Answer:
Cell theory is a fundamental theory for biology formulated in the mid-19th century, providing a basis for understanding the laws of the living world and for developing evolutionary teachings. The Englishman Robert Hooke was the first in 1665 using magnifying lenses to observe the division of cork oak bark tissues into cells, although it was ascertained that he discovered not cells (in his own concept of the term), but only the outer shells of plant cells. Later, the world of unicellular organisms was discovered by Leeuwenhoek. He first saw animal cells (red blood cells). Later, animal cells were described by F. Fontana, but these studies at that time did not lead to the concept of the universality of the cell structure, because there was no clear idea of what a cell was.
Leeuwenhoek did not represent the described morphological structures as cell formations. His research was random, not systematic. G. Link, G. Travenarius and C. Rudolph showed with their studies that cells are not voids, but independent ones limited by the walls of formation. It was found that the cells have contents that Purkyne called protoplasm. R. Brown described the nucleus as a constant part of the cells.
Matthias Schleiden and Theodor Schwann formulated the cellular theory based on many studies on the cell (1838-1839). Rudolf Virchow later (1855) supplemented it with the most important provision “every cell comes from another cell”. Schleiden and Schwann, summarizing the existing knowledge about the cell, proved that the cell is the basic unit of any organism. The cells of animals, 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 the fundamental idea of the cell into science: there is no life outside the cells.
The intensive development of cytology in the 20th and 21st centuries confirmed the basic principles of cell theory and revealed some incorrect theses of Schwann's cell theory, namely, that a single cell of a multicellular organism can function independently, that a multicellular organism is a simple collection of cells, and the development of a cell comes from a non-cellular “blastema.”
To bring the cellular theory into more complete correspondence with the data of modern cellular biology, the list of its positions is often supplemented and expanded. In many sources, these additional provisions differ, and their set is quite arbitrary.
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