The organisms that we call protozoa are one of the links that play an important role in ecology and represent a special level of organization of living matter.
Most protozoa are cosmopolitan and have a wide geographical distribution.
These are tiny organisms, invisible to the naked eye, leading both a free lifestyle and living in other organisms.
The vegetative forms of some protozoa are a bare lump of protoplasm, with a constantly changing shape (rhizopods), others have a shell that maintains a more or less constant shape of their body (flagellates, ciliates). Some move with the help of pseudopodia (amoeba), others have special organs of movement - flagella, cilia (flagellates, ciliates).
They are eukaryotes. The protozoan cell, like all eukaryotes, consists of a nucleus, protoplasm and a membrane or membrane. The shells of many protozoa become compacted, a pellicle is formed, giving them a certain shape and enhancing the body’s protection from mechanical damage. In many free-living protozoan species, the cell is enclosed in a shell formed by it.
Protoplasm is a complex colloidal system and connects all parts of the cell with each other.
Protoplasm is divided into a surface layer - ectoplasm, which is denser, homogeneous, and an inner layer - endoplasm, which is more liquid and granular.
The protoplasm of the cell contains organelles: lysosomes (providing the decomposition of organic substances), ribosomes (participating in protein synthesis), endoplasmic reticulum (carbohydrates and fats are synthesized on the walls of its channels, and the channels themselves serve to transport substances), mitochondria (in which energy is stored necessary for metabolic processes), the Golgi apparatus (providing the release of metabolites to the outside). Near the nucleus is the nuclear center.
In addition to organelles, protoplasm contains various inclusions: reserve nutrients in the form of fat, glycogen, volutin, absorbed food, etc.
Organelles are permanent components of the cell; the number and composition of inclusions can vary.
One of the distinguishing features of protozoa is the structure of the nucleus.
Protozoa are characterized by irritability resulting from the action of chemical, physical, light, and mechanical factors. Directed movements under the influence of these stimuli are called taxis. Taxis can be positive or negative and vary depending on environmental conditions.
Most protozoa can move slowly or quickly due to pseudopodia, flagella, cilia, due to contractions of special myoneme fibers, or due to the secretion of fluid from the back of the body.
In protozoa leading a sedentary lifestyle, flagella and cilia contract, and due to their movement, a current of water is created, bringing them food.
The feeding mechanism is different in different types of protozoa.
Each protozoan has all the basic vital functions - metabolism with assimilation and dissimilation.
Based on their feeding method, protozoa are divided into three groups:
1. Autotrophic organisms. They synthesize organic substances from carbon dioxide and water using chlorophyll. The source of energy is sunlight.
2. Heterotrophic organisms. They do not have chlorophyll. They feed on organic matter created by plants or animals.
3. Mixotrophic organisms. They feed as autotrophs and heterotrophs (due to inorganic and organic substances).
Reproduction in protozoa occurs sexually and asexually.
Protozoa have certain life cycles. Many protozoa are characterized by prolonged asexual reproduction, followed by a sexual process, after which a period of asexual reproduction begins again.
One of the stages of the life cycles of protozoa is often a state of rest (cyst formation). In the cyst stage, protozoa can tolerate various unfavorable environmental conditions.
A cyst for a protozoan is a form of preservation of the species in unfavorable conditions. Protozoa are an important component of geological rocks, fresh and sea waters, and soils. They participate in the processes of circulation of substances in nature, in the formation of trophic connections.
Protozoa are tiny organisms, invisible to the naked eye, leading both a free lifestyle and living in other organisms.
The overwhelming majority are unicellular organisms, but representatives of some species have multicellular stages in their development cycle, and a small number of protozoan species lead a colonial lifestyle. However, such multicellular protozoa cannot be considered true multicellular, since these organisms do not have division of functions between cells.
Each protozoan is a complete organism that performs all the functions characteristic of living beings.
