To date, green algae are considered the most extensive group, which has about 20 thousand species. This includes both unicellular organisms and colonial forms, as well as plants with a multicellular thallus. large sizes. There are representatives that live in water (sea and fresh), as well as organisms adapted to survive on land in conditions high humidity.

Department of Green Algae: a brief description of

Main hallmark representatives of this group is their color - all species are characterized by a green or green-yellow color. This is due to the main pigment of cells - chlorophyll.

As already mentioned, the department brings together completely different representatives. There are unicellular and colonial forms, as well as multicellular organisms with a large, differentiated thallus. Some unicellular representatives move with the help of flagella, multicellular ones, as a rule, are attached to the bottom or live in the water column.

Although there are organisms with naked cells, most representatives have a cell wall. Main structural component the cell wall is cellulose, which, by the way, is considered an important systematic characteristic.

The number, size and shape of chloroplasts in a cell can vary depending on the type of plant. The main pigment is chlorophyll, in particular the a and b forms. As for carotenoids, plastids contain mainly beta-carotene and lutein, as well as small amounts of neosanthine, zeaxanthin and violaxanthin. Interestingly, the cells of some organisms have an intense yellow or even orange color - this is due to the accumulation of carotenes outside the chloroplast.

Some unicellular green algae have a specific structure - an eye that reacts to light in the blue and green spectrum.

The main storage product is starch, the granules of which are contained mainly in plastids. Only in some members of the order, reserve substances are deposited in the cytoplasm.

Department of Green Algae: Reproduction Methods

In fact, representatives of this detachment are characterized by almost all possible ways breeding. can occur by (unicellular representatives without a cell membrane), fragmentation of the thallus (this method is typical for multicellular and colonial forms). In some species, specific nodules are formed.

Asexual reproduction is represented by the following forms:

• zoospores - cells with flagella, capable of active movement;
• aplanospores - such spores do not have a flagellar apparatus, but well-developed cells are not capable of active movement;
• autospores - this type of spores is primarily associated with adaptation to the external environment. In this form, the body can wait dry and other adverse conditions.

Sexual reproduction can also be diverse - this is oogamy, and heterogamy, and hologamy, as well as isogamy and conjugation.

Squad Green algae: characteristics of some representatives

This group includes many famous representatives flora. For example, spirogyra and chlorella are also included in the order.

Chlamydomonas is a fairly well-known genus of green algae, which has an important practical value. This group includes single-celled organisms with a red eye and a large chromatophore that contains pigments. It is chlamydomonas that causes the "bloom" of reservoirs, puddles and aquariums. In the presence sunlight organic matter is produced by photosynthesis. But this organism can absorb substances from external environment. Therefore, chlamydomonas are often used to purify water.

green algae

The species richest division of algae are green algae, numbering up to 20 thousand species. They are distinguished by the pure green color of the thalli, which is associated with the predominance of chlorophyll over all other pigments. Along with chlorophyll, identical to chlorophyll higher plants, in the chloroplast there are also carotenes and xanthophylls. Sometimes the green color of algae can be masked by a red pigment (hematochrome). The reserve nutrient is the same as in higher plants - starch. Green algae are typical eukaryotes; cells may contain one or more nuclei. The shape of the cell is clearly fixed by dense cellulose and pectin membranes.

The morphological structure of representatives of this department is very diverse. Among green algae there are unicellular, colonial, coenobial (unlike a colony in a coenobia, the number of cells is always constant) and multicellular species. All types of vegetative body structure inherent in algae as a whole, except for amoeboid and tissue structures, can be found in the study of green algae. Green algae vary greatly in size: along with microscopic forms, there are species whose thallus length reaches several tens of centimeters and even a meter.

Green algae have all types of asexual and sexual reproduction. They often reproduce vegetatively.

The department of green algae is a very systematically fractional group. Until now, there is no consensus regarding the position in the system of the department of various classes. The criteria by which the department is divided into taxonomic ranks have not been established, which is associated with the extraordinary diversity of green algae. Most scientists divide the department into classes, depending on the structure of the vegetative body: volvox, chlorococcal (or protococcal), ulotrix, siphon, conjugates.

Volvox algae have a monadic structure of the thallus; most Volvox are solitary species, but some species form coenobia. The cell has a dense cellulose membrane, sometimes pectin, one cup-shaped chloroplast, in which pigments are concentrated. A light-sensitive eye is associated with the chloroplast - stigma, there is one or two pulsating vacuoles. The reserve nutrient is starch. Volvox algae are predominantly autotrophic, but there are cases mixed type nutrition, and sometimes heterotrophic. These algae usually reproduce vegetatively - by cell division, asexual and sexual reproduction is also found.

Among the volvox algae, only a small number of species can live in water bodies with high salinity. Most of them are inhabitants of stagnant, well-heated water bodies with fresh water, Their usual habitats are ditches, puddles, ponds. They feel very well, actively moving in the water column with the help of flagella, in reservoirs. treatment facilities rich in organic matter. Due to the ability to heterotrophic nutrition, they play an important role in the processes of self-purification of water in Wastewater oemah, are a food base for other inhabitants of the aquatic environment. With sufficient illumination, appropriate temperature and the presence of biogenic elements, they develop especially quickly, causing green and red "blooming" of water.

In the reservoirs of the region, such species as chlamydomonas spherical, Reinhard's chlamydomonas, marine carteria, lenticular phacotus, pectoral gonium, blackberry pandorina, graceful evdorina, spherical volvox, golden yellow volvox live in the reservoirs of the region.

Volvox algae originated from primary primitive amoeboid ancestors, their evolution followed the path of complicating the sexual process and the structure of the thallus.

Cells of representatives of the class of chlorococcal algae in a vegetative state are completely immobile. These are unicellular or coenobial species. The most primitive representatives of this class inherited the ocellus and flagella from their ancestors, but the latter are motionless and are called pseudocilia. Most species are microscopic and have the most different shape cells - spherical, fusiform, sickle-shaped. Cell membranes are cellulose, sometimes equipped with setae and spines. They reproduce vegetatively or asexually. The sexual process is known in a few species and is rarely observed.

