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  Cytology (Greek kutos, ‘vessel’ + ology), in the life sciences, is the study of the living cell, the basic unit of all life according to the cell theory stated in 1839 by the German biologists Theodor Schwann and Matthias Schleiden. They postulated that all living organisms are composed of one or more cells—and, in 1855, Rudolf Virchow added that cells can only arise by the division of pre-existing cells. Cytology was established as a science in 1892 when the German anatomist Oscar Hertwig proposed that the function of the organism reflects the function of its constituent cells. Modern cytology involves the study of cellular metabolism and of the genetic control of the cell.

The living cell is divided from its environment by a membrane, composed of fatty molecules, and the space within is filled with an aqueous solution (the cytoplasm) of molecules including proteins and carbohydrates. Discrete membrane-bounded regions of this cytoplasm, termed organelles, are found within all cells and have varying functions, including energy storage, energy transduction and protein production. Higher cells (eukaryotes) possess nuclei which are membrane-bounded organelles, containing the chromosomes which bear the genetic material as DNA. Communication between the nucleus and the cytoplasm is by RNA which passes out of the nucleus bearing genetic information in usable chunks. Simpler cells (prokaryotes), such as bacteria, have fewer organelles and no nucleus or chromosomes: genetic information, in the form of DNA or RNA, exists in the cytoplasm. Plant and bacterial cells have rigid cell walls in addition to the plasma membrane; animal cells have no cell wall but the plasma membrane is reinforced by networks of filaments which act as a scaffold and which may also be contractile, allowing the cell to move. A feature of cells is that they are specialized according to function, especially where they are part of a complex multicellular organism; thus a muscle cell is rich in contractile fibres and mitochondria, organelles which produce usable energy from sugars. RB

Further reading Christian de Duve, Blueprint for a Cell.



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