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Unit 19: Biology Part 2 Page 104 of 137

The job of the kidney is to filter liquid waste. In this activity, you will model
the action of the kidney by filtering sandy water.

1. Mix sand, water, and yellow food coloring.
2. Place a piece of cheesecloth over a large bowl.
3. Slowly pour the sandy water over the cheesecloth and into the bowl.
4. Make observations about the liquid that goes into the bowl.

What’s happening: The cheesecloth, just like the kidney, serves as a filter.
Sand is kept out while the water gets through. This is important in
maintaining the body’s salt balance.

Experiment: A Model Colon

The colon, also called the large intestine, is an important part of both the
digestive and excretory systems, which removes solid waste. This model

colon will demonstrate the creation of solid waste.

Materials:

 Cheesecloth
 Colander
 Regular yogurt

 Bowl

1. Place a piece of cheesecloth into a colander.
2. Add regular yogurt (not light) into the colander.

3. Place the colander with the yogurt in it into a bowl and place it into the
refrigerator for several days
4. After several days, make observations about both what’s in the bowl
and what’s left in the colander.

What’s happening: The colon filters out liquids from the digested material
(that’s modeled by what’s in the bowl) and leaves us with solid waste
(modeled by what’s in the colander.)

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