The emergence of unicellular. The simplest unicellular. Methods and methodological techniques

1. Introduction…………………………………………………………………….2

2. The evolution of life on earth……………………………………………………3

2.1. The evolution of unicellular organisms…………………………………3

2.2. Evolution of multicellular organisms……………………………..6

2.3. The evolution of the plant world……………………….……………….8

2.4. The evolution of the animal world…………………………………………...10

2.5 Evolution of the biosphere……………………………………..……….…….12

3. Conclusion………………………………………………………………….18

4. References………………………………………………………….19

Introduction.

It often seems that organisms are entirely at the mercy of the environment: the environment sets limits for them, and within these limits they must either succeed or perish. But organisms themselves influence the 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 appearance of an oxidizing atmosphere, thus preparing the conditions for the emergence and evolution of the respiration process.

The presence of oxygen in the atmosphere caused 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 traps ultraviolet radiation that is harmful to proteins and nucleic acids and prevents it from reaching the Earth's surface.

The first organisms lived in water, and the water shielded them by absorbing ultraviolet radiation energy. The first settlers of the land found sunshine and minerals in abundance here, so that in the beginning they were practically free from competition. Trees and grasses, which soon covered the vegetative part of the earth's surface, replenished the supply of oxygen in the atmosphere, in addition, they changed the nature of the water flow on the Earth and accelerated the formation of soils from rocks. A giant step towards the evolution of life was associated with the emergence of the main biochemical metabolic processes - photosynthesis and respiration, as well as with the formation of a eukaryotic cellular organization containing a nuclear apparatus.

The evolution of life on earth.

2.1 Evolution of unicellular organisms.

The earliest of bacteria (prokaryotes) already existed about 3.5 billion years ago. To date, two families of bacteria have survived: ancient, or archaebacteria (halophilic, methane, thermophilic), and eubacteria (all the rest). Thus, the only living beings on Earth for 3 billion years were primitive microorganisms. Perhaps they were single-celled creatures similar to modern bacteria, such as Clostridium, 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, not their producers.

A giant step towards the evolution of life was associated with the emergence of the main 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 largely survived in modern organisms. The methods of molecular biology have established the striking uniformity of the biochemical foundations of life, with a huge difference in other organisms. The proteins of almost all living things are made up of 20 amino acids. Nucleic acids encoding proteins are assembled from four nucleotides. Protein biosynthesis is carried out according to a uniform scheme, the place of their synthesis is ribosomes, it involves i-RNA and t-RNA. 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 anoxic environment and in an environment with different oxygen content, while eukaryotes, with a few exceptions, require oxygen. All these differences were important 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 about 3 billion years ago. These were anaerobic bacteria, precursors of modern photosynthetic bacteria. It is assumed that they formed the most ancient environments of known stromatolites. The combination of the environment with nitrogenous organic compounds caused the appearance of living beings capable of using atmospheric nitrogen. Such organisms that can exist 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 primary unicellular organisms had three consequences that had a decisive influence on the entire further evolution of living things. First, photosynthesis freed organisms from competition for natural reserves of abiogenic organic compounds, the amount of which in the environment has been significantly reduced. Autotrophic nutrition, which developed through photosynthesis, and the storage of ready-made nutrients in plant tissues then created the conditions for the emergence of an enormous 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 the processes of respiration. Thirdly, as a result of photosynthesis, an ozone screen was formed in the upper part of the atmosphere, protecting terrestrial 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. Probably, anaerobic fermentation appeared at an earlier stage of evolution. After the appearance of a sufficient amount of free oxygen in the atmosphere, aerobic metabolism turned out to be much more profitable, since the oxidation of carbon increases the yield of biologically useful energy by 18 times compared to fermentation. Thus, an aerobic way of extracting energy by unicellular organisms joined the anaerobic metabolism.

It is not known exactly when eukaryotic cells appeared, according to research, we can say that their age is about 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 - agamous arakaryoginaya - is represented by cyanide and bacteria. The morphology of these organisms is the simplest in comparison with other unicellular organisms. However, already at this stage, differentiation into the cytoplasm, nuclear elements, basal grains, and the cytoplasmic membrane appears. In bacteria, the exchange of genetic material through conjugation is known. A wide variety of bacterial species, the ability to exist in the most different conditions environments testify to the high adaptability of their organization.

