Single-celled prokaryotic organisms. The simplest unicellular organisms. Who discovered single-celled organisms

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 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?
Radiolarians and foraminifera live in the marine environment.

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 activity.

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;
• 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, sporozoa).

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.

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 Kelleker 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.

The simplest animals are single-celled organisms, characteristics, nutrition, presence in water and in the human body

general characteristics

Or unicellular organisms, as their name suggests, are made up of a single cell. The phylum Protozoa includes more than 28,000 species. The structure of protozoa can be compared with the structure of cells of multicellular organisms. Both of them are based on the nucleus and cytoplasm with various organelles (organelles) and inclusions. However, we must not forget that any cell of a multicellular organism is part of any tissue or organ where it performs its specific functions. All cells of a multicellular organism are specialized and are not capable of independent existence. In contrast, the simplest animals combine the functions of a cell and an independent organism. (Physiologically, the Protozoa cell is similar not to individual cells of multicellular animals, but to a whole multicellular organism.

The simplest all functions inherent in any living organisms are characteristic: nutrition, metabolism, excretion, perception of external stimuli and reaction to them, movement, growth, reproduction and death.

Protozoa Cell structure

The nucleus and cytoplasm, as indicated, are the main structural and functional components of any cell, including unicellular animals. The body of the latter contains organelles, skeletal and contractile elements and various inclusions. It is always covered with a cell membrane, more or less thin, but clearly visible in an electron microscope. The cytoplasm of protozoa is liquid, but its viscosity varies among different species and varies depending on the condition of the animal and the environment (its temperature and chemical composition). In most species the cytoplasm is transparent or milky white, but in some it is colored blue or greenish (Stentor, Fabrea saliva). The chemical composition of the nucleus and cytoplasm of protozoa has not been fully studied, mainly due to the small size of these animals. It is known that the basis of the cytoplasm and nucleus, as in all animals, is made up of proteins. Nucleic acids are closely related to proteins; they form nucleoproteins, the role of which in the life of all organisms is extremely large. DNA (deoxyribonucleic acid) is part of the chromosomes of the protozoan nucleus and ensures the transmission of hereditary information from generation to generation. RNA (ribonucleic acid) is found in protozoa both in the nucleus and in the cytoplasm. It implements the hereditary properties of single-celled organisms encoded in DNA, as it plays a leading role in the synthesis of proteins.

Very important chemical components of the cytoplasm - fat-like substances lipids - take part in metabolism. Some of them contain phosphorus (phosphatides), many are associated with proteins and form lipoprotein complexes. The cytoplasm also contains reserve nutrients in the form of inclusions - droplets or granules. These are carbohydrates (glycogen, paramyl), fats and lipids. They serve as the energy reserve of the protozoan body.

In addition to organic substances, the cytoplasm contains a large amount of water and mineral salts (cations: K+, Ca2+, Mg2+, Na+, Fe3+ and anions: Cl~, P043“, N03“). In the cytoplasm of protozoa, many enzymes involved in metabolism are found: proteases, which ensure the breakdown of proteins; carbohydrases that break down polysaccharides; lipases that promote fat digestion; a large number of enzymes that regulate gas exchange, namely alkaline and acid phosphatases, oxidases, peroxidases and cytochrome oxidases.

Previous ideas about the fibrillar, granular or foamy-cellular structure of the cytoplasm of protozoa were based on studies of fixed and stained preparations. New methods for studying protozoa (in a dark field, in polarized light, using intravital staining and electron microscopy) have made it possible to establish that the cytoplasm of protozoa is a complex dynamic system of hydrophilic colloids (mainly protein complexes), which has a liquid or semi-liquid consistency. During ultramicroscopic examination in a dark field, the cytoplasm of protozoa appears optically empty, only the cell organelles and its inclusions are visible.

The colloidal state of cytoplasmic proteins ensures the variability of its structure. In the cytoplasm, changes in the aggregate state of proteins constantly occur: they pass from a liquid state (sol) to a more solid, gelatinous state (gel). These processes are associated with the release of a denser layer of ectoplasm, the formation of a shell - pellicles, and the amoeboid movement of many protozoa.

The nuclei of protozoa, like the nuclei of multicellular cells, consist of chromatin material, nuclear juice, and contain nucleoli and a nuclear envelope. Most protozoa contain only one nucleus, but there are also multinucleate forms. In this case, the nuclei can be the same (multinucleate amoebas from the genus Pelomyxa, multinucleate flagellates Polymastigida, Opalinida) or differ in shape and function. In the latter case, they talk about nuclear differentiation, or nuclear dualism. Thus, the entire class of ciliates and some foraminifera are characterized by nuclear dualism. i.e. nuclei unequal in shape and function.

