Green algae: general information and characteristics

The main signs of algae

We usually call all plants living in water algae. They really love moisture, but this is far from their only sign. They represent a large group of organisms of different origins, which are united by some common features:

presence of chlorophyll;
photoautotrophy;
lack of division of the body into functional parts;
lack of a covering shell;
lack of a distinct conduction system.

Algae live in damp areas. They can live in the soil, on the surface of the earth, on the bark of plants, in the seas, oceans, swamps and other bodies of water. They are important participants in ecological and biological processes. It is with algae that marine and some terrestrial food chains begin.

By type of nutrition they are photoautotrophs. This means that they can produce organic substances from inorganic ones and do this using light energy and carbon dioxide. Through their activities, they produce approximately half of the total oxygen produced by plants.

Their body is called thallus, or thallus. Unlike the body of higher plants, it is not divided into different organs and tissues. And although outwardly algae may have visible stems, roots, and leaves, this is just a deception. All their parts are composed of the same type of cells that perform the same functions.

Algae - modern witnesses of the evolution of the eukaryotic cell

The first living organisms on Earth appeared more than three billion years ago. These were prokaryotes - the predecessors of bacteria or archaea. Some time later, perhaps less than a billion years after this, eukaryotic cells arose. Initially, they were also extremely simple. They had the rudiments of a membrane-bounded nucleus, endoplasmic reticulum, and microtubules, but were devoid of mitochondria and plastids.

Mitochondria appeared first when an early eukaryotic cell engulfed but did not digest a bacterium capable of aerobic respiration. These two organisms lived together, one inside the other, and both benefited from it. Such beneficial cohabitation is called endosymbiosis . Over hundreds of millions of years, this tandem gradually evolved into a more complex form of eukaryotic cell with true mitochondria. And once this happened, the cell was able to give rise to many new species. Some of them died out quite quickly; others were more successful and persisted, also forming diverse new forms.

Today, numerous groups of organisms called protozoa and algae are living descendants of eukaryotic cells that evolved early in life. Eventually one of the clans of these cells founded a clan of animals and fungi, whose cells had a nucleus and mitochondria, but no plastids.

Another lineage of early eukaryotes entered into another endosymbiosis with photosynthetic cyanobacteria, which later developed into chloroplasts. This line gave rise to a more advanced group of algae, including green algae, which are true plants - embryophytes. However, the diversity of photosynthetic organisms indicates that this process occurred repeatedly.

The most ancient photosynthetic eukaryotic organisms are glaucophytes, red and green algae. Their chloroplasts have two membranes, derived from two membranes of a gram-negative cyanobacterium; the outer membrane, the membrane of the digestive vacuole, is reduced. Chloroplasts in these algae arose as a result of primary endosymbiosis. At the same time, glaucophyte and red algae retain phycobilisomes - protein complexes characteristic of cyanobacteria, which contain phycobiliproteins and are attached to thylakoid membranes.

As in Paulinella, many important genes from the prokaryotic endosymbiont were transferred to the eukaryotic nucleus, and the endosymbiont lost its independence. Red or green algae were incorporated into the cells of other eukaryotic organisms as a result of secondary endosymbiosis. With the integration of green algae into the cells of other eukaryotes, euglenophytes and chlorarachniophytes arose; red algae, as endosymbionts, gave rise to the remaining groups.

As a result, chloroplasts emerged that have four membranes, the first two are preserved from the primary chloroplasts, the third is the cytoplasmic membrane of the endosymbiont cell and the outer one is the membrane of the digestive vacuole of the new host cell. In euglenophytes and some dinophytes, the outer shell is further reduced and three shells remain.

In a number of algae, the reduction, on the contrary, does not go very far. Thus, in chlorarachniophytes and cryptomonads, between the second and third membranes of the chloroplast, a nucleomorph is preserved - a highly reduced remnant of the endosymbiont nucleus, consisting of three chromosomes.

There is also tertiary endosymbiosis, which is observed in a number of dinophyte algae. Thus, the structure of chloroplasts in some representatives of this group differs significantly from that in most genera. The genus Lepidodinium has a double-membrane chloroplast with chlorophylls a and b, while Kryptoperidinium has a five-membrane chloroplast. Genetic methods have shown that in the first genus the chloroplasts originate from endosymbiotic green algae, and in the second - from diatoms. Dinophytes are also characterized by the presence of kleptochloroplasts, which they inherit from prey algae and are capable of short-term existence in their cells.

We are also very lucky in that there are still organisms that have the ancestral features present in early eukaryotes. They are almost always single-celled and were previously grouped into a kingdom called Protista. But this was an artificial classification, based on the fact that they are supposedly too simply structured, being at a low evolutionary level, and having derived characteristics of plants, animals and fungi. Thanks to the decoding of their DNA, confirmed by electron microscopy and other methods, representatives of this group were classified into different groups of organisms.

