This demo illustrates testing for the presence of starch in foods. Collect a slice of apple and potato. Put slices on a paper plate. Place 2-3 drops of iodine on each slice. The iodine will go from orange-rust to brown on the potato and the iodine on the apple will not change color.
Iodine changes color in the presence of starch.
This exercise illustrates how bile fluid in the intestines emulsifies oils and fats. It is necessary for the body to emulsify fats to separate them and expose them to more enzymes. In this exercise, the dishwashing liquid represents the bile fluid. Fill two glasses with warm water. Add a tablespoon of cooking oil to each glass.