Family of amoeba vulgaris. Movement and reaction to stimuli. Irritability in unicellular organisms. Taxis

The cytoplasm is completely surrounded by a membrane, which is divided into three layers: outer, middle and inner. The inner layer, which is called endoplasm, contains the necessary elements for an independent organism:

ribosomes;
elements of the Golgi apparatus;
supporting and contractile fibers;
digestive vacuoles.

Digestive system

A unicellular organism can actively reproduce only in moisture; in the dry habitat of the amoeba, nutrition and reproduction are impossible.

Respiratory system and response to irritation

Amoeba proteus

Amoeba division

The most favorable living environment is found in the reservoir and human body . Under these conditions, the amoeba multiplies quickly, actively feeds on bacteria in bodies of water and gradually destroys the tissues of the organs of its permanent host, which is a person.

Amoeba reproduces asexually. Asexual reproduction involves cell division and the formation of a new one-celled organism.

It is noted that one adult can divide several times a day. This determines the greatest danger for a person who suffers from amoebiasis.

That is why, at the first symptoms of the disease, doctors strongly recommend seeking help from a specialist rather than starting self-medication. Incorrectly selected medications can actually cause more harm to the patient than good.

In contact with

The subkingdom Unicellular includes animals whose body consists of only one cell, mostly microscopic in size, but with all the functions inherent in the body. Physiologically, this cell represents a whole independent organism.

The two main components of the unicellular body are the cytoplasm and the nucleus (one or more). The cytoplasm is surrounded by an outer membrane. It has two layers: the outer (lighter and denser) - ectoplasm - and the inner - endoplasm. The endoplasm contains cellular organelles: mitochondria, endoplasmic reticulum, ribosomes, elements of the Golgi apparatus, various supporting and contractile fibers, contractile and digestive vacuoles, etc.

Habitat and external structure of the common amoeba

The simplest lives in water. This could be lake water, a drop of dew, soil moisture, or even water inside us. The surface of their body is very delicate and dries out instantly without water. Externally, the amoeba looks like a grayish gelatinous lump (0.2-05 mm), which does not have a permanent shape.

Movement

The amoeba “flows” along the bottom. On the body, outgrowths that change their shape are constantly formed - pseudopodia (pseudopods). Cytoplasm gradually flows into one of these protrusions, the false stalk attaches to the substrate at several points, and movement occurs.

Internal structure

Internal structure of amoeba

Nutrition

While moving, the amoeba encounters unicellular algae, bacteria, and small unicellular organisms, “flows around” them and includes them in the cytoplasm, forming a digestive vacuole.

Amoeba nutrition

Enzymes that break down proteins, carbohydrates and lipids enter the digestive vacuole, and intracellular digestion occurs. Food is digested and absorbed into the cytoplasm. The method of capturing food using false legs is called phagocytosis.

Breath

Oxygen is used for cellular respiration. When it becomes less than in the external environment, new molecules pass into the cell.

Amoeba breathing

Molecules of carbon dioxide and harmful substances accumulated as a result of vital activity, on the contrary, come out.

Selection

The digestive vacuole approaches the cell membrane and opens outwards to release undigested residues to the outside anywhere in the body. The liquid enters the amoeba’s body through the thin tube-like channels that are formed, by pinocytosis. Contractile vacuoles pump out excess water from the body. They gradually fill, and every 5-10 minutes they sharply contract and push the water out. Vacuoles can appear in any part of the cell.

Reproduction

Amoebas reproduce only asexually.

Amoeba reproduction

The grown amoeba begins to reproduce. It occurs through cell division. Before cell division, the nucleus doubles so that each daughter cell receives its own copy of the hereditary information (1). Reproduction begins with a change in the nucleus. It stretches out (2), and then gradually lengthens (3.4) and is pulled in the middle. The transverse groove divides into two halves, which diverge in different directions - two new nuclei are formed. The body of the amoeba is divided into two parts by a constriction and two new amoebas are formed. Each of them contains one core (5). During division, the formation of missing organelles occurs.

