Eukaryotes are unicellular or multicellular. Single-celled protozoa
1. Introduction……………………………………………………………………………….2
2. Evolution of life on earth……………………………………………………………3
2.1. Evolution of single-celled organisms……………………………3
2.2. Evolution of multicellular organisms……………………………..6
2.3. Evolution of the plant world……………………….……………….8
2.4. Evolution of the animal world……………………………………………………...10
2.5 Evolution of the biosphere……………………………………..……….…….12
3. Conclusion……………………………………………………………………………….18
4. List of references……………………………………………………….19
Introduction.
It often seems that organisms are completely at the mercy of their environment: the environment sets limits for them, and within these limits they must either succeed or perish. But organisms themselves influence their environment. They change it directly during their short existence and over long periods of evolutionary time. It is known that heterotrophs absorbed nutrients from the primary “broth” and that autotrophs contributed to the emergence of an oxidizing atmosphere, thus preparing the conditions for the emergence and evolution of the respiration process.
The appearance of oxygen in the atmosphere led to the formation of the ozone layer. Ozone is formed from oxygen under the influence of ultraviolet radiation from the Sun and acts as a filter that blocks ultraviolet radiation, which is harmful to proteins and nucleic acids, and prevents it from reaching the surface of the Earth.
The first organisms lived in water, and the water shielded them by absorbing the energy of ultraviolet radiation. The first land settlers found sunlight and minerals in abundance here, so that in the beginning they were practically free from competition. Trees and grasses, which soon covered the plant part of the earth's surface, replenished the supply of oxygen in the atmosphere; in addition, they changed the nature of water flow on the Earth and accelerated the process of formation of soils from rocks. A giant step on the path of the evolution of life was associated with the emergence of the basic biochemical metabolic processes - photosynthesis and respiration, as well as with the formation of a eukaryotic cellular organization containing a nuclear apparatus.
Evolution of life on earth.
2.1 Evolution of single-celled organisms.
The earliest of bacteria (prokaryotes) existed already about 3.5 billion years ago. To date, two families of bacteria have been preserved: ancient, or archaebacteria (halophilic, methane, thermophilic), and eubacteria (all others). Thus, the only living creatures on Earth for 3 billion years were primitive microorganisms. Perhaps they were single-celled creatures similar to modern bacteria, for example clostridia, living on the basis of fermentation and the use of energy-rich organic compounds that arise abiogenically under the influence of electrical discharges and ultraviolet rays. Consequently, in this era, living beings were consumers of organic substances, and not their producers.
A giant step on the path of the evolution of life was associated with the emergence of the basic biochemical metabolic processes - photosynthesis and respiration and with the formation of a cellular organization containing a nuclear apparatus (eukaryotes). These “inventions,” made in the early stages of biological evolution, have been largely preserved in modern organisms. Using the methods of molecular biology, a striking uniformity of the biochemical foundations of life has been established, with a huge difference in organisms in other characteristics. The proteins of almost all living things are made up of 20 amino acids. Nucleic acids that encode proteins are assembled from four nucleotides. Protein biosynthesis is carried out according to a uniform pattern; the site of their synthesis is ribosomes; mRNA and tRNA are involved in it. The vast majority of organisms use the energy of oxidation, respiration and glycolysis, which is stored in ATP.
The difference between prokaryotes and eukaryotes also lies in the fact that the former can live both in an oxygen-free environment and in an environment with different oxygen content, while eukaryotes, with few exceptions, require oxygen. All of these differences were significant for understanding the early stages of biological evolution.
A comparison of prokaryotes and eukaryotes in terms of oxygen demand leads to the conclusion that prokaryotes arose during a period when the oxygen content in the environment changed. By the time eukaryotes appeared, the oxygen concentration was high and relatively constant.
The first photosynthetic organisms appeared approximately 3 billion years ago. These were anaerobic bacteria, the predecessors of modern photosynthetic bacteria. It is assumed that they formed the most ancient environments of known stromatolites. The unification of the environment with nitrogenous organic compounds caused the emergence of living creatures capable of using atmospheric nitrogen. Such organisms, capable of existing in an environment completely devoid of organic carbon and nitrogen compounds, are photosynthetic nitrogen-fixing blue-green algae. These organisms carried out aerobic photosynthesis. They are resistant to the oxygen they produce and can use it for their own metabolism. Since blue-green algae arose during a period when the concentration of oxygen in the atmosphere fluctuated, it is quite possible that they are intermediate organisms between anaerobes and aerobes.
The photosynthetic activity of primordial unicellular organisms had three consequences that had a decisive influence on the entire further evolution of living things. Firstly, photosynthesis freed organisms from competition for natural reserves of abiogenic organic compounds, the amount of which in the environment had significantly decreased. Autotrophic nutrition, which developed through photosynthesis and the storage of ready-made nutrients in plant tissues, then created the conditions for the emergence of a huge variety of autotrophic and heterotrophic organisms. Secondly, photosynthesis ensured the saturation of the atmosphere with a sufficient amount of oxygen for the emergence and development of organisms whose energy metabolism is based on respiration processes. Thirdly, as a result of photosynthesis, an ozone shield was formed in the upper part of the atmosphere, protecting earthly life from the destructive ultraviolet radiation of space.
