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  He studied the developement of organisms and how they develope gradualy
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  In the 1590's he invented the compound optical microscope which made observing cells much easier.
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  In the 1600's he observed the first cells from an organism, these ideas lead to cell theory.
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  In 1643 he did an experiment on the generation of miceprocing the did not just spontaneously appear. This is one of many experiments that lead to the rejection of spontaneous generation.
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  In 1674 he discovered single celled organisms while examining pound water under a microscope. And he coined the term cell theory.
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  Made the statement "All living organisms originate from and consist of cells" in 1805 which might have been the first statement of cell theory
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  In 1831 he discovered the nucleus and it role, which helped develope the second half of cell theory.
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  In 1839 he concluded that tissues are made of cells, laying the foundation for cell theory.
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  In 1839 he concluded that plants were made of cells and cells were the building blocks of all plant matter.
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  In 1840 he discovered that sperm and eggs are also made of cells, showing that humans were made of cells from beginning to end.
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  He is the one that dicovered that cells come from other prexiting cells, which was later used to study cells on the cellular level.
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  Louis Pateur was the one who disproved spontanius generation by proving that cells only for from prexisting cells.