Cracker Lab-Academic
Starch, a complex carbohydrate polymer, can be found in grains like wheat, corn and oats. Starch, which is
a polymer made from thousands of sugar molecules bonded together, stores energy for plants. Digestion of starch
normally begins in the mouth of humans where an enzyme catalyst, salivary amylase, is secreted to speed up the
breaking of starch into it’s monomer sugars.
Enzymes are specific. Each chemical reaction uses a different enzyme that has a specific active site shaped
perfectly to fit the specific substrate/reactant. The substrate fits into the active site of the enzyme allowing for bond
breaking or making to catalyze the reaction. Enzymes are denatured when excessively heated in that they unravel
and their shape is permanently altered making them ineffective.
Pre-lab Questions:
What molecule should be in the cracker and why?
What are complex carbs for and what are their monomers?
What type of organic molecule are enzymes? What do they do?
Purpose:
If a digestive enzyme (amylase) found in saliva is added to a cracker, what should happen?
How will high heat (boiling) affect the effectiveness of the enzyme?
Hypothesis:
Procedure:
A. Amylase enzyme-preparing the saliva
1. Rinse your mouth with water to be sure it is free of food. Test saliva, in a test tube, with Benedict’s and
iodine to be sure that it is free of both sugar and starch. Continue until a lab partner has a clean saliva
sample.
2.
Start with clean test tubes and label them A, B, C, D and E.
3.
Spit about 1 mL of plain saliva in test tube E and put in a water bath.
4.
Record your chemical results for both tests-what color and what can you conclude?
B. Cracker BEFORE adding the amylase enzyme.
5. Place about 1 mL of crumbled cracker in the first two test tubes (A and B) and add water up to about 2mL.
6.
Test the cracker in A for sugar and the cracker in B for starch. Record your results-color and conclusion.
C. Test cracker AFTER amylase enzyme
7. Place a cracker in your mouth and chew without swallowing. Spit half of the cracker/amylase mixture in
test tube C and half in D.
8.
Test the cracker-amylase in C for sugar and the cracker-amylase in D for starch. Record your results-color
and conclusion
D. Heated amylase enzyme
9. Remove test tube E from the water bath, place some un-chewed cracker in it and test for sugar. Record
your results-color and conclusion.
10. Wash all test tubes and return all materials to the lab tray.
E. Graph results
11. Create a bar graph of test tube contents vs positive results-a full bar for a positive and no bar for negative.