Buddha's Parents Achieve Nirvana When Suddhadana became old and ill, he sent for his son to come so that he could be seen one more time before his death. The Blessed One came and remained at the bedside, and Suddhadana, having achieved perfect enlightenment, died on

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Main factors influencing the distribution and development of algae

Algae are photoautotrophic organisms. The leading factors influencing their development are light, temperature, the presence of droplet liquid water, as well as sources of carbon, minerals and organic substances. Algae, like other plants, inhabit almost all possible habitats in the hydrosphere, atmosphere and lithosphere of the Earth. They can be found in water, in the soil and on its surface, on the bark of trees, the walls of wooden and stone buildings, and even in such inhospitable habitats as deserts and firn fields.

Factors influencing the development of algae are divided into abiotic, not related to the activity of living organisms, and biotic, caused by such activity. Many factors, especially abiotic ones, are limiting, that is, they can limit the development of algae. In aquatic ecosystems, limiting factors include: temperature, transparency, presence of current, concentration of oxygen, carbon dioxide, salts, and nutrients. In terrestrial habitats, among the main limiting factors, climatic ones should be highlighted - temperature, humidity, light, etc., as well as the composition and structure of the substrate.

Abiotic factors

Abiotic factors include: temperature, light, physical and chemical properties of water and substrate, the state and composition of air masses (which is especially important for aerophytic algae living outside aquatic conditions) and some others.

The entire set of abiotic factors can, with a certain degree of convention, be divided into chemical and physical.

Chemical factors

Water as a limiting factor. Most of the algae cell is water. The cytoplasm on average contains 85-90% water, and even such lipid-rich cellular organelles as chloroplasts and mitochondria contain at least 50% water. Water in a plant cell exists in two forms: constitutional water, bound by hydrogen bonds to the structures of macromolecules, and reserve water, not bound, usually contained in vacuoles. Sugars, various organic acids, etc. are usually dissolved in reserve water, as a result of which it can participate in stabilizing intracellular osmotic pressure. During the polymerization of highly active small molecules into macromolecules (for example, during the conversion of sugars into starch) and during the reverse process - the hydrolysis of high-molecular compounds, the osmotic pressure in the cell can change rapidly. This mechanism ensures the resistance of certain types of algae to drying out and to sharp fluctuations in water salinity.

For most algae, water is a permanent habitat, but many algae can live outside of water. Based on resistance to desiccation, among land-dwelling plants there are distinguished (according to Walter) poikilohydric - unable to maintain a constant water content in tissues, and homoyohydric - capable of maintaining constant hydration of tissues. In poikilohydric plants (blue-green and some green algae), cells shrink upon drying without irreversibly changing the ultrastructure and, therefore, do not lose viability. When hydrated, they resume normal metabolism. The minimum humidity at which normal life activity of such plants is possible varies. Its significance determines, in particular, the distribution of aerophytes. For homoyohydric plants, the presence of a large central vacuole is required, with the help of which the water supply of the cell is stabilized. However, cells with large vacuoles largely lose their ability to dry out. Homoyohydric algae include, for example, some aerophytes of green and yellow-green algae, which usually settle in conditions of constant excess moisture.

Salinity and mineral composition of water. These are the most important limiting factors affecting the distribution of algae. According to the international classification, the bulk of natural reservoirs are marine - euhaline, with an average salinity of 35 ‰). Among continental reservoirs, freshwater ones predominate - ahaline ones, the mineralization of which usually does not exceed 0.5 (among them there are also more mineralized ones). Continental reservoirs, united under the name mineralized, are very diverse in the degree of mineralization: these are brackish or mixohaline, among which there are oligohaline (with a salinity of 0.5-5 ‰), mesohaline (5-18 ‰) and polyhaline (18-30 ‰ ), as well as euhaline (30-40 ‰) and ultrahaline (at least 40 ‰) - Among the ultrahaline, extremely saline - hyperhaline reservoirs are often distinguished, the salt concentration in which is close to the maximum. Continental reservoirs also differ in the nature of mineralization. Among them, hydrocarbonate, sulfate and chloride reservoirs are distinguished, which, depending on the degree and nature of mineralization, are divided into groups and types.

In accordance with the mentioned classifications of reservoirs and depending on the salt tolerance of algae, oligohaline, mesohaline, euhaline, ultrahaline, freshwater and other species are distinguished among them. Species richness (number of species) is closely related to water salinity.

