In 1838, Matthias Schleiden and Theodor Schwann proposed the first two beliefs of the cell theory. All organisms are composed of one or more cells. The smallest living unit of structure and function of all organisms is the cell. More than ten years later, Rudolf Virchow, proposed the third idea or belief of the cell theory. All cells arise from preexisting cells.
All cells are either prokaryotic or eukaryotic.
Prokaryotic cells are bacteria and eukaryotic cells make up all other organisms. They are distinguishable by the types of organelles or internal structures they contain. Eukaryotic cells are larger and more complex. Prokaryotes are smaller and do not have a true nucleus. The genetic material floats freely in the cytoplasm of the cell.