Organelles of protozoa. Type protozoa

In the middle part of the body sporozoite available round hole, micropyle. It is known that after the sporozoite penetrates the cell of a vertebrate host, it immediately becomes rounded, which is difficult to explain, given the density of its pellicle. Garnham and co-workers (1963) suggested that the sporozoite cytoplasm with the nucleus at this moment emerges through the micropyle, from the shell.

Installed similarity in structure sporozoites and merozoites; in blood trophozoites, a micropyle-like formation has been described, possibly serving as a cytostome (Aikawa, 1966).

Digestion and absorption of food in protozoa it occurs in digestive vacuoles - vesicles located in the inner layer of the cytoplasm. The food for protozoa can be both formed particles (including various living organisms) and substances dissolved in the environment. The absorption of formed particles is carried out through phagocytosis. Their capture in sarcodes occurs at any point on the surface.

However, a significant part protozoa For this process, any one part of the body is specialized: a depression is formed - the cell mouth of the cytostome. The structure of the centostome of ciliates is especially complex, in which it can be surrounded by special organelles- elongated cilia and membranellae.

Absorption dissolved nutrients carried out through the capture of droplets by the surface of the cytoplasm environment. The resulting vesicles pass through the cell membrane, detach from it and move into the cytoplasm. This process is called pinocytosis.

Cell organelles, also known as organelles, are specialized structures of the cell itself, responsible for various important and vital functions. Why “organelles” after all? It’s just that here these cell components are compared with the organs of a multicellular organism.

What organelles make up the cell?

Also, sometimes organelles mean only the permanent structures of the cell that are located in it. For the same reason, the cell nucleus and its nucleolus are not called organelles, just as cilia and flagella are not organelles. But the organelles that make up the cell include: , complex , endoplasmic reticulum, ribosomes, microtubules, microfilaments, lysosomes. In fact, these are the main organelles of the cell.

If we're talking about about animal cells, their organelles also include centrioles and microfibrils. But the number of organelles of a plant cell still includes only plastids characteristic of plants. In general, the composition of organelles in cells can differ significantly depending on the type of cell itself.

Drawing of the structure of a cell, including its organelles.

Double membrane cell organelles

Also in biology, there is such a phenomenon as double-membrane cell organelles, these include mitochondria and plastids. Below we will describe their inherent functions, as well as all other main organelles.

Functions of cell organelles

Now let us briefly describe the main functions of animal cell organelles. So:

• The plasma membrane is a thin film around the cell consisting of lipids and proteins. A very important organelle that transports water, minerals and organic substances into the cell, removes harmful waste products and protects the cell.
• Cytoplasm is the internal semi-liquid environment of the cell. Provides communication between the nucleus and organelles.
• The endoplasmic reticulum is also a network of channels in the cytoplasm. Takes an active part in the synthesis of proteins, carbohydrates and lipids, and is involved in the transport of nutrients.
• Mitochondria are organelles in which organic substances are oxidized and ATP molecules are synthesized with the participation of enzymes. Essentially, mitochondria are a cell organelle that synthesizes energy.
• Plastids (chloroplasts, leucoplasts, chromoplasts) - as we mentioned above, are found exclusively in plant cells, in general their presence is main feature plant organism. Play a very important function, for example, chloroplasts containing green pigment chlorophyll, in plants, is responsible for the phenomenon.
• The Golgi complex is a system of cavities delimited from the cytoplasm by a membrane. Carry out the synthesis of fats and carbohydrates on the membrane.
• Lysosomes are bodies separated from the cytoplasm by a membrane. The special enzymes they contain accelerate the breakdown of complex molecules. The lysosome is also an organelle that ensures protein assembly in cells.
• - cavities in the cytoplasm filled with cell sap, a place of accumulation of reserve nutrients; they regulate the water content in the cell.

In general, all organelles are important, because they regulate the life of the cell.

Basic cell organelles, video

And finally, a thematic video about cell organelles.

