Give a description of all the provisions of modern cell theory. The cell as a biological system (multiple choice)

A cell is the elementary unit of a living system. elementary unit it can be named because in nature there are no smaller systems that would have all the signs of life without exception.

A cell has all the properties of a living system: it exchanges matter and energy, grows, reproduces and inherits its characteristics, reacts to external stimuli and is able to move.

The history of the study of the cell is associated with the names of a number of scientists:

R. Hooke - for the first time used a microscope to study tissues and saw cells on a cut of a cork and an elderberry core, which he called cells.
A. Levenguk - first saw cells under a magnification of 270 times, discovered unicellular organisms.
T. Schwann and M. Schleiden - generalized knowledge about the cell, formed the basic position of the cell theory: all plant and animal organisms consist of cells that are similar in structure. They mistakenly believed that the cells in the body arise from the primary non-cellular substance.
R. Virchow - argued that each cell comes only from a cell as a result of its division.
R. Brown - discovered the nucleus in the cell.
K. Bar - established that all organisms begin their development from one cell.

The significance of the cell theory in the development of science is great. It became obvious that the cell is the most important component of all living organisms. It is their main component morphologically; The cell is the embryonic basis of a multicellular organism. The cell theory made it possible to conclude that the chemical composition of all cells is similar and once again confirmed the unity of the entire organic world.

The main provisions of the cell theory at the present stage of development of biological science can be formulated as follows:

A cell is the basic unit of structure and functioning of a living organism.
The cell is a self-regulating open system.
The cells of all organisms are in principle similar in chemical composition, structure and function.
The life of an organism as a whole is determined by the interaction of its constituent cells.
All new cells are formed when the original cells divide.
In multicellular organisms, cells are specialized according to their functions and form tissues.

Further improvement of microscopic technology, the creation of an electron microscope and the emergence of molecular biology methods open up wide opportunities for penetrating the secrets of the cell, understanding its complex structure, and the variety of biochemical processes occurring in it.

Almost 400 years have passed since the discovery of cells, before the current state of the cell theory was formulated. For the first time a cell was investigated in 1665 by a naturalist from England. Having noticed cellular structures on a thin section of cork, he gave them the name of cells.

In his primitive microscope, Hooke could not yet see all the features, but as optical instruments improved and methods for staining preparations appeared, scientists became more and more immersed in the world of fine cytological structures.

How did the cell theory come about?

A landmark discovery that influenced the further course of research and the current state of cell theory was made in the 30s of the 19th century. The Scot R. Brown, studying the leaf of a plant with a light microscope, found similar rounded seals in plant cells, which he later called nuclei.

From that moment, an important feature appeared for comparing the structural units of various organisms with each other, which became the basis for conclusions about the unity of the origin of the living. It is not for nothing that even the current position of cell theory contains a reference to this conclusion.

The question of the origin of cells was raised in 1838 by the German botanist Matthias Schleiden. Massively studying plant material, he noted that in all living plant tissues, the presence of nuclei is mandatory.

His compatriot zoologist Theodor Schwann made the same conclusions about animal tissue. Having studied the works of Schleiden and comparing many plant and animal cells, he concluded: despite the diversity, they all have a common feature - a formed nucleus.

The cell theory of Schwann and Schleiden

Having put together the available facts about the cell, T. Schwann and M. Schleiden put forward the main postulate. It was that all organisms (plants and animals) consist of cells that are similar in structure.

In 1858, another addition to the cell theory was made. proved that the body grows by increasing the number of cells by dividing the original maternal. It seems obvious to us, but for those times his discovery was very advanced and modern.

At that time, the current position of Schwann's cell theory in textbooks is formulated as follows:

All tissues of living organisms have a cellular structure.
Animal and plant cells are formed in the same way (cell division) and have a similar structure.
The body consists of groups of cells, each of them is capable of independent life.

Having become one of the most important discoveries of the 19th century, the cell theory laid the foundation for the idea of the unity of origin and commonality of the evolutionary development of living organisms.

Further development of cytological knowledge

The improvement of research methods and equipment has allowed scientists to significantly deepen their knowledge of the structure and life of cells:

the relationship between the structure and function of both individual organelles and cells as a whole (specialization of cytostructures) has been proven;
each cell individually demonstrates all the properties inherent in living organisms (grows, reproduces, exchanges matter and energy with the environment, is mobile to one degree or another, adapts to changes, etc.);
organelles cannot individually exhibit similar properties;
in animals, fungi, plants, organelles identical in structure and function are found;
All cells in the body are interconnected and work together to perform complex tasks.

Thanks to new discoveries, the provisions of the theory of Schwann and Schleiden were refined and supplemented. The modern scientific world uses the extended postulates of the fundamental theory in biology.

In the literature, you can find a different number of postulates of modern cell theory, the most complete version contains five points:

The cell is the smallest (elementary) living system, the basis of the structure, reproduction, development and life of organisms. Non-cellular structures cannot be called living.
Cells appear exclusively by dividing existing ones.
The chemical composition and structure of the structural units of all living organisms are similar.
A multicellular organism develops and grows by dividing one/several original cells.
The similar cellular structure of the organisms inhabiting the Earth indicates a single source of their origin.

The original and modern provisions of the cell theory have much in common. Deep and extended postulates reflect the current level of knowledge on the structure, life and interaction of cells.

They have a similar structure. Later, these conclusions became the basis for proving the unity of organisms. T. Schwann and M. Schleiden introduced the fundamental concept of the cell into science: there is no life outside the cells.

The cell theory has been repeatedly supplemented and edited.

Provisions of the cell theory of Schleiden-Schwann

The creators of the theory formulated its main provisions as follows:

All animals and plants are made up of cells.
Plants and animals grow and develop through the formation of new cells.
A cell is the smallest unit of life, and the whole organism is a collection of cells.

