This activity is a simulation to explore how conditions affect the population of rabbits, or of micro-organisms in a petri-dish. The rabbit population activity is for pupils to explore population changes over a fixed period. They can explore the effect of changing the conditions under which the rabbits live to highlight the importance of several life essential requirements. They can predict the effects of the conditions that they set before they run the program. The activity can be extended by introducing predators (foxes) to explore predator-prey relationships. The microorganism activity follows the same principles but has been designed for pupils to explore the growth of a population of microbes. Pupils can explore the effect of changing the conditions under which the microbes divide. The activity can be extended by introducing antibiotics to see how they affect population growth.