Multicellular algae. Variety of multicellular algae.

The body is a thallus, or thallus, covered with a cell wall, made of cellulose and pectin, and mucus. Cytoplasm, vacuoles filled with cell sap, the cell contains one or more nuclei, and plastids, or chromatophores containing pigments.

Department of green algae.

thalli pure green. Cell chromatophores contain pigments chlorophyll, carotene and xanthophyll, with the green pigment quantitatively predominating over the yellow ones. The department has about 6 thousand species.

Department	Representative	Description	habitat
Greens	Ulotrix	The filaments are made up of a number of short cells. One core. Chromatophore in the form of an open ring.	Lives in marine and flowing fresh waters
	Spirogyra	Cells are elongated, cylindrical, covered with mucus. Chromatophores in the form of spirally twisted ribbons. Forms large cotton-like accumulations on the surface of the water.	Distributed in fresh stagnant and slowly flowing waters.
	Ulva or sea lettuce	Thallus lamellar, whole, dissected or branched, length 30-150 cm, consists of 2 densely closed layers of cells.	The most widespread in the seas of subtropical and temperate zones
	Nitella (flexible glitter)	The plant forms dense thickets in the water column, it is a thicket of tangled dark green vitreous threads, the latter are formed by long cylindrical cells. In appearance it is similar to horsetail. Often grown in aquariums. Chara algae have formations that, in form and function, resemble the organs of higher plants.	Widespread in fresh waters of Europe, Asia, North America.

Algae are multicellular

Multicellular forms arose after the cell had gone through a long and complex path of development as an independent organism. Traces of this history have been preserved in modern plants. The transition from a unicellular to a multicellular state was accompanied by a loss of individuality and associated changes in the structure and functions of the cell. Qualitatively different relationships develop inside the thalli of multicellular algae than between the cells of unicellular algae. With the emergence of multicellularity, differentiation and specialization of cells in the thallus are associated, which should be considered as the first step towards the formation of tissues (gistogenesis) and organs (organogenesis). Depending on the location of cells in the thallus, multicellular algae can be represented by filamentous or lamellar forms.[ ...]

ALGAE - a group of lower autotrophic plants containing chlorophyll and living mainly in water. Includes unicellular, colonial, multicellular and non-cellular plants.[ ...]

The multicellular antheridia and archegonia of higher plants most likely originated from the multicellular reproductive organs that some algae, in particular green ones, have. But in multicellular gametangia of algae, all cells of the genital organs are fertile and lack a protective wall.[ ...]

Multicellular hairs are usually more or less strongly branched. They are found only in some algae from the order Ceramiaceae. As shown in experiments, the main role of the hairs is that they contribute to the absorption of nutrients from the environment.[ ...]

The body of multicellular algae is called the thallus or thallus. They absorb water and mineral salts with the entire surface.[ ...]

Brown algae are exclusively multicellular plants. Their cell membrane consists of an inner cellulose layer and an outer pectin layer, consisting mainly of alginic acid and its salts and compounds with protein substances. The cellulose of brown algae differs in its properties from the cellulose of higher plants, therefore it is sometimes called algulose.[ ...]

Chara algae, or, as they are also called, charophytes, or rays, are completely peculiar large plants that differ sharply from all other algae. At a cursory glance, they are more like some higher plants: some of them are most of all like horsetail, which grows in forests in shady and damp places; others - on the water plant hornwort. But this similarity, of course, is purely external, since the body of charophytes does not consist of stems, leaves and roots, but is a real multicellular thallus (thallus), characteristic of lower plants, although very complex and peculiarly arranged. They are widely distributed in freshwater ponds and lakes, especially those with hard calcareous water, and some of them are found in sea bays and brackish continental waters. As a rule, characeae do not grow singly, but form thickets, often very extensive, covering the bottom of reservoirs with a continuous carpet. And in these habitats, characeae are the largest representatives of the world of algae - the height of their thalli is usually 20-30 cm, but can reach 1 or even 2 m. All parts of their body, including reproductive organs, are clearly visible to the naked eye.[ ...]

Green algae have a variety of shapes (spherical, oval, etc.), the cell wall consists of cellulose. Most often in fresh water bodies they are found from unicellular forms of chlorella, chlamydomonas gonium, from multicellular forms - ulotrix.[ ...]

Green algae are widely distributed in surface water bodies. Among them there are unicellular, multicellular and colonial forms. Their pigments are concentrated in special formations - chromatophores. They reproduce by dividing the cytoplasm with the formation of daughter cells or sexually. Some species reproduce by producing motile spores. Colonies are formed as a result of asexual division, in which daughter cells remain associated with each other. Cells of green algae have a variety of shapes (spherical, oval, etc.) and contain organelles characteristic of cells of higher plants. Their nucleus is differentiated and separated from the cytoplasm by a membrane. The cell wall is made up of cellulose. The cytoplasm may contain grains of starch, which is a product of photosynthesis. Chlorella vulgaris, chlamydomonas (Chlamidomonas) are most often found in fresh water bodies, volvox (Volvox aureus), gonium (Gonium pectorale) from colonial forms, and ulotrix from multicellular ones.[ ...]

An example of multicellular green algae is the pond dweller Volvox. Forming a colony, this organism consists of 500-60,000 cells, each of which is equipped with two flagella, and also contains an eye, a differentiated nucleus, and a chloroplast. A thick gelatinous membrane surrounds each cell and separates it from neighboring cells. If one cell in a colony dies, the rest continue to live. The location of the cells in the colony ensures the movement of this organism.[ ...]

Golden algae are unicellular (Fig. 66 and 68), colonial (Fig. 67 and 69) and multicellular (Fig. 75). In addition, among them there is one very peculiar representative with a multinuclear thallus in the form of a naked plasmodium (Fig. 67, 3-5).[ ...]

Blue-green algae are the most primitive division of photosynthetic lower plants. Unicellular, multicellular and colonial organisms that have a characteristic blue-green color, due to a specific complex of pigments.[ ...]

It does not have a typical nucleus and chromatophores. The protoplast of blue-green algae is differentiated into a peripherally colored layer (chromatoplasm) and a central part (centroplasm). In the cells are special little bodies - endoplasts of a dense or viscous consistency. In the plasma walls of the cells between the endoplasts there is a “chromatin substance” stained with nuclear dyes.[ ...]

Algae reproduce more often asexually: unicellular - by cell division into two or four, and multicellular - vegetatively by parts of the thallus or spores. During sexual reproduction, gametes fuse in pairs and form a zygote. From the zygote, after a dormant period, spores arise by division, giving rise to new organisms. In some algae, the sexual process is more complex.[ ...]

Type I. Green algae (Chlorophyceae), the most common type among algae, uniting extremely diverse organisms in structure. Among green algae there are unicellular, multicellular and colonial forms.[ ...]

