About Cell (biology)

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Title Cell (biology)
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The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. Organisms can be classified as unicellular (consisting of a single cell; including most bacteria) or multicellular (including plants and animals). Humans contain about 100 trillion cells; a typical cell size is 10 µm and a typical cell mass is 1 nanogram. The human cell extrema are: largest - anterior horn in the spinal cord (135 μ vs. 120 μ for the ovum), longest - pseudounipolar cells which reach from extremities, including the toes to the lower brain stem, and smallest - granule cells in the cerebellum, at 4 µ. The largest known cells are unfertilised ostrich egg cells, which weigh 3.3 pounds. The cell was discovered by Robert Hooke in 1665. In 1835, before the final cell theory was developed, Jan Evangelista Purkyně observed small "granules" while looking at the plant tissue through...
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