A characteristic feature of all representatives is the presence of one or more flagella, which serve for movement. They are located mainly at the anterior end of the cell and are filamentous outgrowths of ectoplasm. Inside each flagellum are microfibrils built from contractile proteins. The flagellum is attached to the basal body located in the ectoplasm. The base of the flagellum is always associated with the kinetosome, which performs an energy function.
The body of the flagellar protozoan, in addition to the cytoplasmic membrane, is covered on the outside with a pellicle - a special peripheral film (derivative of ectoplasm). It also ensures the constancy of the shape of the cell.
Sometimes a wavy cytoplasmic membrane passes between the flagellum and the pellicle - an undulating membrane (a specific organelle of movement). The movements of the flagellum cause the membrane to wave-like vibrations, which are transmitted to the entire cell.
A number of flagellates have a supporting organelle - axo-style, which passes through the entire cell in the form of a dense strand.
Flagella - heterotrophs (feed on ready-made substances). Some are also capable of autotrophic nutrition and are mixotrophs (for example, Euglena). Many free-living representatives are characterized by swallowing lumps of food (holozoic nutrition), which occurs with the help of flagellum contractions. At the base of the flagellum is a cellular mouth (cystostomy), followed by a pharynx. Digestive vacuoles form at its inner end.
Reproduction is usually asexual, occurring by transverse division. There is also a sexual process in the form of copulation.
A typical representative of free-living flagellates is green euglena (Euglena viridis). Inhabits polluted ponds and puddles. A characteristic feature is the presence of a special light-perceiving organ (stigma). The euglena is about 0.5 mm long, the body shape is oval, the posterior end is pointed. Flagellum one, located at the anterior end. Movement with the help of a flagellum resembles screwing. The nucleus is closer to the posterior end. Euglena has characteristics of both a plant and an animal. In the light, nutrition is autotrophic due to chlorophyll, in the dark - heterotrophic. Such mixed type food is called mixo-trophic. Euglena stores carbohydrates in the form of paramyl, similar in structure to starch. The breathing of euglena is the same as that of wameba. The pigment of the red light-sensitive eye (stigma) - astaxanthin - is not found in the plant kingdom. Reproduction is asexual.
Of particular interest are the colonial flagellates - pandorina, eudorina and volvox. Their example can be seen historical development sexual process.
33. Trichomonas. Species, morphological characteristics. Diagnostics. Prevention
Trichomonas (flagellate class) are the causative agents of diseases called trichomoniasis.
Urogenital trichomonas (Trichomonas vagi-nalis) is the causative agent of urogenital trichomoniasis. In women, this form lives in the vagina and cervix, in men - in the urethra, bladder and prostate gland. It is found in 30-40% of women and 15% of men. The disease is ubiquitous.
Infection occurs most often through sexual contact with unprotected sexual contact, as well as when using shared bedding and personal hygiene items: towels, washcloths, etc. Both non-sterile gynecological instruments and gloves during a gynecological examination can serve as a transmission factor.
In men, the disease can spontaneously end in recovery 1–2 months after infection. Women get sick longer (up to several years).
Diagnostics. Based on the detection of vegetative forms in a smear of discharge from the genitourinary tract.
Prevention - compliance with the rules of personal hygiene, the use of personal protective equipment during sexual intercourse.
Intestinal Trichomonas (Trichomonas hominis) is a small flagellate (length - 5-15 microns) that lives in the large intestine. It has 3–4 flagella, one nucleus, an undulating membrane and an axostyle. It feeds on intestinal bacteria. The formation of cysts was not established.
Diagnostics. Based on the detection of vegetative forms in feces.
Prevention.
1. Personal. Compliance with the rules of personal hygiene, heat treatment of food and water, thorough washing of vegetables and fruits (especially those contaminated with earth).
2. Public. Sanitary arrangement of public places, monitoring of public water supply sources, sanitary and educational work with the population.
Flagella - the oldest group of protozoa, lying at the root of the genealogical tree of the animal world and connecting animals with the plant world. Back in the middle of the century before last, the famous Russian biologist L. S. Tsenkovsky (1822-1887) pointed out the absence of a sharp boundary between flagellated protozoa and unicellular algae. Indeed, some of the flagellates (euglenoids and phytomonads) with with good reason are classified both as a type of protozoa, i.e., animals, and as a type of green algae, i.e., plants.
Class characteristic
One of the most important features used in the classification of protozoa is the organelles of movement. In flagellates, these are bundles, or scourges - thin cytoplasmic outgrowths. They are usually located at the anterior end of the body and arise from special basal grains (basal body or kinetosome). The number of flagella in different species ranges from 1 to 8 or more. In some flagella (leishmania, trypanosomes), at the base of the flagellum, in addition, a special organoid, the kinetoplast, is placed. In its ultrastructure, it corresponds to mitochondria, but differs high content DNA. It is believed that in the kinetoplast energy is generated for the movement of the flagellum, which performs a rotational movement and, as it were, is screwed into the water. In some representatives of the class, the flagellum runs along the body, connecting with it with a thin outgrowth of the cytoplasm. The said outgrowth, or undulating membrane, performs undulating movements and serves as an additional organelle of movement.
