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Contractile vacuole: concept, role. Vacuole, its features: structure, composition, functions Contractile vacuole of amoeba Proteus

Two groups of animals have contractile vacuoles: protozoa and sponges. Apparently, all freshwater protozoa have such vacuoles. It is not so clear whether they are present in all marine forms, but they are found in at least some marine ciliates. The presence of contractile vacuoles in freshwater sponges was previously questioned, but has now been proven beyond doubt (Jepps, 1947).
Since freshwater forms are always hyperosmogic in relation to the environment and their surface is permeable to water, they constantly have to remove water from the body. They must not only remove excess water, but also replace lost solutes, probably by actively absorbing salts from external environment. Determination of the water permeability of the large Chaos chaos amoeba showed that the calculated osmotic water influx is in good agreement with the observed rate of fluid excretion by the contractile vacuole. This confirms the widely held belief that main function contractile vacuole consists of homoregulation and regulation of cell volume (L^vtrup, Pigon, 1951).
By observing the contractile vacuole in freshwater protozoa under a microscope, one can see continuous cyclic changes. The vacuole takes in water and gradually increases in volume until it reaches a critical size. Then it suddenly throws its contents out and decreases

Rice. 10.1. The contractile vacuole of Amoeba proteus is bounded by a membrane and surrounded by a layer of small vesicles, which are filled with fluid and apparently empty into the vacuole. Around this structure lies a layer of mitochondria, which likely supplies energy for the secretory process. (Mercer,

in volume, after which it begins to increase again, and the cycle repeats.
The lumen of the contractile vacuole in amoeba is surrounded by a single thin membrane. Adjacent to this membrane on the outside is a thick (0.5-2 µm) layer of densely packed small bubbles with a diameter of 0.02 to 0.2 µm. Around this layer of small vesicles lies a layer of mitochondria, which apparently supply energy for osmotic work, creating hypotonicity of the contents of the vacuole (Fig. 10.1). Based on electron micrographs, the vesicles are emptied into a contractile vacuole by membrane fusion.
The role of the contractile vacuole in osmoregulation is well demonstrated in the euryhaline amoeba Amoeba lacerata. This amoeba is originally a freshwater organism, but has a high tolerance to salt and can even adapt to 50% sea ​​water. Reduce the rate of emptying -
body vacuole, when adapting to different salt concentrations, is in inverse relationship on the osmotic concentration of the medium (Fig. 10.2).
Apparently, contractile vacuoles remove water at the same rate as its osmotic influx, so. how, as the concentration of the medium increases, the amount of

Rice. 10.2. The rate of fluid excretion by the contractile vacuole of Amoeba lacerate depending on the concentration of the external environment (expressed as a percentage of the concentration of seawater). Amoebas were studied in the same solution in which they were grown. (Hopkins, 1946.)

drinking water decreases. IN marine environment, where, as one must assume, the internal and external osmotic concentrations are almost the same, contractile vacuoles (in those forms in which they were observed) are emptied very slowly. In these cases, we have to assume that they do not serve primarily for osmoregulation, but perform other excretory functions.
If in freshwater protozoa the main function of the contractile vacuole is to remove water, then its contents should be hypotonic with respect to the rest of the cell. This is how things really are. In microscopic fluid samples taken from the contractile vacuole, the osmotic concentration is approximately three times lower than in the cytoplasm, but several times higher than in the external environment (B. Sichmidt-Nielsen, Schrauger, 1963).

The contractile vacuole can remove hypotonic fluid and serve to excrete water. But because the excreted fluid has a higher osmotic concentration than the external environment, there is a continuous loss of solutes, and it follows that the amoeba must be able to absorb the substances it needs, probably by actively transferring them directly from the external environment .
How can a vacuole increase in volume and at the same time contain a fluid less concentrated than the cytoplasm? Possible here different explanations. According to one of them, active transport of water into the vacuole occurs. But for a number of reasons such a hypothesis is hardly plausible. Another possibility is that the vacuole initially contains an isotonic fluid from which osmotically active substances are extracted before the fluid is expelled. But this assumption contradicts the data that the fluid is hypotonic and its composition is relatively constant throughout the entire period of vacuole enlargement.
Information on the composition of the vacuolar fluid allows us to suggest a third mechanism. As can be seen from table. 10.1, osmo-
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Concentration of substances dissolved in the cytoplasm and contractile vacuole of freshwater amoeba. The average vacuole volume was about 0.2 nl. (Riddick, 1968)

The concentration of liquid in the vacuole is approximately half that in the cytoplasm, but is more than 25 times higher than the concentration in the external environment. The sodium content in the vacuole fluid is relatively high - it is 3 times higher than in the cytoplasm. At the same time, there is relatively little potassium in the vacuole; its concentration here is significantly lower than in the cytoplasm. In total, sodium and potassium in the vacuolar fluid are about 25 mmol/l, and if the anion is C’1_, then these three ions provide almost the entire osmotic concentration of the fluid (51 mmol/l).