Every living organism is made up of cells, many of which are capable of movement. In this article we will talk about movement organelles, their structure and functions.

Organelles of movement of unicellular organisms

In modern biology, cells are divided into prokaryotes and eukaryotes. The first include representatives of the simplest organisms that contain one strand of DNA and do not have a nucleus (blue-green algae, viruses).

Eukaryotes have a nucleus and consist of a variety of organelles, one of which is the organelles of movement.

Organelles of movement of unicellular organisms include cilia, flagella, thread-like formations - myofibrils, pseudopods. With their help, the cell can move freely.

Rice. 1. Varieties of movement organelles.

Movement organelles are also found in multicellular organisms. For example, in humans, the bronchial epithelium is covered with many cilia, which move strictly in the same order. In this case, a so-called “wave” is formed that can protect the respiratory tract from dust and foreign particles. Spermatozoa (specialized cells of the male body that serve for reproduction) also have flagella.

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The motor function can also be carried out due to the contraction of microfibers (myonemes), which are located in the cytoplasm under the integument.

Structure and functions of movement organelles

Movement organelles are membrane outgrowths that reach 0.25 µm in diameter. In terms of their structure, flagella are much longer than cilia.

The length of the sperm flagellum in some mammals can reach 100 microns, while the size of the cilia is up to 15 microns.

Despite such differences, internal structure These organelles are absolutely identical. They are formed from microtubules, which are similar in structure to the centrioles of the cell center.

Motor movements are formed due to the sliding of microtubules among themselves, as a result of which they bend. At the base of these organelles there is a basal body that attaches them to the cell cytoplasm. To ensure the functioning of movement organelles, the cell consumes ATP energy.

Rice. 2. Structure of the flagellum.

Some cells (amoebas, leukocytes) move due to pseudopodia, in other words, pseudopods. However, unlike flagella and cilia, pseudopodia are temporary structures. They can disappear and appear in different places in the cytoplasm. Their functions include locomotion and the capture of food and other particles.

Flagella consist of a filament, a hook and a basal body. According to the number and location of these organelles on the surface of bacteria they are divided into:

• Monotrichs(one flagellum);
• Amphitrichy(one flagellum at different poles);
• Lophotrichs(a bunch of formations on one or both poles);
• Peritrichous(many flagella located over the entire surface of the cell).

Rice. 3. Varieties of flagellates.

Among the functions performed by movement organelles are:

• providing movement to a single-celled organism;
• the ability of muscles to contract;
• protective reaction of the respiratory tract from foreign particles;
• fluid advancement.

Flagellates play a large role in the cycle of substances in the environment; many of them are good indicators of pollution of water bodies.

What have we learned?

One of the constituent elements of the cell are organelles of movement. These include flagella and cilia, which are formed with the help of microtubules. Their functions include providing movement to a unicellular organism and promoting fluids inside a multicellular organism.

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The simplest animals are single-celled organisms, characteristics, nutrition, presence in water and in the human body

general characteristics

Or unicellular organisms, as their name suggests, are made up of a single cell. The phylum Protozoa includes more than 28,000 species. The structure of protozoa can be compared with the structure of cells of multicellular organisms. Both of them are based on the nucleus and cytoplasm with various organelles (organelles) and inclusions. However, we must not forget that any cell of a multicellular organism is part of any tissue or organ where it performs its specific functions. All cells of a multicellular organism are specialized and are not capable of independent existence. In contrast, the simplest animals combine the functions of a cell and an independent organism. (Physiologically, the Protozoa cell is similar not to individual cells of multicellular animals, but to a whole multicellular organism.

The simplest all functions inherent in any living organisms are characteristic: nutrition, metabolism, excretion, perception of external stimuli and reaction to them, movement, growth, reproduction and death.

