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Single-celled organisms are considered the most primitive representatives of the animal kingdom. They form an extensive type of protozoa, the diversity of which we will consider today. The Latin name for this phylum is Protozoa. Because single-celled organisms are difficult to divide into animals (Protozoa) and plants (Protophyta), they are often grouped together as the Protista group. The variety of protozoa is amazing. There are more than 30,000 species, and most of them are invisible to the naked eye because they are no larger than the tip of a needle. Let's try to briefly characterize the whole variety of protozoa.

Brief characteristics of protozoa

Flagellates

Sarcodaceae

Sarcodidae is another group that includes a large number of species. All this diversity of protozoa is difficult to characterize, so let’s say a few words about the most famous. Since school, we are all familiar with such a representative of Sarcodidae as the free-living one (pictured below). Amoeba is a single-celled animal belonging to a broad phylum of protozoa that thrive wherever there is sufficient moisture.

Rays, sunflowers and sporophores

Ciliate slipper

Paramecium (slipper ciliate) is a specialized single-celled animal. It is certainly worth telling about it, characterizing the diversity of aquatic protozoa. The outer layer of the cell's contents - ectoplasm - is limited by a dense membrane bearing many tiny cilia. Their rhythmic, coordinated beats allow the animal to move. The peristome leads into a blind outgrowth - the pharynx, surrounded by granular endoplasm. Food particles enter the pharynx through the movements of cilia and then enter the vacuole. The contents of digestive vacuoles moving in the endoplasm are digested by enzymes. Undigested residues are thrown out through the powder. Water balance is maintained through the activity of two pulsating vacuoles. Of the two nuclei, the larger one (macronucleus) is associated with metabolism in the cell, and the smaller one (micronucleus) is involved in the sexual process.

Plasmodium vivax

During asexual reproduction, protozoa divide in half, forming two individuals. This division of fully formed cells captures both the protoplasm and the nucleus. As a result, two identical daughter cells are formed. Under unfavorable conditions, some flagellates and sarcodeids secrete a dense, impenetrable protective shell (cyst), inside which the cell can divide. When exposed to favorable conditions, the cyst is destroyed, and individuals appear that reproduce asexually.

Protozoan nutrition

Like other animals, protozoa obtain energy by feeding on complex organic compounds. Amoeba sp. It captures food particles with pseudopodia, and they are digested in digestive vacuoles with the participation of enzymes. Paramecium sp. lives mainly at the expense of bacteria, driving them into the cirrus with the movements of the cilia. Trichonympha sp. lives in the intestines of termites and feeds there on substances that are not absorbed by the host. Acineta sp. (pictured below) use only certain types of ciliates for food, which are sometimes larger than themselves.

Movement

Protozoa move in three main ways. Sarcodidae “crawl” by forming protoplasmic outgrowths. The movement is created due to the direction of the endoplasm current in one direction and its reversible transformation at the periphery into gelatinous ectoplasm. Thanks to the sharp blows of the flagellum, the flagellates move. Ciliates move using many tiny, oscillating cilia.

Bacteria and viruses

The general characteristics and diversity of protozoa should be supplemented a short story which are often confused with them. They cause a lot of trouble for humans, but they play their own special role in nature. Bacteria and viruses are the smallest organisms on the planet. Although these are relatively simply organized creatures, they cannot be called primitive. They are able to survive in very unfavorable conditions, and their great ability to adapt to changed conditions puts them on a par with the most advanced and successful forms. Viruses are not cells, so they cannot be classified as single-celled, but bacteria can be considered as such. However, they are not protozoans because they do not have a nucleus. Let's tell you more about them.

Where do bacteria live?

Unlike viruses, bacteria are cells. However, they are much simpler in structure than the cells of highly organized creatures, and vary greatly in size and shape. Bacteria are found everywhere. They can live even under conditions that exclude the existence of more complex organisms. They are found in the ocean even at a depth of 9 km. If conditions worsen external environment bacteria form a stable resting stage - an endospore. This is the most resistant known living organism: some endospores do not die even when boiled.