The most likely mechanism for the formation of a contractile vacuole is the following. The small vesicles surrounding it are initially filled with liquid, isotene with the cytoplasm. The bubbles then, by active transport, pump sodium into this liquid and remove potassium - such that the removal of potassium exceeds the accumulation of sodium. The membrane of the vesicles must be relatively impermeable to water so that a fluid that is hypotonic with respect to the cytoplasm can form in the vesicle. If these hypotonic vesicles then fuse and empty into a contractile vacuole, as the electron micrographs indicate, then the vacuole would be the receptacle for the fluid produced by the vesicles. The energy for osmotic work is supplied by the layer of mitochondria adjacent to the vesicles. Since the activity of the contractile vacuole leads to continuous loss of sodium, it must be assumed. that this loss is compensated by the active uptake of sodium by the cell surface (Riddick, 1968).

Amoeba vulgaris is a type of protozoan eukaryotic creature, a typical representative of the genus Amoeba.

Taxonomy. The species of common amoeba belongs to the kingdom - Animals, phylum - Amoebozoa. Amoebas are united in the class Lobosa and order - Amoebida, family - Amoebidae, genus - Amoeba.

Characteristic processes. Although amoebas are simple, single-celled creatures that do not have any organs, they possess all vital processes. They are able to move, get food, reproduce, absorb oxygen, and remove metabolic products.

Structure

The common amoeba is a unicellular animal, the body shape is uncertain and changes due to constant movement pseudopods. The dimensions do not exceed half a millimeter, and the outside of its body is surrounded by a membrane - plasmalem. Inside there is cytoplasm with structural elements. Cytoplasm is a heterogeneous mass, where two parts are distinguished:

  • External - ectoplasm;
  • internal, with a granular structure - endoplasm, where all intracellular organelles are concentrated.

The common amoeba has a large nucleus, which is located approximately in the center of the animal's body. It has nuclear sap, chromatin and is covered with a membrane with numerous pores.

Under a microscope it can be seen that the common amoeba forms pseudopodia into which the cytoplasm of the animal is poured. At the moment of pseudopodia formation, endoplasm rushes into it, which in the peripheral areas becomes denser and turns into ectoplasm. At this time, on the opposite part of the body, ectoplasm partially transforms into endoplasm. Thus, the formation of pseudopodia is based on the reversible phenomenon of the transformation of ectoplasm into endoplasm and vice versa.

Breath

Amoeba receives O 2 from water, which diffuses into internal cavity through the outer integument. The whole body is involved in respiratory act. Oxygen entering the cytoplasm is necessary for the breakdown nutrients into simple components that Amoeba proteus can digest, and also to obtain energy.

Habitat

Inhabits fresh water in ditches, small ponds and swamps. Can also live in aquariums. Amoeba vulgaris culture can be easily propagated in the laboratory. It is one of the large free-living amoebas, reaching 50 microns in diameter and visible to the naked eye.

Nutrition

The common amoeba moves with the help of pseudopods. She covers one centimeter in five minutes. While moving, amoebas encounter various small objects: unicellular algae, bacteria, small protozoa, etc. If the object is small enough, the amoeba flows around it from all sides and it, together with a small amount liquid appears inside the cytoplasm of the protozoan.


Amoeba vulgaris nutritional diagram

The process of absorption of solid food by the common amoeba is called phagocytosis. Thus, in the endoplasm are formed digestive vacuoles, into which they enter from the endoplasm digestive enzymes and intracellular digestion occurs. Liquid products digestion penetrates the endoplasm, the vacuole with undigested food remains approaches the surface of the body and is thrown out.

In addition to digestive vacuoles, the body of amoebas also contains a so-called contractile, or pulsating, vacuole. This is a bubble of watery liquid that periodically grows and, having reached a certain volume, bursts, emptying its contents out.