The main provisions of modern cell theory

A cell is an elementary, functional unit of the structure of all living things. The multicellular organism is complex system from a multitude of cells united and integrated into systems of tissues and organs connected to each other (except for viruses, which do not have a cellular structure).
A cell is a single system, it includes many naturally interconnected elements, representing a holistic formation, consisting of conjugated functional units - organelles.
The cells of all organisms are homologous.
The cell occurs only by dividing the mother cell.

Additional Provisions of Cell Theory

In order to bring the cellular theory more fully into line with the data of modern cell biology, the list of its provisions is often supplemented and expanded. In many sources, these additional provisions differ, their set is quite arbitrary.

Prokaryotic and eukaryotic cells are systems different levels complexity and are not completely homologous to each other.
The basis of cell division and reproduction of organisms is the copying of hereditary information - nucleic acid molecules ("each molecule from a molecule"). The provisions on genetic continuity apply not only to the cell as a whole, but also to some of its smaller components - to mitochondria, chloroplasts, genes and chromosomes.
Multicellular cells are totipotent, that is, they have the genetic potencies of all cells of a given organism, are equivalent in genetic information, but differ from each other in different expression (work) of various genes, which leads to their morphological and functional diversity - to differentiation.

Story

17th century

Link and Moldenhower establish that plant cells have independent walls. It turns out that the cell is a kind of morphologically isolated structure. In 1831 G. Mol proves that even such seemingly non-cellular structures of plants as aquifers develop from cells.

F. Meyen in "Phytotomy" (1830) describes plant cells, which "are either single, so that each cell is a separate individual, as is found in algae and fungi, or, forming more highly organized plants, they combine into more or less significant masses." Meyen emphasizes the independence of the metabolism of each cell.

In 1831, Robert Brown describes the nucleus and suggests that it is a permanent part of the plant cell.

Purkinje School

In 1801, Vigia introduced the concept of animal tissues, but he isolated tissues on the basis of anatomical preparation and did not use a microscope. The development of ideas about the microscopic structure of animal tissues is associated primarily with the research of Purkinje, who founded his school in Breslau.

Purkinje and his students (G. Valentin should be especially noted) revealed in the first and most general form the microscopic structure of tissues and organs of mammals (including humans). Purkinje and Valentin compared individual plant cells with individual microscopic animal tissue structures, which Purkinje most often called "seeds" (for some animal structures, the term "cell" was used in his school).

In 1837 Purkinje delivered a series of lectures in Prague. In them, he reported on his observations on the structure of the gastric glands, nervous system etc. In the table attached to his report, clear images of some cells of animal tissues were given. Nevertheless, Purkinje could not establish the homology of plant cells and animal cells:

firstly, by grains he understood either cells or cell nuclei;
secondly, the term "cell" was then understood literally as "a space bounded by walls."

Purkinje compared plant cells and animal "seeds" in terms of analogy, not homology of these structures (understanding the terms "analogy" and "homology" in the modern sense).

Müller school and Schwann's work

The second school where the microscopic structure of animal tissues was studied was the laboratory of Johannes Müller in Berlin. Müller studied the microscopic structure of the dorsal string (chord); his student Henle published a study on the intestinal epithelium, in which he gave a description of its various types and their cellular structure.

Here the classic studies of Theodor Schwann were carried out, laying the foundation for the cell theory. Schwann's work was strongly influenced by the school of Purkinje and Henle. Schwann found right principle comparison of plant cells and elementary microscopic structures of animals. Schwann was able to establish homology and prove correspondence in the structure and growth of the elementary microscopic structures of plants and animals.

The significance of the nucleus in the Schwann cell was prompted by the research of Matthias Schleiden, who in 1838 published the work Materials on Phytogenesis. Therefore, Schleiden is often called a co-author of the cell theory. The basic idea of the cell theory - the correspondence of plant cells and the elementary structures of animals - was alien to Schleiden. He formulated the theory of new cell formation from a structureless substance, according to which, first, the nucleolus condenses from the smallest granularity, and a nucleus is formed around it, which is the cell's former (cytoblast). However, this theory was based on incorrect facts.

In 1838, Schwann published 3 preliminary reports, and in 1839 his classic work “Microscopic studies on the correspondence in the structure and growth of animals and plants” appeared, in the very title of which the main idea of the cell theory is expressed:

In the first part of the book, he examines the structure of the notochord and cartilage, showing that their elementary structures - cells develop in the same way. Further, he proves that the microscopic structures of other tissues and organs of the animal organism are also cells, quite comparable with the cells of cartilage and chord.
The second part of the book compares plant cells and animal cells and shows their correspondence.
The third part develops theoretical provisions and formulates the principles of cell theory. It was Schwann's research that formalized the cell theory and proved (at the level of knowledge of that time) the unity of the elementary structure of animals and plants. Schwann's main mistake was his opinion, following Schleiden, about the possibility of the emergence of cells from a structureless non-cellular substance.

Development of cell theory in the second half of the 19th century

Since the 1840s of the 19th century, the theory of the cell has been at the center of attention of all biology and has been rapidly developing, turning into an independent branch of science - cytology.

For further development In the cellular theory, its extension to protists (protozoa), which were recognized as free-living cells, was essential (Siebold, 1848).

At this time, the idea of the composition of the cell changes. The secondary importance of the cell membrane, which was previously recognized as the most essential part of the cell, is clarified, and the importance of protoplasm (cytoplasm) and the cell nucleus (Mol, Cohn, L. S. Tsenkovsky, Leydig, Huxley) is brought to the fore, which found its expression in the definition of the cell given by M. Schulze in 1861:

A cell is a lump of protoplasm with a nucleus contained inside.

In 1861, Brucco puts forward a theory about the complex structure of the cell, which he defines as an “elementary organism”, clarifies the theory of cell formation from a structureless substance (cytoblastema) further developed by Schleiden and Schwann. It was found that the method of formation of new cells is cell division, which was first studied by Mole on filamentous algae. In the refutation of the theory of cytoblastema on botanical material, the studies of Negeli and N. I. Zhele played an important role.