Protozoa Cell structure

The nucleus and cytoplasm, as indicated, are the main structural and functional components of any cell, including unicellular animals. The body of the latter contains organelles, skeletal and contractile elements and various inclusions. It's always covered cell membrane, more or less thin, but clearly visible in an electron microscope. The cytoplasm of protozoa is liquid, but its viscosity varies among different types and varies depending on the condition of the animal and the environment (its temperature and chemical composition). In most species the cytoplasm is transparent or milky white, but in some it is colored blue or greenish (Stentor, Fabrea saliva). Chemical composition The nuclei and cytoplasm of protozoa have not been fully studied, mainly due to the small size of these animals. It is known that the basis of the cytoplasm and nucleus, as in all animals, is made up of proteins. Nucleic acids They are closely related to proteins; they form nucleoproteins, the role of which in the life of all organisms is extremely large. DNA (deoxyribonucleic acid) is part of the chromosomes of the protozoan nucleus and ensures the transmission of hereditary information from generation to generation. RNA (ribonucleic acid) is found in protozoa both in the nucleus and in the cytoplasm. It implements the hereditary properties of single-celled organisms encoded in DNA, as it plays a leading role in the synthesis of proteins.

Very important chemical components of the cytoplasm - fat-like substances lipids - take part in metabolism. Some of them contain phosphorus (phosphatides), many are associated with proteins and form lipoprotein complexes. The cytoplasm also contains reserve nutrients in the form of inclusions - droplets or granules. These are carbohydrates (glycogen, paramyl), fats and lipids. They serve as the energy reserve of the protozoan body.

In addition to organic substances, the cytoplasm includes a large number of water, mineral salts are present (cations: K+, Ca2+, Mg2+, Na+, Fe3+ and anions: Cl~, Р043“, N03“). In the cytoplasm of protozoa, many enzymes involved in metabolism are found: proteases, which ensure the breakdown of proteins; carbohydrases that break down polysaccharides; lipases that promote fat digestion; a large number of enzymes that regulate gas exchange, namely alkaline and acid phosphatases, oxidases, peroxidases and cytochrome oxidases.

Previous ideas about the fibrillar, granular or foamy-cellular structure of the cytoplasm of protozoa were based on studies of fixed and stained preparations. New methods for studying protozoa (in a dark field, in polarized light, using intravital staining and electron microscopy) have made it possible to establish that the cytoplasm of protozoa is a complex dynamic system of hydrophilic colloids (mainly protein complexes), which has a liquid or semi-liquid consistency. During ultramicroscopic examination in a dark field, the cytoplasm of protozoa appears optically empty, only the cell organelles and its inclusions are visible.

The colloidal state of cytoplasmic proteins ensures the variability of its structure. Changes are constantly occurring in the cytoplasm state of aggregation proteins: they come from liquid state(sol) into a harder, gelatinous (gel). These processes are associated with the release of a denser layer of ectoplasm, the formation of a shell - pellicles, and the amoeboid movement of many protozoa.

The nuclei of protozoa, like the nuclei of multicellular cells, consist of chromatin material, nuclear juice, and contain nucleoli and a nuclear membrane. Most protozoa contain only one nucleus, but there are also multinucleate forms. In this case, the nuclei can be the same (multinucleate amoebas from the genus Pelomyxa, multinucleate flagellates Polymastigida, Opalinida) or differ in shape and function. In the latter case, they talk about nuclear differentiation, or nuclear dualism. Thus, the entire class of ciliates and some foraminifera are characterized by nuclear dualism. i.e. nuclei unequal in shape and function.

These types of protozoa, like other organisms, obey the law of constancy of the number of chromosomes. Their number can be single, or haploid (most flagellates and sporozoans), or double, or diploid (ciliates, opalines and, apparently, sarcodae). The number of chromosomes in different species of protozoa varies widely: from 2-4 to 100-125 (in the haploid set). In addition, nuclei with a multiple increase in the number of sets of chromosomes are observed. They are called polyploid. It was found that large nuclei, or macronuclei, of ciliates and the nuclei of some radiolarians are polyploid. It is very likely that the nucleus of Amoeba proteus is also polyploid; the number of chromosomes in this species reaches 500.