During the day, division can be repeated several times.

Asexual reproduction- simple and quick way increase the number of your descendants. This method of reproduction is no different from cell division during the growth of the body of a multicellular organism. The difference is that the daughter cells of a unicellular organism diverge as independent ones.

Reaction to irritation

Amoeba has irritability - the ability to sense and respond to signals from external environment. Crawling onto objects, it distinguishes edible from inedible and grabs them with its pseudopods. She crawls away and hides from the bright light (1),

mechanical irritations and increased concentrations of substances harmful to it (2).

This behavior, consisting of movement towards or away from a stimulus, is called taxis.

Sexual process

Absent.

Experiencing adverse conditions

A single-celled animal is very sensitive to environmental changes.

In unfavorable conditions (when the reservoir dries out, in the cold season), amoebas retract pseudopodia. A significant amount of water and substances are released from the cytoplasm onto the surface of the body, which form a durable double shell. There is a transition to a resting state - a cyst (1). In the cyst, life processes are suspended.

Cysts carried by the wind contribute to the spread of the amoeba.

When favorable conditions occur, the amoeba leaves the cyst shell. She releases pseudopodia and turns into active state (2-3).

Another form of protection is the ability to regenerate (recovery). A damaged cell can complete its destroyed part, but only if the nucleus is preserved, since all the information about the structure is stored there.

Life cycle of amoeba

The life cycle of an amoeba is simple. The cell grows, develops (1) and divides asexually (2). IN bad conditions any organism can “temporarily die” - turn into a cyst (3). When conditions improve, it “comes back to life” and multiplies vigorously.

Amoeba is a representative of single-celled animals capable of actively moving with the help of special specialized organelles. The structural features and significance of these organisms in nature will be revealed in our article.

Characteristics of the subkingdom Protozoa

Despite the fact that protozoa have this name, their structure is quite complex. After all, one microscopic cell is capable of performing the functions of an entire organism. Amoeba is another proof that an organism up to 0.5 mm in size is capable of breathing, moving, reproducing, growing and developing.

Protozoan movement

Single-celled organisms move with the help of special organelles. In ciliates they are called cilia. Just imagine: on the surface of a cell, up to 0.3 mm in size, there are about 15 thousand of these organelles. Each of them makes pendulum-like movements.

Euglena has a flagellum. Unlike cilia, it makes helical movements. But what these organelles have in common is that they are permanent outgrowths of the cell.

The movement of the amoeba is due to the presence of pseudopods. They are also called pseudopodia. These are unstable cellular structures. Due to the elasticity of the membrane, they can form anywhere. First, the cytoplasm moves outward and a protrusion is formed. Then the reverse process follows, the pseudopods are directed into the cell. As a result, the amoeba moves slowly. The presence of pseudopods is distinctive characteristic feature this representative of the subkingdom Unicellular.

Amoeba proteus

Amoeba structure

All protozoan cells are eukaryotic - they contain a nucleus. The organs of the amoeba, or rather its organelles, are capable of carrying out all life processes. The pseudopods are not only involved in movement, but also provide the amoeba with nutrition. With their help, a single-celled animal embraces a food particle, which is surrounded by a membrane and ends up inside the cell. This is the process of formation of digestive vacuoles in which the breakdown of substances occurs. This method of absorption of solid particles is called phagocytosis. Undigested food remains are released anywhere in the cell through the membrane.

Amoeba, like all protozoa, does not have specialized respiratory organelles, carrying out gas exchange through the membrane.

But the process of regulation of intracellular pressure is carried out with the help of contractile vacuoles. The salt content in the environment is higher than inside the body itself. Therefore, according to the laws of physics, water will flow into the amoeba - from an area with a higher concentration to a lower one. regulate this process by removing some metabolic products along with water.