According to the method of nutrition (assimilation) are divided into:
Reproduction is usually asexual, by longitudinal division into two parts. Many species also have a sexual process, during which the sexual forms merge (copulation).
In stagnant freshwater reservoirs, numerous species of green bichenos (euglena and phytomonads) live. At times they appear in such large quantities that the water becomes green (water bloom).
Solitary free-living forms
A typical representative of single forms is green euglena (Euglena viridis). Its body shape is fusiform, constant due to the compaction of the outer layer of protoplasm. In the cytoplasm, in the back of the body, there is a large spherical nucleus.
At the front end of the body of green euglena there is a thin flagellum, due to the rotation of which it moves. There is also a pulsating vacuole, its reservoir and several chlorophyll-containing chromatophores, in which carbohydrates are synthesized from carbon dioxide and water (photosynthesis) in the light, i.e. autotrophic nutrition is noted. The products of photosynthesis are deposited in the form of a starch-like substance - paramyl. Euglena searches for illuminated places with the help of a light-sensitive eye - a red-colored photoreceptor, also located at the front end of the body.
Euglena can also feed in the holozoic way, swallowing shaped food particles. If the habitat is rich in dissolved organic substances, then they enter the euglena body by osmosis. Thus, in the structure and mode of nutrition of euglena, a combination of the properties of an animal and a plant organism is noted.
Maintaining a certain concentration of salts in the cytoplasm, i.e., osmotic pressure, is carried out by a special organoid - a pulsating, or contractile, vacuole located at the front end of the body. The pulsating vacuole periodically increases in volume. Having reached a certain size, it pours out the accumulated liquid through the reservoir and after a while begins to grow again. Fluid enters the vacuole through adductor channels.
Euglena reproduction is asexual, by longitudinal division of the body. First, the nucleus divides, the basal body, chromatophores double, and then the cytoplasm divides. The flagellum is discarded or passes to one individual, and in another it is formed anew. Division in the longitudinal direction is one of characteristic features flagella class. Under unfavorable conditions, encystation occurs: the flagellum retracts, the euglena rounds off and forms a dense shell. The encysted euglena may divide one or more times while remaining inside the shells.
Different types of euglena are characteristic of water bodies with varying degrees of organic pollution, therefore, along with algae, they can serve as a criterion for the sanitary assessment of water supply sources.
Colonial forms
Colonial flagellates (volvox, pandorina, eudorina, etc.) are considered as transitional forms from unicellular to multicellular organisms. The most simply arranged colonies consist of 4-16 absolutely identical unicellular individuals connected together - zooids. Each zooid has a flagellum, an ocellus, chromatophores, and a contractile vacuole.
The representative of the colonial flagellate species - volvox (Volvox globator) forms large spherical colonies consisting of many thousands of vegetative zooids - small pear-shaped cells, each of which has two flagella. The ball diameter is 1-2 mm. Its cavity is filled with gelatinous substance. All Volvox cells (zooids) are interconnected by thin protoplasmic bridges, which makes it possible to coordinate the movement of the flagella. The colony moves in the water due to the coordinated movement of the flagella of individual individuals.
In Volvox, a division of the function of the cells of the colony is already observed. So, at one pole of the colony, by which it moves forward, there are cells with more developed light-sensitive eyes, and in the lower part of the colony (where the eyes are poorly developed) there are cells capable of division (reproductive cells, generative zooids), i.e. differentiation into somatic and sexual individuals is noted.
Reproduction of Volvox is carried out at the expense of special - generative - zooids. They leave the surface inside the colonies and here, multiplying by division, form daughter colonies. After the death of the mother colony, the daughter colonies begin independent life. In autumn, due to generative individuals, sexual forms are also formed: large immobile macrogametes (female reproductive zooids) and small microgametes equipped with two cords (male reproductive zooids). In the process of gametogenesis, individuals that turn into macrogametes do not divide and increase in size. Individuals that give microgametes divide many times and form a large number of small biflagellated individuals. Microgametes actively seek out immobile macrogametes and fuse with them to form zygotes. Zygotes give rise to new colonies. The first two divisions of the zygote are meiotic. Consequently, in colonial flagellates, only the zygote has a diploid set of chromosomes, all other stages of the life cycle are haploid.
Order primary monads (Protomonadina) Family Trypanosomes (Trypanosomatidae) Genus Leishmania (Leishmania)
Leishmania - causative agents of leishmaniasis - transmissible diseases with natural foci. Leishmanias were discovered by the Russian doctor P.F. Borovsky in 1898. Representatives of the genus Leishmania, belonging to the Trypanosome family, are of the greatest importance, the distinguishing feature of which is the ability to form several morphologically various forms depending on the conditions of existence. Shapeshifting occurs in both invertebrate and vertebrate hosts.