These types of protozoa, like other organisms, obey the law of constancy of the number of chromosomes. Their number can be single, or haploid (most flagellates and sporozoans), or double, or diploid (ciliates, opalines and, apparently, sarcodae). The number of chromosomes in different species of protozoa varies widely: from 2-4 to 100-125 (in the haploid set). In addition, nuclei with a multiple increase in the number of sets of chromosomes are observed. They are called polyploid. It was found that large nuclei, or macronuclei, of ciliates and the nuclei of some radiolarians are polyploid. It is very likely that the nucleus of Amoeba proteus is also polyploid; the number of chromosomes in this species reaches 500.

Reproduction Nuclear division

The main type of nuclear division in both protozoa and multicellular organisms is mitosis, or karyokinesis. During mitosis, the correct, uniform distribution of chromosomal material occurs between the nuclei of dividing cells. This is ensured by the longitudinal splitting of each chromosome into two daughter chromosomes in the metaphase of mitosis, with both daughter chromosomes going to different poles of the dividing cell.

When the nucleus of Monocystis magna gregarina divides, all the mitotic figures characteristic of multicellular organisms can be observed. In prophase, thread-like chromosomes are visible in the nucleus, some of them are associated with the nucleolus (Fig. 1, 1, 2). In the cytoplasm, two centrosomes can be distinguished, in the center of which there are centrioles with star rays diverging radially. Centrosomes approach the nucleus, adjoin its shell and move to the opposite poles of the nucleus. The nuclear envelope dissolves and an achromatin spindle is formed (Fig. 1, 2-4). Spiralization of chromosomes occurs, as a result of which they are greatly shortened and collected in the center of the nucleus, the nucleolus dissolves. In metaphase, chromosomes move to the equatorial plane. Each chromosome consists of two chromatids lying parallel to each other and held together by one centromere. The star figure around each centrosome disappears, and the centrioles are divided in half (Fig. 1, 4, 5). In anaphase, the centromeres of each chromosome divide in half and their chromatids begin to diverge towards the spindle poles. It is characteristic of protozoa that the pulling spindle filaments attached to the centromeres are distinguishable only in some species. The entire spindle is stretched, and its threads, running continuously from pole to pole, lengthen. The separation of chromatids that have turned into chromosomes is ensured by two mechanisms: their pulling apart under the action of contraction of the pulling spindle threads and the stretching of continuous spindle threads. The latter leads to the removal of the cell poles from each other (Fig. 1, 6, 7). In telophase, the process proceeds in the reverse order: at each pole, a group of chromosomes is clothed with a nuclear envelope. The chromosomes despiral and become thinner, and nucleoli are formed again. The spindle disappears, and around the divided centrioles two independent centrosomes with star rays are formed. Each daughter cell has two centrosomes - the future centers of the next mitotic division (Fig. 1, 9, 10). Following nuclear division, the cytoplasm is usually divided. However, in some protozoa , including in Monocystis, a series of successive nuclear divisions occur, as a result of which temporarily multinuclear stages arise in the life cycle.Later, a section of cytoplasm is isolated around each nucleus and many small cells are formed simultaneously.

There are various deviations from the process of mitosis described above: the nuclear envelope can be preserved throughout the entire mitotic division, the achromatin spindle can form under the nuclear envelope, and in some forms centrioles are not formed. The most significant deviations are in some euglenidae: they lack a typical metaphase, and the spindle passes outside the nucleus. In metaphase, chromosomes, consisting of two chromatids, are located along the axis of the nucleus, the equatorial plate is not formed, the nuclear membrane and nucleolus are preserved, the latter is divided in half and passes into the daughter nuclei. There are no fundamental differences between the behavior of chromosomes in mitosis in protozoa and multicellular organisms.

Before the use of new research methods, the nuclear division of many protozoa was described as amitosis, or direct division. True amitosis is now understood as the division of nuclei without proper separation of chromatids (chromosomes) into daughter nuclei. As a result, nuclei with incomplete sets of chromosomes are formed. They are not capable of further normal mitotic divisions. It is difficult to expect such nuclear divisions in the simplest organisms normally. Amitosis is observed optionally as a more or less pathological process.

The body of protozoa is quite complex. Within one cell, differentiation of its individual parts occurs, which perform different functions. Thus, by analogy with the organs of multicellular animals, these parts of protozoa were called organelles or organelles. There are organelles of movement, nutrition, perception of light and other stimuli, excretory organelles, etc.