The most famous in the algoflora of the region are common chlorella, four-tailed scenedesmus, beautiful dictyospherium, square crucigenia, perforated pediastrum and others.

Chlorococcal algae, leading their ancestry from Volvox, in turn, in the process of evolution gave rise to the next class - ulotrix. In the class of chlorococcal algae, the beginnings of new structures appeared for the first time in the organization of the vegetative body of algae - filamentous and lamellar.

Most representatives of the ulotrix class have a multicellular filamentous thallus, although lamellar species are also found. The thread consists of one or two layers of cells; it serves as the basis for all more complexly organized thalli. The latter are formed as a result of cell division in different axes. The lamellar thallus is single-layer, two-layer, may have a cavity inside. Ulothrix cells have one nucleus, one chloroplast, which occupies a parietal position in the form of a plate. Ulotriksovye can lead both an attached lifestyle and lie freely at the bottom of reservoirs. Reproduction - sexual, asexual, and also vegetative - by pieces of thallus. Pleurococcus vulgaris, trentepolia shady, ulothrix zona, enteromorpha enteromorpha, stygeoclonium slender are found in the region from the class of ulothrixes in the region.

Siphon algae have a so-called non-cellular structure. The thallus of these algae is one large cell, sometimes of very complex outlines. This group of algae is quite ancient, and at present its representatives are found mainly in tropical seas. Our flora is characterized by species in which the vegetative body is divided into multinuclear sections, or segments. These are weak cladophora, twisted cladophora, egagropile cladophora, hieroglyphic rhizoclonium, ringed spheroplea, graceful chetophora, Kützing's microtumnion, curly praziola. The chloroplast in such segments has a mesh structure. Sometimes these algae are even isolated as an independent class of siphonocladium ex. They usually reproduce sexually and asexually. In the life cycle, there is an alternation of generations - gametophyte and sporophyte.

Conjugates, or couplings, are predominantly microscopic algae, unicellular or filamentous. Unicellular linkages have bizarre outlines, distinguishable, of course, only under a microscope, and clusters of threads are visible to the naked eye. The algae of this department got their name from the method of reproduction: conjugation is a temporary connection of two individuals, which exchange parts of the nuclear apparatus and cytoplasm. In nature, conjugation occurs at a fairly high water temperature (not lower than 25 ° C), on a bright sunny day. Two cells or two filaments approach each other, and their contents merge, most often with the help of a bridge connecting either cells of different filaments or adjacent cells of the same filament. As a result of the fusion, a zygote is formed, which, after a dormant period, gives rise to a new plant. The cells of the conjugates in appearance are distinguished by exceptional elegance, delicacy of the ornaments covering their shells.

Conjugates can also reproduce vegetatively: in unicellular organisms, this is cell division, and in filamentous ones, the breakdown of filaments into separate cells, from which new filaments subsequently grow.

Conjugates are quite numerous in the reservoirs of the region. These are spirogyra, muzhotia, signema, Kützing's closterium, graceful closterium, needle closterium, lined closterium, truncated mycrasterium, Maltese cross mikrasteria, grape-like cosmarium, low cosmarium, shortened cosmarium, strange staurastrum, moon-shaped staurastrum, xanthidium ray.

Bright green, silky to the touch clusters of spirogyra are called "mermaid hair"

Green algae - the largest and most specific group among algae, characterized by a huge variety of species included here. Their evolution went from primitive flagellar species to multicellular ones, although the latter did not reach high level differentiation. Green algae in the process of development gave rise to charophytes - this is one branch of their evolution, the other branch led to the emergence of higher plants.

Algae, unicellular and multicellular forms of benthic algae. All morphological types of thallus are found here, except for rhizopodial unicellular and large multicellular forms with a complex structure. Many filamentous green algae are attached to the substrate only on early stages development, then they become free-living, forming mats or balls.

green algae
Diversity of siphon algae. Illustration from Ernst Haeckel's book Kunstformen der Natur, 1904
scientific classification
International scientific name
Chlorophyta Pascher, 1914
Systematics on Wikispecies Images at Wikimedia Commons ITIS NCBI EOL

Green algae are the most extensive given time department of algae: according to rough estimates, this includes from 13,000 to 20,000 species. All of them differ primarily in the pure green color of their thalli, similar to the color of higher plants and caused by the predominance of chlorophyll over other pigments.

Structure

Flagella cells of green algae are isoconts - flagella have a similar structure, although they can vary in length. There are usually two flagella, but there may also be four or more. Flagella of green algae do not have mastigonemes (unlike heterokonts), but may have fine hairs or scales.

Life cycles

The life cycles of green algae are very diverse. There are all sorts of types here.

Haplobiont with zygotic reduction ( Hydrodictyon reticulatum, Eudorina). Biflagellated gametes are released from the parent cell through a pore in its membrane, the fusion of gametes is carried out using a tube. Further, the zygote turns into a resting zygospore, and after a period of physiological rest, it germinates with the formation of 4 zoospores (as a result of meiotic division). Each zoospore forms a polyhedron and germinates, forming small spherical nets of adherent zoospores.

Haplo-diplobiont with spore reduction ( Ulva, Ulothrix, some types Cladophora). Biflagellated isogametes emerge from the mother cell, after which the gametes formed by different filaments merge in water. A four-flagellated zygote is formed, which actively soars in the water. After that, it descends on some kind of substrate and is covered with a dense shell, thus turning into a club-shaped cell (codiolum), followed by a stage of physiological rest. On the onset favorable conditions germinates into 4-16 zoospores or aplanospores, which, after a short period of swimming, attach to the substrate and germinate into new filaments. Various factors activate the exit from the dormant state: temperature increase, environmental change, etc.

