Biology. Systematic group of protozoa

Various systematic groups of protozoa (photo of some organisms presented in this article) unite single-celled animals belonging to the group of eukaryotes. From all other eukaryotes, they differ in that they usually consist of only one cell, although there may be several. Consequently, the cellular level of the organization is their highest. The systematic groups of protozoa do not include organisms that do not meet this requirement. Virtually all representatives have microscopic dimensions.

Morphophysiological features

In terms of their morpho-physiological differentiation, they are different. For example, the amoebae are relatively simply arranged (they do not have differentiated organoids of contraction, movement, seizure of food, etc.). And if we talk about infusoria, then their organization is quite complicated. These protozoans have superficial pellicular structures, contractile and supporting fibrils, as well as organoids of movement, defense, seizure of food, etc.). All systematic groups of the simplest animals are characterized by the presence of a peculiar cellular ultrastructure, as well as organelles of general purpose: lysosomes, ribosomes, Golgi apparatus, endoplasmic reticulum, mitochondria. The core is surrounded by a two-membrane shell, in which there are pores. It contains nucleoli, a karyoplasm and chromosomes (usually in the interphase nucleus they are despiralized).

Number of species

To date, the main systematic groups of protozoa have been investigated. About 25-30 thousand of their species are known. And these are only those that were discovered by scientists. The number of protists that exist in nature should be more than several times, because they are insufficiently investigated due to technical difficulties and their microscopic dimensions. Hundreds of new species of protozoa are described annually. All of them are divided into five classes: cetosporidia, infusorians, sporoviks, flagella and sarcodes. Comparative characteristics of systematic groups of protozoa allow us to distinguish their characteristic features. About many of them we will tell in this article.

Role in nature

Protozoa are very common in nature. They occupy a significant place in food chains, as well as in the biosphere as a whole. Many of them (infusorians, radiolarians, flagellates) are an integral part of marine plankton. Rapidly multiplying, they often reach a large number. These microorganisms are an important part of the diet of marine zooplankton, especially copepods. Often the protozoa (infusoria, foraminifera) are included in the marine benthos, which occurs from the littoral to very large depths. A number of microorganisms are part of freshwater benthos and plankton. Species composition of protozoa living in fresh waters is an indicator of saprobity, that is, contamination of water bodies with organic substances. The food of many fish fry, including commercial fish, are some of the simplest, especially infusoria.

Parasitic species

This systematic group of protozoa is numerous. Whole parasites consist of two classes - cognosporidia and sporoviks. Of particular importance among these protozoa are parasites of man, commercial and domestic mammals, fish and birds. Human diseases caused by them include giardiasis, leishmaniasis, amoebiasis, and malaria. The most severe for cattle are diseases that cause blood parasites - trypanosomiasis, theilerosis, pyroplasmidosis.

This systematic group of protozoa causes great damage also to poultry (coccidiosis). From the protozoan diseases in fish farming, the youngest of commercial fish suffers. In particular, ichthyophthirius, a parasitic infusoria (pictured above), can cause the fry to die. In a large part of the class of cndosporidia consists of parasites of fish and useful insects - silkworm and bees. Today, ways are being developed to use such protozoa, namely microsporidia, to fight insect pests. Encouraging results have already been obtained in this direction.

Sea Protozoa

This systematic group of protozoa played an important role in the formation of sedimentary rocks. This applies in particular to radiolarians and foraminifera. Many Cretaceous sediments, limestones and other sedimentary rocks formed at different geological periods on the bottom of sea water bodies are partially or completely formed by skeletons (flint or calcareous) of fossil protozoans. Micro-palaeontological analysis in this connection is carried out during geological exploration, especially in oil exploration.

Use in laboratory practice

In laboratory practice, various types of protozoans (infusoria, amoebae) are widely used in the study of biophysical, genetic and cytological problems. The technique of laboratory cultures is well developed. Protistology is a science that deals with the study of protozoa.

Microanatomy

The structure of the cell of the protozoa depends primarily on the lifestyle of a particular species, as well as on its physiological adaptations. Note that there is always one or more nuclei surrounded by a double membrane. Such a conclusion allowed scientists to make a comparative description of the systematic groups of protozoa. There are chromosomes in the nuclei. Their mandatory presence in all species also allowed us to identify the comparative characteristics of systematic groups of protozoa. Photo infusoria is presented below.