About the simplest organism we can say that in morphological terms it is a cell, and in functional terms it is an organism.
Protozoa live wherever there is a humid environment (in seas, rivers, lakes, puddles, swamps, in damp soil, etc.). They can be found even in small accumulations of water, for example in the axils of leaves, in moss, and in the water film that surrounds soil particles. In fresh water bodies and sea water there are bottom-dwelling (benthic) and free-floating (planktic) species of protozoa.
In standing water, protozoa are found more often and in greater numbers than in running water.
Most protozoa are cosmopolitan and have a wide geographic distribution.
Despite their cosmopolitanism, protozoa are very sensitive to various environmental factors.
The species composition of protozoa, their morphological structure, metabolic and energy processes that ensure the life activity of protozoa are significantly negatively affected by chemical, thermal, radiation, and anthropogenic pollution of both natural waters and waters of artificial reservoirs.
Mass destruction of forests, drainage of swamps, formation of cascades in lakes, ponds and reservoirs, violation of parameters when creating artificial reservoirs, disruption of gas exchange in reservoirs, pollution of reservoirs with industrial waste, construction of hydroelectric power stations, chemical control of weeds and plant pests, violation of agricultural practices and many other reasons negatively affect protozoa.
The practical significance of protozoa is very great.
Protozoa feed intensively and actively reproduce, and as a result, they have a huge impact on the cycle of substances in nature. Being inhabitants of the aquatic environment, they absorb small quantities of substances from the water and concentrate them in their bodies. After the death of the protozoa, these substances accumulate at the bottom of the reservoir, which in turn contributes to the formation of geological deposits of useful elements and compounds. Many Cretaceous deposits were formed from the shells of pseudopod protozoans.
However, we should not forget that the mass reproduction of protozoa in water bodies can also lead to negative consequences - a sharp decrease in the amount of oxygen, and this in turn contributes to the mass death of fish, increased putrefactive processes, etc.
Protozoa can be indicators of the biological characteristics of soil water. The purity of water and its suitability for drinking mainly depends on the content of organic compounds in it. The species composition of protozoa in soil or a reservoir can characterize certain features of the soil and reservoir. This is explained by the fact that various protozoa are adapted to life in water or soil with a certain content of these substances and therefore they can be indicators of the degree of saturation of water or soil with these substances.
For example, in heavily polluted and rotting water they live Euglena viridans, Colpidium colpeda, Paramaecium putrinum, Vorticella microstoma.
Representatives of the genera live in water in which the breakdown of organic substances with energetic oxidation occurs Cryptomonas, Chlamydomonas, Spirostomum, Actinoprys, Actinosphaerium, Paramaecium.
In water with a low content of organic matter and a large amount of mineral compounds, representatives of the genera predominate Volvox, Gonium, Eudorina, Lacrymaria, Amoeba.
Many protozoa are producers of biologically active substances that play a certain role in the metabolic processes of other organisms. For example, protozoa that live in the rumen of ruminants, producing the enzyme cellulase, contribute to the decomposition of fiber. Protozoa are active producers of not only enzymes, but also substances such as histones, serotonin, lipopolysaccharides, lipopolypeptidoglucans, amino acids, metabolites used in medicine and veterinary medicine, food and textile industries.
Protozoa are one of the objects used in biotechnology.
Thus, the causative agent of South American trypanosomiasis Trypanosoma cruzi is a producer of the antitumor drug crucin and its analogue, trypanose. These drugs have a cytotoxic effect on malignant cells. Producers of anti-blastoma inhibitors are also Trypanosoma lewisi, Crithidia oncopelti, Astasia longa.
The drug astaliside, produced Astasia longa, has not only an anti-blastoma effect, but also antibacterial (in relation to E.coli and Ps.aeruginosa), and antiprotozoal (against Leiscmania).
Protozoa are used to produce polyunsaturated fatty acids, polysaccharides, histones, serotonin, enzymes, glucans for medical purposes, as well as in the food and textile industries.
