The cell

The cell
    Cell is the basic structural land functional unit of life. The cell is the simplest and smallest unit capable of carrying all the life activities. The cell may be defined as a "unit of biological activity delimited by a selectivity premeable membrane and capable of self- reproduction in a medium free of other living systems."
    Each cell is capable of performing the basic functions of life such as respiration, reproduction, excretion, growth and so on. All the life activities exhibited by the living organism are the result of combined action of these cells. In the unicellur organism a single cell performs all the life activities. Hence cell is considered as the structural and functional unit of life.

Discovery of cell
   
The science of cells began to develop only after the discovery of compound microscope by Jansens in 1590. The term "cell" was introduced by an English Scientist Robert Hooke in his book Micrographia published in London in 1665. He observed plant cells for the first time in 1665 using the compound microscope. He observed a thin section of cork and found that the bottle cork was not a homogeneous compact material but consisted many empty small cavities bounded by definite walls.
Anton Van Leeuwenhoek, the famous Dutch microscopist observed for the first time green colored bodies in the cells of plants. These bodies are now called chloroplasts. He also observed and described the bacteria and uncellur organisms.
In 1831, Robert Brown, an English Botanist described nucleus as a spherical body in plant cells. German biologists Schleiden (Botanist) and Theodar Schwann (Zoologist) formulated their well known "cell theory" in 1839, out of their parallel and independent studies of the tissues or plants and animals.
    Purkinje, the Bohemian physiologist in 1839 introduced the term protoplasm for the living content of the cell. In 1855, Rudolf Virchow stated the fact that all the cells in the body arise from pre-existing cells by cell division.