In discrete and continuous time models of life sciences, physics and engineering, it very often happens, that the difference/differential equation contains parameters and the value of these parameters are often only known approximately. In particular, they are generally determined by measurments which are not exact. For that reason, it is important to study the the behavior of the solutions and examine their dependence of parameters. This study leads to the bifurcation theory what is getting more and more important in most fields of engineering and sciences. Nevertheless, these theories are hardly included in standard university curricula.