More than 2 million animals live on Earth, and this list is constantly growing.

The science that studies the structure, behavior, and vital functions of animals is called zoology.

The sizes of animals range from a few microns to 30 m. Some of them are visible only through a microscope, such as amoeba and ciliates, while others are giants. These are whales, elephants, giraffes. The habitat of animals is very diverse: water, land, soil and even living organisms.

Having common features with other representatives of eukaryotes, animals also have significant differences. Animal cells lack membranes and plastids. They feed on ready-made organic substances. A significant part of animals actively move and have special organs of movement.

animal kingdom divided into two sub-kingdoms: unicellular (protozoa) And multicellular.

Rice. 77. Protozoa: 1 - amoeba; 2 - green euglena; 3 - foraminifera (shells); 4 - ciliate-slipper ( 1 - large core; 2 - small core; 3 - cell mouth; 4 - cell pharynx; 5 - digestive vacuole; 6 - powder; 7 - contractile vacuoles; 8 - eyelashes)

Protozoa are divided into several types, the most widespread and significant of which are Sarcodaceae, Flagellates, Sporozoans and Ciliates.

Sarcodaceae (Rhizopods). A typical representative of Sarcodaceae is the amoeba. Amoeba is a freshwater, free-living animal that does not have a constant body shape. When an amoeba cell moves, it forms pseudopodia, or pseudopods, which also serve to capture food. In the cell, the nucleus and digestive vacuoles are clearly visible, which are formed at the site where the amoeba captures food. In addition, there is also contractile vacuole, through which excess water and liquid metabolic products are removed. Amoeba reproduces by simple division. Respiration occurs across the entire surface of the cell. Amoeba has irritability: a positive reaction to light and food, a negative reaction to salt.

Testate amoebas - foraminifera have an external skeleton - a shell. It consists of an organic layer impregnated with limestone. The shell has numerous openings - holes through which pseudopodia protrude. The size of the shells is usually small, but in some species it can reach 2-3 cm. The shells of dead foraminifera form sediments on the seabed - limestones. Other shell amoebas also live there - radiolarians (rays). Unlike foraminifera, they have an internal skeleton, which is located in the cytoplasm and forms needles - rays, often of an openwork design. In addition to organic matter, the skeleton contains strontium salts - this is the only case in nature. These needles form the mineral celestine.

Flagellates. These microscopic animals have a constant body shape and move with the help of flagella (one or more). Euglena green - a single-celled organism that lives in water. Its cell is spindle-shaped and has one flagellum at its end. At the base of the flagellum there is a contractile vacuole and a light-sensitive eye (stigma). In addition, the cell contains chromatophores containing chlorophyll. Therefore, euglena photosynthesizes in the light and feeds on ready-made organic substances in the dark.

After several asexual generations, cells appear in the erythrocytes from which gametes develop. For further development, they must enter the intestines of the Anopheles mosquito. When a mosquito bites a person with malaria, the gametes are carried through the blood into the digestive tract, where sexual reproduction and the formation of sporozoites occur.

Ciliates- the most complex representatives of protozoa, there are more than 7 thousand species. One of the most famous representatives - ciliate-slipper. This is a fairly large single-celled animal that lives in fresh water bodies. Its body is shaped like the footprint of a shoe and is covered with a dense shell with cilia, the synchronous movement of which ensures the movement of the ciliate. It has a cellular mouth surrounded by cilia. With their help, the ciliate creates a current of water, with which bacteria and other small organisms on which it feeds enter the “mouth”. A digestive vacuole is formed in the body of the ciliate, which can move throughout the cell. Undigested food remains are thrown out through a special place - powder. Ciliates have two nuclei - large and small. The small nucleus takes part in the sexual process, and the large one controls protein synthesis and cell growth. The slipper reproduces both sexually and asexually. Asexual reproduction after several generations is replaced by sexual reproduction. Next (§ 58-65) multicellular organisms of the Animal Kingdom are considered.

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§ 56. Seed plants§ 58. Animal Kingdom. Multicellular organisms: sponges and coelenterates

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 (lower 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. 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 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 through the entire surface of the body: oxygen dissolved in water directly penetrates into its body through diffusion, and carbon dioxide formed in the cell during respiration is released outside.

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 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 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 a 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.

The slipper ciliate belongs to the phylum of Ciliates, which belongs to Protozoa (single-celled eukaryotes). Often several similar species are called slipper ciliates. Characteristic features of all ciliates are the presence of cilia (which are organs of movement) and the more complex structure of their cell-organism compared to other protozoa (for example, amoebas and euglena).

The slipper ciliate lives in freshwater, usually polluted, reservoirs. Cell sizes range from 0.2 to 0.6 mm. The body shape is similar to the sole of a shoe. In this case, the front end with which the ciliate swims forward is the “heel of the shoe”; and the "toe" is the back end.