The division of tissue cells in animals was discovered in 1841 by Remak. It turned out that the fragmentation of blastomeres is a series of successive divisions (Bishtyuf, N. A. Kelliker). The idea of the universal spread of cell division as a way to form new cells is fixed by R. Virchow in the form of an aphorism:

"Omnis cellula ex cellula".
Every cell from a cell.

In the development of cellular theory in the 19th century, sharp contradictions arise, reflecting the dual nature of the cellular theory that developed within the framework of a mechanistic conception of nature. Already in Schwann there is an attempt to consider the organism as a sum of cells. This trend is especially developed in Virchow's "Cellular Pathology" (1858).

Virchow's work had an ambiguous impact on the development of cellular science:

He extended the cellular theory to the field of pathology, which contributed to the recognition of the universality of the cellular doctrine. Virchow's work consolidated the rejection of Schleiden and Schwann's theory of cytoblastema, drew attention to the protoplasm and nucleus, recognized as the most essential parts of the cell.
Virchow directed the development of cell theory along the path of a purely mechanistic interpretation of the organism.
Virchow raised cells to the level of an independent being, as a result of which the organism was considered not as a whole, but simply as a sum of cells.

20th century

From the second half of the 19th century, cell theory acquired an increasingly metaphysical character, reinforced by Ferworn's Cellular Physiology, who considered any physiological process occurring in the body as a simple sum of the physiological manifestations of individual cells. At the end of this line of development of the cellular theory, the mechanistic theory of the "cellular state" appeared, which was supported by Haeckel, among others. According to this theory, the body is compared with the state, and its cells - with citizens. Such a theory contradicted the principle of the integrity of the organism.

The mechanistic direction in the development of cell theory has been sharply criticized. In 1860, I. M. Sechenov criticized Virchow's idea of a cell. Later, the cellular theory was subjected to critical evaluations by other authors. The most serious and fundamental objections were made by Hertwig, A. G. Gurvich (1904), M. Heidenhain (1907), and Dobell (1911). The Czech histologist Studnička (1929, 1934) made an extensive critique of the cellular theory.

In the 1930s, the Soviet biologist O. B. Lepeshinskaya, based on the data of her research, put forward a “new cell theory” as opposed to “Virchowianism”. It was based on the idea that in ontogenesis cells can develop from some non-cellular living substance. A critical verification of the facts put by O. B. Lepeshinskaya and her adherents as the basis of the theory put forward by her did not confirm the data on the development of cell nuclei from a nuclear-free “living substance”.

Modern cell theory

Modern cellular theory proceeds from the fact that the cellular structure is the main form of existence of life, inherent in all living organisms, except for viruses. The improvement of the cellular structure was the main direction of evolutionary development in both plants and animals, and the cellular structure was firmly held in most modern organisms.

At the same time, the dogmatic and methodologically incorrect provisions of the cell theory should be reassessed:

The cellular structure is the main, but not the only form of existence of life. Viruses can be considered non-cellular life forms. True, they show signs of living things (metabolism, the ability to reproduce, etc.) only inside cells; outside cells, the virus is complex chemical. According to most scientists, in their origin, viruses are associated with the cell, are part of its genetic material, "wild" genes.
It turned out that there are two types of cells - prokaryotic (cells of bacteria and archaebacteria), which do not have a nucleus delimited by membranes, and eukaryotic (cells of plants, animals, fungi and protists), having a nucleus surrounded by a double membrane with nuclear pores. There are many other differences between prokaryotic and eukaryotic cells. Most prokaryotes do not have internal membrane organelles, while most eukaryotes have mitochondria and chloroplasts. According to the theory of symbiogenesis, these semi-autonomous organelles are the descendants of bacterial cells. Thus, a eukaryotic cell is a system of a higher level of organization; it cannot be considered entirely homologous to a bacterial cell (a bacterial cell is homologous to one mitochondria of a human cell). The homology of all cells, thus, was reduced to the presence of a closed outer membrane from a double layer of phospholipids (in archaebacteria, it has a different chemical composition than other groups of organisms), ribosomes and chromosomes - hereditary material in the form of DNA molecules that form a complex with proteins. This, of course, does not negate the common origin of all cells, which is confirmed by the commonality of their chemical composition.
The cellular theory considered the organism as a sum of cells, and dissolved the manifestations of the life of the organism in the sum of the manifestations of the life of its constituent cells. This ignored the integrity of the organism, the patterns of the whole were replaced by the sum of the parts.
Considering the cell as a universal structural element, the cellular theory considered tissue cells and gametes, protists and blastomeres as completely homologous structures. The applicability of the concept of a cell to protists is a debatable issue of cellular science in the sense that many complex multinucleated cells of protists can be considered as supracellular structures. In tissue cells, germ cells, protists, a common cellular organization is manifested, expressed in the morphological isolation of karyoplasm in the form of a nucleus, however, these structures cannot be considered qualitatively equivalent, taking all their specific features beyond the concept of "cell". In particular, gametes of animals or plants are not just cells of a multicellular organism, but a special haploid generation of their life cycle, which has genetic, morphological, and sometimes ecological features and is subject to the independent action of natural selection. At the same time, almost all eukaryotic cells undoubtedly have a common origin and a set of homologous structures - elements of the cytoskeleton, ribosomes of the eukaryotic type, etc.
The dogmatic cellular theory ignored the specificity of non-cellular structures in the body or even recognized them, as Virchow did, as inanimate. In fact, in addition to cells, the body has multinuclear supracellular structures (syncytia, symplasts) and a nuclear-free intercellular substance that has the ability to metabolize and therefore is alive. To establish the specificity of their vital manifestations and significance for the organism is the task of modern cytology. At the same time, both multinuclear structures and extracellular substance appear only from cells. Syncytia and symplasts of multicellular organisms are the product of the fusion of the original cells, and the extracellular substance is the product of their secretion, that is, it is formed as a result of cell metabolism.
The problem of the part and the whole was resolved metaphysically by the orthodox cellular theory: all attention was transferred to the parts of the organism - cells or "elementary organisms".