The main thing that distinguishes algae from real plants is their reproductive system. Algae are now defined as photosynthetic eukaryotic organisms in which the reproductive structures are completely converted into spores or gametes, leaving nothing but empty walls when released. In plants, reproductive systems are always complex and multicellular, and only some of their internal cells become reproductive.

The way algae reproduce is a process that reflects the simple cellular level of organization of the organism itself. In plants, unlike algae, the reproductive system includes two types of tissues - reproductive and sterile, which function together as an organ. This reflects the more complex organ level of body integration of true plants.

What types of algae are there?

More than 100 thousand species of algae are known. They are divided into sections: brown, diatoms, red, green algae. All of them are eukaryotes because their cells contain a nucleus. However, science also knows blue-green algae, which are prokaryotic organisms. For their ability to photosynthesize, they were once classified as plants, but are now considered bacteria and are found under the names “cyanium” or “cyanobacteria”.

Green algae belong to the plant kingdom and include organisms of a wide variety of shapes and sizes. They most often live in fresh water bodies and humid regions, but are also found in salt and brackish waters.

There are several classes of green algae:

ulfociaceae;
bryopsidaceae;
Chlorophyaceae;
trebuxiaceae;
prasine;

Their sizes range from a few micrometers to two meters. Their characteristic green color is due to their high chlorophyll content. In addition, algae contain the pigment lutein and neoxanthin. Due to the presence of carotenoids, some of them have a reddish or orange tint.

Department of red algae or purple algae

The department Red algae, or Crimson algae (Rhodophyta), includes predominantly multicellular algae, which are distributed mainly in salt water bodies and are attached to the substrate. Smaller in size than brown ones. About 4000 species are known. The appearance is varied: thread-like, lamellar, coral-shaped with varying degrees of dissection. The color of the thallus is varied: from yellow or azure green to red. This is due to the fact that in addition to chlorophyll (a and d) there are red and yellow pigments (carotenes, xanthophylls, phycoerythrins) that mask it. Chlorophyll d is characteristic only of red algae. The crimson color is given by a special pigment – phycoerythrin. Red pigments allow algae to detect weak light at great depths (up to 250 m). In shallow water, the predominant color is azure-green, caused by the blue pigment phycocyan.

The cells are covered with a two-layer shell: the inner one is cellulose, the outer one is pectin. The shells are impregnated with calcium carbonate. They have one or many nuclei, one or many chloroplasts with pyrenoids. A structural feature is the presence of special glandular cells in some representatives. The cells of the thallus are connected in pairs. The storage substance is purple starch, which is deposited in the cytoplasm.

Reproduction is sexual and asexual. Vegetative propagation occurs rarely. During asexual reproduction, there are no flagellated forms - zoospores. In sporangia, meiosis occurs before spore formation. Spores and male gametes are passively transported by water. The sexual process is oogamy. The zygote undergoes a complex development, as a result of which spores (carpospores) are formed, from which the sporophyte is formed. The life cycle is complex.

Representatives of red algae

The most famous representatives are porphyra, deleseria , etc. Very rarely found in fresh water bodies ( batrachospermum ), terrestrial fouling in humid places ( porphyridium ). In the Black Sea you can find red algae of a spherical shape - ceramia , bushes similar to corals - coralline , cord-shaped - nemalion .

Agar-agar polysaccharides are obtained from different types of scarlet grass, which is used in the food, confectionery, paper, textile and medical industries. Some species are used as food and animal feed. Bromine and iodine are extracted from red algae, anti-clotting drugs, blood substitutes, etc. are made.

Appearance and structure

The internal and external structure of green algae is very diverse. They can be mononuclear or multinucleate, consist of a different number of cells, or even have a noncellular thallus. Some of them do not attach to surfaces and live freely in the aquatic environment. Others are firmly attached to objects and various substrates.

Among green algae there are those that consist of only one cell. It is impossible to see them without a microscope, because their size is extremely small. But in summer and spring you can observe how, due to their active reproduction, the water in puddles, ponds and swamps turns green.

Multicellular green algae are more reminiscent of ordinary higher plants. Their body can consist of many threads, forming something like stems and leaves. Colonials are an intermediate option between multicellular and unicellular. They are a group of interconnected cells or organisms. Despite the unification, they can maintain their independence and react differently to stimuli. If the colony breaks, they continue to exist quietly and are able to form new groups by dividing their cells.

Why do they appear in the aquarium?

Unlike aquatic plants, almost all types of algae in aquariums are undesirable and even harmful, in fact they are an analogue of garden weeds. They muddy the water, settle on the walls and destroy the plants on which they parasitize.

How to get rid of it?

