This figure illustrates 3 hypotheses of how a cancer stem cell may arise: (1) A stem cell undergoes a mutation, (2) A progenitor cell undergoes two or more mutations, or (3) A fully differentiated cell undergoes several mutations that drive it back to a stem-like state.
A chemical change has occurred because the wood has turned into a substance that can't be changed back to it's original form. The wood has turned to ash, chemical changes are non reversible.
