What is cell ? - Concept of cell - "The cell is smallest, systematically organised and functional unit of an organism"

                            CELL

 The cell is the the basic unit of organisation or structure of all living matter. With in a selective and relative semipermeable membrane, it contains a complete set of different kinds of unit necessary to permit its own growth and reproduction from simple nutrients. It has always been quite difficult to define cell.Different cell biologists have defined the cell differently as follows;A.G.Loewy and P.Siekevitz have defined a cell as " a unit of biological activity delimited by a a semipermeable membrane and capable of self reproduction in a medium free of of other living systems".Wilson and Morrison have defined the cell as " an integrated and continuously changing system m".John Paul has defined "the cell as the simplest integrated organisation in living systems capable of independent survival".

          All these definitions have excluded the virus. A virus is neither and organism nor a cell, yet it consists of a core of nucleic acid enclosed in a external mantle of a protein. In the free state virus are quite inert. They become activated only when they are in fact a living host cell and in the process only the nucleic acid core enter the host's cell. The nucleic acid which is the genetic substance, takes over the metabolic activity of the host cell and utilises the cell machinery for the formation of more viruses, ultimately killing the host cell. In a way, thus, viruses are cellular parasites that cannot reproduce by itself. But,because viruses are primitive and simpler units of life therefore, this should be discussed priir to other cell.

   

                           Cell  Pic.

         CELLS OF CELLULAR ORGANISMS

The body of all living organism (bacteria,blue green algae, plants and animals) except virus has cellular organism and may contain one or many cells. The organisms with only one cell in their body are cold unicellular organism (e.g., bacteria, blue green algae, some algae, protozoa etc.).The organisms having many cells in their body are called multicellular organisms that is most plants and animals. Any cellular organisms may contain only one type of cell from the following types of cells:

     A.Prokaryotic cells; B.Eukaryotic cells

The terms prokaryotic and eukaryotic was suggested by Hans Ris in the 1960's.

           TECHNIQUES IN CELL BIOLOGY 

                 Cells are tiny but complex bodies. it is difficult to see their structure; more difficult to understand their molecular composition and still difficult to find out the function of their various components. what one can learn about cells, depends on the toolsat one's disposal and in fact, major, advances in cell biology have frequently taken place with the introduction of new tools and techniques to the study of cell.Thus, to gain divergent types of information regarding cell's structure, molecular organisation and function, cell biologists have developed and employed various instruments and techniques.A basic knowledge of some of these methods is currently required.

                       MICROSCOPY

in the search for information about the structure and composition of cells, the cell biology test immediately face to limitations; the exceedingly small dimensions of cells and their component parts and the transparent nature of cells. the diameters of the majority of cells fall within a range of 0.2 and 50 micron metre. The human eyes have limited distinguishing or resolving power. The ability of an observational instrument such as a human eye for a microscope to reveal details of structure is expressed in terms of LIMIT OF RESOLUTION.