There are various ways to control algae. Firstly, the aquarium can simply be cleaned manually, removing harmful plants and cleaning the walls and soil on which they have fallen, changing most of the water.

Secondly, you can use the inhabitants of the aquarium themselves. Among the fish, Siamese algae eaters, otocinclus and ancistrus catfishes, poecilliids, and a number of mollusks are well suited. The most suitable clams are theodocus clams and cardina multidentate shrimp, also known as amano shrimp. It should be borne in mind that they are needed in large quantities, otherwise they will not bring much benefit.

Finally, these are various drugs for controlling underwater weeds. Examples include Sidex, TetraAlguMin, Tetra Algetten, Tetra AlgoStop (from Algae - the Latin name for algae).

However, these drugs must be used extremely carefully and in dosage; some of them may not be safe for fish and plants.

Prevention

Algae love light, so you should reduce the lighting time and do not place the aquarium near windows. The light should not be too strong or weak - the first promotes the growth of green algae, and the second - brown algae. A large amount of organic residues also contributes to their reproduction, so the water must be regularly cleaned and changed, as well as selecting feed that leaves less organic residues and not overfeeding the fish. The temperature should not be too high - algae love it. It is also not recommended to use powerful filters that create a strong current in the water - red algae species like this. Long-stemmed plants like hornwort and elodea are good - if they grow quickly, they make it difficult for algae to feed. Just like with fish, it is important to monitor the feeding of plants - its excess also promotes their growth.

Relationships with other organisms

Green algae can exist in almost any damp place. They are found in the soil, on the shady side of stones and even in the snow of high mountains and the Arctic belt of the Earth. If you leave a glass of water in a sunny place for several days, they will appear there too.

Algae easily enter into symbiotic relationships with other organisms. They coexist well with mollusks, sponges, protozoa, hydra and flatworms. Their cooperation with mushrooms turned out to be so productive that they even received a separate name - lichen. Once upon a time, such an association was considered a complete plant organism, such as moss. About 80 algae are involved in the formation of lichens, of which representatives of the genus Trebuxia are most often found.

Single-celled green algae sometimes develop in the fur or skin of mammals, as well as on higher plants. Their presence is not always beneficial to others. Sometimes they simply parasitize and lead to diseases in the host. They can cause mastitis in cattle, cause some human skin diseases, and deplete tea plants, leading to yellowing of the leaves.

Sexual reproduction

In addition to the above methods, algae reproduce sexually. It is characterized, first of all, by fertilization, that is, the fusion of two cells - gametes. After this, a zygote is formed, which subsequently becomes the ancestor of a new organism.

Algae have several methods of sexual reproduction:

Isogamy - implies the fusion of two gametes of the same size and structure.
Heterogamy. This is the name given to the fusion of two gametes, in which one is larger than the other. Moreover, the one that is larger in size is usually female.
Oogamy. With this method of reproduction, a sedentary female cell merges with a mobile male gamete.
Conjugation. This concept refers to a type of reproduction in which two vegetative cells lacking flagella join together.

In primitive algae, the same individual is capable of both sexual and asexual reproduction. In the most developed ones, the function is performed by individuals called gametophytes, that is, they form gametes.

Chlamydomonas

The genus Chlamydomonas includes more than 500 species of green algae that live mainly in fresh water bodies. These are single-celled pear-shaped or oval-shaped organisms. They are equipped with special light-sensitive eyes and a pair of flagella, the rotational movements of which help Chlamydomonas move in water to more illuminated places.

Most of them live in small, well-warmed bodies of water and can contribute to their flowering. The most unusual representative is Chlamydomonas snowy, which lives at low temperatures. It lives in snow and ice, and thanks to the pigment astaxanthin, it colors them pinkish.

Distribution of algae in nature

According to their mode of existence, algae are divided into two large groups: aquatic and those living on land - outside the water.

In turn, water can be divided into several categories:

Planktonic. They are suspended in the water. At the same time, they are absolutely adapted to this lifestyle.
Benthic. They live at the bottom of reservoirs.
Periphyton. They live on underwater rocks and grow on deep-sea objects.
Neuston. This type of algae floats in a semi-submerged state. One part is above the surface of the water, the other must be immersed in water.

Algae living on dry land are divided into two subgroups:

Aerophyton. Algae that grows on ground objects, fallen objects, stumps.
Algae growing on the surface of the soil.

In addition to the above species, there are those that live in salty reservoirs, on snow or ice, and also live in limestone substrate.

Spirogyra

Spirogyra is the most common multicellular algae. It is colored bright green and consists of many thin threads of varying lengths. Spirogyra is found in both fresh and salt waters. It appears in slowly flowing and stagnant bodies of water, in aquariums that are not properly cared for. Together with other algae, it forms a sticky mud that feels like cotton wool.

