General characteristics of unicellular animals. Single-celled organisms - list with names and examples

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.

The sub-kingdom of Unicellular, or Protozoa, includes animals whose body consists of one cell. The size of the simplest is on average 0.1-0.5 mm. There are individuals of even smaller size - about 0.01 mm. There are also quite large organisms, several millimeters and even centimeters long.

inhabit protozoan unicellular animals predominantly in a liquid medium - in sea and fresh water, moist soil, in other organisms. Outwardly, they are very diverse. Some resemble shapeless gelatinous lumps (for example, amoeba), others have a geometrically regular shape (for example, ray).

Protozoa has about 30 thousand species.

The structure of ciliates shoe and amoeba

The structure of euglena green

Table signs of protozoa unicellular animals

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A source of information: Biology in tables and diagrams. / Edition 2e, - St. Petersburg: 2004.

Subkingdom Unicellular animals includes animals whose body consists of one cell. This cell is a complex organism with its own physiological processes: respiration, digestion, excretion, reproduction and irritation.

The shape of their cells is varied and can be permanent(flagellates, ciliates) and fickle(amoeba). The organelles of movement are pseudopods, flagella and cilia. Nutrition in protozoa is autotrophic(photosynthesis) and heterotrophic(phagocytosis, pinocytosis). Reproduction in unicellular asexual(nuclear fission - mitosis, and then longitudinal or transverse cytokinesis, as well as multiple division) and sexual: conjugation (ciliates), copulation (flagellates).

About 30,000 species of unicellular organisms are grouped into several types. The most numerous are types of sarcoflagellates and type of infusoria.

Type of Infusoria has over 7,500 species. It's in highly organized protozoa that have a constant body shape.

A typical type representative is infusoria-shoe. The body of the ciliates is covered with a dense shell. She has two cores: large ( macronucleus), which regulates all life processes, and small ( micronucleus), which plays a major role in reproduction. Infusoria shoe It feeds on algae, bacteria, and some protozoa. The cilia of ciliates oscillate, which "promotes" food into the mouth opening. e, and then into the pharynx, at the bottom of which are formed digestive vacuoles where food is digested and nutrients are absorbed. Through powder- a special organ - undigested residues are removed. Selection functions are carried out contractile vacuoles. breeds infusoria-shoe like an amoeba asexually(transverse division of the cytoplasm, the small nucleus divides mitotically, the large nucleus divides amitotically). Characteristic and sexual process- conjugation. This is a temporary connection of two individuals, between which a cytoplasmic bridge, through which they exchange separated small nuclei. The sexual process serves to update genetic information.

ciliates are link in food chains. Living in the stomachs of ruminants, ciliates contribute to their digestion.

A typical representative is amoeba common.

The amoeba lives in fresh water. Her body shape is inconsistent. The prolegs also serve to capture food - bacteria, unicellular algae, and some protozoa. Undigested residues are ejected from anywhere in the amoeba. The animal breathes with its entire body surface: oxygen dissolved in water penetrates into the body of the amoeba through diffusion, and carbon dioxide formed during respiration in the cell is released outside. The animal is irritable. Amoeba breeds division: first, the nucleus divides mitotically, and then the division of the cytoplasm occurs. Under unfavorable conditions, encystation.

Typical representation flagellator - euglena green- has a spindle shape. A long thin flagellum departs from the front end of the body of the euglena: by rotating it, the euglena moves, as if screwing into the water. In the cytoplasm of euglena, the nucleus and several stained oval bodies - chromatophores(20 pieces) containing chlorophyll(Euglena feeds autotrophically in the light). Photosensitive eye helps euglena find lighted places. When kept in the dark for a long time, euglena loses its chlorophyll and proceeds to nutrition with ready-made organic substances, which it absorbs from the water with the entire surface of the body. Euglena breathes the entire surface of the body. Reproduction is carried out halving(longitudinal).

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For the first time, unicellular organisms were discovered to the human eye in the 1670s, thanks to the Dutch naturalist, endowed with a great passion for understanding the world, Anthony van Leeuwenhoek. It was he who first considered these "little animals" with the help of his incredible lenses. Their scientific study began later - and does not stop until now. Unicellular organisms live everywhere, including in conditions where other organisms cannot survive.

What are the distinguishing features inherent in unicellular?

1. Morphologically, unicellular are single cell. However, in terms of its functions, it is self-sufficient organism, which knows how to move in space, multiply, eat. The sizes of unicellular organisms vary from a few microns to several centimeters. A few years ago, multinucleated xenophyophores with a diameter of at least 10 centimeters were discovered in the Mariana Trench.

2. Liquid medium- the fundamental condition for the existence of unicellular. Moreover, this is not only a sea or a swamp, but also liquids inside the body of a person or other creatures.