Another significant difference between prokaryotes and eukaryotes is that in the latter the central mechanism of metabolism is respiration, while in most prokaryotes energy metabolism is carried out in fermentation processes. Comparison of the metabolism of prokaryotes and eukaryotes leads to the conclusion about the evolutionary relationship between them. Anaerobic fermentation probably appeared at an earlier stage of evolution. After a sufficient amount of free oxygen appeared in the atmosphere, aerobic metabolism turned out to be much more profitable, since the oxidation of carbons increases the yield of biologically useful energy by 18 times in comparison with fermentation. Thus, anaerobic metabolism was joined by the aerobic method of extracting energy by single-celled organisms.
It is not known exactly when eukaryotic cells appeared; according to research, we can say that their age is approximately 1.5 billion years ago.
In the evolution of a unicellular organization, intermediate steps are distinguished, associated with the complication of the structure of the organism, the improvement of the genetic apparatus and methods of reproduction.
The most primitive stage, the agamic aracariogine, is represented by cyanides and bacteria. The morphology of these organisms is the simplest in comparison with other single-celled organisms. However, already at this stage differentiation into cytoplasm, nuclear elements, basal granules, and cytoplasmic membrane appears. Bacteria are known to exchange genetic material through conjugation. A wide variety of bacterial species and the ability to exist in a wide variety of environmental conditions indicate the high adaptability of their organization.
The next stage - agamic eukaryogyne - is characterized by further differentiation of the internal structure with the formation of highly specialized organelles (membranes, nucleus, cytoplasm, ribosomes, mitochondria, etc.). Particularly significant here was the evolution of the nuclear apparatus - the formation of real chromosomes in comparison with prokaryotes, in which the hereditary substance is diffusely distributed throughout the cell. This stage is characteristic of protozoa, the progressive evolution of which followed the path of increasing the number of identical organelles (polymerization), increasing the number of chromosomes in the nucleus (polyploidization), and the appearance of generative and vegetative nuclei - macronucleus (nuclear dualism). Among unicellular eukaryotic organisms, there are many species with agamous reproduction (naked amoebas, shell rhizomes, flagellates).
A progressive phenomenon in the phylogeny of protozoa was the emergence of sexual reproduction (gamogony), which differs from ordinary conjugation. Protozoa have meiosis with two divisions and crossing over at the chromatid level, and gametes with a haploid set of chromosomes are formed. In some flagellates, gametes are almost indistinguishable from asexual individuals and there is still no division into male and female gametes, i.e. Isogamy is observed. Gradually, in the course of progressive evolution, a transition occurs from isogamy to anisogamy, or the division of generative cells into female and male, and to anisogamous copulation. When gametes fuse, a diploid zygote is formed. Consequently, in protozoa there has been a transition from the agamic eukarytic stage to the zygotic stage - the initial stage of xenogamy (reproduction by cross-fertilization). The subsequent development of multicellular organisms followed the path of improving methods of xenogamous reproduction.
Animals consisting of a single cell with a nucleus are called unicellular organisms.
They combine the characteristic features of a cell and an independent organism.
Unicellular animals
Animals of the subkingdom Unicellular or Protozoa live in liquid environments. Their external forms are varied - from amorphous individuals that do not have a definite outline, to representatives with complex geometric shapes.
There are about 40 thousand species of single-celled animals. The most famous include:
- amoeba;
- green euglena;
- ciliate-slipper.
Amoeba
It belongs to the rhizome class and is distinguished by its variable shape.
It consists of a membrane, cytoplasm, contractile vacuole and nucleus.
Nutrient absorption is carried out using the digestive vacuole, and other protozoa, such as algae and, serve as food. For respiration, amoeba requires oxygen dissolved in water and penetrating through the surface of the body.
Green euglena
It has an elongated fan-shaped shape. It feeds by converting carbon dioxide and water into oxygen and food products thanks to light energy, as well as ready-made organic substances in the absence of light.
Belongs to the class Flagellates.
Ciliate slipper
A class of ciliates, its outline resembles a shoe.
Bacteria serve as food.
Unicellular fungi
Fungi are classified as lower non-chlorophyll eukaryotes. They differ in external digestion and chitin content in the cell wall. The body forms a mycelium consisting of hyphae.
Unicellular fungi are systematized into 4 main classes:
- deuteromycetes;
- chytridiomycetes;
- zygomycetes;
- ascomycetes.
A striking example of ascomycetes is yeast, which is widespread in nature. The speed of their growth and reproduction is high due to their special structure. Yeast consists of a single round cell that reproduces by budding.
Unicellular plants
A typical representative of lower unicellular plants often found in nature are algae:
- chlamydomonas;
- chlorella;
- spirogyra;
- chlorococcus;
- Volvox.
Chlamydomonas differs from all algae in its mobility and the presence of a light-sensitive eye, which determines the places of greatest accumulation of solar energy for photosynthesis.
Numerous chloroplasts are replaced by one large chromatophore. The role of pumps that pump out excess fluid is performed by contractile vacuoles. Movement is carried out using two flagella.
Green algae, Chlorella, unlike Chlamydomonas, have typical plant cells. A dense shell protects the membrane, and the cytoplasm contains the nucleus and chromatophore. The functions of the chromatophore are similar to the role of chloroplasts in land plants.
The spherical algae Chlorococcus is similar to Chlorella. Its habitat is not only water, but also land, tree trunks growing in a humid environment.
Who discovered single-celled organisms
The honor of discovering microorganisms belongs to the Dutch scientist A. Leeuwenhoek.
