Who first examined the cell. Cell. History of the study of the cell. Cell theory. History of cell discovery

The great Russian physiologist I.P. Pavlov wrote:

Science is usually compared to construction. As here and there, there are many people working, and here and there there is a division of labor. Who draws up the plan, some lay the foundation, others build the walls, and so on...

The "construction" of the cell theory began almost 350 years ago.

So, 1665, London, the office of the physicist Robert Hooke. The owner adjusts the microscope of his own design. Professor Hooke is thirty years old, he graduated from Oxford University, worked as an assistant to the famous Robert Boyle.

Hooke was an extraordinary researcher. He did not limit his attempts to look beyond the horizon of human knowledge to any one area. He designed buildings, set “reference points” on the thermometer - boiling and freezing of water, invented an air pump and a device for determining wind strength ... Then he became interested in the capabilities of a microscope. He examined under a hundredfold magnification everything that came to hand - an ant and a flea, a grain of sand and algae. Once there was a piece of cork under the lens. What did the young scientist see? An amazing picture - correctly located voids, similar to a honeycomb. Later, he found the same cells not only in dead plant tissue, but also in living tissue. Hooke called them cells (English) cells) and, together with fifty other observations, described in the book Micrography. However, it was this observation under No. 18 that brought him fame as the discoverer of the cellular structure of living organisms. Glory that Hooke himself did not need. Soon he was taken over by other ideas, and he never returned to the microscope, and he forgot to think about cells.

But for other scientists, Hooke's discovery aroused extreme curiosity. The Italian Marcello Malpighi called this feeling "the human itch of knowledge." He also began to examine different parts of plants through a microscope. And I found that they consist of the smallest tubes, sacs, bubbles. He looked at Malpighi under a microscope and pieces of human and animal tissue. Alas, the technology of that time was too weak. Therefore, the scientist did not recognize the cellular structure of the animal organism.

The further history of the discovery continued in Holland. Anthony van Leeuwenhoek (1632-1723) never thought that his name would stand among the great scientists. The son of an industrialist and merchant from Delft, he also traded in cloth. And Leeuwenhoek would have lived as an inconspicuous businessman, if not for his passion and curiosity. In his spare time, he enjoyed grinding glass, making lenses. Holland was famous for its opticians, but Leeuwenhoek achieved unprecedented skill. His microscopes, which consisted of only one lens, were much stronger than those that had several magnifying glasses. He himself claimed that he had designed 200 such devices, which gave an increase of up to 270 times. But they were very difficult to use. Here is what the physicist D. S. Rozhdestvensky wrote about this: “You can imagine the terrible inconvenience of these tiny lenses. The object is close to the lens, the lens is close to the eye, there is nowhere to put the nose.” By the way, Leeuwenhoek until his last days, and he lived to be 90 years old, managed to maintain visual acuity.

Through his lenses, the naturalist saw a new world, the existence of which even desperate dreamers had no idea. Leeuwenhoek was most struck by its inhabitants - microorganisms. These tiny creatures were found everywhere: in a drop of water and a clod of earth, in saliva, and even on Leeuwenhoek itself. From 1673 detailed descriptions and the researcher sent sketches of his amazing observations to the Royal Society of London. But pundits were in no hurry to believe him. After all, their pride was hurt: "ignorant", "profane", "manufacturer", and there, in science. Leeuwenhoek, meanwhile, tirelessly sent new letters about his remarkable discoveries. As a result, the academicians had to recognize the merits of the Dutchman. In 1680 the Royal Society elected him a full member. Leeuwenhoek became a world celebrity. From everywhere they went to Delft to look at the curiosities discovered by his microscopes. One of the most distinguished guests was the Russian Tsar Peter I, a great hunter of everything new... Levenguk, who did not stop his research, was only hindered by numerous guests. Curiosity and excitement drove the discoverer. Over 50 years of observation, Leeuwenhoek discovered more than 200 types of microorganisms and was the first to be able to describe the structures that, as we now know, are human cells. In particular, he saw red blood cells and spermatozoa (in his then terminology, “balls” and “animals”). Of course, Leeuwenhoek did not assume that these were cells. But he examined and sketched in great detail the structure of the fiber of the heart muscle. Amazing observation for a person with such a primitive technique!