Amoebas are characterized by asexual reproduction by two. This is the most primitive of all known methods, however, it ensures accurate preservation and transmission of hereditary information. In this case, first the organelles occur, and then the separation of the cell membrane occurs.

This simplest organism able to respond to environmental factors: light, temperature, change chemical composition reservoir

Single-celled organisms tolerate unfavorable conditions in the form of cysts. Such a cell stops moving, its water content decreases, and the pseudopods are retracted. And it itself is covered with a very dense shell. This is a cyst. When advancing favorable conditions The amoebas emerge from the cysts and proceed to normal life processes.

Dysenteric amoeba

Many species of these protozoa also play a positive role in nature. Amoebas are a source of food for many animals, namely fry of fish, worms, mollusks, and small crustaceans. They clean fresh water bodies of bacteria and rotting algae and are an indicator of the cleanliness of the environment. took part in the formation of limestone and chalk deposits.

This class includes single-celled animals that are characterized by a variable body shape. This is due to the formation of pseudopods, which serve to move and capture food. Many rhizomes have internal or exoskeleton in the form of shells. After death, these skeletons settle to the bottom of reservoirs and form silt, which gradually turns into chalk.

A typical representative of this class is the common amoeba (Fig. 1).

The structure and reproduction of amoeba

Amoeba is one of the most simply structured animals, devoid of a skeleton. It lives in the mud at the bottom of ditches and ponds. Externally, the body of the amoeba is a grayish gelatinous lump 200-700 microns in size, which does not have a permanent shape, which consists of cytoplasm and a vesicular nucleus and does not have a shell. In protoplasm there is an outer, more viscous (ectoplasm) and an inner granular, more liquid (endoplasm) layer.

On the body of the amoeba, outgrowths that change their shape are constantly formed - false legs (pseudopodia). Cytoplasm gradually flows into one of these protrusions, the false stalk attaches to the substrate at several points, and the amoeba moves. While moving, the amoeba encounters unicellular algae, bacteria, small unicellular organisms, and covers them with pseudopods so that they end up inside the body, forming a digestive vacuole around the swallowed piece in which intracellular digestion occurs. Undigested residues are thrown out in any part of the body. The method of capturing food using false legs is called phagocytosis. The liquid enters the amoeba’s body through the thin tube-like channels that are formed, i.e. by pinocytosis. End products of life (carbon dioxide and other harmful substances and undigested food debris) are excreted with water through a pulsating (contractile) vacuole, which removes excess fluid every 1-5 minutes.

The amoeba does not have a special respiratory organelle. It absorbs the oxygen necessary for life over the entire surface of the body.

Amoebas reproduce only asexually (mitosis). Under unfavorable conditions (for example, when a reservoir dries out), amoebas retract pseudopodia, become covered with a strong double membrane and form cysts (encysts).

When exposed to external stimuli (light, changes in the chemical composition of the environment), the amoeba responds with a motor reaction (taxis), which, depending on the direction of movement, can be positive or negative.

Other class representatives

Many species of sarcodidae live in marine and fresh waters. Some sarcoids have a shell-shaped skeleton on the surface of the body (shell rhizomes, foraminifera). The shells of such sarcoids are permeated with pores, from which pseudopodia protrude. In shell rhizomes, reproduction is observed by multiple fission - schizogony. Marine rhizomes (foraminifera) are characterized by alternating asexual and sexual generations.

Possessing a skeleton, sarcodae are among the oldest inhabitants of the Earth. Chalk and limestone were formed from their skeletons. Each geological period is characterized by its own foraminifera, and the age of geological strata is often determined from them. The skeletons of certain types of shell rhizomes accompany the deposition of oil, which is taken into account during geological exploration.

Dysenteric amoeba(Entamoeba histolytica) is the causative agent of amoebic dysentery (amoebiasis). Discovered by F. A. Lesh in 1875

Localization. Human intestines.
. Everywhere, but more often in countries with hot climates.

