Purpose: Model how kidneys filter blood.
- Add one teaspoon of cornstarch to 1/8 cup of water.
- Add 3/4 cup of hot water and stir well.
- Measure 1/4 cup of cornstarch mixture…
- …and pour into sandwich baggie. Use a twist tie to close the bag tightly.
- In a separate glass, mix together one teaspoon of iodine with 3/4 cup of water.
- Gently place the baggie into the iodine solution. Do not allow the tied end to get wet.
- Check the bag every three minutes for a total of fifteen minutes.
- Look for a color change inside the sandwich baggie.
The baggie acts as a filter by allowing iodine molecules to slowly flow into the cornstarch mixture. When the iodine comes into contact with the cornstarch, a chemical reaction occurs that causes the water inside the baggie to turn dark blue or purple . Note that even though the iodine is passing through the baggie, the water in the iodine solution is not passing through the baggie (i.e., the baggie is not swelling up with water even though it is changing color). Similarly, your kidneys filter blood to get rid of harmful chemicals found in your body but leave the good fluids (e.g., red & white blood cells) in your body.
Make a Kidney Model
Two empty water bottles
Tape (not pictured)
Coffee grounds (not pictured)
Water (not pictured)
Glass measuring cup or small pitcher (not pictured)
Container (not pictured)
- Cut two water bottles in half.
- Attach a 10-inch piece of plastic tubing to the bottle using modeling clay, making a clay plug to place into the opening of the water bottle (where the lid normally screws onto the bottle). Ensure that the plastic tubing is open to the inside of the bottle but that there are no gaps between the tubing and the clay and between the bottle and the clay. The bottles are the two “kidneys,” and the tubes are the “ureters.”
- Tape the two “kidney” water bottles onto the cardboard box.
- Tape a funnel to the cardboard underneath the two “kidneys,” and tape the two “ureters” to the inside of the funnel.
- Carefully place a few coffee filters into each “kidney.”
- Mix some coffee grounds into some water.
- After placing a container underneath the funnel, pour the coffee ground solution into the “kidneys.”
- Observe the “kidneys” filtering out the coffee grounds…
- …as the water runs down the ureters and exits through the funnel. The coffee grounds actually change the water to a yellowish color! (Eww! Gross!)