Anthony van Leeuwenhoek was, perhaps, the only scientist in the entire history of building a cell theory without a special education. But all the other, no less famous cell researchers studied at universities and were highly educated people. The German scientist Caspar Friedrich Wolff (1733–1794), for example, studied medicine in Berlin and then in Halle. Already at the age of 26, he wrote the work "Theory of Origin", for which he was sharply criticized by his colleagues in his homeland. (After that, at the invitation of the St. Petersburg Academy of Sciences, Wolf came to Russia and stayed there until the end of his life.) What was new for the development of cellular theory Wolf's research? Describing "bubbles", "seeds", "cells", he saw them common features in animals and plants. In addition, Wolff was the first to suggest that cells may play a role in the development of an organism. His work helped other scientists to correctly understand the role of cells.

It is now well known that the main part of the cell is the nucleus. For the first time, by the way, Leeuwenhoek described the nucleus (in fish erythrocytes) back in 1700. But neither he nor many other scientists who saw the nucleus attached much importance to it. Only in 1825, the Czech biologist Jan Evangelista Purkinje (1787-1869), while studying the egg of birds, drew attention to the nucleus. “A compressed spherical bubble, dressed in the thinnest shell. It ... is full of productive power, which is why I called it the "embryonic vesicle," the scientist wrote.

In 1837, Purkinje reported to the scientific world the results of many years of work: in every cell of the animal and human body there is a nucleus. This was very important news. At that time, only the presence of a nucleus in plant cells was known. This conclusion was reached by the English botanist Robert Brown (1773–1858) a few years before Purkinje's discovery. Brown, by the way, introduced the term “nucleus” itself (lat. Nucleus). And Purkinje, unfortunately, failed to generalize the accumulated knowledge about cells. An excellent experimenter, he turned out to be too cautious in his conclusions.

By the middle of the XIX century. science has finally come close to completing the edifice called "cell theory". The German biologists Matthias Jakob Schleiden (1804–1881) and Theodor Schwann (1810–1882) were friends. Their destinies have a lot in common, but the main thing that united them was the “human itch of knowledge” and a passion for science. The son of a doctor, a lawyer by education, Matthias Schleiden, at the age of 26, decided to drastically change his fate. He again entered the university - at the Faculty of Medicine and after graduating he took up plant physiology. The goal of his work was to understand how cells are formed. Schleiden quite rightly believed that the leading role in this process belongs to the nucleus. But, describing the emergence of cells, the scientist, alas, was mistaken. He believed that each new cell develops inside the old one. And this, of course, is not so. In addition, Schleiden thought that animal and plant cells have nothing in common. That is why he did not formulate the basic postulates of the cell theory. This was done by Theodor Schwann.

Growing up in a very religious family, Schwann dreamed of becoming a clergyman. In order to better prepare for a spiritual career, he entered the Faculty of Philosophy at the University of Bonn. But soon the love for the natural sciences overpowered, and Schwann moved to the medical faculty. After graduation, he worked at the University of Berlin, where he studied the structure of the dorsal string, the main organ of the nervous system of animals from the order of cyclostomes (a class of aquatic vertebrates, which include lampreys and hagfishes). The scientist discovered the sheath of nerve fibers in humans (later called Schwann). Schwann was engaged in serious scientific work for only five years. In the prime of life and fame, he suddenly abandoned his studies, left for a small, quiet Liege and began to teach. Religion and science never managed to get along in this remarkable man.

In October 1837, a most important event for science took place in Berlin. It all happened in a small restaurant where two young men went to eat. Years later, one of them, Theodor Schwann, recalled: “Once, when I was having lunch with Herr Schleiden, this famous botanist pointed out to me the important role that the nucleus plays in the development of plant cells. I immediately remembered that I had seen a similar organ in the cells of the dorsal string, and at the same moment I realized the extreme importance that my discovery would have if I could show that in the cells of the dorsal string this nucleus plays the same role as the nucleus plants in the development of their cells ... From that moment on, all my efforts were directed towards finding evidence for the preexistence of the cell nucleus.