In 1675, he examined them through a microscope of his own making. The name ciliates was assigned to the smallest creatures, and since 1820 they began to be called the simplest animals.
Zoologists Kellecker and Siebold in 1845 classified unicellular organisms as a special type of the animal kingdom and divided them into two groups:
- rhizomes;
- ciliates.
What does a single cell animal cell look like?
The structure of single-celled organisms can only be studied using a microscope. The body of the simplest creatures consists of a single cell that acts as an independent organism.
The cell contains:
- cytoplasm;
- organoids;
- core.
Over time, as a result of adaptation to the environment, certain species of unicellular organisms developed special organelles for movement, excretion and nutrition.
Who are the protozoa?
Modern biology classifies protozoa as a paraphyletic group of animal-like protists. The presence of a nucleus in a cell, unlike bacteria, includes them in the list of eukaryotes.
Cellular structures differ from those of multicellular organisms. In the living system of protozoa, digestive and contractile vacuoles are present; some have organelles similar to the oral cavity and anus.
Protozoan classes
In the modern classification based on characteristics, there is no separate rank and significance of unicellular organisms.
Labyrinthula
They are usually divided into the following types:
- sarcomastigophores;
- apicomplexans;
- myxosporidium;
- ciliates;
- labyrinthula;
- Ascestosporadia.
An outdated classification is considered to be the division of protozoans into flagellates, sarcodes, ciliates and sporozoans.
In what environments do unicellular organisms live?
The habitat of the simplest unicellular organisms is any humid environment. Common amoeba, green euglena and slipper ciliates are typical inhabitants of polluted fresh water sources.
Science has long classified opalines as ciliates, due to the external similarity of flagella to cilia and the presence of two nuclei. As a result of careful research, the relationship was refuted. Sexual reproduction of opalines occurs as a result of copulation, the nuclei are identical, and the ciliary apparatus is absent.
Conclusion
It is impossible to imagine a biological system without single-celled organisms, which are the source of nutrition for other animals.
The simplest organisms contribute to the formation of rocks, serve as indicators of pollution of water bodies, and participate in the carbon cycle. Microorganisms have found widespread use in biotechnology.
Has a long history. It all started approximately 4 billion years ago. The Earth's atmosphere does not yet have an ozone layer, the concentration of oxygen in the air is very low and nothing can be heard on the surface of the planet except erupting volcanoes and the noise of the wind. Scientists believe that this is what our planet looked like when life began to appear on it. It is very difficult to confirm or refute this. Rocks that could provide more information to people were destroyed a long time ago, thanks to the geological processes of the planet. So, the main stages of the evolution of life on Earth.
Evolution of life on Earth. Unicellular organisms.
Life began with the appearance of the simplest forms of life - single-celled organisms. The first unicellular organisms were prokaryotes. These organisms were the first to appear after the Earth became suitable for life. would not allow even the simplest forms of life to appear on its surface and in the atmosphere. This organism did not require oxygen for its existence. The concentration of oxygen in the atmosphere increased, which led to the appearance eukaryotes. For these organisms, oxygen became the main thing for life; in an environment where the oxygen concentration was low, they did not survive.
The first organisms capable of photosynthesis appeared 1 billion years after the appearance of life. These photosynthetic organisms were anaerobic bacteria. Life gradually began to develop and after the content of nitrogenous organic compounds fell, new living organisms appeared that were able to use nitrogen from the Earth’s atmosphere. Such creatures were blue-green algae. The evolution of single-celled organisms took place after terrible events in the life of the planet and all stages of evolution were protected under the earth's magnetic field.
Over time, the simplest organisms began to develop and improve their genetic apparatus and develop methods of reproduction. Then, in the life of single-celled organisms, a transition occurred to the division of their generative cells into male and female.
Evolution of life on Earth. Multicellular organisms.
After the emergence of single-celled organisms, more complex forms of life appeared - multicellular organisms. The evolution of life on planet Earth has acquired more complex organisms, characterized by a more complex structure and complex transitional stages of life.
First stage of life - Colonial unicellular stage. The transition from unicellular organisms to multicellular ones, the structure of organisms and the genetic apparatus becomes more complex. This stage is considered the simplest in the life of multicellular organisms.
Second stage of life - Primary differentiated stage. A more complex stage is characterized by the beginning of the principle of “division of labor” between organisms of one colony. At this stage, specialization of body functions occurred at the tissue, organ and systemic organ levels. Thanks to this, a nervous system began to form in simple multicellular organisms. The system did not yet have a nerve center, but there was a coordination center.
Third stage of life - Centrally differentiated stage. During this stage, the morphophysiological structure of organisms becomes more complex. Improvement of this structure occurs through increased tissue specialization. The nutritional, excretory, generative and other systems of multicellular organisms become more complex. Nervous systems develop a well-defined nerve center. Reproduction methods are improving - from external to internal fertilization.
The conclusion of the third stage of life of multicellular organisms is the appearance of man.
Vegetable world.
The evolutionary tree of the simplest eukaryotes was divided into several branches. Multicellular plants and fungi appeared. Some of these plants could float freely on the surface of the water, while others were attached to the bottom.
Psilophytes- plants that first mastered land. Then other groups of terrestrial plants arose: ferns, mosses and others. These plants reproduced by spores, but preferred an aquatic habitat.
