A cell is a structural and functional unit of all living organisms, which is characterized by its own metabolism and ability to reproduce. From the environment that surrounds it, the cell is delimited by the plasma membrane. There are two main types of cells: prokaryotic, which has an unformed nucleus, characteristic of bacteria and archaea, and eukaryotic, in which there is a nucleus, characteristic of all others. cell forms life, including plants, fungi and animals. Only viruses belong to non-cellular life forms, but they do not have their own metabolism and cannot reproduce outside living cells.

All organisms are divided into unicellular, colonial and multicellular. Unicellular organisms include bacteria, archaea, some algae and fungi, as well as protozoa. Colonial and multicellular organisms consist of a large number of cells. The difference between the two is that colonial organisms are made up of undifferentiated or weakly differentiated cells that can survive without each other. The cells of multicellular organisms are more or less specialized in performing certain functions and dependent on each other in the processes of life. In multicellular organisms belongs to the number and man, whose body consists of about 10 cells.

History of discovery and research of cells

Most eukaryotic cells are up to 100 microns in size, and prokaryotic cells are an order of magnitude smaller, so a person cannot see them with the naked eye. The discovery and study of cells became possible only after the invention by Jansen optical microscope(1590). to the most important events related to early development cell biology include
1665 - Robert Hooke first saw dead cells while examining the structure of cork under a microscope. Hooke believed that cells are empty, and cell walls are living matter.
1650-1700 - Anthony van Leeuwenhoek first observed living cells under a microscope, in particular protozoa, as well as red blood cells.
1831-1839 - Robert Brown described the nucleus as a spherical body found in plant cells.
1838-1839 - botanist Matthias Schleiden and zoologist Theodor Schwann, combining the ideas of different scientists, created a cellular theory, according to which the cell is the basic structural and functional unit of living organisms.
1840 - Purkinje proposed the name protoplasm to refer to the cellular content, making sure that it is the content, and not the cell walls, that is the living substance.
1855 - Virchow proved that all cells are formed from other cells by division.
1866 - Haeckel established that the nucleus carries out the preservation and transmission of hereditary traits.
1866-1898 - describes the main components of the cell, which can be seen under an optical microscope. Cytology acquires the character of an experimental science.
1900 - after the advent of genetics, cytogenetics begins to develop, studying the behavior of chromosomes during division and fertilization, its influence on the hereditary characteristics of organisms.
1946 - use began in biology electron microscope, which made it possible to study the ultrastructure of cells.

cell theory

The cell theory was formulated in 1838-1839 by the botanist Matthias Schleiden and the zoologist Theodor Schwann. These scientists proved the fundamental similarity between animals and plant cells, and based on all the knowledge accumulated by that time, it was postulated that the cell is the structural and functional unit of all living organisms. 1855 Rudolf Virchow supplemented the cell theory with the assertion of Lat. "Omnis cellula ex cellula" - "Each cell is from a cell."

The cell theory is one of the fundamental ideas modern biology, it became indisputable proof of the unity of all living things and the foundation for the development of such disciplines as embryology, histology and physiology. Key points cell theory have not lost their relevance, however, after the creation it was supplemented, and now it includes the following statements:
A cell is an elementary unit of structure, functioning, reproduction and development of all living organisms; there is no life outside the cell.
Cell - complete system containing a large number of bound friend with other elements - organelles.
Cells of different organisms are similar (homologous) in structure and basic properties and have a common origin.
The increase in the number of cells occurs by their division, after the replication of its DNA: a cell - from a cell.
A multicellular organism is new system, a complex ensemble of many cells, united and integrated into systems of tissues and organs, interconnected by chemical factors: humoral and nervous.
Cells of multicellular organisms have the same set of genetic information, but differ in the level of expression (work) of individual genes, which leads to their morphological and functional diversity - differentiation.

Recall from sections 6 and 7 of the grades when the first studies of plant and animal cells began. What instruments are used to study the cellular structure of organisms?

Rice. 36. Robert Hooke's microscope and the section of cork he saw

Most organisms on Earth have a cellular structure. A cell is a structural and functional unit of the living, capable of self-reproduction, which is characterized by all the signs of the living.

The history of the discovery of the cellular structure of organisms. The cell was discovered in the middle of the 17th century. Then the English naturalist Robert Hooke (1635-1703) for the first time saw and described the cellular structure of plants with the help of a microscope.