The next stage - agamic eukaryogic - 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 true chromosomes in comparison with prokaryotes, in which the hereditary substance is diffusely distributed throughout the cell. This stage is typical for 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), the appearance of generative and vegetative nuclei - the macronucleus (nuclear dualism). Among unicellular eukaryotic organisms, there are many species with agamous reproduction (naked amoeba, testate rhizomes, flagellates).

A progressive phenomenon in the phylogeny of protozoa was the emergence of sexual reproduction (gamogony) in them, which differs from ordinary conjugation. Protozoa have meiosis with two divisions and crossing over at the level of chromatids, 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, there is a transition from isogamy to anisogamy, or the division of generative cells into female and male, and to anisogamous copulation. The fusion of gametes produces a diploid zygote. Consequently, in protozoa, there has been a transition from the agamous eukaritic stage to the zygotic stage - the initial stage of xenogamy (reproduction by cross-fertilization). The subsequent development of already multicellular organisms followed the path of improving the methods of xenogamous reproduction.

Instruction

More than 3.5 billion years ago, the first living organisms appeared in the depths of the sea, consisting of a single cell. Some believe that single-celled spores could have ended up on Earth with the help of meteorites that came from outer space. Most scientists associate the origin of life with what is happening in the atmosphere and oceans. chemical reactions.

The body, consisting of only one cell, is a holistic organism with microscopic dimensions, but in the protozoan classes there are species that reach lengths of several millimeters and even centimeters. Among these organisms, separate classes are distinguished, characterized by certain characteristics.

Amoeba is a colorless lump that constantly changes shape and lives in fresh water. The prolegs help this organism, which lives in the silt and on the leaves of rotting plants, to quietly flow to another place. Amoebas feed on algae and bacteria, and they multiply by dividing into two parts.

The structure of other representatives of the simplest - ciliates is more complicated. The cell of these organisms contains two nuclei that perform different functions, and the cilia they have are a means of transportation.

Resembling elegant women's shoes, the ciliate shoe has a constant body shape and lives in shallow stagnant water. Numerous cilia arranged in regular rows fluctuate in waves, and the shoe moves. The infusoria feeds on bacteria, unicellular algae, dead organic matter (detritus). The cilia help food to enter the mouth, which then moves to the pharynx. The slipper is voracious if it lives in favorable conditions. At asexual reproduction the body of the ciliates is divided in half in the transverse direction, and the daughter individuals begin to develop anew. But after a few generations, such reproduction will be replaced by a sexual process called conjugation.

The body of representatives of the flagellate class, covered with an elastic membrane, determines its shape. These protozoa have one or more flagella and nuclei. Reproduction depends on the type of unicellular organism.

Euglena green lives in stagnant fresh water. She swims quickly, thanks to the streamlined shape of her body. The only flagellum located in front, screwed into the water, contributes to the movement. This simplest organism feeds in a special way, which helps it survive under different conditions of existence. The most illuminated areas, where the euglena body containing chlorophyll is arranged for favorable photosynthesis, are found by it with the help of a light-sensitive red eye. If euglena stays in the dark for a long time, chlorophyll is destroyed. In such cases, organic matter serves as a means of nutrition. Propagated by cell division in the longitudinal direction into two parts. If conditions are favorable, this single-celled creature is able to multiply every day.

A mysterious group of microscopic single-celled organisms, considered as a sub-kingdom of the Animal kingdom, and sometimes separated into a separate kingdom.

The simplest unicellular

For the first time, people learned about the existence of protozoa in the 7th century from the discovery of a Dutch naturalist, it was he who was the first to be honored to observe them in a drop of water, in a microscope he invented.

Over many years of development of biology, with the advent of electron microscopy and genetics, this group of organisms has been increasingly studied and its taxonomy has undergone significant changes.

Today they are increasingly defined in a separate kingdom, since among the simplest unicellular organisms there are organisms that have features that are different from those of animals. For example, Euglena green has the ability to photosynthesis, which is characteristic of plants. Or, for example, the type of Labyrinthula - used to be attributed to mushrooms.