Ecology DIRECTORY

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

Algae form the basis of various associations. Blue-green algae (cyanobacteria) in natural and non-sterile conditions usually develop together with a variety of microorganisms. Each blue-green thallus is not an organism or a population of a certain species, but an entire cenosis in which, in addition to the edificator algae, many bacteria, fungi, and algae of other species are found. The price-forming role of blue-green algae is due to the formation of mucous sheaths, colonial mucus and extracellular organic secretions. The ecological significance of the mucus of blue-green algae for the microorganisms that settle in it is associated, first of all, with the ability of the mucus to absorb and retain large quantities of water. At the same time, organic substances in mucus are used by companion microorganisms as a source of nutrition.[...]

Among algae of this level of organization, colonial forms are often found, which are a collection of individual cells of a monad structure, united by mucus into one whole. The shape of such colonies and the structure of mucus in different algae can vary significantly; in some cases, cells are connected to each other by plasmodes-m a m i. [...]

Algae primordia are capable of attaching to soil particles of any size. As they grow, those thalli that grow on insufficiently large stones are eliminated and die. When algae grows on loose soils, such as sand, there is a danger of the soil moving by bottom currents, as a result of which the plants are either covered with soil or rubbed by it. But even in such places, the sand does not remain completely devoid of algae. Microscopic unicellular and colonial species live in the irregularities of sand grains.[...]

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

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 multinucleate 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.[...]

The Volvox algae are a large and well-defined systematic group of green algae, which are most naturally accepted at class rank. The Volvoxaceae class is divided into two subclasses that are quite unequal in volume: protochlorinaceae (Protochlorinaceae) and Volvoxaceae proper (Volvocosyceae). The first of them, which combines a very small number of genera and species with a primitive body structure, has not yet been studied completely enough, and we will not consider it here. On the contrary, Volvoxidae itself includes a very large number of species, and we will consider them in more detail. The vast majority of them have a well-defined dense shell and usually two, less often four equal flagella.[...]

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

In most colonial forms of a monadic structure, the cells within the colonies do not show any differences; only in a few of them is there a division into vegetative ones, which are smaller in size, and larger ones, which serve for reproduction (for example, in Volvox and pleudo-rsus from the department of green algae). [...]

The section Diatomaceae, or diatoms (Clubeaor a) is represented mainly by multicellular organisms, and sometimes even by colonial forms (Fig. 7). Single-celled forms are also found. There are 5,700 known species. They are characterized by a clear differentiation of the body into 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 shell contains pectin substances. In some groups the shell is heavily impregnated with lime or silica. Some cells contain one or several nuclei, others do not have a typical nucleus, only in the protoplast a colored peripheral part and an unstained central body are noticeable. In some algae, coloring substances 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. Starch, which is one of the assimilation products, is deposited around the pyrenoids. Spare nutrients include oils, fats, leukosin, mannitol and glucose.[...]

Type III. Blue-green algae (Cyanophyceae) include unicellular, colonial and filamentous forms. A distinctive feature of these algae is a peculiar blue-green color, due to the presence of four pigments in their cells: green, blue, red and yellow. Depending on the quantitative ratios of pigments, the color of algae also changes.[...]

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

Cell shape. Desmid algae are mostly single-celled organisms. Less common among them are colonial organisms that form long threads and chains or loose colonies. A typical cell of desmidian algae (Fig. 247) consists of two symmetrical halves, the so-called half-cells, each of which is a mirror image of the other. Due to the peculiar method of cell division in desmidiaceae, which will be described below, one half-cell is always older than the other. Both semi-cells are connected to each other by a narrower part - an isthmus. The angle arising between two half-cells as a result of compression or narrowing of the cell is called sine.[...]

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 shape or a lamellar structure. [...]

Many algae, especially unicellular and colonial algae, belonging to different divisions, represent an important part of the plankton of the World Ocean. They are the primary producers of organic matter, due to which the entire animal world of the ocean exists.[...]

Sexual reproduction is characteristic of all algae from the class Florideaceae, while in the class Banguiaceae it is characteristic only of the most highly organized forms. In unicellular and colonial bangieids, the ability for sexual reproduction has not yet developed. For some floridaeids, only asexual reproduction is known, but the absence of sexual reproduction in them is always the result of secondary loss.[...]

Chlorophyceae include protococcal algae, which live mainly in fresh water bodies, where they inhabit the aquatic layer. They are nonmotile, single-celled or colonial organisms. In colonies, cells are sometimes held together by common mucus, sometimes due to the fusion of cellulose membranes of individual cells. The simplest representative of protococcals is Chlorella vulgaris.[...]

RIF [German] R. are distinguished as barrier, coastal, crustal, and ring-shaped (atolls). REALTOR SERVICES [from Amer. realtor - real estate agent] - services provided by firms and individual specialists in the economic (monetary) valuation of physical objects, including natural resources.[...]

