We describe an envisionment-based qualitative simulation program. The program implements part of an axiomatic, first order theory that has been developed to represent and reason about space and time. Topological information from the modelled domain is expressed as sets of distinct topological relations holding between sets of objects. These form the qualitative states in the underlying theory and simulation. Processes in the theory are represented as paths in the envisionment tree. The algorithm is illustrated with an example of a simulation of phagocytosis and exocytosis - two processes used by unicellular organisms for garnering food and expelling waste material respectively.