Cut a flatworm in half

Learning biological scales through an experiment with planaria in a classroom of Biology.

Students DUSU

The planaria (Schmidtea mediterranea) are unique organisms. They are flatworms and usually found in freshwater, and can reproduce asexually. Planaria are one of the most primitive organisms to have a central nervous system. And if you cut them up, they grow back, nervous system intact, no matter what part you slice. Each piece grows into its own, fully formed organism. Most of all, they can be found quite close to where we live and learn in the undergraduate programme of Biology.

An experiment with the planaria in the classroom

At our University, our faculty at the undergraduate science programme has biologists from intensive scientific backgrounds. They like to think of biological scales: from molecules, cells, tissues, organisms to ecological environments. This is a core part of what they bring to coursework, asking students to think about how biological scales are distinct yet related. What happens at the cellular level does not happen in isolation.

In our classroom exploring these questions, our students sometimes take us in interesting directions. Pooja Pravinbabu, a student of third year Biology, chose to study the planaria or flatworm. In her thesis work, Pooja Pravinbabu took a look at this ability of the flatworm to regenerate to ask a few questions:

If you cut the planaria in half, what would both parts be like? 

A planaria can be cut up into 250 pieces, each of which can grow back into a unique organism. One of the many interesting aspects of this unique regenerative power is that it is useful for understanding the link between cellular to molecular biological scales.

Is the daughter planaria’ is identical to its parent, and is memory passed through generations? How do living organisms retain memory across generations? How does the stockhouse of memory then get transmitted across generations? 

Guided by our colleague Sravanti Uppaluri, Pooja set up a small experiment. Setting up the planaria in a box with a unidirectional Y path, a blue light (that the organism did not like) was shined on the organism to direct their movement. Pooja began to train the flatworms to respond to certain stimuli to remember a small behaviour. With simple Pavlovian negative and positive stimulus response, the flatworms could be trained to remember what to do and what not to do. 

  • Planaria
  • Y path

Schematic representation of planaria and conditioning experiment. 


Once the planaria was conditioned to move in a particular direction, it could be cut up into further pieces on any part of its 1 – 3 cm body, and each resulting part regenerated into a fully formed organism. 

Could the cut up flatworm remember’?

The spliced up new flatworms had their own simple nervous system. What was interesting was that the progeny remembered’ to move in the same direction as the first planaria. Not in the way that you remember an appointment you have the day after, but the way dogs can be trained to expect to eat at 4 pm. 

In observing the daughter planaria move and inherit memory, Pooja found that answer to the question where does memory lie’ was the memory was all over the body of the flatworm. Each amputated part of the planaria could remember the direction in which it moved, which helped Pooja learn about the cells where the memory was stored, and the tissue and nervous system, and about natural habitat.

Pooja went on to write her undergraduate thesis Memory Transmission Following Amputation and Nerve Regeneration in Planaria’.

Meet our faculty member, Sravanti Uppaluri, who guides students in their thesis questions.