Reproduction Nuclear division

The main type of nuclear division in both protozoa and multicellular organisms is mitosis, or karyokinesis. During mitosis, the correct, uniform distribution of chromosomal material occurs between the nuclei of dividing cells. This is ensured by the longitudinal splitting of each chromosome into two daughter chromosomes in the metaphase of mitosis, with both daughter chromosomes going to different poles of the dividing cell.

When the nucleus of Monocystis magna gregarina divides, all the mitotic figures characteristic of multicellular organisms can be observed. In prophase, thread-like chromosomes are visible in the nucleus, some of them are associated with the nucleolus (Fig. 1, 1, 2). In the cytoplasm, two centrosomes can be distinguished, in the center of which there are centrioles with star rays diverging radially. Centrosomes approach the nucleus, adjoin its shell and move to the opposite poles of the nucleus. The nuclear envelope dissolves and an achromatin spindle is formed (Fig. 1, 2-4). Spiralization of chromosomes occurs, as a result of which they are greatly shortened and collected in the center of the nucleus, the nucleolus dissolves. In metaphase, chromosomes move to the equatorial plane. Each chromosome consists of two chromatids lying parallel to each other and held together by one centromere. The star figure around each centrosome disappears, and the centrioles are divided in half (Fig. 1, 4, 5). In anaphase, the centromeres of each chromosome divide in half and their chromatids begin to diverge towards the spindle poles. It is characteristic of protozoa that the pulling spindle filaments attached to the centromeres are distinguishable only in some species. The entire spindle is stretched, and its threads, running continuously from pole to pole, lengthen. The separation of chromatids that have turned into chromosomes is ensured by two mechanisms: their pulling apart under the action of contraction of the pulling spindle threads and the stretching of continuous spindle threads. The latter leads to the removal of the cell poles from each other (Fig. 1, 6, 7). In telophase, the process proceeds in the reverse order: at each pole, a group of chromosomes is clothed with a nuclear envelope. The chromosomes despiral and become thinner, and nucleoli are formed again. The spindle disappears, and around the divided centrioles two independent centrosomes with star rays are formed. Each daughter cell has two centrosomes - the future centers of the next mitotic division (Fig. 1, 9, 10). Following nuclear division, the cytoplasm is usually divided. However, in some protozoa , including Monocystis, a series of successive nuclear divisions occurs, as a result of which life cycle Temporarily multinucleated stages occur. Later, a section of cytoplasm separates around each nucleus and many small cells are formed simultaneously.

There are various deviations from the process of mitosis described above: the nuclear envelope can be preserved throughout the entire mitotic division, the achromatin spindle can form under the nuclear envelope, and in some forms centrioles are not formed. The most significant deviations are in some euglenidae: they lack a typical metaphase, and the spindle passes outside the nucleus. In metaphase, chromosomes, consisting of two chromatids, are located along the axis of the nucleus, the equatorial plate is not formed, the nuclear membrane and nucleolus are preserved, the latter is divided in half and passes into the daughter nuclei. There are no fundamental differences between the behavior of chromosomes in mitosis in protozoa and multicellular organisms.

Before the use of new research methods, the nuclear division of many protozoa was described as amitosis, or direct division. True amitosis is now understood as the division of nuclei without proper separation of chromatids (chromosomes) into daughter nuclei. As a result, nuclei with incomplete sets of chromosomes are formed. They are not capable of further normal mitotic divisions. It is difficult to expect such nuclear divisions in the simplest organisms normally. Amitosis is observed optionally as a more or less pathological process.

The body of protozoa is quite complex. Within one cell, differentiation occurs individual parts, which perform various functions. Thus, by analogy with the organs of multicellular animals, these parts of protozoa were called organelles or organelles. There are organelles of movement, nutrition, perception of light and other stimuli, excretory organelles, etc.