Diplobiont with gametic reduction ( Bryopsis). The planozygote settles and germinates into a filamentous thallus with a large nucleus, the nucleus divides thus forming stephanocont zoospores germinating in the vegetative thallus.

Especially a lot of green algae develops in the spring, when all the stones in the littoral are covered with a continuous emerald coating of green algae, which contrasts sharply with the white snow lying on the coastal stones. A fleecy green carpet on the stones is formed by developing threads - ulotrix ( Ulothrix) and urospore ( Urospora). In summer, a lot of egagropila often develops ( Aegagropila linnaei) (syn. Cladophora aegagropila), which often has the appearance of a green mucous mass. On an open rocky coast, acrosiphonia forms bright green branched bushes ( acrosiphonia).

Role in nature and use

Some green algae (for example, ulva) are widely eaten. Chlorella is used as an indicator of the level of water pollution and is kept on spacecraft, submarines to clean the air from carbon dioxide.

Green algae is the most extensive of all algae divisions, numbering, according to various estimates, from 4 to 13 - 20 thousand species. All of them have a green color of the thalli, which is due to the predominance of chlorophyll in the chloroplasts. a and b over other pigments. Cells of some representatives of green algae ( Chlamydomonas, Trentepolia, Hematococcus) are colored red or orange, which is associated with the accumulation of carotenoid pigments and their derivatives outside the chloroplast.

Morphologically, they are very diverse. Among green algae, there are unicellular, colonial, multicellular and non-cellular representatives, actively mobile and immobile, attached and free-living. The range of their sizes is also extremely large - from several micrometers (which is comparable in size to bacterial cells) to 1–2 meters.

Cells are mononuclear or multinuclear, with one or more chromatophores containing chlorophyll and carotenoids. Chloroplasts are covered with two membranes and usually have a stigma, or peephole, a filter that conducts blue and green light to the photoreceptor. The eye consists of several rows of lipid globules. Thylakoids - structures where photosynthetic pigments are localized - are collected in stacks (lamellae) of 2–6. There is a stellate formation in the transition zone of the flagella. There are usually two flagella. The main component of the cell wall is cellulose.

Chlorophytes have different types of nutrition: phototrophic, mixotrophic and heterotrophic. The reserve polysaccharide of green algae - starch - is deposited inside the chloroplast. Chlorophytes can also accumulate lipids, which are deposited as droplets in the stroma of the chloroplast and in the cytoplasm.

Multicellular thalli are filamentous, tubular, lamellar, bushy or of a different structure and of various shapes. Of the known types of organization of the thallus in green algae, only the amoeboid is absent.

They are widely distributed in fresh and marine waters, in soil and in terrestrial habitats (on soil, rocks, tree bark, house walls, etc.). About 1/10 of the total number of species is distributed in the seas, which usually grow in the upper layers of water up to 20 m. Among them are planktonic, periphyton and benthic forms. In other words, green algae have mastered three main habitats of living organisms: water - earth - air.

Green algae have positive (movement towards a light source) and negative (movement away from a bright light source) phototaxis. In addition to light intensity, temperature also affects phototaxis. Positive phototaxis at a temperature of 160°C is exhibited by zoospores of species of the genera Hematococcus, Ulothrix, Ulva, as well as certain types of desmid algae, in which the movement of cells is carried out by secreting mucus through the pores in the shell.

Reproduction. Green algae are characterized by the presence of all known methods of reproduction: vegetative, asexual and sexual. .

Vegetative propagation in unicellular forms, the cell divides in half. Colonial and multicellular forms of chlorophyte reproduce by parts of the body (thallus, or thallus).

asexual reproduction in green algae it is widely represented. It is carried out more often by mobile zoospores, less often by immobile aplanospores and hypnospores. The cells in which spores (sporangia) are formed, in most cases, do not differ in any way from the rest of the vegetative cells of the thallus, less often they have a different shape and larger sizes. The zoospores that form may be naked or covered with a rigid cell wall. The number of flagella in zoospores varies from 2 to 120. Zoospores are of various shapes: spherical, ellipsoid or pear-shaped, mononuclear, devoid of a separate membrane, with 2–4 flagella at the anterior, more pointed end and a chloroplast at an expanded posterior end. They usually have pulsating vacuoles and a stigma. Zoospores are formed singly or, more often, among several of the internal contents of the mother cell, go outside through a round or slit-like hole formed in the shell, less often due to its general mucus. At the moment of exit from the mother cell, the zoospores are sometimes surrounded by a thin mucous bladder, which soon spreads out (Ulotrix genus).

In many species, instead of zoospores or along with them, motionless spores are formed - aplanospores. Aplanospores are asexual spores that lack flagella, but have contractile vacuoles. Aplanospores are considered as cells in which further development into zoospores is suspended. They also arise from the protoplast of the cell, among one or more, but do not produce flagella, but, having taken on a spherical shape, dress with their own membrane, in the formation of which the membrane of the mother cell does not participate. Aplanospores are released due to rupture or mucilage of the membranes of the mother cells and germinate after a period of dormancy. Aplanospores with very thick shells are called hypnospores. They usually take over the function of the resting stage. Autospores, which are smaller copies of immobile vegetative cells, lack contractile vacuoles. The formation of autospores correlates with the conquest of terrestrial conditions in which water cannot always be present in sufficient quantity.

sexual reproduction is carried out by gametes that occur in unchanged, slightly altered or significantly transformed cells - gametangia. Motile gametes of a monadic structure, biflagellated. The sexual process in green algae is represented by various forms: hologamy, conjugation, isogamy, heterogamy, oogamy. With isogamy, gametes are morphologically completely similar to each other and the differences between them are purely physiological. The zygote is dressed in a thick shell, often with sculptural outgrowths, contains a large amount of reserve substances and germinates immediately or after a certain dormant period. During germination, the contents of the zygote in most species are divided into four parts, which emerge from the shell and germinate into new individuals. Much less often, gametes develop into a new organism without fusion, on their own, without the formation of a zygote. This kind of reproduction is called parthenogenesis, and spores formed from individual gametes - parthenospores.

