What is characteristic of an amoeba. What is an amoeba? Life cycle of the dysenteric amoeba

The sub-kingdom Unicellular includes animals whose body consists of only one cell, for the most part 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 body of unicellular organisms 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. In the endoplasm there are 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. It can be lake water, a dew drop, soil moisture, and even water inside us. The surface of their body is very delicate and dries instantly without water. Outwardly, the amoeba looks like a grayish gelatinous lump (0.2-05 mm), which does not have a permanent shape.

Motion

Amoeba "flows" along the bottom. Outgrowths that change their shape are constantly formed on the body - pseudopodia (pseudopodia). The cytoplasm gradually overflows into one of these protrusions, the false leg attaches to the substrate at several points, and movement occurs.

Internal structure

The internal structure of the amoeba

Nutrition

Moving, the amoeba encounters unicellular algae, bacteria, 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 with the help of 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 breath

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

Selection

The digestive vacuole approaches the cell membrane and opens outward to throw out undigested residues anywhere in the body. The fluid enters the body of the amoeba through the resulting thin tubular channels, by pinocytosis. Contractile vacuoles are involved in pumping out excess water from the body. They gradually fill up, and every 5-10 minutes they are sharply reduced and push the water out. Vacuoles can occur anywhere in the cell.

reproduction

Amoeba reproduce only asexually.

amoeba reproduction

The grown amoeba begins to reproduce. It occurs through cell division. Prior to cell division, the nucleus doubles up so that each daughter cell receives its own copy of hereditary information (1). Reproduction begins with a change in the nucleus. It stretches (2), and then gradually lengthens (3,4) and is pulled in the middle. The transverse groove is divided into two halves, which diverge in different directions - two new nuclei are formed. The body of the amoeba is divided into two parts by constriction and two new amoeba are formed. Each of them gets one core (5). During division, the formation of missing organelles occurs.

During the day, division can be repeated several times.

asexual reproduction is a simple and quick way to increase the number of your descendants. This method of reproduction does not differ 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 feel and respond to signals from the external environment. Crawling on objects, it distinguishes edible from inedible and captures them with pseudopods. She crawls and hides from the bright light (1)

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

This behavior, consisting in moving towards or away from the stimulus, is called taxis.

sexual process

Is absent.

Experiencing Adverse Conditions

A unicellular animal is very sensitive to environmental changes.

Under unfavorable conditions (when the reservoir dries up, during the cold season), amoeba draw in pseudopodia. A significant amount of water and substances are released onto the surface of the body from the cytoplasm, which form a strong double membrane. 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 dispersal of the amoeba.

When favorable conditions occur, the amoeba leaves the cyst shell. It releases pseudopodia and becomes active (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 information about the structure is stored there.

Amoeba life cycle

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 intensively.

After I re-read the author's text about my program for the second time, I still had the feeling of an unaccepted linguoenuresis. Deciding to still download and test this program, I re-read the annotation again. This attempt also did not bring success in the final understanding of the purpose of the program, therefore it was downloaded and installed without delay (look for the text with the description below). And what would you think? The program turned out...

…an offline RSS application that downloads feed headlines generated by ameba.ru. First you have to register an account on ameba.ru. When registering, you can specify what type of news you want to read. No sources of information are mentioned.

Having noted three points, installed. But at startup, the program still downloaded all the news. I had to remove the checkboxes that were unnecessary for me in the channel selection menu, nevertheless, there was a feeling that the program still downloads all the titles, but only shows the marked ones.

Headings can be customized by changing the highlight color and font, as well as making the list translucent. You can watch news for 1, 2 and 3 past days. Judging by the links that the program sends me to, most of the news is accumulated from lenta.ru.

In general, the program is still far from software 2.0, it's just an offline viewer for news feeds on the original site. But below I give the text of the description itself from the developer's website, and whether you download it or not is up to you.

Amoeba is the first program with artificial intelligence that learns itself by adopting the habits of its owner and, thanks to which, over time it becomes more and more indispensable and convenient. The most important and fresh news that is needed not by your neighbors, but by you. A lot of information services that do not concern some American Bill, but directly to you.

Amoeba can be called software 2.0, all because the program is made based on your wishes, namely, on the wishes of direct users, and not some higher mind. This is a program that will change, guided only by the opinions and wishes of those for whom it was created.

The simplest organism is the amoeba proteus, although there are different types of amoebas. It got its name in honor of Proteus - a character of 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 a heterotrophic type, a eukaryote, which is able to feed on microorganisms and unicellular algae. Despite its simplicity and short life cycle, this type of animal plays an important role in nature.