Plants reached great diversity during the Carboniferous period. Plants developed and could reach a height of up to 30 meters. During this period, the first gymnosperms appeared. The most widespread species were lycophytes and cordaites. Cordaites resembled coniferous plants in their trunk shape and had long leaves. After this period, the surface of the Earth was diversified with various plants that reached 30 meters in height. After a lot of time, our planet became similar to the one we know now. Now there is a huge variety of animals and plants on the planet, and man has appeared. Man, as a rational being, after he got “on his feet”, devoted his life to studying. Riddles began to interest people, as well as the most important thing - where did man come from and why does he exist. As you know, there are still no answers to these questions, there are only theories that contradict each other.
1. What structure does a protozoan cell have? Why is it an independent organism?
A protozoan cell performs all the functions of an independent organism: it feeds, moves, breathes, processes food, and reproduces.
In what environments do unicellular organisms live? Why is the presence of water a prerequisite for their existence?
Protozoa live only in an aquatic environment, because they breathe oxygen dissolved in water and can only move in a liquid environment.
What is the function of vacuoles in the body of unicellular organisms?
In the body of unicellular organisms there are digestive and contractile vacuoles. Digestion of food occurs in the digestive vacuole, and the contractile vacuole removes harmful substances and excess water from the cell.
Name the organelles of movement. What are the modes of movement of unicellular organisms?
The amoeba moves with the help of pseudopods, as if flowing. Euglena green moves due to the rotation of the flagellum, and ciliates move due to the oscillatory movements of the cilia.
5. How do protozoa reproduce? Briefly describe these methods.
Representatives of the Phylum Sarcodae and flagellates reproduce asexually.
First, the nucleus is divided in half, and then a constriction is formed, dividing the cell into two full-fledged organisms.
The protozoa of the Ciliates type are characterized by a sexual process in which the number of individuals does not increase.
The sexual method redistributes genetic material between individuals and increases the vitality of organisms.
6. How do protozoa tolerate unfavorable conditions?
When unfavorable conditions occur (low water temperature, drying out of the habitat), the protozoa secrete a protective shell around themselves - a cyst.
In the cyst state, the organism can wait for favorable conditions to arise or, with the help of the wind, be transported to another habitat.
7. Name two or three representatives of protozoa that live in the marine environment. What role do they play in nature?
The marine environment is inhabited by radiolarians and foraminifera.
They participate in the formation of sedimentary rock layers.
8. Name the diseases known to you that are caused by protozoa, and measures to prevent these diseases.
Amoebic dysentery, malaria. To prevent these diseases, you should follow the rules of personal hygiene, thoroughly wash fruits and vegetables before eating, and use mosquito repellents.
Which statements are true?
1.
The protozoan cell acts as an independent organism.
2. Reproduction in the amoeba is asexual, while in the slipper ciliate it is both asexual and sexual.
4. Euglena green is a transitional form from plants to animals: it has chlorophyll, like plants, and feeds heterotrophically and moves like animals.
6.
The small nucleus of ciliates is involved in sexual reproduction, and the large one is responsible for vital functions.
Reproduction, or reproduction, is one of the most important properties of living organisms. Reproduction refers to the ability of organisms to produce others like themselves. In other words, reproduction is the reproduction of genetically similar individuals of a given species. Typically, reproduction is characterized by an increase in the number of individuals in the daughter generation compared to the parent generation.
Reproduction ensures continuity and continuity of life. Thanks to the change of generations, certain species and their populations can exist indefinitely, since the decrease in their numbers due to the natural death of individuals is compensated by the constant reproduction of organisms and the replacement of dead ones by those born.
Species of organisms, being represented by mortal individuals, due to the change of generations not only preserve and transmit to their descendants the main features of their structure and functioning, but also change. Hereditary changes in organisms over a number of generations lead to a change in species or the emergence of new species.
There are usually two main types of reproduction: asexual and sexual.
Sexual reproduction is associated with the formation of germ cells - gametes, their fusion (fertilization), the formation of a zygote and its further development. Asexual reproduction does not involve the formation of gametes.
The forms of reproduction of different organisms can be represented in the following diagram:
- Asexual:
- Unicellular:
- Simple binary fission;
- Multiple fission (schizogony);
- Budding;
- Sporulation;
- Multicellular:
- Vegetative;
- Fragmentation;
- Budding;
- Polyembryony;
- Sporulation;
- Unicellular:
- Sexual:
- Unicellular:
- Multicellular:
- With fertilization;
- No fertilization.
Asexual reproduction.
In asexual reproduction, offspring develop from one mother cell or group of somatic cells (parts of the mother's body).
Asexual reproduction of unicellular organisms. Bacteria and protozoa (amoebas, euglena, ciliates, etc.) reproduce by dividing the cell in two. Bacteria divide by simple binary fission; protozoa - by mitosis. In this case, daughter cells receive an equal amount of genetic information.
Organelles are usually evenly distributed. After division, the daughter cells grow and, having reached the size of the mother’s body, divide again.
Multiple division (schizogony) is characteristic of some algae and protozoa (foraminifera, sporozoans).
With this method of reproduction, multiple divisions of the nucleus are first observed without division of the cytoplasm, and then a small area of cytoplasm is isolated around each of the nuclei, and cell division ends with the formation of many daughter cells.
Budding consists of the formation of a small tubercle containing a daughter nucleus on the mother cell.
The bud grows, reaches the size of the mother and then separates from it. A similar type of reproduction occurs in yeast, sucking ciliates and some bacteria.
Sporulation occurs in algae, protozoa (sporophytes) and some groups of bacteria.
