Spit Lab (R. Daniels)
Title: Spit Lab
Principle(s) Investigated: How saliva aids in the digestion of starch, and how this can differ from person to person.
Standards : 7.1.a Students know cells function similarly in all living organisms.
7.2. A typical cell of any organism contains genetic instructions that specify its traits. Those traits may be modified by environmental influences. As a basis for understanding this concept:
c.Students know an inherited trait can be determined by one or more genes.
Materials: 5 crackers, 6 toothpicks, 6 small cups, 1 small cup of water, bottle of iodine with dropper, pippettes
Procedure:
Part 1- Testing for the Presence of Starch
1. Assign one person in the group to each of the following roles:
Spitter/Chewer: This person needs to properly clean out their mouth. Rinse mouth thoroughly several times by swishing clean water throughout your mouth.
Scientist/Instructor: Reads the instructions to the group and checks off each step as they are completed.
Time Keeper: This person will time every step of the lab.
Organizer: Makes certain all the cups are labeled and the data is recorded.
2. Take two cups and have the Organizers label one cracker and the other spit.
3. Scientist, grind up 1 cracker in your hands.
4. Fill the cracker cup with cracker crumbs.
5. Add 1 mL of water to the cracker cup (best if done with pippettes).
6. Have the Spitter rinse his/her mouth out with water and fill the spit cup with spit only.
7. Add 2 drops of iodine to each cup. Stir with a toothpick.
8. Iodine is an indicator. When it touches starch, it changes from a pale brown to a black/dark purple.
9. Write your results on the data sheet (or Quickwrite??)
10. Throw away these two cups.
Part 2 - Testing if starch is broken down into sugar by amylase.
1. Take 4 new cups and label them: 15 seconds, 30 seconds, 60 seconds, and 90 seconds.
2. The Spitter will chew one cracker for each amount of time (tracked by the Time Keeper), and spit the chewed cracker into the appropriately labeled cup.
3. Add one drop of iodine to each cup and stir with a toothpick (do not use the same toothpick for each cup).
4. Record the color results on your data sheet (or Quickwrite??)
Student prior knowledge: Iodine is the indicator for Starch.
Explanation: Iodine is an indicator for starch, which is broken down into glucose monomers by the enzyme amylase found in saliva. The longer the starch is exposed to the amylase, the more starch is broken down and the more sugar is produced. This should affect how dark the iodine becomes with each cup that is labeled 15, 30, 60 and 90 seconds. However, note that even though the iodine should be getting progressively lighter with each cup, there are times when the iodine color remains constant. Why?
Questions & Answers:
1.In part 1, what would you conclude if the contents in the cracker cup did not turn purple?
The conclusion would be that there is no starch present in the cracker or cup.
2. How is it possible that some of the iodine may be a consistent color in all of the cups?
Genetics- some people, based on their genetics, produce more amylase than others.
3. What happened to the color of the iodine when added to the cup labeled spit?
Nothing. There is no starch present.
Applications to Everyday Life: http://www.healthcentral.com/diabetes/c/5068/151882/salivary-glucose/
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