The cell of the simplest unicellular organism has an organization common to eukaryotic cells. But also most protozoa have specific organelles:

• contractile vacuoles, which serve to remove excess fluid and maintain the desired osmotic pressure;
• various organelles of movement: flagella, cilia and pseudopodia (pseudopodia). Prolegs, as the name implies, are not real organelles, they are just protrusions of the cell.

Sub-kingdom (or realm) The simplest unicellular represented by 7 main types:

Let's look at the types in more detail.

Type Sarcomastigophora

It is divided into three subtypes: Flagella, Opalina, Sarcod.

Flagella- a group of organisms, as the name implies, they are characterized by common organelles of movement - flagella.

Habitats: fresh waters, seas, soils. There are flagella that live in multicellular organisms. Flagella are characterized by the preservation of a constant body shape, thanks to the pellicle, or shell.

They reproduce mainly asexually: by longitudinal division in two.

Types of nutrition heterotrophic, autotrophic, mixotrophic.

Let's look at the structure with an example Euglena green.

• It is characterized by a mixotrophic (mixed) type of nutrition.
• There are special organelles - chlorophyll-containing chromatophores, in which the process of photosynthesis takes place, similar to the photosynthesis of plants.
• In connection with the ability to photosynthesis, Euglena green has a light-sensitive organelle - stigma, it is also sometimes called a light-sensitive eye.
• The removal of excess fluid occurs due to the work of the contractile vacuole.

Some types of trypanosomes cause sleeping sickness. The carrier of African trypanosomiasis (as this disease is scientifically called) is the tsetse fly. This is a blood-sucking insect.

Trypanosomes. They swim and cause a dangerous disease.

Giardia. Looks like a pear. Mnemonic rule: giardia is in the form of a pear, therefore, in order not to get infected, it is necessary to wash the pear.

Sarcodes are protozoans that do not have a permanent body shape.

The organelles of movement are pseudopodia (pseudopodia). Previously, sarcodes and flagellates were classified as two different types, contrasting them with organelles of movement: pseudopodia and flagella. But it turned out that at some stages of development, sarcodes have flagella, and some organisms have signs of both flagella and sarcodes.

The Sarcode subtype includes the classes: Rhizomes, Radiolarians (Raybeams), Solnechniki.

Rhizomes. This class includes the orders: Amoeba, testate amoeba, foraminifera.

• Amoebas feed by phagocytosis. A digestive vacuole forms around the captured piece of food.
• They reproduce by division in two.
• If Euglena green moves towards the light (since she needs it for photosynthesis), then Amoeba vulgaris, on the contrary, moves away from the light. The amoeba also avoids other stimuli.

Usually, such an experiment is considered: a salt crystal is placed in a drop of water with an amoeba on one side, and the movement of the amoeba in the opposite direction can be observed.

testate amoeba. They have a similar structure with amoeba, only they have a shell, with a hole (mouth) from which pseudopodia “look out”. All testate amoebae are free-living, living in fresh waters. Since the shell cannot split in two, division occurs in a special way: a daughter individual is formed, but it does not immediately separate from the mother. A new shell forms around the daughter. Then the amoeba separates.

Foraminifera are one of the most numerous orders of the simplest unicellular - rhizopods. They are part of the marine plankton. Foraminifera, like testate amoebae, have a shell.

radiolarians very interesting microorganisms that are part of marine plankton. They are characterized by the presence of an internal skeleton. Radiolarians have the largest number of chromosomes of all living things.

Radiolarians, Foraminifera, and testate amoebae leave behind shells and internal skeletons when they die. The accumulation of all this goodness forms deposits of limestone, chalk, quartz and other things.

sunflowers - small group of protozoa. They got their name because of the similarity appearance pseudopodia with rays of the sun. Such pseudopodia are called axopodia.

Type of Infusoria

Characteristics:

• permanent body shape, due to the presence of pellicle;
• some ciliates are characterized by specific protective organelles;
• nuclear dualism, i.e. the presence of two nuclei: a polyploid macronucleus ( vegetative nucleus) and diploid micronucleus (generative nucleus). Such a situation with the nuclei is necessary for the implementation of the sexual process: . And directly reproduction is only asexual: by longitudinal division in two.
• The organelles of locomotion are cilia. The structure of the cilia is the same as that of the flagella.

