Digestion Experiment

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Even though digestion takes place inside our bodies, we can do this simple digestion experiment to see the first steps of digestion in action.

Written by Marci Goodwin of The Homeschool Scientist.

We eat food to obtain the nutrients our bodies need to stay alive and perform all our daily tasks. Digestion is the process of breaking down food into the nutrients our bodies can use. 

Even though digestion takes place inside our bodies, we can do this simple digestion experiment to see the first steps of digestion in action.

The First Steps Of Digestion

When we first put food into our mouths, we use our teeth to chew it into smaller pieces. This part of the process is called physical digestion. It makes it easier for the next steps of digestion to take place.

As we chew, the food mixes with saliva. Saliva contains chemicals and enzymes that break down food into simpler pieces. The stomach and small intestine will break the food down even further. When enzymes and chemicals break down food, this is called chemical digestion.

Seeing Digestion At Work

Try this simple test to see physical and chemical digestion at work.

Digestion Experiment

Supplies

  • saltine or oyster crackers
  • Two bowls
  • iodine
  • tablespoon

Procedure

digestion experiment

Step 1: Crumble half of a saltine cracker or a couple of oyster crackers into a bowl.

digestion experiment

Step 2:  Add 1 or 2 tablespoons of water to the cracker crumbs. Lightly stir to mix the water and the crumbs.

Step 3: Chew the other half of the saltine cracker or 2 or 3 oyster crackers in your mouth very well so that it mixes with the saliva. Spit the cracker and saliva mix into the second bowl. Yes, it’s gross, but it’s for science, so it’s okay!

Add 1 or 2 tablespoons of water to the bowl.

digestion experiment

Step 4: Note the difference between the two bowls.

digestion experiment

Step 5: Add two drops of iodine to each bowl, swirling to spread the iodine. Note what you see.

What Is Happening?

We can see physical changes in the crackers in the bowls even before we add the iodine. In the first bowl, you can still tell that it is a cracker, just in smaller pieces and somewhat soggy. This is what happens in physical digestion. Although chewing broke the food into smaller pieces, the chemical composition didn’t change.

In the second bowl, the cracker mixed with saliva may not look like crackers. It may be more like a paste. The enzymes and other chemicals in saliva are already breaking down the cracker at the chemical level. This process is the beginning of chemical digestion.

What happened when you added the iodine? When starch is present, iodine will turn a dark blue color. Crackers contain lots of starch. The crackers in the first bowl should be a dark color from the added iodine.

Saliva contains the enzyme amylase that breaks down starch into simpler sugars such as maltose and dextrin. Your body cannot use large starch molecules so, using enzymes, it breaks them down into smaller sugar molecules, allowing the body to use them.

When you add the iodine to the second bowl, there isn’t as much starch present since the amylase broke it down. The color of the second bowl is much lighter than in the first bowl.

Try this at home, or use iodine to test for the presence of starch in other foods.

Find more about the digestive system and more experiments like this one in Apologia’s General Science.

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This article was written by a Weird, Unsocialized Homeschoolers guest author. See the author's full bio in the body of the post.

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