Movement

The organelles of movement in Protozoa are pseudopodia, or pseudopods, flagella and cilia. Pseudopodia are formed for the most part at the moment of movement and can disappear as soon as the protozoan stops moving. Pseudopodia are temporary plasmatic outgrowths of the body of protozoa that do not have a permanent shape. Their shell is represented by a very thin (70-100 A) and elastic cell membrane. Pseudopodia are characteristic of sarcodae, some flagellates and sporozoans.

Flagella and cilia are permanent outgrowths of the outer layer of the cytoplasm, capable of rhythmic movements. The ultrafine structure of these organelles was studied using an electron microscope. It was found that they are constructed in much the same way. The free part of the flagellum or cilium extends from the surface of the cell.

The internal part is immersed in ectoplasm and is called the basal body or blepharoplast. On ultrathin sections of a flagellum or cilium, 11 longitudinal fibrils can be distinguished, 2 of which are located in the center, and 9 along the periphery (Fig. 2). The central fibrils in some species have helical striations. Each peripheral fibril consists of two connected tubes, or subfbrils. Peripheral fibrils pass into the basal body, but central fibrils do not reach it. The flagellum membrane passes into the membrane of the protozoan body.

Despite the similarity in structure of cilia and flagella, the nature of their movement is different. If flagella make complex screw movements, then the work of cilia can most easily be compared with the movement of oars.

In addition to the basal body, the cytoplasm of some protozoa contains a parabasal body. The basal body is the basis of the entire musculoskeletal system; in addition, it regulates the process of mitotic division of the protozoan. The parabasal body plays a role in the metabolism of the protozoan; at times it disappears and then may appear again.

Sense organs

Protozoa have the ability to determine light intensity (illuminance) using a photosensitive organelle - the ocellus. A study of the ultrathin structure of the eye of the marine flagellate Chromulina psammobia showed that it includes a modified flagellum immersed in the cytoplasm.

In connection with the different types of nutrition, which will be discussed in detail later, protozoa have a very wide variety of digestive organelles: from simple digestive vacuoles or vesicles to such specialized formations as the cellular mouth, oral funnel, pharynx, powder.

Excretory system

Most protozoa are characterized by the ability to withstand unfavorable environmental conditions (drying out of temporary reservoirs, heat, cold, etc.) in the form of cysts. In preparation for encystment, the protozoan releases a significant amount of water, which leads to an increase in the density of the cytoplasm. The remains of food particles are thrown out, the cilia and flagella disappear, and the pseudopodia are retracted. The overall metabolism decreases, a protective shell is formed, often consisting of two layers. The formation of cysts in many forms is preceded by the accumulation of reserve nutrients in the cytoplasm.

Protozoa do not lose viability in cysts for a very long time. In experiments, these periods exceeded 5 years for the genus Oicomonas (Protomonadida), 8 years for Haematococcus pluvialis, and for Peridinium cinctum the maximum survival period of cysts exceeded 16 years.

In the form of cysts, protozoa are transported by wind over considerable distances, which explains the homogeneity of the protozoan fauna throughout the globe. Thus, cysts not only have a protective function, but also serve as the main means of dispersal of protozoa.

Main groups

Main article: Groups

The main groups of unicellular organisms:

• Ciliates (12 microns - 3 mm)...
• Amoebas (up to 0.3 mm)
• Ciliary
• Euglena

Prokaryotes

Prokaryotes are predominantly unicellular, with the exception of some cyanobacteria and actinomycetes. Among eukaryotes, protozoa, a number of fungi, and some algae have a unicellular structure. Unicellular organisms can form colonies.

Emergence and evolution

It is believed that the first living organisms on Earth were single-celled. The most ancient of them are considered to be bacteria and archaea. Unicellular animals and prokaryotes were discovered by A. Leeuwenhoek.

Eukaryotes

Eukaryotes, or Nuclear (Latin Eucaryota from the Greek εύ- - good and κάρυον - core) - a domain (superkingdom) of living organisms, whose cells contain nuclei. All organisms except bacteria and archaea are nuclear (viruses and viroids are also not eukaryotes, but not all biologists consider them living organisms).

Animals, plants, fungi, and groups of organisms collectively called protists are all eukaryotic organisms. They can be unicellular or multicellular, but they all have a common cell structure. All these very dissimilar organisms are believed to have a common origin, so the nuclear group is considered the highest-ranking monophyletic taxon. According to the most common hypotheses, eukaryotes appeared 1.5-2 billion years ago. An important role in the evolution of eukaryotes was played by symbiogenesis - a symbiosis between a eukaryotic cell, which apparently already had a nucleus and was capable of phagocytosis, and bacteria swallowed by this cell - the precursors of mitochondria and chloroplasts.

