(A) Relationship [Eqn. (15)] between the probability of kill for all k cells vs. normalized cumulative singlet oxygen concentration ([1O2]rx/[1O2]rx0), where [1O2]rx0 is the cumulative singlet oxygen to produce 1/e cell kill [Eqn. (14)]. The number of cells k varies between 106 and 1014. (B) [1O2]rx,sh/[1O2]rx0 vs. k based on P=0.5 [Eqn. (16)].