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The Cell Theory Biology 11 S. Dosman What are cells? • Cells are defined as the smallest unit of life. • All living things are either unicellular (composed of only one cell) or multicellular (composed of more than one cell). Robert Hooke • In 1665, English scientist Robert Hooke discovered cells while looking at cork under his primitive microscope . • Hooke first viewed cells in a thin slice of cork. He named them “cells” as they reminded him of the shape of the cells (rooms) in a monastery. Cork cells • Hooke did not realize that what he was seeing was the cell walls and the empty space inside the dead cork cells. • So although he was the first to see cells he did not fully understand what he was seeing. Anton van Leeuenhoek • Anton von Leeuenhoek was one of the major contributors to the invention of the microscope. • In 1674, Leeuenhoek first described living cells – blood, bacteria & unicellular pond organisms. Robert Brown • Robert Brown was a Scottish botanist who is credited with naming the nucleus of the cell around 1820. • The nucleus had been observed before however he was the first to name it. Felix Dujardin • In 1835, Felix Dujardin recognized the existence of one-celled organisms and that protoplasm seemed to be associated with all forms of life. Matthias Schleiden • In 1838, the German botanist Schleiden stated that all plants are composed of cells. Theodor Schwann • One year later in 1839, another German physiologist named Theodor Schwann stated that all animals are composed of cells. Rudolph Virchow • In 1858, the Polish scientist Rudolph Virchow made a very important generalization that all cells come from other cells. • In other words, all cells come from pre-existing cells. And after many, many years we have what many refer to as the cornerstone of modern Biology…. The Cell Theory 1. All living things are composed of cells. 2. The cell is the basic living unit of organization 3. All cells arise from pre-existing cells.
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