We will consider the structure using the example of ciliates-shoes. This is a classic, you need to know this.

Infusoria-shoe is a predator. It feeds on bacteria. The prey is captured by specialized cilia and directed to the cellular mouth, followed by the cellular pharynx, then the digestive vacuole. Undigested residues are thrown out through the powder into the external environment.

AT digestive system ruminants are inhabited by symbiotic ciliates that help digest fiber:

Infusoria-trumpeter

Suvoyki - ciliates leading an attached lifestyle.

Type Apicomplexes

For example, the protozoa of the genus Plasmodium cause dangerous disease- malaria.

Labyrinth type

Protozoa are single-celled free-living colonial protozoa that live on seaweed. Previously referred to as mushrooms. This name was given because the colony really resembles a labyrinth.

Type of Ascetosporidia

Type of Myxosporidium

Type of microsporidia

So, we examined the types of the kingdom (sub-kingdom) of the simplest unicellular organisms. To consolidate all knowledge, let's look at the systematics:

Despite their small size, the simplest unicellular are of great importance:

• protozoa enter food chains;
• form plankton;
• perform the role of saprophytes, absorbing decaying remains;
• protozoa clean water bodies not only from decaying residues, but also from bacteria;
• participate in the formation of soils and deposits of chalk and limestone.
• are good indicators of water purity.
• autotrophic and mixotrophic protozoa, together with plants, perform a very important mission - replenishing the atmosphere with oxygen.

Topic 2. SINGLE-CELLULAR ORGANISMS. TRANSITION TO WEALTH

§fifteen. SINGLE-CELLULAR EUKARYOTES

We will talk about microorganisms, the body of which is only one cell, but this cell, unlike bacteria, has a nucleus.

Euglena green - is it an animal or a plant? What small organisms and algae are important for our life?

K ey car io t includes most of the species that inhabit our planet and differ from bacteria in that their cells have a nucleus.

The eukaryotic nucleus contains DNA molecules organized into chromosomes. characteristic feature eukaryotes is the presence of mitochondria. The eukaryotes that are capable of photosynthesis are the chloroplasts. The cytoplasm of eukaryotic cells contains most of the other organelles, including lysosomes and various vacuoles.

Eukaryotes can be either single-celled or rich-celled. Examples of eukaryotes are all those animals, fungi, plants that you see without the use of magnifying devices.

Unicellular eukaryotes are organisms consisting of a single eukaryotic cell, which often does not look at all like the cells of multicellular plants, animals or fungi. Although all multicellular eukaryotes and descended from unicellular organisms.

Sometimes multicellular eukaryotes, adapting to special environmental conditions, "returned" to a unicellular structure. An example of such organisms are unicellular fungi known to every housewife - ordinary baker's yeast ( rice. 39, f, g). More than 100 thousand species of unicellular eukaryotes are now known.

Single-celled eukaryotic organisms differ significantly in their feeding habits. Part of unicellular eukaryotes feeds heterotrophically, the other part - autotrophically. In heterotrophic unicellular eukaryotes, animal and fungal ways of absorbing organic substances are distinguished. In the animal form, the cell captures solid particles of food, and then digests them in the cytoplasm, often in special organelles - digestive vacuoles. With the fungal method, cells can only absorb dissolved organic substances, absorbing them with their entire surface. Autotrophic nutrition in unicellular eukaryotes occurs solely due to photosynthesis.

Creature-like and growth-like unicellular eukaryotes. Single-celled eukaryotes with an animal mode of nutrition are called single-celled animal-like organisms. unicellular eukaryotes with vegetable method nutrition is one cell algae. In addition, many unicellular eukaryotes (both critter-like and dew-like) are capable of absorbing nutrients mushroom method - by absorption by the entire surface of the cell.