The integrity of the organism is the result of natural, material relationships that are quite accessible to research and disclosure. The cells of a multicellular organism are not individuals capable of existing independently (the so-called cell cultures outside the organism are artificially created biological systems). As a rule, only those multicellular cells that give rise to new individuals (gametes, zygotes or spores) and can be considered as separate organisms are capable of independent existence. The cell cannot be torn from environment(as, indeed, any living system). Focusing all attention on individual cells inevitably leads to unification and a mechanistic understanding of the organism as a sum of parts.

Purified from mechanism and supplemented with new data, the cellular theory remains one of the most important biological generalizations.

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Literature

Katsnelson Z.S. The cell theory in its historical development. - Leningrad: MEDGIZ, 1963. - S. 344. - ISBN 5-0260781.
Shimkevich V. M.// Encyclopedic Dictionary of Brockhaus and Efron: in 86 volumes (82 volumes and 4 additional). - St. Petersburg. , 1890-1907.

An excerpt characterizing the Cell Theory

- Ash? - Plato said (he was already asleep). - Read what? He prayed to God. And don't you pray?
“No, and I pray,” said Pierre. - But what did you say: Frola and Lavra?
- But what about, - Plato answered quickly, - a horse festival. And you need to feel sorry for the cattle, - said Karataev. - Look, the rogue, curled up. You've warmed up, you son of a bitch," he said, feeling the dog at his feet, and, turning again, immediately fell asleep.
Outside, weeping and shouting were heard somewhere in the distance, and fire was visible through the cracks of the booth; but it was quiet and dark in the booth. Pierre did not sleep for a long time and with open eyes lay in the darkness in his place, listening to the measured snoring of Plato, who lay beside him, and felt that the previously destroyed world was now being erected in his soul with new beauty, on some new and unshakable foundations.

In the booth, which Pierre entered and in which he stayed for four weeks, there were twenty-three captured soldiers, three officers and two officials.
All of them then appeared to Pierre as if in a fog, but Platon Karataev remained forever in Pierre's soul the strongest and dearest memory and personification of everything Russian, kind and round. When the next day, at dawn, Pierre saw his neighbor, the first impression of something round was completely confirmed: the whole figure of Plato in his French overcoat belted with a rope, in a cap and bast shoes, was round, his head was completely round, back, chest, shoulders, even the arms that he wore, as if always about to embrace something, were round; a pleasant smile and large brown gentle eyes were round.
Platon Karataev must have been over fifty years old, judging by his stories about the campaigns in which he participated as a longtime soldier. He himself did not know and could not in any way determine how old he was; but his teeth, bright white and strong, which kept rolling out in their two semicircles when he laughed (as he often did), were all good and whole; not a single gray hair was in his beard and hair, and his whole body had the appearance of flexibility and especially hardness and endurance.
His face, despite the small round wrinkles, had an expression of innocence and youth; his voice was pleasant and melodious. But the main feature of his speech was immediacy and argumentativeness. He apparently never thought about what he said and what he would say; and from this there was a special irresistible persuasiveness in the speed and fidelity of his intonations.
His physical strength and agility were such during the first time of captivity that he did not seem to understand what fatigue and illness were. Every day in the morning and in the evening, lying down, he said: “Lord, put it down with a pebble, raise it up with a ball”; in the morning, getting up, always shrugging his shoulders in the same way, he would say: "Lie down - curled up, get up - shake yourself." And indeed, as soon as he lay down to immediately fall asleep like a stone, and as soon as he shook himself, in order to immediately, without a second of delay, take up some business, the children, having risen, take up toys. He knew how to do everything, not very well, but not badly either. He baked, steamed, sewed, planed, made boots. He was always busy and only at night allowed himself to talk, which he loved, and songs. He sang songs, not like songwriters sing, knowing that they are being listened to, but he sang like birds sing, obviously because it was just as necessary for him to make these sounds, as it is necessary to stretch or disperse; and these sounds were always subtle, tender, almost feminine, mournful, and his face was very serious at the same time.
Having been captured and overgrown with a beard, he, apparently, threw away everything that was put on him, alien, soldierly, and involuntarily returned to the former, peasant, people's warehouse.
“A soldier on leave is a shirt made of trousers,” he used to say. He reluctantly spoke about his time as a soldier, although he did not complain, and often repeated that he had never been beaten during his entire service. When he told, he mainly told from his old and, apparently, dear memories of the "Christian", as he pronounced, peasant life. The proverbs that filled his speech were not those, for the most part, indecent and glib sayings that the soldiers say, but these were those folk sayings that seem so insignificant, taken separately, and which suddenly take on the meaning of deep wisdom when they are said by the way.
Often he said the exact opposite of what he had said before, but both were true. He loved to talk and spoke well, embellishing his speech with endearing and proverbs, which, it seemed to Pierre, he himself invented; but the main charm of his stories was that in his speech the simplest events, sometimes the very ones that, without noticing them, Pierre saw, took on the character of solemn decorum. He liked to listen to fairy tales that one soldier told in the evenings (all the same), but most of all he liked to listen to stories about real life. He smiled joyfully as he listened to such stories, inserting words and asking questions that tended to make clear to himself the beauty of what was being told to him. Attachments, friendship, love, as Pierre understood them, Karataev did not have any; but he loved and lived lovingly with everything that life brought him, and especially with a person - not with some famous person, but with those people who were before his eyes. He loved his mutt, loved his comrades, the French, loved Pierre, who was his neighbor; but Pierre felt that Karataev, in spite of all his affectionate tenderness for him (with which he involuntarily paid tribute to Pierre's spiritual life), would not have been upset for a minute by parting from him. And Pierre began to experience the same feeling for Karataev.
Platon Karataev was for all the other prisoners the most ordinary soldier; his name was falcon or Platosha, they good-naturedly mocked him, sent him for parcels. But for Pierre, as he presented himself on the first night, an incomprehensible, round and eternal personification of the spirit of simplicity and truth, he remained so forever.
Platon Karataev knew nothing by heart, except for his prayer. When he spoke his speeches, he, starting them, seemed not to know how he would end them.
When Pierre, sometimes struck by the meaning of his speech, asked to repeat what was said, Plato could not remember what he had said a minute ago, just as he could not in any way tell Pierre his favorite song with words. There it was: “dear, birch and I feel sick,” but the words did not make any sense. He did not understand and could not understand the meaning of words taken separately from the speech. Every word of his and every action was a manifestation of an activity unknown to him, which was his life. But his life, as he himself looked at it, had no meaning as a separate life. It only made sense as a part of the whole, which he constantly felt. His words and actions poured out of him as evenly, as necessary and immediately, as a scent separates from a flower. He could not understand either the price or the meaning of a single action or word.

