Exploring Regeneration Using an Interesting Model Organism, the Planarian
Students may be surprised at how much they can learn about themselves using model organisms like planarians! The unassuming planarian often makes its appearance in biology as a nonparasitic representative of the flatworms (phylum Platyhelminthes) during an exploration of animal phyla. But students can easily use planarians to investigate a variety of biological phenomena like animal behavior, mitosis, taxonomy, and more. The planarian is also a cost-effective, engaging, and easy-to-manage model organism that is used in both research and biology classrooms. Planarian cultures are easy to obtain. I purchase mine from a biological supply house, but you may choose to send your students into the field to collect them or get them from a researcher on campus.
As a college biology instructor in a health science–focused program, I use planarians along with BioInteractive resources to elicit student questions about regeneration of tissues and apply what we learn to human health topics. This lesson falls about mid-semester for my second-semester biology students, who are in a pre–physician assistant program. The BioInteractive activity “Investigating Planarian Behavior and Regeneration" is the basis for this lesson’s investigation.
I begin the activity by distributing planarians in small petri dishes along with a soft paintbrush (which can be used to nudge the planarians) and allowing the students to make observations. These cute critters immediately gain student interest. The planarian’s physical form and eyespots become visible with a simple hand lens or dissection microscope. I encourage students to generate questions about the planarians, such as: How do planarians move? What senses do planarians use to explore their environment? Students often move to making inferences about where planarians exist naturally, what planarians eat, and other ideas about planarians’ niche. If time allows, I may give students a chance to share their observations via a quick Google Jamboard. If not, students simply share their observations within their groups.
Once students are engaged, I use a video segment to answer some of their questions. This segment is from the BioInteractive Identifying the Key Genes for Regeneration Scientists at Work video (1:18–1:45) and follows biologist Alejandro Sánchez Alvarado as he collects planarians from a local stream. At this point, the goal is for students to generate questions, so I make sure to stop the video at the 1:45 time stamp. Moving further in the video could provide answers to student questions before they have an opportunity to investigate.
Now it is time to encourage students to explore similarities between humans and planarians. I show a short clip from the video Planarian Regeneration and Stem Cells (1:46–4:13) to allow students to learn more about the habitat of planarians, how and what planarians eat, characteristics of the planarian digestive and nervous systems, and anything else students can ascertain from the clip. At the 4:13 time stamp, the video moves on to other topics, so I stop it here.
I ask students to make note of the characteristics of planarians and then share within their small groups for a few minutes after the clip. At this point, the goal is to get students thinking about the similarities and differences between basic planarian anatomy and human anatomy and about differences in the regenerative ability of planarian and human structures. Example student questions include: How does regeneration differ at various levels (cell, tissue, organ, etc.)? And how could we test regeneration in humans?
Now we begin to generate a research plan and hypothesis for how planarians will respond to being cut in various ways. For this, we follow the instructions in Part 2 of the activity "Investigating Planarian Behavior and Regeneration.” As described in this activity, students generate preliminary hypotheses about the possible outcomes of cutting planarians in certain ways. Students may decide to test how small fragments regenerate in comparison to larger fragments, or they may look for differences in tissue regeneration after making longitudinal and transverse cuts through the planarian’s body. Students could also investigate the speed at which regeneration will occur or what the regenerated part will look like. I ask my students to explain how they came to their hypothesis as a result of their observations, their new knowledge from the video segments, and their wonderings.
Over the next two weeks, students make observations and measurements while feeding the planarians. (The “Educator Materials” document for “Investigating Planarian Behavior and Regeneration” includes protocols for feeding and caring for the planarians.) At this point, students draw their results (comparisons of their planarians right after cutting and after two weeks) on whiteboards. Student groups can do a gallery walk and share their thoughts by placing sticky notes on the whiteboards. Alternatively, a representative from each table can summarize their findings to the class, using the whiteboard as a visual aid.
I now show them the "Why Two Heads?" Phenomenal Image and ask: How is this image different from your drawings?
Students notice that in their experiments, the planarians regenerate the structure that was removed. However, the image shows a planarian that has two heads instead of a head and tail. After students propose ideas about why this could have occurred, they watch the remainder of the Identifying Key Genes for Regeneration video (1:45 to the end).
The final section of the video efficiently and effectively explains how genes interact to guide regeneration and how scientists can disrupt normal regenerative processes in planarians to find out how the genes work. I ask students to make note of information that may be helpful in understanding what is occurring in their own planarians. Students then collaborate within their lab groups to generate claims, provide evidence, and discuss the biology behind their observations. They use this “claim, evidence, reasoning” framework to make sense of new information learned through the videos and their experiment.
Students also use this framework to write an abstract that serves as the assessment for this activity. Throughout the semester, I also guide my students in reading scientific papers (a great source for annotated scientific papers is Science in the Classroom) and ask them to make an outline of what they find in an abstract. Once I give them feedback on their outline, students can use it as a template to generate abstracts throughout the semester.
The final assessment for this lab includes their abstract and a simple digital poster (using a Google Slide). The poster contains any important images and representation of data and is shared in a Google Folder or Padlet. Students are invited to provide comments and questions on the abstracts of other students as a simple peer review.
I like this activity because it pulls together a number of science practices, such as applying the process of science, communicating and collaborating with other disciplines, asking questions and defining problems, planning and carrying out investigations, analyzing and interpreting data, and constructing explanations. The activity also requires students to pull from content in different areas of biology, emphasizing the highly interconnected nature of biological systems. It allows students to use an engaging but affordable model organism that is easy to store and feed. Finally, the activity is well supported by the educational materials that come with the lab, allowing teachers to learn about planarians and their care quickly. An additional resource, the Tissue Regeneration in Animals Click & Learn, may be helpful in scaffolding student learning or customizing this lesson to your own classroom.
If you have been hesitant in the past to use live organisms in your classroom, this may be a simple way to get comfortable with them. Who knows what you may be ready to tackle next!