Class Flagellates are the smallest organisms that, in the process of evolution, have taken an intermediate position between plants and animals. Their significance in nature is great: plant species are involved in the processing of organic matter in water bodies and form plankton, which is an important part of the food chain, while other species of flagellates cause dangerous diseases.
Class Flagellates: general characteristics
Class Mastigophora (or Flagellates) unites a group of protists that do not belong to animals, plants, or fungi. This is a large category of living creatures, the distinguishing feature of which is the presence of one or more flagella used to move and get food.
The habitat for representatives of the flagella class is fresh and sea water, soil, and some parasitize or live in symbiosis in the body of animals and plants. An active lifestyle is typical for them only in a humid environment.
Morphologically, they can be both unicellular and multicellular, and also form colonies of up to 20 thousand cells. Most of them are small, spherical, ovalor fusiform body. It is covered with a membrane or a layer of flat membrane vesicles that provide a stable shape.
The configuration and location of the flagella can be different. In some organisms, they are located along the entire body, forming, together with a fold on its surface, an organoid of movement in the form of a membrane. This structure is often found in parasitic species.
The flagellum moves in the medium in a helical manner, due to which the bodies of the flagellates "screw" into the surrounding liquid. This organoid has a rather complex structure: on the outside it is covered with a membrane of 3 layers, and inside there are filamentous structures of fused microtubules.
Classification
The group of protists, in addition to the flagellate class, includes protozoa, algae and fungi. These living beings were isolated according to the residual principle. The English zoologist and paleontologist Richard Owen and the German naturalist Ernst Haeckel proposed to define them as a separate kingdom (pictured below). Before them, these organisms were considered lower green algae, or protozoa.
Already in the XIX century. scientists noted that the lower the stage at which representatives of the animal or plant kingdom are located, the more difficult it is to draw a clear line between them. So, green euglena, which is a “classic” representative of the flagellates, feeds like a plant in the light, and like an animal in poor light, by absorbing ready-made organic compounds.
However, the selectionflagellates into a separate group became generally accepted only in 1969. In the old classifications describing the kingdom of protists, the classes Sarcodaceae and Flagellates were assigned to the type Sarcomastigophora.
It is possible that the existing systematization will still change due to the development of molecular phylogenetics, which allows you to determine the relationship between organisms based on the study of their DNA.
Food
One of the common characteristics of the class of flagellates is that the representatives of this group have a wide variety of forms of nutrition:
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Osmotrophic - heterotrophic and autotrophic. Absorption of substances is produced by passive transport of dissolved elements across the cell surface. Autotrophs, unlike heterotrophs, can independently synthesize organic compounds from inorganic ones (using photosynthesis). They accumulate reserve nutrients that are similar in composition to starch and fat.
- Phagotrophic. In such protozoa of the flagellate class, there is an organelle, which is called the "cellular mouth". It is a specialized area of the body for capturing food (bacteria and other protists). In many phototrophic flagellates, the "cellular mouth" also performs the function of excretion.
- Mixotrophic (mixed).
According to the method of feeding, flagellates are divided into vegetable (Phytomas tigophorea) and animal (Zoomastigophorea). The excretion of metabolic products in freshwater species most often occurs withwith the help of another organoid - the contractile vacuole, which opens outward through the pore.
Reproduction
Reproduction of organisms of the class Flagellates occurs in most cases by longitudinal binary fission, less often with the formation of germ cells containing a single set of chromosomes, and subsequent copulation. Immediately after fertilization, a reduction in the number of chromosomes occurs. This type of reproduction is characteristic mainly for plant species.
When dividing in two, the flagellum passes to one of the daughter cells, and in the other it is formed anew. In colonial organisms, division occurs in two ways:
- the total number of cells increases, they immediately grow to the size of the mother, and then the colony is "laced";
- daughter colony consists of small cells that divide many times.
If the environmental conditions for flagellates are unfavorable, they form cysts with dense shells that help them survive. Subsequently, a large number of young individuals emerge from them.
Evolution
The flagella class is one of the intermediate groups between plants and animals, being at the same time their ancestor. Those organisms that were capable of photosynthesis evolved in 2 directions. Some of them developed an additional type of chlorophyll c and began to form laminaran, a polysaccharide inherent in brown algae. In other flagellates, green chlorophyll a and b began to predominate. Appeared andintermediate link - yellow-green algae with green color, without chlorophyll b.
As a result, 2 divisions of algae were formed: with a predominance of brown pigments and green ones. The former "captured" the sea, and from the latter, photosynthetic higher land plants later arose.
Features
Distinguishing characteristics of the Flagella class are as follows:
- permanent body shape;
- outer shell or chitin shell;
- motion organelles - flagella, which are outgrowths of the cytoplasm;
- presence of chlorophyll and photosensitive organelle (stigma) in plant flagellates, their free way of life in water;
- the presence of a kinetoplast at the base of the flagellum, which ensures its mobility and contains an additional large amount of DNA.
Representatives of Phytomas tigophorea
Class Flagella includes about 8 thousand species. Among the plant flagellates, the most common and important orders are:
- Chrysomonas. Unicellular organisms with 1-3 flagella. Inhabits marine and fresh waters. They are typical representatives of plankton.
- Papace. Their cell wall is made up of fiber plates. They have two flagella in front of the body. They are also part of the plankton. Among the flagellates of this group there are organisms living in symbiosis with radiolarians (single-celled planktonicmicroorganisms) and coral polyps.
- Primnesiids. They have a calcareous shell. After dying, they fall to the bottom and form chalk deposits.
- Euglenaceae. Characteristic of freshwater plankton. Absorb organic matter that pollutes the water. Widely used in experimental biology.
- Volvox . Most of them are unicellular organisms with 2-4 flagella. They form plankton mainly in fresh water.
Class Zoomastigophorea
Most of the flagellates of the class Zoomastigophorea are parasites of plants and animals. Among them, the most prominent representatives are the following:
- Collar. Presumably, other animals descended from them. They have 1 flagellum surrounded by microvilli for better food capture. There are both solitary and colonial forms.
- Kinetoplastids. Among them are dangerous human parasites from the genus Trypanosoma and Leishmania. The former parasitize in the blood and cerebrospinal fluid, leading to the development of sleeping sickness and other serious pathologies. The Gambian and Rhodesian forms of trypanosomiasis are transmitted by the tse-tse fly, and leishmaniasis by mosquitoes.
- Diplomonades. Of these, the most famous are representatives of the genus Giardia. When parasitizing in the intestine, the development of a disease similar to colitis occurs. A characteristic feature of these microorganisms is the double structure of the body, shaped like a dividing cell.
- Trichomonas. They have 4-6 flagella,one of which is the manager. One of the common parasitic diseases caused by these microorganisms is urogenital trichomoniasis.
Role in nature
Green flagellates perform important functions:
- self-purification of water bodies from organic pollution, participation in the processing and mineralization of organic matter;
- deposition of sapropels, calcareous and silicic rocks, which are part of the earth's crust;
- the formation of plankton, which is food for larger living organisms (the rapid development of phytoplankton leads to "blooming" of water);
- beneficial symbiosis with animals.
Medicines are made from some species of the class Flagellates.
Animal flagellates, as mentioned above, play a big role in the development of many diseases in humans and other animals.
