Morgan purplish in color once potassium iodide is added.



Morgan Winkler

PLTW: Human Body Systems

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Semester I, 2017




            The purpose of this experiment is to
determine how quickly salivary amylase will break down the complex carbohydrates,
or starches, in saltine crackers and Rice Chex cereal. Potassium iodide was
added to a cracker or cereal-water mixture as an indicator. Then, spit, containing
salivary amylase, was added to the mixture, and a timer was started. Data was
collected after the color from the iodide faded from the mixture. The Rice
Chex-saliva blend was the quickest to turn back into its original color.
Therefore, it was concluded that saltine crackers contain more starches than
Rice Chex.


Salivary Amylase is an enzyme located in
the oral cavity, or more specifically, in saliva. A single 496 amino acid chain
makes up this enzyme (Maffezzoli). Complex carbohydrates are broken down and
converted into maltose by salivary amylase. Complex carbohydrates are long
chains of glucose molecules, while maltose is only two glucose molecules bonded
together (“Maltose: Good or Bad?”). Food is broken down by salivary amylase until
entering the stomach, where gastric acid lowers the pH, inactivating the enzyme
(“What are the Functions…”).

            Indicators are utilized in experiments
to show if a specific substance is in a mixture. Potassium iodide is an indicator
used to confirm the presence of complex carbohydrates. A mixture containing
starch will turn purplish in color once potassium iodide is added. This is
because the iodide ion in potassium iodide is able to get trapped in the coils
of the carbohydrates, changing the electron arrangement. The molecule is then
able to absorb light differently, so instead of looking orange, the indicator
shows up as purple (“Lab Experiments…”)

            In the experiment, potassium iodine was
used to determine how long it took salivary amylase to break down foods
containing different amounts of complex carbohydrates.  The hypothesis was that if Rice Chex cereal and saltine
crackers were tested to see how long it takes for the color to disappear from
their solutions, then the cracker’s color would the quickest because it
contains less complex carbohydrates.


            Test tubes and a
150mL graduated cylinder were obtained for this experiment. Also, a mortar,
pestle, saltine cracker, glass stirring rod, 150mL beaker, and potassium iodide
were used. A timer was used for the experiment as well as Rice Chex cereal and
an eye dropper.


For the control trials, a
quarter of a saltine cracker was ground into a fine powder using a mortar and
pestle to imitate chewing. The crushed cracker was placed into a 250 mL beaker.
150 mL of distilled water was added to the beaker using a graduated cylinder.
The mixture was stirred with a glass stirring rod. 3 mL of the mixture was
measured into a test tube. 10 drops of potassium iodide were added to the test
tube containing the water cracker mixture. Roughly 2mL of spit were placed into
a separate test tube. The cracker mixture was poured into the saliva filled
test tube and a timer was started immediately. The mixture was stirred with a
glass stirring rod. The timer was stopped once the purple color of the mixture
faded away. The experiment was repeated four more times. For the experiment
trials, Rice Chex cereal was used in place of a saltine cracker, but everything
else remained the same.


Graph 1: Data about each trial and the means for both the control
(cracker) and variable (Rice Chex) are displayed in the graph. The average time
taken for the saltine cracker mixture’s color to fade was 29.358 seconds, while
the Rice Chex took 15.464 seconds.



The data
collected shows that the saltine cracker was digested by the salivary amylase
much slower than the Rice Chex was.  The
results are not consistent with the data collected about the amount of complex
carbohydrates in each food. According to the nutrition labels, 1.625
carbohydrates were in the cracker, and .689 were in the Rice Chex. It
was difficult to tell when the color of the potassium iodide had completely
faded, which could have led to error. Without proper equipment, it is too hard
to stop the timer at the exact point the color fades, so that specific error
would be challenging to correct. The results could have also been affected by
the hunger level of the person supplying the saliva during the trials The
experiment could be improved by controlling the person who was spitting’s diet
leading up to the experiment or using several subjects.  In
accordance with our data, the conclusion can be made that there is less starch
in Rice Chex than saltine crackers, suggesting that the hypothesis is incorrect.