The body of the slipper ciliate is surrounded by cilia. In drawings and diagrams, cilia are shown only around the cell. In fact, they run in kind of cords throughout the body (i.e., also above and below, which we do not see in the flat picture).

The cell moves thanks to the wave-like contractions of the cilia (each next one in the row bends a little later than the previous one). In this case, each eyelash moves sharply in one direction, after which it slowly returns to its place. The speed of movement of ciliates is about 2 mm per second.

The cilia are attached to basal bodies. Moreover, half of them do not have eyelashes. Basal bodies with and without cilia alternate.

The outer part of the cytoplasm (under the cell membrane) has structures that allow the slipper ciliate to maintain its shape. This part of the cytoplasm is called cytoskeleton.

The membrane has trichocysts, which are sticks that are thrown out and “sting” predators attacking ciliates-slippers.

The ciliate slipper cell has a fairly deep depression (as if the membrane is concave into the cell). This formation is called cell mouth, turning into cell pharynx. They are surrounded by longer and thicker cilia that force food into them. Most often, bacteria and single-celled algae serve as food. Ciliates are found by the substances they secrete.

Separated from the cell pharynx digestive vacuoles. Each such vacuole, after its formation, first passes to the back of the cell, then moves to the front, and then again to the back. This movement is ensured by the constant movement of the cytoplasm. Lysosomes and various enzymes approach the digestive vacuole; nutrients in the vacuoles are broken down and enter the cytoplasm. When the digestive vacuole goes around the circle and returns to the back of the cell, its contents will be thrown out through powder.

The ciliate has two slippers contractile vacuoles. One is in the front of the cage, the other is in the back. These vacuoles are more complex than those of Euglena. It consists of a central reservoir and tubules extending from it. Excess water and harmful substances first end up in the tubules, after which they go into the reservoirs. The filled reservoirs are separated from the tubules and, through the surface of the cell, contracting, the solution is released. The vacuoles contract alternately.

The slipper ciliate breathes oxygen dissolved in water. However, with a lack of oxygen, it can switch to oxygen-free breathing.

Slipper ciliates reproduce by dividing cells in two. Unlike Euglena green, the parent cell is divided not along, but across (that is, one daughter cell receives the back part of the parent cell, and the other the front, after which they complete the missing parts).

In addition to the asexual method of reproduction, ciliates have a sexual process. With it, there is no increase in the number of individuals, but an exchange of genetic information occurs.

The slipper ciliate has two nuclei - large (macronucleus) and small (micronucleus). The macronucleus is polyploid (it contains several sets of chromosomes). Micronucleus is diploden. The macronucleus is responsible for controlling the life of the cell. On the DNA contained in it, RNA is synthesized, which is responsible for the synthesis of proteins. The micronucleus is responsible for the sexual process.

During the sexual process, two ciliates-slippers approach each other from the side of the cell mouths. A cytoplasmic bridge is formed between cells. At this time, the macronucleus in each cell dissolves, and the micronucleus divides by meiosis. The result is four haploid nuclei. Three of them dissolve, and the rest is divided by mitosis. The result is two haploid nuclei. One of them remains in its cell, and the other goes along the cytoplasmic bridge to another ciliate. One of its haploid nuclei moves from the second ciliate. Next, two nuclei (one our own and one foreign) merge in each cell. The already formed diploid nucleus (micronucleus) then divides to form a macronucleus.

The class of Ciliates includes about 6 thousand species. These animals are the most highly organized among the protozoa.

Let's get acquainted with the morphological and biological features of the structure of ciliates using the example of a typical representative - the slipper ciliate.

The structure of the ciliate slipper

External and internal structure of the ciliate slipper

The slipper ciliate has a size of about 0.1-0.3 mm. The body shape resembles a shoe, which is why it got its name.

This animal has a constant body shape, since the ectoplasm is compacted on the outside and forms pellicle. The body of ciliates is covered with cilia. There are about 10-15 thousand of them.

A characteristic feature of the structure of ciliates is the presence of two nuclei: large (macronucleus) and small (micronucleus). The small nucleus is associated with the transmission of hereditary information, and the large nucleus is associated with the regulation of vital functions. The slipper ciliate moves with the help of cilia, with the anterior (blunt) end forward and at the same time rotates to the right along the axis of its body. The high speed of movement of the ciliate depends on the paddle-like movement of the cilia.

The ectoplasm of the slipper contains formations called trichocysts. They perform a protective function. When the slipper ciliates are irritated, the trichocysts “shoot” out and turn into thin long threads that infect the predator. After using some trichocysts, new ones develop in their place in the ectoplasm of the protozoan.

Nutrition and excretory organs

The nutritional organelles of the slipper ciliate are: the preoral cavity, the cellular mouth and the cellular pharynx. Bacteria and other particles suspended in water, along with water, are driven by perioral cilia through the mouth into the pharynx and enter the digestive vacuole.