3. Unicellular organisms master space and attract food closer with the help of prolegs(temporary, constantly changing outgrowths of ectoplasm, like an amoeba), flagella(thin, long organelles, filaments of cytoplasm located in the front of the body, like in green euglena) and cilia(multiple outgrowths of the cytoplasm throughout the body, like in ciliates). The flagella twist into the liquid like a corkscrew, and the cilia “pop” creating a wave motion.

4. Most unicellular - heterotrophs, that is, they feed on ready-made organic substances. Euglena green - mixotroph, but the colonial volvox - autotroph.

5. Irritability(the ability of a cell to change physico-chemical properties under the influence of environmental conditions), one of the basic properties of a living organism, manifests itself in protozoa taxis: reactions to any irritation. Unicellular organisms move either in the direction of the stimulus (for example, a fragment of food) or away from it.

6. reflexes unicellular do not have due to the lack of a nervous system.

8. With asexual reproduction of protozoa, unlike multicellular ones, there is no destruction nuclear envelope during cell division.

9. Of course, the simplest have mitochondria.

Significance of unicellular animals

1. Protozoa are eaten by larger invertebrates.

2. The external and internal skeletons of testate amoebae, foraminifera, radiolarians and other similar creatures have formed marine sedimentary rocks for hundreds of thousands of years, which people use in construction (for example, shell rock).

Protozoa are unicellular animals whose body consists of one cell. However, they cannot be considered as simply organized forms, because morphologically a cell of protozoa is equivalent to a cell of a multicellular organism. Physiologically, a cell of protozoa is an integral organism, which has all manifestations of life: metabolism, irritability, growth, reproduction, etc. Organoids play the role of organs in them.

The protozoa were discovered in 1675 by the Dutch naturalist Antoine van Lievenhoek. In the first classification of animals, proposed in 1759 by the Swedish botanist Carl Linnaeus, the protozoa were combined into one genus called "chaos" (Chaos), which was part of the phylum of worms. Only in 1845 did Kelliker and Siebold single them out as an independent type of animal. And only very recently, in 1980, Levine established a separate sub-kingdom for protozoa.

There are from 5 to 7 types of protozoa, each type includes several classes. To date, more than 30 thousand species have been described, but there are many more.

Origin of unicellular

As you know, the first living beings arose in the primeval world ocean and looked like the smallest slimy lumps. They had neither nuclei, nor vacuoles, nor other parts of cells, but they could grow by absorbing nutrients from the environment and multiply. As a result of natural selection, these organisms gradually became more complex. From them originated the first single-celled organisms with nuclei. As established, they gave rise to unicellular animals and primitive fungi at the earliest stages of the evolution of living nature. Their ancestors were the most ancient unicellular organisms - the simplest flagellates (as many biologists believe).

Findings:

1. The first of the animals on Earth appeared unicellular animals related to protozoa.

2. Among the protozoa, there are not only unicellular forms, but also colonial ones (volvox).

General characteristics of protozoa

1. The simplest are unicellular animals whose body consists of one cell. Morphologically, a cell of protozoa is equivalent to a cell of a multicellular organism. Physiologically, a cell of protozoa is an integral organism, which has all manifestations of life: metabolism, irritability, growth, reproduction, etc. Organoids play the role of organs in them.

2. This is a widespread group of animals that is in a state of biological progress. In the course of evolution, they have acquired numerous adaptations to living conditions in different habitats (seas, fresh water bodies, damp soil, liquid environment of other organisms).

3. The sizes of protozoa are microscopically small. Their body (cell) consists of cytoplasm, in which the outer layer is distinguished - ectoplasm and inner - endoplasm. In most species, the cell is covered on the outside with a shell, which gives the animal a permanent shape (an exception is sarcodes). In the endoplasm, in addition to the organelles inherent in all cells, there are organelles that perform the functions of digestion, excretion, movement (flagella, cilia), protection (trichocysts in ciliates), a light-sensitive eye (in free-living flagellates).

4. According to the method of nutrition, these are typical heterotrophic organisms (the exception is green euglena).

5. Breathe the entire surface of the body.

7. Reproduction is carried out asexually or sexually.

8. The simplest, as full-fledged living organisms, react to the influence of the external environment, i.e. have irritability, which manifests itself in various movements (taxis). There are positive taxises (when the animal moves towards the stimulus) and negative taxises (when it moves away from the stimulus).

9. Encystation - an important biological feature of protozoa - is the ability to form a cyst when exposed to adverse conditions. Encystation provides not only the experience of adverse conditions, but also contributes to a wide settlement.

10. This is the most ancient type of animal. The most ancient classes of this type include flagellates and sarcods, which originated from a primitive group of eukaryotic heterotrophic organisms that has now become extinct. Ciliates are related in their origin to the flagellates. All multicellular animals also originated from flagellates (through colonial forms).

The type includes the following classes:

flagella, sarcode or rhizopods, ciliates, sporozoans and others.