Morphological features and life cycle . The following forms are found in the human intestine in the life cycle:

cysts - 1, 2, 5-10 (Fig. 2).
small vegetative form living in the intestinal lumen (forma minuta) - 3, 4;
large vegetative form living in the intestinal lumen (forma magna) - 13-14
tissue, pathogenic, large vegetative form (forma magna) - 12;

A characteristic feature of dysenteric amoeba cysts is the presence of 4 nuclei in them (a distinctive feature of the species), the size of the cysts is from 8 to 18 microns.

Dysenteric amoeba usually enters the human intestine in the form of cysts. Here, the shell of the swallowed cyst dissolves and a quadruple amoeba emerges from it, which quickly divides into 4 single-nucleate small (7-15 microns in diameter) vegetative forms (f. minuta). This is the main form of existence of E. histolytica.

The small vegetative form lives in the lumen of the large intestine, feeds mainly on bacteria, reproduces and does not cause disease. If conditions are not favorable for the transition to the tissue form, then the amoebas, entering the lower intestines, encyst (turn into a cyst) with the formation of a 4-nuclear cyst and are excreted into the external environment with feces.

If conditions favor the transition to the tissue form (E. histolytica forma magna), the amoeba increases in size to an average of 23 microns, sometimes reaching 30 and even 50 microns, and acquires the ability to secrete hyaluronidase, proteolytic enzymes that dissolve tissue proteins and penetrate the walls intestines, where it multiplies intensively and causes damage to the mucous membrane with the formation of ulcers. In this case, the walls of blood vessels are destroyed and bleeding occurs into the intestinal cavity.

When amoebic intestinal lesions appear, small vegetative forms located in the intestinal lumen begin to transform into a large vegetative form. The latter is characterized by large size (30-40 microns) and the structure of the nucleus: the chromatin of the nucleus forms radial structures, a large lump of chromatin - the karyosome - is located strictly in the center, the forma magna begins to feed on erythrocytes, i.e. it becomes an erythrophage. Characterized by blunt, wide pseudopodia and jerky movement.

Amoebas that multiply in the tissues of the intestinal wall - the tissue form - enter the intestinal lumen and become similar in structure and size to the large vegetative form, but are not able to swallow red blood cells.

With treatment or an increase in the body's protective reaction, the large vegetative form (E. histolytica forma magna) again turns into a small one (E. histolytica forma minuta), which begins to encyst. Subsequently, either recovery occurs, or the disease becomes chronic.

The conditions necessary for the transformation of some forms of dysenteric amoeba into others were studied by the Soviet protistologist V. Gnezdilov. It turned out that various unfavorable factors - hypothermia, overheating, malnutrition, overwork, etc. - contribute to the transition of forma minuta to forma magna. A necessary condition is also the presence of certain types of intestinal bacteria. Sometimes an infected person secretes cysts for many years without signs of disease. Such people are called cyst carriers. They represent great danger, as they serve as a source of infection for others. One cyst carrier releases up to 600 million cysts per day. Cyst carriers are subject to identification and mandatory treatment.

The only one source of the disease amoebiasis - man. Cysts released in feces contaminate soil and water. Since feces are often used as fertilizer, cysts end up in gardens and gardens, where they contaminate vegetables and fruits. Cysts are resistant to environmental influences. They enter the intestines with unwashed vegetables and fruits, through unboiled water, dirty hands. Mechanical carriers are flies and cockroaches that contaminate food.

Pathogenic effect. When the amoeba penetrates the intestinal wall, it develops serious disease, the main symptoms of which are: bleeding ulcers in the intestines, frequent and loose stool(up to 10-20 times a day) with an admixture of blood and mucus. Sometimes by blood vessels dysenteric amoeba - erythrophage can be carried into the liver and other organs, causing the formation of abscesses (focal suppuration) there. If left untreated, the mortality rate reaches 40%.

