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.
A person was given a piece of Double Bubble Gum. They cut it in half and placed one half
in a petri dish and began chewing the other half.
The non-chewed piece was flatted out and iodine was placed on it for 5 minutes. The
original color of iodine was a brownish/yellowish and after 5 minutes the student noticed
that it turned a bluish/blackish.
1. What chemical change occurred and why?
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
After 20 minutes of chewing the Double Bubble, the student flatted out the chewed gum and added 5 drops of
iodine to the chewed gum sample in the Petri dish. Again the original color of the iodine was a
brownish/yellowish and after 20 minutes the student noticed that it remained the same, brownish/yellowish.
2. Was the reaction between the gum and iodine the same as in the previous experiment? Why or why not?
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
3. What enzyme is digesting the starch into glucose and caused this change in taste and reaction with iodine?
__________________________________
4. 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
_________________________________.
5. What is the difference between chemical and mechanical digestion? Look in your Biology book page 979
Figure 32.11.
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
Part B: Length of your Digestive System
A student measured and constructed a representation of the length of their digestive tracts using yarn pieces.
Data Table 1:
Organ
Length (inches)
Mouth
5.5
Esophagus
13
Stomach
7
Small intestine
296
Large intestine
74
Total Digestive
System Length
395.5
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)!
Analysis:
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?
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
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?
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
6. Which macromolecule is initially broken down in your stomach? ____________________________________
7. Why don’t all humans have the same length digestive system?
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
Use page 978 from the Biology book, to fill in the chart.
Enzyme
Digestive Organ
Function