Unicellular and multicellular green algae are capable of photosynthesis, because they contain chloroplasts, in which chlorophyll is concentrated and from the presence of which they have a green color. They also have xanthophylls and carotenes.[ ...]

The division Diatoms, or diatoms (Chgueop a) is represented mainly by multicellular organisms, and sometimes even by colonial forms (Fig. 7). meet and unicellular forms. 5700 species are known. They are characterized by a clear differentiation of the body into the cytoplasm and nucleus. The cell wall is "impregnated" with silica, as a result of which it is called the shell. They are inhabitants of fresh water bodies, seas and oceans and are part of phytoplankton.[ ...]

According to their structure, algae can be unicellular, multicellular and colonial forms. Some of them have a cell without a dense shell and only with a compacted outer layer of protoplasm, as a result of which they have the ability to change their shape. Others are characterized by a dense shell, mostly consisting of cellulose. Often the composition of the shell includes pectin. In some groups, the shell is heavily impregnated with lime or silica. Some cells contain one or more nuclei, others do not have a typical nucleus, only in the protoplast a stained peripheral part and an unstained central body. In some algae, dyes are located in special plasma bodies of various shapes, which are called chromatophores. For the most part, dense bodies - pyrenoids, rich in protein substances, are included in the chromatophores. Around the pyrenoids, starch is deposited, which is one of the products of assimilation. Reserve nutrients are oils, fats, leukosin, mannitol and glucose.[ ...]

Unlike other multicellular algae, brown algae, along with the usual single-celled sporangia (Fig. 121, 2), have multi-celled sporangia and gametangia, which are incorrectly called multicellular (Fig. 128, 1 a). Before the formation of zoospores or gametes, the contents of multi-cell receptacles are divided by thin partitions into chambers, in which they are enclosed in one nucleus with a portion of the cytoplasm. Each chamber develops one, rarely two zoospores or gametes. On the surface of the thallus of many brown algae, special multicellular hairs develop, which look like a thread from one row of cells with a growth zone at the base; cells of the growth zone divide more often than others and therefore have small sizes (Fig. 121, 1 b).[ ...]

Among the yellow-green algae there are representatives with a unicellular thallus (Fig. 188, 1,2,5; 190, 191), colonial (Fig. 189), multicellular (Fig. 192.1, 2) and non-cellular structure (Fig. 192 , 3). In addition, very peculiar algae with a multinuclear thallus in the form of a naked plasmodium are known here (Fig. 188, 3).[ ...]

Real algae are plants whose body is represented by a thallus. About 30,000 species of these organisms are known. There are both unicellular and multicellular algae. They are inhabitants mainly of freshwater reservoirs and seas, but soil algae and even snow and ice algae are found. Reproduction of unicellular algae occurs by division, multicellular forms reproduce both asexually and sexually. Once Virgil wrote - "nigilvilor algo" (there is nothing worse than algae). In our time, algae have acquired other assessments.[ ...]

Bacteria and blue-green algae (cyanoea) - two phylogenetically related groups - differ sharply from all other living things (including fungi) by the absence of a true nucleus and by the fact that DNA lies freely in their cell, immersed in the so-called nucleoplasm that is not separated from the cytoplasm by a nuclear membrane. They also lack mitochondria and complex flagella. Flagella in them (when they are available) are simpler and have a fundamentally different structure than in other organisms; their cell wall consists of a heteropolymeric substance murein, which has not been found in any other group of organisms. These organisms are called prokaryotes (Prokaryo-1a - pre-nuclear). All other organisms, both unicellular and multicellular, have a true nucleus, surrounded by a nuclear membrane and thus sharply separated from the cytoplasm. Such organisms are called eukaryotes (Eicaguola - nuclear). In addition to a clearly differentiated nucleus and cytoplasm, they also have mitochondria, and many also have plastids and complex flagella. Gradually, it became clear that the differences between prokaryotes and eukaryotes are much deeper and more fundamental than, for example, the differences between higher animals and higher plants (both are eukaryotes).[ ...]

Golden algae reproduce by simple cell division (Fig. 66, 4), as well as by the breakdown of colonies or multicellular thallus into separate parts. The sexual process is also known in the form of a typical isogamy, ho-logamy or autogamy. As a result of the lathing process, endogenous siliceous cysts (Fig. 68, 2; 73, 3) are formed, which are very diverse in the nature of the shell sculpture (Fig. 68, 2; 73, 3), which help golden algae survive adverse conditions.[ ...]

The filamentous structure in the world of algae is the simplest form multicellular thallus and is characteristic of a huge number of representatives from different departments. Cells in filamentous thalli are closely related to each other; in many cases, the presence of pores and plasmodesmata passing through transverse cell septa has been proven here. At the same time, the disintegration of filaments into sections and even into individual cells is a common method of vegetative propagation of many filamentous algae.[ ...]

Yellow-green algae reproduce by simple cell division or by the disintegration of colonies and multicellular thalli into separate parts. The sexual process is known in a few species and is represented by isogamy and oogamy. In some species, exogenous and endogenous cysts with a bivalve, often silicified shell are known in the development cycle (Fig. 189, 3).[ ...]

A distinctive feature of algae is the lack of differentiation into tissues and organs. The body of the simplest algae consists of one cell. Groups of cells can unite and form colonies - colonial forms. Multicellular algae can have a filamentous form or a lamellar structure.[ ...]

This vast class includes multicellular filamentous algae, whose cells are connected to each other by means of plasmodesmata, forming trichomes. Trichomes are naked or covered with mucous sheaths; trichomes contain or lack heterocysts. Reproduction is carried out by hormogonies, less often by spores.[ ...]

Decay products of blue-green algae. Blue-green algae belong to the group of the lowest, most primitive plants. In most cases, these are unicellular organisms, usually united in colonies. In some cells, with the help of mucus and outgrowths, they are connected in coenobia in the form of threads, giving an external picture of multicellularity (Fig. 9.1). They reproduce primarily by cell division. Blue-green algae live not only in water, but also on land (on the banks of water bodies, in soils and on their surface). These are the most common plants in the world. They are the first to populate unstructured soils and, together with bacteria, prepare them for development by other plants. These algae are generally aerobic organisms. They are capable of synthesizing carbohydrates, but they also use decaying organic substances.[ ...]

Morphologically, green algae are also the most diverse in comparison with other divisions. The range of their sizes is also extremely large, from the smallest single cells with a diameter of 1 - 2 microns to macroscopic plants measured in tens of centimeters in length. All the main types of asexual and sexual reproduction and all the main types of change in the forms of development are also found here. Most representatives in the vegetative state are haploid, some are diploid.[ ...]