Examining a thin section of cork at high magnification of the microscope, Hooke was struck by its complex structure. He wrote: “Taking a piece of clean light cork, I cut off a very thin plate from it with a razor-sharp penknife. When I then began to examine it under a microscope, ... I clearly saw that it was all riddled with holes and pores ... These pores were not deep, but consisted of very many small cells, isolated from a continuous pore by special partitions. Such a structure is not characteristic of cork alone” (Fig. 36).

With these words, in 1665, Robert Hooke first reported the existence of the cell. He was also the first to use the term "cell" (cellula) to refer to the cell wall he saw. This term has firmly entered biology, and its discovery marked the beginning of the study of the cellular structure of organisms.

Further study of the cellular structure of organisms is associated with the name of the Dutch researcher A. Leeuwenhoek. The lenses made by the scientist gave a magnification of 300 times, which made it possible to make a number of great discoveries: to describe bacteria, protozoa (ciliates), erythrocytes, spermatozoa. After the publication of his research, Leeuwenhoek became widely known as the greatest scientist of his time (Fig. 37).

Rice. 37. Anton van Leeuwenhoek (1632-1723)

Creation of the first cell theory. Cells began to be studied especially intensively in the 19th century, which was associated with the improvement of microscopes. In 1939, summarizing numerous microscopic studies cells, German scientists zoologist Theodor Schwann and botanist Matthias Schleiden (Fig. 38) formulated the main provisions of the cell theory: 1) all organisms are made up of cells; 2) cells are the smallest structural units of life; 3) cells in the body arise by neoplasms from non-cellular substances.

In some conclusions, scientists were wrong. In particular, the position on the emergence of new cells turned out to be incorrect. But the basic idea of ​​the cellular structure of organisms was correct.

After the creation of the cell theory, cell research became leading in biology. Thanks to the work of many scientists, the structure of the cell nucleus was studied in detail, and the most important biological processes that occur with cells were analyzed. Particularly significant were the studies of the German physician and scientist Rudolf Virchow (Fig. 38), who corrected and supplemented the cellular theory. In 1858, he substantiated the principle of cell succession: "each cell comes from a cell by dividing the original cell."

Rice. 38. The founders of the cell theory (from left to right): Matthias Schleiden (1804-1881), Theodor Schwann (1810-1882) and Rudolf Virchow (1821 - 1902)

The cell theory has basically been formulated. However, the methods of studying the cell were imperfect, and the science of the cell had not yet taken shape as an independent scientific discipline.

Cytology is the science of the cell. On the turn of XIX-XX centuries a new section of biology arose and formed - cytology (from the Greek kitos - vessel, here - cell and logos - doctrine) - a science that studies the structure and functions of cells. The further development of this science was directly related to discoveries in physics, chemistry and the improvement of microscopic technology.

Rice. 39. Microscopes: 1 - light; 2 - electronic. Images of cells obtained from different microscopes: 3 - light; 4 - electronic

Currently, to study cells, scientists use various methods. The microscopy method makes it possible to study in detail the appearance of cells, their microstructure (Fig. 39). In a light microscope, you can see fairly large organelles, such as the nucleus, mitochondria, chloroplasts, the Golgi apparatus. An electron microscope gives a magnification 1000 times greater than a light microscope, which allows you to examine in detail the structure of individual organelles.

With the help of physicochemical and biochemical methods, organic and inorganic substances of the living, their functions and pathways of transformations in the cell have been studied. The use of cell and tissue culture methods made it possible to observe the growth and reproduction of cells outside the body, to isolate growth factors, to determine the effect of various substances on cells, and to obtain cell hybrids by cell fusion.

The main provisions of modern cell theory:

1. a cell is a structural and functional unit of the living, which is an elementary living system, which is characterized by all the main features of the living;
2. cells of all organisms have a similar chemical composition and general structural plan;
3. a new cell arises as a result of the division of the original cell;
4. multicellular organisms develop from a single source cell;
5. the similarity of the cellular structure of organisms indicates the unity of their origin.

The light microscope was significantly improved in the period from 1887-1900. The development of chemistry and biochemistry has led to the development of new methods for fixing and staining micropreparations. From that moment on, cytology as a science acquired an experimental character. In 1930, an electron microscope was constructed, which made it possible to study the ultrastructure of the cell.

