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Hooke and Leeuwenhoek were two of the first scientists to use microscopes to study the microscopic world of cells. Hooke coined the term "cell" after observing the tiny compartments in cork, while Leeuwenhoek discovered a variety of living creatures in pond water, blood, and other samples. They contributed to cell theory, which states that 1) all living things are made of one or more cells, 2) cells are the basic unit of life, and 3) all cells come from other cells.

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