Notes

see also

Wikimedia Foundation. 2010.

Topic: “SINGLE CELL ORGANISMS: PROKARYOTES AND EUKARYOTES”

Lesson 1 : Structure of eukaryotic cells".

The purpose of the lesson: give students a general idea of ​​the structure of eukaryotic cells, the features of their functions in connection with their 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 that schoolchildren already have. Based on knowledge about eukaryotic cells, give (in comparison) information about simpler prokaryotic cells. Tell us in more detail about prokaryotes due to the fact that schoolchildren still do not have much information about these organisms.

STRUCTURE AND CONTENT OF THE LESSON:

I. Updating basic knowledge and motivating learning activities:

What organelles are characteristic of plant cells?

What organelles are characteristic of animal cells?

What functions do chloroplasts perform?

What do you know about mitochondria?

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

II. LEARNING NEW MATERIAL

Teacher's opening speech.

PROKARYOTES.

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

Prokaryotes (from lat. about - before, instead of and Greek. karyon - core) - a superkingdom of organisms, which includes the kingdoms of Bacteria and Cyanobacteria (the outdated 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 water bodies or soil capillaries filled with water - have special gas vacuoles. By changing the volume of gases in them, these bacteria can move in an aquatic environment with minimal energy expenditure. The surface apparatus of prokaryotic cells includes plasma membrane, cell wall, Sometimes - mucous capsule.

(Fig. 1).

The cytoplasm of prokaryotes contains ribosomes, various inclusions, and one or more nuclear zones (nucleoids) containing hereditary material. Hereditary material prokaryotes are represented by 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 and ribosomes can be located on folded membrane formations, and photosynthetic pigments can be located on smooth ones. In the cells of cyanobacteria, rounded closed membrane structures were found - chromatophores, in which photosynthetic pigments are located.

The cells of some bacteria have organelles of movement - one, several or many flagella. Prokaryotic flagella consist of one specific protein molecule with 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 under a light microscope. In addition to flagella, the surface of bacterial cells often has filamentous and tubular formations consisting of proteins or polysaccharides. It ensures the attachment of the cell to the substrate or takes part in the transmission of hereditary information during the sexual process.

Prokaryotic cells are small in size (do not exceed 30 microns, and there are species whose cell diameter is about 0.2 microns). Most prokaryotes are single-celled organisms, including colonial forms. Clusters of prokaryotic cells can take the form of 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 varied: spherical (cocci), rod-shaped (bacilli), curved (vibrios) or spirally twisted (spirilla) rods, etc. (Fig.2)

(Fig.2)

***

(student’s message – excerpt from the essay – up to 5 minutes)

Discovery of viruses and their place in the system of living nature. The existence of viruses was first proven by the Russian scientist D.I. Ivanovsky in 1892. While studying a tobacco disease - 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 retain this pathogen, and the filtered juice of a diseased plant caused disease in healthy ones. The scientist suggested the existence of some unknown organism, significantly smaller in size than bacteria. Later, the existence of similar particles was proven to cause diseases in animals. All these particles, invisible under a light microscope, are collectively called viruses (from Lat. virus - I). However, the real study of viruses became possible only in the 30s of the XIX century. after the invention of the electron microscope. The science that studies viruses is called virology.

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

(Fig.3)

The life cycle of viruses consists of two phases: extracellular and intracellular.

Each viral particle consists of a DNA molecule or a special RNA coated with a protein shell (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, circular or secondarily twisted.

Depending on the structure and chemical composition of the 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 spiral or polyhedral structures (for example, tobacco mosaic virus) (Fig. 28). They have different shapes - 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 (smallpox viruses, hepatitis B, etc.). The latter serve to recognize specific receptors on the host cell membrane and attach the viral particle to it. Sometimes the virus membrane 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 sunlight, low or high temperatures (and hepatitis B virus particles 1 - even short-term boiling). Poliomyelitis virus 2 in the external environment retains the ability to infect a host for several days, and smallpox virus for many months.

Mechanisms of virus penetration into the host cell. Most viruses specific: they infect only certain types of host cells in multicellular organisms (target cells) or certain types of single-celled 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 viral particle contains special proteins (attached) that “recognize” these areas, which ensures the specificity of the virus. If a viral particle attaches to a cell on the membrane of which there are no receptors sensitive to it, then infection does not occur. In simple viruses, attachment proteins are located in the protein shell; in complex viruses, they are located on needle-shaped or subulate-shaped projections of the surface membrane.