In almost every department you can find species that can live in conditions of extreme salinity, and species that live in water bodies with very low mineralization. Thus, blue-green algae are overwhelmingly freshwater organisms, but among them there are species that can develop in ultra-haline reservoirs. Among typical marine inhabitants - golden algae of the order Coccolithophores - there are species that are also common in continental water bodies with extremely low mineralization. Diatoms are generally equally common in marine and continental waters; they are found in environments with varying salinity. However, specific species of diatoms often develop only at a certain salinity and are so sensitive to its changes that they can be used as indicator organisms.

Brown algae are also very sensitive to changes in salinity. Many of them cannot grow even with slight desalination. Therefore, they are poorly represented in the waters of the Baltic Sea with relatively low salinity. Red algae also show a similar dependence on the degree of salinity of the reservoir: in the Mediterranean Sea (salinity 37-39 ‰) more than 300 species of red algae were found, in the Black Sea (17-18 ‰) - 129, in the Caspian Sea (10 ‰) - 22. Green algae predominantly freshwater organisms, only 10% of them are found in the seas. However, among them there are species that can withstand significant salinity and even cause “blooming” of ultra-haline water bodies (for example, Dunaliella salina).

Thus, algae in general are characterized by a very wide range of salt tolerance. As for specific species, only a few of them are able to exist in water bodies with different salinities, i.e. most algae are stenohaline species. There are relatively few euryhaline species that can exist at different salinities (for example, Bangia, Enteromorpha, Dunaliella).

Water acidity. This factor is also of great importance for the life of algae. The tolerance of different algae taxa to changes in acidity (pH) varies as much as it does to changes in salinity. In relation to the acidity of the environment, there are species living in alkaline waters - alkaliphiles and those living in acidic waters at low pH values ​​- acidophiles. For example, most Desmidiales are acidophiles. The greatest species richness of desmidia algae is observed in eutrophic and mesotrophic swamps, in conditions of low acidity, however, some desmidiaceae can also be found in alkaline waters with high mineralization (for example, Closterum acerosum). Characeae, on the contrary, are predominantly alkaliphiles. Their greatest species diversity is observed in slightly alkaline waters, but some of them (Chara vulgaris) develop in acidic waters, at pH 5.0.

Nutrients. The presence in the environment of macro- and microelements, which are necessary components of the algae body, is crucial for the intensity of their development.

Elements and their compounds related to macroelements (often called macrotrophic nutrients) are required by organisms in relatively large quantities. A special role among them belongs to nitrogen and phosphorus. Nitrogen is part of all protein molecules, and phosphorus is an essential component of nuclear matter, which also plays a significant role in redox reactions. Potassium, calcium, sulfur and magnesium are almost as essential as nitrogen and phosphorus. Calcium is used in large quantities by marine and freshwater algae, which deposit “cases” of calcium salts around the thalli (some red and chara algae). Magnesium is part of chlorophyll, which is the main photosynthetic pigment of algae in most departments.

Microelements are necessary for plants in extremely small quantities, but are of great importance for their life, since they are part of many vital enzymes. Moreover, with the small need of plants for microelements, their content in the environment is also insignificant. Microelements often act as limiting factors. These include 10 elements: iron, manganese, zinc, copper, boron, silicon, molybdenum, chlorine, vanadium and cobalt. From a physiological point of view, they can be divided into three groups:

1) substances necessary for photosynthesis: manganese, iron, chlorine, zinc and vanadium;

2) substances necessary for nitrogen metabolism: molybdenum, boron, cobalt, iron;

3) substances necessary for other metabolic functions: manganese, boron, cobalt, copper and silicon.

Algae of different departments have unequal needs for macro- and microelements. Thus, for the normal development of diatoms, quite significant amounts of silicon are needed, which is used to build their shell. In the absence or deficiency of silicon, the shells of diatoms become thinner, sometimes to an extreme degree.

In almost all freshwater ecosystems, the limiting factors include nitrates and phosphates. In lakes and rivers with soft water, they may also include calcium salts and some others. In sea waters, the concentration of dissolved nutrients such as nitrates, phosphates and some others is also low, and they are limiting factors, unlike sodium chloride and some other salts. Low concentrations of a number of nutrients in seawater, despite the fact that they are constantly washed into the sea, are due to the fact that their lifetime in a dissolved state is rather short.

Physical factors

Light. Solar radiation is no less important in the life of plants than water. Light is necessary for the plant as a source of energy for photochemical reactions and as a regulator of development. Its excess, as well as its deficiency, can cause serious disturbances in the development of algae. Therefore, light is also a limiting factor at maximum and minimum illumination. Each process dependent on solar radiation is carried out with the participation of certain perceiving structures - acceptors, which are usually played by the pigments of algae chloroplasts.