Having received news from Nikolai that her brother was with the Rostovs in Yaroslavl, Princess Marya, despite her aunt's dissuades, immediately prepared to go, and not only alone, but with her nephew. Whether it was difficult, easy, possible or impossible, she did not ask and did not want to know: her duty was not only to be near, perhaps, her dying brother, but also to do everything possible to bring him a son, and she got up. drive. If Prince Andrei himself did not notify her, then Princess Mary explained this either by the fact that he was too weak to write, or by the fact that he considered this long journey too difficult and dangerous for her and his son.
In a few days, Princess Mary got ready for the journey. Her crews consisted of a huge princely carriage, in which she arrived in Voronezh, chaises and wagons. M lle Bourienne, Nikolushka with her tutor, an old nanny, three girls, Tikhon, a young footman and a haiduk, whom her aunt had let go with her, rode with her.
It was impossible to even think of going to Moscow in the usual way, and therefore the roundabout way that Princess Mary had to take: to Lipetsk, Ryazan, Vladimir, Shuya, was very long, due to the lack of post horses everywhere, it was very difficult and near Ryazan, where, as they said, the French showed up, even dangerous.
During this difficult journey, m lle Bourienne, Dessalles and the servants of Princess Mary were surprised by her fortitude and activity. She went to bed later than everyone else, got up earlier than everyone else, and no difficulties could stop her. Thanks to her activity and energy, which aroused her companions, by the end of the second week they were approaching Yaroslavl.
IN Lately During her stay in Voronezh, Princess Marya experienced the best happiness in her life. Her love for Rostov no longer tormented her, did not excite her. This love filled her whole soul, became an indivisible part of herself, and she no longer fought against it. Of late, Princess Marya became convinced—although she never said this clearly to herself in words—she was convinced that she was loved and loved. She was convinced of this during her last meeting with Nikolai, when he came to her to announce that her brother was with the Rostovs. Nikolai did not hint in a single word that now (in the event of the recovery of Prince Andrei) the former relations between him and Natasha could be resumed, but Princess Marya saw from his face that he knew and thought this. And, despite the fact that his attitude towards her - cautious, tender and loving - not only did not change, but he seemed to be glad that now the relationship between him and Princess Marya allowed him to more freely express his friendship to her, love, as she sometimes thought Princess Mary. Princess Marya knew that she loved for the first and last time in her life, and felt that she was loved, and was happy, calm in this respect.
But this happiness of one side of her soul not only did not prevent her from feeling sorrow for her brother with all her strength, but, on the contrary, this peace of mind in one respect gave her a great opportunity to give herself completely to her feelings for her brother. This feeling was so strong in the first minute of leaving Voronezh that those who saw her off were sure, looking at her exhausted, desperate face, that she would certainly fall ill on the way; but it was precisely the difficulties and worries of the journey, which Princess Marya undertook with such activity, saved her for a while from her grief and gave her strength.
As always happens during a trip, Princess Marya thought about only one trip, forgetting what was his goal. But, approaching Yaroslavl, when something that could lie ahead of her again opened up, and not many days later, but this evening, Princess Mary's excitement reached its extreme limits.
When a haiduk sent ahead to find out in Yaroslavl where the Rostovs were and in what position Prince Andrei was, he met a large carriage driving in at the outpost, he was horrified to see the terribly pale face of the princess, which stuck out to him from the window.
- I found out everything, Your Excellency: the Rostov people are standing on the square, in the house of the merchant Bronnikov. Not far, above the Volga itself, - said the haiduk.
Princess Mary looked at his face in a frightened questioning way, not understanding what he was saying to her, not understanding why he did not answer the main question: what is a brother? M lle Bourienne made this question for Princess Mary.
- What is the prince? she asked.
“Their excellencies are in the same house with them.
“So he is alive,” thought the princess, and quietly asked: what is he?
“People said they were all in the same position.
What did "everything in the same position" mean, the princess did not ask, and only briefly, glancing imperceptibly at the seven-year-old Nikolushka, who was sitting in front of her and rejoicing at the city, lowered her head and did not raise it until the heavy carriage, rattling, shaking and swaying, did not stop somewhere. The folding footboards rattled.
The doors opened. On the left was water - a big river, on the right was a porch; there were people on the porch, servants, and some sort of ruddy-faced girl with a big black plait, who smiled unpleasantly feignedly, as it seemed to Princess Marya (it was Sonya). The princess ran up the stairs, the smiling girl said: “Here, here!” - and the princess found herself in the hall in front of an old woman with an oriental type of face, who, with a touched expression, quickly walked towards her. It was the Countess. She embraced Princess Mary and began to kiss her.
- Mon enfant! she said, je vous aime et vous connais depuis longtemps. [My child! I love you and have known you for a long time.]
Despite all her excitement, Princess Marya realized that it was the countess and that she had to say something. She, not knowing how herself, uttered some kind of courteous French words, in the same tone as those who spoke to her, and asked: what is he?
“The doctor says there is no danger,” said the countess, but while she was saying this, she raised her eyes with a sigh, and in this gesture there was an expression that contradicted her words.
- Where is he? Can you see him, can you? the princess asked.
- Now, princess, now, my friend. Is this his son? she said, turning to Nikolushka, who was entering with Desalle. We can all fit, the house is big. Oh what a lovely boy!
The countess led the princess into the drawing room. Sonya was talking to m lle Bourienne. The countess caressed the boy. The old count entered the room, greeting the princess. The old count has changed tremendously since the princess last saw him. Then he was a lively, cheerful, self-confident old man, now he seemed a miserable, lost person. He, speaking with the princess, constantly looked around, as if asking everyone whether he was doing what was necessary. After the ruin of Moscow and his estate, knocked out of his usual rut, he apparently lost consciousness of his significance and felt that he no longer had a place in life.
Despite the excitement in which she was, despite one desire to see her brother as soon as possible and annoyance because at that moment, when she only wants to see him, she is occupied and her nephew is pretended to be praised, the princess noticed everything that was going on around her, and felt the need for a time to submit to this new order into which she was entering. She knew that all this was necessary, and it was difficult for her, but she did not get annoyed with them.
“This is my niece,” said the count, introducing Sonya, “do you not know her, princess?”
The princess turned to her and, trying to extinguish the hostile feeling for this girl that had risen in her soul, kissed her. But it became difficult for her because the mood of everyone around her was so far from what was in her soul.
- Where is he? she asked again, addressing everyone.
“He’s downstairs, Natasha is with him,” answered Sonya, blushing. - Let's go find out. I think you are tired, princess?
The princess had tears of annoyance in her eyes. She turned away and wanted to ask the countess again where to go to him, when light, swift, as if cheerful steps were heard at the door. The princess looked round and saw Natasha almost running in, the same Natasha whom she did not like so much on that old meeting in Moscow.
But before the princess had time to look at the face of this Natasha, she realized that this was her sincere comrade in grief, and therefore her friend. She rushed to meet her and, embracing her, wept on her shoulder.
As soon as Natasha, who was sitting at the head of Prince Andrei, found out about the arrival of Princess Marya, she quietly left his room with those quick, as it seemed to Princess Marya, as if with cheerful steps, and ran to her.
On her excited face, when she ran into the room, there was only one expression - an expression of love, boundless love for him, for her, for everything that was close to a loved one, an expression of pity, suffering for others and a passionate desire to give herself all for in order to help them. It was evident that at that moment not a single thought about herself, about her relationship to him, was in Natasha's soul.
The sensitive Princess Marya, at the first glance at Natasha's face, understood all this and wept on her shoulder with sorrowful pleasure.
“Come on, let’s go to him, Marie,” Natasha said, taking her to another room.
Princess Mary raised her face, wiped her eyes, and turned to Natasha. She felt that she would understand and learn everything from her.
“What…” she began to question, but suddenly stopped. She felt that words could neither ask nor answer. Natasha's face and eyes should have said everything more clearly and deeply.
Natasha looked at her, but seemed to be in fear and doubt - to say or not to say everything that she knew; she seemed to feel that before those radiant eyes, penetrating into the very depths of her heart, it was impossible not to tell the whole, the whole truth as she saw it. Natasha's lip suddenly trembled, ugly wrinkles formed around her mouth, and she, sobbing, covered her face with her hands.
Princess Mary understood everything.
But she still hoped and asked in words in which she did not believe:
But how is his wound? In general, what position is he in?
“You, you ... will see,” Natasha could only say.
They sat for some time downstairs near his room in order to stop crying and come in to him with calm faces.
- How was the illness? Has he gotten worse? When did it happen? asked Princess Mary.
Natasha said that at first there was a danger from a feverish state and from suffering, but in the Trinity this passed, and the doctor was afraid of one thing - Antonov's fire. But that danger was over. When we arrived in Yaroslavl, the wound began to fester (Natasha knew everything about suppuration, etc.), and the doctor said that suppuration could go right. There was a fever. The doctor said that this fever was not so dangerous.
“But two days ago,” Natasha began, “it suddenly happened ...” She restrained her sobs. “I don't know why, but you'll see what he's become.
- Weakened? lost weight? .. - the princess asked.
No, not that, but worse. You will see. Ah, Marie, Marie, he's too good, he can't, can't live... because...