In heterogamy, both gametes differ in size and sometimes in shape. Larger gametes, often less mobile, are considered to be female, smaller in size and more mobile - male. In some cases, these differences are small, and then they simply talk about heterogamy, in others they are very significant.

If the female gamete is immobile and resembles an egg, then the mobile male becomes a spermatozoon, and the sexual process is called oogamy. The gametangia in which eggs are produced are called oogonia, they differ from vegetative cells both in shape and size. The gametangia in which spermatozoa are produced are called antheridia. The zygote, resulting from the fertilization of the egg by the sperm, forms a thick shell and is called oospore.

With typical oogamy, the eggs are large, immobile and most often develop one at a time in the oogonium, the spermatozoa are small, mobile, and are formed in large numbers in the antheridium. Oogonia and antheridia can develop on the same individual, in which case the algae are monoecious; if they develop on different individuals, they are dioecious. The fertilized egg is dressed in a thick brown shell; often, the cells adjacent to it give short branches that grow over the oospore, braiding it with a single-layer bark.

Life cycles. Most of the green algae life cycle haplobiont with zygotic reduction. In such species, only the zygote is the diploid stage - the cell resulting from the fertilization of the egg by the sperm. Another type of life cycle - haplodiplobiont with spore reduction - is found in Ulva, Cladophora and some Trentepoli. These algae are characterized by alternation of diploid sporophyte and haploid gametophyte. The haplodiplobiont life cycle with somatic reduction is known only in Praziols. The presence of a diplobiont life cycle in Briopsids and Dasikladiis is questioned.

In some Ulothrixes, the same individual can give rise to both zoospores and gametes. In other cases, zoospores and gametes are formed on different individuals, i.e. The life cycle of algae includes both sexual (gametophyte) and asexual (sporophyte) forms of development. The sporophyte is usually diploid; has a double set of chromosomes in cells, the gametophyte is haploid, i.e. has a single set of chromosomes. This is observed in cases where meiosis occurs during the formation of spores (spore reduction) and part of the life cycle of the alga from the zygote to the formation of spores takes place in the diplophase, and part from the spore to the formation of gametes in the haplophase. Such a development cycle is typical for species of the genus Ulva.

Within Ulotrix algae, zygotic reduction is widespread, when meiosis occurs during the germination of the zygote. In this case, only the zygote turns out to be diploid, the rest of the life cycle proceeds in the haplophase. Much less common is gametic reduction, when meiosis occurs during the formation of gametes. In this case, only gametes are haploid, and the rest of the cycle is diploid.

Systematics

So far, there is no single, well-established system of green algae, especially with regard to the grouping of orders into various proposed classes. For a very long time, the type of differentiation of the thallus was given primary importance in the allocation of orders in green algae. However, in recent times in connection with the accumulation of data on the ultrastructural features of flagellar cells, the type of mitosis and cytokinesis, etc., the heterogeneity of many of these orders is obvious.

The department includes 5 classes: Ulvophyceous - Ulvophyceae, Bripsodid - Bryopsidophyceae, Chlorophyceous - Chlorophyceae, Trebuxian - Trebouxiophyceae, Prasin - Prasinophyceae.

Class Ulvofiaceae -Ulvophyceae

About 1,000 species are known. The name of the class comes from the type genus Ulva. Includes species with filamentous and lamellar thallus. Life cycles are varied. Species are predominantly marine, less often freshwater and terrestrial. Some are part of lichens. In marine representatives, lime can be deposited in the cell walls.

Order Ulotrix -Ulotrichales.

Genus Ulotrix(Fig. 54). Kinds Ulothrix live more often in fresh water, less often in marine, brackish water bodies and in the soil. They attach to underwater objects, forming bright green bushes up to 10 cm in size or more. Unbranched threads Ulothrix, 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).

Rice. 54. Ulothrikc (by:): 1 - filamentous thallus, 2 - zoospore, 3 - gamete, 4 - copulation of gametes

asexual reproduction Ulothrix It is carried out in the following 2 ways: by disintegration of the filament into short sections that develop into a new filament, or by the formation of four-flagellated zoospores in the cells. Zoospores emerge from the mother cell, drop flagella one by one, attach sideways to the substrate, are covered with a thin cellulose membrane and germinate into a new thread. 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. So in the life cycle Ulothrix 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.

Order Ulviaceae -Ulvales. They have a lamellar, sac-like, tubular or, rarely, filamentous thallus of various shades of green. Along the edge of the plate, they can be wavy or folded; for attachment to the substrate, they are equipped with a short leg or base with a small basal disc. Marine and freshwater species. The most common in the coastal waters of the Far Eastern seas are the species of the genera Ulva, Monostroma, Kornmannia and Ulvaria.

Genus Ulva(Fig. 55). The thallus is a light green or bright green, thin two-layer, often perforated plate or a single-layer hollow tube attached to the substrate with a base narrowed into a short petiole.

Rice. 55. Ulva: BUT- appearance Ulva fenestrated, B- cross section of the thallus, AT- appearance Ulva intestines

Change of forms of development in the life cycle Ulva reduced to isomorphic, when the asexual stage (sporophyte) and sexual stage (gametophyte) are morphologically similar to each other, and heteromorphic, when they are morphologically different. The gametophyte is multicellular, lamellar, the sporophyte is unicellular. On gametophytes, biflagellated gametes are formed, on sporophytes, four-flagellated zoospores are formed.

Species of the genus are found in the seas of all climatic zones, although they prefer warm waters. For example, in the shallow waters of the Black and Japanese Seas, Ulva is one of the most widespread genera of algae. many kinds Ulva endure water desalination; they are often found in river mouths.

