Microorganisms differ in their effectiveness in uptake and selection of substances that they bring in from the environment. They also differ in how they balance the allocation of nutrients for immediate and for delayed use. Moreover, they may not take up resources as fast as they seemingly could, and they may extrude derivatives of substances just pumped in. A good deal of these apparent choices must reside in the uptake systems and the linkage of these with the cell's intermediate metabolism. An important feature is that a resource may vary in concentration from time to time, nutrient to nutrient, and habitat to habitat. This variation must have been critical to the evolution of regulatory processes. Some possibilities for the combined uptake and consumption are considered for substrates serving the same (homologous) and different (heterologous) roles for the bacterium. From the membrane transport processes diagrammed in Fig. 1c and Fig. 2 and corresponding computer program given in Appendix A, the combined effect of uptake processes and cell growth can be studied. The model can be modified for various alternate models to study the possible control of cellular uptake and metabolism for the range of ecological roles of the bacterium.