When Natasha, with a habitual movement, opened his door, letting the princess pass in front of her, Princess Marya already felt ready sobs in her throat. No matter how much she prepared herself, or tried to calm down, she knew that she would not be able to see him without tears.
Princess Mary understood what Natasha meant in words: it happened to him two days ago. She understood that this meant that he suddenly softened, and that softening, tenderness, these were signs of death. As she approached the door, she already saw in her imagination that face of Andryusha, which she had known since childhood, tender, meek, tender, which he had so rarely seen and therefore always had such a strong effect on her. She knew that he would say to her quiet, tender words, like those that her father had said to her before his death, and that she could not bear it and burst into tears over him. But, sooner or later, it had to be, and she entered the room. Sobs came closer and closer to her throat, while with her short-sighted eyes she more and more clearly distinguished his form and searched for his features, and now she saw his face and met his gaze.
He was lying on the sofa, padded with pillows, in a squirrel-fur robe. He was thin and pale. One thin, transparently white hand held a handkerchief, with the other, with quiet movements of his fingers, he touched his thin overgrown mustache. His eyes were on those who entered.
Seeing his face and meeting his gaze, Princess Mary suddenly slowed down the speed of her step and felt that her tears had suddenly dried up and her sobs had stopped. Catching the expression on his face and eyes, she suddenly became shy and felt guilty.
“Yes, what am I guilty of?” she asked herself. “In the fact that you live and think about the living, and I! ..” answered his cold, stern look.
There was almost hostility in the deep, not out of himself, but looking into himself look, when he slowly looked around at his sister and Natasha.
He kissed his sister hand in hand, as was their habit.
Hello Marie, how did you get there? he said in a voice as even and alien as his eyes were. If he screamed desperate cry, then this cry would have terrified Princess Mary less than the sound of this voice.