Morphologically, green algae are also distinguished by the greatest diversity compared to other departments. The range of their sizes is also extremely large, from the smallest single cells with a diameter of 1 - 2 microns to macroscopic plants measuring tens of centimeters in length. All the main types of asexual and sexual reproduction and all the main types of changes in developmental forms are also found here. Most representatives in the vegetative state are haploid, some are diploid.[...]

Most algae belonging to the conjugates are unicellular (less often colonial), symmetrically built organisms, the cells of which are usually laced in the middle and consist of two completely identical half-cells (desmidial). Many forms have a typically filamentous structure. In this case, the cells forming the threads are not laced in the middle (zygnema cells). Some of the conjugates form very fragile threads that easily break up into individual cells (gonatozoic). The cells released after the filament disintegrate usually continue to live completely independently. And finally, this also includes very simply organized unicellular algae, the shells of which always consist of one inseparable piece, without division into special semi-cells (mesothenial), which is why they differ sharply from desmidian algae. [...]

Phytoplankton includes unicellular and colonial algae, motile and equipped with flagella. Their density is very close to that of water, and they are morphologically adapted to life in suspension; these devices take the form of spines, thin filaments (Micractinium, Fig. 28.11), teeth (Pediastrum, Fig. 28.10), lobes, curvatures, etc. Secretion of plant mucus, the presence of fat granules in the cell and gas vacuoles in some blue-greens algae (see paragraph 28.7.3.1, D) are also ways of adapting to the planktic way of life. [...]

Representatives of this class of golden algae are characterized by further complication of the thallus, represented here by a pal-melloid (mucosal) structure. Unlike the first two classes, Chrysocapsaceae include stationary, attached, or passively floating colonial forms. Their cells have neither surface protrusions nor flagella. They are united by a common mucus 1 olonium, usually located in its peripheral layers, less often in the central part. [...]

Algae that settle on the surface of exposed rocks are found in even more severe conditions, but their systematic composition is different. Along with diatoms and some, mostly unicellular, green algae, blue-green algae are the most common here, forming a variety of plaques and crusts. When dry they are almost black and crumble easily, and when moistened they become slimy and lighten significantly.[...]

Unlike Volvox, protococcal algae are characterized in the vegetative state by the complete absence of a monadic body structure. In the vast majority of species, the thallus has a coccoid structure. A palmelloid structure is observed less frequently; in one species (Protosiphon botryoides) a primitive siphonal structure is known, and in several genera a primitive filamentous and primitive lamellar structure is known. These are mainly unicellular and coenobial, less often colonial forms, and only in species with primitive filamentous and lamellar structures can one speak of multicellularity of the thallus.[...]

Formation of colonies. Colonies of diatoms come in different sizes and shapes, this depends both on the amount of common mucus and on the way the cells connect to each other (Fig. 95). Colonies are always formed from one cell as a result of successive and multiple divisions of itself and all other cells that arise. All cells remain independent, and the collapse of the colony does not lead to their death. Cells are connected with the help of mucus, outgrowths, spines, bristles, horns, etc. Colonial forms live both in plankton and benthos on various substrates - on plants and animals, on rocky, sandy and muddy soils, on technical structures and other objects introduced into water by humans.[...]

The Woronichiniaceae family includes algae with elongated cells located in mucous colonies in one layer, the outer colonial mucus is radial tubular. [...]

Nostoc is a terrestrial alga that forms blue-green macroscopic colonies. Studies have shown that consort algae settle in the colonial Nostoc mucus.[...]

Protococcales include unicellular and colonial forms. The cells are most often spherical or oval with one nucleus in the center and a chromatophore with a pyrenoid. The shell contains cellulose. More highly organized representatives of protococcal algae, for example water mesh (Hydrodiction), have many nuclear cells with a dissected wall chromatophore and a large number of pyrenoids. [...]

The order includes widespread unicellular and colonial forms that do not form a thallus, free-living or sitting on the substrate. These algae reproduce almost without exception by cell division. The main families are in order 7.[...]

The class of chrysospheres includes representatives of golden algae with a coccoid body structure. Their cells are covered with a dense cellulose membrane, and rhizopodia and cords are completely absent. These are immobile unicellular, less often colonial (Table 6, 4) forms. The latter look like clusters of cells that are not immersed in mucus and are weakly connected to each other. When multiplying, they do not form threads or plates.[...]

The laced species of desmidiaceae, to which most of these algae belong, are characterized by a huge variety of cell shapes (Fig. 249, 250). In some, the cells are highly elongated, cylindrical, rounded or stellate in cross section; in others, they are highly compressed and flat. Some representatives develop special processes and spines at the corners of the semicells. In loose-colonial and pitched desmidian cells, cells are connected by special formations (tubercles, granules, protrusions) or mucus (Fig. 248, 4, 5). [...]