Briopsid class–Bryopsidophyceae

About 500 species are known. The thallus is non-cellular. Formed by simple or intertwined siphon threads forming complex structures. Thallus in the form of bubbles, bushes, spongy, dichotomously branched bushes. The thallus is segmented, imitating multicellular, from several or many nuclear cells. Threads and bushes of all shades of green or brownish.

Briopsid order– Bryopsidales

Most species are found in fresh and brackish waters. Some of them grow on soil, rocks, sand, and sometimes salt marshes.

Genus bryopsis- filiform bushes up to 6-8 cm in height, pinnately or irregularly branched, upper branches with constrictions at the base. Thallus of siphon non-cellular structure. It grows in single bushes or small clumps in the coastal zone, lives in warm and temperate seas (Appendix, 7B).

Genus Codium- cord-like dichotomously branched bushes 10–20 cm tall, spongy. soft, attached with a disc-shaped sole. The inner part of the thallus is formed by intricately intertwined siphon threads. It grows on soft and hard soils in the sublittoral zone up to a depth of 20 m as single plants or in small groups (Appendix, 7A, B).

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

Rice. 56. Caulerpa: A - appearance of the thallus; B - cut of thallus with cellulose beams

Caulerpa thallus, despite its large size, does not have a cellular structure - it completely lacks transverse partitions, and formally it is one giant cell (Fig. 56). This structure of the thallus is called siphon. Inside the thallus of the caulerpa is a central vacuole surrounded by a layer of cytoplasm containing numerous nuclei and chloroplasts. Various parts of the thallus grow at their tops, where the cytoplasm accumulates. The central cavity in all parts of the thallus is crossed by cylindrical skeletal cords - cellulose beams, which give the body of the algae mechanical strength.

Caulerpa easily reproduces vegetatively: when the older parts of the thallus die off, some sections of it with vertical shoots become independent plants. Species of this genus live mainly in tropical seas, and only a few enter subtropical latitudes, for example, common in the Mediterranean Sea Caulerpa sprouting. This algae prefers shallow, calm waters, such as lagoons that are sheltered from the constant surf. coral reefs, and settles both on various solid substrates - stones, reefs, rocks, on sandy and silty soil.

Class Chlorophyceous–Chlorophyceae

About 2.5 thousand species are known. Thallus unicellular or colonial monnadous, free-living.

Volvox order -Volvocales.

Genus Chlamydomonas(Fig. 57) includes over 500 species of unicellular algae that live in fresh, shallow, well-heated and polluted water bodies: ponds, puddles, ditches, etc. With their mass reproduction, the water acquires a green color. Chlamydomonas also lives on soil and snow. Her body is oval, pear-shaped or spherical. The cell is covered with a dense sheath, often lagging behind the protoplast, with two identical flagella at the anterior end; with their help, chlamydomonas actively moves in the water. The protoplast contains 1 nucleus, cup-shaped chromatophore, stigma and pulsating vacuoles.

Rice. 57. Structure and development of Chlamydomonas: A - vegetative individual; B - palmeloid stage; B - reproduction (young individuals inside the mother cell)

Chlamydomonas reproduces predominantly asexually. When the water body dries up, they multiply by dividing the cell in half. The cells stop, lose their flagella, their cell walls become mucilaginous, and in this immobile state, the cells begin to divide. The walls of the resulting daughter cells are also mucilaginous, so that as a result a system of mucous wrappers nested into each other is formed, in which immobile cells are located in groups. This is palmelle algal condition. When they enter the water, the cells again form flagella, leave the mother cell in the form of zoospores, and pass to a single monadic state.

Under favorable conditions, chlamydomonas intensively reproduces in a different way - the cell stops, and its protoplast, somewhat lagging behind the wall, sequentially divides longitudinally into two, four or eight parts. These daughter cells form flagella and emerge as zoospores, which soon begin to reproduce again.

The sexual process in Chlamydomonas is isogamous or oogamous. Smaller gametes are formed inside the mother cell in the same way as zoospores, but in more(16, 32 or 64). Fertilization takes place in water. The fertilized egg is covered with a multi-layered membrane and settles to the bottom of the reservoir. After a dormant period, the zygote divides meiotically to form 4 haploid daughter Chlamydomonas.

Genus Volvox- the most highly organized representatives of the order, form giant colonies consisting of hundreds and thousands of cells. The colonies look like slimy, up to 2 mm in diameter, balls, in the peripheral layer of which there are up to 50 thousand cells with flagella, fused with their mucilaginous side walls with each other and connected by plasmodesmata (Fig. 58). Internal cavity

Rice. 58. Appearance Volvox colonies

the ball is filled with liquid mucus. There is a specialization of cells in the colony: its peripheral part is made up of vegetative cells, and larger reproductive cells are scattered between them.

About a dozen of the colony cells are gonidia, cells of asexual reproduction. As a result of repeated divisions, they give rise to young, daughter colonies, which fall inside the parent ball and are released only after its destruction. The sexual process is oogamy. Oogonia and antheridia also arise from reproductive cells. Colonies are monoecious and dioecious. Species of the genus are found in ponds and oxbows of rivers, where during the period of intensive reproduction they cause "blooming" of water.

Class Trebux -Trebouxiophyceae

The class is named after the type genus Trebouxia. Includes mostly unicellular coccoid forms. There are sarcinoid and filamentous representatives. Freshwater and terrestrial, rarely marine forms, many form symbioses. About 170 species.

Chlorella order -Chlorellales. Unites coccoid autospore representatives.

Genus Chlorella- unicellular algae in the form of a motionless ball. The cell is dressed in a smooth shell; contains one nucleus and parietal, whole, dissected or lobed chromatophore with pyrenoid. The cell wall of a number of species, along with cellulose, contains sporopollenin, a substance extremely resistant to the action of various enzymes, which is also found in pollen grains and spores of higher plants. Chlorella reproduces asexually, producing up to 64 immobile autospores. There is no sexual reproduction. Chlorella common in various water bodies, found on damp soil, tree bark, is part of lichens.

Trebux order - Trebouxiales . Includes genera and species that are part of lichens.

