The modern understanding of cells is largely determined on the basis of Cell Theory. A lot of people say "theory" when what they really mean is "hypothesis." A hypothesis is a tentative explanation for something that has been observed or experienced, and can be tested for validity.
You can learn more about Hypothesizing in Science in the SOS package.
A theory, on the other hand, is a set of statements or principles made to explain a set of facts or circumstances. Lots of experiments and observations are done to test the ideas before it is accepted as a theory. Since new discoveries are being made every day, theories can be revised and refuted (disproved) through experimentation.
The discovery of the microscope in the 1600s allowed living material to be viewed in much greater detail than ever before. The next few hundred years brought refinements to the microscope's design, with the details of cells becoming more and more visible during this time. In the 1800s, on the basis of what scientists could see, cell theory was introduced.
To learn more about the microscope go to The Microscope section in the SOS package.
Cell theory has resulted from the evidence viewed in the microscope. The three basic ideas of modern cell theory are:
The cell is the fundamental unit of structure and function in living things.
All living things are composed of cells.
Cells come from preexisting cells.
Many scientists contributed to the theory, each adding details and observations, providing even more evidence. One scientist, Matthias Jacob Schleiden said all animals are made of cells, and another, Thomas Schwann, said the same of plants. Schwann later combined the two concepts and formulated the generalization, "all living things are made of cells."
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