SINGLE-CELLULAR EUKARYOTES

Mol. 39. Examples of unicellular aukaryotes; a-amoeba; b - and nfusoria; in - collar flagella; g-diatoms; d - eugleno algae; there is - unicellular green algae; e, g-single-celled fungi - yeast

For example, the unicellular algae Euglena (Fig. 39, e), which is sometimes mistakenly called "on the pіvtvarinoyu-napіvroslinoy", has green chloroplasts, and in the presence of light it feeds due to photosynthesis. If there are a lot of dissolved organic substances in the water, but there is no light, euglena switches to a heterotrophic (mushroom) type of nutrition, and can even become colorless. Euglena absorbs only dissolved organic substances, absorbing them with the entire surface of the cell. Before the capture and digestion of solid particles of food, that is, before animal nutrition, euglena is not capable. On the other hand, amoeba and some ciliates(rice. 39, a, b), which belong to animal-like unicellular organisms that absorb organic matter both in an animal and fungal way, but due to the absence of chloroplasts, they cannot eat like plants.

In nature, unicellular creature-like organisms and algae serve as food for many animals, especially those that live in water. Modern representatives of the world of unicellular eukaryotes play an important role in the processes of self-purification of water bodies, and the remains of fossil unicellular creature-like organisms and algae are used by geologists to determine the age of sedimentary rocks and in the search for mineral deposits, in particular oil.

FINDINGS

1. Eukaryotic cells have a much more complex structure than prokaryotes. The main feature of eukaryotes is the presence of a nucleus.

2. Eukaryotic organisms can be both single-celled and rich-celled.

3. Unicellular eukaryotes are characterized by different ways nutrition - animal, mushroom, vegetable and their various combinations.

4. Unicellular eukaryotes with an animal mode of nutrition are called unicellular creature-like organisms, with a plant - unicellular algae.

TERMS AND CONCEPTS TO LEARN

Eukaryotes, unicellular eukaryotes, unicellular creature-like organisms, unicellular algae.

TEST QUESTIONS

1. How do unicellular eukaryotes differ from bacteria and cyanoprokaryotes?

2. What methods of nutrition are inherent in unicellular eukaryotes?

3. What is the difference between unicellular creature-like organisms and unicellular algae?

4. Often in the literature you can find the statement that euglena in the dark eats like an animal. Is this statement completely correct?

FOR INQUIRY

Why are unicellular eukaryotes famous?

(The answer to the question of schoolchildren: Why does the sea glow? What do algae and unicellular creature-like organisms give us and do we need them?)

Breeding in in large numbers, unicellular eukaryotes are able to cause some phenomena, known to man since ancient times and are described in legends. These include "blood rains" and "bloody snow" caused by the single-celled algae hematococcus, a dangerous toxic "bloom" of water in the seas and oceans, known as "red tides" - it is caused by distant relatives of ciliates - dinoflagellates, green and red " flowering" of the bark of trees - phenomena due to the massive development of green algae related to chlorella. At night in the summer you can watch how a silvery-blue stripe of light stretches in the sea behind a boat or a fin; it is usually unicellular nightlights that glow.

At the treatment facilities, the army of relatives of ciliates, amoebas and euglena tirelessly removes organic matter from the water and lays out in their cells the shares of organic matter, thereby ensuring the process of self-purification of polluted waters.

The remains of dead single-celled eukaryotes that lived in the ocean ten million years ago formed many different sedimentary rocks that humans use. For example, ordinary school chalk is the remains of foraminifera shells and cocolithophorid scales.(Fig. 40).

Rice. 40. Rocks formed by fossil unicellular eukaryotes. Chalk (a) and its composition (remains of foraminifera and cocolithophorids (b); modern cococolithophoride with limestone cocolites (c) from which chalk was formed)

Topic: "SINGLE-CELLULAR ORGANISMS: PROKARYOTES AND EUKARYOTES"

Lesson 1 : The structure of eukaryotic cells.

The purpose of the lesson: to give students a general idea of ​​the structure of eukaryotic cells, the features of their functions in connection with the structure.

Equipment and materials: diagram of the structure of a eukaryotic cell; photographs of organelles taken under a light and electron microscope.

Basic concepts and t terms:

Lesson concept: show the structure of eukaryotic cells (later, in comparison, give information about simpler prokaryotic cells). When talking about eukaryotes, use the knowledge already available to schoolchildren. Based on knowledge about eukaryotic cells, give (in comparison) information about simpler prokaryotic cells. To tell about prokaryotes in more detail due to the fact that schoolchildren still do not have much information about these organisms.

STRUCTURE AND CONTENT OF THE LESSON:

I. Update basic knowledge and motivation of educational activity:

What organelles are characteristic of plant cells?

