to miniature trees); they have formations resembling roots, stems, leaves and seeds, but anatomically they have nothing to do with these organs of higher plants. Some of the species of characeae have highly calcified cell walls, therefore they are well preserved in the fossil state, in addition, they soften hard water. Their growth is apical, as in 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 dormant period.
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 of brown algae. General characteristics.
Brown algae are common in the seas and oceans of the whole world, they live mainly in coastal shallow waters, but also far from the coast, for example, in the Sargasso Sea. They are an important component of benthos.
The brown color of the thallus is due to a mixture of different pigments: chlorophyll, carotenoids, fucoxanthin. A set of pigments enables photosynthetic processes, since chlorophyll does not capture those wavelengths of light that penetrate to depth.
In lowly organized filamentous brown algae, the thallus consists of one row of cells, while in highly organized cells not only divide in different planes, but partly differentiate, as if forming "petioles", "leaves" and rhizoids, with the help of which the plant is fixed in the substrate.
Cells of brown algae are mononuclear, chromatophores are granular, numerous. Spare products are contained in them in the form of polysaccharide and oil. Pectin-cellulose walls are easily mucilaginous, growth is apical or intercalary.
Asexual reproduction (absent only in fucus) is provided by numerous biflagellate zoospores, which are 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.
In all brown algae, except for Fucus, a change in the phases of development is expressed. Reduction division occurs in zoosporangia or sporangia, they give rise to a haploid gametophyte, which is bisexual or dioecious. The zygote without a dormant period germinates into a diploid sporophyte. In some species, the sporophyte and gametophyte do not differ externally, while in others (for example, in kelp), the sporophyte is more powerful and more durable. In fucus, gametophyte reduction is observed, since the gametes fuse outside the mother plant, in the water. The zygote, without a dormant 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, giving a large amount of extracted biomass, per day the algae thallus grows by 0.5 meters. In the thallus of macrocystis, sieve tubes similar to those found in vascular plants appeared during evolution. 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, cosmetic, pharmaceutical, pulp and paper, and welding industries. Macrocystis can produce several crops per year. Now attempts are being made to cultivate it on an industrial scale. In the thickets of macrocystis, hundreds of species of animals find protection, food, breeding grounds. C. Darwin compared its thickets with terrestrial tropical forests: “If forests were destroyed in any country, then I don’t think that approximately the same number of animal species would die as with the destruction of thickets of this algae.”
Fucus is a dichotomously branching brown alga with air bubbles at the ends of the plates. The thalli reach 0.5-1.2 m in length and 1-5 cm in width. These algae densely cover many rocky areas exposed at low tide. When algae are flooded with water, air-filled bubbles carry them to the light. The rate of photosynthesis in frequently exposed seaweeds can be up to seven times faster in air than in water. Therefore, algae occupy the coastal zone. Fucus does not have an alternation of generations, but there is only a change in nuclear phases: the whole algae is diploid, only gametes are haploid. There is no reproduction by spores.
Two species of the genus sargassum, which do not reproduce sexually, form huge, free-floating masses in the Atlantic Ocean, this place is called the Sargasso Sea. Sargassum swim, forming continuous thickets near the surface of the water. These thickets stretch for many kilometers. Plants are kept afloat thanks to air bubbles in the thallus.
L 
aminariaceae ("kombu") in China and Japan are regularly used as vegetables; sometimes they are bred, but mainly they are taken from natural populations. Seaweed (kelp) has the greatest economic importance; it is prescribed for sclerosis, impaired thyroid activity, as a mild laxative. Previously, it was burned, the ash was washed, the solution was evaporated, in this way soda was obtained. Soda was used to make soap and glass. As early as the beginning of the 19th century, 100,000 tons of dry algae were burned in Scotland per year. 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 alga 0.5-6 m long, consists of leaf-like plates, legs (trunk) and structures for attachment to the substrate (rhizoids). The meristem zone is located between the plate and the stem, which is very important for industrial use. When the fishermen cut off the regrown plates of this algae, its deeper parts regenerate. The trunk and rhizoids are perennial, and the plate changes annually. This structure is characteristic of a mature sporophyte. On the plate, unilocular zoosporangia are formed, in which mobile zoospores mature, germinating into gametophytes. They are represented by microscopic, filamentous outgrowths consisting of several cells that carry the genitals. Thus, kelp has a heteromorphic cycle with a mandatory alternation of generations.