For the first time, a faunistic study of colonial invertebrates - bryozoans and sponges - was carried out for the Volga reservoirs. Natural food spectra have been identified in common species of bryozoans. It has been established that they mainly use various algae, the mass components of which have sizes of 6-45 microns. Using a specially developed technique, the rate of sedimentation of suspension by some species of bryozoans was determined. It has been shown that in summer these values are comparable to those for underyearlings of zebra mussels. Bryozoans can be promising objects for introduction into water bodies for the purpose of biological water purification.[...]

Currently, there are 9 main types of morphological body structure of algae. Of these, 4 belong to unicellular forms, 1 to non-cellular forms, the remaining 4 to multicellular forms (colonial forms, being a significant step towards the complication of the organization of algae, are still only a type of unicellular structure).[...]

Thus, based on the above, it is easy to derive the exact scientific definition of algae. Algae are lower, i.e., layered (lacking division into stems and leaves), spore-bearing plants that contain chlorophyll in their cells and live primarily in water. This definition, however, does not give an idea of the enormous diversity in body structure that is characteristic of algae. Here we encounter microscopic organisms - unicellular, colonial and multicellular, and large forms of various structures. The methods of reproduction and the structure of the reproductive organs also achieve great diversity here. Even in color, algae are not the same, since some contain only chlorophyll, others contain a number of additional pigments that color them in different colors. [...]

The class Chamaesiphonales is divided into 4 orders and 5 families. It includes unicellular and colonial blue-green algae attached to the substrate. The threads in the thalli can grow together and form false parenchyma. Unicellular organisms have a different base and apex.[...]

Relatively few algae have adapted to the unfavorable conditions of terrestrial habitats, but still the total number of algae capable of leading a terrestrial lifestyle exceeds several hundred. Terrestrial habitats are inhabited by microscopic unicellular, colonial and filamentous algae, usually capable of developing in large quantities in the form of powdery or mucous deposits, felt-like masses, soft or hard films and crusts. Most of them belong to blue-green (division Cyanophyta) and green (division Chlorophyta) algae; a significantly smaller number of species are represented by diatoms (division Bacillariophyta). [...]

Planktonic organisms include 2 groups: phytoplankton - a collection 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 a particular pigment, algae have different colors. They differ in the supply of nutrients and method of reproduction.[...]

The diversity of the pigment composition can also explain the variety of colors of cells and trichomes of blue-green algae. Their color varies from pure blue-green to violet or reddish, sometimes to purple or brownish-red, from yellow to pale blue or almost black. The color of the protoplast depends on the systematic position of the species, as well as on the age of the cells and living conditions. Very often it is masked by the color of vaginal mucus or colonial mucus. Pigments are also found in mucus and give the threads or colonies a yellow, brown, reddish, purple or blue tint. The color of mucus, in turn, depends on environmental conditions - on light, chemistry and pH of the environment, on the amount of moisture in the air (for aerophytes).[...]

Freshwater phytoplankton differs from typical marine phytoplankton in its huge diversity of green and blue-green algae.[...]

This class includes unicellular representatives with thalli differentiated into base and apex, colonial forms, filamentous or forming simple thalli by fusion of filaments with their lateral sides. Almost all live attached and are quite rare. Their development at individual stages is similar to the development of algae from the classes Chroococcus and Hormogonium. Chamesiphonidae grow epiphytically or on stones, preferring clear-water and nutrient-poor mountain streams, where their thalli form colored crusts or spots on stones, shells and plants. Some species live in the seas.[...]

From the above it is clear that the class Volvocophyceae is a relatively homogeneous group of the department of green algae (Chlorophyta). They are characterized by only one monadic body structure. Their thallus is predominantly unicellular, in some it is typically coenobial, in a few it is colonial. The structure of the cell is generally homogeneous, in almost all species it is Chlamydomonas-like.[...]

Apparently, this algae comes with transit runoff from a cascade of reservoirs, since in the alkaline watercourses Akhtuba and Berekeg in September it was 0.9 and 4.4 billion cells/m3, respectively (table), which is typical for shallow channels even reserve /2/.[ …]

A group of lower aquatic plants that usually contain chlorophyll and produce organic matter through the process of photosynthesis. The body of algae is a thallus, which does not have true roots, stems and leaves, from fractions of a micron to 60 meters. Noncellular, unicellular, multicellular, colonial organisms. Reproduction is asexual, vegetative and sexual. Divisions (or types) of algae: green, brown, red, golden, yellow-green, diatoms, etc. They are part of plankton and benthos. Some algae are edible (for example, kelp, porphyry), others are raw materials for producing feed mass, agar, carrogen, iodine, etc. [...]

