General characteristics of the structure and life of unicellular organisms. General characteristics of unicellular (protozoa)

There are about 70,000 species of unicellular animals in the world fauna.

Almost all simple ones are microscopic in size (from 2 microns to 0.2 mm), among them there are also colonial forms (volvox). Single-celled organisms live in freshwater (common amoeba, green euglena, infusoria-shoe, volvox) and marine water bodies (foraminifera, promenyaks), in the soil (some types of amoebae, flagellates, ciliates).

The simplest are representatives of the animal world, located at the cellular level of organization. Morphologically, they constitute one cell, and functionally they constitute an integral organism. Therefore, the cell of the simplest is built much more complicated than the cell of a multicellular organism.

This is due to the fact that the cells of multicellular organisms perform only certain functions, while one cell of the simplest performs all the vital functions inherent in the whole organism: nutrition, movement, excretion, respiration, reproduction, etc.

Features of the structure and vital activity of unicellular organisms (protozoa)

The protozoan cell, like any eukaryotic cell, has general cellular organelles. In the cytoplasm of protozoa, two layers are distinguished: the outer - ectoplasm and the inner - endoplasm. In addition, the protozoa have organelles characteristic only of them: movements (pseudopodia, flagella, cilia), digestion (digestive vacuoles, ciliates have a cellular mouth, pharynx), excretion and osmoregulation (contractile vacuoles).

A cell of unicellular animals contains one (ameba, euglena) or several (ciliates) nuclei. The vast majority of unicellular organisms have the ability to move. With the help of temporary bulges of the cytoplasm - false legs (pseudo-legs), simple ones, devoid of a dense cell membrane (ameba), move. Flagella (euglena green) and cilia (ciliates-shoe) contribute to the rapid movement of unicellular organisms.

The ways of feeding protozoa are varied. Most of them feed heterotrophically. In amoeba, food enters the cytoplasm with the help of pseudopodia, which capture it. In ciliates, vibrations of the cilia cause food to enter the cellular mouth and pharynx.

Digestion of food occurs in digestive vacuoles. Undigested food residues are removed from the cell in any place to which the digestive vacuole (amoeba) approaches or through special openings (powder in ciliates-shoes).

Among unicellular animals, there are species that feed like green plants (volvox). In their cytoplasm there are chromatophores - organelles with photosynthetic pigments. For some flagellates with chromatophores (euglena green), a characteristic mixed (mixotrophic) type of nutrition. In the light, they are capable of photosynthesis, and in the dark they feed on ready-made organic substances.

Respiration is carried out by the supply of oxygen through the entire surface of the cell. It oxidizes complex organic substances to CO 2 , H 2 O and other compounds. At the same time, energy is released, which is used for the life processes of animals.

For protozoa, asexual and sexual methods of reproduction are characteristic. Asexual reproduction is carried out by division and budding. More often single-celled ones reproduce by dividing the mother's organism into two daughter cells.

For ciliates-shoes, in addition to the section, there is a characteristic sexual process, during which two ciliates are temporarily connected to each other and exchange small nuclei. Thus ciliates exchange genetic (hereditary) information contained in their nuclei.

Unicellular is characterized by irritability - the response-reaction of the body to external influences. Unicellular organisms endure unfavorable environmental conditions in the state of a cyst - the cell is rounded, compressed, draws in the organelles of movement and is covered with a thick membrane.

Soil formation processes are also carried out with the help of protozoa. Flagellar unicellular serve for the biological assessment of the degree of purity of water bodies (biodiagnostics). Foraminifers and promenacs play a significant role in the formation of chalk and limestone deposits, which are valuable building materials.

The main terms and concepts tested in the examination paper: amoeba, balantidia, flagellates, ciliates, coccidia, malarial plasmodium, digestive vacuole, sexual progress, powder, sarcodes, contractile vacuole, sporozoans, green euglena.

The body of the simplest animals consists of a single cell that performs all the functions of life. Representatives of this sub-kingdom have all the properties of an independent organism. Free-living protozoa have additional organelles for movement, nutrition, excretion, protection, etc. Some of these organelles are temporary (amoeba prolegs), some are permanent (euglena flagellum, ciliate cilia).

The role of protozoa in nature and human life:

- are indispensable participants in the circulation of substances and energy in ecosystems, acting as micro-consumers and decomposers;

- form geological deposits of limestone, chalk;

- are objects of scientific research;

Flagella class. Representatives of this class have a constant body shape, due to the presence of a compacted cell membrane.

