Cell Theory Cell theory states: All living things are composed of one or more cells. The cell is the smallest unit that retains the properties of life. New cells arise from pre-existing cells.

Abiogenesis vs. biogenesis Abiogenesis (aka spontaneous generation): the theory that living things can come from non-living things. Ex. Aristotle said that flies could be produced by rotting food. Biogenesis: the theory that living things must come from other, pre-existing living things. Ex. Flies come from the reproduction of other flies.  Accepted