T. Schwann. According to this theory, All organisms have a cellular structure. The cell theory asserted the unity of the animal and plant worlds, the presence of a single element of the body of a living organism - the cell. Like any major scientific generalization, the cell theory did not arise suddenly: it was preceded by individual discoveries of various researchers.
The discovery of the cell belongs to the English naturalist R. Hooke, who in 1665 first examined a thin section of a cork under a microscope. The cut showed that the cork had a cellular structure, like a honeycomb. R. Hooke called these cells cells. Following Hooke, the cellular structure of plants was confirmed by the Italian biologist and physician M. Malpighi (1675) and the English botanist N. Grew (1682). Their attention was attracted by the shape of the cells and the structure of their membranes. As a result, the idea of cells was given as “bags” or “bubbles” filled with “nutritional juice”.
Further improvement of the microscope and intensive microscopic studies led to the establishment by the French scientist C. Brissot-Mirbe (1802, 1808) of the fact that all plant organisms are formed by tissues that consist of cells. J.B. Lamarck (1809) went even further in generalizations, who extended Brissot-Mirbet’s idea of cellular structure to animal organisms.
At the beginning of the 19th century. Attempts are being made to study the internal contents of the cell. In 1825, a Czech scientist I. Purkin discovered the nucleus in the egg of birds. 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 the cell changed: the main thing in its organization began to be considered not the cell wall, but the contents.
The closest person to the formulation of the cell theory was the German botanist M. Schleiden, who established that the body of plants consists of cells.
Numerous observations regarding the structure of the cell and a generalization of the accumulated data allowed T. Schwann in 1839 to draw a number of conclusions, which were later called the cell theory. The scientist showed that all living organisms consist of cells, that the cells of plants and animals are fundamentally similar to each other.
The cell theory was further developed in the works of the German scientist R. Virchow (1858), who suggested that cells are formed from previous mother cells. In 1874, the Russian botanist I.D. Chistyakov, and in 1875, the Polish botanist E. Strassburger, discovered cell division - mitosis, and thus, R. Virchow's assumption was confirmed.
The creation of the cell theory became the most important event in biology, one of the decisive proofs of the unity of living nature. Cell theory had a significant influence on the development of biology as a science and served as the foundation for the development of such disciplines as embryology, histology and physiology. It made it possible to create the basis for understanding life, the individual development of organisms, and to explain the evolutionary connection between them. The basic principles of cell theory have retained their significance today, although more than in one hundred and fifty years new information was obtained about the structure, vital activity and development of the cell.
9. Basic provisions of the cell theory of Schleiden and Schwann. What additions did Virchow make to this theory? Current state of cell theory.
The main provisions of T. Schwann's cell theory can be formulated as follows.
The cell is the elementary structural unit of the structure of all living beings.
Cells of plants and animals are independent, homologous to each other in origin and structure.
M. Schdeiden and T. Schwann mistakenly believed that the main role in the cell belongs to the membrane and new cells are formed from intercellular structureless substance. Subsequently, clarifications and additions were made to the cell theory by other scientists.
In 1855, the German physician R. Virchow came to the conclusion that a cell can only arise from a previous cell by dividing it.
At the current level of development of biology, the main provisions of cell theory can be presented as follows.
A cell is an elementary living system, a unit of structure, life activity, reproduction and individual development of organisms.
The cells of all living organisms are similar in structure and chemical composition.
New cells arise only by dividing pre-existing cells.
The cellular structure of organisms is proof of the unity of origin of all living things.
10. Chemical composition of the cell
11. Types of cellular organization. The structure of pro- and eukaryotic cells. Organization of hereditary material in pro- and eukaryotes.
There are two types of cellular organization:
1) prokaryotic, 2) eukaryotic.
What is common to both types of cells is that the cells are limited by the membrane, the internal contents are represented by the cytoplasm. The cytoplasm contains organelles and inclusions. Organoids- permanent, necessarily present, components of the cell that perform specific functions. Organelles may be bounded by one or two membranes (membrane organelles) or not bounded by membranes (non-membrane organelles). Inclusions- non-permanent components of the cell, which are deposits of substances temporarily removed from metabolism or its final products.