This class includes exclusively multicellular forms of yellow-green algae, characterized by filamentous, multi-filamentous and lamellar body structures. Usually they lead an attached lifestyle. The thallus here looks like simple or branched, single-row or multi-row filaments and bushes or single-layer and multi-layer parenchymal plates, the cells of which are not immersed in the common mucus.[ ...]

The cells of multicellular filamentous algae are very diverse and peculiar. unicellular plants(Fig. 26 and 27). The cell of any of the latter is also very different from the cells of multicellular plants. She alone has to perform several functions, which in multicellular plants are divided between cells of different tissues.[ ...]

Finally, in the ubiquitous green protococcus algae (Protococcus viridis, Fig. 215, 5), which, together with other species, forms a green coating on the bark and stumps of trees, the ability of cells to divide in two mutually perpendicular directions is well expressed. Due to this, it can form parenchymal multicellular plates or raznotitchat thalli. The systematic position of this species is considered differently, and some algologists attribute it (under the name Pleurococcus vulgaris) to ulotrix algae. We consider this alga the pinnacle of the complication of organization that was achieved precisely within the protococcal as an independent class.[ ...]

Vegetative propagation of unicellular algae consists in dividing individuals in two. In multicellular algae, it occurs in several ways, including the mechanical destruction of the thallus into parts (by waves, current, as a result of nibbling by animals) or due to processes accompanied by the breakdown of threads into multicellular or unicellular parts. For example, the division of filaments of blue-green algae into parts is often preceded by the death of individual cells. Sometimes special formations are used for vegetative propagation. On the thalli of spha-celaria (from brown algae) buds grow, which fall off and germinate into new thalli. Chara algae form unicellular or multicellular nodules that overwinter and give new plants. In a number of filamentous algae (for example, in the green ulothrix), individual cells become rounded, accumulate a large amount of reserve nutrients and pigments, and their membrane thickens at the same time. They are able to survive adverse conditions when normal vegetative cells die, leading to the destruction of the thread. Filamentous blue-green algae have a similar type of akinetes, but they are sometimes called spores. Some red, brown, green and chara algae have creeping shoots on which new thalli grow.[ ...]

Cell - the basic structural unit of the body of algae, represented by either unicellular or multicellular forms. A completely unique group is made up of siphon algae: their thalli are not divided into cells, but there are unicellular stages in the development cycle. It is quite obvious that the cell here retains its significance as the main element, the development and differentiation of which lead to the formation of an unusual thallus.[ ...]

With all the variety of external forms, red algae are distinguished by a single plan of the structure of the thallus - at the heart of it in all multicellular crimson is a cellular branched thread. The parenchymal type of organization is virtually absent here.[ ...]

The flora is very diverse. Along with multicellular organisms, there are also unicellular organisms. They belong to the most primitive, evolutionarily more ancient forms. The plant kingdom is divided into two sub-kingdoms - Lower and Higher plants. The lower plants include various algae, the higher ones include spores (mosses, club mosses, horsetails, ferns) and seed plants (gymnosperms and angiosperms).[ ...]

Sexual reproduction in blue-green algae (bacteria) has not been found. They reproduce exclusively by vegetative means, often by simple equal-half cell division. It is possible to reproduce by spores, which, however, are never more than one in each cell. Spores contribute to survival under adverse conditions, since they are more resistant to them than vegetative cells. The spores are usually larger than the vegetative cells, their shell is thicker and the contents appear to be more condensed. Filamentous forms also reproduce by mobile multicellular sections of filaments, which are called hormogonia (Fig. 20). Hormogonia are capable of independent movement by sliding. Mobile hormogonia are formed both in trichomes, which are characterized by active movement, and in species with immobile trichomes. Hormogonia are multicellular, but may consist of several or only one cell. One organism is able to form several and even many hormogonia along the entire length of the trichome. Hormogonia do not have involucre like trichomes; they are covered only with mucus secreted by cells. There are unicellular formations of filamentous cyanophytes, which also serve the body for reproduction: gonidia - single cells covered with a mucous membrane; cocci - unicellular fragments without an individual shell; planococci are naked cells capable of active movement (they, in fact, do not differ from unicellular hormogonia). Under unfavorable conditions, some vegetative cells of cyanophycea become covered with a thicker shell, turning into resting spores, or akine-you. The formation of resting hormospores, consisting of 7-9 cells covered with an envelope, is also observed. Finally, it should be noted that sometimes several tens of small spores (endospores) are formed in several cells of a trichome.[ ...]

Then, 1.5-2 billion years ago, the first unicellular eukaryotes appeared and, as a result of the initial dominance of r-selection, a powerful population explosion of autotrophic algae occurred, which led to an excess of oxygen in the water and its release into the atmosphere. There was a transition of the reducing atmosphere into oxygen, which contributed to the development of eukaryotic organisms and the emergence of multicellular organisms about 1.4 billion years ago.[ ...]

Lower plants include a large group of unicellular and multicellular plants, united by the common name "algae".[ ...]

At the bottom of the reservoirs you can find green "pillows" formed by an accumulation of filamentous algae - spirogyra. This is a multicellular alga, each thread of which consists of elongated cylindrical cells with a spirally twisted chromatophore. Another representative of filamentous multicellular algae is ulotrix. Its structure is similar to spirogyra, but the chromatophore has the shape of a half ring.[ ...]

The most numerous group consists of endosymbioses of unicellular green and yellow-green algae with unicellular animals (Fig. 48, 1). These algae are called zoochlorella and zooxanthella, respectively. Of multicellular animals, green and yellow-green algae form endosymbioses with freshwater sponges, hydras, and others (Fig. 48, 2). Blue-green algae form with protozoa and some other organisms a peculiar group of endosymbioses, called syncyanoses; the resulting morphological complex of two organisms is called c and a no o m o m, and the blue-green algae in it are called c and a nells (Fig. 48, 3).[ ...]

The composition of planktonic organisms includes 2 groups: phytoplankton - a set of microscopic algae and zooplankton - animal plankton, including protozoa, rotifers and crustaceans. Among algae there are unicellular, multicellular and colonial forms. Depending on the predominance of one or another pigment, algae have a different color. They differ in the supply of nutrients and the method of reproduction.[ ...]

The genus Streblonema (S1; heliopeta) is an example of microscopic ectocarps growing on the surface of other algae and devoid of vertical vegetative branches, and if they do exist, they are short and do not differ from creeping threads. There are multicellular hairs with a basal growth zone (Fig. 121, 1).[ ...]

Microorganisms do not represent a single systematic group. These include unicellular and multicellular organisms of plant and animal origin: bacteria, bacteriophages, viruses, some algae and fungi, protozoa. The common distinguishing features of all microorganisms is their small size, which determines their features of high metabolic rate.[ ...]