The distribution of algae in the water column is largely determined by the availability of light necessary for normal photosynthesis. Water absorbs solar radiation much more strongly than the atmosphere. Long-wave thermal rays are absorbed at the very surface of the water, infrared rays penetrate several centimeters deep, ultraviolet rays several decimeters (up to a meter), photosynthetically active radiation (light wavelength about 500 nm) penetrates to a depth of 200 m.

The light regime of the reservoir depends on:

1) on lighting conditions above the water surface;

2) on the degree of reflection of light by its surface (when the sun is high, a smooth water surface reflects on average 6% of the incident light, with strong waves - about 10%, when the sun is low, the reflection increases so significantly that most of the light no longer penetrates into the water : the day is shorter under water than on land);

3) on the degree of absorption and scattering of rays when passing through water. As depth increases, illumination decreases sharply. Light is absorbed and scattered by the water itself, solutes, suspended mineral particles, detritus, and planktonic organisms. In turbid running waters, already at a depth of 50 cm, the illumination is the same as under the canopy of a spruce forest, where only the most shade-tolerant species of higher plants can develop, but algae actively photosynthesize even at such a depth. In clear waters, algae attached to the bottom (benthic) are found to a depth of 30 m, and suspended in the water column (planktonic) - up to 140 m.

The layer of water above the habitat of photoautotrophic organisms is called the euphotic zone. In the sea, the boundary of the euphotic zone is usually located at a depth of 60 m, occasionally dropping to a depth of 100-120 m, and in clear ocean waters - to approximately 140 m. In lake, much less transparent waters, the boundary of this zone runs at a depth of 10-15 m , in the most transparent glacial and karst lakes - at a depth of 20-30 m.

Optimal illumination values ​​for different types of algae vary widely. In relation to light, heliophilic and heliophobic algae are distinguished. Heliophilic (light-loving) algae require a significant amount of light for normal life activity and photosynthesis. These include the majority of blue-green algae and a significant amount of green algae, which grow abundantly in the surface layers of water in the summer. Heliophobic (fearful, avoiding bright light) algae are adapted to low light conditions. For example, most diatoms avoid the brightly lit surface layer of water and in low-transparent waters of lakes they develop intensively at a depth of 2-3 m, and in clear waters of the seas - at a depth of 10-15 m. However, not all algae living in conditions of excessive illumination, need large amounts of light, i.e. they are truly heliophilic. Thus, Dunaliella salina - an inhabitant of open salty reservoirs and Trentepohlia jolitus, living on open rocks in the mountains, capable of accumulating oils with excess carotene, obviously playing a protective role, are essentially not light-loving, but light-resistant organisms.

Algae have different divisions depending on the composition of pigments - photoreceptors, the maximum intensity of photosynthesis is observed at different light wavelengths. Under terrestrial conditions, the quality characteristics of light are quite constant, as is the intensity of photosynthesis. When passing through water, light from the red and blue regions of the spectrum is absorbed and greenish light, weakly perceived by chlorophyll, penetrates to the depth. Therefore, mainly red and brown algae survive there, having additional photosynthetic pigments (phycocyans, phycoerythrins, etc.) that can use the energy of green light. This makes clear the enormous influence of light on the vertical distribution of algae in the seas and oceans: in the near-surface layers, as a rule, green algae predominate, deeper - brown, and in the deepest areas - red. However, this pattern is not absolute. Many algae are able to exist in conditions of extremely low illumination, which is not typical for them, and sometimes in complete darkness. At the same time, they may experience certain changes in the pigment composition or in the way they eat. Thus, in blue-green algae, under low light conditions, the pigment composition can change towards the predominance of phycobilins (phycocyan, phycoerythrin), and the color of trichomes changes from blue-green to purple. Representatives of many divisions of algae (for example, Euglenophyta, Chrysophyta) are capable of switching to a saprotrophic mode of nutrition in the absence of light and an excess of organic substances.

Water movement. Water movement plays a huge role in the life of algae, inhabitants of aquatic biotopes. Absolutely stagnant, motionless water does not exist, and therefore, almost all algae are inhabitants of flowing waters. In any continental and marine reservoirs, there is a relative movement of algae and water masses, ensuring the influx of nutrients and the removal of waste products of algae. Only in special extreme conditions are algae surrounded by a constant layer of water - in the thickness of the ice, on the soil surface, in the voids of rocks, on other plants, etc. The movement of water as a result of wind mixing is observed even in small puddles. In large lakes there are constant tidal currents, as well as vertical mixing. In the seas and oceans, which essentially form a single water system, in addition to tidal phenomena and vertical mixing, there are constant currents that are of great importance in the life of algae.