What organelles are characteristic of animal cells?

What are the functions of chloroplasts?

What do you know about mitochondria?

What is a cell wall for? What cells have it?

II. STUDY NEW MATERIAL

Introduction by the teacher.

PROKARYOTES.

Depending on the level of organization of the cell, organisms are divided into prokaryotes and eukaryotes.

Prokaryotes (from lat. pro- before, instead of and Greek. karyon - core) - the super-kingdom of organisms, which includes the kingdoms of Bacteria and Cyanobacteria (the obsolete name is "blue-green algae").

Prokaryotic cells are characterized by a simple structure: they do not have a nucleus and many organelles (mitochondria, plastids, endoplasmic reticulum, Golgi complex, lysosomes, cell center). Only some bacteria - inhabitants of reservoirs or soil capillaries filled with water - have special gas vacuoles. By changing the volume of gases in them, these bacteria can move in the aquatic environment with minimal energy consumption. The composition of the surface apparatus of prokaryotic cells includes plasma membrane, cell wall, sometimes - mucous capsule.

(Fig. 1).

In the cytoplasm of prokaryotes there are ribosomes, various inclusions, one or more nuclear zones (nucleoids) containing hereditary material. hereditary material A prokaryote is a circular DNA molecule attached at a specific location to the inner surface of the plasma membrane. (Fig. 1).

Ribosomes prokaryotes are similar in structure to ribosomes located in the cytoplasm and on the membranes of the endoplasmic reticulum of eukaryotic cells, but differ in smaller sizes. plasma membrane prokaryotic cells can form smooth or folded protrusions directed into the cytoplasm. Enzymes, ribosomes can be located on folded membrane formations, and photosynthetic pigments can be located on smooth ones. Rounded closed membrane structures were found in cyanobacteria cells - chromatophores, where photosynthetic pigments are located.

The cells of some bacteria have organelles of movement one, several or many flagella. The flagella of prokaryotes consist of a single molecule of a specific protein that has a tubular structure. Flagella can be several times longer than the cell itself, but their diameter is insignificant (10-25 nm), so they are not visible in a light microscope. In addition to flagella, the surface of bacterial cells often has filamentous and tubular formations consisting of proteins or polysaccharides. They provide attachment of the cell to the substrate or take part in the transfer of hereditary information during the sexual process.

Prokaryotic cells are small (do not exceed 30 microns, but there are species whose cell diameter is about 0.2 microns). Most prokaryotes are unicellular organisms there are also colonial forms among them. Accumulations of prokaryotic cells may look like threads, clusters, etc.; sometimes they are surrounded by: a common mucous membrane - capsule. In some colonial cyanobacteria, neighboring cells contact each other through microscopic tubules filled with cytoplasm.

The shape of prokaryotic cells is diverse: spherical (cocci), rod-shaped (bacilli), in the form of curved (vibrios) or spirally twisted (spirilla) rods, etc. (fig.2)

(fig.2)

***

(student's message - excerpt from the abstract - up to 5 minutes)

Discovery of viruses and their place in the living system. The existence of viruses was first proved by the Russian scientist D.I. Ivanovsky in 1892. While studying the disease of tobacco - the so-called leaf mosaic, he tried to isolate the causative agent of this disease using microbiological filters. But even filters with the smallest pore diameter could not trap this pathogen, and the filtered juice of a diseased plant caused a disease in healthy ones. The scientist suggested the existence of some unknown organism, much smaller than bacteria. Later, the existence of similar particles that caused diseases in animals was proved. All these particles invisible in a light microscope are collectively called viruses (from lat. virus - I). However, the real study of viruses became possible only in the 1930s. years XIX Art. after the invention of the electron microscope. The science that studies viruses is called virology.

Features of the structure and functioning of viruses. The exchange of viral particles ranges from 15 to several hundred, sometimes up to 2 thousand (some plant viruses) nanometers. (fig.3)

(fig.3)

Life cycle Viruses consist of two phases: extracellular and intracellular.

Each viral particle consists of a DNA or special RNA molecule covered with a protein coat (respectively, they are called: DNA - or RNA-containing viruses). (fig.4)

(fig.4)

Both of these nucleic acids carry hereditary information about viral particles.