Unilocular and myocell hosts are often incorrectly referred to as unicellular and multicellular, respectively. Both those and others can develop from one and from many cells. When in single-row thalli a group of cells turns into single-celled sporangia, then they speak of a chain of single-celled sporangia. Each of them, when ripe, opens with an independent hole. In the case of multi-cell receptacles, a chain of initial cells, each of which increases in size, gives a single multicellular multi-cell receptacle (Fig. 122, 1, 2). After the formation of chambers in it, it can be seen that some transverse partitions are thicker than others - these are the partitions of the mother cells. When ripe, the contents of such a container exits through one hole at the top. In some brown algae, unicellular multi-cell receptacles are narrow and the chambers are located in them in one row. Such formations are called single-row multi-celled sporangia (gametangia, Fig. 123). Multi-nest receptacles with nests located in several rows are considered multi-row.[ ...]

A cell is the basic structural and functional unit of all living organisms, an elementary living system. It can exist as a separate organism (bacteria, protozoa, some algae and fungi), and as part of the tissues of multicellular organisms. Only viruses are non-cellular forms of life.[ ...]

Against the background of primary zoning, based mainly on physical factors, secondary zoning is clearly visible - both vertical and horizontal; this secondary zoning manifests itself in the distribution of communities. The communities of each primary zone, with the exception of the euphotic zone, are subdivided into two fairly distinct vertical components - benthic, or bottom (benthos), and pelagic. In the sea, as well as in large lakes, plant producers are represented by microscopic phytoplankton, although large multicellular algae (macrophytes) may be of significant importance in some coastal areas. The primary consumers, therefore, are predominantly zooplankton. Medium-sized animals feed on either plankton or plankton-derived detritus, while large animals are mostly predators. There are only a small number of large animals, which, like large land animals such as deer, cows and horses, feed exclusively on plant foods.[ ...]

This family includes only one genus Splachnidium (Splachnidium) with a single species. Splachnidium rugosum (Splachnidium rugosum) grows in the southern hemisphere at the Cape of Good Hope and along the southern coast of Australia. The thallus of this plant is gelatinous, with a cavity inside; it consists of a central thick vertical shoot with a few weakly branched thick side branches. At the base of the thallus there is a disc for attaching to the ground. Conceptacles are formed at some points on the surface of the thallus, near the tops of the shoots. Here, intensive cell division and growth begin, with invaginations occurring inside the thallus. The formation of conceptacles is facilitated by the fact that the thallus has a loose filamentous structure and is equipped with cavities filled with mucus. In the past, wrinkled splanchnidium was attributed to fucus on the grounds that it has concept-culae and special large cells are located on the tops of the shoots. However, over time, it turned out that their conceptacles are formed in a completely different way than in Fucus, and special cells turned out to be unicellular endophytic green algae Codiolum, which is constantly present in the crustal layer of young shoot tops. Assimilation threads in Splanchnidium rugosa develop only on young parts, then they fall off, and the surface turns out to be formed by a dense bark of small cells. Splachnidium has multicellular hairs with an internal growth zone that grow on the inner surface of the conceptculae and protrude outward through their openings.

The value of algae in nature and human life.

The ubiquity of algae determines their great importance in the biosphere and economic activity person. Due to the ability to photosynthesis, they are the main producers of a huge amount of organic matter in water bodies, which are widely used by animals and humans.

Absorbing from the water carbon dioxide, algae saturate it with oxygen, necessary for all living organisms of water bodies. Their role is great in the biological cycle of substances, in the cyclic nature of which nature has solved the problem of the long existence and development of life on Earth.

In the historical and geological past, algae took part in the formation of rocks and chalk rocks, limestones, reefs, special varieties of coal, a number of oil shale, and were the ancestors of plants that inhabited the land.

Algae are extremely widely used in various branches of human economic activity, including the food, pharmaceutical and perfume industries. In eastern Southeast Asia, seaweed has long been used to make soups. They are grown in estuaries on bamboo sticks stuck in the mud or on wooden frames lowered into the water of narrow bays.

Marine and water cultures have begun to show encouraging results in many countries. Japanese cuisine uses seaweed to bake bread, add it to cakes, puddings and ice cream. Even the preservation of mushrooms is done with the help of algae. One row of mushrooms is placed in tubs, then one row of seaweed, etc. In many cities around the world, specialized cafes are open where you can try a variety of algae dishes. In addition, the presence of vitamins A, B1, B2, B12, C and D, iodine, bromine, arsenic and other substances was found in seaweed.

Algae have penetrated into agriculture and animal husbandry. Tomatoes, peppers, and watermelons ripen faster and yield more when sprinkled with seaweed meal. Cows and chickens become more productive when fed with algae concentrates.

The unicellular green chlorella produces a large amount of oxygen, accumulates organic matter using a smaller suspension volume, has a shorter growing season, reproduces very quickly, and the entire biomass of the algae can be used as food. Its nutritional qualities are the highest in flora. The protein content is 50% of the dry mass, it also contains all 8 amino acids necessary for human life, and all vitamins. These abilities of chlorella make it possible to use these microalgae for air regeneration in closed biological human life support systems during long-term space flights and scuba diving.

In our country and abroad, microalgae are cultivated in domestic and industrial Wastewater ah for the purpose of biological treatment and further use of their biomass for methane production or use in industry and agricultural production.

MEANING:

In nature:

enrich the atmosphere and hydrosphere with oxygen;

the main source of organic matter in water bodies;

participate in self-purification of natural and waste waters;

·indicators of pollution and salinity;

· participate in the circulation of calcium and silicon in soil formation;

In human life:

The most important components of ecosystems: food, dietary products, sources of raw materials for obtaining substances needed in industries (pharmacological, paper, textile), are used as fertilizers.

Algae are classified as lower plants. There are more than 30 thousand of them. Among them there are both unicellular and multicellular forms. Some algae are very big sizes(several meters in length).

The name "algae" suggests that these plants live in water (in fresh and marine). However, algae can be found in many humid places. For example, in the soil and on the bark of trees. Some types of algae are able, like a number of bacteria, to live on glaciers and in hot springs.

Algae are classified as lower plants because they do not have true tissues. In unicellular algae, the body consists of one cell, some algae form colonies of cells. In multicellular algae, the body is represented thallus(other name - thallus).

Since algae are classified as plants, they are all autotrophs. In addition to chlorophyll, the cells of many algae contain red, blue, brown, and orange pigments. The pigments are in chromatophores, which have a membrane structure and look like ribbons or plates, etc. A reserve nutrient (starch) is often deposited in chromatophores.

Algae breeding

Algae reproduce both asexually and sexually. Among the types asexual reproduction prevails vegetative. So, unicellular algae reproduce by dividing their cells in two. In multicellular forms, fragmentation of the thallus occurs.