Movement

The organelles of movement in Protozoa are pseudopodia, or pseudopods, flagella and cilia. Pseudopodia are formed for the most part at the moment of movement and can disappear as soon as the protozoan stops moving. Pseudopodia are temporary plasmatic outgrowths of the body of protozoa that do not have a permanent shape. Their shell is represented by a very thin (70-100 A) and elastic cell membrane. Pseudopodia are characteristic of sarcodae, some flagellates and sporozoans.

Flagella and cilia are permanent outgrowths of the outer layer of the cytoplasm, capable of rhythmic movements. The ultrafine structure of these organelles was studied using an electron microscope. It was found that they are constructed in much the same way. The free part of the flagellum or cilium extends from the surface of the cell.

The internal part is immersed in ectoplasm and is called the basal body or blepharoplast. On ultrathin sections of a flagellum or cilium, 11 longitudinal fibrils can be distinguished, 2 of which are located in the center, and 9 along the periphery (Fig. 2). The central fibrils in some species have helical striations. Each peripheral fibril consists of two connected tubes, or subfbrils. Peripheral fibrils pass into the basal body, but central fibrils do not reach it. The flagellum membrane passes into the membrane of the protozoan body.

Despite the similarity in structure of cilia and flagella, the nature of their movement is different. If flagella make complex screw movements, then the work of cilia can most easily be compared with the movement of oars.

In addition to the basal body, the cytoplasm of some protozoa contains a parabasal body. The basal body is the basis of the entire musculoskeletal system; in addition, it regulates the process of mitotic division of the protozoan. The parabasal body plays a role in the metabolism of the protozoan; at times it disappears and then may appear again.

Sense organs

Protozoa have the ability to determine light intensity (illuminance) using a photosensitive organelle - the ocellus. A study of the ultrathin structure of the eye of the marine flagellate Chromulina psammobia showed that it includes a modified flagellum immersed in the cytoplasm.

Due to various types nutrition, which will be discussed in detail later, protozoa have a very wide variety of digestive organelles: from simple digestive vacuoles or vesicles to such specialized formations as the cellular mouth, oral funnel, pharynx, powder.

Excretory system

Most protozoa are characterized by the ability to withstand unfavorable environmental conditions (drying out of temporary reservoirs, heat, cold, etc.) in the form of cysts. In preparation for encystment, the protozoan releases a significant amount of water, which leads to an increase in the density of the cytoplasm. The remains of food particles are thrown out, the cilia and flagella disappear, and the pseudopodia are retracted. The overall metabolism decreases, a protective shell is formed, often consisting of two layers. The formation of cysts in many forms is preceded by the accumulation of reserve nutrients in the cytoplasm.

Protozoa do not lose viability in cysts for a very long time. In experiments, these periods exceeded 5 years for the genus Oicomonas (Protomonadida), 8 years for Haematococcus pluvialis, and for Peridinium cinctum the maximum survival period of cysts exceeded 16 years.

In the form of cysts, protozoa are transported by the wind over considerable distances, which explains the homogeneity of the protozoan fauna throughout globe. Thus, cysts not only carry protective function, but also serve as the main means of dispersal of protozoa.

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 matter. 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 a dense protective shell. The formation of a cyst is not only an adaptation to survival under 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 the life cycle of most protozoa, asexual and sexual reproduction alternate.

There are over 90,000 species of unicellular organisms. All of them are eukaryotes (have a separate nucleus), but are at the cellular level of organization.

Amoeba

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

Having surrounded the prey with pseudopods, the food ends up in the cytoplasm, where a digestive vacuole forms around it. In it, under the influence of digestive juice coming from the cytoplasm, digestion occurs, as a result of which digestive substances are formed. 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 decay 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, the outer layer of cytoplasm is compacted and forms a shell that helps maintain this shape.

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 goes to heterotrophic method nutrition, that is, it feeds on ready-made organic substances, absorbing them from 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 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 all life processes, small- plays an important role in the reproduction of the shoe. 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 ciliate slipper has the most complex structure.

Irritability

When characterizing the simplest organisms, you should pay special attention to 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.