This type of reproduction involves the formation of spores. Spores are special cells that can grow into new organisms. They are usually formed in large numbers as a result of many successive divisions. In bacteria, spores, as a rule, do not serve for reproduction, but only help them survive unfavorable conditions.
Asexual reproduction of multicellular organisms. Vegetative propagation is widespread in plants, in which the beginning of a new organism is given by vegetative organs - roots, stems, leaves, or specialized modified shoots - tubers, bulbs, rhizomes, brood buds, etc.
In the case of fragmentation, new individuals arise from fragments (parts) of the maternal organism. For example, filamentous algae, fungi, some flat (ciliated) and annelid worms can reproduce by fragmentation.
Budding is characteristic of sponges, some coelenterates (hydra) and tunicates (ascidians), in which protrusions (buds) are formed due to the multiplication of a group of cells on the body. The kidney increases in size, then the rudiments of all the structures and organs characteristic of the mother’s body appear.
Then the separation (budding) of the daughter individual occurs, which grows and reaches the size of the mother’s body. If the daughter individuals do not separate from the mother, then colonies (coral polyps) are formed.
In some groups of animals, polyembryony is observed, in which the first divisions during the fragmentation of the zygote are accompanied by the separation of blastomeres, from which independent organisms subsequently develop (from 2 to 8). Polyembryony is common in flatworms (Echinococcus) and in some groups of insects (hoppers).
In this way, identical twins are formed in humans and other mammals (for example, in South American armadillos).
Sporulation is inherent in all spore-bearing plants and fungi. With this method of reproduction, spores are formed from certain cells of the mother’s body as a result of their division (mitosis or meiosis), which, upon germination, can become the ancestors of daughter organisms.
Sexual reproduction.
During sexual reproduction, offspring grow from fertilized cells containing the genetic material of female and male reproductive cells - gametes, fused into a zygote. In this case, the gamete nuclei form one zygote nucleus.
As a result of fertilization, i.e., the fusion of female and male gametes, a diploid zygote is formed with a new combination of hereditary characteristics, which becomes the ancestor of a new organism.
Sexual reproduction of unicellular organisms. The forms of the sexual process are conjugation and copulation.
Conjugation is a peculiar form of the sexual process in which fertilization occurs through the mutual exchange of migrating nuclei moving from one cell to another along a cytoplasmic bridge formed by two individuals.
During conjugation, there is usually no increase in the number of individuals, but an exchange of genetic material between cells occurs, which ensures a recombination of hereditary properties. Conjugation is typical for ciliated protozoa (for example, ciliates).
During conjugation in bacteria, DNA sections are exchanged.
In this case, new properties may arise (for example, resistance to certain antibiotics).
Thus, conjugation in unicellular organisms, although it does not lead to an increase in the number of individuals, causes the appearance of organisms with new combinations of characters and properties.
Copulation is a form of sexual reproduction in which two individuals acquire sexual differences, i.e. turn into gametes and fuse to form a zygote.
In the process of evolution of sexual reproduction, the degree of difference between gametes increases.
At the early stages of the evolution of sexual reproduction, gametes do not differ in appearance from each other. Further complication is associated with the differentiation of gametes into small and large. Finally, in some groups of organisms the large gamete becomes immobile. It is many times larger than small motile gametes. In accordance with these, the following main forms of copulation are distinguished: isogamy, anisogamy and oogamy.
With isogamy, mobile, morphologically identical gametes are formed, but physiologically they differ into “male” and “female” (isogamy occurs in the testicular rhizome of Polystomella).
With anisogamy (heterogamy), mobile, morphologically and physiologically different gametes are formed (this type of reproduction is characteristic of some colonial flagellates).
In the case of oogamy, the gametes are very different from each other. The female gamete is a large immobile egg containing a large supply of nutrients. Male gametes - sperm - are small, most often motile cells that move with the help of one or more flagella (volvox).
Sexual reproduction in multicellular organisms.
During sexual reproduction in animals, only oogamy occurs. All forms of the sexual process occur in algae and fungi. Higher plants are characterized by oogamy. In seed plants, male gametes - sperm - do not have flagella and are delivered to the egg using a pollen tube.
In some algae (for example, Spirogyra), during sexual reproduction, the contents of two vegetative undifferentiated cells merge, physiologically performing the function of gametes.
This sexual process is called conjugation. The zygote formed as a result of the fusion of protoplasts of conjugating cells enters a resting state. Subsequently, during germination of the zygote, reduction division occurs. New individuals are formed from haploid cells. Since many cells of spirogyra organisms arranged in pairs simultaneously conjugate, this process leads to the formation of a large number of descendants.
In multicellular organisms, the most common method of sexual reproduction is fertilization.
As an exception, there is a special form of development of organisms from unfertilized eggs (apomixis in plants and parthenogenesis in animals).
Ministry of Higher and Secondary Education of the Russian Federation
Moscow State University of Food Production
Institute of Economics and Entrepreneurship
Abstract on the topic:
Single-celled organisms as the simplest forms of life
Completed by a student
Groups 06 E-5
Pantyukhina O.S.
Checked by Prof.
Butova S.V.
