SUMMARY: Planarians are tiny squishy worms that go through binary fission by ripping themselves in two parts: the head part and the tail part. This article looks at the mechanism by which they do the ripping. First, there is the formation of the waist, then pulsation of the head, then ripping. The waist can form anywhere either before or after the pharynx and is necessary to make sure gut contents don’t spill out. The pulsation provides the tension for the ripping and the two parts regenerate in a week due to stem cells.
LESSON COMMENTS: At first glance, this seems like a simple biology lesson, but physics teachers can use this as an example of forces. Planarians are easy to order and grow in the classroom. Teachers can decapitate the worms and induce the binary fission of planarians in the classroom so students can observe first hand. Some physics concepts include: leverage, force, and friction.
Malinowski, P. T., Cochet-Escartin, O., Kaj, K. J., Ronan, E., Groisman, A., Diamond, P. H., & Collins, E. S. (2017). Mechanics dictate where and how freshwater planarians fission. Proceedings of the National Academy of Sciences of the United States of America, 114(41), 10888-10893.