The table lists the main differences between prokaryotic and eukaryotic cells.
|
Sign |
Prokaryotic cells |
Eukaryotic cells |
|
Structurally formed core |
Absent | |
|
Genetic material |
Circular non-protein bound DNA |
Linear protein-bound nuclear DNA and circular non-protein-bound DNA of mitochondria and plastids |
|
Membrane organelles |
None | |
|
Ribosomes |
80-S type (in mitochondria and plastids - 70-S type) |
|
|
Not limited by membrane |
Bounded by the membrane, inside the microtubules: 1 pair in the center and 9 pairs at the periphery |
|
|
Main component of the cell wall |
Plants have cellulose, fungi have chitin. |
12. Similarities and differences between plant and animal cells. Organoids for special and general purposes.
The structure of a plant cell.
There are plastids;
Autotrophic type of nutrition;
ATP synthesis occurs in chloroplasts and mitochondria;
There is a cellulose cell wall;
Large vacuoles;
The cellular center is only found in lower animals.
The structure of an animal cell.
There are no plastids;
Heterotrophic type of nutrition;
ATP synthesis occurs in mitochondria;
There is no cellulosic cell wall;
Vacuoles are small;
All cells have a cell center.
Similarities
Fundamental unity of structure (surface cell apparatus, cytoplasm, nucleus.)
Similarities in the occurrence of many chemical processes in the cytoplasm and nucleus.
The unity of the principle of transmission of hereditary information during cell division.
Similar membrane structure.
Unity of chemical composition.
ABOUTgeneral purpose organella : endoplasmic reticulum: smooth, rough; Golgi complex, mitochondria, ribosomes, lysosomes (primary, secondary), cell center, plastids (chloroplasts, chromoplasts, leucoplasts);
Organelles for special purposes: flagella, cilia, myofibrils, neurofibrils; inclusion (non-permanent components of the cell): spare, secretory, specific.
|
Major organelles |
Structure |
Functions |
|
Cytoplasm |
Internal semi-liquid medium of fine-grained structure. Contains nucleus and organelles |
Provides interaction between the nucleus and organelles Regulates the speed of biochemical processes Performs a transport function |
|
ER - endoplasmic reticulum |
A membrane system in the cytoplasm" that forms channels and larger cavities; EPS is of 2 types: granular (rough), on which many ribosomes are located, and smooth |
Carries out reactions associated with the synthesis of proteins, carbohydrates, fats Promotes the transport and circulation of nutrients within the cell Protein is synthesized on granular EPS, carbohydrates and fats are synthesized on smooth EPS. |
|
Ribosomes |
Small bodies with a diameter of 15-20 mm |
Carry out the synthesis of protein molecules and their assembly from amino acids |
|
Mitochondria |
They have spherical, thread-like, oval and other shapes. Inside the mitochondria there are folds (length from 0.2 to 0.7 µm). The outer cover of mitochondria consists of 2 membranes: the outer one is smooth, and the inner one forms cross-shaped outgrowths on which respiratory enzymes are located. |
Provides the cell with energy. Energy is released by the breakdown of adenosine triphosphoric acid (ATP) ATP synthesis is carried out by enzymes on mitochondrial membranes |
|
Plastids are characteristic only of plant cells and come in three types: |
Double-membrane cell organelles | |
|
chloroplasts |
They are green in color, oval in shape, and are bounded from the cytoplasm by two three-layer membranes. Inside the chloroplast there are faces where all the chlorophyll is concentrated |
Use light energy from the sun and create organic substances from inorganic ones |
|
chromoplasts |
Yellow, orange, red or brown, formed as a result of the accumulation of carotene |
Gives different parts of plants red and yellow colors |
|
leucoplasts |
Colorless plastids (found in roots, tubers, bulbs) |
They store reserve nutrients |
|
Golgi complex |
It can have different shapes and consists of cavities delimited by membranes and tubes extending from them with bubbles at the end |
Accumulates and removes organic substances synthesized in the endoplasmic reticulum Forms lysosomes |
|
Lysosomes |
Round bodies with a diameter of about 1 micron. They have a membrane (skin) on the surface, inside which there is a complex of enzymes |
Perform a digestive function - digest food particles and remove dead organelles |
|
Cell movement organelles |
Flagella and cilia, which are cell outgrowths and have the same structure in animals and plants Myofibrils - thin filaments more than 1 cm long with a diameter of 1 micron, located in bundles along the muscle fiber Pseudopodia |
Perform the function of movement They cause muscle contraction Locomotion due to the contraction of a special contractile protein |
|
Cellular inclusions |
These are the unstable components of the cell - carbohydrates, fats and proteins |
Spare nutrients used during cell life |
|
Cell center |
Consists of two small bodies - centrioles and centrosphere - a compacted section of the cytoplasm |
Plays an important role in cell division |
– an elementary structural and functional unit of all living organisms. It can exist as a separate organism (bacteria, protozoa, algae, fungi) or as part of the tissues of multicellular animals, plants and fungi.