The following morphological forms are distinguished:
- trypanosomal form - characterized by a flattened ribbon-like body, in the center of which is an oval nucleus. The flagellum begins behind the nucleus. The axial filament of the flagellum goes to the anterior end of the body, forming a well-developed undulating membrane. At the anterior end of the body, it ends, and the flagellum protrudes forward, forming a long free end.
- Critidial form - the flagellum begins slightly anterior to the nucleus, moving forward, forming a short undulating membrane and a free end.
- leptomonas form - the flagellum begins at the very edge of the anterior end of the body, there is no undulating membrane, the free end of the flagellum is of considerable length.
- leishmanial form - has a rounded shape and a large round nucleus. The rod-shaped kinetoplast is located at the anterior end of the body. The flagellum is either absent, or there is only its intracellular part, it does not go beyond the body.
- metacyclic form - similar to the critidial, but devoid of a free flagellum. (Fig. 1).
Flagellates of the genus Leishmania have two morphological forms - leptomonas and leishmanial (Fig. 2) or intracellular.
Leishmania are divided into dermatotropic (located in the skin) and viscerotropic species (located in the internal organs).
The causative agent of visceral leishmaniasis (Leischmania donovani, L. infantum)
Localization. Cells of the liver, spleen, bone marrow, lymph nodes, reticuloendothelial cells of the subcutaneous tissue.
. Visceral leishmaniasis is most common in India (pathogen L. donovani), occurs in the Mediterranean countries, in Transcaucasia and Central Asia (pathogen L. infantum), where it is called kala-azar. In several countries in Asia, Africa and South America Leishmaniasis diseases are also caused by other types of Leishmania.
. Leptomonad and Leishmanial forms.
AT recent times Leishmania has also been found to reside in the reticuloendothelial cells of the skin, which explains the mode of infection of mosquitoes. Affected cells sometimes form a continuous layer or are concentrated near the sweat glands and vessels.
Pathogenic action. There is irregular, persistent fever. The spleen and liver gradually increase and can reach enormous sizes (Fig. 3). Exhaustion develops, the content of erythrocytes in the blood decreases, anemia occurs. The disease can be acute or take a chronic course (1-3 years). Mortality is very high. Mostly children are ill.
Prevention: personal - individual protection against mosquito bites; public - a set of measures to combat mosquitoes and rodents, the destruction of stray and leishmaniasis dogs, jackals. At the same time, it is necessary to carry out sanitary-educational work and treatment of patients.
Cutaneous leishmaniasis (Leishmania tropica)
Three subspecies of the dermatotropic species of Leishmania are known: L. tropica minor and L. tropica major (in the eastern hemisphere) and L. tropica mexicana (in the western hemisphere).
Geographic distribution. Widespread in a number of countries in Europe, Asia, America, Africa. In Russia, cutaneous leishmaniasis caused by L. tropica (Borovsky's disease) has been eliminated, and caused by L. major occurs in the Transcaucasus and Central Asia, especially in a number of regions of Turkmenistan.
Morphophysiological characteristics. The leptomonas and leishmanial forms are indistinguishable from the forms of viscerotropic leishmania.
Life cycle. Almost does not differ from the causative agent of visceral leishmaniasis. The source of infection is humans and wild animals (small rodents living in the zones of sandy semi-deserts and deserts - gerbils, ground squirrels, hamsters, some types of rats and mice). Infection of reservoir animals in natural conditions sometimes reaches 70%. The disease in animals also manifests itself in the form of skin ulcers. Mosquitoes serve as carriers. There is close contact between reservoir rodents and vector mosquitoes. The rodent burrow is a permanent habitat and breeding ground for mosquitoes, the infestation of which can reach 35%. Human role in the spread of cutaneous leishmaniasis is small, except in some areas the globe(India).
Pathogenic action. With cutaneous leishmaniasis, rounded, long (about a year) non-healing ulcers are formed on exposed parts of the body, mainly on the face. After healing, a disfiguring scar remains (Fig. 4). After a disease, immunity lasts a lifetime.
Laboratory diagnostics. Microscopic examination of discharge ulcers.
Prevention: personal - individual protection against mosquito bites; it is recommended to carry out prophylactic vaccinations of strains of cutaneous leishmaniasis from an animal in closed areas of the skin. Such vaccinations further protect against the appearance of disfiguring ulcers and scars on the face and other exposed parts of the body. As a public prevention, mosquitoes and rodents are being fought. In particular, they introduce chloropicrin into the burrows, plow up plots of land inhabited by gerbils in the territories adjacent to the villages.
Genus Trypanosoma
Trypanosoma gambiense is the causative agent of trypanosomiasis, African sleeping sickness in humans.
Localization. In the body of humans and other vertebrates, it lives in blood plasma, lymph, lymph nodes, cerebrospinal fluid, tissues of the spinal cord and brain.