Moscow 2006
1. Introduction. . . . . . . . . . . .3
2. Protozoa. . . . . . . . . . . 4-5
3. Four main classes of protozoa. . . . .5-7
4. Reproduction is the basis of life. . . . . . . . . 8-9
5. The great role of small protozoa. . . . . 9-11
6. Conclusion. . . . . . . . . . . . .12
Bibliography. . . . . . .13
Introduction
Single-celled organisms perform the same functions as multicellular organisms: they feed, move and reproduce. Their cells must be<<мастером на все руки>> to do all this that other animals do have special organs. Therefore, single-celled animals are so different from the rest that they are separated into separate subkingdoms of protozoa.
Protozoa
To the type of protozoa (Protozoa) includes over 15,000 species of animals living in the seas, fresh waters, and soil.
The body of a protozoan consists of only one cell. The body shape of protozoa is varied.
It can be permanent, have radial, bilateral symmetry (flagellates, ciliates) or not have a permanent shape at all (amoeba). The body sizes of protozoa are usually small - from 2-4 microns to 1.5 mm, although some large individuals reach 5 mm in length, and fossil shell rhizomes had a diameter of 3 cm or more.
The body of protozoa consists of cytoplasm and nucleus.
The cytoplasm is limited by the outer cytoplasmic membrane; it contains organelles - mitochondria, ribosomes, endoplasmic reticulum, and Golgi apparatus.
The simplest have one or several nuclei. The form of nuclear division is mitosis. There is also the sexual process. It involves the formation of a zygote. Organelles of movement of protozoa are flagella, cilia, pseudopods; or there are none at all.
Most protozoa, like all other representatives of the animal kingdom, are heterotrophic. However, among them there are also autotrophic ones.
The peculiarity of protozoa to tolerate unfavorable environmental conditions is their ability incistidy up , i.e.
form cyst . When a cyst is formed, the movement organelles disappear, the volume of the animal decreases, it acquires a rounded shape, and the cell is covered with a dense membrane. The animal goes into a state of rest and, when favorable conditions occur, returns to active life.
The reproduction of protozoa is very diverse, from simple division (asexual reproduction) to a rather complex sexual process - conjugation and copulation.
The habitat of protozoa is varied - the sea, fresh water, moist soil.
Four main classes of protozoa
1 – flagella (Flagellata, or Mastigophora);
2 – sarcodaceae (Sarcodina, or Rhizopoda);
3 – sporozoa (Sporozoa);
4 – ciliates (Infusoria, or Ciliata).
1. About 1000 species, mainly with an elongated oval or pear-shaped body, make up the class of flagellates (Flagellata or Mastigophora). The organelles of movement are flagella, of which different representatives of the class can have from 1 to 8 or more.
Flagellum- a thin cytoplasmic outgrowth consisting of the finest fibrils. Its base is attached to basal body or kinetoplast . Flagellates move forward with a cord, creating vortex whirlpools with their movement and, as it were, “screwing in” the animal
into the surrounding liquid environment.
Way nutrition : Flagellates are divided into those that have chlorophyll and feed autotrophically, and those that do not have chlorophyll and feed, like other animals, heterotrophically.
Heterotrophs on the front side of the body have a special depression - cytostome , through which, when the flagellum moves, food is driven into the digestive vacuole.
A number of flagellate forms feed osmotically, absorbing dissolved organic substances from the environment over the entire surface of the body.
Methods reproduction : Reproduction most often occurs by dividing in two: usually one individual gives rise to two daughters. Sometimes reproduction occurs very quickly, with the formation of countless individuals (nightlight).
2. Representatives of the class of sarcodes, or rhizomes ( Sarcodina or Rhizopoda), move with the help of pseudopods - pseudo-similarities.
The class includes a variety of aquatic unicellular organisms: amoebae, sunfish, and rayfish.
Among amoebas, in addition to forms that do not have a skeleton or shell, there are species that have a house.
Most sarcodae are inhabitants of the seas; there are also freshwater ones that live in the soil.
Sarcodidae are characterized by an inconsistent body shape. Breathing is carried out over its entire surface. Nutrition is heterotrophic. Reproduction is asexual; there is also a sexual process.
Fever, anemia, and jaundice are typical signs of sporozoan disease. Piroplasma, Babesia belong to the order of blood sporozoans, affecting the red blood cells of mammals (cows, horses, dogs and other domestic animals). Disease carriers are ticks. In addition to the blood ones, there are two more orders of sporozoans - the occidia and gregarines .
in vertebrates - mammals, fish, birds.
Coccidia toxoplasmosis causes the human disease toxoplasmosis. It can be contracted from any member of the cat family.
Representatives of the ciliate class ( Infusorians or Ciliata) have organelles of movement - cilia, usually in large numbers.
So, at the shoe ( Parameciumcaudatum) the number of cilia is more than 2000. Cilia (like flagella) are special complex cytoplasmic projections.
The body of ciliates is covered with a membrane permeated with tiny pores through which cilia emerge.
The type of ciliates includes the most highly organized protozoa. They are the pinnacle of the achievements made by evolution in this sub-realm. Ciliates lead a free-swimming or attached lifestyle.
They live like
All ciliates have at least two nuclei.
The large core regulates all life processes. The small nucleus plays a major role in the sexual process.
Ciliates reproduce by division (across the axis of the body). In addition, they periodically undergo sexual intercourse - conjugation . Ciliate “ shoe” is shared daily, some others - several times a day, and “ trumpeter" - once
in a few days.
Food enters the animal’s body through the cellular “mouth”, where it is driven by the movement of the cilia; are formed at the bottom of the pharynx digestive vacuoles .
Undigested residues are excreted.