Euglena green has a spindle-shaped body. The cell size is about 0.05 mm. Euglena moves with the help of a flagellum - a cytoplasmic outgrowth consisting of thin fibrils. At the front end is a light-sensitive eye. In the cytoplasm, in addition to all the organelles characteristic of animal cells, there are chromatophores containing chlorophyll. In the light, Euglena is capable of photosynthesis. Therefore, it is referred to as intermediate, between plants and animals, evolutionary forms. Euglena reproduces asexually by dividing in two along the longitudinal axis. Sexual reproduction is carried out by copulation(cell fusion).

Volvox belongs to the colonial forms of flagellates.

type of infusoria. Class ciliary infusoria. The type has about 6 thousand species.

Representatives - infusoria-shoe, infusoria-trumpeter.

Infusoria-shoe - an animal 0.1-0.3 mm in size.

Its cell membrane is covered with cilia that serve for movement. There are two nuclei in a cell vegetative , polyploid And generative , diploid. The oral recess on the body forms an oral funnel, passing into the cellular mouth, leading to throat. Formed in the throat digestive vacuoles that digest food. Undigested food remains are removed through the opening - powder .

The ciliate shoe has two contractile vacuoles located at opposite ends of the body. Through them, excess water and metabolic products are excreted.

Reproduction of ciliates occurs both asexually and sexually. During asexual reproduction, longitudinal cell division occurs. During the sexual process, a cytoplasmic bridge is formed between two ciliates. Polyploid (large) nuclei are destroyed, and diploid (small) nuclei are divided by meiosis with the formation of four haploid nuclei, three of which die, and the fourth is divided in half, but by mitosis. Two nuclei are formed. One is stationary and the other is migratory. Then between the ciliates there is an exchange of migrating nuclei. Then the stationary and migrating nuclei merge, the individuals disperse, and large and small nuclei are again formed in them.

To the sub-kingdom Protozoa are unicellular animals. Some species form colonies.

The protozoan cell has the same structural scheme as the cell of a multicellular animal: it is limited by a membrane, the inner space is filled with cytoplasm, in which the nucleus (nuclei), organelles and inclusions are located.

The cell membrane in some species is represented by an outer (cytoplasmic) membrane, in others - by a membrane and a pellicle. Some groups of protozoa form a shell around themselves. The membrane has a structure typical of a eukaryotic cell: it consists of two layers of phospholipids, into which proteins “sink” to different depths.

The number of cores is one, two or more. The shape of the nucleus is usually rounded. The nucleus is bounded by two membranes, these membranes are permeated with pores. The internal content of the nucleus is the nuclear juice (karyoplasm), which contains chromatin and nucleoli. Chromatin consists of DNA and proteins and is an interphase form of the existence of chromosomes (decondensed chromosomes). The nucleolus is composed of rRNA and proteins and is the site where ribosome subunits are formed.

The outer layer of the cytoplasm is usually lighter and denser - ectoplasm, the inner - endoplasm.

In the cytoplasm there are organelles that are characteristic of both cells of multicellular animals, and organelles that are characteristic only of this group of animals. Organelles of protozoa, common with organelles of a multicellular animal cell: mitochondria (ATP synthesis, oxidation of organic substances), endoplasmic reticulum (transport of substances, synthesis of various organic substances, compartmentalization), Golgi complex (accumulation, modification, secretion of various organic substances, synthesis of carbohydrates and lipids , the site of formation of primary lysosomes), lysosomes (cleavage of organic substances), ribosomes (protein synthesis), cell center with centrioles (formation of microtubules, in particular, spindle microtubules), microtubules and microfilaments (cytoskeleton). Protozoan organelles, characteristic only for this group of animals: stigmas (light perception), trichocysts (protection), axtostyle (support), contractile vacuoles (osmoregulation), etc. Photosynthesis organelles found in plant flagellates are called chromatophores. The organelles of protozoan movement are represented by pseudopodia, cilia, and flagella.

Nutrition - heterotrophic; in plant flagellates - autotrophic, may be mixotrophic.

Gas exchange occurs through the cell membrane, the vast majority of protozoa are aerobic organisms.

The response to environmental influences (irritability) manifests itself in the form of taxis.

When adverse conditions occur, most protozoa form cysts. Encystation is a way of experiencing adverse conditions.

The main method of protozoan reproduction is asexual reproduction: a) division of the mother cell into two daughter cells, b) division of the mother cell into many daughter cells (schizogony), c) budding. Mitosis is the basis of asexual reproduction. In a number of species, the sexual process takes place - conjugation (ciliates) and sexual reproduction (sporozoans).

Habitats: marine and fresh waters, soil, plant, animal and human organisms.