The main function of the contractile vacuole is to regulate osmotic pressure inside the protozoan body. Due to the fact that the concentration of substances in the cytoplasm of the amoeba is higher than in fresh water, a difference in osmotic pressure is created inside and outside the body of the protozoa. That's why fresh water penetrates the body of the amoeba, but its quantity remains within the limits physiological norm, as the pulsating vacuole “pumps” excess water out of the body. This function of vacuoles is confirmed by their presence only in freshwater protozoa. In marine animals it is either absent or reduced very rarely.

In addition to the osmoregulatory function, the contractile vacuole partially performs excretory function, removing along with water into environment metabolic products. However, the main function of excretion is carried out directly through the outer membrane. The contractile vacuole probably plays a certain role in the process of respiration, since water penetrating into the cytoplasm as a result of osmosis carries dissolved oxygen.

Reproduction

Amoebas are characterized by asexual reproduction, carried out by dividing in two. This process begins with mitotic division of the nucleus, which lengthens longitudinally and is separated by a septum into 2 independent organelles. They move away and form new nuclei. The cytoplasm with the membrane is divided by a constriction. The contractile vacuole does not divide, but enters one of the newly formed amoebae; in the second, the vacuole forms independently. Amoebas reproduce quite quickly; the division process can occur several times during the day.

In the summer, amoebas grow and divide, but with the arrival of autumn cold, due to the drying up of water bodies, it is difficult to find nutrients. Therefore, the amoeba turns into a cyst, finding itself in critical conditions and becomes covered with a durable double protein shell. At the same time, cysts easily spread with the wind.

Meaning in nature and human life

Amoeba proteus is an important component of ecological systems. It regulates the number of bacterial organisms in lakes and ponds. Cleanses aquatic environment from excessive pollution. It is also an important component of food chains. Single-celled organisms are food for small fish and insects.

Scientists use the amoeba as a laboratory animal, conducting many studies on it. The amoeba cleans not only reservoirs, but also by settling in human body, it absorbs destroyed particles epithelial tissue digestive tract.

- a convenient organ where food is digested, broken down into simple compounds, which are then absorbed by the body and used for its needs. However, tiny ones - protozoa and sponges - of course, do not have a stomach. Its role is played by the phagosome, also called the digestive vacuole - vesicle, membrane. It forms around a solid particle or cell that the body decides to eat. A digestive vacuole also appears around the swallowed drop of liquid. The phagosome merges with the lysosome, enzymes are activated and the digestion process begins, which lasts about an hour. During digestion, the environment inside the phagosome changes from acidic to alkaline. Once all the nutrients have been extracted, the undigested food remains are eliminated from the body through the powder or cell membrane.

The digestion of solid food is called phagocytosis, and the digestion of liquid food is called pinocytosis.

Contractile vacuole

Many sponge representatives have a contractile vacuole. The main function of this organelle is the regulation of osmotic pressure. Through the cell membrane, water enters the cell of a sponge or protozoa, and periodically, at equal intervals of time, the liquid is excreted using a contractile vacuole, which grows to certain point, then begins to contract with the help of the elastic bundles present in it.

There is a hypothesis that the contractile vacuole also takes part in cellular respiration.

Vacuole in a plant cell

Plants also have vacuoles. In a young cell, as a rule, there are several small pieces of them, but as the cell grows, they increase and merge into one large vacuole, which can occupy 70-80% of the entire cell. The plant vacuole contains cell sap, which contains minerals, sugars and organic substances. The main function of this organelle is to maintain turgor. Also plant vacuoles participate in water-salt metabolism, breakdown and absorption of nutrients and disposal of compounds that can harm the cell. The green parts of plants that are not covered with wood retain their shape thanks to a strong cell wall and vacuoles, which keep the cell shape unchanged and prevent deformation.

The subkingdom of unicellular organisms or protozoa include the smallest creatures whose body consists of one cell. These cells represent an independent organism with all its characteristic functions (metabolism, irritability, movement, reproduction).

The body of unicellular organisms can have a permanent shape (slipper ciliates, flagellates) or a non-permanent shape (amoebas). The main components of the body of protozoa are − core And cytoplasm. In the cytoplasm of protozoa, along with general cellular organelles (mitochondria, ribosomes, Galgi apparatus, etc.), there are special organelles (digestive and contractile vacuoles) that perform the functions of digestion, osmoregulation, and excretion. Almost all protozoa are capable of active movement. The movement is carried out using pseudopods(in amoeba and other rhizomes), flagella(green euglena) or eyelashes(ciliates). Protozoa are capable of capturing solid particles (amoeba), which is called phagocytosis. Most protozoa feed on bacteria and decaying organic substances. After swallowing, food is digested in digestive vacuoles. The function of excretion in protozoa is performed by contractile vacuoles, or special holes - powder(in ciliates).