However, asexual reproduction in algae can be not only vegetative, but also with the help of zoospore that are produced in zoosporangia. Zoospores are motile cells with flagella. They are able to actively swim. After some time, zoospores discard flagella, become covered with a shell and give rise to algae.

Some algae have sexual process, or conjugation. In this case, DNA exchange occurs between the cells of different individuals.

At sexual reproduction Multicellular algae produce male and female gametes. They are formed in special cells. At the same time, gametes of both types or only one (only male or only female) can be formed on one plant. After the release of the gametes, they merge to form a zygote. Conditions Usually, after wintering, algae spores give rise to new plants.

unicellular algae

Chlamydomonas

Chlamydomonas lives in organically polluted shallow reservoirs, puddles. Chlamydomonas is a unicellular algae. Its cell has an oval shape, but one of the ends is slightly pointed and has a pair of flagella on it. Flagella allow you to move quickly enough in the water by screwing.

The name of this algae comes from the words "chlamys" (clothes of the ancient Greeks) and "monad" (the simplest organism). The chlamydomonas cell is covered with a pectin membrane, which is transparent and does not adhere tightly to the membrane.

In the cytoplasm of chlamydomonas there is a nucleus, a photosensitive eye (stigma), a large vacuole containing cell sap, and a pair of small pulsating vacuoles.

Chlamydomonas has the ability to move towards light (thanks to stigma) and oxygen. Those. it has positive phototaxis and aerotaxis. Therefore, Chlamydomonas usually swims in the upper layers of water bodies.

Chlorophyll is located in a large chromatophore, which looks like a bowl. This is where the process of photosynthesis takes place.

Although Chlamydomonas is a plant capable of photosynthesis, it can also absorb ready-made organic substances present in the water. This property is used by man to purify polluted waters.

Under favorable conditions, Chlamydomonas reproduces asexually. At the same time, its cell discards flagella and divides, forming 4 or 8 new cells. As a result, chlamydomonas multiplies quite quickly, which leads to the so-called water bloom.

Under unfavorable conditions (cold, drought), chlamydomonas under its shell forms gametes in the amount of 32 or 64 pieces. Gametes enter the water and merge in pairs. As a result, zygotes are formed, which are covered with a dense shell. In this form, chlamydomonas tolerates adverse environmental conditions. When conditions become favorable (spring, rainy season), the zygote divides, forming four chlamydomonas cells.

Chlorella

Chlorella is a single-celled alga that lives in fresh water and moist soil. Chlorella has a spherical shape without flagella. She also does not have a light-sensitive eye. Thus, chlorella is immobile.

The shell of chlorella is dense, it contains cellulose.

The cytoplasm contains a nucleus and a chromatophore with chlorophyll. Photosynthesis is very intensive, so chlorella releases a lot of oxygen and produces a lot of organic matter. Just like chlamydomonas, chlorella is able to assimilate ready-made organic substances present in water.

Chlorella reproduces asexually by division.

Pleurococcus

Pleurococcus forms a green plaque on the soil, tree bark, rocks. It is a unicellular algae.

The pleurococcus cell has a nucleus, a vacuole, and a chromatophore in the form of a plate.

Pleurococcus does not form motile spores. It reproduces by cell division in two.

Pleurococcus cells can form small groups (4-6 cells each).

Multicellular algae

Ulotrix

Ulothrix is ​​a green multicellular filamentous algae. Usually lives in rivers on surfaces located near the surface of the water. Ulothrix has a bright green color.

Ulothrix threads do not branch, they are attached to the substrate at one end. Each thread consists of a number of small cells. Threads grow due to transverse cell division.

The chromatophore in ulotrix has the form of an open ring.

Under favorable conditions, some cells of the ulotrix filament form zoospores. Spores have 2 or 4 flagella. When a floating zoospore attaches to an object, it begins to divide, forming a filament of algae.

Under adverse conditions, ulotrix is ​​able to reproduce sexually. In some cells of its thread, gametes are formed that have two flagella. After leaving the cells, they merge in pairs, forming zygotes. Subsequently, the zygote will divide into 4 cells, each of which will give rise to a separate thread of algae.

Spirogyra

Spirogyra, like ulothrix, is a green filamentous algae. In fresh water, it is spirogyra that is most often found. Accumulating, it forms mud.

Spirogyra filaments do not branch, they consist of cylindrical cells. Cells are covered with mucus and have dense cellulose membranes.

The spirogyra chromatophore looks like a spirally twisted ribbon.

The nucleus of spirogyra is suspended in the cytoplasm on protoplasmic filaments. Also in the cells there is a vacuole with cell sap.

Asexual reproduction in spirogyra is carried out vegetatively: by dividing the thread into fragments.

Spirogyra has a sexual process in the form of conjugation. In this case, two threads are located side by side, a channel is formed between their cells. Through this channel, the content from one cell passes to another. After that, a zygote is formed, which, covered with a dense shell, overwinter. In the spring, a new spirogyra grows from it.

The value of algae

Algae are actively involved in the cycle of substances in nature. As a result of photosynthesis, they release large amounts of oxygen and fix carbon into organic substances that animals feed on.

Algae are involved in the formation of soil and the formation of sedimentary rocks.

Many types of algae are used by humans. So, agar-agar, iodine, bromine, potassium salts, and adhesives are obtained from seaweed.

AT agriculture algae are used as a feed additive in the diet of animals, as well as a potash fertilizer.

With the help of algae, polluted water bodies are cleaned.

Some types of algae are used by humans for food (kelp, porphyry).

Multicellular green algae

Examples of multicellular green algae are ulotrix and spirogyra. . Kinds genus, aulotriks They live mainly in fresh, less often in marine and brackish water bodies, as well as in the soil. Algae attach themselves to underwater objects, forming bright green bushes up to 10 cm in size or more.

Unbranched ulotrix filaments, consisting of one row of cylindrical cells with thick cellulose membranes, are attached to the substrate by a colorless conical basal cell that acts as a rhizoid. Characteristic is the structure of the chromatophore, which has the form of a parietal plate, forming an open belt or ring (cylinder). All cells, except for the basal one, are able to divide, causing a continuous growth of the thallus.

Asexual reproduction is carried out in two ways: by breaking up the filament into short sections, each of which develops into a new filament, or by the formation of four flagellar zoospores in the cells. They emerge from the mother cell, shed flagella one by one, attach sideways to the substrate, become covered with a thin cellulose membrane and grow into a new thread.

Reproduction of filamentous algae ulotrix: red arrows - asexual reproduction, blue arrows - sexual reproduction.