Viral nucleic acids have the form of one- or two-chain spirals, which, in turn, are linear, annular or secondarily twisted.

Depending on the structure and chemical composition shell viruses are divided into simple and complex.

Simple viruses have a shell consisting of the same type of protein formations (subunits) in the form of helical or multifaceted structures (for example, tobacco mosaic virus) (Fig. 28). They have different shape- rod-shaped, filamentous, spherical, etc.

Complex viruses additionally covered with a lipoprotein membrane. It is part of the plasma membrane of the host cell and contains glycoproteins (pox virus, hepatitis B, etc.). The latter serve to recognize specific receptors on the host cell membrane and attach the viral particle to it. Sometimes the membrane of the virus contains enzymes that ensure the synthesis of viral nucleic acids in the host cell and some other reactions.

In the extracellular phase, viruses are able to exist for a long time and withstand exposure to sun rays, low or high temperatures(and particles of the hepatitis B virus 1 - even short-term boiling). The polio virus 2 in the external environment retains the ability to infect the host for several days, and smallpox - for many months.

Mechanisms of virus entry into the host cell. Most viruses specific: they only affect certain types of host cells in multicellular organisms (target cells) or certain types unicellular organisms. Penetration into the host cell begins with the interaction of the viral particle with the cell membrane, on which special receptor sites are located. The shell of the virus particle contains special proteins (attached) that “recognize” these areas, which ensures the specificity of the virus. If a viral particle attaches to a cell whose membrane does not have receptors sensitive to it, then infection does not occur. At simple viruses attachment proteins are located in the protein shell, in complex proteins - on needle-like or awl-shaped outgrowths of the surface membrane.

Virus particles enter the host cell in different ways. Many complex viruses - due to the fact that their shell merges with the membrane of the host cell (eg, like the flu virus). Often, a viral particle enters the cell by pinocytosis (eg, polio virus). Most plant viruses penetrate the host cells at the sites of damage to the cell walls.

It consists of extended heads, protein coat containing DNA process, in the form of a cover resembling a stretched spring, inside of which there is a hollow rod, and tail threads. With the help of these threads, the virus connects to the receptor sites of the host cell and attaches to its surface. Then the sheath contracts sharply, as a result of which the rod passes through the shell of the bacterium and injects the viral DNA into it. The empty shell of the bacteriophage remains on the surface of the host cell.

(teacher summary - up to 1 min.)

EUKARYOTES.

(student's message - excerpt from the abstract - up to 5 minutes)

It is known that cells are very diverse. Their diversity is so great that at first, when examining cells through a microscope, scientists did not notice similar features and properties in them. But later it was discovered that behind all the diversity of cells their fundamental unity, common manifestations of life characteristic of them, are hidden.

Why are cells the same?

The contents of any cell is separated from the external environment by a special structure - plasma membrane(plasmalemma). This separation allows you to create a very special environment inside the cell, not similar to the one that surrounds it. Therefore, those processes can take place in the cell that do not occur anywhere else. They are called life processes.

All contents of the cell, with the exception of the nucleus, are called cytoplasm. Since the cell must perform many functions, there are various structures in the cytoplasm that ensure the performance of these functions. Such structures are called organelles(or organoids are synonyms, but organelles is a more modern term).

What are the main organelles of the cell?

The largest cell organelle is core, in which hereditary information is stored and from which hereditary information is copied. This is the metabolic control center of the cell, it controls the activity of all other organelles.

The core has nucleolus- this is the place where other important organelles involved in protein synthesis are formed. They are called ribosomes. But ribosomes are only formed in the nucleus, and they work (i.e. synthesize protein) in the cytoplasm. Some of them are free in the cytoplasm, and some are attached to membranes that form a network called endoplasmic. Endoplasmic reticulum is a network of tubules bounded by membranes. There are two types of endoplasmic reticulum: smooth and rough. Ribosomes are located on the membranes of the rough endoplasmic reticulum, therefore, the synthesis and transport of proteins takes place in it. And the smooth endoplasmic reticulum is the place of synthesis and transport of carbohydrates and lipids.