Geographic distribution. Found in equatorial Africa. In the foci of the disease, trypanosome was found in the blood of antelopes, which serve as its natural reservoir. The carrier is an African blood-sucking insect - the tse-tse fly (Glossina palpalis). The disease occurs only in the distribution area of this fly.
Morphophysiological features. Size from 13 to 39 microns. The body is curved, flattened in one plane, narrowed at both ends, equipped with one flagellum and an undulating membrane. Feeds osmotically. Reproduction occurs asexually, by longitudinal division.
Life cycle. Trypanosomiasis caused by T. gambiense is a typical transmissible disease with natural foci. The causative agent of trypanosomiasis develops with a change of hosts. The first part of the trypanosome life cycle takes place in the digestive tract of the tsetse fly (Glossina palpalis), outside the range of which trypanosomiasis (African sleeping sickness) does not occur, the second part - in the body of vertebrate animals (cattle and small cattle, pigs, dogs, some wild animals ), as well as humans. When a fly sucks the blood of a sick person, trypanosomes enter its stomach. Here they multiply and undergo a series of stages. The full development cycle is about 20 days. Flies, in the body of which there are trypanosomes of the invasive stage, can infect a person when bitten.
Pathogenic action. A patient with trypanosomiasis has severe lesions central nervous system: observed muscle weakness, exhaustion, mental depression, drowsiness. The disease state lasts 7-10 years and, if left untreated, ends in death.
Laboratory diagnostics. For laboratory diagnostics, blood, punctates of lymph nodes and cerebrospinal fluid are examined.
Prevention. Personal prevention comes down to taking medications that can protect against infection when bitten by a tsetse fly. Public prevention consists in the destruction of the carrier. For this purpose, the breeding sites of flies - shrubs near the dwelling and along the banks of water bodies - are treated with insecticides or cut down.
Order polyflagellates (Polymastigina)
Intestinal Trichomonas (Trichomonas hominis). Causes intestinal trichomoniasis.
Localization. Colon.
Geographic distribution. Everywhere.
Morphophysiological characteristics. The body has an oval shape with a pointed outgrowth at the posterior end, with one bubble-shaped nucleus. The body length is 5-15 microns, 4 free flagella extend from the anterior end, going forward, and one directed backward, which is connected with the undulating membrane. The body is pierced in the middle by a support rod ending in a pointed spike at the posterior end of the body. The cell mouth is located near the nucleus. In the cytoplasm are digestive vacuoles that serve to digest bacteria and intestinal contents swallowed by the cell mouth. Osmotic nutrition is also possible - liquid substances. Reproduction is asexual, by longitudinal division. The ability to form cysts is disputed.
Infection occurs through vegetables and fruits, dirty hands contaminated with feces containing Trichomonas, unboiled water.
Pathogenic action not proven, since intestinal Trichomonas occurs in the intestines of healthy people and patients with intestinal diseases. There is an opinion that intestinal trichomonas does not cause disease, but only accompanies pathological processes caused by other causes.
Laboratory diagnostics. Microscopic examination of smears of feces, finding vegetative forms in feces.
Prevention. Personal - washing hands before eating and after visiting the restroom, heat treatment of food and drinking water, thorough washing of vegetables and fruits eaten raw, protection of food and water from dust and flies, which can be mechanical carriers of various pathogens. Public prevention consists in monitoring the sanitary condition of water supply sources, food enterprises and grocery stores, public places, fighting flies, and disseminating hygiene knowledge.
Urogenital Trichomonas (Trichomonas vaginalis)- the causative agent of urogenital trichomonadosis.
Localization. Urinary tract of men and women.
Geographic distribution. Everywhere.
Morphophysiological characteristics. The structure is very similar to the intestinal Trichomonas. The hallmarks are big sizes body (length ranges from 7 to 30 microns). The body shape is most often pear-shaped, there are 4 flagella, an undulating membrane and a support rod ending in a spike.
Pathogenic action. Causes inflammatory processes in the genital tract, which are protracted. It is believed that the predisposing moment for the manifestation of pathogenicity is the presence in the genital tract of a certain type of bacteria.
In women, the vagina is initially affected, but subsequently the disease becomes multifocal. In acute course, abundant liquid discharge, itching and burning are characteristic. In men, most of the disease is asymptomatic.
Infection occurs sexually, as well as when using bedding, linen, sponge of the patient. Infection is possible when examined by a gynecologist through contaminated instruments and gloves.
Laboratory diagnostics. Microscopic examination of smears from the discharge of the urinary tract. The diagnosis is made on the basis of finding vegetative forms in the patient's secretions.
Prevention. determined by the mode of infection.
Lamblia (Lamblia intestinalis). Causes the disease giardiasis. This flagellate was discovered by professor of Kharkov University D.F. Lyamble in 1859.
Localization. The duodenum, for the second time can penetrate into the bile ducts.
Geographic distribution. Everywhere.
