Unicellular algae.
Algae are characterized by a wide variety of structures
niya. They are unicellular, colonial and multicellular.
In the conditions of Belarus, such autotrophic and autoheterotrophic unicellular algae as chlorella, green euglena, etc. are widespread.
Chlorella is often found in fresh water, on damp earth, tree bark. Chlorella is a single-celled, spherical organism. Its cell is covered with a dense smooth shell. The cytoplasm contains the nucleus, cup-shaped chloroplast and other organelles.
Chlorella reproduces asexually, producing many spores. Spores still inside the mother cell are covered with their own membrane and then go outside. In the future, the dispute grows into an adult.
Euglena green lives in small fresh water bodies with stagnant water - puddles, lakes, swamps, and also on moist soil. In the summer, it is praying to watch how in a small pond or puddle the water turns green - “blooms”. The reason for this "flowering" may be the massive development of euglena. Under a microscope, in a drop of water taken from such a reservoir, one can examine its structure.
The structure of euglena green: 1 - peephole; 2 - chloroplast; 3 - nucleus; 4 - reserve nutrients; 5 - contractile vacuole; 6 - flagellum.
Euglena's green body is about 0.05 mm long and has an elongated, streamlined shape, well adapted to movement in water. The outer layer of the cytoplasm in Euglena is compacted and is called the pellicle, which gives the cell its shape. At the front end of the body of euglena there is a depression. It is the excretory canal of the contractile vacuole, and the flagellum- organoid of movement. Constantly rotating the flagellum, the euglena, as it were, is screwed into the water and due to this it swims forward. In the cytoplasm of euglena there is a nucleus, a bright red light-sensitive eye and about 20 chloroplasts containing chlorophyll.
Food. A feature of euglena is the ability to change the nature of nutrition and metabolism depending on environmental conditions. In the light, it has an autotrophic type of nutrition. Euglenas are always found in the illuminated part of the reservoir, where there are more favorable conditions for photosynthesis. Euglene helps to find illuminated places photosensitive eye, located at the anterior end of the body.
If euglena is placed in the dark for a long time, it loses chlorophyll and becomes colorless. In the absence of chlorophyll, photosynthesis stops, euglena begins to assimilate ready-made organic substances, i.e. switches from autotrophic to heterotrophic (saprotrophic) mode of nutrition. That is why in waters enriched with organic substances, euglena develops in mass quantities.
Heterotrophic nutrition in euglena is carried out by the absorption of organic substances by the entire surface of the body.
Often, developing in polluted water bodies, where there is a large amount of dissolved organic matter, euglena combines both types of nutrition - both autotrophic and heterotrophic. The ability of euglena to change the nature of nutrition provides the possibility of survival in various conditions of existence. Thus, Euglena green is an autoheterotrophic protist.
Distinctive feature autoheterotrophic protists is their ability to eat in two ways: in the light - like plants, and in the dark - like animals. This means that in the light they carry out the process of photosynthesis and create organic substances. With insufficient lighting for photosynthesis and with an abundance of organic substances in the water, they assimilate ready-made organic substances that are formed in the reservoir during the breakdown of dead parts of living organisms.
Respiration and excretion Euglena green occurs in the same way as in other freshwater protists.
The contractile vacuole, in which excess water accumulates with dissolved metabolic products, when reduced, brings its contents out. This process occurs rhythmically every 20-30 s.
Reproduction. Asexual reproduction of euglena begins with the division of the nucleus, chloroplasts, photosensitive eye and the formation of a second flagellum. Then, at the anterior end of the cell between the flagella, a dividing slit appears, which gradually increases. At the end of the longitudinal division, the daughter cells, interconnected by their posterior ends, diverge. Under favorable conditions, the process of cell division lasts 2-4 hours.
Sexual reproduction in Euglena has not been scientifically established.
Euglena, like the amoeba, endures unfavorable environmental conditions in the state of a cyst.
Chlamydomonas often found in the same organically polluted water bodies as euglena. Last year you got acquainted with its structure, nutrition, reproduction. To this should be added another very important feature of chlamydomonas. It turns out that, along with the autotrophic mode of nutrition, it is able to absorb organic substances dissolved in water through the shell and thus participate in the purification of polluted water.
