We show numerical results of a system conformed by two ordinary differential equations coupled with a diffusion equation, arising in a previous model of differentiated growth of fungal biomass governed by the oxygen present at different levels. Using finite differences we solve the diffusion problem and compare the influence of different boundary conditions. Times of biomass changes from vegetative to competent at each depthlevel inside the medium are determined. Calculations of the critical substrate thickness and the distribution of biomass respect to time and depth, are showed. The oxygen flow through the open boundary is also studied.