Multi-year ice in the Arctic is renewed annually by 1 m, melting in summer from the upper surface and growing in winter from the lower, sea surface. Algae, especially diatoms, are found throughout Arctic sea ice. Their active activity in the summer contributes to the destruction of the strength of the ice and its melting. I. A. Melnikov, 1984). The abundance of diatoms, which give the lower surface of the ice a yellow-brown color, is also characteristic of multi-year ice in the Antarctic (A.P. Lisitsyn, 1961).[...]

Conjugation is most common in forms that have the greatest potential for meeting physiologically different cells. This possibility most often occurs in filamentous and colonial algae. Therefore, for example, representatives of Hyalotheca and Desmidium are often found in a state of conjugation. However, in the colonial cosmocladium, where the proximity of cells seems to be sufficiently ensured by the common colonial mucus, conjugation is rare. Probably, colonies here often represent pure clones (a clone is the offspring of one cell, formed through vegetative propagation), and then conjugation becomes impossible due to the absence of physiologically different cells. [...]

During the Archean era, life traveled a giant path from probionts to cellular organisms (bacteria and cyanobacteria), and at the end of the Archean, the first eukaryotes with a real nucleus (green algae) appeared. In addition, two more major evolutionary events occurred during this period: the sexual form of reproduction appeared and the first multicellular organisms arose. Sexual reproduction dramatically increases the possibilities of adaptation to environmental conditions due to the creation of countless combinations in chromosomes. The predecessors of multicellular organisms were colonial-unicellular (filamentous or spherical) creatures, which, as a result of differentiation of colony cells, gave rise to most modern organisms.[...]

Colorless flagellates. They have a thin plasma membrane, a fairly constant body shape with one or more flagella; continuously flickering organisms that are difficult to identify. The size of flagellates is usually from 10 to 20 µm, not exceeding 50 µm; Both solitary and colonial forms are found. In polluted waters, spherical colonies of Ocomonas form, each individual of which has one long flagellum. At the same time, Bodo are present - solitary with two flagella: one, swimming, directed forward, the second - backward and serves for attachment to the substrate. Their main food consists of bacteria, small organic particles of sludge, and dissolved organic matter. Of the colorless euglena flagellates, Astasia is common, distinguished by the presence in the plasma of grains of the reserve product paramylon, the number of grains of which increases with the abundance of food. As an addition to the class of flagellates, the unicellular colorless algae chrysomonads, which have a structure similar to them, are considered. In aeration tanks, especially in ponds, on filtration fields in the warm season, with good cleaning, green euglena Euglena, Phacus, Trachelomonas develop in the mass. The largest representative of this class - the predatory Peranema trichophorum - develops in the biocenosis of aeration tanks working for complete biological treatment, in sludge with good nitrifying properties. [...]

Volvox

Volvox is a mobile colonial algae that lives in stagnant fresh water bodies. During the period of mass reproduction, they contribute to the blooming of water, turning it green. About 20 species of Volvox are known.

A Volvox colony looks like a green ball with a maximum size of 3 mm. Each of these balls contains from 10 to 200 thousand microscopic cells, which are connected by threads of protoplasm. Like Chlamydomonas, they have flagella for movement within a body of water. Cells are not the same and are divided according to their specificity. Some are vegetative, others are generative and take part in sexual reproduction.

Mobile colonial green algae

Cells of motile colonial forms are similar to Chlamydomonas. They are formed as a result of division of the zygote. The cells are held together by a mucous substance.

Volvox

Colonial algae in the form of mobile green balls. A colony includes about 20-50 thousand cells, most of which are vegetative. Cells communicate with each other through cytoplasmic bridges.

Rice. 4. Volvox

Volvox is characterized by vegetative and sexual reproduction. As a result of vegetative growth, daughter colonies are formed, separated from the mother colony by successive longitudinal divisions. After this, they fall out into the middle of the mother’s body and are released after the destruction of the latter.

Rice. 5. Asexual reproduction of Volvox

Sexual reproduction is carried out by specialized cells without flagella. One part is transformed into female germ cells - oogonia, from which eggs (n) are formed, and the other part - into male cells - sperm (n). When they fuse, a zygote is formed - an oospore (2n). It divides first by meiosis and then by mitosis. As a result, a plate of haploid cells develops.

Ulva

The genus Ulva represents marine green algae that live within the subtropical and temperate zones of the globe. They are multicellular organisms with a branched lamellar thallus measuring from 30 centimeters to 1.5 meters. At the base of the algae’s body there are thread-like formations, rhizoids, with the help of which they cling to various surfaces.

Ulva needs sunlight, so it lives at shallow depths. It serves as food for marine animals and is an excellent place for fish to lay eggs. Some types of ulva are eaten by people. In cooking, it is better known as sea salad.

Reproduction by spores

In addition to vegetative propagation, algae reproduce using spores. This is a specific subtype of asexual reproduction.