Temperature. The temperature range in which life can survive is very wide: -20 - +100 °C. Algae are organisms that are characterized by perhaps the widest ranges of temperature stability. They are able to exist in extreme temperature conditions - in hot springs, the temperature of which is close to the boiling point of water, and on the surface of ice and snow, where temperatures fluctuate around 0 ° C.

In relation to the temperature factor, algae are divided into: eurythermal species, existing in a wide temperature range (for example, green algae from the order Oedogoniales, the sterile ripples of which can be found in shallow water bodies from early spring to late autumn), and stenothermic species, adapted to very narrow, sometimes extreme temperature zones. Stenothermic algae include, for example, cryophilic (cold-loving) algae, which grow only at temperatures close to the freezing point of water. On the surface of ice and snow you can find representatives of various taxa of algae: Desmidiales, Ulotrichales, Volvocales, etc. In the colored snow in the Caucasus, 55 species of algae were found, of which 18 species were green, 10 were blue, 26 were diatoms, and 1 view - to red. 80 species of cryophilic diatoms have been found in the waters of the Arctic and Antarctic. In total, about 100 species of algae are known that can actively grow on the surface of ice and snow. These species are united by the ability to withstand freezing without damaging fine cellular structures, and then, upon thawing, quickly resume vegetation using a minimum amount of heat.

Algae, as mentioned above, often withstand high temperatures, settling in hot springs, geysers, volcanic lakes, cooling ponds of industrial enterprises, etc. Such species are called thermophilic. The maximum temperatures at which it was possible to find thermophilic algae range from 35 - 52 to 84 ° C and higher. Among thermophilic algae, representatives of various departments can be found, but the vast majority of them belong to blue-green. In total, more than 200 species of algae were found in hot springs, but there are relatively few obligate thermophilic species among them. Most algae found in hot springs can withstand high temperatures, but grow more abundantly at normal temperatures, meaning they are essentially mesothermic species. Only two species can be considered truly thermophilic: Mastigocladus laminosus and Phormidium laminosum, the mass development of which occurs at a temperature of 45-50 °C. The bulk of algae are generally mesothermic organisms, but among them it is always possible to distinguish more or less thermophilic ones that develop in certain temperature ranges.

The relationship of algae to the temperature factor affects their vertical distribution in water bodies. In various reservoirs and watercourses, due to the absorption of solar radiation by the upper layers of water, only these layers are heated. Warm water is less dense than cold water, and wind-induced currents equalize its density only to a certain depth. With the beginning of the growing season, a season of intense solar radiation, a very stable temperature stratification of water columns arises in fairly deep continental stagnant reservoirs. In these reservoirs, masses of water that are limited from each other are formed: a warm and light surface layer - the epilimnion and an underlying mass of colder and denser water - the hypolimnion. In autumn, the water in the reservoir cools and temperature stratification disappears. In the seas and oceans there is also a constant layer of temperature jump. Algae can develop only in the epilimnion (namely in the euphotic zone), and the most heat-loving and light-loving organisms settle in the surface, well-warmed layers of water.

The influence of temperature on algae developing in an aquatic environment is unusually great. It is the temperature that determines their geographical distribution. Thus, species of brown algae of the genus Lessonia are found only within the summer isotherm of 10 ° C, species of the genera Laminaria, Agarum, Alaria do not cross the summer isotherm of 20 ° C, some species of Sargassum live only at a temperature of 22-23 ° C (Sargasso Sea). Even in the Baltic Sea, among the communities of red algae, one can distinguish less thermophilic ones (Furcellaria, Delesseria, Dumontia), living at temperatures below 4 ° C, and more thermophilic ones (Nemalion), living at temperatures above 4 ° C. In general, with the exception of widespread eurythermal species (for example, some Fucales), the distribution of algae exhibits geographic zonation: specific toxons of marine planktonic and benthic algae are confined to certain geographic zones. Thus, large brown algae (Macrocystis) dominate the northern seas. As we move south, red algae begin to play an increasingly prominent role, and brown algae fade into the background. The ratio of the number of red and brown algae species in the Arctic seas is 1.5, in the English Channel - 2, in the Mediterranean Sea - 3, and off the Atlantic coast of Central America - 4.6. This relationship is an important characteristic of the zonal affiliation of the benthic flora.

Among green algae, more and less heat-loving species are also known. For example, Caulerpa prolifera and Cladophoropsis fasciculatus are confined to the equatorial zone of the world's oceans, and Codium ritteri - to northern latitudes.

Geographical zonation is also well expressed in marine planktonic algae. Marine tropical phytoplankton are characterized by significant species richness but very low productivity. The plankton of tropical waters is extremely rich in dinophyte and golden algae. Tropical waters are poor in diatoms, which dominate the northern seas.