Description

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

Amoeba is a eukaryote, a single-celled independent animal. Its characteristic is as follows: the body is semi-liquid, the size reaches 0.2-0.7 mm in length, and the creature can be clearly seen only under a microscope. Over the entire surface, the amoebic cell is covered with cytoplasm, which protects the “insides”. Above is the cytoplasmic membrane. In amoeba, the structure of the cytoplasm is two-layered. The outer layer is transparent and dense, the inner one is granular and fluid. In the cytoplasm are the contractile vacuole of the amoeba (due to it, unnecessary substances are released to the outside), the nucleus and the digestive vacuole. When moving, the shape of the cytoplasm is constantly changing. After examining the images, scientists determined that Proteus has more than five hundred chromosomes, so small that it is impossible to observe them.

Breathing is carried out by the whole body. The skeleton is missing. Amoeba reproduction is asexual. The amoebic cell also does not have a sense organ (including respiration).

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

One of the features 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 pseudopodia, the so-called non-permanent outgrowths of the cytoplasm, which are also called pseudopodia. The cell membrane is very elastic and can be stretched anywhere. To form a pseudopod, the cytoplasm first bulges outward from the body, so that they look like thick tentacles. After - the same actions are performed, only in the 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 permanent body shape. Despite their small size, creatures move relatively quickly - about 10 mm / hour.

The amoeba moves with the help of pseudopods, which is why it does not have a permanent body shape.

How do unicellular organisms eat and breathe?

The amoebic life cycle depends entirely on how the animal feeds and what the environment is like. The diet of the proteus includes the remains of decay, unicellular algae, bacteria, as well as microorganisms of a suitable size. Amoeba nutrition occurs by capturing the “prey” with pseudopods and pulling it inside the body. A vacuole forms around the food, into which the 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. The nutrients obtained during digestion enter the cytoplasm and are spent on building the body of the amoeba. In the process of resorption of algae and bacteria, protozoa immediately bring out the remnants of vital activity, and this can also occur in any part of the cytoplasm.

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

How do they reproduce?

To produce offspring, asexual reproduction is used with the division of the body into two identical parts. More details on how many stages a cell goes through during division.

The process occurs only in the warm season and includes several stages:

1. The nucleus undergoes division first. It protrudes, stretches, constrictions appear in it, with the help of which it then divides into two completely identical parts. In this case, there is a discrepancy between the daughter chromosomes to the opposite poles of the mother cell.
2. Next, the division of the cytoplasm between the two nuclei occurs. Its zones are located and concentrated around the nuclei, thereby forming two new cells.
3. Since in the body of an amoeba there is only a single copy of the contractile vacuole, it goes to only one new cell. In the other, it is re-formed. 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 the exchange of chromosomes also does not occur.

Common amoebas reproduce very quickly. Judging by time, the creature divides into 2 cells every 3 hours, so the amoebic organism lives a little.

Features of existence and development

The life cycle is simple. The only cell, which is part-time and the body of an animal, grows in the process of development, and upon reaching the adult state, “reproduces”, dividing into two bodies asexually with a divergence of maternal chromosomes for “children”. Getting into conditions that are negative for life (cold season, drying up of a reservoir), such a cell is able to “die” for a while. In this case, the body undergoes changes: pseudopodia are drawn in, water is released from the cytoplasm and covers the entire amoebic organism, forming a double membrane, followed by the formation of a cyst. Protea freezes. When the environment becomes habitable, the creature is "reborn", the amoeba cyst ruptures, the prolegs are released (to move around), and the creature reproduces. You can learn in detail what an amoeba is in the video.

The animal is of great importance in nature. It is a source of food for multicellular organisms (worms, crustaceans, fish fry, and various molluscs feed on amoebas). The protea that lives in water bodies cleans water bodies in the process of life, eating various types of microorganism, bacteria and rotting parts of algae, the simplest testate amoebae are involved in the formation of chalk deposits and limestones.

abstract

Subject: Amoeba

Completed by: 1st year student Davletkulova A.R.

Checked by: Satarov V.N.

