READ: Discovery of Cells

The Cell Theory

The Cell Theory is one of the fundamental theories of biology. For two centuries after the discovery of the microscope by Robert Hooke and Anton van Leeuwenhoek, biologists found cells everywhere. Biologists in the early part of the 19^th century suggested that all living things were made of cells, but the role of cells as the primary building block of life was not discovered until  two German scientists, Theodor Schwann, a zoologist (studies animals), and Matthias Jakob Schleiden, a botanist (studies plants), suggested that cells were the basic unit of structure and function of all life. In 1838 Schleiden said that all plants were made from cells. In 1839 Schwann said all animals were made from cells. Later, in 1858, the German doctor Rudolf Virchow observed that cells divide to produce more cells. He proposed that all cells arise only from other cells. The collective observations of all three scientists form the Cell Theory, which states that:

• all organisms are made up of one or more cells,
• all the life functions of an organism occur within cells,
• all cells come from preexisting cells.