Formally established by Theodor Schleider and Matthias Schwann in 1839, cell theory (or cell doctrine) is the most basic tenet underlying the field of biology. Modern cell theory states that
- The cell is the structural and functional unit of all living things.
- All organisms are composed of one or more cells.
- New cells come from pre-existing cells; lifeforms today have descended in unbroken continuity from the first primitive cells that arose on earth more than 3.5 billion years ago.
- Hereditary information passes from parent cell to child cell.
- All cells have the same basic chemical structure.
- The fundamental biochemical reactions of life take place within cells.