First to observe cells – named cells Robert Hooke in 1665

First to view Living cells Anton van Leeuwenhoek, who in 1674 described the algae Spirogyra and named the moving organisms animalcules

All Plants are made of cells. schleiden All Plants are made of cells.

All animals are made of cells Schwann All animals are made of cells

All cells come from other cells Virchow All cells come from other cells

The cell theory states: 1) All organisms are made of cells The observations of Hooke, Leeuwenhoek, Schleiden, Schwann, Virchow, and others led to the development of the cell theory. The cell theory states: 1) All organisms are made of cells 2) New cells come from reproduction of other cells 3) Cells are the basic units of life. (smallest unit that can be alive on its own)

Cell Theory Developed by Schwann, Schleiden, and Virchow. In 1839, Schwann and Schleiden suggested that cells were the basic unit of life. However, the cell theory of Schleiden proposed a method of cell production by spontaneous crystallization In 1855, Virchow said all cells come from pre-existing cells, thus completing the classical cell theory. (Note that the idea that all cells come from pre-existing cells had in fact already been proposed by Robert Remak; it has been suggested that Virchow plagiarised Remak.)[9]