Laboratory diagnostics. Detection of cysts in faeces or vegetative forms in the contents of the duodenum during probing.
Prevention. a) thermal treatment of food and drinking water; boiling kills giardia cysts; b) thorough washing of fruits, vegetables and other foods consumed raw; c) storage of cooked food and drinking water in a sealed container. It should be borne in mind that Giardia cysts can get on food with dust and be introduced to it by flies; d) fight against flies. Flies visit sewage dumps, cesspools, they sit on human feces, rotting food and, having stained their bodies in feces, fly into a person’s dwelling, where they sit on food, dishes, human skin; e) washing hands before meals and after going to the toilet.
The date:Subject: biology.
Teacher: Loginova A. A.
Lesson # 5.
Class: 7th.
Topic: “Features of the structure and life of Euglena green. Colonial flagellates»
Target: To acquaint students with the structure and life of the green euglena, substantiating its intermediate position between the plant and animal kingdoms; to show the complication in the structure of the organization of colonial forms of flagellates, and the importance of flagellates in nature and human life.
Tasks:
Educational: to reveal the features of the structure and life processes of green euglena;
Developing: develop skills and abilities independent work with textbook; highlight the main thing, formulate conclusions;
Educational: fostering respect for nature. continue to form healthy lifestyle life.
Lesson type: lesson learning new material.
Equipment: Textbook, presentation.
Lesson plan:
I . Organizing time.
II . Updating of basic knowledge.
Let's remember:
1) What does biology study?
III . Motivation and goal setting
IV
V . Physical education minute
VI
VII . Repetition of a new theme.
- subtle questions
- thick questions
Answers:
II. Flagella - B, C, D, H, I.
VIII
IX . Homework.
During the classes:
I . Organizing time.
Introductory part. Announcement of the topic and purpose of the lesson.
II . Updating of basic knowledge
Let's remember:
1) What does biology study?
2) What biological sciences do you know?
3) What ancient biologists do you know?
4) What organisms are called protozoa?
5) What groups are the simplest divided into?
6) What are common features the external structure of unicellular?
III . Motivation and goal setting
Today we will proceed to the study of unicellular animals and talk in more detail about the green euglena.
IV . Presentation of new material.
Actively moving protozoa - flagellates have special outgrowths on the surface of the cell, called organelles of movement. Representatives of flagellates are unicellular organisms whose organelles of movement are long outgrowths called flagella. The number of flagella in different species is different - from one to several hundred. The biology of flagellates can be considered using the example of green euglena.
Habitat, structure and locomotion. Euglena green lives in heavily polluted small freshwater bodies and often causes "blooming" of the water. The body of the euglena is covered with a thin and elastic shell - the pellicle, which allows it to contract, stretch and bend. Thanks to the pellicle, the body of the euglena has a constant fusiform shape (Fig. 25). At the front end of the Euglena body there is one long flagellum. It rotates rapidly and pulls the euglena forward. During movement, the body of the euglena slowly rotates around its axis in the direction opposite to the rotation of the flagellum. At the base of the flagellum is a dense basal body, which serves as a support for the flagellum. At the front end of the body is a cellular mouth and a bright red eye. With its help, Euglena distinguishes between changes in illumination. The contractile vacuole is located in the anterior part of the body, and the nucleus is located in the posterior third. The cytoplasm contains green chloroplasts, carrying the green pigment - chlorophyll, and a digestive vacuole.
Rice. 25. The structure of green euglena: 1 - core; 2 - contractile vacuole; 3 - shell; 4 - cell mouth: 5 - flagellum. 6 - peephole. 7 - basal body; 8-chloroplast
Food. Euglena is able to change the nature of nutrition depending on environmental conditions. In the light, due to the ability to photosynthesis, it is characterized by autotrophic nutrition - synthesis organic matter from inorganic. In the dark, Euglena feeds heterotrophically - it uses ready-made organic substances. It is able to absorb nutrients dissolved in water through the pellicle. A thin tube protrudes into the cytoplasm through which liquid food is absorbed into the cell. A digestive vacuole forms around it. In addition, due to the movement of the flagellum, organic microparticles are drawn into the cell mouth. Digestive vacuoles form around them, which move in the cytoplasm (as in the amoeba). Undigested food residues are thrown out at the rear end of the body.
Breath. Euglena breathes oxygen dissolved in water. Gas exchange occurs, like in an amoeba, through the entire surface of the body. Oxygen dissolved in water enters the cell, where it is consumed in the process of life, carbon dioxide is released outside.
Selection. Harmful substances (decay products) and excess water are collected in the contractile vacuole, which are then pushed out.
Reproduction. Euglena reproduces asexually: the cell divides in two along the longitudinal axis of the body (Fig. 26). First, the core is divided. Then the body of the euglena is divided by a longitudinal constriction into two approximately identical parts. If any organelle (for example, an eye or a flagellum) did not get into one of the daughter cells, then it subsequently forms there.
