Modeling Digestion in the Mouth
- erinplukas
- Dec 6, 2022
- 3 min read
Updated: Dec 6, 2022
This lesson and assessment are part of a larger project-based learning (PBL) experience on human body systems. The driving question for the unit is "How and why does my body use food?" Throughout the unit, we try to understand the phenomenon of food ENTERING our bodies looking one way...
...and EXITING our bodies looking totally different!
I've found that middle school students just love learning (and talking) about POOP!
The learning experiences and assessments in this unit are aligned to the following NGSS crosscutting concepts:
structure and function
cause and effect
scale, proportion, and quantity
systems and system models
First stop...the MOUTH!
We begin by investigating food's first stop in the digestive system, the mouth! We look at the mouth as a system of parts all working together, with the common goal of preparing the food for swallowing.
Students chew up a cracker and explore the various structures and substances that the cracker encounters on its way to the back of their mouth. Then, we watch (and laugh) as volunteers try to eat another cracker using ONLY ONE part of their mouth (just their incisors, molars, tongue, or saliva), which reinforces the fact that the mouth is a system of parts that work together.
Then, I give groups another cracker and some various tools (hammer, scissors, wrench, sandpaper) and I ask them to use the tools to simulate what happens in the mouth from beginning to end. They compare the function of the tools with the function of different parts of the mouth.
In the end, someone usually points out that they can use the tools to get the cracker close to what our food looks like in our mouth, but they need something to represent the saliva. The food needs to be wet when it is swallowed!
That leads us into an investigation into the function and composition of saliva. Most students suspect that it contains a lot of water, but there is probably some other "stuff" in there.
We set up an experiment where students spit into large centrifuge tubes and place crackers inside to see what happens to the cracker overnight. I also give a few students a chunk of Crisco (fat) or a chunk of egg (protein) to place in their tube (instead of the cracker) for comparison. We also set up additional "control" tubes that just contain water.
In some of the tubes that contain crackers, we place a couple of drops of iodine, which immediately turns a dark blue, indicating starch. After 24 hours, it is very clear that the amount of starch has decreased. See the evidence below!
Students realize that there must be other stuff in the saliva, in addition to the water, that helps to start breaking down the food before we start swallowing it. The iodine is indicating that the starch in the cracker chemically changed into another substance. So, we utilize some text and video resources to see what scientists have figured out about the composition of saliva. For example, this video from SciShow Kids:
Through these resources, we learn more about enzymes, like salivary amylase, and the difference between MECHANICAL digestion and CHEMICAL digestion.
Digestion in the Mouth Assessment:
To assess learning and to practice the skill of modeling (which students will use throughout the this PBL project), I ask students to design a 2D model of the mouth that shows HOW and WHY the mouth breaks down food. Students receive the documents pictured below to support them in drawing their model. These models also receive one round of peer critique before students submit them. You can download a copy of these materials below.
To view samples of student work for this assessment, look through the pages in the flip book below:
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