Of all the possible habitats, the riskiest is another organism. Bacteria usually enter it through wounds. But once inside, they must resist the defenses of their victim, especially phagocytes (cells that can capture and digest them) and antibodies that can neutralize their harmful effects. Therefore, some bacteria are surrounded on the outside by a mucous membrane that is invulnerable to phagocytes; others, after being captured by phagocytes, can live in them; finally, still others produce masking substances that help them hide their presence in the affected cells, and the latter do not produce antibodies.

Harmful and beneficial bacteria

Bacteria can cause harm in three ways: for example, by blocking various vital important channels in the body due to its abundance; release of toxic substances (the toxin of the soil bacterium Clostridium tetani (pictured below), which causes tetanus, is one of the most powerful poisons known to science); as well as stimulation allergic reactions at the victims.

For some time, antibiotics were effective against microbial infections, but many bacteria have developed resistance to a number of drugs. They reproduce quickly, dividing every 10 minutes in favorable conditions. At the same time, naturally, the chances of the emergence of mutants resistant to certain antibiotics increase. But not all bacteria living in other organisms are harmful. So, in gastrointestinal tract cows, sheep or goats have a special section - the rumen, which contains many bacteria that help animals digest plant fiber.

Mycoplasmas

Mycoplasmas, the smallest of all cellular organisms and possibly a transitional stage between viruses and bacteria, occur naturally in wastewater, but can also affect animals, causing them diseases such as, for example, some forms of arthritis in pigs.

The importance of bacteria

Thanks to these organisms, corpses decompose and the organic substances they contain are returned to the soil. Without this constant circulation of organic building blocks, life could not exist. Man widely uses the activity of bacteria to convert organic waste and raw materials into healthy foods when composting, making cheese, butter, vinegar.

Finally

As you can see, the diversity and importance of protozoa is great. Despite the fact that their sizes are very small, they play important role in maintaining life on our planet. Of course, we have only briefly described the diversity of the simplest animals. We hope you have a desire to get to know them better. The systematics and diversity of protozoa is an interesting and extensive topic.

Who are the protozoa?

Protozoa, or eukaryotes, are microscopic organisms with a cellular type of organization; previously they represented a whole kingdom of living organisms; now in biology they are classified as animal-like protists. Despite the fact that the body of protozoa is represented by one cell, they are independent organisms with all basic functions.

The bulk of eukaryotes are microscopic in size. It is not for nothing that the study of protozoa began around the same time when the microscope was invented in the world, namely at the beginning of the 17th century. The Dutch naturalist Anton Leeuwenhoek is considered the discoverer of the whole kingdom of living nature; in 1675, while examining a drop of water through his microscope, he discovered a number of organisms unknown to science at that time, including representatives of single-celled animals. The very concept of protozoa was finally formulated only in the second half of the 19th century, thanks to the work of German natural scientists Albert Kölliker and Karl Theodor Siebold.

Basic characteristics and structure of protozoa

The dimensions of the protozoa reach a length of 10-50 micrometers and are clearly visible only with an optical microscope, since they are indistinguishable to the naked human eye.

The main habitats of unicellular organisms are aquatic and soil; organisms occupy different positions or trophic levels food chains. Reproduction is both sexual and asexual (dividing the eukaryotic body into two parts).

Based on the type of nutrition, protozoa are divided into:

• predators, they feed on algae, microscopic fungi and single-celled organisms;
• those that consume food by endocytosis, for example, amoeba, when ingestion is carried out by the entire cell of the microorganism;
• those who absorb food using a cellular mouth - cytosts;
• those who have an osmotrophic type of nutrition, that is, nutrition is provided without ingesting solid food particles due to transportation nutrients through the cell surface.

If we talk about the physiological structure of unicellular organisms, then they all have two main components:

The cytoplasm of unicellular organisms is usually represented by 2 layers:

1. ectoplasm - external;
2. endoplasm - internal.