Chlamydomonas reproduces asexually and sexually. In favorable conditions chlamydomonas breeds asexual way. At the same time, chlamydomonas loses flagella, stops moving. Its nucleus divides twice: four daughter nuclei are formed. The protoplast is then divided into four parts. Thus, four, and sometimes eight zoospores are formed inside the mother cell. Each of them is covered with a shell, and two flagella are formed at the anterior end. The shell of the mother cell breaks, and the zoospores develop into daughter chlamydomonas, which begin an independent existence. They grow rapidly and in a day are capable of a new division.
In adverse conditions(for example, when a pond dries up) in chlamydomonas, sexual reproduction. At the same time, its contents are divided into 6, 32, 64 small mobile
sex cells - gametes. They swim out into the water and merge with the gametes of another individual. This is how fertilization occurs, as a result of which one cell is formed - a zygote. It does not have flagella, is covered with a thick shell and is resistant to adverse conditions. When favorable conditions occur, several chlamydomonas develop from the zygote.
Diatoms. Diatoms are found in the seas and fresh waters of all climatic zones. Under a microscope, you can see that the shape of these unicellular organisms is very diverse. Common to all diatoms is the presence of a strong silica shell. This shell consists of two halves, which fit one to the other, like a box with a lid. The yellow-brown color is given to diatoms by pigments that mask chlorophyll. Reproduction of diatoms occurs sexually and asexually through cell division. As a result of an increase in the volume of the cytoplasm, the halves of the shell diverge, and the nucleus and cytoplasm divide. Each daughter cell re-forms the missing half of the shell.
In fresh waters, diatoms are mainly found at the bottom of reservoirs. Marine diatoms live in water in suspension. A drop of fat contained in the algae cell allows it to easily maintain this state. Diatoms form an important food base for animals living on the shallows, such as molluscs. On one square centimeter of land flooded by the tide, often over a million diatoms live, forming a brown coating there. Mollusks “graze” on diatoms, and other animals, such as herring gull and eider, feed on them.
Diatoms are at the very beginning of the food chain: diatoms → molluscs → birds.
Almost non-decomposing shells dia-
Diatoms of marine and fresh water bodies: 1 - tabellaria; 2- pinnularia; 3 - tabellaria; 4 - rhizosalting; 5 - fragilaria; 6 - stephanodiscus; 7 - navicula; 8 - asterionella; 9 - cyclotella.
tom algae have formed thick layers of sedimentary rock over geological epochs diatomite. Today these deposits are being developed. Due to the fine structure and hardness of the shells, diatomite is used as a grinding and polishing material, as well as for the manufacture of filters. In pharmacies, silica is offered as a skin, hair and nail care product. The structure of diatom shells is so fine and regular that they can be used to check the quality of microscopes.
colonial algae. Volvox. In small freshwater reservoirs (ponds, lakes) there are floating green balls with a diameter of 1-2 mm. This is Volvox. When viewed under a microscope, it can be seen that it is formed by many individual cells located along the periphery of the ball in one layer. Their number ranges from 500 to 60,000.
The bulk of the colony consists of a semi-liquid gelatinous substance, which was formed as a result of the mucus of the cell walls. The outer layer of the gelatinous substance is denser, which gives the entire colony a certain shape.
In a Volvox colony, individual individuals are not completely isolated from one another. They are fused with their side walls and interconnected by thin cytoplasmic bridges.
Volvox is characterized by differentiation, or specialization, of cells in a colony. Some of them are vegetative, incapable of reproduction, others are cells of asexual and sexual reproduction. There are few reproductive cells in the Volvox colony - from 4 to 10. In the summer, these cells divide many times and form several new daughter colonies inside the mother colony. When the size of the daughter colonies increases so much that they cannot fit inside the mother colony, the latter bursts and dies, and the daughter colonies come out.
During sexual reproduction, gametes develop in specialized cells of the colony, as a result of the fusion of which a zygote is formed. After a dormant period, a new colony develops from the zygote after a series of successive divisions.
The presence of organisms such as Volvox with specialized cells that perform different functions suggests that the development of multicellular organisms from unicellular organisms could go through colonial forms.
