A stem cell is a cell that can divide an unlimited number of times by mitosis. When it divides, each new cell has the potential to remain a stem cell or to differentiate into a specialised cell. The extent of the power of a stem cell to produce different cell types is variable and referred to as its potency. A simple yet enjoyable way to demonstrate the potency of different types of stem cell is to use plasticine or modeling clay.
Start by giving each student an identical ball of plasticine and ask them to model it into an animal of their choosing. As you can see, in today’s lesson we had a snail, a penguin, a pig, a cat, two fish and a snake. In other words, the plasticine has the potential to be absolutely any animal in the world. As such, it can be described as having high potency, much like the embryonic totipotent stem cells which can differentiate into any type of cell.
Next, explain that some of the totipotent stem cells differentiate into specialised cells in the placenta (demonstrate this by removing a few of the now ‘specialised’ animals but provide their sculptors with a new ball of plasticine in order for them to continue with the activity) whereas others become a second type of stem cell, called pluripotent stem cells.
Pluripotent stem cells have lower potency than the totipotent cells but can still form all of the cells that will lead to the development of the embryo and later the adult. Demonstrate this reduced potency by asking the students to roll their plasticine back into a ball before modeling it into an animal of their choosing but stipulating that it must now be an animal with four legs. In case you were wondering, we now have an elephant, two pigs, two lizards, a tortoise, and a cat.
Again, explain that many of the pluripotent stem cells differentiate into specialised cells (as before, remove some of the now ‘specialised’ animals and replace with a new ball of plasticine) but that some become multipotent stem cells, found in the organs and tissues of adults. Multipotent stem cells have far lower potency than embryonic stem cells and can typically only differentiate into a very small number of specialised cell types. So, once again, ask the students to roll their plasticine back into a ball before modeling it into an animal of their choosing…so long as that animal is either a dog or a cat!