Question

DIGESTING STARCH

Items you will need:

Very small Dixie cups

Eye Dropper

Lemon juice

Cornstarch

Water

Cooking Pan

Stove

Sugarless gum

Tincture of Iodine (Can buy at the local Drug Store)

Thermometer

Container to hold warm water

Pen or Pencil

Notebook

Soda Cracker

Plastic wrap

Starch is a carbohydrate that can be identified by the addition of iodine. It will cause the carbohydrate to form a dark blue color. The digestion of starch begins in the mouth, where it is acted on by amylase, an enzyme found in saliva. Saliva is secreted by the salivary glands in your cheeks.

To see the action of amylase, you will need to collect some saliva. To begin, simply let saliva collect in your mouth for a period of 5 minutes. Spit the accumulating saliva into a Dixie cup. Measure the amount of saliva that accumulated?

Next, use a clean eyedropper to place a few drops of lemon juice on your tongue. Do not swallow! Again, measure the volume of saliva that collects after a 5 minute period. How do the two volumes of saliva compare? What do your results suggest about the response of your salivary glands to the presence of food in your mouth?

Next, to test the effect of amylase on starch, you will need to prepare a starch mixture. You can do this by mixing a teaspoon of cornstarch with water in a Dixie cup (fill the Dixie cup ½ full with water). Pour the mixture into a small cooking pan and bring the mixture to a boil on the stove.

While the mixture is heating, chew some sugarless gum. How will this help to provide an abundant supply of saliva? Why are you using sugarless gum? Spit the saliva you generate into a Dixie cup. This is the saliva you will use to react with the cornstarch solution.

Once the cornstarch mixture is boiling, remove it from the stove and let it cool. Use an eyedropper to remove a small amount of the cooled cornstarch solution and put it into a Dixie cup. Place another small amount of the cooled cornstarch solution into another Dixie cup. In the first cup, add about the same amount of saliva to it. Then, add a drop of Tincture of Iodine to that first cup. To the second cup, add a small amount of plain water, NOT SALIVA, and a drop of the Tincture of Iodine to it. Let both cups sit for 3 hours. Stir them with a toothpick every 15 minutes. What are the color changes you observe in cup 1 and cup 2? What do you think causes color changes? What do you think would happen if you were able to heat the contents of the cups? What do you conclude about the effect of saliva on starch?

Another way to see the action of amylase is to look at its effect on the starch in food. To see this effect, chew a soda cracker for 5 minutes, so it becomes thoroughly mixed with saliva. Then, spit the chewed cracker and saliva into a Dixie cup.

Remove a small amount of the chewed cracker and place it into another Dixie cup. Then, add a drop of Tincture of Iodine. Is there a color change? What can you conclude? Do you think all of the starch has been digested?

Cover the cup that contains the chewed cracker and saliva with a piece of plastic wrap. After several hours, test another small sample of the chewed cracker, in a separate Dixie cup, with the drop of the Tincture of Iodine. Continue to test a sample of the chewed cracker by this method for 2 days, at 6-8 hour intervals. Is the starch eventually digested? If it is, how long did it take?

Answer 1

Answer: The salivary glands secrete saliva in response to various stimulus. Secretion of saliva naturally without any food or substances in it is lower and hence is less accumulated. In the presence of lemon juice, the saliva secretion by te salivary gland will be more due to stimulus. Presence of food in the mouth increases the secretion of saliva by the salivary gland.

Chewing of sugarless gum will induce the secretion of saliva by the salivary gland. Since there is no sugar in the gum, the secreted saliva will not be consumed by the mouth to the stomach. In cup2, there will be formation of a blue coloured substance. While, in cup 1, there will be no formation of blue coloured substance. The presence of starch changes the iodine solution (yellow or brown colour) to blue substance. In cup 2, the starch has been converted to maltose by saliva