The temperature factor also affects the vertical distribution of marine planktonic and benthic algae.

The vertical optimum of seaweed growth is usually determined by the complex influence of thermal and light regimes. It is known that as temperature decreases, the intensity of plant respiration weakens faster than the intensity of photosynthesis. The moment when the processes of respiration and photosynthesis balance each other is called the compensation point. The conditions under which the compensation point is established are optimal for the development of specific types of algae. In northern latitudes, due to low temperatures, the compensation point is established at greater depths than in southern latitudes. Thus, it is not uncommon for the same types of algae to be found at greater depths in northern latitudes than in southern latitudes.

It is obvious that temperature affects the geographic distribution of these (and other) algae primarily indirectly - by accelerating or slowing down the growth rate of individual species, which leads to their displacement by others that grow more intensively in a given temperature regime.

All of the listed abiotic factors act on the development and distribution of algae in a complex, compensating or complementing each other.

Biotic factors

Algae, being part of ecosystems, are usually connected with their other components by multiple connections. The direct and indirect impacts that algae undergo due to the vital activity of other organisms are classified as biotic factors.

Trophic factors. In most cases, algae in ecosystems act as producers of organic matter. In this regard, the most important factor limiting the development of algae in a particular ecosystem is the presence of consumers who exist by eating algae. For example, the development of communities dominated by species of the genus Laminaria off the Atlantic coast of Canada is limited by the number of sea urchins that feed primarily on this algae. In tropical waters in coral reef zones, there are areas in which fish completely eat up green, brown and red algae with soft thalli, leaving blue-green algae with hard calcified shells uneaten. Something similar to the effect of intensive grazing on meadow communities of higher plants is observed. Gastropods also primarily feed on algae. Crawling along the bottom, they eat microscopic algae and seedlings of macroscopic species. With the massive development of these mollusks, serious disturbances can occur in the algal communities of the littoral zone.

Allelopathic factors. The influence of algae on each other is often due to various allelopathic relationships. Benthic algae, for example, begin to exert mutual influence from the moment of sedimentation and spore germination. It has been experimentally proven that zoospores of Laminaria do not germinate in the vicinity of fragments of thalli of brown algae from the genus Ascophylum.

Competition. The development of individual algae species may also be affected by competition. Thus, species of the genus Fucales usually live in the tidal zone, subject to periodic (sometimes up to two days) drying out. Below, in the constantly flooded zone, there are usually dense thickets of other brown and red algae. However, in places where these thickets are not very dense, Fucales grow at greater depths.

Symbiosis. Of particular interest are cases of algae cohabiting with other organisms. Most often, algae use living organisms as a substrate. Based on the nature of the substrate on which fouling algae settle, they are divided into epiphytes, which live on plants, and epizoites, which live on animals. Thus, species of the genera Cladophora or Oedogonium can often be found on calcified shells of mollusks; some green, blue-green and diatom algae are common in the fouling of sponges. In fouling communities, weak and short-term connections are established between the host plant and the fouling plant.

Algae can also live in the tissues of other organisms - both extracellularly (in mucus, intercellular spaces of algae, sometimes in the membranes of dead cells) and intracellularly. Algae that live in the tissues or cells of other organisms are called endophytes. Extracellular and intracellular endophytes from among algae form rather complex symbioses - endosymbioses. They are characterized by the presence of more or less permanent and strong ties between partners. Endosymbioites can be a variety of algae - blue-green, green, brown, red and others, but the most numerous are endosymbioses of unicellular green and yellow-green algae with unicellular animals. The algae involved in them are called zoochlorella and zooxanthellae.

Yellow-green and green algae also form endosymbioses with multicellular organisms - freshwater sponges, hydras, etc. Peculiar endosymbioses of blue-green algae with protozoa and some other organisms are called syncyanosis. The resulting morphological complex is called cyanome, and the blue-green algae in it are called cyanella. Often, other species of this department can settle in the mucus of some blue-green species. They usually use ready-made organic compounds, which are formed in abundance during the breakdown of the mucus of the colony of the host plant, and multiply intensively. Sometimes their rapid development leads to the death of the colony of the host plant.

Among the symbioses formed by algae, the most interesting is their symbiosis with fungi, known as lichen symbiosis, as a result of which a peculiar group of plant organisms arose, called “ lichens" This symbiosis demonstrates a unique biological unity that led to the emergence of a fundamentally new organism. At the same time, each partner of the lichen symbiosis retains the features of the group of organisms to which it belongs. Lichens represent the only proven case of the emergence of a new organism as a result of the symbiosis of two.

