Stochastic models play an important part in many fields of science like physics and biology. In this thesis the influence of randomness in two such models is considered. It is therefore divided into two parts.

The first part deals with diffraction. Starting from a deterministic model we analyze the influence of randomness. The main result is the proof of the absence of singular continuous parts in the diffraction measure of particle gases with short range interaction.

The second part deals with recognition in the immune system. In this part the main focus lies in the probabilistic modeling itself, preparation of the mathematical tools, and the analysis to show the ability of the models to explain the reliable recognition of foreign invaders by certain white blood cells.