Laboratory diagnostics. Microscopy: fecal smears. IN acute period the smear contains large vegetative forms containing red blood cells; cysts are usually absent, since f. magna is unable to encyst. At chronic form or cyst carriage, quadruple cysts are found in the feces.

Prevention: personal - washing vegetables and fruits boiled water, use for drinking only boiled water, washing hands before eating, after visiting the toilet, etc.; public - combating soil and water contamination with feces, extermination of flies, sanitary educational work, screening for cyst carriage of persons working in public catering establishments, treatment of patients.

Non-pathogenic amoebae include intestinal and oral amoebae.

Intestinal amoeba (Entamoeba coli).

Localization. Upper section colon, lives only in the intestinal lumen.

Geographical distribution. Found in approximately 40-50% of the population various areas globe.

. The vegetative form has dimensions of 20-40 microns, but sometimes larger forms are also found. There is no sharp boundary between ectoplasm and endoplasm. Possesses in a characteristic way movement - simultaneously releases pseudopodia with different sides and, as it were, “marking time.” The nucleus contains large clumps of chromatin, the nucleolus lies eccentrically, and there is no radial structure. It does not secrete a proteolytic enzyme, does not penetrate the intestinal wall, and feeds on bacteria, fungi, and the remains of plant and animal food. The endoplasm contains many vacuoles. Does not swallow red blood cells, even if they are contained in the intestines in large quantities(in patients with bacterial dysentery). IN lower section the digestive tract forms eight- and two-core cysts.

Oral amoeba (Entamoeba gingivalis).

Localization. Oral cavity, dental plaque healthy people and those with oral diseases, carious cavities teeth.

Geographical distribution. Everywhere.

Morphophysiological characteristics. The vegetative form has dimensions from 10 to 30 microns, highly vacuolated cytoplasm. The type of movement and structure of the nucleus resembles a dysentery amoeba. It does not swallow red blood cells; it feeds on bacteria and fungi. In addition, leukocyte nuclei or so-called salivary corpuscles are found in the vacuoles, which, after staining, may resemble red blood cells. It is believed that it does not form cysts. The pathogenic effect is currently denied. It is found in dental plaque of healthy people in 60-70%. It is more common in people with dental and oral diseases.

The simplest organism is amoeba proteus, although there are different types amoeb. It got its name in honor of Proteus - the character Greek mythology, whose feature was to change his appearance. The creature is a prokaryote because it is not a bacterium, as many people think. This is a colorless organism of the heterotrophic type, eukaryotes, which is capable of feeding on microorganisms and unicellular algae. Despite its simplicity and short life cycle, this type of animal plays important role in nature.

Description

According to the classification, the common amoeba belongs to the kingdom “Animals”, the subkingdom “Protozoa”, and the class of free-living sarcodes. The structure of the creature is primitive, and it moves thanks to temporarily appearing protrusions of the cytoplasm (also called a rhizome). The body of Proteus consists of only a single cell, which is an independent and complete organism.

The common amoeba is a eukaryote, a single-celled independent animal. Its characteristics are as follows: the body is semi-liquid, the size reaches 0.2-0.7 mm in length, and the creature can only be clearly seen under a microscope. The entire surface of the amebic cell is covered with cytoplasm, which protects the “insides”. On top is the cytoplasmic membrane. The amoeba has a two-layer cytoplasm. The outer layer is transparent and dense, the inner layer is granular and fluid. The cytoplasm contains the contractile vacuole of the amoeba (due to which unnecessary substances are released out), the nucleus and the digestive vacuole. When moving, the shape of the cytoplasm constantly changes. After examining the images, scientists determined that Proteus has more than five hundred chromosomes, so small that they cannot be observed.

Breathing is carried out throughout the body. The skeleton is missing. Amoeba reproduction is asexual. The amoeba cell also does not have a sense organ (including breathing).

However, the single-celled amoeba breathes and is sensitive to chemicals, mechanical irritants and avoids sunlight.

