The flagellate class is the smallest organisms that, in the process of evolution, occupy an intermediate position between plants and animals. Their importance in nature is great: plant species participate in the processing of the organics of water bodies and form plankton, which is an important component of the food chain, while other species of flagellates cause dangerous diseases.
Class Flagellum: general characteristic
The Mastigophora class (or Flagella) unites a group of protists that do not apply 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 receive food.
The habitat for representatives of the flagellum 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 characteristic of them only in a humid environment.
Morphologically, they can be either unicellular or multicellular, as well as form colonies of up to 20 thousand cells. Most of them are small, spherical, oval or fusiform. It is covered with a membrane or a layer of flat membrane vesicles, providing a stable shape.
The configuration and location of the flagella may vary. In some organisms, they are located along the entire body, forming, together with a fold on its surface, a motion organoid in the form of a membrane. Such a structure is often found in parasitic species.
The flagellum moves helically in the medium, due to which the bodies of the flagella are “screwed” into the surrounding fluid. This organoid has a rather complex structure: on the outside it is covered with a membrane of 3 layers, and inside there are threadlike structures from soldered microtubules.
Classification
The protists, in addition to the class of flagellates, include protozoa, algae and mushrooms. These living beings were isolated according to the residual principle. The British zoologist and paleontologist Richard Owen and the German natural scientist Ernst Haeckel proposed to identify them in a separate kingdom (pictured below). Before them, these organisms were considered the lowest green algae, or protozoa.
Already in the XIX century. scientists noted that the lower the level 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 flagella, eats like a plant in the light, and like an animal in poor light, by absorbing ready-made organic compounds.
However, the isolation of flagellates in a separate group became generally accepted only in 1969. In the old classifications describing the kingdom of the protists, the Sarcode and Flagellum classes were classified as Sarcomastigofora.
It is possible that the existing systematization will still change in connection with the development of molecular phylogenetics, which allows us to determine the relationship between organisms based on the study of their DNA.
Nutrition
One of the common characteristics of the class of flagella is that the representatives of this group have the most diverse forms of nutrition:
Osmotrophic - heterotrophic and autotrophic. The absorption of substances is carried out by passive transport of dissolved elements through the surface of the cell. Autotrophs, unlike heterotrophs, can independently synthesize organic compounds from inorganic ones (using photosynthesis). They accumulate reserve nutrients that are close in composition to starch and fat.
Phagotrophic. Such protozoa of the Flagellum class have an organelle, which is called the "cell mouth". It is a specialized area of the body to capture food (bacteria and other protists). In many phototrophic flagella, the “cell mouth” also serves as an excretion.
Mixotrophic (mixed).
According to the method of nutrition, flagella are divided into plant (Phytomas tigophorea) and animals (Zoomastigophorea). Isolation of metabolic products in freshwater species most often occurs with the help of another organoid - contractile vacuole, which opens out through the pore.
Breeding
Reproduction of flagellate organisms occurs in most cases by longitudinal binary division, less often with the formation of germ cells containing a single set of chromosomes, and subsequent copulation. Immediately after fertilization, the number of chromosomes decreases. This type of reproduction is characteristic mainly of plant species.
When dividing in two, the flagellum passes to one of the daughter cells, while in the other it forms again. In colonial organisms, division is carried out in two ways:
the total number of cells increases, they immediately grow to the size of the mother cells, and then the colony is "laced";
the daughter colony consists of small cells that divide multiple times.
If the environmental conditions for flagella are unfavorable, then they form cysts with dense shells that help them survive. Subsequently, a large number of young individuals are released.
Evolution
The flagellate class is one of the intermediate groups between plants and animals, being simultaneously their ancestor. Those organisms that were capable of photosynthesis evolved in 2 directions. In some of them, an additional species of chlorophyll c appeared and laminaran, a polysaccharide inherent in brown algae, began to form. Other flagellates became dominated by green chlorophyll a and b. An intermediate link also appeared - yellow-green algae with a green color, not having chlorophyll b.
As a result, 2 divisions of algae formed: with a predominance of brown pigments and green. The former “captured” the sea, and of the latter, photosynthetic higher terrestrial plants subsequently arose.
Features
Distinctive characteristics of the flagellum class are as follows:
permanent body shape;
outer shell or chitinous shell;
organelles of movement - flagella, which are outgrowths of the cytoplasm;
the presence of chlorophyll and a photosensitive organelle (stigma) in plant flagella, their free way of life in water;
the presence of kinetoplast at the base of the flagellum, which ensures its mobility and contains an additional large amount of DNA.
Representatives of Phytomas tigophorea
The flagellate class includes about 8 thousand species. Among plant flagella, the most common and important orders are:
Chrysomonas. Unicellular organisms with 1-3 flagella. Inhabit sea and fresh waters. They are typical representatives of plankton.
Armored. Their cell membrane consists of fiber plates. They have two flagella in front of the body. Also included in plankton. Among the flagellates of this group, there are organisms living in symbiosis with radiolarians (unicellular planktonic microorganisms) and coral polyps.
Primesiidae. They have a calcareous shell. After dying, they fall to the bottom and form chalk deposits.
Euglena. Characteristic of freshwater plankton. Absorb organic substances that pollute water. Widely used in experimental biology.
Volvox . Most of them are unicellular organisms with 2-4 flagella. Plankton is formed mainly in fresh water bodies.
Class Zoomastigophorea
Most Zoomastigophorea flagellates are plant and animal parasites. Among them, the most prominent representatives are the following:
Collar. Presumably from them other animals have descended. They have 1 flagellum surrounded by microvilli for better food capture. There are both single and colonial forms.
Kinetoplastides. Among them there are dangerous parasites of a person from the genus trypanosomes and Leishmania. The first parasitize in the blood and cerebrospinal fluid, leading to the development of sleeping sickness and other serious pathologies. The carriers of the Gambian and Rhodesian forms of trypanosomiasis are the tsetse fly, and leishmaniasis is mosquitoes.
Diplomas. Of these, the most famous are representatives of the genus Giardia. With parasitization in the intestine, a disease similar to colitis develops. A characteristic feature of these microorganisms is the doubled structure of the body, resembling a dividing cell in shape.
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 flagella carry important functions:
self-cleaning of water bodies from organic pollution, participation in the processing and mineralization of organics;
deposition of sapropels, calcareous and silicon 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 the "bloom" of water);
useful symbiosis with animals.
Of some types of class, flagellates make drugs.
Animal flagella, as mentioned above, play a large role in the development of many diseases in humans and other animals.