Digestion Lab
Part A: Digestion in the Mouth
All food enters the digestive system through the mouth. Food is chewed to begin breaking it down and carbohydrates
(sugars) are initially broken down by the enzyme amylase.
Starch is a long chain (polymer) of glucose molecules found in foods such as the gum used in this lab. Iodine is used as a
starch indicator because the chemical reaction between the two causes a color change.
1. One person in your group needs one piece of gum.
2. Cut your piece of gum in half, immediately put half in your mouth, and chew.
3. Flatten out the second half (non-chewed) piece of gum and put it in the Petri dish. Place 3-5 drops of iodine on it
and record observations below.
Observations: ________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
4. Continue to chew the piece of gum until the last 10 minutes of class.
5. Start on Part B of the lab while waiting until the time for step 4 is complete.
6. 10 minutes before the end of class, put your chewed gum into the petri dish. Stretch it out and shape it similar to
the non-chewed gum already in the petri dish. Answer the following questions.
What physical changes did you notice? _______________________________________________________________
_______________________________________________________________________________________________
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What chemical changes (changes in taste) did you notice? _______________________________________________
_______________________________________________________________________________________________
7. Add 5 drops of iodine to the chewed gum sample in the Petri dish and record your observations.
Observations: ___________________________________________________________________________________
_______________________________________________________________________________________________
Was the reaction between the gum and iodine the same as in the previous experiment? Why or why not?
_______________________________________________________________________________________________
_______________________________________________________________________________________________
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What enzyme is digesting the starch into glucose and caused this change in taste and reaction with iodine?
__________________________________
One starch is breaking down into many glucose molecules. A large molecule made of many small molecules is called
a _______________________________. The small molecules are known as _________________________________.
What is the difference between chemical and mechanical digestion? _______________________________________
_______________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
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Part B: Length of your Digestive System
You will measure and construct a representation of the length of a person’s digestive tracts using yarn pieces.
1. Choose the group member whose digestive tract you want to measure.
2. Cut a piece of yarn (red) the length of the distance from the back of your ears to the front center of your lips to get
the length of your mouth. Record the length in Data Table 1.
3. Cut a piece of yarn (yellow) the distance from the top of your neck to bottom of your sternum to get the lengths of
their esophagus. Record the length in Data Table 1.
4. Cut a piece of yarn (yellow) the distance from the tip of your thumb to the tip of your pinkie to get the length of your
stomach. Record the length in Data Table 1.
5. Cut a piece of yarn (green) the distance from the top of your forehead to your feet. Cut 4 more pieces of yarn the
same length to get the total length of your small intestines. Record the length (total of all 4 pieces of yarn) in Data
Table 1.
6. Cut a piece of yarn (blue) the distance from the top of your forehead to your feet once to get the length of your
large intestines. Record the length in Data Table 1.
7. Connect the pieces of yarn in the correct digestive order using tape.
Group Data Table 1:
Organ
Length (inches)
Mouth
Esophagus
Stomach
Small intestine
Large intestine
Total Digestive
System Length
8. Record your group member’s digestive system total length on the white board. Create a Bar Graph to compare the
tract lengths of lab group to lab group. Don’t forget to label your x-axis and y-axis and title your graph (make it a
winning graph)!
Class Data Table 2:
Group #
1
2
3
4
5
Total Digestive System
Length (inches)
Graph Rubric:
 Clear title (+2pts)
 X-axis label and unit of
measurement (+2pts)
 Y-axis label and unit (+2pts)
 Bar graph for each groups data
(+2pts)
6
7
8
1. Are all organs of the digestive system the same length? _________________________________________________
2. What is the longest organ in your digestive system? ____________________________________________________
3. How does the length of the small intestine relate to its function?
_______________________________________________________________________________________________
_______________________________________________________________________________________________
4. Why are the names “small intestine” and “large intestine” misleading?
_______________________________________________________________________________________________
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5. Accessory organs such as the liver, gallbladder and pancreas produce enzymes which help to breakdown food during
digestion. Why are they not included in the list of organs food travels through?
_______________________________________________________________________________________________
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6. Which macromolecule is initially broken down in your stomach? __________________________________________
7. Why don’t all humans have the same length digestive system?
_______________________________________________________________________________________________
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