Why do you think you need to add NaCl?
ANSWER THE QUESTIONS (IN BOLD) FOUND IN THE FOLLOWING EXPERIMENT PROCEDURES.
Salivary Amylase Preparation
Collect about 15 mL saliva in a small beaker. Transfer 10 mL of the collected saliva in a beaker filled
with 10 mL distilled water. Filter through a coarse filter paper.
Starch Mixture Preparation
Put 10 mL of 1% starch solution and 4 mL of 1% NaCl solution in a clean big test tube. Why do you think
you need to add NaCl? Place this mixture in a hot water bath and maintain it at 38°C. You may leave a
thermometer inside the test tube to check on the temperature. Why is this step important?
Monitoring Salivary Amylase Activity
You are now ready to allow digestion of starch by salivary amylase and monitor its progress by testing
for both undigested starch (I2KI test) and free glucose (Benedict’s test). Get 10 test tubes and fill each test tube
with 1 mL Benedict’s solution. These tubes will be used for the test for glucose so we shall label these tubes G1
to G10. Obtain another set of 10 empty test tubes. Label them as S1 to S10. These tubes will be used for the
test for starch.
Add 10 mL of the saliva preparation into the starch mixture. Gently mix by shaking from side to side.
Pipette out two 1 mL portions of this saliva-starch mixture at 0 minute and every five minutes thereafter and
test for starch and glucose content. Remember to mix the contents of the tube by stirring once in a while during
the duration of the whole experiment.
For the Benedict’s test, pipette 1 mL of the saliva-starch mixture into the G1 tube. Place the tube in a water
bath maintained at 38°C for 15 minutes. Remove it from the water bath and immediately record the resulting
color of the mixture.
Do this same procedure on another 1 mL of the saliva-starch mixture every after 5 minutes until the G7
tube. Instead of pouring saliva-starch mixture into the remaining three G tubes, pour 1 mL 1% glucose into G8,
1 mL 1% starch into G9 and 1 mL distilled water into G10. What is the purpose of these three tubes? What
specific type of control set-ups do they represent?
For the I2KI test, pipette 1 mL of the starch-saliva mixture into the S1 tube. Add 2 drops of I2KI solution.
Keep the tube at room temperature. Observe for appearance of a bluish-black color, an indication of the
presence of starch. Indicate its intensity with plus (+) signs. Do this same procedure on another 1 mL of the
saliva-starch mixture every after five minutes until the S7 tube. Instead of pouring saliva-starch mixture into
the remaining three S tubes, pour 1 mL 1% glucose into S8, 1 mL 1% starch into S9 and 1 mL distilled water into
S10. What is the purpose of these three tubes? What specific type of control set-ups do they represent?
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