Genus Trebuxia- unicellular algae. Spherical cells have a single axial stellate chloroplast with one pyrenoid. Asexual reproduction is carried out by naked zoospores. It occurs either in a free-living form in terrestrial habitats (on the bark of trees), or as a lichen photobiont.

Class Prazinovye -Prasinophyceae

The name of the class comes from the Greek prasinos - green. Flagellated or, less commonly, coccoid or palmelloid unicellular organisms.

Order Pyramimonadaceae - Pyramimonadales. Cells bear 4 or more flagella, three layers of scales. Mitosis is open, with the spindle remaining in telophase, cytokinesis occurs due to the formation of a fission furrow.

Genus Pyramimonas- unicellular organisms (Fig. 59). From the anterior end of the cell, 4–16 flagella extend, which can be five times longer than the cell. The chloroplast is usually single, with one pyrenoid and one or more ocelli. Cells and flagella are covered with several layers of scales. Widespread in fresh, brackish and marine waters. Found in plankton and benthos, can cause "bloom" of water.

Rice. 59. Algae appearance Pyramimonas

Order Chlorodendrous– Chlorodendrales. The cells are compressed, with four flagella, covered with theca, mitosis is closed, cytokinesis occurs due to the formation of a fission furrow.

Genus Tetraselmis may occur as motile four-flagellated cells or as immobile cells attached by mucous stalks. The cells are covered with theca. During cell division, a new theca is formed around each daughter cell within the maternal theca. At the anterior end of the cell, flagella emerge through an opening in the theca, which are covered with hairs and scales. Chloroplast one, with basal pyrenodes. The cells are usually green, but sometimes turn red due to the accumulation of carotenoids. Marine representatives, can live in marine flatworms.

Ecology and significance

Green algae are widely distributed throughout the world. Most of them can be found in fresh water, but there are many brackish and marine forms. Filamentous green algae, attached or loose, along with diatoms and blue-greens, are the predominant benthic algae in continental waters. They are found in water bodies of different trophicity (from dystrophic to eutrophic) and with different content of organic substances (from xeno- to polysaprobic), hydrogen ions (from alkaline to acid), at different temperatures (thermo-, meso- and cryophiles).

Among green algae there are planktonic, periphyton and benthic forms. In the group of marine picoplankton, prazine algae Acuteococcus considered the smallest eukaryotic free-living cell. There are species of green algae that have adapted to life in soil and terrestrial habitats. They can be found on the bark of trees, rocks, various buildings, on the soil surface and in the air column. In these habitats, representatives of the genera are especially common. Trentepolia and Trebuxia. Green algae vegetate in hot springs at a temperature of 35–52°C, and in some cases up to 84°C and above, often with an increased content of mineral salts or organic substances (heavily polluted hot wastewater from factories, factories, power plants or nuclear power plants). They also predominate among cryophilic algae species. They can cause green, yellow, blue, red, brown, brown or black "blooms" of snow or ice. These algae are found in the surface layers of snow or ice and multiply intensively in melt water at a temperature of about 0 °C. Only a few species have dormant stages, while most lack any special morphological adaptations to low temperatures.

In oversalted water bodies, unicellular mobile green algae predominate - hyperhalobes, the cells of which are devoid of a membrane and are surrounded only by a plasmalemma. These algae are distinguished by a high content of sodium chloride in the protoplasm, high intracellular osmotic pressure, accumulation of carotenoids and glycerol in cells, and a high lability of enzyme systems and metabolic processes. In salt water bodies, they often develop in large numbers, causing red or green "bloom" of salt water bodies.

Microscopic unicellular, colonial and filamentous forms of green algae have adapted to the adverse conditions of existence in the air. Depending on the degree of moisture, they are divided into 2 groups: air algae, living in conditions of only atmospheric moisture, and, therefore, experiencing a constant change in humidity and drying; aquatic algae exposed to constant irrigation with water (under the spray of a waterfall, surf, etc.). The conditions for the existence of algae in aerophilic communities are very peculiar and are characterized, first of all, by frequent and abrupt changes in two factors - humidity and temperature.

Hundreds of species of green algae live in the soil layer. The soil as a biotope is similar to both aquatic and air habitats: it contains air, but saturated with water vapor, which ensures breathing of atmospheric air without the threat of drying out. Intensive development of algae as phototrophic organisms is possible only within the limits of light penetration. In virgin soils, this is a surface layer of soil up to 1 cm thick; in cultivated soils, it is slightly thicker. However, in the thickness of the soil, where light does not penetrate, viable algae are found at a depth of up to 2 m in virgin soils and up to 3 m in arable soils. This is explained by the ability of some algae to switch to heterotrophic nutrition in the dark. Many algae remain dormant in the soil.

To maintain their vital activity, soil algae have some morphological and physiological features. These are relatively small sizes of soil species, as well as the ability to abundantly form mucus - mucous colonies, sheaths and wrappers. Due to the presence of mucus, algae quickly absorb water when moistened and store it, slowing down drying. A characteristic feature of soil algae is the "ephemeral nature" of their vegetation - the ability to quickly move from a state of rest to active life and vice versa. They are also able to tolerate different fluctuations in soil temperature. The range of survival of a number of species lies in the range from -200 to +84 °C and above. Terrestrial algae form an important part of the vegetation of Antarctica. They are painted almost black, so their body temperature is higher than the temperature environment. Soil algae are also important components of the biocenoses of the arid (dry) zone, where the soil heats up to 60–80°C in summer. Dark mucous covers around the cells serve as protection against excessive insolation.

A peculiar group is represented by endolithophilic algae associated with a calcareous substrate. First, it is drilling algae. For example, algae from the genus Homontia they drill shells of barley and toothless, they are introduced into the calcareous substrate in fresh water. They make the lime substrate loose, easily amenable to various effects of chemical and physical factors. Secondly, a number of algae in fresh and marine water bodies are able to convert calcium salts dissolved in water into insoluble ones and deposit them on their thalli. A number of tropical green algae, in particular Galimedes deposits calcium carbonate in the thallus. They accept Active participation in reef building. Giant deposits of remains Galimedes, sometimes reaching 50 m in height, are found in continental shelf waters associated with the Great Barrier Reef in Australia and other regions, at a depth of 12 to 100 m.

