First we talked nutrition: proteins, fats, carbohydrates, and calories.
Then we talked about physical digestion: breaking food into smaller pieces.
We ground up some bath salt crystals in a mortar and pestle, and tried
dissolving equal amounts of large crystals and ground up small
crystals. We talked about the importance of maximizing surface area
for chemical reactions.
We also talked about chemical digestion: breaking food down into absorbable nutrients.
We did a couple of experiments here. One was to try iodine on a wide
variety of foods. Based on their observations, I asked them to come up
with which nutrient the iodine reacted with. They correctly said,
"Complex carbohydrates!" I love these kids!!
We also did an emulsification experiment. Each kid had a jar of 1/4
cup of oil and 1/4 cup of water, and we tried 5 different possible
emulsifiers (left to right in the picture): nothing, egg white,, egg yolk, whole egg, and mustard.
Emulsification is pretty critical. If oils and fats aren't broken down
into smaller particles, they tend to coat the food and disallow
digestion and absorption.
And, of course we talked about all the parts and pieces of the system as shown here:
I'm sorry I can't seem to embed any videos, but you can follow the link.