Classification of protozoa

• Subkingdom Protozoa, or Unicellular (Protozoa)
  • Type Sarcomastigophora (Sarcomastigophora)
    • Subtype Flagellates (Mastigophora)
      • Class Plant flagellates (Phytomastigophorea)
      • Class Animal flagellates (Zoomastigophorea)
    • Opalina subtype (Opalinata)
    • Subtype Sarcodaceae (Sarcodina)
      • Rhizopeda class (Rhizopoda)
      • Class Radiolaria, or Beams (Radiolaria)
      • Class Sunflowers (Heliozoa)
  • Type Apicomplexa (Apicomplexa)
    • • Perkinsea class
      • Class Sporozoa (Sporozoea)
  • Type of Myxosporidium (Myxozoa)
    • • Class Myxosporea (Myxosporea)
      • Class Actinosporidia (Actinosporea)
  • Type of Microsporidia (Microspora)
  • Type of ciliates (Ciliophora)
    • • Class Ciliary ciliates (Ciliata)
      • Class Sucking ciliates (Suctoria)
  • Type Labyrinthula (Labirinthomorpha)
  • Ascetosporidia type (Ascetospora)

The simplest appeared about 1.5 billion years ago.

The simplest belong to the primitive unicellular eukaryotes (superkingdom Eucariota). It is now generally accepted that eukaryotes evolved from prokaryotes. There are two hypotheses of the origin of eukaryotes from prokaryotes: a) successive, b) symbiotic. According to the successive hypothesis, membranous organelles arise gradually from the plasmalemma of prokaryotes. According to the symbiotic hypothesis (endosymbiotic hypothesis, symbiogenesis hypothesis), a eukaryotic cell arises as a result of a series of symbioses of several ancient prokaryotic cells.

Unicellular, or protozoa, are animals whose body morphologically corresponds to one cell, while being at the same time an independent holistic organism with all the inherent functions. The total number of protozoan species exceeds 30 thousand.

emergence unicellular animals was accompanied by aromorphoses: 1. Diploidy (a double set of chromosomes) appeared in a nucleus limited by a shell as a structure that separates the genetic apparatus of the cell from the cytoplasm and creates a specific environment for the interaction of genes in the diploid set of chromosomes. 2. There were organelles capable of self-reproduction. 3. Internal membranes have formed. 4. A highly specialized and dynamic internal skeleton - the cytoskeleton - appeared. b. The sexual process arose as a form of exchange of genetic information between two individuals.

Structure. The structural plan of the protozoa corresponds to the general features of the organization of the eukaryotic cell.

genetic algorithm unicellular is represented by one or more nuclei. If there are two nuclei, then, as a rule, one of them, diploid, is generative, and the other, polyploid, is vegetative. The generative nucleus performs functions related to reproduction. The vegetative nucleus provides all the vital processes of the body.

Cytoplasm consists of a light outer part, devoid of organelles, - ectoplasm and a darker inner part containing the main organelles - endoplasm. The endoplasm contains general purpose organelles.

Unlike the cells of a Multicellular Organism, unicellular organisms have special-purpose organelles. These are organoids of movement - pseudopodia - pseudopodia; flagella, cilia. There are also organelles of osmoregulation - contractile vacuoles. There are specialized organelles that provide irritability.

Unicellular organisms with a constant body shape have permanent digestive organelles: a cellular funnel, a cellular mouth, a pharynx, as well as an organoid for excreting undigested residues - powder.

INunfavorable conditions of existence, the nucleus with a small amount of cytoplasm containing the necessary organelles is surrounded by a thick multilayer capsule - a cyst and passes from an active state to rest. When exposed to favorable conditions, the cysts "open", and protozoa emerge from them in the form of active and mobile individuals.

Reproduction. The main form of reproduction of the "protozoa" is asexual reproduction by mitotic cell division. However, the sexual process is common.

Sarcode class. or Roots.

Amoeba

The amoeba detachment is part of the class. A characteristic feature is the ability to form cytoplasmic outgrowths - pseudopodia (pseudopodia), thanks to which they move.

Amoeba: 1 - nucleus, 2 - cytoplasm, 3 - pseudopodia, 4 - contractile vacuole, 5 - formed digestive vacuole

Structure. The shape of the body is inconsistent. The hereditary apparatus is represented by one, as a rule, polyploid nucleus. The cytoplasm has a distinct division into ectoplasm and endoplasm, in which general-purpose organelles are located. Free-living freshwater forms have a simply arranged contractile vacuole.

Nutrition method. All rhizopods feed by phagocytosis, capturing food with pseudopods.