Herpetomonas sp. And Crithidia fasciculate are used to obtain polysaccharides that protect animals from Trypanosoma cruzi.
Since protozoan biomass contains up to 50% protein, free-living protozoa are used as a source of feed protein for animals.
Among protozoa there are many species that cause severe and sometimes fatal diseases in humans, domestic and wild animals, birds, fish, and plants.
Diseases caused by pathogenic protozoa are called protozoans, in contrast to infectious diseases, the causative agents of which are bacteria, spirochetes, viruses, mycoplasmas, rickettsia, and chlamydia.
It should be remembered that protozoa can damage almost any organ of the human or animal body (liver and spleen, genitourinary system, skin, bone and brain, etc.).
Vegetative individuals – trophozoites – actively feed and reproduce.
In the body of humans, monkeys, dogs, horses, cattle, pigs and other animals, amoebas are found in three stages: in the stage of an actively motile form called trophozoites, in the precyst stage - slightly mobile, and in the cyst stage - immobile.
A distinctive feature of representatives of flagellates ( Flagelata) is the presence of organs of movement - flagella, which are complex outgrowths of the outer layer of ectoplasm. They have a dense shell. Divided longitudinally. In some, the sexual division process alternates with asexual division.
Among flagellates there are autotrophs, heterotrophs and mixotrophs. They live in fresh and salt waters. They can cause water blooms during mass reproduction.
Giardia cysts can enter the body of humans and animals along with water and food products ( Lamblia intestinalis). In the vegetative form, Giardia lives in the small intestines, duodenum, and gall bladder, attaching to epithelial cells using a suction disk. They feed on the products of hydrolysis of nutrients extracted from the host cells. Giardia's allies in the host's body are imperfect fungi and gram-positive bacteria. In the colon they turn back into a cyst.
Pathogenic flagellates include trypanosomes ( Trypanosoma cruzi, Tr.gambiense, Tr.rhodesiense), causing African and American trypanosomiasis. They live in the blood and lymph nodes. They have a fusiform shape, a flagellum and an undulating membrane. Tissue forms - amastigotes develop in the heart muscle, liver, and brain. Reservoir Tr.gambiense is a person Tr.rhodesiense– antelopes, Tr.cruzi – rats, armadillos. Carriers: Tse-tse fly, triatomine bugs.
The flagellates also include giardia ( Giardia). They are characterized by the fact that they have a double set of all organelles (they have two nuclei, two sets of flagella, and some have two cystomes). They are obligate inhabitants of amphibians.
Ciliates ( Ciliata), representing an independent group of protozoa. These are the most complex protozoa.
Ciliates have organs of movement - cilia, which either evenly cover the entire body or are grouped in individual areas.
Based on the number and location of cilia, there are round-ciliated, uniformly ciliated, and spiral-ciliated ciliates.
Many ciliates have special organs of attack and defense - rod-shaped trichocysts. They are located in the outer layer of the cytoplasm. Under the influence of mechanical or chemical irritation, trichocysts turn into long threads that are thrown out and penetrate the cells of other organisms.
Ciliates reproduce asexually and sexually.
Among the ciliates, there are subclasses ciliated ( Euciliata) and sucking ( Suctoria).
Sucking ciliates ( Suctoria) are mainly predators. They lead an attached lifestyle, settling on various substrates, including the body surface of many invertebrates.
The vast majority of sporozoans have adapted to living inside the cytoplasm (less often inside the nucleus) of various host cells.
They live in the digestive tract, body cavity, circulatory system and other organs of their hosts.
Many of these protozoa emerge from the host in stages surrounded by thick membranes, often called spores. That's why they got the name Sporozoa.
The most characteristic feature of sporozoans is the presence of complex cycles associated with changes in hosts, forms of reproduction (sexual and asexual), and habitat.
