Cell: The Unit of Life

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The cell is the fundamental structural and functional unit of all living beings. In unicellular organisms, one cell performs all life processes. In multicellular organisms, cells specialize and work t…

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A. G. Loewy and P. Siekevitz defined the cell in 1963 as a unit of biological activity delimited by a semipermeable membrane and capable of self-reproduction in a medium free of other living systems.

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Robert Hooke observed a honeycomb-like pattern in cork under a primitive microscope in 1665 and coined the term cells. These were dead cell walls enclosing empty spaces, not living cells.

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Anton van Leeuwenhoek first described a live cell with a simple microscope. He observed bacteria, protozoa, spermatozoa, and red blood cells.

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Cell theory states that the cell is the unit of structure and function of all living beings, all cells arise from previously existing cells, all cells are basically alike in chemical composition and m…

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Rudolf Virchow extended cell theory in 1858 by stating that all living cells arise from pre-existing living cells. This idea is expressed as Omnis cellula-e-cellula.

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Totipotency is the capability of a single cell to develop into a whole organism under specific conditions. It shows that a living cell can retain the potential to form a complete plant.

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Viruses are acellular organisms. They do not have cellular organisation and do not possess metabolic machinery for vital activities, so they are not truly cellular.