All living organisms are made up of cells - from one cell (single-celled organisms) or many (multicellular). A cell is one of the main structural, functional and reproducing elements of living matter; it is an elementary living system. There are non-cellular organisms (viruses), but they can only reproduce in cells. There are organisms that have lost their cellular structure for the second time (some algae). The history of the study of the cell is associated with the names of a number of scientists. R. Hooke was the first to use a microscope to study tissues and on a cut of a cork and an elderberry core he saw cells, which he called cells. Anthony van Leeuwenhoek first saw cells under 270x magnification. M. Schleiden and T. Schwann were the creators of the cell theory. They mistakenly believed that the cells in the body arise from the primary non-cellular substance. Later, R. Virchow formulated one of the most important provisions of the cellular theory: "Every cell comes from another cell ..." The significance of the cellular theory in the development of science is great. It became obvious that the cell is the most important component of all living organisms. It is their main component morphologically; the cell is the embryonic basis of a multicellular organism, because the development of an organism begins with a single cell - a zygote; cell - the basis of physiological and biochemical processes in the body. The cell theory made it possible to conclude that the chemical composition of all cells is similar and once again confirmed the unity of the entire organic world.

Modern cell theory includes the following provisions:

The cell is the basic unit of the structure and development of all living organisms, the smallest unit of the living;

The cells of all unicellular and multicellular organisms are similar (homologous) in their structure, chemical composition, basic manifestations of vital activity and metabolism;

Reproduction of cells occurs by their division, and each new cell is formed as a result of the division of the original (mother) cell;

In complex multicellular organisms, cells are specialized in their function and form tissues; tissues consist of organs that are closely interconnected and subordinate to the nervous and humoral systems of regulation.

Significance of cell theory in the development of science lies in the fact that thanks to it it became clear that the cell is the most important component of all living organisms. It is their main "building" component, the cell is the embryonic basis of a multicellular organism, because The development of an organism begins with a single cell, the zygote. The cell is the basis of physiological and biochemical processes in the body, because Ultimately, all physiological and biochemical processes take place at the cellular level. The cell theory made it possible to come to the conclusion that the chemical composition of all cells is similar and once again confirmed the unity of the entire organic world. All living organisms are made up of cells - from one cell (protozoa) or many (multicellular). A cell is one of the main structural, functional and reproducing elements of living matter; it is an elementary living system. There are evolutionarily non-cellular organisms (viruses), but they can only reproduce in cells. Different cells differ from each other both in structure and size (cell sizes range from 1 μm to several centimeters - these are the eggs of fish and birds), and in shape (they can be round like erythrocytes, tree-like like neurons), and in biochemical characteristics ( for example, in cells containing chlorofall or bacteriochlorophyll, photosynthesis processes take place that are impossible in the absence of these pigments), and by function (there are sex cells - gametes and somatic - body cells, which in turn are divided into many different types).

8. Hypotheses of the origin of eukaryotic cells: symbiotic, invagination, cloning. Most popular at present symbiotic hypothesis origin of eukaryotic cells, according to which the basis, or host cell, in the evolution of a cell of the eukaryotic type was an anaerobic prokaryote, capable only of amoeboid movement. The transition to aerobic respiration is associated with the presence of mitochondria in the cell, which occurred through changes in symbionts - aerobic bacteria that penetrated into the host cell and coexisted with it.

A similar origin is suggested for flagella, the ancestors of which were bacterial symbionts that had a flagellum and resembled modern spirochetes. The acquisition by the cell of flagella, along with the development of an active mode of locomotion, had an important consequence of a general order. It is assumed that the basal bodies, which are supplied with flagella, could evolve into centrioles during the emergence of the mechanism of mitosis.

The ability of green plants to photosynthesis is due to the presence of chloroplasts in their cells. Supporters of the symbiotic hypothesis believe that prokaryotic blue-green algae served as symbionts of the host cell that gave rise to chloroplasts.

A strong argument in favor symbiotic The origin of mitochondria, centrioles and chloroplasts is that these organelles have their own DNA. At the same time, the proteins bacillin and tubulin, which make up flagella and cilia, respectively, of modern prokaryotes and eukaryotes, have a different structure.

Central and difficult to answer is the question of the origin of the nucleus. It is believed that it could also be formed from a prokaryotic symbiont. The increase in the amount of nuclear DNA, many times greater than in the modern eukaryotic cell, its amount in the mitochondria or chloroplast, apparently occurred gradually by moving groups of genes from the genomes of symbionts. It cannot be ruled out, however, that the nuclear genome was formed by extending the genome of the host cell (without the participation of symbionts).

According to invagination hypothesis, the ancestral form of the eukaryotic cell was the aerobic prokaryote. Inside such a host cell, several genomes were located simultaneously, initially attached to the cell membrane. Organelles that have DNA, as well as a nucleus, arose by invagination and lacing of sections of the membrane, followed by functional specialization into the nucleus, mitochondria, and chloroplasts. In the process of further evolution, the nuclear genome became more complex, and a system of cytoplasmic membranes appeared.

Invagination hypothesis well explains the presence in the shells of the nucleus, mitochondria, chloroplasts, two membranes. However, it cannot answer the question why protein biosynthesis in chloroplasts and mitochondria corresponds in detail to that in modern prokaryotic cells, but differs from protein biosynthesis in the cytoplasm of a eukaryotic cell.

