In Petri Dish, cells reproduce by binary fission. One parent cell splits into two daughter cells, and each daughter cell inherits half of the parent’s molecules.

To trigger binary fission, a parent cell must meet certain conditions:

1. It must build enough nucleotides to duplicate its genome. Daughter cells are clones of the parent cell, so they share the same genetic material. In order for both daughter cells to inherit the parent’s genome, the parent must have two copies of it.
2. It must build enough phospholipids so that its cell membrane is twice the minimum size. Cells in Petri Dish must have a minimum surface area in order to be viable, and when the parent cell splits in two, each daughter cell will only inherit half of the parent’s cell membrane. In Petri Dish, the number of phospholipids in the cell membrane determines the cell’s surface area, which then determines the cell’s volume.
3. It must stockpile a certain number of amino acids and energy units. These amino acids and energy units are used to build and operate specialized proteins that divide up the cell’s molecules and transport them to separate locations.

When the parent cell does divide, one daughter cell will occupy the same location in the petri dish that the parent cell occupied; the other daughter cell will occupy one of the adjacent locations. This is how a multicellular colony develops and grows.