Lesson learned exercises

1. By whom and when was the cellular structure of organisms first discovered?
2. Name the authors of the first cell theory and formulate its main provisions.
3. Why did it take about 200 years from the discovery of cells to the formation of cell theory?
4. What does cytology study?
5. What methods are used by modern cytologists?
6. What are the advantages of an electron microscope over a light microscope?

"Biology. General biology. A basic level of. Grades 10-11 ". V.I. Sivoglazov (gdz)

History of the discovery and study of the cell. cell theory

Question 1. Tell us about the history of the discovery of the cell.
The discovery of the cellular structure of living organisms became possible thanks to the advent of the microscope. Its prototype was invented in 1590 by the Dutch glass grinder Zachary Jansen. The first microscope is known to have consisted of a tube attached to a stand and had two magnifying glasses.
The importance of the microscope for studying the structure of sections of plant and animal objects was first appreciated by the English physicist and botanist Robert Hooke. In 1665, on sections of cork, he discovered structures resembling honeycombs, and called them cells or cells. However, Hooke was wrong, believing that cells are empty, and living matter is cell walls.
Dutch naturalist Anthony van Leeuwenhoek in the second half of the 17th century. improved the microscope and was the first to see living cells. He observed and drew a number of protozoa, spermatozoa, bacteria, erythrocytes and even their movement in capillaries.

Question 2. By whom and when was the cell theory first formulated?
The study of plant and animal cells made it possible to generalize all the features of their structure. In 1838, M. Schleiden created the theory of cytogenesis (cell formation). His main merit is to raise the question of the origin of cells in the body. In 1839, T. Schwann, based on the work of M. Schleiden, created a cell theory. The main provisions of the cell theory (M. Schleiden and T Schwann):
1) all tissues are made up of cells;
2) plant and animal cells have common principles of structure, tk. arise in the same way;
3) each individual cell is independent, and the activity of the organism is the sum of the vital activity of individual cells.
In 1858, R. Virchow also paid great attention to the further development of the cellular theory. He not only brought together all the numerous disparate facts, but also convincingly showed that cells are a permanent structure and arise only by multiplying their own kind - “every cell comes from another cell as a result of division, just like a plant is formed from a plant, and from animals animals”, i.e. discovered cell division.

Question 3. List modern provisions cell theory.
In our time, cytology, using the achievements of genetics, molecular and physico-chemical biology, is developing very rapidly. And although the main provisions of the theory of T. Schwann and M. Schleiden remain relevant, the data obtained made it possible to form a deeper understanding of the structure and functions of the cell. Based on them, the modern cellular theory was formulated. We list its main provisions:
1) a cell is a unit of structure, functioning, reproduction and development of living organisms;
2) the cells of all organisms are similar in structure and chemical composition;
3) cell reproduction occurs by dividing the mother cell;
4) cells of multicellular organisms are specialized: they perform different functions and form tissues.

Question 4. Describe the importance of cell theory for the development of biology.
According to philosophers who have studied the history of science (for example, Friedrich Engels), cell theory is one of the greatest discoveries 19th century She played a huge role in the development of not only biology, but also natural science in general. Protozoa, bacteria, many fungi and algae are cells that exist separately from each other. The body of all multicellular organisms - plants, fungi and animals - is built from more or less cells, which are the elementary structures that make up a complex organism. Regardless of whether a cell is an integral living system or a part of it, it has a set of features and properties common to all cells.
The cell theory for the first time unequivocally pointed to the unity of the living world. With its appearance, the gap between the animal kingdom and the plant kingdom disappeared. On the basis of cell theory in the middle of the XIX century. Cytology arose - a science that studies the structure and functions of the cell.
Consider which representatives organic world the concepts of "cell" and "organism" are the same.
A cell is the basic structural, functional and genetic unit of the organization of living things, an elementary living system. A cell can exist as a separate organism.
The concepts of "cell" and "organism" coincide in the case when we are talking about unicellular organisms. These include prokaryotes, or non-nuclear ones (in particular, bacteria), and from eukaryotes, or nuclear ones, the simplest ones (such as ciliates shoe, chlamydomonas, green euglena). Their body consists of one cell, which implements all the functions of the body - metabolism, irritability, reproduction, movement. Various organelles contribute to these functions, including special purpose(for example, flagella and cilia provide movement). unicellular organisms often able to form clusters - colonies. However, the concept of a “multicellular organism” is still inapplicable to a colony, since the cells that make up it have the same type of structure (they are not divided into tissues), interact weakly with each other and, being isolated from the colony, continue to independently exist and multiply without any problems.