Q. Who expanded the cell theory and suggested that all the cells arise from pre-existing cells?
Answer: Rudolf Virchow
Notes: Credit for developing cell theory is usually given to three scientists: Theodor Schwann, Matthias Jakob Schleiden, and Rudolf Virchow. In 1839, Schwann and Schleiden suggested that cells were the basic unit of life. In 1858, Rudolf Virchow concluded that all cells come from pre-existing cells, thus completing the classical cell theory.