Many ciliates feed only on bacteria, while others are predators. For example, the most dangerous enemies “ shoes” – didinia ciliates. They are smaller than her, but, attacking in twos or fours, they surround her from all sides.” shoe” and kill her by throwing a special “ stick ”.
Some didinia eat up to 12 “shoes” per day.
Organelles of secretion of ciliates are two contractile vacuoles; in 30 minutes they remove from the ciliate an amount of water equal to the volume of its entire body.
Reproduction is the basis of life
Asexual reproduction - cell division: Most often found in protozoa asexual reproduction.
It occurs through cell division. First the nucleus divides. The development program of an organism is located in the cell nucleus in the form of a set of DNA molecules. Therefore, even before cell division, the nucleus doubles so that each of the daughter cells receives its own copy of the hereditary text.
Unicellular organisms
Then the cell divides into two approximately equal parts. Each of the descendants receives only half of the cytoplasm with organelles, but a complete copy of the maternal DNA and, using the instructions, builds itself into a whole cell.
Asexual reproduction is a simple and quick way to increase the number of your offspring.
This method of reproduction is essentially no different from cell division during the growth of the body of a multicellular organism. The whole difference is that the daughter cells of unicellular organisms eventually disperse as independent organisms.
During cell division, the parent individual does not disappear, but simply turns into two twin individuals. This means that with asexual reproduction, an organism can live forever, repeating itself exactly in its descendants. Indeed, scientists managed to preserve a culture of protozoa with the same hereditary properties for several decades.
But, firstly, in nature the number of animals is strictly limited by food supplies, so that only a few descendants survive. Secondly, absolutely identical organisms may soon turn out to be equally unadapted to changing conditions and all will die.
The sexual process helps to avoid this catastrophe.
Unicellular organisms
Unicellular organisms are organisms whose body consists of only one cell with a nucleus. They combine the properties of a cell and an independent organism.
Unicellular plants
Single-celled plants are the most common algae. Single-celled algae live in fresh water bodies, seas, and soil.
The globular unicellular alga Chlorella is widespread in nature. It is protected by a dense shell, under which there is a membrane.
The cytoplasm contains a nucleus and one chloroplast, which in algae is called a chromatophore. It contains chlorophyll. Organic substances are formed in the chromatophore under the influence of solar energy, as in the chloroplasts of land plants.
The globular algae Chlorococcus (“green ball”) is similar to chlorella.
Some types of chlorococcus also live on land. They give the trunks of old trees growing in humid conditions a greenish color.
Among unicellular algae there are also mobile forms, for example Chlamydomonas. The organ of its movement is flagella - thin outgrowths of the cytoplasm.
Unicellular fungi
Packs of yeast sold in stores are compressed single-celled yeast fungi.
What are single-celled organisms?
A yeast cell has the typical structure of a fungal cell.
The single-celled late blight fungus infects living leaves and tubers of potatoes, leaves and fruits of tomatoes.
Unicellular animals
Like single-celled plants and fungi, there are animals in which the functions of the whole organism are performed by one cell. Scientists have united all single-celled animals into a large group - protozoa.
Despite the diversity of organisms in this group, their structure is based on one animal cell.
Since it does not contain chloroplasts, protozoa are not able to produce organic substances, but consume them in finished form. They feed on bacteria. single-celled algae, pieces of decomposing organisms.
Among them there are many causative agents of serious diseases in humans and animals (dysenteric amoeba, Giardia, malarial plasmodium).
Protozoa that are widespread in fresh water bodies include the amoeba and the slipper ciliate. Their body consists of cytoplasm and one (amoeba) or two (slipper ciliates) nuclei. Digestive vacuoles are formed in the cytoplasm, where food is digested.
Excess water and metabolic products are removed through contractile vacuoles. The outside of the body is covered with a permeable membrane.
Oxygen and water enter through it, and various substances are released. Most protozoa have special organs of movement - flagella or cilia. The slipper ciliates cover their entire body with cilia; there are 10-15 thousand of them.
The movement of the amoeba occurs with the help of pseudopods - protrusions of the body.
The presence of special organelles (organs of movement, contractile and digestive vacuoles) allows protozoan cells to perform the functions of a living organism.
Protozoan habitat
Protozoa live in a wide variety of environmental conditions. Most of them are aquatic organisms, widespread in both fresh and marine waters.
Many species live in the bottom layers and are part of the benthos. Of great interest is the adaptation of protozoa to life in the thickness of sand and in the water column (plankton).
A small number of Protozoa species have adapted to life in soil. Their habitat is the thinnest films of water surrounding soil particles and filling capillary gaps in the soil.
It is interesting to note that even in the sands of the Karakum desert protozoa live. The fact is that under the topmost layer of sand there is a wet layer saturated with water, whose composition is close to sea water.
In this wet layer, living protozoa from the order of foraminifera were discovered, which are apparently the remains of the marine fauna that inhabited the seas that were previously located on the site of the modern desert. This unique relict fauna in the Karakum sands was first discovered by Prof.
L. L. Brodsky when studying water taken from desert wells.
Habitats of the simplest single-celled organisms
Acanthamoeba. Photo: Yasser
The microscopic world has its own herbivores and predators. The former feed on organic remains and plant organisms, the latter sometimes passively, and sometimes actively hunt bacteria and even their own kind - other protozoa.
Predators are usually quite mobile, they move quickly with the help of flagella - one or several cilia covering the body or growing pseudopods.
