Animal cell culture has already established itself as a mature technology able to make a wide range of valuable products, the actual focus being to find the competitive bioreactor design and operating conditions for increasing production. A complex analysis, implying sensitivity calculus and optimal control computation, is done for a system composed of a continuous perfectly mixed bioreactor, with cell recirculation, a cell separator, a mixer and a purge. The bioreactor's sensitivity to the control parameters is measured by a new concept, entropic density, developed from the notion of Shannon entropy. An optimization procedure based on a genetic-algorithms approach is applied for the computation of the inlet flow profile in time, which guarantees optimum monoclonal-antibody production. Our studies, including the present one, proved that the best approach to obtain high production is to use a hybrid operating sequence: fed-batch mode followed by the continuous mode.