The sexual process is isogamous. After fertilization, the zygote first swims, then settles to the bottom, loses flagella, develops a dense membrane and a mucous stalk, which is attached to the substrate. This is a resting sporophyte. After a dormant period, the reduction division of the nucleus occurs and the zygote germinates with zoospores.

Thus, in the life cycle of ulotrix, there is an alternation of generations, or a change in sexual and asexual forms of development: a filamentous multicellular gametophyte (the generation that forms gametes) is replaced by a unicellular sporophyte - a generation that is represented by a kind of zygote on a stem and is able to form spores.

Spirogyra common in stagnant and slowly flowing waters, where it often forms large masses of "mud" of bright green color. It is a thin thread consisting of long cylindrical cells arranged in one row with a clearly visible cell wall. Outside, the threads are covered with a mucous membrane.

Spirogyra filamentous alga cell

A characteristic feature of spirogyra is a ribbon-like, spirally curved chromatophore located in the wall layer of the cytoplasm. In the center of the cell is the nucleus, enclosed in a cytoplasmic sac and suspended on cytoplasmic strands in a large vacuole.

Asexual reproduction is carried out by breaking the thread into short sections, while there is no sporulation. The sexual process is conjugation. In this case, two threads are usually located parallel to each other and grow together with the help of copulatory outgrowths or bridges. Their shells dissolve at the point of contact, and a through channel is formed, through which the compressed contents of the cell of one thread moves into the cell of another and merges with its protoplast. The zygote formed as a result of fertilization germinates after a dormant period. This is preceded by a reduction division of the nucleus: out of the four nuclei formed, three die off, and one remains the nucleus of a single seedling that emerges through a rupture in the outer layers of the zygote shell.

Spirogyra
(Spirogyra)

Spirogyra(Spirogyra Link.) green algae from the conjugate group (see Conjugatae), belongs to the Zygnemeae family. The body of Spirogyra is a non-branching thread, consisting of cylindrical cells. In the latter there is a chromatophore characteristic of Spirogyra (see): one or more spirally curled, green ribbons. Colorless bodies are placed in the chromatophores, around which starch grains, the so-called pyrenoids, are grouped. Very well visible in the microscope, the nucleus, suspended on protoplasmic filaments, is located in the middle of the cell. Spirogyra grows by intercalary (uniform) cell division. The sexual process of Spirogyra is copulation or conjugation: the cells of 2 adjacent filaments are interconnected by lateral outgrowths; the membranes separating these outgrowths are destroyed and, thus, a copulatory canal is obtained, through which the entire contents of one cell (male) passes into another (female) and merges with the contents of the latter; the cell in which the fusion has taken place (zygote) rounds off, separates from the filament and, dressing in a thick shell, turns into a zygospore. The zygospore overwinters and germinates into a young thread in spring. In the zygote, after the contents of the male and female cells merge, the chromatophore of the first cell dies and only the second remains, the nuclei first merge into one, which is then divided into 4 unequal in size (unequal division of the nucleus); of these, 2 smaller ones blur in the surrounding plasma, and 2 large ones, merging, form the nucleus of the zygote.

The described copulation between cells of different filaments (dioecious) is called ladder. In the case when a channel is formed between two adjacent cells of the same thread, copulation (single-house) is called lateral. In most Spirogyra, during the sexual process, the copulatory canal is always developed (subgenus Euspirogyra) and male and female cells are the same, in some, these cells are unequal in size, and the copulatory canal is very weakly developed or completely absent, so that the cells merge with each other directly ( subgenus Sirogonium). Due to the size of Spirogyra cells, reaching up to 0.01 mm in some of its species, due to the clarity of their structure, this algae is one of the best studied and serves as a classic object in the study of the anatomy of the cell and nucleus.

Green algae spirogyra

Spirogyra is one of the most common green algae in fresh waters of all parts of the world, and is also found in brackish waters. Its threads are collected in large green clusters that float on the surface of the water or creep along the bottom and are very often found in the mud of stagnant and flowing waters, in ponds, swamps, ditches, rivers, streams, pools, etc.

Spirogyra under the microscope

In total, up to 70 species of Spirogyra are known, differing from each other in the shape and size of cells and zygospores, as well as in the shape and number of m chromatophore ribbons located in them, and belonging, as mentioned above, to the 2nd departments - Euspirogyra (the most common: Sp tenuissima Hass., longata Kg. with one ribbon, Sp. nitida Kg. with several ribbons, Sp. grassa Kg. with very thick cells, etc.) and Sirogonium (Sp. stiktica Sm., etc.). For Russia, up to 40 types of Spirogyra are indicated

Ulotrix

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

The thallus of the ulotrix is ​​built according to the type of a single-row unbranched thread. It is composed of cells similar to each other in structure and function (Table 30, 2). Potentially, all cells are capable of dividing and participating in the growth of a plant, just as all cells can form spores and gametes. Only the cell at the base of the thread differs from the rest: with its help, the thallus is attached to the substrate (in attached forms). Ulothrix cells have considerable autonomy. This property is associated with the ability to regenerate and vegetative reproduction - individual cells or sections of threads easily break away from the threads and proceed to independent growth.

The order includes more than 16 genera. Despite the fact that all of their representatives are built as a simple single-row thread, important differences can be found in their organization, on the basis of which the whole order is divided into three groups. In algae of the first group, the thread is a series of cells loosely located in a thick mucous membrane. For example, algae genus geminella geminella. Interestingly, all ulotrix with a similar structure are planktonic organisms.

The second group includes those filamentous algae that vegetate as single cells or as short chains of 2-4 cells very loosely connected to each other. Threads are formed rarely and for a short time. An example of such a structure is genus Stichococcus(Stichococcus, Fig. 216, 2). The algae included in this group lead a terrestrial lifestyle.

The central group of the order is the third group, which includes algae, built like a typical multicellular filament, in which the cells are tightly connected to each other without the help of a mucous sheath. The algae belonging to this group are overwhelmingly attached organisms, at least when young. Their filaments are more permanent formations, they no longer break up so easily, and one can distinguish between the basal and apical parts in them. This includes several genera, including the central genus of the order - ulotrix(Ulothrix).

Species of ulotrix (at present, more than 25 of them are known) live mainly in fresh water bodies, and only a very few enter brackish and sea ​​waters. These algae can also settle on wet surfaces periodically wetted by splashes of surf or waterfalls.

One of the most widespread and well-studied species - ulothrix girdled(Ulothrix zonata).

The thallus of ulotrix consists of unbranched filaments of indeterminate length, which are attached to the substrate by a basal cell at the beginning of growth. Filament cells are cylindrical or slightly barrel-shaped, often short. Cell walls are usually thin, but often they thicken and may become stratified. Ulothrix cells, like cells of all algae of this order, contain a single parietal chloroplast with one or more pyrenoids and one nucleus located along the longitudinal axis of the cell. The chloroplast has the shape of a girdle that encircles the entire protoplast or only part of it.