Green trebux algae, entering into a symbiotic relationship with fungi, are part of lichens. About 85% of lichens contain unicellular and filamentous green algae as a photobiont, 10% - cyanobacteria, and 4% (or more) contain both blue-green and green algae. They exist as endosymbionts in the cells of protozoans, cryptophytes, hydras, sponges, and some flatworms. Even the chloroplasts of individual siphon algae, for example Codium, become symbionts for nudibranch molluscs. These animals feed on algae, the chloroplasts of which remain viable in the cells of the respiratory cavity, and in the light they photosynthesize very efficiently. A number of green algae develop on the fur of mammals. Endosymbionts, undergoing morphological changes in comparison with free-living representatives, do not lose the ability to photosynthesize and multiply inside the host cells.

Economic importance. The ubiquity of green algae determines their great importance in the biosphere and human economic activity. Due to their ability to photosynthesize, they are major producers huge amount organic matter in water bodies which are widely used by animals and humans. Absorbing carbon dioxide from water, green algae saturate it with oxygen, which is necessary for all living organisms. Their role in the biological cycle of substances is great. Rapid reproduction and a very high assimilation rate (approximately 3-5 times higher than that of land plants) lead to the fact that the mass of algae increases more than 10 times per day. At the same time, carbohydrates accumulate in chlorella cells (in breeding strains, their content reaches 60%), lipids (up to 85%), vitamins B, C and K. Chlorella protein, which can account for up to 50% of the dry mass of the cell, contains all the essential amino acids. Species Unique Ability Chlorella to assimilate from 10 to 18% of light energy (against 1–2% in terrestrial plants) allows this green algae to be used for air regeneration in closed biological human life support systems during long-term space flights and scuba diving.

A number of green algae species are used as indicator organisms in the monitoring system of aquatic ecosystems. Along with the phototrophic way of feeding, many unicellular green algae (chlamydomonas) are able to absorb organic substances dissolved in water through the shell, which contributes to the active purification of polluted waters in which these species develop. Therefore they are used for cleaning and post-treatment polluted waters , as well as how feed in fishery waters.

Some types of green algae are used by the population of a number of countries for food. For food purposes, for example, in Japan, species of the genus Ulva. These algae are widely used, especially in countries South-East Asia, called Sea lettuce. Ulvae in terms of protein content (up to 20%) are noticeably superior to other types of algae. Certain types of green algae are used in as producers of physiologically active substances. Green algae are a good model object for various biological studies. Types of Hematococcus are cultivated to obtain astaxanthin, Botryococcus - to obtain lipids. At the same time, the death of fish is associated with the “blooming” of the water of one of the lakes in Taiwan, caused by Botryococcus.

Types of childbirth Chlorella and Chlamydomonas - model objects to study photosynthesis in plant cells. Chlorella, due to its very high reproduction rate, is an object of mass cultivation for use in various fields

The surface films of green algae have a large anti-erosion value. Certain unicellular species of green algae, which secrete abundant mucus, are of binding importance. The mucous membranes of the cell membranes stick the soil particles together. The development of algae affects the structuring of fine earth, giving it water resistance and preventing removal from the surface layer. Soil moisture under algal films is usually higher than where they are absent. In addition, the films reduce the water permeability of the soil and slow down the evaporation of water, which also affects the salt regime of the soil. The leaching of easily soluble salts from the soil is reduced; their content under algae macrogrowths is higher than in other areas. At the same time, the flow of salts from the deep layers of the soil slows down.

Soil algae also influence the growth and development of higher plants. By releasing physiologically active substances, they accelerate the growth of seedlings, especially their roots.

Among the green algae that live in polluted water bodies, chlorococcal algae, which are resistant to long-term exposure to many toxic substances, usually dominate.

Algae cells are capable of accumulating various chemical elements, and their accumulation coefficients are quite high. Powerful concentrators are freshwater green algae, especially filamentous ones. At the same time, the intensity of accumulation of metals in them is much higher than in other freshwater hydrobionts. Of considerable interest is the ability of algae to concentrate radioactive elements. Dead cells of algae retain the accumulated elements no less firmly than living ones, and in some cases desorption from dead cells is less than from living ones. The ability of a number of genera ( Chlorella, Scenedesmus etc.) to concentrate and firmly retain chemical elements and radionuclides in their cells, which makes it possible to use them in specialized purification systems for decontamination industrial wastewater, for example, for additional treatment of low-level wastewater from nuclear power plants.

Some green algae are antagonists of the influenza virus, poliovirus and others. Biologically active substances secreted by algae play an important role in water disinfection and suppression of vital activity of pathogenic microflora.

In special biological ponds, algal and bacterial communities use for breaking down and detoxifying herbicides. The ability of a number of green algae to hydrolyze the herbicide propanil, which is rapidly destroyed by bacteria, has been proven.

test questions

Name the characteristic features of the cell structure of green algae.

What pigments and types of nutrition are known in green algae?

How do green algae reproduce? What are zoospores, aplanospores, autospores?

What are the classes of green algae?

name characteristics green algae of the class Ulvophycia.

Name the characteristic features of green algae of the class Briopsida.

Name the characteristic features of green algae of the Chlorophyceous class.

Name the characteristic features of green algae of the class Trebuxia.

Name the characteristic features of green algae of the class Prasinaceae.

Where are green algae found? Describe their main ecological groups.

The role and importance of green algae in nature.

What is the economic importance of green algae?

What is "water bloom"? Participation of green algae in biological water treatment.

Green algae as non-traditional sources of energy.