The size of sporozoans living in tissue cells or blood cells is very small (measured in micrometers). Sporozoans that live in blood cells are smaller in size than those that live in the intestinal cavity or body.
Sporozoans include coccidia, plasmodia, toxoplasma, hemosporidium, piroplasma, sarcosporidia, gregarines, myxosporidium, microsporidia.
Infection with coccidia occurs through nutrition. Oocysts enter the body along with water and feed. In the intestine, the oocyst shell is destroyed and the released sporozoites invade the cells of the intestine, liver, and pancreas and turn into trophozoites. Trophozoites transform into schizonts, producing merozoites that infect intact cells.
Blood sporozoans include Plasmodium ( Plasmodium) and piroplasmids ( Piroplasmida).
Plasmodium is transmitted from one organism to another by blood-sucking mosquitoes from the genera Culex, Anopheles, Aedes.
Red blood cells are affected. They hemolyze, anemia develops, and hemorrhages occur. The digestive and nervous systems are affected. Animals become severely emaciated, lose mobility, and develop intestinal atrophy. Animals die.
Toxoplasma ( Toxoplasma) are very widespread in nature and cause the disease toxoplasmosis in humans, domestic and wild birds, cats, dogs, large and small cattle, pigs, rodents and many other species of animals, including cold-blooded animals.
Infection occurs when cysts enter through damaged skin, through the consumption of food and water contaminated with cysts, or in utero through the placenta from a sick mother to the fetus. Toxoplasma can be transmitted by blood-sucking ticks. Flies and cockroaches are mechanical carriers of cysts.
Toxoplasma is excreted in the form of a cyst with milk, urine, saliva, and feces.
Sarcosporidium infections in humans are rare. Infection occurs through nutritional intake of meat contaminated with sarcosporidium spores.
Infection occurs when microsporidia spores equipped with stinging threads are ingested along with food and water.
| Systematic distribution of some protozoan species | ||
|---|---|---|
| Sarcodina | Acanthamoeba | A.astronyxis, A.culberstoni |
| Endolimax | E.nana | |
| Entamoeba | E.histolytica, E.coli, E.suis, E.hartmani, E.gingivali, E.anatis, E.gallinarum, E.haulista, E.dispar, E.dysenteriae, E.ranarum and others | |
| Iodamoeba | I.butshlii | |
| Hydramoeba | H.hydroxena | |
| Naegleria | N.aerebia, N.foleri - syn | |
| Vahlkampfia | V.enterica, V.lacertae | |
| Cnidosporidia s/c Myxosporidia |
Ceratomyxa | C. racemosa, C. coris |
| Chloromyxum | Ch.leydigi, Ch.truttae | |
| Hennegaya | H.oviperda, H.psorospermica | |
| Hoferella | H.cyprini | |
| Myxodium | M.lieberkuhni, M.bergense, M.laticurum | |
| Myxobulus | M.pfefferi, M.neurubius, M.musculi, M.talievi, M.exiguus | |
| Myxosoma | M. ranae, M. cerebralis | |
| Ortholinea | O.divergens | |
| Sphaeromyxa | Sp.cottidarum, Sp.polymorpha | |
| Sphaerospora or Spirrgularis | Sp.cyprini | |
| Telohanellus | T.pyrifotmis | |
| s/c Microsporidia | Glugea | G.anomala |
| Nozema | N.apis, N.bombicis, N.malionis, N.balantidii, N.franzelinae, N.mensinii, N.notabilis | |
| Perezia | P. lankesteriae | |
| Ciliata p/c Suctoria |
Ephelota | E. gemmipara |
| Tachyblaston | T. ephelotensis | |
| s/c Holotrichia | Chilodonella | C.cyprini |
| Foettingeria | F.actinarum | |
| Ichthyophthirius | I.multifiliis | |
| Radiophrya | R.hoplites | |