Anthropogenic factors

Like any other living creature, a person, as a member of a biocenosis, is a biotic factor for other organisms of the ecosystem in which he is located. By laying canals and constructing reservoirs, people create new habitats for aquatic organisms, often fundamentally different from the reservoirs of a given region in hydrological and thermal conditions. Currently, the level of productivity of many continental water bodies is often determined not so much by natural conditions as by social and economic relations. Wastewater discharges often lead to depletion of species composition and death of algae or to the massive development of individual species. The first occurs when toxic substances are discharged into a reservoir, the second occurs when the reservoir is enriched with nutrients (especially nitrogen and phosphorus compounds) in mineral or organic form - i.e. anthropogenic eutrophication of water bodies. In many cases, the spontaneous enrichment of a reservoir with nutrients occurs on such a scale that the reservoir as an ecological system becomes overloaded with them. The consequence of this is excessive rapid development of algae - “water bloom”. Algae, especially aerophytic and soil algae, can also be affected by atmospheric emissions of toxic industrial waste. Often the consequences of involuntary or deliberate human intervention in the life of ecosystems are irreversible.

Lecture 2. Plant diversity. Seaweed

Plant taxonomy deals with the study and description of plant species and their distribution into groups based on the similarity of structure and family relationships between them, creating a classification.

Table 1. Taxonomic categories and taxa using potatoes as an example:

Lower plants, or algae

General characteristics. Algae are a large group of photosynthetic, predominantly aquatic, photoautotrophic eukaryotic plants. Most algae are characterized by: mainly an aquatic habitat, but a large number of species are also found on land (on the soil surface, wet stones, tree bark, etc.).

Most algae are suspended in the water column or actively floating ( phytoplankton ), some lead an attached lifestyle ( phytobenthos ). Green algae live in the coastal zone at shallow depths, brown algae contain pigments that allow them to live at a depth of up to 50 m, and a set of photosynthetic pigments of red algae allows them to live at a depth of 100-200 m, and some representatives are found at a depth of up to 500 m.

The body of algae can be unicellular, colonial or multicellular. If it is a multicellular organism, then its body is not differentiated into organs and tissues and is called thallus, or thallus. In complexly organized algae, elementary differentiation of the body can be observed, imitating the organs of higher plants - rhizoids, stem-like and leaf-like formations appear.

Cell structure. The cells of most algae have a cell wall formed by cellulose and pectin (only in primitive motile unicellular and colonial algae; in zoospores and gametes, the cells are limited only by the plasmalemma); the cell wall is almost always covered with mucus. The protoplast of cells consists of cytoplasm, one or more nuclei and chromatophores (plastids) containing chlorophyll and other pigments; chromatophores contain special formations - pyrenoids - protein bodies around which starch accumulates, formed during photosynthesis. Vacuoles are usually well developed; sometimes (especially in motile cells) there are special contractile vacuoles; Most mobile algae have flagella and a light-sensitive formation - an eye, or stigma, thanks to which the algae have phototaxis (the ability to actively move the entire organism towards the light).

Reproduction is asexual and sexual, asexual reproduction carried out using zoospores (motile) or spores (immobile). Asexual reproduction can also be carried out using vegetative propagation by fragmentation of the thallus, cell division of unicellular algae, and in colonial algae - due to the collapse of colonies.

Sexual reproduction occurs through the formation of many specialized germ cells - gametes and their fusion (fertilization), which is a sexual process. As a result of the fusion, a zygote is formed, which is covered with a thick protective shell. After a period of rest (less often immediately), the zygote grows into a new individual, formed mainly by meiotic division (zygotic reduction).

The cell wall is pectin-cellulose, capable of strong mucus formation, as a result of which in some algae the entire thallus acquires a slimy consistency. Many people may have calcium carbonate (CaCO 3) or magnesium (MgCO 3) deposited in their walls.

The product of assimilation is purple starch, similar in structure to glycogen. Unlike ordinary starch, when stained with iodine, it acquires a brown-red color.

Scarlet flowers are of great practical importance. Agar-agar is obtained from them, which is used in the confectionery and microbiological industries; many of them are raw materials for the production of glue. Iodine and bromine are obtained from the ash of scarlet plants. Some red algae are used to feed livestock. In Japan, China, the islands of Oceania and the USA, scarlet mushrooms are used as food. Purple considered a delicacy. red algae Chondrus used to produce carrageens - special polysaccharides that suppress the reproduction of the AIDS virus.