One of the characteristics of the animal is the ability to regenerate. This means that in case of damage, the cell will be able to repair itself by completing the missing fragments. The only condition is the complete preservation of the core, since it is the carrier of all information about the structure. Without a nucleus, the amoebic organism will simply die.

The movement of amoebas occurs with the help of pseudopods, the so-called non-permanent outgrowths of the cytoplasm, which are also called pseudopodia. The cell membrane is very elastic and can stretch anywhere. To form a pseudopod, cytoplasm first protrudes outward from the body, so that it looks like thick tentacles. Afterwards, the same actions are performed, only in reverse order - the cytoplasm moves inward, the pseudopod hides and appears in another part of the body. It is this method of movement that prevents the animal from having a constant body shape. Despite their small size, the creatures move relatively quickly - about 10 mm/hour.

Amoeba moves with the help of pseudopods, which is why it does not have a constant body shape

How do single-celled animals eat and breathe?

The amoebic life cycle depends entirely on how the animal feeds and what environment. The diet of Proteus includes decay residues, unicellular algae, bacteria, as well as microorganisms of a suitable size. The amoeba feeds by capturing “prey” with its pseudopods and dragging it inside the body. A vacuole is formed around the food, into which digestive juice then enters. Interestingly, the process of capture and further digestion can occur in any part of the body and even in several parts at the same time. Obtained by digestion nutrients enter the cytoplasm and are spent on building the body of the amoeba. In the process of resorption of algae and bacteria, protozoa immediately remove the remains of vital activity to the outside, and this can also occur in any part of the cytoplasm.

Like all protozoa of the unicellular class, Proteas lack special organelles. Respiration in amoeba occurs due to the absorption of oxygen dissolved in water (or liquid) by the surface apparatus. The cell membrane of an animal is permeable, and carbon dioxide and oxygen pass through it freely.

How do they reproduce?

To produce offspring, asexual reproduction is used with the division of the body into two identical parts. Learn more about how many stages a cell goes through when dividing.

The process occurs only in warm seasons and includes several stages:

The first thing that undergoes fission is the nucleus. It protrudes, stretches, constrictions appear in it, with the help of which it then divides into two completely identical parts. In this case, the divergence of daughter chromosomes to the opposite poles of the mother cell is observed.
Next, the cytoplasm is divided between the two nuclei. Its zones are located and concentrated around the nuclei, thereby forming two new cells.
Since in the body of the amoeba the contractile vacuole is present only in a single copy, it goes to only one new cell. In another, it is formed anew. A more detailed description of the process of division and divergence of chromosomes is shown in the figure.

Cell division in this way is called mitosis, so the resulting two organisms are a copy of the “mother”. There is no sexual process, so chromosome exchange also does not occur.

Ordinary amoebas reproduce very quickly. Judging by time, the creature divides into 2 cells every 3 hours, so the amoebic organism does not live long.

Features of existence and development

The life cycle is simple. A single cell, which is also the body of an animal, grows during development, and upon reaching the adult state, “multiplies”, dividing into two bodies asexually with the divergence of maternal chromosomes to “children”. Finding itself in conditions negative for life (cold season, drying out of the reservoir), such a cell is able to “die” for a while. At the same time, the body undergoes changes: the pseudopodia are retracted, water is released from the cytoplasm and covers the entire amoebic organism, forming a double shell with the subsequent formation of a cyst. Protea “freezes.” When the environment becomes habitable, the creature is "reborn", the amoeba cyst breaks open, prolegs are released (to move around), and the creature reproduces. You can find out in detail what an amoeba is in the video.

The animal has great value in nature. It is a source of food for multicellular organisms (amoebas feed on worms, crustaceans, fish fry, and various mollusks). Protea, which lives in water bodies, cleans water bodies during its life by eating various types microorganism, bacteria and decaying parts of algae, protozoan testate amoebas are involved in the formation of chalk deposits and limestones.