To introduce the idea that bacteria and yeast can reproduce by "splitting," or binary fission. The cell doubles in size and then splits into two.

Reproduction of these microorganisms can be modeled as simple doubling. We introduced the students to the concept of population growth by doubling [1 cell -> 2 cells, those 2 cells -> 4 cells (2 each)] and then they worked through a series of ten doublings to see how the population can go from one to many.

Some students initially thought they could find how many cells there would be after 10 doublings by simply multiplying 2 x 10. However, after having them calculate the results of each doubling, they soon realized that this was not a simple multiplicative process. See " Representing Doubling " for more examples of students' thinking.