Department Brown algae. The department includes about 1500 species of multicellular, mainly macroscopic (up to 60-100 m) algae, leading attached ( benthic) Lifestyle. Most often they are found in shallow coastal waters of all seas and oceans, sometimes far from the coast (for example, in the Sargasso Sea).

Structure. The thalli of brown algae have the most complex structure among algae. Unicellular and colonial forms are absent. In highly organized cells, the thallus partially differentiates, forming tissue-like anatomical structures (for example, sieve tubes with oblique partitions). As a result of this, the formation of “stem” and “leaf” parts of the thallus occurs, performing heterogeneous functions. Algae are fixed in the substrate using rhizoids.

The cells of brown algae are mononuclear with numerous chromatophores that look like disks or grains. The brown color of algae is due to a mixture of pigments (chlorophyll, carotenoids, fucoxanthin). The main reserve substance is laminarin(a polysaccharide with bonds between glucose residues other than starch), deposited in the cytoplasm. The cell walls are heavily mucused. The mucus helps retain water and thus prevent dehydration, which is important for intertidal algae.

Reproduction sexual and asexual. Vegetative propagation is carried out by parts of the thallus.

Kelp. Representatives of the kelp genus are known as “sea kale” (Fig.). They are widespread in the northern seas. A mature sporophyte of kelp is a diploid plant with a length of 0.5 to 6 or more meters.

The kelp thallus has one or more leaf-like plates located on a simple or branched stem-like structure attached to the substrate by rhizoids. The stem-like formation with rhizoids is perennial, and the blade dies every year and grows back in the spring.

Typical representatives brown algae are kelp, macrocystis (its huge thallus reaches a length of 50-60 m), fucus, sargassum.

Meaning. Being autotrophs, algae are the main producers (i.e. producers) of organic substances in various bodies of water. In addition, during the process of photosynthesis they release oxygen, thereby creating favorable conditions for the life of not only aquatic, but also terrestrial organisms.

Algae play a huge role in human life: they are food for many commercial fish and other animals, they serve as additives in various nutritional mixtures, they are part of compound feeds, and some algae (for example, “sea kale”) are eaten. The cells of brown algae on top of the cellulose cell wall are covered with pectin, consisting of alginic acid or its salts; when mixed with water (in a ratio of 1/300), alginates form a viscous solution. Alginates are used in the food industry (for the production of marshmallows, marmalades), in perfumery (for the production of gels), in medicine (for the production of ointments), in the chemical industry (for the production of adhesives, varnishes). In the textile industry, they are used to make fade-resistant and waterproof fabrics. Seaweed is used to produce fertilizers, iodine, and bromine. Iodine was previously obtained exclusively from brown algae. Brown algae can serve as an indicator of the location of gold; they are able to accumulate it in the cells of the thallus.

Green algae department. The department unites about 13,000 species, this is the most extensive department among algae. A distinctive feature is the pure green color of the thalli, caused by the predominance of chlorophyll over other pigments. Distributed everywhere. Mostly green algae are inhabitants of fresh water bodies, but there are also marine species. Some live on land. There are species that enter into symbiotic relationships with some animals (sponges, coelenterates, tunicates) and fungi.

Structure. Green algae are represented by unicellular, colonial and multicellular forms. The cells have a dense cellulose-pectin shell and can be mononuclear or multinuclear. The cytoplasm contains chromatophores with pigments (mainly chlorophyll a and b). In addition to chlorophyll, cells contain carotenoids, xanthophylls and other pigments. Chloroplasts are similar to plastids of higher plants. The main storage substance accumulated in chloroplasts is starch.

Green algae are considered the ancestors of land plants: they have the same sets of photosynthetic pigments, the shell contains not only cellulose, but also pectin, a reserve substance is starch, reserve nutrients accumulate not in the cytoplasm (like other algae), but in plastids.

Genus Chlamydomonas. In translation - a single organism covered with ancient Greek clothing - chlamys. Single-celled algae that live mainly in shallow water bodies polluted with organic matter (Fig. 60). The Chlamydomonas cell has a round or oval shape, the front end is pointed in the form of a spout. It contains two flagella of equal size, with the help of which Chlamydomonas moves in water. The cell membrane is pectin-cellulose. In the center of the cell there is a cup-shaped chromatophore with a large pyrenoid. The nucleus is located in the recess of the chromatophore. At the anterior end of the cell there is a stigma and pulsating vacuoles.

Chlamydomonas reproduces both asexually and sexually. The haploid phase predominates in the life cycle. During asexual reproduction, Chlamydomonas loses its flagella, the contents of the cell are divided mitotically twice, and four daughter cells are formed under the shell of the mother cell. Each of them secretes a shell and forms flagella, turning into zoospores.