The cell cytoplasm is characterized by the presence of the following cellular organelles:

1. ribosomes - responsible for the synthesis of protein and amino acids according to the genetic information in the nucleus;
2. endoplasmic reticulum - responsible for the transport of proteins and lipids;
3. mitochondria - responsible for the oxidation of organic substances and the further use of the energy released from them;
4. Golgi apparatus - participates in the formation of three protein streams in the protozoan cell.

Classification of protozoa

Until the beginning of the 20th century, science considered protozoa as a whole sub-kingdom of the animal kingdom and their study was carried out by protozoology - a branch of zoology that deals with the study of single-celled animals. Now the simplest ones along with algae, fungi and fungus-like groups of living organisms belong to the kingdom of protists, mainly animal-like.

The modern classification of the animal world does not give a separate rank and significance to single-celled organisms.

Classification - Subkingdom Unicellular (Protozoa)

• Type Sarcomastigophora
• Type Apicomplexa
• Phylum Myxosporidium (Myxozoa)
• Type Microsporidia (Microspora)
• Type of Ciliates (Ciliophora)
• Type Labyrinthula (Labirinthomorpha)
• Type Ascetosporidia

Examples of simple organisms

The phylum protozoa includes approximately 25 thousand species of single-celled animals that live in water, soil or the organisms of other animals and humans. Having morphological similarities in the structure of cells with multicellular organisms, protozoa differ significantly from them in functional terms.

If the cells of a multicellular animal perform special functions, then the cell of a protozoan is an independent organism, capable of metabolism, irritability, movement and reproduction.

Protozoa are organisms cellular level organizations. Morphologically, a protozoan is equivalent to a cell, but physiologically it is a whole independent organism. The vast majority of them are microscopically small in size (from 2 to 150 microns). However, some of the living protozoa reach 1 cm, and the shells of a number of fossil rhizomes have a diameter of up to 5-6 cm. The total number known species exceeds 25 thousand

The structure of protozoa is extremely diverse, but they all have features characteristic of the organization and function of the cell. What is common in the structure of protozoa are the two main components of the body - the cytoplasm and the nucleus.

Cytaplasm

The cytoplasm is bounded by an outer membrane, which regulates the flow of substances into the cell. In many protozoa it is complicated by additional structures that increase the thickness and mechanical strength outer layer. Thus, formations such as pellicles and membranes arise.

The cytoplasm of protozoa is usually divided into 2 layers - the outer one is lighter and denser - ectoplasm and internal, equipped with numerous inclusions, - endoplasm.

General cellular organelles are localized in the cytoplasm. In addition, a variety of special organelles may be present in the cytoplasm of many protozoa. Various fibrillar formations are especially widespread - supporting and contractile fibers, contractile vacuoles, digestive vacuoles, etc.

Core

Protozoa have a typical cell nucleus, one or more. The nucleus of protozoa has a typical two-layer nuclear envelope. Chromatin material and nucleoli are distributed in the nucleus. The nuclei of protozoa are characterized by exceptional morphological diversity in size, number of nucleoli, amount of nuclear juice, etc.

Features of the life activity of protozoa

Unlike somatic cells, multicellular protozoa are characterized by the presence life cycle. It consists of a number of successive stages, which are repeated with a certain pattern in the existence of each species.

Most often, the cycle begins with the zygote stage, corresponding to the fertilized egg of multicellular organisms. This stage is followed by single or multiple repeated asexual reproduction, carried out by cell division. Then sex cells (gametes) are formed, the pairwise fusion of which again produces a zygote.

Important biological feature of many protozoa is the ability to encystment. In this case, the animals become rounded, shed or retract the organelles of movement, secrete a dense shell on their surface and fall into a state of rest. In the encysted state, protozoa can tolerate dramatic changes environment, maintaining viability. When conditions favorable for life return, the cysts open and the protozoa emerge from them in the form of active, mobile individuals.

