Developing biofilm using the CA modeling approach on a flat surface due to diffusion of a single limiting substrate from the top boundary. The system is transport limited [Used by permission of John Wiley and Sons, from Picioreanu C, van Loosdrecht MCM, Heijnen JJ (1998) Mathematical modeling of biofilm structure with a hybrid differential-discrete cellular automaton approach. Biotechnology and Bioengineering, Vol. 58, Fig. 6, p. 111].