Rice. 26. Asexual reproduction of euglena
Euglena as an organism that combines the characteristics of an animal and a plant.On the one hand, Euglena is characterized by autotrophic nutrition due to the presence of chlorophyll involved in photosynthesis, which is typical for plants. On the other hand, as an animal, Euglena actively moves, has heterotrophic nutrition - it eats particles of organic substances, small animals, unicellular algae. If Euglena green is in the dark for a long time, then its chlorophyll disappears and it feeds only on organic substances.
The example with green euglena shows that the boundary between animals and plants is rather arbitrary. Flagellates occupy, as it were, an intermediate position between the plant and animal kingdoms. From plant flagellates, like euglena, animal flagellates could form in ancient times.
V . Physical education minute
I go and you go - one, two, three. (We walk in place.)
I sing and you sing - one, two, three. (We clap our hands.)
We go and we sing - one, two, three. (Jumping in place.)
We live very friendly - one, two, three. (We walk in place.)
VI . Continuation of the presentation of the material.
The story of the teacher with a demonstration of the presentation.
The bodies of colonial flagellates consist of many cells. Volvox is a large spherical colony about 8 mm in diameter, on the surface of which cells are located in one layer (Fig. 27, 2). There can be more than 60 thousand cells in a Volvox colony. The inner cavity of the ball is occupied by liquid mucus. Individual cells of the Volvox colony are connected by cytoplasmic "bridges".
Rice. 27. Colonial flagellates: 1 - gonium: 2 - volvox
During asexual reproduction, colonial flagellates form daughter colonies. In Gonium (Fig. 27, 1), each cell of the colony is capable of giving rise to a new colony, while in Volvox only 8-10 cells can participate in asexual reproduction, and they form new colonies.
The first colonies arise due to the fact that after cell division they do not diverge, but remain together. So, the gonium forms a colony in the form of a plate, built from 16 cells arranged in one layer. There are 32 cells in a spherical colony of Eudorina. They have flagella that are turned outward.
During sexual reproduction of Volvox, male germ cells form 5-10 cells, female - 25-30. Thus, in the Volvox colony there are different types cells, which is typical for multicellular animals.
Volvox can serve as a model showing how multicellular organisms could evolve from unicellular organisms.
Variety of flagellates.
More than 7,000 species are classified as flagellates. According to the nature of nutrition and metabolism, they are divided into plant and animal. The flagellates include bodo (Fig. 28), which lives in the same places as the plant flagellate euglena green. Bodo moves in water with the help of two flagella located at the front end of the body. This animal does not have chlorophyll, therefore, only heterotrophic nutrition is characteristic of it. It feeds on bacteria, unicellular algae and microscopic animals, which Bodo drives to the mouth with the help of flagella and swallows.
Rice. 94. The structure of the bodo flagellate: 1 - cellular mouth; 2 - flagella; 3 - membrane; 4 - cytoplasm; 5 - core; 6 - mitochondrion; 7 - digestive vacuole
Rice. 94. Pathogenic protozoa: 1 - trypanosoma; 2 - lamblia
VII . Repetition of a new theme.
- subtle questions
1. Where does the green euglena live.
2. How does she get around?
3. What forms when attacked adverse conditions?
- thick questions
1. Why euglena and autotroph and heterotroph?
2. Compare the way amoeba and green euglena feed.
3. What do amoeba and green euglena have in common.
1) draw the structure of the green euglena and label the organelles of the cell (the figure is issued).
2) differentiated tasks (individual approach to talented and gifted children). Task cards are included.
Answers:
1) I. Sarcode (Rhizopods) - A, G, E, F.
II. Flagella - B, C, D, H, I.
2) I. Amoeba ordinary - A, B, C, D, E, I.
II. Euglena green - A, B, C, F, F, H, I.
VIII . Rating with comments.
IX . Homework.
Learn new concepts and definitions.
1 option
F. I. class __________________________________
Find a match. From the following characteristics, write down the characteristics of the class:
I. Sarcodal (Rhizopods) _____________________________________________
II. Flagella ________________________________________
A. Ability to form cytoplasmic outgrowths
B. The presence of flagella
B. Movement due to flagella
D. Capturing food with the help of prolegs
D. Flagella contribute to the capture of food.
E. Move with the help of pseudopodia
G. Heterotrophic nutrition
H. Nutrition, both autotrophic and heterotrophic
I. There are colonial forms.
Option 2
F. I. class __________________________________
Find a match.
From the listed organelles, write out the organelles characteristic of:
I. Amoeba ordinary ____________________________________________
II. Euglena green ____________________________________________
A. Core
B. Shell
B. Contractile vacuole
G. Digestive vacuole
D. pseudopods
E. flagellum
G. Photosensitive eye
3. Chloroplasts
I. Cytoplasm
A characteristic feature of all representatives is the presence of one or more flagella, which are used for movement. They are located mainly at the anterior end of the cell and are filamentous outgrowths of ectoplasm. Inside each flagellum are microfibrils built from contractile proteins. The flagellum is attached to the basal body located in the ectoplasm. The base of the flagellum is always associated with kinetosome performing an energy function.
