All processes in organisms, from the interaction of molecules to complex functions of the brain and other organs, obey physical laws. Mathematical modeling is an important step towards uncovering the organizational principles and dynamic behavior of biological systems. In general mathematical models can take many forms depending on the time scale and the space structure of the problem. For example, in population dynamics, if there is a complete overlap between generations, then the population changes in a continuous manner and studies of such systems involve the
use of differential equations. For example, the equation