Efforts were not in vain. Two years later, his book "Microscopic studies on the correspondence in the structure and growth of animals and plants" was published. It outlined the basic ideas of cell theory. Schwann was not only the first to see in the cell that which unites both animals and plant organisms, but also showed the similarity in the development of all cells.

Of course, the authorship with Schwann is shared by all the scientists who erected the “building”. And especially Matthias Schleiden, who gave a friend a brilliant idea. There is a well-known aphorism: "Schwann stood on the shoulders of Schleiden." Its author is Rudolf Virchow, an outstanding German biologist (1821-1902). Virchow also owns another popular expression: "Omnis cellula e cellula", which is translated from Latin "Every cell is from a cell." It was this postulate that became the triumphant laurel wreath for Schwann's theory.

Rudolf Virchow studied the importance of the cell for the whole organism. He, who graduated from the Faculty of Medicine, was especially interested in the role of cells in diseases. Virchow's work on diseases served as the basis for new science — pathological anatomy. It was Virchow who introduced the concept of cellular pathology into the science of disease. But in his quest, he went too far. Representing a living organism as a "cellular state", Virchow considered the cell to be a full-fledged personality. “The cell... yes, it is precisely a person, moreover, an active, active person, and its activity is... a product of phenomena connected with the continuation of life.”

Years passed, technology developed, an electron microscope appeared, giving an increase of tens of thousands of times. Scientists have managed to unravel many mysteries contained in the cell. Division was described in detail, cell organelles were discovered, biochemical processes in the cell were understood, and finally the structure of DNA was deciphered. It would seem that there is nothing new to learn about the cell. And yet there is still a lot of misunderstood, unsolved, and for sure, future generations of researchers will lay new bricks in the building of cell science!

Who first discovered the cage? and got the best answer

Answer from Irina Ruderfer[guru]
1665 - English physicist R. Hooke in his work "Micrography" describes the structure of cork, on thin sections of which he found correctly located voids. Hooke called these voids "pores, or cells." The presence of a similar structure was known to him in some other parts of plants.
1670s - the Italian physician and naturalist M. Malpighi and the English naturalist N. Gru described "sacs or vesicles" in various plant organs and showed the wide distribution of the cellular structure in plants. Cells were depicted in his drawings by the Dutch microscopist A. Leeuwenhoek. He was the first to discover the world of unicellular organisms - he described bacteria and protists (ciliates).
The researchers of the 17th century, who showed the prevalence of the "cellular structure" of plants, did not appreciate the significance of the discovery of the cell. They imagined cells as voids in a continuous mass of plant tissue. Grew considered cell walls as fibers, so he introduced the term "tissue", by analogy with textile fabric. Studies of the microscopic structure of animal organs were of a random nature and did not provide any knowledge about their cellular structure.

Answer from Alienne[guru]
Anthony van Leeuwenhoek

Answer from Polina Gavrikova[newbie]
Hook)

Answer from Pavel Khudyakov[newbie]
gook

Answer from 3 answers[guru]

Hello! Here is a selection of topics with answers to your question: Who was the first to open the cage?

1. For the first time I saw and described plant cells: R. Virchow; R. Hooke; K. Baer; A. Leeuwenhoek. 2. Improved the microscope and saw unicellular organisms for the first time: M. Schleiden; A. Levenguk; R. Virchow; R. Hooke.

3. The creators of the cell theory are: Ch. Darwin and A. Wallace; T. Schwann and M. Schleiden; G. Mendel and T. Morgan; R. Hooke and N. G. 4. cell theory unacceptable for: fungi and bacteria; viruses and bacteria; animals and plants; bacteria and plants. 5. The cellular structure of all living organisms testifies to: the unity of the chemical composition; variety of living organisms; the unity of the origin of all living things; unity of animate and inanimate nature

Prokaryotes are organisms whose cells do not have a nucleus. Prokaryotes (from lat. about - before, instead of Greek. karion core) - over the kingdom of organisms, which includes the kingdoms of Archaea (Archaebacteria) and Real bacteria (Eubacteria). True bacteria include bacteria proper and cyanobacteria (the obsolete name is "blue-green algae"). Nuclear analogue - a structure consisting of DNA, proteins and RNA.