In any living environment, animals occupy areas that are most favorable for their existence. A specific area of the living environment inhabited by certain animals is called the habitat of these animals.
A variety of protozoa are found in activated sludge: sarcodaceae, flagellates, ciliated ciliates, sucking ciliates and others.
Single-celled animals are usually microscopic in size.
Their body consists of one cell. It is based on cytoplasm with one or several nuclei. They live in bodies of water (from puddles to oceans), in moist soil, in the organs of plants, animals and humans.
The habitat of the ciliate slipper is any freshwater body of water with stagnant water and the presence of decomposing organic substances in the water.
It can even be detected in an aquarium by taking samples of water with sludge and examining them under a microscope.
Can such tiny creatures as protozoa seriously influence the life of our planet? Here's a small example. Throughout the history of the Earth, countless tiny single-celled creatures have been born and died in its oceans.
After death, their microscopic mineral skeletons sank to the bottom. Over tens of millions of years, they layered, forming thick deposits - chalk, limestone. If we look at ordinary chalk under a microscope, we will see that it consists of many protozoan shells.
Marine protozoa - radiolarians and especially foraminifera - played an important role in the formation of sedimentary rocks. Many limestones, chalk deposits and other sedimentary rocks that formed on the bottom of sea reservoirs in various geological periods are formed entirely or partially by the skeletons (calcareous or flint) of fossil protozoa.
In this regard, micropaleontological analysis is used in geological exploration work, mainly in oil exploration.
Organisms whose body contains only one cell are classified as protozoa. They can have different shapes and all kinds of methods of movement. Everyone knows at least one name that the simplest living organism has, but not everyone realizes that it is exactly such a creature. So, what are they, and what types are the most common? And what kind of creatures are these? Like the most complex and coelenterate organisms, unicellular organisms deserve detailed study.
Subkingdom of unicellular organisms
Protozoa are the smallest creatures. Their bodies have all the functions necessary for life. Thus, the simplest single-celled organisms are capable of showing irritability, moving and reproducing. Some have a constant body shape, while others constantly change it. The main component of the body is the nucleus surrounded by cytoplasm. It contains several types of organelles. The first are general cellular. These include ribosomes, mitochondria, the Galgi apparatus, and the like. The second ones are special. These include digestive and almost all protozoan single-celled organisms can move without much difficulty. In this they are helped by pseudopods, flagella or cilia. A distinctive feature of organisms is phagocytosis - the ability to capture solid particles and digest them. Some can also carry out photosynthesis.
How do unicellular organisms spread?
Protozoa can be found everywhere - in fresh water, soil or sea. Their ability to encyst provides them with a high degree of survival. This means that under unfavorable conditions the body enters a resting stage, becoming covered with a dense protective shell. The creation of a cyst promotes not only survival, but also proliferation - this way the organism can find itself in a more comfortable environment where it will receive nutrition and the opportunity to reproduce. Protozoan organisms accomplish the latter by dividing into two new cells. Some also have the ability to reproduce sexually, and there are species that combine both.
Amoeba
It is worth listing the most common organisms. Protozoa are often associated with this particular species - amoebas. They do not have a permanent body shape, and use pseudopods for movement. With them, the amoeba captures food - algae, bacteria or other protozoa. Surrounding it with pseudopods, the body forms a digestive vacuole. From it, all substances obtained enter the cytoplasm, and undigested substances are thrown out. The amoeba carries out respiration throughout the body using diffusion. Excess water is removed from the body by the contractile vacuole. The process of reproduction occurs through nuclear division, after which two cells are obtained from one cell. Amoebas are freshwater. Protozoa are found in humans and animals, in which case they can lead to a variety of diseases or worsen the general condition.
Euglena green
Another organism common in fresh water bodies is also a protozoa. Euglena green has a spindle-shaped body with a dense outer layer of cytoplasm. The anterior end of the body ends with a long flagellum, with the help of which the body moves. In the cytoplasm there are several oval chromatophores in which chlorophyll is located. This means that in the light, euglena feeds autotrophically - not all organisms can do this. Protozoa navigate with the help of an eye. If the euglena stays in the dark for a long time, the chlorophyll will disappear and the body will switch to a heterotrophic method of nutrition with the absorption of organic substances from the water. Like amoebas, these protozoa reproduce by division and also breathe throughout the body.
Volvox
Among unicellular organisms there are also colonial organisms. A protozoan called volvox lives this way. They have a spherical shape and gelatinous bodies formed by individual members of the colony. Each Volvox has two flagella. The coordinated movement of all cells ensures movement in space. Some of them are capable of reproduction. This is how daughter Volvox colonies arise. The simplest algae known as Chlamydomonas also have the same structure.
Ciliate slipper
This is another common inhabitant of fresh water. The ciliates get their name from the shape of their own cell, which resembles a shoe. The organelles used for movement are called cilia. The body has a constant shape with a dense shell and two cores, small and large. The first is necessary for reproduction, and the second controls all life processes. Ciliates use bacteria, algae and other single-celled organisms as food. Protozoa often create a digestive vacuole; in slippers it is located in a specific place near the mouth opening. To remove undigested residues, powder is present, and excretion is carried out using a contractile vacuole. This is typical for ciliates, but it can also be accompanied by the union of two individuals to exchange nuclear material. This process is called conjugation. Among all freshwater protozoa, the slipper ciliate is the most complex in its structure.