Viral particles enter the host cell in different ways. Many complex viruses - due to the fact that their envelope fuses with the membrane of the host cell (for example, like the influenza virus). Often the viral particle enters the cell by pinocytosis (eg, polio virus). Most plant viruses enter host cells at sites where cell walls are damaged.

It consists of an extended heads, the protein shell of which contains DNA, process, in the form of a case resembling an extended spring, inside of which there is a hollow rod, and tail filaments. Using these threads, the virus connects to the receptor sites of the host cell and attaches to its surface. The sheath then sharply contracts, causing the rod to pass through the bacterial shell and inject viral DNA inside it. The empty bacteriophage shell remains on the surface of the host cell.

(teacher’s summary – up to 1 min.)

EUKARYOTES.

(student’s message - excerpt from the essay - up to 5 minutes)

It is known that cells are very diverse. Their diversity is so great that at first, when examining cells under 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, the common manifestations of life characteristic of them, are hidden.

Why are cells the same?

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

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

What are the main organelles of a cell?

The largest organelle of the cell is core, in which hereditary information is stored and rewritten. This is the metabolic control center of the cell; it controls the activities 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, which form a reticulum called the endoplasmic reticulum. Endoplasmic reticulum is a network of membrane-bounded tubules. There are two types of endoplasmic reticulum: smooth and rough. Ribosomes are located on the membranes of the rough endoplasmic reticulum, so protein synthesis and transport takes place there. And the smooth endoplasmic reticulum is the site of synthesis and transport of carbohydrates and lipids.

The synthesis of proteins, carbohydrates and fats requires energy, which is produced by the cell's energy stations - mitochondria. Mitochondria- double-membrane organelles in which the process of cellular respiration occurs. Food products are oxidized on mitochondrial membranes and chemical energy is accumulated in the form of special energy molecules.

The cell also has a place where organic compounds can accumulate and from where they can be transported. This Golgi apparatus- system of flat membrane bags. It takes part in the transport of proteins, lipids, carbohydrates, and renewal of the plasma membrane. The Golgi apparatus also produces organelles for intracellular digestion - lysosomes.

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 metabolic and energy processes.

A cell may contain organelles 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 characteristic only of plant cells - plastids.

There are three types of plastids: chloroplasts, chromoplasts and leucoplasts. In chloroplasts, as you already know, the process of photosynthesis occurs. Plants also have vacuoles - these are 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’s summary – up to 1 min.)

(Work in pairs with flashcards and drawings )

The results of studying the eukaryotic cell can be summarized in a table.

Organelles of a eukaryotic cell

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

Indicate the main structural elements (organelles) of plant and animal cells ON THE TEAM CARDS.

(work in pairs with flashcards)

(Samples of flashcards:

V. Homework:

§ 25, 26 of the textbook (pp. 100-107), - study; drawings - look at them.

§ 9, - repeat. Prepare for laboratory work.

LESSON 2 : "Structure of a prokaryotic cell."

Laboratory work : “Structure of cells of prokaryotes and eukaryotes.”

The purpose of the lesson: continue to form in students a general understanding of 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 and epithelial tissue. For laboratory work: light microscope, cover glasses, 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: based on knowledge about eukaryotic cells, give (in comparison) information about simpler prokaryotic cells. Tell us in more detail about prokaryotes due to the fact that schoolchildren still do not have much information about these organisms.

STRUCTURE AND CONTENT OF THE LESSON:

I. Updating basic knowledge and motivating learning activities:

What organelles are there in any cell?

Do all cells have a nucleus?

What functions does the nucleus perform in a cell?

Can there be nuclear-free cells?

II. Learning new material:

Working with a table.

Prokaryotes are single-celled organisms that do not have a 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? The differences in the characteristics of prokaryotes and eukaryotes are visible in the following table:

(Work in pairs with tables)

Laboratory work: “Structural features of prokaryotic and eukaryotic cells.”

PROGRESS:

Prepare the microscope for use.

At low magnification, examine a permanent 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. Sketch what you saw.

4. Draw a conclusion.

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

What are the main differences between eukaryotic and prokaryotic cells?

What are their similarities?

Which cells are more ancient?

What functions do they perform in a cell: nucleus, mitochondria, chloroplasts?

IV. Independent work of students:

Name the parts with which prokaryotic cells perform vital functions.

V. Homework:

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