Prokaryotic cells have a surface apparatus and cytoplasm, which contains a few organelles and various inclusions. Prokaryotic cells do not have most organelles (mitochondria, plastids, endoplasmic reticulum, Golgi complex, lysosomes, cell center, etc.).

The sizes of prokaryotes usually vary between 0.2-30 µm in diameter or length. Sometimes their cells are much larger; thus, some species of the genus Spirochaete can reach up to 250 microns in length. The shape of prokaryotic cells is diverse: spherical, rod-shaped, in the form of a comma or a spirally twisted thread, etc.

The composition of the surface apparatus of prokaryotic cells includes a plasma membrane, a cell wall, and sometimes a mucous capsule. In most bacteria, the cell wall consists of the high molecular weight organic compound murein. This compound forms a mesh structure that stiffens the cell wall.

In cyanobacteria, the outer layer of the cell wall contains the polysaccharide pectin and specific contractile proteins. They provide forms of movement such as sliding or rotating.

The cell wall often includes a thin layer - the so-called outer membrane, which, like the plasma membrane, contains proteins, phospholipids and other substances. It provides an increased degree of protection of the contents of the cell. The cell wall of bacteria has antigenic properties.

The mucous capsule consists of mucopolysaccharides, proteins or polysaccharides with protein inclusions. It is not very tightly bound to the cell and is easily destroyed by certain compounds. The surface of the cells of some bacteria is covered with numerous thin filamentous outgrowths. With their help, bacterial cells exchange hereditary information, interlock with each other or attach to the substrate.

The ribosomes of prokaryotes are smaller than the ribosomes of eukaryotic cells. The plasma membrane can form smooth or folded protrusions into the cytoplasm. On folded membrane invaginations are respiratory enzymes and ribosomes, and on smooth - photosynthetic pigments.

In the cells of some bacteria (for example, purple ones), photosynthetic pigments are located in closed sac-like structures formed by invaginations of the plasma membrane. Such bags can be located singly or collected in heaps. Similar formations of cyanobacteria are called thylakoids; they contain chlorophyll and are located singly in the surface layer of the cytoplasm.

Some bacteria and cyanobacteria that inhabit reservoirs or soil capillaries filled with water have special gas vacuoles filled with a gas mixture. By changing their volume, bacteria can move through the water column with minimal energy consumption.

Many true bacteria have one, several, or many flagella. Flagella can be several times longer than the cell itself, and their diameter is insignificant (10-25 nm). The flagella of prokaryotes only superficially resemble the flagella of eukaryotic cells and consist of a single tube formed by a special protein. Cyanobacteria cells lack flagella.

Features of the vital processes of prokaryotes § Prokaryotic cells can absorb substances with only a small molecular weight. Their entry into the cell is provided by the mechanisms of diffusion and active transport. § Prokaryotic cells reproduce exclusively asexually: by dividing in two, occasionally by budding. Before division, the hereditary material of the cell (DNA molecule) doubles.

Transfer of adverse conditions by prokaryotes When adverse conditions occur, sporulation occurs in some prokaryotes. Some prokaryotes are capable of encysting (from Latin in - in, inside and Greek cystis - bubble). In this case, the entire cell is covered with a dense membrane. Prokaryotic cysts are resistant to radiation and desiccation, but, unlike spores, they are unable to withstand exposure to high temperatures. In addition to experiencing adverse conditions, spores and cysts ensure the spread of prokaryotes with the help of water, wind or other organisms.

