Randomness is inherent in many biological processes, from the dynamics of the populations in an ecosystem down to the systems of biochemical reactions occurring within a single cell. Therefore, when trying to analyze these processes, we might consider using a stochastic model — that is, one that includes some form of randomness.

Can stochastic models behave significantly differently from deterministic models? (Yes!) What might a stochastic model look like? How exactly does one use a stochastic model to say anything useful? We'll look at a few biological examples, introduce a particular stochastic model called a Markov chain, and see how, using a tool called Monte Carlo simulation, we can gain some insight into the biological systems we model.