| s.c. Spirotrichia | Balantidium | B.coli |
| Cycloposthium | C.edenntatum | |
| Diplodinium | D. cameli | |
| Nictotherus | N.cardiformis | |
| Ophryoscolex | O.purkinjei | |
| s/c Peritrichia | Apiosoma | A.doliaris |
| Galiperdia | G.brevipes | |
| Trichodina | T.domerguei, T.urinaria, T.strelcowi, T.urinicola, T.pediculus | |
| Sporosoa s/c Coccidiomorfa |
Aggregata | A.eberthi |
| Eimeria | E.anguillae, E.intestinalis, E.carpelli, E.intricata, E.faurei, E.parva, E.ranarum, E.stidaum, E.sardinae, E.truncata | |
| Haemoproteus | H. columbae | |
| Grellia | G.dinophili | |
| Isospora | I.mesnili, I.ardeae, I.hominis, I.natalensis, I.belli | |
| Karyolysus | K.lacertae | |
| Leucocytozoon | L.simondi | |
| Lankesterella | L.minima | |
| Parahaemjprjteus | P.vilans | |
| Plasmodium | Pl.vivax, Pl.jvale, Pl.malariae, Pl.falciparum, Pl.gallinacem | |
| Sarcocystis | S.fusiformis, S.tenella, S.mischeriana, S.suihominis | |
| Toxoplasma | T. gondii | |
| s/c Piroplasmida | Anthemosoma | A.garnhami |
| Babesia | B.bigemia, B.bovis, B.canis, B.divergens, B.ovis | |
| Nuttflina | N.eque | |
| Theileria | T.parva, T.annulata, T.mutans | |
| p/c Gregarina | Corycella | C. carmata |
| Diplauxis | D.hatti | |
| Enterocystis | E.funcides | |
| Gregarina | G.garnhami, G.fernandoi, G.munieri, G.polymorpha | |
| Lecudina | L.pellucida | |
| Lancesteria | L. barretti, L. clarki | |
| Menospora | M.polycantha | |
| Monocystis | M. pfeiformis | |
| Pielocephalus | P.pellunada, P.blabera | |
| Pyxinoides | P.balani | |
| Rhynchocystis | R.pilosa | |
| Selenidum | S. sabellariae, S. faushaldi | |
| Schizocystis | S.gregarinoides | |
| Schneideria | S.mucronata | |
| Stylocephalus | S.longicolis | |
| Taeniocystis | T.mira | |
| Trichorhynchus | T.pulcher | |
| Mastigophora s/c Phytomastigina |
Euglena | E. viridis |
| Nauplicola | N.ocelli | |
| Parastasia | P.coelomae | |
| p/c Zoomastigina | Blastocrithidia | B.fanuliaris, D.gerridis |
| Ichthyobodo | I.nicator | |
| Giardia | G.agilis | |
| Lamblia | L.intestinalis, L.mocrotis, L.duodenalis, L.oncopelti | |
| Leishmania | L.donovani, L.tropica, L.brasilienis, L.mexicana | |
| Leptomonas | L.oncopelti | |
| Pentatrichomonas | P.hominis | |
| Phytomonas | P.elmassiani | |
| Trypanosoma | T.brucei, T.congolense, T.vivax, T.zapi, T.lewe, T.cruzi, | |
| Trichomonas | T.vaginalis, T.muris, T.batrachorum, T.foetus, T.angusta, T.lacertae, T.gallinae | |
| p/c Opalina | Opalina | O.ranarum |
The main advantage of cultured cells is the possibility of intravital observation of cells using a microscope.
It is important that when working with cell cultures, healthy cells are used in the experiment, and they remain viable throughout the experiment. In experiments on a whole animal, the condition of the kidneys, for example, can be assessed only at the end of the experiment, and moreover, usually only qualitatively.
Cell cultures are a genetically homogeneous population of cells growing under constant conditions. Moreover, the researcher can change these conditions within certain limits, which allows him to assess the influence of a variety of factors on cell growth - pH, temperature, concentration of amino acids, vitamins, etc. Growth can be assessed over a short period of time either by an increase in number or size cells, or by the incorporation of radioactive precursors into cellular DNA.