Algae are characterized by both sexual and asexual reproduction, which can take place vegetatively (separation of sections of the thallus) or with the help of sporulation. Algae form two types of spores: motile, having flagella (zoospores) and immobile, without flagella (aplanospores).

Sexual reproduction takes place in four main forms.

1. hologamy - non-specialized cells-organisms merge. It is inherent in low-organized unicellular algae.

2. isogamy - gametes are the same (there is no separation of sexes)

3. heterogamy - gametes are morphologically the same, but differ physiologically or genetically (there is a separation of sexes)

4. oogamy - gametes differ in structure and mobility: the egg is large and immobile, and the spermatozoa are small and equipped with a flagellum.

In addition to these four ways sexual reproduction of algae is inherent in the sexual process (but not reproduction) in the form conjugations. In this case, the fusion of two non-specialized cells of the thallus occurs. First, the thalli of algae approach each other, then a cytoplasmic bridge is formed between the cells of two individuals, along which the contents of one cell flows into another. After the fusion of the nuclei, a diploid zygote is formed.

3. Department of Green Algae. Features of the structure and reproduction.

Division Green algae is a fairly numerous group of algae (13,000) living in fresh and salt water bodies, rarely on the soil. This group includes unicellular, multicellular and colonial organisms. For multicellular green algae, the most common form of thallus is filamentous and lamellar.

Green algae are a relatively low-organized and non-specialized group of algae. Based on this, many scientists believe that it was green algae that gave rise to higher land plants.

Features of the structure of the cell of green algae

The cell wall consists of carbohydrates, the structure of which is similar to that of higher plants.

Chromatophores (1 large or several small) are diverse in structure (stellate, reticulate, lamellar, spiral), but rarely in the form of a biconvex lens

there are always pyrenoids around which starch is deposited

chlorophylls A and B participate in photosynthesis, carotenoids (carotenes, xanthophylls) act as additional pigments

Starch acts as a reserve

Features of reproduction of green algae

In green algae, both asexual and sexual reproduction are noted, and sexual reproduction may differ in different types. For most species of green algae, the main phase in ontogenesis is the gametophyte, and only the zygote (a primitive feature of organization) is the diploid stage in the life cycle.

We will analyze the life cycle of green algae using the example of chlamydomonas and spirogyra.

It is a unicellular, motile, biflagellate algae with a cup-shaped chromatophore. The organism itself is haploid, in favorable conditions it reproduces with the help of zoospores. The cell stops, loses its flagella, and undergoes several mitotic divisions. As a result, 4 or 8 haploid biflagellated spores are formed under the membrane of the mother cell. Then the shell of the mother cell breaks, the zoospores enter the water and germinate into an adult plant.

When unfavorable conditions occur, the sexual process occurs in the form of chologamy. Two Chlamydomonas approach each other, lose their flagella, and fuse to form a zygote. The zygote is covered with a very dense shell and sinks to the bottom. The zygote will be at rest until the onset of favorable conditions. Then she will share meiosis with the formation of 4 haploid cells, each of which will give rise to a new organism. The sexual process also occurs in the case of overpopulation of the reservoir.

S p i r o g i r a – one of the most common green filamentous algae in freshwater basins. Long threads of thalli form a mud of bright Green colour floating freely in the water.

Spirogyra filaments consist of one row of identical, elongated, cylindrical cells, having a length of several millimeters to 8-10 cm. Each cell is covered with a two-layer membrane surrounded by a mucous membrane. Chromatophores (1-3) look like a spirally twisted ribbon. A large nucleus seems to be suspended in the center of the cell on strands of cytoplasm.

During the summer, spirogyra can reproduce by immobile spores, or vegetatively by random breaking of the filament. From each segment of the thread, new threads are formed.

Spirogyra is characterized by a sexual process in the form conjugations. There are no special sex cells. Two outwardly similar strands of spirogyra approach each other, being parallel. In the contact area, outgrowths are formed through which the contents of one cell overflow into another. The nuclei merge, the zygote is covered with a dense shell and sinks to the bottom of the reservoir. After some time, the zygote germinates. At the same time, its diploid nucleus divides meiotically, forming 4 haploid nuclei. The nuclei are not the same in size: one is large and three are small, they soon die. From a large nucleus, together with the contents of the zygote, it forms a seedling of a new individual, which gives rise to a new thread. Thus, the life cycle of spirogyra takes place in the haploid phase, only the zygote is diploid.

Other representatives of green algae are spirogyra, ulotrix (filamentous forms) and ulva (lamellar form). Thus, the department of green algae is a non-specialized group of algae, in which cytological and biological features are very similar to higher plants.

4. Department of Green Algae. Ecology and meaning.

Most green algae are freshwater organisms that live in stagnant or flowing bodies of water with varying degrees of water purity. For example, unicellular planktonic algae chlamydomonas and chlorella live in water bodies polluted with organic and inorganic substances. With their mass reproduction, water blooms are observed (the water is green and opaque). On the other hand, the filamentous algae Spirogyra lives exclusively in clean flowing water bodies.

Green algae inhabiting marine reservoirs have practically no competitors in the face of higher plants. They live at depths from X cm to 200 m.

Seaweeds can be planktonic (single-celled algae suspended in the water column) and benthic (attached to the bottom with the help of rhizoids - ulva). The deepest (200m and >) are red algae.

In autumn near the coasts of some warm seas there are red tides. They are associated with the reproduction of microscopic algae - dinoflagellates.

Algae can also live on land, but only on highly moistened soil. Terrestrial algae are often epiphytes, inhabit tree trunks, buildings, rocks (where there is a lot of moisture).

Soil algae are microscopic in size, they are widely found in the soils of most climatic zones. They play an important role in soil formation.

The algae of snow and ice are also microscopically small: only their large accumulations are visible to the eye. The phenomenon of “red snow”, caused by one of the species, has been most famous since ancient times. snow chlamydomonas. The red color is due to carotenoids, and is a protection from sunlight (primarily UV).