Algae include unicellular, colonial and multicellular organisms capable of photosynthesis. The ability to photosynthesis is provided by the presence of chloroplasts in their cells. Algae have different shapes and sizes. They live mainly in water and inhabit those water depths where light penetrates. Euglena green and chlamydomonas are typical representatives of autoheterotrophic protists (algae).
Multicellular algae are widespread in freshwater and marine reservoirs. The body of multicellular algae is called thallus. From A distinctive feature of the thallus is the similarity of cells and the absence of tissues and organs. All cells of the thallus are arranged in almost the same way, and all parts of the body perform the same functions. In the body of algae, substances move from cell to cell, and this happens very slowly.
Thallus cells can divide in one direction, forming filaments, or in two directions, forming plates. Among the algae, there are species not only microscopically small in size, but also those that reach a length of over 100 m (for example, the brown alga Macrocystis pearus reaches a length of 160 m).
Algae play an important role in nature, participating in the formation of organic matter and oxygen.
Multicellular algae are filamentous, lamellar, bushy. They tend to lead an attached lifestyle.
Ulotrix. This alga lives mainly in fresh, less often in marine waters. It attaches to underwater objects, forming bright green bushes up to 10 cm high.
The ulotrix filaments consist of one row of cylindrical cells with thick cellulose membranes. Ulotrix is characterized by chloroplasts in the form of a plate that forms an open belt.
Asexual reproduction is carried out by breaking the filament into short sections, each of which develops into a new filament, or by 4-flagellated zoospores. They emerge from the mother cell, lose their flagella, attach sideways to the substrate, and grow into a new filament. During sexual reproduction
Reproduction of ulotrix and alternation of generations: a - daughter (new) algae; b - algae that form gametes (gametophytes): 1 - germination of zoospores; 2 - gametes; 3 - fusion of gametes; 4 - zygote (sporophyte); 5 - germination of the zygote with four flagellated zoospores.
sac connected by strands to the parietal cytoplasm.
Asexual reproduction in spirogyra is carried out by breaking the thread into separate short sections. reproduction
Spirogyra: a - part of the thread; b - sexual process (conjugation): 1 - chloroplast; 2 - nucleus; 3 - zygote.
disputes are absent. Spirogyra is also characterized by sexual reproduction.
During sexual reproduction, usually two threads are located side by side. In their cells, protrusions of the walls arise, which grow towards each other. In the place of their contact, the walls dissolve, and a through channel is formed between the cells of the two threads. Through this channel, the content of the cell of one thread moves to the cell of another thread and merges with its content. As a result, a zygote is formed. This type of sexual process is called conjugation. The formed zygotes with a thick shell germinate after a dormant period. This is preceded by a double fission of the nucleus: out of the four resulting nuclei, three die off, 
Seaweed: 1 - ulva; 2 - fucus.
and one remains the nucleus of a single seedling, which emerges at the rupture of the zygote shell and develops into an adult algae.
Ulva. Ulva is known under the name "sea lettuce", as the population of many coastal countries eats it. Ulva is one of the mass algae in the shallow waters of the Black and Japan Seas. It is easily recognizable by its wide two-layer lamellar thallus of bright green color.
Ulva thallus consists of almost the same type of cells. Only at the base they are larger and are equipped with processes, with the help of which the plants are attached to the substrate. Ulva reproduces asexually (four-flagellated zoospores) and sexually. She does not have specialized reproductive organs, zoospores and gametes are formed in ordinary cells.
Kelp. The seas are inhabited by algae, which have a yellow-brown color of the thallus. These are the so-called brown algae. The color of their thallus is due to the high content of special pigments in the cells. The body of brown algae looks like filaments or plates. A typical representative of this group of algae is kelp, which is known as "seaweed". It has a lamellar thallus up to 10 - 15 m long. Laminaria is attached to the substrate by outgrowths of the thallus - rhizoids. It reproduces by zoospores and sexually.
Laminaria is used as food, goes to livestock feed as a food supplement containing many chemical elements and a large amount of iodine. Laminaria is also used to obtain iodine and carbohydrates used in the food, medical and microbiological industries.
Forms dense thickets in shallow water fucus. Its thallus is more dissected than that of kelp. In the upper part of the thallus there are special air bubbles, due to which the body of the fucus is held in an upright position.