Reproduction. The most primitive representatives of the orders of amoebas and testate amoebas are characterized only by asexual reproduction by mitotic cell division.

Class Flagella

Structure. Flagellates have flagella that serve as organelles of movement and contribute to the capture of food. There may be one, two or many. The movement of the flagellum in the surrounding water causes a whirlpool, due to which small particles suspended in water are carried away to the base of the flagellum, where there is a small opening - a cellular mouth leading to a deep canal-pharynx.

Euglena green: 1 - flagellum, 2 - contractile vacuole, 3 - chloroplasts, 4 - nucleus, 5 - contractile vacuole

Almost all flagellates are covered with a dense elastic membrane, which, along with the developed elements of the cytoskeleton, determines the permanent shape of the body.

genetic apparatus in most flagellates, it is represented by a single nucleus, but there are also binuclear (for example, Giardia) and multinuclear (for example, opal) species.

Cytoplasm it is clearly divided into a thin outer layer - a transparent ectoplasm and a deeper lying endoplasm.

Nutrition method. According to the method of feeding, flagellates are divided into three groups. autotrophic organisms, as an exception in the animal kingdom, synthesize organic substances (carbohydrates) from carbon dioxide and water using chlorophyll and the energy of solar radiation. Chlorophyll is found in chromatophores similar in organization to plant plastids. Many flagellates with a vegetable type of nutrition have special apparatuses that perceive light stimuli - stigmas.

Heterotrophic organisms (trypanosoma - the causative agent of sleeping sickness) do not have chlorophyll and therefore cannot synthesize carbohydrates from inorganic substances. Mixotrophic organisms are capable of photosynthesis, but also feed on mineral and organic substances created by other organisms (euglena green).

Osmoregulatory And in part, the excretory functions are performed in flagella, as in sarcodes, by contractile vacuoles, which are present in free-living freshwater forms.

Reproduction. Flagellates have sexual and asexual reproduction. The usual form of asexual reproduction is longitudinal fission.

Type Ciliates, or Ciliary

General characteristics. TO more than 7 thousand species belong to the type of ciliates. The organelles of movement are cilia. There are two nuclei: a large polyploid - vegetative nucleus(macronucleus) and small diploid - generative core(micronucleus).

Structure. Ciliates can be of various shapes, most often oval, like a ciliate shoe. Their dimensions reach a length of 1 mm . Outside, the body is covered with a pellicle. Cytoplasm always clearly divided into ectoderm and endoderm. The ectoplasm contains the basal bodies of the cilia. Elements of the cytoskeleton are closely related to the basal bodies of cilia.

How to feed infusoria. IN in the front half of the body there is a longitudinal notch - the perioral cavity. In its depths there is an oval opening - a cellular mouth leading to a curved pharynx, which is supported by a system of skeletal pharyngeal filaments. The pharynx opens directly into the endoplasm.

Osmoregulation. Free-living ciliates have contractile vacuoles.

Infusoria shoe: 1 - cilia, 2 - digestive vacuoles, 3 - small nucleus, 4 - large nucleus, 5 - cell mouth, c - cell pharynx, 7 - powder, 8 - contractile vacuole<

Reproduction. For ciliates, alternation of sexual and asexual reproduction is characteristic. With asexual reproduction, transverse division of ciliates occurs.

Habitat. Free-living ciliates are found both in fresh waters and in the seas. Their lifestyle is diverse.

Type of protozoa

Sarcomastigophores

Sarcode

Proteus amoeba (common), dysenteric amoeba, radiolaria

Flagella

Euglena green, Volvox, African trypanosoma, Leishmania, Trichomonas, Giardia hepatic

spores

coccidiae

Malarial Plasmodium

ciliates

Eyelash

Infusoria-balantidia, infusoria-shoe, infusoria-trumpeter

Trichofriosis

Used Books:
1. Biology: a complete guide to preparing for the exam. / G.I. Lerner. - M.: AST: Astrel; Vladimir; VKT, 2009 2. Biology: Animals: textbook. for 7-8 cells. general education institutions. - 7th ed. - M.: Education, 2000. 3. Biology: study guide / A.G. Lebedev. M.: AST: Astrel. 2009. 4. Biology. Full course of secondary school: textbook for schoolchildren and applicants / M.A.Valovaya, N.A.Sokolova, A.A. Kamensky. - M.: Exam, 2002. 5. Biology for university applicants. Intensive course / G.L. Bilich, V.A. Kryzhanovsky. - M.: Onyx Publishing House, 2006.
Used Internet resources: