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Features of unicellular animals. Subkingdom Unicellular or Protozoa. General characteristics. What environment do unicellular organisms live in?

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.
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 solar radiation energy. 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 (green euglena).
Osmoregulatory and partly excretory functions are carried out in flagellates, 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.
Habitat. Flagellates are widely distributed in fresh water bodies, especially small and polluted with organic residues, as well as in the seas. Many species parasitize various animals and humans and thus cause great harm (tryponosomes, intestinal parasites, etc.).

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.

The phylum Protozoa includes approximately 25,000 species of unicellular animals living in water, soil, or organisms of other animals and humans. Having a morphological similarity in the structure of cells with multicellular organisms, the protozoa differ significantly from them in functional terms.

If the cells of a multicellular animal perform special functions, then the cell of the simplest is an independent organism capable of metabolism, irritability, movement and reproduction.

The simplest are organisms at the cellular level of organization. Morphologically, the protozoan is equivalent to a cell, but physiologically it is a whole independent organism. The vast majority of them are microscopically small in size (from 2 to 150 microns). However, some of the living protozoa reach 1 cm, and the shells of a number of fossil rhizopods are up to 5-6 cm in diameter. The total number of known species exceeds 25 thousand.

The structure of the protozoa is extremely diverse, but they all have features characteristic of the organization and function of the cell. Common in the structure in the structure of protozoa are the two main components of the body - the cytoplasm and the nucleus.

cytoplasm

The cytoplasm is bounded by an outer membrane that regulates the flow of substances into the cell. In many protozoa, it is complicated by additional structures that increase the thickness and mechanical strength of the outer layer. Thus, formations such as pellicles and shells arise.

The cytoplasm of protozoa usually breaks up into 2 layers - the outer one is lighter and denser - ectoplasm and internal, equipped with numerous inclusions, - endoplasm.

General cellular organelles are localized in the cytoplasm. In addition, a variety of special organelles may be present in the cytoplasm of many protozoa. Various fibrillar formations are especially widespread - supporting and contractile fibers, contractile vacuoles, digestive vacuoles, etc.

Core

The simplest have a typical cell nucleus, one or more. The nucleus of protozoa has a typical two-layer nuclear envelope. Chromatin material and nucleoli are distributed in the nucleus. The nuclei of protozoa are characterized by exceptional morphological diversity in terms of size, number of nucleoli, amount of nuclear juice, etc.

Features of the vital activity of protozoa

Unlike somatic cells, multicellular protozoa are characterized by the presence of a life cycle. It is composed of a series of successive stages, which are repeated in the existence of each species with a certain regularity.

Most often, the cycle begins with the stage of the zygote, which corresponds to the fertilized egg of multicellular organisms. This stage is followed by singly or repeatedly repeated asexual reproduction, carried out by cell division. Then sex cells (gametes) are formed, the pairwise fusion of which again gives a zygote.

An important biological feature of many protozoa is the ability to encystment. At the same time, the animals round out, shed or draw in the organelles of movement, secrete a dense shell on their surface, and fall into a state of rest. In the encysted state, protozoa can tolerate drastic environmental changes while remaining viable. When conditions favorable for life return, the cysts open and the protozoa emerge from them in the form of active, mobile individuals.

According to the structure of the organelles of movement and the characteristics of reproduction, the protozoan type is divided into 6 classes. The main 4 classes are Sarcodaceae, Flagellates, Sporozoans and Ciliates.

Definition 1

Unicellular (protozoa) - organisms in which all the functions of a living organism are performed by one cell.

In addition to prokaryotes, they include unicellular eukaryotes, among which there are plants, animals, and fungi.

Features of unicellular organisms

Protozoa are microscopically small. The features of unicellular organisms include the fact that they perform all the functions of a living thing with the help of cellular organelles and are a separate independent organism, represented by only one cell. In terms of structure and set of organelles, the cells of unicellular organisms are similar to the cells of multicellular organisms. Among unicellular eukaryotes, both simply built organisms (amoeba, chlorella) and quite complex ones (ciliates, acetabularia) are distinguished.

If the cells of multicellular organisms are characterized by differentiation of functions and the inability to perform all the functions of a living thing at once, then unicellular organisms retain this ability. Their high level of organization is cellular. A cell of unicellular organisms is a holistic organism that has all the properties of a living thing: metabolism, irritability, growth, reproduction, and the like.

Their body consists of cytoplasm, in which the outer layer is distinguished - ectoplasm, and the inner - endoplasm. In most species, the cell is covered on the outside with a shell that provides the single-celled animal with a permanent shape. In protozoa, organelles appear that perform various functions:

  • digestion (digestive vacuoles),
  • secretions (contractile vacuoles),
  • movements (flagella, cilia),
  • perception of light (photosensitive eye)

and other organelles that provide all life processes. According to the method of nutrition, these are heterotrophic organisms. The simplest are characterized by irritability, which manifests itself in various movements - taxis. There are positive taxises - movements towards the stimulus, and negative taxises - movements away from the stimulus.

Getting into unfavorable conditions, the protozoa form cysts. Encystation is an important biological feature of protozoa. It not only ensures the experience of unfavorable conditions, but also contributes to widespread settlement.

Aquatic unicellular

Marine unicellular animals, such as foraminifera and radiolarians, have an external skeleton in the form of a calcareous shell. Ciliates are highly organized unicellular animals. Cilia act as organelles of movement in them, the body is covered with a strong elastic shell, which gives it a permanent shape. Most ciliates have two cores: large and small. Large vegetative nucleus - regulates the processes of movement, nutrition, excretion, as well as asexual reproduction, carried out by transverse cell division in half. The small nucleus is generative, it performs an important function in the sexual process.

Among aquatic unicellular organisms, mixotrophs are also distinguished - organisms that can feed both through photosynthesis and heterotrophically. For example, Euglena is green.

Euglena lives in freshwater reservoirs and swims with the help of a single flagellum located at the front end of the body. In the cytoplasm of euglena there are chloroplasts containing chlorophyll, which allows euglena to feed on phototrophs. If there is no light, it switches to heterotrophic nutrition. Thanks to this property, Euglena combines the characteristics of a plant and an animal, which indicates the evolutionary unity of the plant and animal world.

Unicellular plants and fungi

Remark 1

In nature, there are many not only unicellular animals, but also unicellular plants and fungi. For example, among green algae, chlamydomonas and chlorella belong to unicellular representatives, and yeasts are unicellular among fungi.

Unicellular plants and animals are typical eukaryotic cells that have the corresponding organelles:

  • surface membrane,
  • core,
  • mitochondria,
  • golgi apparatus,
  • endoplasmic reticulum,
  • ribosomes.

Differences in the structure of unicellular animals and unicellular plants are associated with differences in the way they feed. Plant cells are characterized by the presence of plastids, vacuoles, cell walls and other features associated with photosynthesis. Animal cells are characterized by the presence of glycocalyx, digestive vacuoles, and other features associated with heterotrophic nutrition.

In fungi, the cell has a cell wall, this shows the similarity of fungi with bacteria and plants. But fungi are heterotrophs, and this makes them related to animals.

Unicellular eukaryotes reproduce predominantly asexually, but in some of them (for example, in ciliates-shoes) a sexual process is observed - the exchange of genetic information, while in others (for example, in chlamydomonas) sexual reproduction occurs. Asexual reproduction occurs by cell division in half by mitosis. During sexual reproduction, gametes are formed, which then fuse to form a zygote.

Remark 2

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.