History of the study of cells. Cell theory.
The life activity of organisms at the cellular level is studied by the science of cytology or cell biology. The emergence of cytology as a science is closely related to the creation of cell theory, the broadest and most fundamental of all biological generalizations.
The history of the study of cells is inextricably linked with the development of research methods, primarily with the development of microscopic technology. The microscope was first used to study plant and animal tissues by the English physicist and botanist Robert Hooke (1665). While studying a section of the elderberry core cork, he discovered separate cavities - cells or cells.
In 1674, the famous Dutch researcher Anthony de Leeuwenhoek improved the microscope (magnified 270 times) and discovered single-celled organisms in a drop of water. He discovered bacteria in dental plaque, discovered and described red blood cells and sperm, and described the structure of the heart muscle from animal tissues.
- 1827 - our compatriot K. Baer discovered the egg.
- 1831 - English botanist Robert Brown described the nucleus in plant cells.
- 1838 - German botanist Matthias Schleiden put forward the idea of the identity of plant cells from the point of view of their development.
- 1839 - German zoologist Theodor Schwann made the final generalization that plant and animal cells have a common structure. In his work “Microscopic Studies on the Correspondence in the Structure and Growth of Animals and Plants,” he formulated the cell theory, according to which cells are the structural and functional basis of living organisms.
- 1858 - German pathologist Rudolf Virchow applied the cell theory in pathology and supplemented it with important provisions:
1) a new cell can only arise from a previous cell;
2) human diseases are based on a violation of the structure of cells.
Cell theory in its modern form includes three main provisions:
1) cell - the elementary structural, functional and genetic unit of all living things - the primary source of life.
2) new cells are formed as a result of the division of previous ones; A cell is an elementary unit of living development.
3) the structural and functional units of multicellular organisms are cells.
Cell theory has had a fruitful influence on all areas of biological research.
, plants and bacteria have a similar structure. Later, these conclusions became the basis for proving the unity of organisms. T. Schwann and M. Schleiden introduced into science the fundamental concept of the cell: there is no life outside cells.
Cell theory has been supplemented and edited several times.
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Subtitles
Provisions of the Schleiden-Schwann cell theory
The creators of the theory formulated its main provisions as follows:
- The cell is the elementary structural unit of the structure of all living beings.
- Plant and animal cells are independent, homologous to each other in origin and structure.
Basic provisions of modern cell theory
Link and Moldnhower established the presence of independent walls in plant cells. It turns out that the cell is a certain morphologically separate structure. In 1831, G. Mol proved that even such seemingly non-cellular plant structures as water-bearing tubes develop from cells.
F. Meyen in “Phytotomy” (1830) describes plant cells that “are either single, so that each cell is a special individual, as is found in algae and fungi, or, forming more highly organized plants, they unite into more and less significant masses." Meyen emphasizes the independence of metabolism of each cell.
In 1831, Robert Brown described the nucleus and suggested that it was a permanent part of the plant cell.
Purkinje School
In 1801, Vigia introduced the concept of animal tissue, but he isolated tissue based on anatomical dissection 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 (especially G. Valentin should be highlighted) revealed in the first and most general form the microscopic structure of the tissues and organs of mammals (including humans). Purkinje and Valentin compared individual plant cells with individual microscopic tissue structures of animals, which Purkinje most often called “grains” (for some animal structures his school used the term “cell”).
In 1837, Purkinje gave a series of talks in Prague. In them, he reported on his observations on the structure of the gastric glands, nervous system, etc. The table attached to his report gave clear images of some cells of animal tissues. Nevertheless, Purkinje was unable to 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 conducted the comparison of plant cells and animal “grains” in terms of analogy, and not homology of these structures (understanding the terms “analogy” and “homology” in the modern sense).
Müller's 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 (notochord); his student Henle published a study on the intestinal epithelium, in which he described its various types and their cellular structure.
Theodor Schwann's classic research was carried out here, laying the foundation for the cell theory. Schwann's work was strongly influenced by the school of Purkinje and Henle. Schwann found the correct principle for comparing plant cells and elementary microscopic structures of animals. Schwann was able to establish homology and prove the correspondence in the structure and growth of the elementary microscopic structures of plants and animals.
The significance of the nucleus in a Schwann cell was prompted by the research of Matthias Schleiden, who published his work “Materials on Phytogenesis” in 1838. Therefore, Schleiden is often called the co-author of the cell theory. The basic idea of cellular 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, a nucleolus condenses from the smallest granularity, and around it a nucleus is formed, which is the cell maker (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, the very title of which expresses the main idea of cellular theory:
- 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. He further proves that the microscopic structures of other tissues and organs of the animal body are also cells, quite comparable to the cells of cartilage and notochord.