Adaptations of algae to living conditions. For organisms that live in the oceans, seas, rivers and other bodies of water, water is their habitat. Conditions of this environment
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Seaweed: 1 - kelp; 2 - allaria; 3 - undaria; 4 - phyllophora; 5 - helidium; 6 - anfeltia.
markedly different from ground conditions. Reservoirs are characterized by a gradual decrease in illumination as they dive deeper, fluctuations in temperature and salinity, low oxygen content in water - 30-35 times less than in air. In addition, algae are at great risk from the movement of water, especially in the coastal (tidal) zone. Here, algae are exposed to such powerful factors as surf and wave impacts, low tides, tides, etc.
The survival of algae in such severe conditions of the aquatic environment is possible due to a number of structural features.
1. With a lack of moisture, cell membranes thicken significantly, are impregnated with inorganic and organic substances, which protect the body from drying out during low tide.
2. Seaweed thallus is firmly attached to the ground, so in case of surf and
wave impacts, they relatively rarely break away from the ground.
3. Deep sea algae contain larger chloroplasts with a high content of chlorophyll and other photosynthetic pigments.
4. Some algae have special bubbles filled with air. They, like floats, hold the thallus at the surface of the water, where it is possible to capture the maximum amount of light for photosynthesis.
5. The release of spores and gametes in algae coincides with the tide. The development of the zygote occurs immediately after fertilization, which prevents it from being carried into the ocean.
The value of algae. The ubiquitous distribution of algae determines their great importance in the biosphere and human economic activity. Due to the ability to photosynthesis, they create a huge amount of organic substances in water bodies that are used by aquatic animals. In other words, algae are the breadwinners of aquatic animals.
Algae are a source of oxygen. Absorbing carbon dioxide from water, algae saturate it with oxygen, which is necessary for all living organisms.
Many algae (euglena, chlamydomonas, etc.) are active orderlies of polluted water bodies, including utility and domestic wastewater from urban sewers.
In the geological past of the Earth, algae played an important role in the formation of rocks and chalk rocks, limestones, reefs, special varieties of coal, and were the ancestors of plants that inhabited the land.
Algae are extremely widely used in various branches of human economic activity, including in the food, pharmaceutical and perfume industries. They are cultivated in large quantities in open-air facilities in order to obtain proteins and vitamins.
Of great importance in nature and human economic activity is chlorella. Rapid reproduction and high intensity of photosynthesis (about 3-5 times higher than in land plants) lead to the fact that the mass of chlorella increases more than 10 times per day. At the same time, proteins (up to 50% of the dry mass of the cell), sugars, fats, vitamins, etc. accumulate in the cells.
The ability of chlorella in the process of photosynthesis to intensively absorb carbon dioxide and release oxygen makes it possible to use it to restore air in the confined spaces of spacecraft and submarines.
Algae serve as a raw material for obtaining valuable organic substances: alcohols, varnish, organic acids, iodine. Special substances are also obtained from algae, on the basis of which glue is made, which has an adhesive strength 14 times greater than that of starch. These substances are used in the textile and paper industries to impart density and gloss to paper.
Obtained from red algae agar-agar. It is used as a solid medium on which fungi and bacteria are grown with the addition of certain nutrients. In large quantities, agar-agar is used in the food industry in the manufacture of marmalade, marshmallow, ice cream and other products.
Man uses algae for food. So, on the Hawaiian Islands, out of 115 species of algae available there, the local population eats about 60. The most famous as a therapeutic and prophylactic agent is "sea kale" (some types of brown algae kelp and red porphyry). It is used against gastrointestinal disorders, thyroid disease, rickets and other diseases. In agriculture, algae are used as organic fertilizers for some plants and as a feed additive in the diets of domestic animals.
Multicellular algae are widespread in freshwater and marine reservoirs. The body of multicellular algae is called the thallus. A distinctive feature of the thallus is the similarity in the structure of cells and the absence of tissues and organs. All cells of the thallus are arranged in almost the same way, and all parts of the body perform the same functions. For living in water, algae have a number of characteristic features. Algae play an important role in the biosphere and human economic activity.
