Friday, December 21, 2012

Model Circulatory System | 7th Grade Science

Do you remember learning about our circulatory system in biology class? If so, you may remember looking at diagrams of the heart, memorizing the names of the various valves and chambers, and understanding how blood flows through the system. But in our 7th grade science class, we decided to try something different.... something a little more "Bourn-ified"!

How might we build a model of the circulatory system that would allow students to simulate the flow of blood, the contraction (aka the "pumping" of the heart muscles, and gain an appreciation for how the sequence of events has to be precisely orchestrated in order for the system to function? Christina Nawas, who has done a number of projects with us this semester, came to us with this original question and we rolled up our sleeves to design a hands-on project to do exactly that.

After some brainstorming, Diego got to work building a prototype using plastic tubing to model arteries and aortas and squeeze bottles to model the chambers of the heart. He first started by playing around with those plastic squeeze bottles that you usually see holding ketchup and various sauces at restaurants, but eventually realized their seals don't hold up and leaked water everywhere when squeezed. Tiny travel-size screw-top bottles ended up working better.

The next challenge was finding one-way valves to model heart valves. Diego started by designing some using laser-cut parts and pieces of thin rubber but these didn't end up being as one-way as we'd like. Then one day in the lab, as the two of us were wrecking our brains trying to solve this problem, I randomly wondered aloud whether people who keep fish for pets need one-way valves for their aquariums. A bit of Googling and a trip to the pet store confirmed our suspicions and thanks to Amazon, we were able to get a large batch of these valves in time for class.

To scaffold the activity, we started by asking the girls to build two-chamber hearts in pairs, using a kit of squeeze bottles, plastic tubing, connectors, and one-way valves. Christina also took some time to explain that the type of two-chamber hearts we're building are different from those found in nature. (We were building hearts where one chamber is the left and one chamber is the right; in nature, two-chamber hearts are usually divided into one ventricle and one atrium instead.) Then they had to work together to get "blood" (clear water, for the sake of not having our lab look like a massacre at the end!) pumping through their model system.

After the two-chamber hearts were built, we then asked the girls to get in groups of four and challenged them to put together four-chamber hearts! Again, after they got their system wired up correctly, with all the valves facing the right way, they had to test it by working together to pump the heart chambers in a proper sequence to get blood to flow. Some groups even came up with chants to help coordinate the proper pumping sequence!

Even though everyone got slightly soggy, it was so great to see how this activity really allowed the students to learn about how the circulatory system works! Don't believe me? See for yourself!

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