Spores are formed in special organs, the so-called sporangia or zoosporangia. When the spore disperses, it begins to germinate and then a new adult independent individual is formed.

Motile spores with flagella that are capable of movement are called zoospores.

The option of asexual reproduction by spores can be considered using the example of an algae such as ulothrix. In favorable living conditions for it, its fragments, which contain spores, are separated from the existing maternal thread. They swim in a free state, then, having attached themselves to an underwater object, they begin to actively divide and form a new thread of algae. It should be noted that this type of algae can simultaneously reproduce both asexually and sexually.

It has been noted that it is possible to stimulate the formation of spores in some species of filament algae; for this to happen, there must be an increase in carbon dioxide in the habitat.

The function of asexual reproduction in this case is performed by individuals called sporophytes, that is, they form spores.

Nitella

Algae of the genus Nitella are widespread throughout the Northern Hemisphere. They live in fresh water bodies of Asia, Europe and North America. Externally, algae are difficult to distinguish from higher plants. Their thallus consists of thin stems with small nodes, from which 5-7 narrow and thin leaves extend in a circle.

They love well-lit places and warm water temperatures - between 20-28 degrees. The plant is quite unpretentious and can make water clearer, which is why it is often planted in aquariums. In natural reservoirs, overgrown nitella becomes a refuge for small fish and a place for their spawning.

When algae reproduce asexually. Types of asexual reproduction

This is the simplest option. Algae reproduce either asexually or vegetatively only in favorable conditions. This means when the water in a reservoir has a certain temperature and conditions are most conducive to asexual reproduction.

If sudden temperature changes, pollution or overcrowding of inhabitants occur in a reservoir or environment, in this case the algae begin to reproduce sexually.

Asexual reproduction can be divided into several types:

Algae reproduce vegetatively - division of vegetative cells occurs.
Sporulation. Or, in another way, algae reproduce using special cells. These cells are called spores.

When algae reproduce asexually, there is only one parent from which all existing genomes are inherited. But in the case of mutations, the genetic material can change significantly.

Often, one organism can reproduce both asexually and vegetatively.

Caulerpa

Bryopsid algae of the genus Caulerpa live mainly in warm tropical and subtropical seas. Externally, they are very diverse and are visually divided into leaves, stems and roots. They can be branched or resemble mushrooms in appearance. Despite the apparent complexity, their internal structure is very simple. The algae thallus consists of only one cell, which contains many nuclei. In some species it can grow greatly, reaching 2-3 meters in size.

Caulerpa is motionless and is always attached to some surface. It often settles at the bottom of reservoirs, clinging to silt or sand. It also grows on underwater rocks and coral reefs. Due to their size, algae of this genus are the largest single-celled organisms in the world. Due to their unusual appearance, they are popular and are often grown in aquariums. In the countries of Southeast and East Asia, some types of caulerpa are eaten.

Application

Like higher plants, algae are also used as food and in medicine and cosmetology.

Cooking

Most edible algae belong to three groups - red, green and brown. They contain a large amount of proteins, vitamins and iodine, in addition, useful substances (such as agar-agar, alginic acid, carotenides) are obtained from them, which are used as food additives. Mostly seaweed dishes are used as food in Southeast Asian countries, especially in Japan.

Edible algae examples:

kelp or seaweed – rich in iodine, stimulates metabolism;
spirulina – rich in protein;
Ulva or sea lettuce – contains a large amount of iron, protein and fiber;
porphyry or nori - a traditional part of Japanese, Chinese and Korean dishes, useful for lowering cholesterol, a source of vitamins A, D and B12;
lithothamnia – rich in vitamins, contains large amounts of magnesium and iron, useful for the prevention of anemia;
ahnfeltia - used to produce agar-agar.

Also, there are various dishes using additives made from algae, for example, Japanese yokan marshmallow, with the addition of agar-agar.

Medicine

Algae are known primarily for their high iodine content, which fights viruses well and improves the synthesis of thyroid hormones. Since ancient times, they have been used to treat constipation, diarrhea, anemia, and thyroid dysfunction. Regular consumption of seaweed compensates for the lack of microelements such as fluorine, manganese, and iron. They also help remove heavy metal salts, radionuclides and other harmful substances from the body. Finally, they contain many vitamins.

Cosmetology

Algae are also actively used in cosmetology, mainly seaweed. Cosmetic preparations with algae provide skin care and nutrition, rejuvenate the skin and have an anti-inflammatory effect, and also improve the structure and appearance of hair and nails. Each group of algae has its own beneficial properties:

green ones are rich in iron and antioxidants, improve microcirculation and metabolic processes;
blue helps strengthen, tone and tighten the skin. Rich in amino acids and beta-carotene;
brown ones contain a high amount of vitamins and minerals and are used to detoxify and moisturize the skin.