Department of Red Algae. general characteristics
Red algae are common in the seas of tropical and subtropical countries and partly in temperate climates (the coasts of the Black Sea and the coasts of Norway). Some species are found in fresh water 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 form of bushes, composed of multicellular branching filaments, less often lamellar or leaf-shaped, up to 2 m in length.
Their color is due to pigments such as chlorophyll, phycoerythrin, phycocyanin. They live in deeper waters than brown ones 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 are disc-shaped, pyrenoids are absent. Spare products are contained in them in the form of oil and purple starch, specific to red algae, which turns red from iodine. Pectin-cellulose cell walls in some species become so mucilaginous that the entire thallus acquires a slimy consistency. Therefore, some species are used to obtain 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 can be encrusted with calcium carbonate and magnesium carbonate, giving them the hardness of stone. Such algae are involved in the formation of coral reefs.
Red algae do not have mobile stages in the development cycle. They are characterized by a very special structure of the organs of sexual reproduction and the form of the sexual process. Most purples are dioecious plants. Mature spermatozoa (one immobile gamete) exit the antheridia into the aquatic environment and are transported by water currents to the karpogon (the female organ of sexual reproduction). The content of the spermatozoa penetrates into the abdomen of the carpogon and merges with the egg there. The zygote without a dormant period divides by mitosis and grows into filiform thalli of different lengths. Thallus is diploid. In the upper part of these threads, spores of sexual reproduction (carpospores) are formed. During asexual reproduction, sporangia are formed on the thallus, which contain one spore - monospore, or four - tetraspores. Before the formation of tetraspores, reduction division occurs. In monospore 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 germinate into a haploid gametophyte with gametangia; diploid carpospores germinate into diploid plants with sporangia (diploid sporophyte). Gametophyte and sporophyte are indistinguishable in appearance. In porphyry and porphyridium, asexual reproduction is carried out by monoploid monospores. They go through the entire development cycle in a haploid state; only the zygote is diploid in them (as in many algae).
Porphyry red algae is the food of many people in the North Pacific and has been cultivated for centuries in Japan and China. More than 30,000 people are employed in the production of this species in Japan alone, and the resulting production is estimated at about 20 million dollars annually. Salads, seasonings, soups are prepared from it. Eaten dried or candied. A famous dish is "nori" - rice or fish wrapped in dried seaweed. In Norway, at low tide, sheep are released on the coastal part, rich in red algae, as if on a pasture. This is one of the typical representatives of crimson. The leaf-like purple thallus of species of this genus is attached to the substrate with its base and reaches 0.5 m in length.
Lives in the Black Sea. Half of the agar obtained in Russia is produced from this purple.
Distribution of algae in water and on land. The value of algae in nature and economy.
Most of these algae live in freshwater reservoirs and seas. However, there are ecological groups of terrestrial, soil algae, snow and ice algae. Algae living in water are divided into two large ecological groups: planktonic and benthic. plankton called a set of small, mostly microscopic organisms freely floating in the water column. The plant part of the plankton, formed by true algae, and some crimson, is phytoplankton. The importance of phytoplankton for all inhabitants of water bodies is enormous, since plankton produces the bulk of organic substances, due to which the rest of the living world of water exists directly or indirectly (through food chains). An important role in the formation of phytoplankton is played by 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 purple 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 usually overlooked due to their microscopically small size. However, the greening of the sidewalks, powdery green coatings on the trunks of thick trees indicate accumulations of soil algae. These organisms are found in the soils of most climatic zones. Many of them contribute to the accumulation of organic matter in soils.
Ice and snow algae are microscopically small and are found only when a large number of individuals accumulate. The phenomenon of the so-called "red snow" has long been most famous. The main organism that causes the reddening of snow is one of the types of unicellular algae - snowy chlamydomonas . In addition to free-living algae, algae play an important role in nature - symbionts, which are the photosynthetic part of lichens.