- The second part of the book compares plant cells and animal cells and shows their correspondence.
- In the third part, theoretical positions are developed and the principles of cell theory are formulated. 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 the opinion he expressed, following Schleiden, about the possibility of the emergence of cells from structureless non-cellular matter.
Development of cell theory in the second half of the 19th century
Since the 1840s of the 19th century, the study of the cell has become the focus of attention throughout biology and has been rapidly developing, becoming an independent branch of science - cytology.
For the further development of cell 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 is brought to the fore (Mol, Cohn, L. S. Tsenkovsky, Leydig, Huxley), which is reflected in the definition of a cell given by M. Schulze in 1861:
A cell is a lump of protoplasm with a nucleus contained inside.
In 1861, Brücko put forward a theory about the complex structure of the cell, which he defines as an “elementary organism,” and further elucidated the theory of the formation of cells from a structureless substance (cytoblastema), developed by Schleiden and Schwann. It was discovered that the method of formation of new cells is cell division, which was first studied by Mohl on filamentous algae. The studies of Negeli and N.I. Zhele played a major role in refuting the theory of cytoblastema using botanical material.
Tissue cell division in animals was discovered in 1841 by Remak. It turned out that the fragmentation of blastomeres is a series of successive divisions (Bishtuf, N.A. Kölliker). The idea of the universal spread of cell division as a way of forming new cells is enshrined by R. Virchow in the form of an aphorism:
"Omnis cellula ex cellula."
Every cell from a cell.
In the development of cell theory in the 19th century, contradictions arose sharply, reflecting the dual nature of cellular theory, which developed within the framework of a mechanistic view of nature. Already in Schwann there is an attempt to consider the organism as a sum of cells. This tendency receives special development in Virchow’s “Cellular Pathology” (1858).
Virchow’s works had a controversial impact on the development of cellular science:
- He extended the cell theory to the field of pathology, which contributed to the recognition of the universality of cellular theory. Virchow's works consolidated the rejection of the theory of cytoblastema by Schleiden and Schwann and 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 elevated 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.
XX century
Since the second half of the 19th century, cell theory has acquired an increasingly metaphysical character, reinforced by Verworn’s “Cellular Physiology,” which 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 cell theory, the mechanistic theory of the “cellular state” appeared, including Haeckel as a proponent. According to this theory, the body is compared to the state, and its cells are compared to citizens. Such a theory contradicted the principle of the integrity of the organism.
The mechanistic direction in the development of cell theory was subjected to severe criticism. In 1860, I.M. Sechenov criticized Virchow’s idea of the cell. Later, the cell theory was criticized by other authors. The most serious and fundamental objections were made by Hertwig, A. G. Gurvich (1904), M. Heidenhain (1907), Dobell (1911). The Czech histologist Studnicka (1929, 1934) made extensive criticism of the cellular theory.
In the 1930s, Soviet biologist O. B. Lepeshinskaya, based on her research data, put forward a “new cell theory” as opposed to “Vierchowianism.” It was based on the idea that in ontogenesis, cells can develop from some non-cellular living substance. A critical verification of the facts laid down by O. B. Lepeshinskaya and her adherents as the basis for the theory she put forward did not confirm the data on the development of cell nuclei from nuclear-free “living matter”.
Modern cell theory
Modern cellular theory proceeds from the fact that cellular structure is the most important form of existence of life, inherent in all living organisms, except viruses. The improvement of cellular structure was the main direction of evolutionary development in both plants and animals, and the cellular structure is firmly retained in most modern organisms.
At the same time, the dogmatic and methodologically incorrect provisions of the cell theory must be re-evaluated:
- 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 life (metabolism, 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, they 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), which have 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, and most eukaryotes have mitochondria and chloroplasts. According to the theory of symbiogenesis, these semi-autonomous organelles are 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, has been reduced to the presence of a closed outer membrane made of a double layer of phospholipids (in archaebacteria it has a different chemical composition than in other groups of organisms), ribosomes and chromosomes - hereditary material in the form of DNA molecules forming 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 viewed 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 laws of the whole were replaced by the sum of the parts.
- Considering the cell to be a universal structural element, the cell 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 controversial issue in cellular theory in the sense that many complex multinucleated protist cells can be considered as supracellular structures. In tissue cells, germ cells, and protists, a general cellular organization is manifested, expressed in the morphological separation 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, possessing genetic, morphological, and sometimes environmental characteristics and 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 - cytoskeletal elements, eukaryotic-type ribosomes, etc.
