Students ’ Protocol

Slime mold cells (Dictyostelium discoideum) are eukaryotes that live in the soil. Much of their life is spent as solitary cells, eating bacteria. When food sources get low, however, the cells come together, or aggregate, into a mound of cells. The gathered population of cells forms a slug that is phototactic and thermotactic. After the slug travels for a while and reaches the soil surface, 25% of the cells form a cellulose stalk that lifts the remaining cells. The remaining cells then produce spores that germinate later when food may be more abundant. Slime-U-Lator is a mathematical model Excel file that helps students understand the emergent property of slime mold aggregation. Aggregation: In order to understand what is happening in the Slime-U-Lator, you must know what happens to real cells during slime mold aggregation. When a cell becomes starved it begins to emit a chemical called cyclic adenosine monophosphate (cAMP) which signals to the other cells the lack of food. The cAMP emanates from the cell like waves of water radiating out from a stone thrown into a pond. When surrounding cells are hit by a cAMP wave, they move towards the higher concentration of cAMP for a minute or so and then release a wave of cAMP on their own to propagate the cAMP wave which in turn attracts more cells. This series of cAMP secretio