Nuclei in infusorians usually refer to two types: one or more small micronuclei and one large macronucleus. The cells of some protozoa are multinucleated. The main systematic groups of protozoa are characterized by the presence of vacuoles. These are spaces separated by a membrane from the rest of the cytoplasm. They differ in functions and in size. Vacuoles serve for digesting incoming food, as well as for the accumulation and removal of solid and liquid products of metabolism. In addition, they can be used to settle algae, which provide hosts, that is, simple organisms, photosynthesized by organics. In the vacuoles or cytoplasm of some species, pigment granules are contained. In addition, they contain plastids - intracellular specialized structures that contain pigments associated with photosynthesis. Their number and shape depend on the species, that is, they refer to the classification characteristics. Under the outer membrane of some protozoa are extrusomes, "firing" organelles. These are, for example, mucocysts that secrete mucus, as well as trichocysts, throwing out thin filaments. Perhaps they serve to protect. The protozoa also have flagella. Depending on the type, they can be from one to many. This locomotor threadlike organelles, having a complex system of longitudinal internal microtubules. By the principle of work and their structure, they are significantly different from the flagella of bacteria. In particular, they are characteristic of flagellates. Let's say a few words about them separately.

Flagellae use flagella to create currents of water and / or locomotion, so they receive food. This systematic group of protozoa includes a multitude of both parasites and free-living forms and symbionts of animals. There are unicellular polyenergic and monoenergetic forms, as well as multicellular and colonial ones. For the flagellates as a whole, there is a tendency towards over-vision feeding and small cell sizes. Although there are also phagotrophic, very large forms among them.

Cilia resemble flagella, however they are shorter and always form whole complexes on the cell coordinated. The nature of the distribution of cilia along the surface is an important classification characteristic applicable to systematic groups of protozoa.

They do not include crustaceans, but some protozoans are covered with mineralized or organic scales, shells or carapaces, different in composition and structure. In addition, they may have a rigid intracellular skeleton, which is usually a complex lattice structure.

Food

As for physiology, the representatives of this systematic group are either autotrophs (that is, they photosynthesize the organics), or heterotrophs (absorb it from the medium), or mixotrophs (use the above two methods of nutrition). Heterotrophs can absorb dissolved substances in the cell surface. In this case, they are called surveyors. In addition, they can swallow solid foods through various mechanisms, and then they are called phagotrophs. The food of phagotrophs can include other organisms. In particular, they can eat other protozoa. Sometimes, in order to seize prey, they pursue it.

Allocation

From the cell to the external environment, solid exchange products are removed by fusing vacuoles containing them with the outer membrane. This happens sometimes in a specialized area (cytoprotection, cellular powder). Reducing vacuoles actively pumped out excess water with metabolic waste dissolved in it.

Breath

Characteristics of systematic groups of protozoa can be supplemented by the features of respiration. It can be both anoxic (anaerobic), and requiring an oxygen medium, that is, aerobic. Oxygen for obligate anaerobes is harmful, and they perish in an environment rich in them. Some species in aquatic habitats, poor in them, breathe through symbiotic bacteria. At the same time, the intensity with which this process occurs is directly proportional to temperature and depends on the type of metabolizable substrate, that is, the cleavable molecules, as well as the taxonomic group.

Reproduction

The description of systematic groups of protozoa completing the features of reproduction. They can breed asexually. In this case, the cell is divided into several children. However, they can carry out this process and sexually, with the participation of two cells. These methods sometimes alternate depending on the stage at which the life cycle is located. Sex cells (they are called gametes) merge during sexual reproduction or a temporary conjugation of two ordinary cells is observed, which leads to the exchange of hereditary material between them. If the outwardly merging gametes are practically the same, we are talking about isogamy. In the event that one of them is considerably larger in size, they speak of anisogamy.

Of course, we only briefly characterized the systematic groups of protozoa. Biology is a science, after studying which, you can discover a whole new world. Our eyes are not able to distinguish between microorganisms, but science allows us to see them. We are faced with whole worlds. Examples of them are various systematic groups of protozoa. Kornozhki, sporoviki, infusoria, flagellates and other organisms are very interesting in many respects.