The body of the flagellar protozoan, in addition to the cytoplasmic membrane, is covered on the outside with a pellicle - a special peripheral film (derivative of ectoplasm). It also ensures the constancy of the shape of the cell.
Sometimes a wavy cytoplasmic membrane passes between the flagellum and the pellicle - undulating membrane(specific organelle of locomotion). The movements of the flagellum cause the membrane to wave-like vibrations, which are transmitted to the entire cell.
A number of flagellates have a supporting organelle - axostyle, which in the form of a dense strand passes through the entire cell.
Flagella- heterotrophs (eat ready-made substances). Some are also capable of autotrophic nutrition and are mixotrophs (for example, Euglena). For many free-living
representatives are characterized by the ingestion of lumps of food (holozoic nutrition), which occurs with the help of contractions of the flagellum. At the base of the flagellum is a cellular mouth (cystostomy), followed by a pharynx. Digestive vacuoles form at its inner end.
Reproduction is usually asexual, occurring by transverse division. There is also a sexual process in the form of copulation.
Euglena green is a typical representative of free-living flagellates. (Euglena viridis) . Inhabits polluted ponds and puddles. A characteristic feature is the presence of a special light-perceiving organ (stigma). The euglena is about 0.5 mm long, the body shape is oval, the posterior end is pointed. Flagellum one, located at the anterior end. Movement with the help of a flagellum resembles screwing. The nucleus is closer to the posterior end. Euglena has characteristics of both a plant and an animal. In the light, nutrition is autotrophic due to chlorophyll, in the dark - heterotrophic. Such a mixed type of nutrition is called mixotrophic. Euglena stores carbohydrates in the form of paramyl, similar in structure to starch. Euglena's breathing is the same as that of an amoeba. The pigment of the red light-sensitive eye (stigma) - astaxanthin - is not found in the plant kingdom. Reproduction is asexual.
Of particular interest are the colonial flagellates - pandorina, eudorina and volvox. On their example, one can trace the historical development of the sexual process.
Latin name Mastigophora or Flagellata
General characteristics of flagella
An extensive class including over 6000 species variety of protozoa.
The body of flagellates has a very diverse, often oval, spherical or fusiform shape. The organelles of movement are cytoplasmic filamentous flagella. Most often there are one or two, but there may be four or more. The flagella are usually placed at the anterior end of the body and point forward in the direction of the animal's movement. However, in some forms, in the presence of two or more flagella, one of them can be bent backward along the body and have the meaning of a rudder. This flagellum is usually connected to the surface of the body by the thinnest plasma film, * thus strengthening the oscillating, or undulating, membrane. The movements of the forward-directed flagella are quite complex and varied. The flagellum performs rotational movements, describing a figure in the shape of a cone. At the same time, he himself undulates. The movement of the flagellum causes the rotational movement of the body of the protozoan, which, as it were, is screwed into the water. Some flagellates (order Rhizomastigida), in addition to permanent flagella, have pseudopodia. These forms indicate the proximity of the classes of flagellates and sarcods.
A-D-ovglenovye: A - green euglena (Euglena viridis); 1, 2 - tourniquet; 3 - reservoir of the contractile vacuole; 4 - stigma; 5 - contractile vacuole; 6 - chromatophores; 7-core; B - E. oxyuris; B - E. acus; G - E. gracilis; D - Phacus longicauda; E-K - armored: E - * Peridinium; G - Ceratium tripos; 3 - Ornithocercus; I - Ceratium hirudinella; K -> nightlight
(Noctiluca miliaris).
Body flagella comprises cytoplasm and usually one bubble nuclei. The cytoplasm is divided into two layers: the outer, more dense, homogeneous and transparent - ectoplasm and the inner, more liquid and granular - endoplasm.
The majority of the body is covered with a rather dense elastic membrane - pellicle formed due to the compaction of ectoplasm. The pellicle allows the animal to temporarily change the shape of the body, or metabolize. In some of them, the body is covered with a hard shell of fiber, which forms a kind of shell.
Food
Some euglenas, in particular, green euglena (Euglena viridis) occupy a special position in terms of feeding method (Fig. A). The green euglena has chromatophores containing chlorophyll. In the light, it feeds like a typical green plant organism. But, placed in darkness, euglena becomes discolored and passes to saprophytic nutrition. Apparently, even in the light, Euglena has a mixed mode of nutrition, that is, it is a mixotrophic organism.
Holophytic flagellates usually have a red or brown spot - an eye, or stigma - located at the anterior end of the body at the base of the flagellum (Fig. A). This is a photosensitive organelle that determines the ability of green flagella to perceive light stimuli. Green flagellates show a positive reaction to light, that is, they usually move towards the light source.
