As a part of teaching of physics it is common to record data on evolution of a physical system and then construct a mathematical model of the system. For example, movement of a simple pendulum can be recorded, and then a mathematical model can be constructed to simulate the observed movement. The comparison between the observed data and the predictions based on the model then tell us how satisfactory the model is. In physical systems the model is usually based on fundamental principles of physics such as Newton's Laws. This article will deal with the application of a mathematical model to a biological process. The process involves the complete reduction of 15um nitrate by a bacterial culture in the presence of 0.01% glucose in 46 hrs. The simple mathematical model captures the observed changes and a deterministic model measures the percentage of fit. Including light and phytoplankton in this mathematical model would elucidate the competition between bacteria and phytoplankton for nitrate.