One of the main means of studying the essence of the laws of process dynamics in living systems is mathematical modelling. Construction of adequate mathematical models is not quite simple a problem and demands joint efforts of physicists, mathematicians, medical men, and biologists. Models can be of different levels of complexity. I would like to confine this discussion to only one of the dynamical processes description methods, that is, by means of ordinary differential equations. At the same time we will not consider spatiatemporal (wave) processes that are the subject for a separate discussion.