Based on the structure of organelles of movement and characteristics of reproduction, the type of protozoa is divided into 6 classes. The main 4 classes: Sarcodaceae, Flagellates, Sporozoans and Ciliates.

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 have and 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 is removed and liquid products exchange. 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 exoskeleton- sink. 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 on seabed sediments - 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. Except 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 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, gametes are carried into the bloodstream. digestive tract, where sexual reproduction and sporozoite formation 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) we consider multicellular organisms Animal kingdoms.

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

Type of Sarcomastigophora

Sarcodina. Animals with inconsistent body shape.

The body is naked and may have an external shell or an internal skeleton.

Locomotion using pseudopodia of various shapes.

Reproduction is asexual, and in some cases sexual. These include amoebas, testate

amoebas, foraminifera, rayfish and sunfish.

Amoebas (Amoebina)- inhabitants of the soil, fresh water bodies, few

plasmalemma. Monoenergetic and polyenergetic. Organoids of movement

Lobopodia. Heterotrophs. Reproduction is asexual (monotomy), in amoeba

Amoeba marina asexual reproduction is a parasexual process.

Testate amoebas (Testacea)- inhabitants of fresh water bodies, soil,

mosses in swamps. The body is enclosed in a shell various shapes. Sink

single-chambered from organic matter, in some formed

grains of sand are included in silica or in an organic base. Type14

pseudopodia - lobopodia and filopodia. Heterotrophs. Reproduction

asexual - monotomy.

Foraminifera- inhabitants of the seas, inhabit the bottom (benthic forms), a few - the water column (planktonic). The body is placed in an organic shell (usually multi-chambered) impregnated with calcium carbonate. The walls of the shell are permeated with pores through which rhizopodia emerge. Foraminifera are heterotrophs. Reproduction is the alternation of sexual and asexual processes (metagenesis).

(Volvox, for example) consists of many thousands of cells forming a hollow ball. The cells are interconnected by cytoplasmic bridges and differentiated into somatic (vegetative) and generative (parthenogonidia and gametogonidia), differing in structure. Animal sizes and body shapes vary.

The organelles of movement are

flagella (1, 2 or many). In some animals the base of the flagellum

continues beyond the kinetosome, a root thread (rhizoplast) is formed,

which is either attached to the core shell or lies free. Part

flagellates have a parabasal body of various shapes, which

located near the flagellum. This organelle is homologous to the apparatus

Golgi. A kinetoplast may be located next to the kinetosome, it

corresponds to mitochondria, contains a significant amount of DNA.

The integument is a membrane (in a few), pellicle or carapace. Availability

pellicles determine the constancy of the body shape.

Flagellates

monoenergetic and polyenergetic animals. In plant

Flagellates have a sensitive eye - stigma. By food type

Autotrophs (Volvox), mixotrophs (Euglena) and heterotrophs. Maybe

presence of a cellular mouth or animals for catching prey

use a section of sticky cytoplasm. Undigested leftovers

are excreted at the posterior end of the body. Contractile vacuole of different structure.

Flagellates characterized by asexual and sexual reproduction.

Asexual reproduction in the form of monotomy and palintomy. Sexual

reproduction - copulation. Consider the reproduction of euglena,

trypanosomes, volvox, opalina.

Euglena reproduces only asexually, by

longitudinal division of an animal in two. First the nucleus divides, then

starting from the anterior end of the body, and the entire body of the protozoa. The flagellum extends to

one of the daughter individuals or both daughter individuals is formed again. 15

Asexual reproduction can also occur in a cyst, reproduction

palintomy.

Trypanosoma also reproduces asexually by fission

in two or multiple divisions. Part of the life cycle takes place in

the human body, the other part in the body of the tsetse fly. Throughout life

cycle, the animal goes through various stages that differ in structure

(trypanosomal, leptomonas, critidial, leishmanial forms).

