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These men were responsible for inventing the compound optical microscope, which made it easier and more practical for scientists to observe cells.

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His biggest contribution to the cell theory was when he discovered the existence of single-cell organisms. He discovered this by using a microscope to examine some pond water.

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Robert Hooke observed the the first organism with cells. After van Leeuwenhoek observed other organisms with cells, he came up with the theory that all organisms are made of cells, all life functions occur in cells, and cells come from other cells

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Robert Brown's discover of the nucleus inside the cell, helped provide more evidence of the cell theory.

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Matthias main contribution to the cell theory was when he defined the cell as the basic unit of plant structure.

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Theodor's main contribution to the cell theory was when he made the observation that all plant and animal tissues are composed of cells. As well as the fact that all cells in an organism are all identical.

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Rudolf Virchow was the final scientist that made a huge contiribution to the cell theory. He proclaimes that all cells come from from pre existing cells. Which from this we were able to lay the groundwork for pathology.