Having filled with food, the vacuole breaks away from the pharynx and is carried away by the current of the cytoplasm. As the vacuole moves, the food in it is digested by digestive enzymes and absorbed into the endoplasm. Then the digestive vacuole approaches the powder and undigested food remains are thrown out. Ciliates stop feeding only during the breeding season.

The organelles of osmoregulation and excretion in the slipper are two contractile, or pulsating, vacuoles with actuator canaliculi.

Thus, ciliates, in comparison with other protozoa, have a more complex structure:

  • Constant body shape;
  • the presence of a cellular mouth;
  • presence of a cellular pharynx;
  • powder;
  • complex nuclear apparatus.

Reproduction of ciliates. Conjugation process

Ciliates reproduce by transverse division, in which nuclear division first occurs. The macronucleus divides amitotically, and the micronucleus divides mitotically.

From time to time they have sexual intercourse, or conjugation. During this, two ciliates come closer and closely attach to each other with their mouth openings. At room temperature in this form they float for about 12 hours. Large nuclei are destroyed and dissolved in the cytoplasm.


As a result of meiotic division, migrating and stationary nuclei are formed from small nuclei. Each of these nuclei contains a haploid set of chromosomes. The migrating nucleus actively moves through the cytoplasmic bridge from one individual to another and merges with its stationary nucleus, that is, the process of fertilization occurs. At this stage, each shoe forms one complex nucleus, or synkaryon, containing a diploid set of chromosomes. Then the ciliates disperse, their normal nuclear apparatus is restored again, and they subsequently multiply intensively by fission.

The process of conjugation contributes to the fact that the hereditary principles of different individuals are combined in one organism. This leads to increased hereditary variability and greater resilience of organisms. In addition, the development of a new nucleus and the destruction of the old one is of great importance in the life of ciliates. This is due to the fact that the basic life processes and protein synthesis in the body of ciliates are controlled by a large nucleus.

With prolonged asexual reproduction in ciliates, the metabolism and rate of division decreases. After conjugation, the level of metabolism and the rate of division are restored.

The importance of ciliates in nature and human life

It has been established that ciliates play a significant role in the cycle of substances in nature. Various species of larger animals (fish fry) feed on ciliates.

They serve as regulators of the number of unicellular algae and bacteria, thereby cleaning water bodies.

Ciliates can serve as indicators of the degree of contamination of surface waters - water supply sources.

Ciliates living in the soil improve its fertility.

Man breeds ciliates in aquariums to feed fish and their fry.

In a number of countries, human and animal diseases caused by ciliates are widespread. Particularly dangerous is the ciliate balantidium, which lives in the intestines of pigs and is transmitted to humans from the animal.

There are many types of ciliates. Most of them live in water, mostly in stagnant water. The most common ciliate in fresh water bodies is the slipper. She lives in a wide variety of bodies of water.

The structure of the ciliate slipper is slightly different from the amoeba Proteus and Euglena green. For example, due to the presence of a shell, the ciliate does not form pseudopods.

The ciliate slipper is larger than amoeba and euglena. The length of its body reaches 0.3 – 0.5 mm. If you look against the light into a glass vessel with water in which the shoes are floating, you can see them with the naked eye in the form of tiny white specks. They move so quickly that it can be difficult to see them even with a microscope at low magnification. The shoes move so quickly because their body is covered with many thin protoplasmic formations - cilia. The cilia oscillate and scoop water, like oars. With the help of cilia, the ciliates (slippers located around the mouth) also feed; they move in one direction, pushing food.

When studying the structure of the ciliate slipper, it is clear that its body is covered with a thin shell, so it has a more or less constant shape. Due to the presence of the ciliate shell, the shoe does not form pseudopods. The body of the slipper ciliate consists of protoplasm, which contains two nuclei: large and small.

Like other invertebrate animals, the ciliate slipper has the ability to respond to external irritations. If you place shoes in a drop of water on a glass slide and brightly illuminate one side, you will notice that they quickly gather on the illuminated part of the glass, while common amoebas gather on the darkened part of the glass. You can place two drops of water with shoes next to each other on a glass slide, and then use a glass rod to make a water bridge between the drops. If you add a crystal of salt to one of them, the shoes will float to the drop where there is no salt.

Slipper ciliates in water gather around food. The ciliate slipper feeds on microscopic organisms. The movement of the shoes is also affected by the temperature of the water. If you place them in a test tube with water, the temperature of which at one end is 30 - 35 °, and at the other - about 15 °, then the shoes will gather in the most favorable temperature zone for them - about 25 - 27 °.

Like amoeba and euglena, slipper ciliates breathe over the entire surface of the body. There are two contractile vacuoles in the body of the slipper ciliate. Harmful substances formed in the protoplasm enter them through the tubules. These vacuoles either expand or contract. By contracting, they free the body of the ciliate slipper from excess water and harmful substances.

Reproduction of the ciliate slipper is carried out like an amoeba, that is, by cell division. Like amoebas, ciliates form cysts under unfavorable conditions.