Ufa-2012

2.structure and life of the amoeba

3.dysentery amoeba

Amoeba

In addition to pseudopodia, due to which the body of the amoeba does not have a definite shape, these organisms are characterized by the absence of a rigid cell membrane. The cell is surrounded only by a special molecular layer, the plasma membrane - an integral part of the living cytoplasm. The latter is subdivided into a thin superficial relatively homogeneous part, called ectoplasm, and a granular endoplasm lying in depth. That, in turn, consists of an outer gelatinous zone, plasmagel, and an internal fluid plasmazole. The endoplasm contains the nucleus, as well as digestive and contractile vacuoles. Food captured by pseudopodia, such as bacteria, algae and protozoa, is surrounded by a digestive vacuole and digested in it. Undigested material is ejected from the cell when the membrane of this vacuole fuses with the plasma membrane. Metabolic waste products are released to the outside by simple diffusion. A certain part of them may be removed through contractile vacuoles, but the main function of the latter is to remove excess water from the cell. They contract from time to time, pushing it outward. Reproduction in amoebas is asexual - by cell division in two. At the same time, the nucleus divides mitotically, and then the cytoplasm is drawn and splits into two parts, approximately equal in volume, containing each daughter nucleus. The two cells formed grow and eventually divide as well.

The structure and activity of the amoeba

This gelatinous unicellular creature is so small that it can only be seen under a microscope. The main amoeba species live in freshwater rivers and ponds. But there are species that live at the bottom of salty reservoirs, in moist soil and food. The amoeba is constantly changing its shape. She moves, pushing forward first one of her half, then the other. Like many jelly-like organisms, the amoeba moves in such a way that it forms a shape called a “false leg,” or pseudopodia. When the pseudopodia reaches the food, it envelops it and takes it into the main body. This is how the amoeba eats. She doesn't have a mouth. Amoeba belongs to the class of protozoa, which are the lowest rank of living beings. She has neither lungs nor gills. But it sucks in oxygen from the water, releases carbon dioxide, digests food, as more complex animals do. Probably, the amoeba also has feelings. When touched or when aroused, she immediately curls up into a tiny ball. Amoeba avoids bright light, too hot or cold water. In an adult amoeba, the nucleus, a tiny dot in the center of the protoplasm, divides into two parts. After that, the amoeba itself bifurcates, forming new independent organisms. When they reach full size, they begin to divide again. In their structure, the protozoa are extremely diverse. The smallest ones are 2-4 microns in diameter (a micrometer is 0.001 mm). Their most common sizes are in the range of 50-150 microns, some reach 1.5 mm and are visible with the naked eye.

The amoeba has the simplest structure. The body of the amoeba is a lump of semi-liquid cytoplasm with a nucleus in the middle. The entire cytoplasm is divided into two layers: the outer, viscous - ectoplasm and the inner, much more liquid - endoplasm. These two layers are not sharply demarcated and can turn into each other. The amoeba does not have a hard shell, and it is able to change the shape of the body. When an amoeba crawls over a leaf of an aquatic plant, protrusions of the cytoplasm are formed in it in the direction in which it moves. Gradually, the rest of the cytoplasm of the amoeba flows into them. Such protrusions are called pseudopodia or pseudopodia. With the help of pseudopodia, the amoeba not only moves, but also captures food. With pseudopodia, it covers a bacterium or microscopic algae, soon the prey is inside the body of the amoeba, and a bubble is formed around it - a digestive vacuole. Undigested food remains are thrown out after a while.

Amoeba proteus: 1 - core; 2 - digestive vacuoles; 3 - contractile vacuole; 4 - pseudopods; 5 - undigested food remnants thrown out.

In the cytoplasm of the amoeba, a light bubble is usually visible, which either appears or disappears. This is a contractile vacuole. It collects excess water that accumulates in the body, as well as the liquid waste products of the amoeba. The amoeba, like all other protozoa, breathes over the entire surface of the body.

Euglena green: 1 - flagellum; 2 - eye spot; 3 - contractile vacuole;

The most complex structure of the simplest ciliates. Unlike the amoeba, their body is covered with the thinnest shell and has a more or less constant shape. The support fibers that run in different directions also support and determine the shape of the body. However, the body of ciliates can quickly contract, change its shape, and then return to its original shape. The contraction is carried out with the help of special fibers, similar in many respects to the muscles of multicellular animals. Ciliates can move very quickly. So, a shoe in a second overcomes a distance exceeding the length of its body by 10-15 times. At the same time, many cilia that cover the entire body of the ciliate make fast rowing movements, up to 30 per second (at room temperature). In the ectoplasm of the shoe there are many trichocyst sticks. When irritated, they are thrown out, turning into long threads, and hit the enemy attacking the ciliate. Instead of those thrown out in the ectoplasm, new trichocysts are formed. On one side, approximately in the middle of the body, the shoe has a deep oral cavity leading to a small tubular pharynx.

Infusoria shoe: 1 - cilia; 2 - digestive vacuoles; 3 - large nucleus (macronucleus); (micronucleus); 5 - mouth opening and pharynx; 6 - undigested food residues thrown out; 7 - trichocysts; 8 - contractile vacuole.