Vegetative propagation of ulotrix is ​​carried out by fragmentation: the threads break up into short segments and each segment develops into a new thread. However, in this way, ulotrix does not reproduce as often as other algae of the order, which have a loose filament structure.

For asexual reproduction, zoospores are used, which are formed in all cells of the filaments, except for the basal one. The development of zoospores, as well as gametes, begins at the top of the thread and gradually captures the underlying cells.

Zoospores are ovoid cells with four flagella at the anterior end. They contain a stigma, several contractile vacuoles, and a parietal chloroplast. Ulothrix girdles has two types of zoospores - macrozoospores and microzoospores. Large macrozoospores have a broadly ovoid shape, often with a pointed posterior end, and a stigma located at the anterior end (. Microzoospores are smaller in size, have a rounded posterior end, and the stigma is located in the middle of the spore. The nature of microzoospores remains not yet entirely clear. Apparently, they represent is a transitional type between macrozoospores and gametes.

Zoospores are released through holes in the side wall of the cell. They are enclosed in a common mucous membrane, which ruptures a few seconds after release. After a short time, zoospores settle with their front end on the substrate, become covered with a thin cellulose membrane and germinate. Growing, the zoospore stretches vertically and differentiates into two parts. The lower part, devoid of a chloroplast, develops into an attachment cell; upper - divides with the formation of vegetative cells. In Ulothrix girdled, however, the zoospores are deposited posteriorly and begin to grow laterally rather than vertically.

Quite often, zoospores do not leave the sporangium, but secrete a thin shell and turn into aplanospores. The latter are released as a result of the destruction of the thread, but sometimes they can begin to germinate while in the sporangium.

During sexual reproduction, gametes are formed in threads in exactly the same way as zoospores. As a rule, they develop in the same threads as zoospores, or in similar ones. Most often, the transition to sexual reproduction is associated with the end of active growth and the onset of adverse conditions. Unlike zoospores, gametes have two flagella. The sexual process is isogamous. Fusion occurs between gametes of the same or different filaments. The zygote remains mobile for a short time, then settles down, loses flagella, dresses with a thick shell and turns into a unicellular sporophyte. It falls into a period of rest, during which the accumulation of reserve substances occurs. The shape of the sporophyte is varied, usually it is spherical with a smooth shell, in some marine species it becomes ovoid and sits on a mucous stalk.

BROWN ALGAE,

brown algae(Phaeophyta), a type of spore plants, including 240 genera (1500 species), of which 3 are freshwater, the rest are marine. Thallus is olive-green to dark brown in color due to the presence of a special brown pigment fucoxanthin (C40H56O6) in the chromatophores, which masks other pigments (chlorophyll a, chlorophyll c, xanthophyll and beta-carotene). Brown algae are diverse in shape and size (from microscopic branched filaments to 40-meter plants). In higher brown algae (for example, kelp algae), tissue differentiation and the appearance of conductive elements are observed. Brown algae are characterized by multicellular hairs with a basal growth zone, which are absent in other algae. Cell membranes contain cellulose and specific substances - algin and fucoidin. Usually there is one nucleus in each cell. Chromatophores are mostly small, discoid. Some species of brown algae have pyrenoids that bear little resemblance to the pyrenoids of other algae. In the cell around the nucleus, colorless vesicles accumulate with fucosan, which has many of the properties of tannin. Mannitol accumulates as a reserve product in the tissues of brown algae ( polyhydric alcohol) and laminarin (polysaccharide), less often oil. Brown algae reproduce sexually and asexually, rarely vegetatively. Typically, brown algae have a sporophyte and a gametophyte; in the higher ones (laminaria, desmarestia, etc.) they strictly alternate; in cyclospores, gametophytes develop on sporophytes; in primitives (ectocarp, chordaria, cutleria, etc.), the gametophyte or sporophyte may drop out of the development cycle or appear every few generations. Reproductive organs are single-celled or multi-celled sporangia. The multilocular sporangium, which more often functions as a gametangium, develops as a single cell or series of cells dividing by septa into chambers containing one gamete or spore inside. Meiosis usually occurs in unilocular sporangia; in dictyotes, in tetrasporangia. The sexual process is isogamy, heterogamy or oogamy. Pear-shaped spores and gametes, usually with an eye, have two flagella on the side, one directed forward, the other backward. brown algae are divided into 3 classes: Aplanosporophyceae (only dictyotes), Phaeosporophyceae (heterogenerate and isogenerate, with the exception of dictyotes) and Cyclosporophyceae (cyclosporophyceae). brown algae are common in all seas, especially in cold ones, where they form large thickets. They are used to obtain alginic acids and their salts - alginates, as well as feed flour and a powder used in medicine containing iodine and other trace elements. Some brown algae are used for food.

Brown algae: 1 - kelp; 2 - dictyota; 3 - ectocarpus; 4 - lessonia; 5 - neocystis; 6 - alaria; 7 - cystoseira; 8 - elachist bushes on the stem of another algae; 9 - fucus; 10 - dictyosiphon; 11 - Sargassum (all except 3 and 8 are greatly reduced; 3 - view under a microscope, enlarged approximately 40 times).

In multicellular representatives of green algae, the body ( thallus) has the form of filaments or flat leaf-shaped formations.

In flowing waters, you can often see bright green clusters of silky threads attached to underwater rocks and snags. This is a multicellular filamentous green alga ulotrix. Its threads consist of a number of short cells. In the cytoplasm of each of them are located nucleus and chromatophore in the form of an open ring. The cells divide and the thread grows.

Also, filamentous multicellular green algae are widespread in ponds and lakes. spirogyra . Together with other filamentous algae, spirogyra forms large accumulations of mud. Silky, slimy to the touch, the thinnest threads of mud are separate plants of spirogyra. The filament of spirogyra consists of many cells arranged in one row.

The structure of spirogyra can be seen under a microscope. Spirogyra cells are large. The cytoplasm in them is located along the membrane. The middle of each cell is occupied by vacuoles with cell sap. In the cytoplasm is a chromatophore in the form of a green spiral ribbon. In the center of the cell is a rounded nucleus, as if suspended on threads extending from the cytoplasm. Therefore, it seems that the nucleus has a stellate shape.

Spirogyra feeds in the same way as Chlamydomonas. In the chromatophores of spirogyra, organic matter, starch, is formed from carbon dioxide and water.

Many multicellular algae, like Chlamydomonas, reproduce asexually and sexually.

Reproduction of the filamentous alga ulotrix: red arrows - asexual reproduction, blue arrows - sexual reproduction

It is more convenient to observe the reproduction of algae in another filamentous multicellular algae, which is called ulotrix. On pitfalls and snags in flowing waters, you can often see bright green tufts of silky threads. This is ulotrix. Ulothrix reproduces asexually and sexually, just like many other algae.