For the synthesis of proteins, carbohydrates and fats, energy is needed, which is produced by the energy stations of the cell - mitochondria. Mitochondria- two-membrane organelles in which the process of cellular respiration takes place. oxidized on mitochondrial membranes food products and accumulates chemical energy in the form of special energy molecules.

There is also a place in the cell where organic compounds can accumulate and from where they can be transported. This is golgi apparatus- a system of flat membrane pouches. He takes part in the transport of proteins, lipids, carbohydrates, renewal of the plasma membrane. Organelles of intracellular digestion - lysosomes - are also formed in the Golgi apparatus.

Lysosomes- single-membrane organelles, characteristic of animal cells, containing enzymes that can destroy proteins, carbohydrates, nucleic acids, lipids.

All cell organelles work together, taking part in the processes of metabolism and energy.

There may be organelles in the cell that do not have a membrane structure.

cytoskeleton- this is the musculoskeletal system of the cell, which includes microfilaments, cilia, flagella, cell center,

producing microtubules and centrioles.

There are organelles that are unique to plant cells. plastids.

Plastids are of three types: chloroplasts, chromoplasts and leukoplasts. In chloroplasts, as you already know, the process of photosynthesis is going on. In plants, there are also vacuoles - these are the waste products of the cell, which are reservoirs of water and compounds dissolved in it. (see fig.6,7,8)

fig.6

fig.7

fig.8

(teacher summary - up to 1 min.)

(Work in pairs with didactic cards and drawings )

The results of the study of eukaryotic cells can be summarized in a table.

eukaryotic cell organelles

III. Generalization, systematization and control of knowledge and skills of students.

indicate on the EDUCATIONAL CARDS the main structural elements(organelles) of plant and animal cells.

(work in pairs with didactic cards)

(Sample didactic cards:

v. Homework :

§ 25, 26 of the textbook (p. 100-107), - study; drawings to consider.

§ 9, - repeat. Prepare for lab work.

LESSON 2 : "The structure of the prokaryotic cell".

Laboratory work : "The structure of cells of prokaryotes and eukaryotes".

The purpose of the lesson: to continue the formation of a general idea among students about the structure of prokaryotic cells (in comparison with eukaryotes), about the features of their functions in connection with the structure.

Equipment and materials: diagram of the structure of prokaryotic and eukaryotic cells; permanent preparations of onion epidermal cells, epithelial tissue. For laboratory work: light microscope, coverslips, tweezers, dissecting needles.

Basic concepts and t terms: organelles, eukaryotes, prokaryotes, nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, mitochondria, chloroplasts, plasma membrane, membrane organelles, non-membrane organelles, cell center.

Lesson concept: on the basis of knowledge about eukaryotic cells, give (in comparison) information about simpler prokaryotic cells. To tell about prokaryotes in more detail due to the fact that schoolchildren still do not have much information about these organisms.

STRUCTURE AND CONTENT OF THE LESSON:

I. Actualization of basic knowledge and motivation of educational activities:

What organelles are in any cell?

Do all cells have a nucleus?

What is the function of the nucleus in the cell?

Can there be nuclear cells?

II. Learning new material:

Working with a table.

Prokaryotes are unicellular organisms that do not have a well-formed nucleus and many other organelles. But since these are living organisms, they must perform all the functions of a living thing. How? With using what? If they do not have those organelles that are characteristic of eukaryotes, then how do they manage without them? Differences in the characteristics of prokaryotes and eukaryotes are visible in the following table:

(Working in pairs with tables)

Laboratory work: "Features of the structure of prokaryotic and eukaryotic cells."

WORKING PROCESS:

Prepare the microscope for work.

At low magnification consider a constant preparation of cells (plants, fungi, animals). Then turn the microscope to high magnification and examine the preparations in more detail.

Compare drugs with each other. Draw what you see.

4. Make a conclusion.

III. Generalization, systematization and control of knowledge and skills of students:

What are the main differences between eukaryotic and prokaryotic cells?

What are their similarities?

Which cells are the oldest?

What are the functions of the cell: nucleus, mitochondria, chloroplasts?

IV. Independent work students:

Name the parts by which prokaryotic cells perform their vital functions.

v. Homework:

§ 26, - textbook (p. 104-108), - repeat. Drawing No. 28 - consider and sketch.