The cell example is very cool. It's not a Markov chain though. The probability that a cell grows from size 2 to size 3 (in probabilistic notation, P(2->3|2) ),

The cell example is very cool. It's not a Markov chain though. The probability that a cell grows from size 2 to size 3 (in probabilistic notation, P(2->3|2) ), for instance, would be 2/(sum of all cell sizes), and the sum of all cell sizes is growing by 1 each period (assuming the unit of food given per period is 1, etc. etc.)