Cloning. In biology, a method of obtaining several identical organisms through asexual (including vegetative) reproduction. This is how, for millions of years, many species of plants and some animals reproduce in nature. However, the term "cloning" is now usually used in a narrower sense and means copying cells, genes, antibodies, and even multicellular organisms in the laboratory. The specimens resulting from asexual reproduction are, by definition, genetically the same, however, they can also observe hereditary variability due to random mutations or created artificially by laboratory methods. The term "clone" as such comes from the Greek word "klon", which means - twig, shoot, stalk, and is related primarily to vegetative propagation. Cloning plants from cuttings, buds or tubers in agriculture has been known for thousands of years. During vegetative reproduction and during cloning, genes are not distributed among the descendants, as in the case of sexual reproduction, but are preserved in their entirety. Only animals are different. As animal cells grow, their specialization occurs, that is, the cells lose the ability to realize all the genetic information embedded in the nucleus of many generations.

For the first time, cells, or rather the cell walls (shells) of dead cells, were discovered in cork sections using a microscope by the English scientist Robert Hooke in 1665. It was he who coined the term "cell".
Later, the Dutchman A. Van Leeuwenhoek discovered many unicellular organisms in drops of water, and in the blood of people there are red blood cells (erythrocytes).

The fact that, in addition to the cell membrane, all living cells have an internal content of a semi-liquid gelatinous substance, scientists were able to discover only in early XIX century. This semi-liquid gelatinous substance was called protoplasm. In 1831, the cell nucleus was discovered, and all the living contents of the cell - protoplasm - began to be divided into the nucleus and cytoplasm.

Later, as the technique of microscopy improved, numerous organelles were found in the cytoplasm (the word "organoid" has Greek roots and means "similar to an organ"), and the cytoplasm began to be divided into organelles and a liquid part - hyaloplasm.

Well-known German scientists, botanist Matthias Schleiden and zoologist Theodor Schwann, who actively worked with plant and animal cells, came to the conclusion that all cells have a similar structure and consist of a nucleus, organelles and hyaloplasm. Later in 1838-1839 they formulated the main provisions of cell theory. According to this theory, the cell is the basic structural unit of all living organisms, both plant and animal, and the process of growth of organisms and tissues is ensured by the process of formation of new cells.

20 years later, the German anatomist Rudolf Virchow made another important generalization: a new cell can only arise from a previous cell. When it turned out that the sperm and the egg are also cells that connect with each other in the process of fertilization, it became clear that life from generation to generation is a continuous sequence of cells. As biology developed and the processes of cell division (mitosis and meiosis) were discovered, the cell theory was supplemented with new provisions. IN modern form The main provisions of the cell theory can be formulated as follows:

1. The cell is the basic structural, functional and genetic unit of all living organisms and the smallest unit of the living.

This postulate has been fully proven by modern cytology. In addition, the cell is a self-regulating and self-reproducing system that is open to exchange with the external environment.

Currently, scientists have learned how to isolate various components of the cell (down to individual molecules). Many of these components can even function on their own if given the right conditions. For example, contractions of the actin-myosin complex can be caused by the addition of ATP to the test tube. The artificial synthesis of proteins and nucleic acids has also become a reality in our time, but all this is just a part of the living. For the full-fledged work of all these complexes that make up the cell, additional substances, enzymes, energy, etc. are needed. And only cells are independent and self-regulating systems, because have everything you need to maintain a full life.

2. The structure of cells, their chemical composition and the main manifestations of vital processes are similar in all living organisms (unicellular and multicellular).

There are two types of cells in nature: prokaryotic and eukaryotic. Despite their some differences, this rule is true for them.
The general principle of cell organization is determined by the need to carry out a number of mandatory functions aimed at maintaining the vital activity of the cells themselves. For example, all cells have a shell that, on the one hand, isolates its contents from the environment, and, on the other hand, controls the flow of substances into and out of the cell.

Organelles or organelles are permanent specialized structures in the cells of living organisms. The organelles of different organisms have a common structural plan and work according to common mechanisms. Each organelle is responsible for certain functions that are vital for the cell. Thanks to organelles in cells, energy metabolism, protein biosynthesis occurs, and the ability to reproduce appears. Organelles began to be compared with the organs of a multicellular organism, hence the term appeared.

In multicellular organisms, a significant diversity of cells is well traced, which is associated with their functional specialization. If we compare, for example, muscle and epithelial cells, we can see that they differ from each other in their predominant development different types organelles. Cells acquire the features of functional specialization, which are necessary to perform specific functions, as a result of cellular differentiation in the process of ontogenesis.

3. Any new cell can be formed only as a result of the division of the mother cell.

Reproduction of cells (i.e., an increase in their number), whether prokaryotes or eukaryotes, can only occur by dividing already existing cells. Division is necessarily preceded by a process of preliminary doubling of the genetic material (DNA replication). The beginning of the life of an organism is a fertilized egg (zygote), i.e. a cell resulting from the fusion of an egg and a sperm. All the rest of the variety of cells in the body is the result of an innumerable number of its divisions. Thus, we can say that all cells in the body are related, develop in the same way from the same source.

4. Multicellular organisms - living organisms consisting of many cells. Most of these cells are differentiated; differ in their structure, functions performed and form different tissues.

Multicellular organisms are integral systems of specialized cells regulated by intercellular, nervous and humoral mechanisms. A distinction should be made between multicellularity and coloniality. Colonial organisms do not have differentiated cells, and therefore there is no division of the body into tissues. In addition to cells, multicellular organisms also include non-cellular elements, for example, the intercellular substance of the connective tissue, bone matrix, and blood plasma.

As a result, we can say that the entire life activity of organisms from their birth to death: heredity, growth, metabolism, disease, aging, etc. - all these are diverse aspects of the activity of various cells of the body.

The cell theory had a huge impact on the development of not only biology, but also natural science in general, since it established the morphological basis for the unity of all living organisms and gave a general biological explanation of life phenomena. In its significance, the cellular theory is not inferior to such outstanding achievements of science as the law of energy conversion or the evolutionary theory of Charles Darwin. So, the cell - the basis of the organization of representatives of the kingdoms of plants, fungi and animals - arose and developed in the process of biological evolution.