The excretory system can be… well… excruciating to teach.
Well, ur-ine for a surprise because I have a model that can help teach the basic structure and basic function of the excretory system.
I bet you’re thinking… what a relief!
And I kidney you not, it will have your students crying “Urethra! I’ve found it!”
When I teach the excretory system, I use exhibition stations where the kids gather information about the stations, observe some materials depending on what is available, and perhaps do a mini lab here and there. It’s a great way to get students up and moving, and learning!
But, for some body systems, it’s hard to have models or hands on stations (the reproductive and endocrine systems, for example). For the excretory system, I knew there had to be some way of modeling our body’s filtration system. Though the excretory system exhibition lab has a couple model stations included, I thought I’d share this simple set up with you!
Excretory System Model Instructions
The model serves as a visual to help students see filtration in action, and using what they have learned about the kidneys, explain how the kidneys act as filtration devices.
The best part about the model is that you can re-use it. All you need to do is be able to take out the old coffee filters and replace them. You will also need a space in your room to secure a piece of cardboard (I had mine on a lab bench resting against the wall secured at the top).
Materials: 2 empty water bottles, clay, tubing (you can get fish tank tubing from amazon), coffee filters, cotton balls large piece of cardboard to mount model onto, packing tape, food coloring, beaker or plastic container
Instructions: Cut the bottoms off the empty water bottles, take off the caps and seal the opening with clay. Use a pen or pencil to create a small hole in the clay. Snip approximately 12-16 inches of tubing (2 pieces). Insert one end of the tube through the hole in the clay. Tip: Make sure the end of the tip is as far down and secure as possible to ensure that the water bottle drains as much as possible. Do the same for the other water bottle. Check both for leaks (water should only travel through the tube). Place ~6-7 quality coffee filters in each water bottle and a couple cotton balls.
Using clear packing tape, affix the water bottles to a large sheet of cardboard or a box leaving approximately 5 inches between each bottle (leave room for funnel and container underneath).
Place ends of tubing into funnel to give you an idea of where to place funnel on cardboard. Use packing tape to secure funnel in the appropriate spot. Secure the model to a wall/countertop. Place beaker or plastic container underneath. You can reuse the bottoms of the water bottles that were cut off to mix food coloring and water. Students can gently pour “waste” into the kidneys and watch what comes out.
Tips: This model may get a lot of wear of tear during the exhibition stations. The clay tends to get soggy and after several rounds the bottle may begin to leak. One way around this is leave the bottle caps on and drill a hole in them that is about the same diameter as the tubing and use glue or a sealant to seal it. If you choose to do the clay method, you may want to have some extra dry clay handy to fix leaks. Change the filters and cotton balls after every few demos to make sure they are not too saturated.
Another idea: Have your students follow these instructions working in pairs to make a model as part of their learning experience. (Extra credit as an in-home assignment might be an option if that many materials are too difficult to obtain).