Volvox reproduces asexually and sexually. Asexual

reproduction - palintomy. Parthenogonidy cells, 4-10 in number, divide

sequentially on the surface of the mother colony, then moves

inside. The resulting cells are initially arranged in the form of a plate,

then they take a cup-shaped shape and later a spherical shape. Exit

daughter colonies from the mother colony are accompanied by rupture of the walls

the last one and her death. Volvox colonies are dioecious and

hermaphroditic. Sex cells are formed from gametogonia. Their

not much: 5-10 male and 25-30 female cells. Microgonidia

divide repeatedly, forming microgametes and macrogonidia

increase in volume, macrogametes are formed. Sexual process

oogamous.

Opalins- polynucleate animals with many flagella. They

reproduce asexually (division in two) and sexually

(copulation). Reproduction is associated with a change of hosts, asexual

reproduction leads to the formation of cysts. The most studied life

Opalina ranarum cycle. Cysts containing 3-12 nuclei are excreted from

frogs during the period of laying eggs. Tadpoles ingest cysts in the body

tadpoles undergo gametogony (formation of gametes) and anisogamy

copulation. The zygote encysts and enters the water. Oocyst, ingested

tadpole, develops either into a trophic form, or is formed

new generation of gametes.

Ciliates(Ciliophora)

humans and animals. All ciliates are characterized by nuclear dualism.

Ciliates heterotrophs. Divided into two classes: ciliary

(Ciliata) and sucking (Suctoria) ciliates.

For ciliated ciliates

characteristic:

 Body shape is varied. More often animals are longitudinally

oval, inhabitants of sand in the form of long thin ribbons, species in

shaped like a bell, trumpet, etc. Ciliated ciliates

freely mobile or attached to the substrate by a stalk.

 The ciliary apparatus (ciliatum) is represented by kinetes, cirri, membranellae and membranes. Many ciliates have immobile tactile cilia.

 The ectoplasm contains myonemes and extrusomes - trichocysts.

mouth opening. The structure of the oral apparatus is associated with the character

food. Digestive vacuoles move around the animal's body (cyclosis

vacuoles). Defecation is performed through the cytoproct.

 The endoplasm contains nuclei. In the simplest case, the slipper ciliate) has one micronucleus and one macronucleus. Other representatives have several micro- and macronuclei.

 The structure of contractile vacuoles and their number varies, they occupy a fixed position in the cell, and open with a vacuoloid pore.

Asexual reproduction - transverse division of the animal (monotomy) or palintomy in a cyst. Sexual reproduction- conjugation. A temporary union of two individuals occurs, resorption of macronuclei in each animal occurs, micronuclei divide twice (meiosis), three nuclei are destroyed, the fourth divides (mitosis). Newly formed nuclei - pronuclei

(stationary and migrating). An exchange of migrating nuclei occurs. The pronuclei fuse to form a synkaryon. Individuals are separated from each other. Conjugants reconstruct the nuclear apparatus. Ciliates

Autogamy is also characteristic - a process in which conjugation occurs in one individual.

Sucking ciliates lead an attached lifestyle. Adults lack cilia. They are characterized by both non-branching and branching tentacles. The tentacles are used to catch prey: the prey sticks to the tentacle, the prey pellicle dissolves and the contents of the victim flow inside through a channel located in the tentacle

ciliates. These ciliates are also characterized by nuclear dualism. Reproduction is asexual - budding (vagrants with cilia are formed) and sexual - conjugation.

Sporozoa

Sporozoans are represented by gregarines and coccidia. All

or the animal becomes infected with the help of animal carriers,

are called transmission. There are three groups of transmissible

diseases: anthroponoses, anthropozoonoses, zoonoses. In the life cycle

distinguish endogenous and exogenous parts.

The intestine is divided into sections (2 or 3): epimerite, protomerite and deuterite with one core. The body of animals inhabiting cavities, gonads, is spherical or worm-shaped. Nutrition is saprophytic. Paraglycogen is deposited in the endoplasm. Reproduction - alternation of gametogony and sporogony, some also have asexual reproduction