Due to the wide distribution of algae, they 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 circulation of calcium and silicon. Making up the bulk of the plant, 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 yield 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 hydrobionts, especially fish, as well as in the enrichment of the Earth's hydrosphere and atmosphere 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. In the process of photosynthesis, algae release oxygen and provide vital activity for other aerobic microorganisms. Many of the algae are indicators of pollution and salinization of habitats. Soil algae are actively involved in soil formation.
The economic significance of algae lies in their direct use as food products or as raw materials for obtaining various substances valuable to humans. For this purpose, especially those species whose ash is rich in sodium and potassium salts are used. Some brown algae are used as fertilizers and for pet food. Algae is not particularly nutritious, because. a person does not have enzymes that allow the breakdown and digestion of cell wall substances, but they are rich in vitamins, iodine and bromine salts, and trace elements.
Seaweed is a raw material for some industries. The most important products derived from them are agar-agar, algin and carrageenan. agar - a polysaccharide that is 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 in the cultivation of microorganisms. Capsules for vitamins and medicines are made from it, they are used to obtain impressions of teeth, in cosmetics. In addition, it is introduced into the composition of bakery products so that they do not stale, in the formulation of quick-setting jellies and confectionery products, and is also used as a temporary casing for meat and fish in tropical countries. Agar is obtained from anfeltia, mined in the White and Far Eastern seas. Algin and alginates , extracted from brown algae (kelp, macrocystis), have excellent adhesive properties, are non-toxic, form gels. They are added to food products, tablets in the manufacture of medicines, used in leather dressing, in the production of paper and fabrics. Soluble threads used in surgery are also made from alginates. Carrageenan similar to agar. It is preferred over agar when stabilizing emulsions, cosmetics and dairy products. The possibilities for the practical use of algae are far from being exhausted.
Under certain conditions, algae "bloom", i.e. accumulate in large quantities in water. "Blossoming" is observed in sufficiently warm weather, when there is observed in the water eutrophication , i.e. a lot of nutrients (industrial effluents, fertilizers from the fields). As a result, the explosive reproduction of primary producers - algae - begins, and they begin to die off before they have time to be eaten. In turn, this causes an intensive reproduction 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, when they enter the human body, cause poisoning and paralysis.
To green algae include both unicellular plants (chlorella, chlamydomonas) and multicellular plants reaching large sizes (spirogyra, ulotrix, etc.). All of them are united by a common feature - the presence in the cells of a green pigment that is not masked by pigments of other colors. All green algae photosynthesize.
A typical representative of unicellular green algae is chlamydomonas, which in its structure is similar to flagella. It is a single-celled oval-shaped algae with two flagella.
An algal cell consists of a cytoplasm, a nucleus, a cup-shaped chromatophore with a pyrenoid, a red eye, a pulsating vacuole, and a membrane.
Chlamydomonas live in puddles, on damp ground. They reproduce both asexually, by zoospores, and sexually. There are all three forms of sexual reproduction: isogamy, heterogamy, oogamy.
An interesting representative of unicellular green algae is chlorella, whose species live in fresh water, on moist soil, on tree trunks, even in symbiosis (mutually beneficial cohabitation) with animals (ciliates, hydras, worms).
Chlorella in translation means greenfinch. It has long attracted the attention of scientists primarily for its extraordinary nutritional properties. Chlorella is interesting in that it photosynthesizes very intensively, while creating a large amount of organic matter, much more than other green plants.
The yield of chlorella during the day is up to 200 kg/ha, which is twice the yield of corn. The collected mass of chlorella is 50% proteins, 22% fats, 12% carbohydrates, 10% mineral salts. Chlorella contains vitamins A, B, C. For example, it contains 100 times more vitamin C, and 500 times more vitamin A than milk. Vitamin C in chlorella is twice as much as in lemon juice. It contains ten essential amino acids for animals.
Finally, chlorella in the near future in a spacecraft will help create a closed circulation of substances necessary to provide astronauts with food and oxygen on long flights, which is reflected in the diagram.