During asexual reproduction, the contents of some cells of this filamentous algae are compressed into lumps. Lumps slip into the water through the holes formed in the cell membrane. They develop four flagella, allowing small cells - zoospores - to swim freely in the water. They are called zoospores because these cells are motile.

Spirogyra filamentous alga cell

Zoospores of ulotrix in structure and shape resemble unicellular chlamydomonas; soon zoospores settle on some underwater object. After that, each cell begins to divide and gradually turns into a multicellular filamentous algae.

In water, small mobile cells formed in different threads of algae merge in pairs and turn into one cell with a thick shell, called a spore.

After a dormant period, the spore begins to divide. Several cells are formed, each of which develops into an adult algae. In asexual reproduction, algal cells divide to form zoospores. Each zoospore then develops into an adult algae.

Multicellular green algae also live in the waters of the seas and oceans. An example of such algae is ulva, or sea lettuce, about 30 cm long and only two cells thick.

The most complex structure in this group of plants is charophytes living in freshwater reservoirs. These numerous green algae resemble horsetails in appearance. Chara alga nitella, or flexible glitter are often grown in aquariums.

The value of green algae in nature is great. Forming organic substances in its body, green algae absorb carbon dioxide from the water and, like all green plants, release oxygen, which is breathed by living organisms that live in the water. In addition, green algae, especially unicellular and multicellular filamentous algae, serve as food for fish and other animals.

brown algae

Brown algae are multicellular, mainly marine, plants with a yellowish-brown color of the thalli.

Their length ranges from microscopic to gigantic (several tens of meters). Thallus of these algae can be filamentous, spherical, lamellar, bushy. Sometimes they contain air bubbles that keep the plant upright in the water. Brown algae attach themselves to the ground rhizoids or disc-like overgrown base of the thallus.

In our Far Eastern seas and the seas of the Arctic Ocean, large brown algae kelp, or seaweed, grows. In the coastal strip of the Black Sea, the brown alga cystoseira is often found.

red algae

red algae, or scarlet, are mostly multicellular marine plants. Only a few species of crimson are found in fresh water. Crimson sizes usually range from a few centimeters to a meter in length (but there are also microscopic forms).

In form, red algae are very diverse and bizarre: filamentous, cylindrical, lamellar and coral-like, dissected and branched to varying degrees. They usually attach themselves to rocks, boulders, man-made structures, and sometimes other algae.

Due to the fact that red pigments are able to capture even a very small amount of light, purples can grow at considerable depths. They can be found even at a depth of 100-200 m.

Phyllophora, porphyry, etc. are widespread in the seas of our country.

In flowing waters, you can often see bright green clusters of silky threads attached to underwater rocks and snags. It is a multicellular filamentous green alga ulotrix 168 . Its threads consist of a number of short cells; located in the cytoplasm of each nucleus and a chromatophore in the form of an open ring. cells share, and the thread grows. Ulothrix feeds in the same way as Chlamydomonas.

At a time favorable for the life of algae, each cell, except for the one with which the thread is attached, can be divided into 2 or 4 motile cells with flagella - zoospores. They go out into the water, swim, then attach themselves to some underwater object and divide. This is how new filaments of algae are formed.

Under unfavorable conditions for life, numerous small motile gametes with flagella are formed in some cells of the algae. The gametes enter the water and merge in pairs.

This is how fertilization occurs. Usually the gametes that have arisen in the cells of different filaments merge. A zygote is formed. It is covered with a thick shell and can be dormant for a long time. Under favorable conditions, the zygote divides into 4 spore cells. Each of them, having landed on an underwater object, can give rise to a new filamentous alga ulotrix.

In stagnant or slowly flowing waters, slippery bright green lumps often float or settle to the bottom. They look like cotton wool and are formed by clusters of filamentous algae spirogyra. Elongated cylindrical cells are covered with mucus. Inside the cells - chromatophores in the form of spirally twisted ribbons 169 .

The value of green algae in nature is great. Forming organic substances, green algae absorb carbon dioxide from the water and, like all green plants They give off oxygen, which is breathed by living organisms that live in water. In addition, green algae, especially unicellular and filamentous, serve as food for fish and other animals.

Excessive growth of algae, for example in irrigation canals or fish ponds, can be harmful. To avoid this, periodically carry out the cleaning of channels and reservoirs from algae.

Marine brown and red algae

Brown and red algae are especially numerous in the seas and oceans."Living barriers" sailors call thickets of giant brown algae - a kind of underwater forests and meadows. Such algae can delay a boat, slow down a larger vessel, or prevent a seaplane from landing.

In our Far Eastern seas and the seas of the Arctic Ocean, a large brown multicellular kelp algae 170. Its body, or thallus, is attached to stones or underwater rocks by root-like outgrowths - rhizoids (from Greek words"riza" - root, "idos" - view). From the rhizoids, a narrow cylindrical part up to 50 cm long, the stem, extends upward. A dissected or whole leaf-shaped plate up to 5.5 m long develops on the stem.

Laminaria lives only at a relatively shallow depth, where enough sunlight penetrates.

Massive, sometimes complexly dissected thalli of other brown algae stretch under water for tens of meters, resembling giant snakes. Such giant algae live along the Pacific coast of South and North America. They also grow off the coast of Argentina, off the west coast South Africa, off the coast of Alaska, the Aleutian, Commander and Kuril Islands.

Red algae usually live at greater depths 170 . Their coloring contributes to the absorption of those rays of the sun that penetrate to a depth of 100 m.

Thallus of some large seaweeds are divided into sections similar to stems and flower leaves plants. But algae do not have roots, stems, leaves, flowers, fruits, or seeds. Reproduction of most marine brown and red algae occurs by spores.

The chromatophores of seaweed cells contain chlorophyll. Thanks to chlorophyll, photosynthesis occurs in the light.

At the same time, oxygen is released into the water, and carbon dioxide is absorbed from the water. In the body of the algae, organic substances are formed: sugar, starch, fats, squirrels.

In addition to chlorophyll, cell chromatophores contain orange, yellow, brown and red pigments. They determine the color of the algae.

Man uses seaweed in the chemical industry. From them, iodine, potassium salts, cellulose, alcohol, acetic acid. In addition, seaweed is used for livestock feed, used as fertilizer.

From red algae, the gelatinous substance agar-agar is extracted, which is widely used in the confectionery industry and in laboratory work related to the cultivation of microorganisms.

The peoples of coastal countries, such as Japan, use algae to prepare a variety of dishes. Laminaria, or, as it is also called, seaweed, is especially often eaten.

How does a person use seaweed?