Many freshwater animals have special excretory organelles- contractile vacuoles, with the help of which excess water is removed from the cell, as well as liquid dissimilation products. The contractile vacuole euglena(Fig. A) is placed in front of the body. The contractile in the "akuole" is periodically filled with liquid
cpm content, which, when the vacuole is compressed, is pushed into a special one: a bubble - a reservoir (Fig. L), and then through a special channel, sometimes incorrectly called the "pharynx", is released outward. Contractile* vacuoles are generally absent in marine flagellates. In addition to the described organelles, there can be various inclusions in the cytoplasm: grains of starch (in green flagellates), grains of paramyl - a carbohydrate similar in composition to starch (in euglena, etc.), droplets of fat, etc.
1 - longitudinal division; 2 and 3 - division in the cyst.
encysting
For flagellates, as well as for many other protozoa, the formation of resting stages by encystation is characteristic. The formation of cysts can have different meanings. encysting observed when adverse conditions occur: cysts endure sudden changes in temperature and lack of humidity. In other cases, encystation may be associated with reproduction, or may be an adaptation for the dispersal of animals.
reproduction
For most flagellates, only asexual reproduction is known. The sexual process has been studied only in green colonial forms from the Volvox family (order Phytomonadida).
Asexual reproduction usually occurs by fission in two. It begins with a mitotic division of the nucleus, followed by a longitudinal division of the body, starting at its anterior end. At the same time, the basal bodies are also divided; the flagella are either discarded or transferred to one of the daughter individuals, while in the other they develop anew from the basal body. When dividing flagellates that have chromatophores, the latter also divide and distribute among daughter cells. In some flagellates, division is preceded by encystation, while division occurs already under the cyst membrane (Fig. 2 and 3).
U - gamete; 2-7 - successive stages of gamete copulation; 8 - encysted zygote.
In colonial flagellates from Volvox, during asexual reproduction, a single cell of the colony divides several times (according to the number of cells that make up the colony), and thus daughter colonies arise.
Sexual reproduction in different flagellates occurs differently. In the simplest case, there is copulation of two outwardly identical and larger sexual individuals - gametes, for example, in Polytoma and some species of chlamydomonas. Such copulation of identical gametes, or isogametes, is called isogamous copulation. In other flagella, the gametes differ in size. Some of them are larger - macrogametes, others are smaller - microgametes. Macro- and microgametes are equipped with flagella. Macro- and microgametes copulate with each other. Copulation of unequal gametes, or anisogametes, is called anisogamous.
Anisogamous copulation in Chlamydomonas braunii: l - microgamete; 2 - macrogamete; 3-5 - successive stages of gamete copulation.
The formation of anisogametes can be considered the first stage of sex differentiation. In Volvox colonies, formed by a huge number of individuals (up to 10-20 thousand), gametes can form only from individual generative individuals. Most individuals of the colony are vegetative, unable to participate in sexual reproduction. In a Volvox colony, only 25-30 cells (individuals) can turn into large immobile macrogametes and only 5-10 cells can form microgametes. During the formation of macrogametes, cell division does not occur, and during the formation of microgametes, a series of divisions occurs, as a result of which 256 smallest microgametes arise, each with a pair of flagella. Microgametes leave the colony and enter the water. Then they penetrate into other colonies, where they copulate with macrogametes.
Macrogametes do not have flagella. They can be compared with multicellular egg cells, and microgametes - with spermatozoa. Such Volvox copulation is called o o g m and e. After oogamous copulation, a fertilized macrogamete is formed - a zygote. The latter secretes a dense shell, and all vegetative individuals of the colony die. The zygote then begins to divide many times and gives rise to a new Volvox colony.
In Volvox globator, micro- and macrogametes develop in the same hermaphroditic colony, while in another species, V. aureus, the colonies are separate sexes: some of them (female) form only macrogametes, others (male) - only microgametes.
Thus, in various representatives of the flagellates, there are, as it were, different stages in the evolution of the sexual process - from isogamous copulation to true oogamy, which is of interest for understanding the origin of the sexual process in metazoans.
Classification
A - part of the polonium; B - schematic section of Volvox; 1 - colony cells; 2 - macrogametes; 3 - formation of microgametes.
Flagella class (Mastigophora, or Flagellata) consists of a large number(13-14) units. The most important of them are the following: J. Eugleiaceae (Euglenida); 2. Shellfish (Dinoflagellata); 3. Phytomonads (Pliytomonadida); 4. Rhizomastigida; 5) Protomonadov (Protomonadida); 6. Polyflagellates (Polymastigida); 7. Hypermastigidae (Hypermastigida); 8. Opaline (Opalinida).
The first three orders (euglenoids, armored, phytomonads) are part of the subclass Phytomastigina - autotrophic plant flagellates. The next four orders (rhizoflagellate, protomonad, polyflagellate, hypermastigin) constitute a subclass of zoomastigina (Zoomastigina) - typical heterotrophic organisms. The last detachment (opaline) is distinguished by many scientists as an independent subclass of Opalinina.