Let's draw conclusions § Prokaryotic cells do not have a nucleus and many organelles (mitochondria, plastids, endoplasmic reticulum, Golgi complex, lysosomes, cell center, etc.). Prokaryotes are unicellular or colonial organisms. § The surface apparatus of prokaryotic cells includes a plasma membrane, a cell wall, and sometimes a mucous capsule placed above it. The composition of the cell wall of most bacteria includes a high-molecular organic compound murein, which gives it rigidity. § In the cytoplasm of prokaryotes there are small ribosomes and various inclusions. The plasma membrane can form smooth or folded protrusions into the cytoplasm. Respiratory enzymes and ribosomes are located on folded membrane invaginations, on

Let's draw conclusions § In the cells of prokaryotes there are one or two nuclear zones of the nucleoid, where the hereditary material is located - the circular DNA molecule. § The cells of some bacteria have organelles of movement, one, several or many flagella. § Prokaryotic cells reproduce by dividing in two, occasionally by budding. For some species, the known process of conjugation, during which cells exchange DNA molecules. Spores and cysts provide prokaryotes with the ability to survive adverse conditions and spread in the biosphere.

The first person to see cells was an English scientist Robert Hooke(known to us thanks to Hooke's law). AT 1665 trying to figure out why Cork tree swims so well, Hooke began to examine thin sections of cork with the help of an improved microscope. He found that the cork was divided into many tiny cells, which reminded him of monastic cells, and he called these cells cells (in English, cell means "cell, cell, cell"). AT 1675 italian doctor M. Malpighi, and in 1682- English botanist N. Gru confirmed the cellular structure of plants. They began to talk about the cell as a "bubble filled with nutritious juice." AT 1674 dutch master Anthony van Leeuwenhoek(Anton van Leeuwenhoek, 1632 -1723 ) using a microscope for the first time I saw “animals” in a drop of water - moving living organisms ( ciliates, amoeba, bacteria). Leeuwenhoek also observed animal cells for the first time - erythrocytes and spermatozoa. Thus, by the beginning of the 18th century, scientists knew that under high magnification plants had a cellular structure, and they saw some organisms, which were later called unicellular. AT 1802 -1808 years French explorer Charles Francois Mirbel found that all plants are composed of tissues formed by cells. J. B. Lamarck in 1809 extended Mirbel's idea of ​​the cellular structure to animal organisms. In 1825 a Czech scientist J. Purkyne discovered the nucleus of the egg cell of birds, and in 1839 coined the term protoplasm". In 1831 an English botanist R. Brown first described the nucleus of a plant cell, and in 1833 established that the nucleus is an essential organelle of a plant cell. Since then, the main thing in the organization of cells is not the membrane, but the content. cell theory the structure of organisms was formed in 1839 German zoologist T. Schwannom and M. Schleiden and included three provisions. In 1858 Rudolf Virchow supplemented it with one more provision, however, there were a number of errors in his ideas: for example, he assumed that cells are weakly connected with each other and each exists “by itself”. Only later was it possible to prove the integrity of the cellular system. AT 1878 Russian scientists I. D. Chistyakov open mitosis in plant cells; in 1878 W. Flemming and PI Peremezhko discover mitosis in animals. AT 1882 V. Flemming observes meiosis in animal cells, and in 1888 E Strasburger - in vegetable.

18. cell theory- one of the most recognized biological generalizations that affirm the unity of the principle of the structure and development of the world plants, animals and other living organisms cellular structure, in which the cell is considered as a common structural element of living organisms.

19.Basic provisions of the cell theory

Modern cell theory includes the following main provisions:

No. 1 A cell is a unit of structure, life activity, growth and development of living organisms, there is no life outside the cell;.

No. 2 A cell is a single system consisting of many elements that are naturally connected with each other, representing a certain integral formation;

No. 3 Cells of all organisms are similar in their chemical composition, structure and functions;

#4 New cells are formed only as a result of the division of the original cells;

№5 Cells of multicellular organisms form tissues, organs from tissues. The life of an organism as a whole is determined by the interaction of its constituent cells;

№6 Cells of multicellular organisms have a complete set of genes, but differ from each other in that they have different groups of genes, which results in morphological and functional diversity of cells - differentiation.