These real advantages over whole animal studies place cell culture as an experimental system on a par with microbial cultures.
Moreover, when working with cell cultures, significant results can be obtained using very small numbers of cells. Experiments that require the use of 100 rats or 1000 people to clarify a particular issue can be carried out with equal statistical reliability using 100 cultures on coverslips. That. one cell can replace an entire clinic of patients. This is an important advantage when it comes to humans, and, in addition, eliminates many of the ethical problems that arise when it is necessary to use a large group of animals for an experiment.
Since cells in culture are easily accessible for various biochemical manipulations, when working with them, radioactive precursors, poisons, hormones, etc. can be introduced in a given concentration and for a given period. The amount of these compounds can be an order of magnitude less than in experiments on the whole animal. There is also no risk that the test compound is metabolized by the liver, stored in the muscles, or excreted by the kidneys. When using cell cultures, it is usually not difficult to determine that at a certain concentration a substance added to the culture is in contact with the cells for a given period of time. This ensures that real values of the rate of incorporation or metabolism of the compounds under study are obtained.
Cell culture is used in various scientific and practical fields:
Genetics
The ability of cells to grow in culture has led to the development of the following methods:
- Cloning
- Cell storage and fusion
- Obtaining and working with mutant cells.
Hybridoma technology: cells that synthesize antibodies of interest to scientists are fused with myeloma cells that produce antibodies of unknown specificity.
The resulting hybridomas made it possible to establish the production of monoclonal antibodies: a mouse is immunized with a crude antigen preparation and then its spleen cells are hybridized with myeloma cells. Among the resulting hybrid cells, there will be at least one that produces antibodies specific to the original antigen.
Biotechnology
Cell cultures can provide a valuable source of hormones and other secreted materials. Cell cultures are already proving to be important producers of the species-specific antiviral agent interferon.
Virology and cell transformation
Progress in the field of virology is largely due to the ability to grow viruses in cell cultures.
These techniques have revealed that viruses can not only infect and kill cells, but can also cause changes in cell growth patterns, a phenomenon known as viral cell transformation. These changes, which result in cells that do not respond to their neighbors in the same way as non-transformed cells, are of particular interest because they may help to understand the nature of transformation, since similar changes that occur in cells in vitro play a role role in tumor induction.
Since most viral diseases are now treated by administering antiserum, virus culture is important both for the identification of viruses and for their use in vaccine production.
These problems are solved mainly using cell cultures.
Protozoa are unicellular animals whose body consists of one cell. However, they cannot be considered as simply organized forms, because morphologically, a protozoan cell is equivalent to a cell of a multicellular organism. Physiologically, a protozoan cell is an integral organism, which is characterized by all manifestations of life: metabolism, irritability, growth, reproduction, etc. The role of organs in them is performed by organelles.
Protozoa were discovered in 1675 by the Dutch naturalist Antoine van Leeuwenhoek. In the first classification of animals, proposed in 1759 by the Swedish botanist Carl Linnaeus, protozoa were combined into one genus called Chaos, which was part of the phylum worms. Only in 1845 Kölliker and Siebold identified them as an independent type of animal. And only very recently, in 1980, Levine established a separate sub-kingdom for protozoa
There are from 5 to 7 types of protozoa, each type includes several classes. To date, more than 30 thousand species have been described, but there are many more of them.
Origin of unicellular organisms
As is known, the first living beings arose in the primeval oceans and looked like tiny mucous lumps. They had neither nuclei, nor vacuoles, nor other parts of cells, but they could grow, absorbing nutrients from the environment, and multiply. As a result of natural selection, these organisms gradually became more complex. From them came the first single-celled organisms with nuclei. As has been established, at the earliest stages of the evolution of living nature they gave rise to single-celled animals and primitive fungi. Their ancestors were the most ancient single-celled organisms - the simplest flagellates (as many biologists believe).
