'All living things are made up of cells'. 'The cell is the basic unit of structure and function'. These generalised statements are known as Cell theory. This theory was forwarded by Mathias Schleiden and Theodor Schwann in 1838 - 39.
Today the cell theory includes four more ideas :
the cells are the building block of structures in living things
the cell is derived from other cells by division
the cell contains information that is used as instructions for growth, development and functioning
the cell is the functioning unit of life; the chemical reactions of life take place within cells.
The idea and concept of cell biology evolved during the 19th century as a result of gradual advancement in the field of microscopy and biochemis-try. Today the study of the structure of cells (cytology) is part of a major branch of biology known as cell biology. Due to its wide application many new branches have sprung up in biology. Some of the new branches related to cytology are, Cytotaxonomy, Cytogenetics, Cell physiology , Cytochemistry,Molecular Biology, Cytopathology and Cytoecology.
The cells are very minute and complex organisations. The small dimensions and transparent nature of cell and its organelles pose problems to cell biologists trying to understand its organisation and functioning. Various instruments and techniques have been developed to study cell structure, molecular organization and function.