Chlorella is a plant that performs a cosmic role, which was dreamed of by the founder of scientific astronautics K. E. Tsiolkovsky. He wrote: "Just as the earth's atmosphere is cleansed by plants with the help of the Sun, so can the artificial atmosphere of a spaceship be renewed."
In addition to unicellular algae, there are also colonial forms, a typical representative of which is volvox, or spinning top. This algae is a spherical colony of cells arranged in a single layer. The inside of the ball is filled with mucus. The number of cells in a colony is up to 50,000. Very large colony balls reach the size of a pinhead and are visible to the naked eye. Volvox lives in fresh sewage reservoirs, non-drying puddles.
Of the multicellular algae, filamentous algae ulothrix and spirogyra are the most common in our country. Ulothrix threads reach 10 cm in length. With them, ulotrix is attached to pitfalls and snags. Ulothrix lives in fresh water.
Asexual reproduction is accomplished by zoospores. Sexual reproduction occurs by the type of isogamy.
Ecological groups and habitats
The department of green algae (Chlorophyta) unites 5700 species. Green algae are one of the most widespread and diverse groups of algae. Unlike red or brown algae, Most green algae live in fresh water and only a few species are in the seas.
Some representatives have adapted to life on land - in the soil or in damp, shady places with periodic moistening (on the bark of trees, boulders, fences).
Green algae are presented unicellular, multicellular and colonial forms. Some green algae have non-cellular thallus. Among multicellular forms, filamentous algae are especially common, which form mud in ponds and rivers.
The evolutionary significance of green algae
Green algae are considered ancestors of 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 land plants; reserve substance- just like land plants - starch(sometimes fat). Spare parts accumulate green algae not in the cytoplasm (as in representatives of other divisions of algae), but in plastids, which also indicates the relationship of green algae and land plants.
Rice. Structure of green algae. Euglena above. Bottom Chlamydomonas
The bright green color of the algae of 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 a red "bloom" of water or snow.
On the example of individual representatives, two directions of evolution of the thallus of green algae can be traced:
- from a unicellular uninuclear thallus to a non-cellular multinuclear thallus, which is one giant supercell (for example, in caulerpa);
- from a unicellular mobile 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 - charophytes and terrestrial plants.
In general, the evolution of the thallus of green algae can be reflected in the scheme shown in Fig. one.
Rice. 1. Evolution of the thallus of green algae
The department of green algae includes 5 classes:
- volvox;
- protococcal;
- ulotrix;
- siphon;
- conjugates, or couplings.
We give a brief description of 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 form of thallus, i.e. unicellular, mobile thallus with 2nd (rarely 4th) identical flagella at the end of the body (for example, representatives of the genus Chlamydomonas). Cells of some Volvox form colonies.
Volvox are typical planktonic algae that live in shallow, often drying up water bodies. Active orderlies of polluted and waste waters, in which they multiply very quickly, causing a green "bloom" of water.
Typical representatives of the Volvox
Genus Chlamydomonas(Chlamydomonas) - from the Greek. "chlamydomonas" - a single organism, covered with 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 mobile algae with flagella (this form of thallus is called monadic). Outside, the chlamydomonas cell is covered with a transparent pectin-cellulose cell wall. At the anterior end of the body are 2 flagella, and in the center of the cell core and photosensitive eye stigma, which allows Chlamydomonas to move towards the light. Photosynthesis takes place in a large chloroplast chromatophore bowl-shaped. In the center of the chromatophore 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 are 2 pulsating vacuoles that remove excess water and harmful metabolic products from the cell.
Rice. 2. Chlamydomonas (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. It is thanks to the mixed type of nutrition that chlamydomonas is an active orderly of polluted and waste waters, rapidly multiplying in sedimentation tanks. Some types of chlamydomonas are able to develop on the surface of snow and ice. They cause a red "bloom" of water and snow (for example, snow chlamydomonas).
Most species of chlamydomonas are characterized by an isogamous sexual process, however, in some species, heterogamy and oogamy are found. Chlamydomonas is cultivated in laboratories as an object of research in the field 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 volvox globular(Volvox globator), the colony of which has the shape of a ball with a diameter of 2-3 mm, consisting of 50-75,000 cells similar to chlamydomonas (Fig. 3). All cells are connected by cytoplasmic bridges, therefore they act as a whole. Inside the ball is filled with mucus.