Conclusions:
1. The first animals to appear on Earth were single-celled animals belonging to the protozoa.
2. Among the protozoa there are not only unicellular forms, but also colonial ones (Volvox).
General characteristics of protozoa
1. Protozoa are unicellular animals whose body consists of one cell. Morphologically, a protozoan cell is equivalent to a cell of a multicellular organism. Physiologically, a protozoan cell is an integral organism, which is characterized by all manifestations of life: metabolism, irritability, growth, reproduction, etc. The role of organs in them is performed by organelles.
2. This is a widespread group of animals in a state of biological progress. During evolution, they acquired numerous adaptations to living conditions in different habitats (sea, fresh water bodies, damp soil, liquid environment of other organisms).
3. The sizes of protozoa are microscopically small. Their body (cell) consists of cytoplasm, in which there is an outer layer - ectoplasm and an inner layer - endoplasm. In most species, the outside of the cell is covered with a membrane, which gives the animal a permanent shape (the exception is sarcodae). In the endoplasm, in addition to the organelles inherent in all cells, there are organelles that perform the functions of digestion, excretion, movement (flagella, cilia), protection (trichocysts in ciliates), and a light-sensitive eye (in free-living flagellates).
4. According to the method of nutrition, these are typical heterotrophic organisms (with the exception of green euglena).
5. Breathe with the entire surface of the body.
7. Reproduction is carried out asexually or sexually.
8. Protozoa, as full-fledged living organisms, react to the influence of the external environment, i.e. have irritability, which manifests itself in various movements (taxis). There are positive taxis (when animals move towards the stimulus) and negative taxis (when they move away from the stimulus).
9. Encystation is an important biological feature of protozoa - this is the ability to form a cyst when exposed to unfavorable conditions. Encystment not only ensures survival of unfavorable conditions, but also contributes to widespread dispersal.
10. This is the most ancient type of animal. The most ancient classes of this type include flagellates and sarcodae, which originated from a primitive, now extinct group of eukaryotic heterotrophic organisms. Ciliates are related in their origin to flagellates. All multicellular animals originated from flagellates (via colonial forms).
The type includes the following classes:
flagellates, sarcodes or rhizomes, ciliates, sporozoans and others.
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 at the cellular level of organization. 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 of 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 of the 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 of a 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.
An 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 sudden changes in the environment while 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.
Modern science divides all nature into living and nonliving. At first glance, this division may seem simple, but sometimes it is quite difficult to decide whether a certain one is truly alive or not. Everyone knows that the main properties, signs of living things are growth and reproduction. Most scientists use seven life processes or characteristics of living organisms that distinguish them from inanimate nature.
What is characteristic of all living beings
All living beings:
- Consist of cells.
- They have different levels of cellular organization. Tissue is a group of cells that perform a common function. An organ is a group of tissues that perform a common function. An organ system is a group of organs that perform a common function. An organism is any living being in a complex.
- They use the energy of the Earth and the Sun, which they need for life and growth.
- React to the environment. Behavior is a complex set of reactions.
- Growing. Cell division is the orderly formation of new cells that grow to a certain size and then divide.
- They reproduce. Reproduction is not essential for the survival of individual organisms, but it is important for the survival of the entire species. All living beings reproduce in one of the following ways: asexual (production of offspring without the use of gametes), sexual (production of offspring by combining sex cells).
- Adapt and adapt to environmental conditions.
Basic characteristics of living organisms
- Movement. All living things can move and change their position. This is more obvious in animals that can walk and run, and less obvious in plants, whose parts can move to track the movement of the sun. Sometimes the movement can be so slow that it is very difficult to see.
- Respiration is a chemical reaction that occurs inside a cell. It is the process of releasing energy from food substances in all living cells.