The sexual process in many species of Chlamydomonas occurs according to the type of isogamy. The cell contents divide to form 8 to 32 gametes, which resemble zoospores but are smaller in size. Cells with different sex signs merge. The resulting zygote becomes covered with a thick membrane and enters a period of rest. When favorable conditions occur, the contents of the zygospore are divided meiotically, and four haploid cells are formed, each of which becomes a new chlamydomonas.

In some species, the sexual process is carried out according to the type of heterogamy (both gametes are mobile, but the female gamete is larger than the male) or according to the type of oogamy (the female gamete is immobile).

Genus Chlorella. A single-celled algae that lives in fresh and salty water bodies, on moist soil, and rocks (Fig. 62). The cells look like green balls with a diameter of up to 15 microns. It has no flagella, ocelli or contractile vacuoles. The cells have a cup-shaped chromatophore with or without a pyrenoid and a small nucleus. Chlorella uses solar energy much more efficiently for photosynthesis. If terrestrial plants use about 1% of solar energy, then chlorella uses 10%. The sexual process for this alga is not known. Asexual reproduction occurs by mitotic division of the contents of the mother cell twice or three times. As a result of division, four or eight immobile spores are formed ( aplanospores). After the maternal membrane ruptures, the cells come out, increase in size and divide again.

Chlorella was the first algae that humans began to grow in culture. It was used as an experimental object to study some stages of photosynthesis. In some countries (USA, Japan, Israel), pilot plants for growing chlorella have been created and the possibility of using chlorella as a source of food for humans has been studied. The Japanese have learned to process chlorella into a white powder rich in proteins and vitamins. It can be added to flour for baking baked goods. In addition, chlorella is used as a source of cheap livestock feed and in biological wastewater treatment.

Class Ulotrix. Multicellular algae, the thallus of which is filamentous or lamellar. The most famous representatives belong to the genus Ulotrix and the genus Ulva. Non-branching threads of ulotrix, attaching to underwater objects - stones, piles, snags, etc., form green tufts. All cells (with the exception of the elongated colorless rhizoidal cell, with the help of which the algae attaches) have a similar structure. In the center of the cell there is a nucleus and a chromatophore, which has the shape of an open ring. The chromatophore contains several pyrenoids. The growth of the thread in length occurs due to cell division in the transverse direction. It grows in fast-flowing rivers and leads an attached lifestyle (Fig. 65).

Subsequently, the zygote divides reductionally, giving rise to four cells, each of which forms a new thread.

An important evolutionary line is associated with the transition from a filamentous thallus to a lamellar one. This is exactly the shape of the thallus in representatives of the genus Ulva (sea lettuce). Externally, the ulva resembles a thin green sheet of cellophane; its thallus up to 150 cm consists of two layers of cells. Ulva is characterized by alternation of generations, and the diploid sporophyte and haploid gametophytes do not differ in appearance. This alternation of generations is called isomorphic.

Genus Spirogyra. Green filamentous algae up to 8-10 cm long (Fig. 63). Numerous species of spirogyra live in fresh water bodies and in stagnant water. Clusters of Spirogyra filaments form mud. The threads are unbranched, formed by one row of cylindrical cells. There are no flagellar stages.

In the center of the cells there is a large nucleus. It is surrounded by cytoplasm, diverging in the form of strands from the center of the cell to the periphery. Here they connect with the wall layer of the cytoplasm. The strands penetrate a large vacuole. The cells contain ribbon-shaped, spiral-shaped chromatophores. They are located wall-to-wall on the inside of the shell. In different species of Spirogyra, the number of chromatophores ranges from 1 to 16. Large colorless pyrenoids are located in large numbers in the chromatophores. Outside, the algae is surrounded by a mucous sheath.

Rice. . Ladder conjugation of Spirogyra

The sexual process is carried out by conjugation (Fig. 64). Conjugation can be ladder or lateral. In ladder conjugation, two strands are parallel to each other. Adjacent cells form dome-shaped outgrowths that grow towards each other.

At the point of contact, the partitions separating the cells dissolve, and a channel is formed connecting both cells. The contents of one cell (male) are rounded and flow through the tube into another (female), and their contents (primarily the nuclei) merge. With lateral conjugation, fertilization occurs within one thread. In this case, the fusion of protoplasts of two adjacent cells is observed.

The zygote formed as a result of fertilization is surrounded by a thick cell wall and enters a period of rest. In spring, the zygote undergoes reduction division and forms four haploid nuclei. Three nuclei degenerate, and the fourth divides mitotically and gives rise to a new haploid thread. Thus, Spirogyra goes through its life cycle in the haploid phase; only its zygote is diploid.