During vegetative reproduction, 8-15 daughter colonies are formed inside 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 accidental) death.
Rice. 3. Colonies of green algae: a) pandorina (rounded colony); b) gonium (colony flat); c) volvox
Volvox can also reproduce sexually, and both monoecious and dioecious species are found. In monoecious species, each colony forms both female and male gametes; in dioecious species, each colony is either male or female and forms, respectively, only male or only female gametes.
Other colonial flagellates also belong to the Volvox class, for example, the gonium having a flat colony. When moving, it looks like a small flying carpet. Colonies of eudorina and pandorina have a rounded shape. The cells of all these colonial flagella are immersed in a common mucus wrapper.
Thus, the most primitive representatives of the Volvox are unicellular motile organisms with flagella. They have a mixed diet.- they can eat both like plants (through photosynthesis) and like animals (assimilating organic substances from the environment), which indicates their origin from ancient flagellates, combining signs of plants and animals.
From primitive mobile unicellular algae (Chlamydomonas mud) 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 mobility, which is typical for members of the protococcal class.
class protococcal
Protococcal(Protococcophyceae) are unicellular or colonial algae, immobile as an adult(only zoospores and gametes are mobile). They live in freshwater bodies of water and in the soil. There are species that live in the air, 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 rounded and lack flagella (see Fig. 4a). Representatives of the genus Chlorococcus are found on the bark of trees, 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 (por. Protococcales): a) chlorococcus (p. Chlorococcum); 6) chlorella (p. Chlorella); 1 - unicellular thallus; 2- formation of zoospores; 3 - zoospore; 4 - young individuals; 5 - formation of autospores
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 with the help of immobile, devoid of flagella spores ( aplanospore). The sexual process is absent. Basically, these are planktonic organisms. They are widespread both in the seas and in freshwater reservoirs. Some species live in the soil and on the bark of trees. Chlorella absorbs and uses solar energy much more efficiently than ordinary land 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% of complete proteins and about 20% of fats and carbohydrates, is used as a feed additive. In terms of protein and fat content, chlorella is not inferior to soy. Vitamins are also present in chlorella biomass. A, B, C, K(moreover, 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.
Genus water mesh(Hydrodiction) is represented by colonial forms. Colonies of the water mesh have the shape of a mesh bag with a length of several centimeters to 5 m (Fig. 5).
From immobile unicellular forms, characteristic of representatives of the protococcal class, in the process of evolution, filamentous, and then lamellar forms of algae, characteristic of representatives of the ulotrix class, arise.
Rice. 5. Water mesh (Hydrodiction reticulum)
Ulotrix class
Ulotrix(Ulotrichophyceae) are multicellular organisms with a filamentous or lamellar structure of the thallus, whose cells have one nucleus and usually one chloroplast.
The most famous representatives of this class are ulotrix and ulva.
genus ulotrix(Ulothrix). This is a genus of thread algae that lives in fresh water. Their thallus is an unbranched thread of one row of cells (Fig. 6).
Rice. 6. Vital cyclothrix (Ulothrix): a) asexual reproduction; 6) sexual reproduction; 1 - the main life form; 2 - formation of zoospores; 3 - exit of zoospores; 4 - empty cell; 5 - zoospores; 6 - formation of gametes; 7- output of gametes; 8 - izgamiya; 9-10 - zygote; 11 - germination of the zygote; 12 - zoospore
They reproduce mainly asexually (4-flagellated zoospores). The sexual process is a classic example of 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 ulotrix, to the lamellar one. It is this form of the thallus that is characteristic of representatives of the genus Ulva.
genus ulva(Ulva) or sea salad. Outwardly, 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. The Ulvae descended directly from the Ulothrix. At the initial stages of development, the ulva develops a single-row filament resembling an ulotrix, and then a two-row filament, after which a tubular structure is formed. In the future, the walls of the tube close and it begins to grow as a two-layer plate. Ulva is characterized by 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 Japan). Residents of many coastal countries use ulva for food, hence its second name is “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.