Through the pharynx, food enters the endoplasm, where it is digested in the resulting digestive vacuole. In ciliates, unlike amoebas, undigested food residues are thrown out in a certain place in the body. Their contractile vacuole is more complex and consists of a central reservoir and conducting channels. The ciliates have two types of nuclei: large - macronucleus and small - micronucleus. Some ciliates may have several macro- and micronuclei. The macronucleus differs from the micronucleus in a significantly larger number of chromosomes. And therefore, it contains a lot of deoxyribonucleic acid (DNA), which is part of the chromosomes.

Different types of ciliates: 1 - ciliates trumpeter; 2-5 - planktonic ciliates.

Dysentery amoeba (Entamoeba histolytica), the simplest of the amoeba order; the causative agent of amoebic dysentery was first described in 1875 by the Russian scientist F.A. Lesh. At hit in intestines of the person D. and. in most cases, it multiplies in the contents of the colon, without penetrating into the tissues and without causing intestinal dysfunction (the person is healthy, but serves as a carrier of D. a.). This form D. and. called translucent (forma minuta) (size about 20 microns) (Fig. 1, a). It moves with the help of pseudopodia. The nucleus is spherical, 3-5 μm in diameter, chromatin is located under the nuclear envelope in the form of small clumps; in the center of the nucleus is a small karyosome. There may be several phagocytosed bacteria in the endoplasm. When feces thicken in the large intestine, the luminal form is surrounded by a membrane and turns into a spherical cyst (about 12 microns in size) with 4 nuclei that do not differ in structure from the nucleus of the vegetative form; immature cysts contain 1-2 or 3 nuclei. There is a vacuole with glycogen; some of the cysts contain short, barlike formations - chromatoid bodies (Fig. 1b). With faeces, cysts are released into the environment and can again enter the human gastrointestinal tract, where, after the metacystic stage of development (dividing into 8 daughter amoebae), they give rise to translucent forms (Fig. 2, A).

Amoeba is a genus of single-celled eukaryotic organisms (they belong to the simplest). They are considered animal-like because they feed heterotrophically.

The structure of amoebas is usually considered on the example of a typical representative - the common amoeba (Proteus amoeba).

Amoeba ordinary (hereinafter amoeba) lives at the bottom of freshwater reservoirs with polluted water. Its size ranges from 0.2 mm to 0.5 mm. In appearance, the amoeba looks like a shapeless, colorless lump that can change its shape.

The amoeba cell does not have a hard shell. It forms protrusions and invaginations. Protrusions (cytoplasmic outgrowths) are called pseudopods or pseudopodia. Thanks to them, the amoeba can move slowly, as if flowing from place to place, and also capture food. The formation of prolegs and the movement of the amoeba occurs due to the movement of the cytoplasm, which gradually flows into the protrusion.

Although the amoeba is a unicellular organism and there can be no talk of organs and their systems, it is characterized by almost all the life processes characteristic of multicellular animals. The amoeba feeds, breathes, releases substances, and reproduces.

The amoeba cytoplasm is not homogeneous. A more transparent and dense outer layer is isolated ( eqtplasma) and a more granular and fluid inner layer of the cytoplasm ( endoplasm).

In the cytoplasm of the amoeba there are various organelles, the nucleus, as well as the digestive and contractile vacuoles.

The amoeba feeds on various unicellular organisms and organic residues. Food is wrapped around the pseudopods and is inside the cell, formed digestiveand Ivacuole. It receives various enzymes that break down nutrients. Those that the amoeba needs then enter the cytoplasm. Unnecessary food residues remain in the vacuole, which approaches the surface of the cell and everything is thrown out of it.

The "organ" of excretion in the amoeba is contractile vacuole. It receives excess water, unnecessary and harmful substances from the cytoplasm. The filled contractile vacuole periodically approaches the cytoplasmic membrane of the amoeba and pushes its contents out.

The amoeba breathes the entire surface of the body. Oxygen comes into it from water, carbon dioxide comes out of it. The process of respiration consists in the oxidation of organic substances in mitochondria with oxygen. As a result, energy is released, which is stored in ATP, and water and carbon dioxide are also formed. The energy stored in ATP is then used for various life processes.

For the amoeba, only asexual reproduction is described by dividing in two. Only large, i.e. grown, individuals divide. First, the nucleus divides, after which the amoeba cell divides by constriction. That daughter cell that does not receive a contractile vacuole forms one subsequently.

With the onset of cold weather or drought, the amoeba forms cyst. Cysts have a dense shell that performs a protective function. They are quite light and can be carried by the wind over long distances.

The amoeba is able to react to light (creeps away from it), mechanical irritation, the presence of certain substances in the water.