Developers:
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Linda Mathews Anastasi
St. Jerome School
Franklin Institute
Philadelphia, PA
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Chuck Jones, Ph.D.
Rohm and Haas Company
Spring House, PA
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Grade
Level:
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5 to 8
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Discipline:
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Biochemistry
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Goals:
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- To have students measure by mls.
and ozs., teaspoons, tablespoons, and drops.
- To have students make solutions
using cornstarch, tincture of iodine, saliva, vinegar,
and baking soda (sodium bicarbonate) and sugar.
- To have students use an indicator
to test chemical reactions.
- To have students use variables to
change results.
- To have students compare results
with their lab partners.
- To show students that chemical
reactions occur in their bodies.
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Specific
Objectives:
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- Students will prepare solutions of
their saliva and the variables assigned -- alcohol,
baking soda and/or vinegar.
- Students will use an indicator and
their saliva solution to demonstrate how starch breaks
down into smaller sugar molecules.
- Students will time their
results.
- Students will compare the time for
objective 3 to the time when a variable is added.
- Students will compare their
results with their lab partners' results.
- Students will graph and chart
their results with the rest of the class.
- Students will see that starch is
broken down to sugar in their mouths.
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Materials:
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hot plate, immersion heater, or
teapot
droppers and bottles
beakers, jars, plastic cups, and/or glasses
quart jars for solutions
teaspoons, tablespoons
graduated cylinders or measuring jars
saliva
corn starch
tincture of iodine
unsalted saltine crackers
vinegar
baking soda (sodium bicarbonate)
sugar
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Background:
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Enzymes are proteins that catalyze the
chemical reactions of living cells. They are composed of 200
to 1000 amino acid residues linked by a unique genetic code.
The unique structure determines the function of the enzyme.
The chemical that the enzyme attaches to is called the
substrate. The enzyme transforms the substrate into
products. In this case starch is broken down into sugar by
the enzyme, Amylase, which is in saliva. Enzymes have been
named by adding the suffix -ase to the substrates that the
enzyme works on. Amylase is an enzyme (-ase) which works on
starch (amylum). Starch turns purple when added to iodine,
but the small sugar molecules do not. In this activity,
saliva will be added to cause the break down of the starch
and prevent it from reacting with iodine.
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Procedure:
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- Make a Starch Solution (The
teacher should do this ahead of time.) Make a watery
paste of about 5g or level teaspoon of corn starch in
30mL or 2 tablespoons of hot water. Dissolve this in
about 100mL or 4ozs of boiling water. Cool the solution
and dilute it with 1L or a quart of water.
- Make an Iodine solution (The
teacher shoul do this ahead of time. Avoid having
children handle because of staining.) 1 part tincture of
iodine to 9 parts water. Pour into dropper bottles. Light
sensitive if the solution is made ahead of time.
- Make a variable solution Use 8
parts water to 1 part of either vinegar, sugar, or baking
soda.
- Make a saliva solution Add 100mL
or 4ozs of water to a jar or beaker. Add about 2mL or a
teaspoon of one's own saliva and stir until dissolved.
Label the saliva solution with your name.
- Test your saliva for amylase Place
an unsalted saltine on your tongue, without chewing, and
close your mouth until you have a sugary taste. The
amylase in your saliva has changed the starch in the
crackers to smaller sugar molecules.
- Experiment with the Indicator and
the indicator and variable. Add 20 drops of iodine
solution to 40 drops of starch solution, twice, to
produce 2 blue indicator solutions. Add 2 drops of
variable solution to one of the bottles. Pour half of the
saliva solution into each bottle. Record the time for the
indicator to turn clear.
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Sample
Results:
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Results of salivary amylase from
various subjects.
1. The time it took for the starch
sample to change to sugar molecules and the blue color to
disappear when various saliva samples were added.
Subject's saliva
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Time for change (purple to clear)
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Ave
Kathy
Chuck
Lester
Andrea
Beth
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6:40
5:15
2:10
8:00
16:00
5:10
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2. The effect of a vinegar on the rate
of reaction. Vinegar is acidic with a pH of 3 to 4 and the
enzyme does not function as efficiently as at pH 7.
Subject's saliva
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Drops of vinegar solution
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Increase in time
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Judy
Ave
Steve
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1 drop
2 drops
2 drops
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10%
20%
41%
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Questions:
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- When the saltine was in your mouth
how did the flavor change? What do uou think caused this
to happen?
- What reaction did you see when you
added iodine to your starch solution, to make your
indicator?
- What reaction did the saliva
solution have on the indicator solution?
- How did your variable solution
change the results?
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Extensions:
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Compare the students' results by use
of a graph or charts. Have the students suck on an orange
first and repeat Develop a general distribution curve with
your students to show differences in amylase. Use other
variables to check for changes in reaction rate. (alcohol,
soda, etc.) Heat saliva to show amylase destroyed by heat
and unable to react with indicator.
Please Note:
Some saliva has a very low or
high concentration of amylase. Adjust saliva solution and
try again if reaction time is too slow or too fast . Stress
the importance of controlling all variables.
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