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

Since the 1840s, the study 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 the further development of 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 Remarque. 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.

XXcentury

Cell theory from the second half of XIX century, it 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 1950s, a Soviet biologist O. B. Lepeshinskaya, based on the data of her research, put forward a "new cellular 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 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 a complex chemical substance. 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 vital manifestations of the organism in the sum of the vital manifestations 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, the gametes of animals or plants are not just cells 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, i.e. 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 off from the 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.

You already know that all living organisms are made up of cells. Some are just one cell (many bacteria and protists), others are multicellular.

A cell is an elementary structural and functional unit of an organism that has all the basic features of a living thing. Cells are capable of multiplying, growing, exchanging matter and energy with environment respond to changes in the environment. Each cell contains hereditary material, which contains information about all the signs and properties of this organism. In order to understand how a living organism exists and works, it is necessary to know how cells are organized and function. Many processes inherent in the body as a whole take place in each of its cells (for example, the synthesis of organic substances, respiration, etc.).

The study of the structure of the cell and the principles of its life is engaged in cytology(from Greek. kitos- cell, cell and logos - teaching, science).

The history of the discovery of the cell. Most of the cells are small and therefore cannot be seen with the naked eye. Today it is known that the diameter of most cells is in the range of 20 - 100 microns, and in spherical bacteria it does not exceed 0.5 microns. Therefore, the discovery of the cell became possible only after the invention of a magnifying device - a microscope. This happened at the end of the 16th - beginning of the 17th century. However, only half a century later, in 1665, the Englishman R. Hooke used a microscope to study living organisms and saw cells. R. Hooke cut off a thin layer of cork and saw its cellular structure, similar to a honeycomb. R. Hooke called these cells cells. Soon the cellular structure of plants was confirmed by the Italian physician and microscopist M. Malpighi and the English botanist N. Gru. Their attention was drawn to the shape of the cells and the structure of their membranes. As a result, the idea of ​​cells was given as "sacs" or "vesicles" filled with "nutritive juice".

A significant contribution to the study of the cell was made by the Dutch microscopist A. van Leeuwenhoek, who discovered unicellular organisms - ciliates, amoeba, and bacteria. He was also the first to observe animal cells - erythrocytes and spermatozoa.

AT early XIX in. attempts are made to study the internal contents of the cell. In 1825, the Czech scientist J. Purkynė discovered the nucleus in the egg of birds. He also introduced the concept of "protoplasm" (from the Greek. protos - first and plasma - decorated), which corresponds to today's concept of the cytoplasm. In 1831, the English botanist R. Brown first described the nucleus in plant cells, and in 1833 he came to the conclusion that the nucleus is an essential part of the plant cell. Thus, at this time, the idea of ​​the structure of cells changed: the main thing in the organization of the cell was considered not the cell wall, but its internal contents. *

Cell theory. In 1838, the work of the German botanist Matthias Schleiden was published, in which he expressed the idea that the cell is the basic structural unit of plants. Based on the works of M. Schleiden, the German zoologist and physiologist T. Schwann just a year later, he published the book Microscopic Studies on Conformity in the Structure and Growth of Animals and Plants, in which he considered the cell as a universal structural component of animals and plants. T. Schwann made a number of generalizations, which were later called cell theory:

All living beings are made up of cells;

Plant and animal cells have a similar structure;

Each cell is capable of independent existence;

The activity of an organism is the sum of the vital processes of its constituent cells.

T. Schwann, like M. Schleiden, mistakenly believed that cells in the body arise from non-cellular substances. Therefore, a very important addition to the cell theory was the principle of Rudolf Virchow: "Each cell is from a cell" (1859).

In 1874, the young Russian botanist I.D. Chistyakov observed cell division for the first time. Later, the German scientist Walter Fleming described in detail the stages of cell division, and Oskar Hertwig and Eduard Strasburger independently concluded that information about the hereditary characteristics of the cell is contained in the nucleus. Thus, the work of many researchers confirmed and supplemented the cellular theory, the basis of which was laid by T. Schwann.

Currently, the cell theory includes the following main provisions.