- Sensitivity is the ability to detect changes in the environment. All living beings are capable of responding to stimuli such as light, temperature, water, gravity, and so on.
- Height. All living things grow. A constant increase in the number of cells and body size is called growth.
- Reproduction is the ability to reproduce and pass on genetic information to one's offspring.
- Excretion - getting rid of waste and toxins. As a result of many chemical reactions occurring in cells, it is necessary to get rid of metabolic products that can poison the cells.
- Nutrition - consumption and use of nutrients (proteins, carbohydrates and fats) necessary for growth, tissue repair and energy. This happens in different ways in different species of living beings.
All living things are made of cells
What are the Basic Features The first thing that makes living organisms unique is that they are all made up of cells, which are considered the building blocks of life. Cells are amazing because despite their small size, they can work together to form large body structures such as tissues and organs. The cells are also specialized - for example, liver cells are found in the organ of the same name, and brain cells function only in the head.
Some organisms are made of just one cell, such as many bacteria, while others are made up of trillions of cells, such as humans. are very complex creatures with incredible cellular organization. This organization begins its journey with DNA and extends to the entire organism.
Reproduction
The main signs of living things (biology describes this even in a school course) also include such a concept as reproduction. How do all living organisms get to Earth? They do not appear out of thin air, but through reproduction. There are two main ways of producing offspring. The first is sexual reproduction, which is known to everyone. This is when organisms produce offspring by combining their gametes. Humans and many animals fall into this category.
Another type of reproduction is asexual: organisms produce offspring without a gamete. Unlike sexual reproduction, where the offspring have a different genetic makeup from either parent, asexual reproduction produces offspring that are genetically identical to their parent.
Growth and development
The main signs of living things also imply growth and development. Once offspring are born, they do not remain that way forever. A great example would be the person himself. People change as they grow, and the more time passes, the more noticeable these differences become. If you compare an adult and the baby he once came into this world with, the differences are simply colossal. Organisms grow and develop throughout life, but these two terms (growth and development) do not mean the same thing.
Growth is when size changes, from small to large. For example, with age, all organs of a living organism grow: fingers, eyes, heart, and so on. Development implies the possibility of change or transformation. This process begins even before birth, when the first cell appears.
Energy
Growth, development, cellular processes and even reproduction can only occur if living organisms accept and can use energy, which is also part of the basic characteristics of a living being. All life energies ultimately come from the sun, and this force gives energy to everything on Earth. Many living organisms, such as plants and some algae, use the sun to produce their own food.
The process of converting sunlight into chemical energy is called photosynthesis, and the organisms that can produce it are called autotrophs. However, many organisms cannot create their own food and therefore must feed on other living organisms for energy and nutrients. Organisms that feed on other organisms are called heterotrophs.
Responsiveness
When listing the main characteristics of living nature, it is important to note the fact that all living organisms have the inherent ability to react in a certain way to various environmental stimuli. This means that any changes in the environment trigger certain reactions in the body. For example, such as the Venus flytrap, will slam its bloodthirsty petals quite quickly if an unsuspecting fly lands there. If possible, the turtle will come out to bask in the sun rather than remain in the shade. When a person hears his stomach growling, he will go to the refrigerator to make a sandwich, and so on.
Stimuli can be external (outside the human body) or internal (within the body), and they help living organisms maintain balance. They are represented in the form of various senses in the body, such as: vision, taste, smell and touch. The speed of response may vary depending on the organism.
Homeostasis
The main characteristics of living organisms include regulation called homeostasis. For example, temperature regulation is very important for all living things because body temperature affects such an important process as metabolism. When the body becomes too cold, these processes slow down and the body may die. The opposite happens if the body overheats, processes accelerate, and all this leads to the same disastrous consequences.
What do living things have in common? They must have all the basic characteristics of a living organism. For example, a cloud can grow in size and move from one place to another, but it is not a living organism, since it does not have all the above characteristics.