Siphon differ from other green algae in that their thallus is one giant multinucleated cell. However, outwardly, the thallus is complexly dissected and often imitates a terrestrial plant with a rhizome, adventitious roots, and large pinnate leaves. An example of such a structure is a seaweed caulerpa(Caulerra) - fig. 7.
Over 90% of siphons are marine organisms that live in tropical seas, covering large expanses of the seabed.
One of the most numerous genera of the siphon class - cladophora genus(Cladophora). Typical member of the genus cladophora sauter(C. zauterii) (Fig. 8), which is widespread in freshwater reservoirs 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 the development of Cladophora show that it is not close to filamentous algae such as Ulothrix, but to siphon algae, which have a non-cellular structure, since at first the Cladophora thallus develops as one giant multinucleated cell, and septa that mimic individual cells appear later.
Figure 7. Caulerpa (Caulerpa sertularioides): a) general view; b) a section of the thallus in a cross section
Rice. 8. Cladophora (r. Cladophora): a) filamentous thallus; b) a cell with a chloroplast; c) cell with zoospores: 1 - mesh chloroplast
Class of conjugates, or couplers
Conjugate class, or couplings(Conjusatophyceae), unites about 4500 species of multicellular and unicellular algae. The sexual process is conjugation. There are no flagellar stages of development.
Conjugation is a side branch of the evolution of the sexual process. During conjugation, not the nuclei of the cells merge, but their entire protoplasts.
A classic example of conjugation is the reproduction of the freshwater filamentous algae Spirogyra ( Spirogyra).
In heterothallic species of spirogyra, the so-called ladder conjugation occurs. Between the cells (+) - and (-) - threads, channels are formed, through which the protoplasts of the cells (-) - threads pass into the cells (+) - threads. Outwardly, a series of conjugating cells connected by copulation channels resembles a ladder.
In homothallic species of Spirogyra, lateral conjugation occurs, in which a conulation canal 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 dormant period, the zygote divides twice, producing four haploid cells. Three of them, smaller, degenerate, and the fourth, the largest, germinates and gives rise to a new individual.
Green algae are a division of lower plants that are characterized by a bright green color due to the large amount of chlorophyll in their cells. These algae contain the same pigments as in higher plants (carotene, xanthophyll and chlorophylls). Plants are divided into several types: colonial, unicellular and multicellular. At the same time, the latter are more often found in a filamentous and occasionally lamellar form. Some of the green algae have a non-cellular structure, which is hard to believe, looking at the large size and seemingly complex external dissection.
Mobile colonial and unicellular species of algae - gametes and zoospores have 2-4, and sometimes more flagella and a light-sensitive eye. The cells of these plants have one, less often several nuclei, usually they are dressed in a cellulose shell. Green algae can reproduce vegetatively (dividing the body in two in unicellular organisms, in filamentous multicellular organisms - in sections of the thallus), asexual (fixed spores and zoospores) and sexually (heterogamy, isogamy, conjugation and oogamy) methods.
What are the types of green algae
Green algae are divided into two subdivisions: conjugates and directly green. Greens, in turn, are divided into six classes: volvox, protococcal (chlorococcal), siphon, siphonoclad and ulotrix. These plants are most densely distributed in fresh waters, but are sometimes found in the seas. Some green algae - pleurococcus and can live in the soil and on tree trunks. Colonial and unicellular plants are included, if they manage to develop in large numbers, they cause water to bloom.
Monostroma and sea lettuce are eaten in East Asian countries. In many countries, scenedesmus, chlorella and other unicellular organisms are used as the basis of feed for farm animals, as well as for the restoration of air in closed (for example, submarines) and for biological wastewater treatment.
The most typical representative of green algae is chlamydomonas, its structure is similar to flagella. This is a single-celled plant, oval in shape and with two flagella. The cell of this algae consists of a red eye, a membrane, a pulsating vacuole, a cytoplasm, a cup-shaped chromatophore with a pyrenoid, and a nucleus. Chlamydomonas live on damp ground and in puddles, reproduce by zoospores, asexually, and all three forms of the sexual tract.