Protozoa live in fresh water bodies, seas and soil. The vast majority of protozoa have the ability to encystment, that is, the formation of a resting stage upon the onset of unfavorable conditions (lowering temperature, drying out of the reservoir) - cysts, covered with dense containment. Cyst formation is not only an adaptation to survival during unfavorable conditions, but also to the spread of protozoa. Once in favorable conditions, the animal leaves the cyst shell and begins to feed and reproduce.

Reproduction of protozoa occurs by cell division into two (asexual); many experience sexual intercourse. IN life cycle Most protozoa alternate between asexual and sexual reproduction.

There are over 90,000 species of unicellular organisms. All of them are eukaryotes (have a separate nucleus), but are located on cellular level organizations.

Amoeba

A representative of the rhizome class is amoeba ordinary. Unlike many protozoa, it does not have a constant body shape. It moves with the help of pseudopods, which also serve to capture food - bacteria, unicellular algae, and some protozoa.

Having surrounded the prey with pseudopods, the food ends up in the cytoplasm, where a digestive vacuole forms around it. In her under the influence digestive juice, coming from the cytoplasm, digestion occurs, resulting in the formation digestive substances. They penetrate the cytoplasm, and undigested food remains are thrown out.

The amoeba breathes over the entire surface of the body: oxygen dissolved in water directly penetrates into its body through diffusion, and oxygen formed in the cell during respiration carbon dioxide stands out.

The concentration of dissolved substances in the body of the amoeba is greater than in water, so water continuously accumulates and its excess is removed outside with the help of contractile vacuole. This vacuole is also involved in removing waste products from the body. Amoeba reproduces by division. The nucleus divides in two, both halves diverge, a constriction forms between them, and then two independent daughter cells arise from one mother cell.

Amoeba is a freshwater animal.

Euglena green

Another widespread species of protozoa lives in fresh water bodies - green euglena. It has a spindle-shaped shape, outer layer The cytoplasm is compacted and forms a shell that helps maintain this form.

A long thin flagellum extends from the front end of the body of the green euglena, rotating which the euglena moves in the water. In the cytoplasm of euglena there is a nucleus and several colored oval bodies - chromatophores containing chlorophyll. Therefore, in the light, euglena feeds like a green plant (autotrophic). A light-sensitive eye helps euglena find illuminated places.

If a euglena is in the dark for a long time, then the chlorophyll disappears and it switches to a heterotrophic mode of nutrition, that is, it feeds on ready-made organic substances, absorbing them from the water over the entire surface of the body. Respiration, reproduction, division in two, and cyst formation in green euglena are similar to those of amoeba.

Volvox

Among the flagellates there are colonial species, for example, Volvox.

Its shape is spherical, the body consists of a gelatinous substance in which individual cells - members of the colony - are immersed. They are small, pear-shaped, and have two flagella. Thanks to the coordinated movement of all flagella, the Volvox moves. In a Volvox colony there are few cells capable of reproduction; Daughter colonies are formed from them.

Ciliate slipper

Another type of protozoa is often found in fresh water bodies - ciliate-slipper, which got its name due to the peculiarities of the shape of the cell (in the form of a shoe). Cilia serve as organelles for movement. The body has a constant shape, as it is covered with a dense shell. The ciliate slipper has two nuclei: large and small.

Big core regulates everything life processes, small- plays important role in slipper propagation. Ciliates feed on bacteria, algae and some protozoa. Vibrations eyelashes food gets into mouth opening, then - in throat, at the bottom of which are formed digestive vacuoles where food is digested and nutrients are absorbed. Undigested residues are removed through a special organ - powder. The selection function is performed by contractile vacuole.

It reproduces, like the amoeba, asexually, but the slipper ciliate also has a sexual process. It consists in the fact that two individuals unite, an exchange of nuclear material occurs between them, after which they disperse (Fig. 73).

This type of sexual reproduction is called conjugation. Thus, among freshwater protozoa the most complex structure has a ciliate slipper.

Irritability

When characterizing the simplest organisms, one should pay attention to special attention on one more property of them - irritability. Protozoa do not have nervous system, they perceive irritations of the entire cell and are able to respond to them with movement - taxis, moving towards or away from the stimulus.