- The dogmatic cell theory ignored the specificity of non-cellular structures in the body or even recognized them, as Virchow did, as non-living. In fact, in the body, in addition to cells, there are multinuclear supracellular structures (syncytia, symplasts) and nuclear-free intercellular substance, which has the ability to metabolize and is therefore alive. To establish the specificity of their life manifestations and their significance for the body 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 parent 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 cell 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 completely accessible to research and discovery. The cells of a multicellular organism are not individuals capable of existing independently (the so-called cell cultures outside the body 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. A cell cannot be separated from its environment (as, indeed, any living systems). Focusing all attention on individual cells inevitably leads to unification and a mechanistic understanding of the organism as a sum of parts.
Cleared of mechanism and supplemented with new data, the cell theory remains one of the most important biological generalizations.
For the first time, cells, or rather the cell walls (shells) of dead cells, were discovered in sections of cork using a microscope by the English scientist Robert Hooke in 1665. It was he who proposed the term “cell”.
Later, the Dutchman A. Van Leeuwenhoek discovered many single-celled organisms in drops of water, and red blood cells (erythrocytes) in human blood.
The fact that in addition to the cell membrane, all living cells have an internal content, a semi-liquid gelatinous substance, scientists were able to discover only at the beginning of the 19th century. This semi-liquid gelatinous substance was called protoplasm. In 1831, the cell nucleus was discovered, and all living contents of the cell - protoplasm - began to be divided into the nucleus and cytoplasm.
Later, as microscopy techniques improved, numerous organelles were discovered in the cytoplasm (the word “organoid” has Greek roots and means “organ-like”), and the cytoplasm began to be divided into organelles and the liquid part - hyaloplasm.
Famous 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 basic principles 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 became clear that the sperm and the egg are also cells that connect with each other during 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, cell theory was supplemented with more and more new provisions. In its modern form, the main provisions of 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 a living thing.
This postulate has been fully proven by modern cytology. In addition, the cell is a self-regulating and self-reproducing system open to exchange with the external environment.
Currently, scientists have learned to isolate various components of the cell (down to individual molecules). Many of these components can even function independently if given the right conditions. For example, contractions of the actin-myosin complex can be caused by adding ATP to the test tube. The artificial synthesis of proteins and nucleic acids has also become a reality in our time, but all these are just parts of life. For the full functioning 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 necessary to maintain 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 membrane, which, on the one hand, isolates its contents from the environment, and on the other, controls the flow of substances into and out of the cell.
Organelles or organelles are permanent specialized structures in the cells of living organisms. 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, energy metabolism, protein biosynthesis occurs in cells, and the ability to reproduce appears. Organelles began to be compared with the organs of a multicellular organism, hence this term.
In multicellular organisms, a significant diversity of cells is clearly visible, which is associated with their functional specialization. If you compare, for example, muscle and epithelial cells, you will notice that they differ from each other in the preferential development of different types of organelles. Cells acquire features of functional specialization, which are necessary to perform specific functions, as a result of cellular differentiation during ontogenesis.
3. Any new cell can be formed only as a result of division of the mother cell.
Reproduction of cells (i.e., increase in their number), whether prokaryotes or eukaryotes, can only occur by dividing existing cells. Division is necessarily preceded by a process of preliminary doubling of genetic material (DNA replication). The beginning of an organism’s life is a fertilized egg (zygote), i.e. a cell formed by the fusion of an egg and a sperm. The rest of the diversity of cells in the body is the result of countless divisions. Thus, we can say that all cells in the body are related, developing in the same way from the same source.
4. Multicellular organisms are living organisms consisting of many cells. Most of these cells are differentiated, i.e. differ in their structure, functions and form different tissues.
Multicellular organisms are integral systems of specialized cells regulated by intercellular, nervous and humoral mechanisms. It is necessary to distinguish 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 contain noncellular elements, for example, the intercellular substance of connective tissue, bone matrix, and blood plasma.
As a result, we can say that all the 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.
Cell theory had a huge influence on the development of not only biology, but also natural science in general, since it established the morphological basis of the unity of all living organisms and provided a general biological explanation of life phenomena. In terms of its significance, cellular theory is not inferior to such outstanding achievements of science as the law of energy transformation or the evolutionary theory of Charles Darwin. So, the cell - the basis for the organization of representatives of the kingdoms of plants, fungi and animals - arose and developed in the process of biological evolution.