Protozoa living in sea water and soil and others

Soil protozoa are representatives of amoebas, flagellates and ciliates, which play an important role in the soil-forming process.

In nature, protozoa participate in the cycle of substances and perform a sanitary role; in food chains they form one of the first links, providing food for many animals, in particular fish; take part in the formation of geological rocks, and their shells determine the age of individual geological rocks.

Question 24. Vacuoles. Paraplasmic (ergastic) inclusions

Functions of giloxisomes

Giloxisomes

Their characteristics

Microbodies- these are smooth-walled bubbles 0.1-1.5 microns in size with a relatively permeable membrane, a fine-grained matrix ( main component- protein) and protein crystalloids or amorphous inclusions.

Their main enzyme, catalase, is found only in microbodies.

Microbodies are formed from dilated and enzyme-filled ER cisterns, which are separated from the ER or, possibly, retain connection with it.

Microbodies are represented by two main types:

  • peroxisomes;
  • gyloxisomes.


2. Peroxisomes

Peroxisomes contain oxidases that form H 2 O 2. Their substrate is substances with general structure type RH 2, for example:

  • uric acid in liver peroxisomes;
  • ethanol or methanol in the liver;
  • glycolic acid in leaf peroxisomes.

H 2 O 2 formed during metabolism is broken down according to the catalase or peroxidase type. These reactions are used in various metabolic processes, for example, during photorespiration in plant leaves.

Giloxisomes- specialized perixisomes with malate synthase as the main enzyme.

They are involved in the formation of carbohydrates from fats, acetate or ethanol (gluconeogenesis). Splitting fatty acids to acetyl-CoA, they then convert it into succinate in the gyloxysonic acid cycle (in a gyloxysome-specific manner). Subsequently, outside of hyloxisomes, succinate can be used for the synthesis of carbohydrates.

Giloxisomes are found in fat-storing tissues of plants, as well as in algae, fungi and some protozoa.

Vacuoles are called large bubbles with predominantly water content. They are formed from vesicular extensions of the ER or from Golgi vesicles.

Contractile (pulsating) vacuoles serve for osmotic regulation (primarily in freshwater protozoa), since water from the surrounding hypotonic solution continuously penetrates into their cells by osmosis. This water, as well as water absorbed by pinocytosis, is osmotically absorbed by the vacuoles and then expelled, periodically contracting with the help of bundles of elastic fibers present in their membrane. U complex shapes wave-like contractions of the central reservoir with an excretory pore leading outward and radial canals occur.

The membrane surrounding it is tonoplast- has a thickness of the ER membrane (6 nm) in contrast to the thicker, denser and less permeable plasmalemma. The contents of the vacuole are cell sap.



In plant embryonic cells, many small vacuoles arise from vesicle-like extensions of the ER. As they increase, they merge into a central vacuole, which occupies most of the cell volume and can be penetrated by strands of protoplasm. However, such a vacuole is absent in many glandular cells.


2. Central vacuoles, their functions

The central vacuole is necessary for the cell as:

  • storage space - for separating soluble intermediate metabolic products:

    Carbohydrates (glucose, fructose);

    Organic acids (malic and citric);

    Amino acids;

  • places for excreta - for separating the final products of metabolism:

    Some pigments (red, violet and blue anthocyanins, yellow flavones and flavonols);

    Toxic substances (polyphenols, alkaloids);

    Other secondary substances;

    Osmotic space. Vacuole plays main role in water absorption plant cells and in the creation of osmotically determined turgor pressure, which stretches the elastic cell wall and thus imparts rigidity to the non-woody parts of the plant;

    The lysosomal space for autophagy, into which lysosomal enzymes from the Golgi vesicles enter already during the formation of vacuoles.


3. Vacuoles in plant tissues

In storage tissues of plants instead of one central vacuole there are often several vacuoles:

  • fat vacuoles with fat emulsion;
  • protein (aleurone) vacuoles with:
    - colloidal proteins;
    - crystalloid proteins;
    - phytin globoids (calcium-magnesium salt of hexaphosphoric acid ester and myoinositol - a form of phosphate accumulation).

Such vacuoles are called storage vacuoles.

Storage proteins are formed in the granular ER and enter dilated cisterns through the smooth ER, which become protein vacuoles. When it is necessary to break down the accumulated protein, protein vacuoles turn into lysosomes.