STEM Club: The Digestive System - Eva Varga

December 18, 20145

The Digestive System is a group of organs working together to convert food into energy and basic nutrients to feed the entire body. Food passes through a long tube inside the body known as the alimentary canal or the gastrointestinal tract (GI tract). The alimentary canal is made up of the oral cavity, pharynx, esophagus, stomach, small intestines, and large intestines.

There are several important accessory organs that help your body to digest food but do not have food pass through them. Accessory organs of the digestive system include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas. To achieve the goal of providing energy and nutrients to the body, six major functions take place in the digestive system:

  • Ingestion
  • Secretion
  • Mixing and movement
  • Digestion
  • Absorption
  • Excretion

There are two types of digestion – mechanical (chewing, stomach sloshing, peristalsis, etc.) and chemical. Chemical digestion is only possible because your body gets help from enzymes! An enzyme is a type of protein that speeds up how quickly a chemical reaction happens in your body.

digestivesystemEnzyme Labs


There are about 700 different enzymes in the body. Amylase is an enzyme that breaks down complex carbohydrate molecules into simpler, sugar molecules. Our salivary glands excrete amylase into our mouth to aide in the digestive process.

Activity 1 :: In the book Head to Toe Science, I came across an activity that I thought would be perfect for STEM Club that was titled “Helpful Spit”. We thereby carried out this activity in class using the following procedure:

  • Divide a plate into four quarters, labeling them as follows: unthawed, 30 seconds, 5 minutes, and 10 minutes. Place a soda cracker in the unchewed section. Place a drop of iodine on the cracker. What happens?
  • Chew another cracker for 15 seconds making sure it becomes well moistened. Place one-third of the chewed cracker in each of the remaining sections. Wait 15 seconds. Place a drop of iodine on the cracker in the 30 seconds section. What happens?
  • Wait five minutes. Place a drop of iodine on the cracker in the 5 minutes section. What happens? Wait another 5 minutes and place a drop of iodine on the cracker in the 10 minutes section. What happens?

Iodine is a chemical that turns dark blue or black when it reacts with starch. We thereby expected the iodine to react with the unchewed cracker by turning dark blue/black and this is exactly what happened.

Saliva is an enzyme present in our saliva and thus the longer it had time to break down the carbohydrates into simple sugar molecules, the less starch would be present to react to the iodine.  We thereby expected that the chewed crackers would show a lighter shade of blue the longer the chewed crackers were left on the plate.

However, there was no discernible difference. Activity fail. We hypothesized what could have gone wrong. What could have affected the outcome of this activity? Not enough saliva? Not enough time?

We tried it again a few days later – assuring the crackers were significantly more moist (more saliva) but again, the same result.

Activity 2 :: An Alternative


  • 2 teaspoons starch powder
  • 1 teaspoon amylase powder
  • Distilled water
  • 2 small glasses
  • 1 spoon or stick with which to stir
  • 2 – 3 glucose testing strips (Lab-grade, with color-coding section)


  1. Pour 1 teaspoon of starch powder into each glass.
  2. Label one glass “WA” (with Amylase) and the other “NA” (no Amylase).
  3. Add about 5 mL of distilled water to each glass, stir to mix.
  4. To the glass marked “WA”, add your 1 teaspoon of Amylase powder and stir to combine thoroughly.
  5. Place 1 glucose testing strip into each glass. Record the color that the testing strips turn for each glass; refer to the color-code on the package to determine how much glucose is present in the solution.


Pepsin, which is found in the stomach, breaks down proteins. It takes the proteins from complex structures into simpler structures. Once those simple proteins get to the small intestine, a number of other enzymes continue to break them down into amino acids – which your body loves.


  • 1 small piece of tough steak
  • 1/8 teaspoon meat tenderizing powder
  • 1 plate


  1. Using a small knife, carefully cut your steak into two pieces.
  2. Place the steak on the plate, and using your masking tape and markers, label one piece “WP” (with Pepsin) and the other “NP” (no Pepsin).
  3. Carefully sprinkle / cover your steak marked “NP” with the meat tenderizing powder and let it sit.
  4. After several minutes, the meat tenderizers should have had time to do their work. Touch both pieces of meat and record any differences between them in your notebook. What difference do you feel?
  5. Do you think that other animals have adaptive digestive systems that might be different from ours? Imagine a creature’s digestive system based on a diet of either: rocks and stones, twigs and leaves, or only meat. Explain how their digestive system is different from ours, naming all of the organs and how they are different based on the diet that you chose.
  6. Many commercial meat tenderizers (powders that you can put on your steak before cooking it to make the meat more tender) contain enzymes, like the enzyme “papain” which comes from the papaya fruit. What is this analogous to in the human digestive system? How?

Bring it Home

  • Make a record of what you eat each day for the week. Compare your diet tot the recommended daily requirements. What kinds of foods are you eating?
  • Make a cast of your teeth with plaster of Paris.
  • If you have a tooth, crack it open gently by tapping with a hammer and look at the internal parts (enamel, dentin, pulp).
  • Watch this great TED-Ed video, What does the liver do? Write a paragraph describing what you learned.
  • Eggshells are similar in their makeup to teeth; both react to acid in a dramatic way. Design a test to see how different soda pops affect the egg shell.
  • Create a “Wanted” poster for a digestive organ (include the following information:
    • The organ’s role(s)/function(s) in the digestive system
    • The type(s) of digestion it performs
    • What enzymes it utilizes
    • What would happen to your digestive process if you no longer had this organ
  • Test a variety of foods to find what group, or groups, to which your favorite foods belong:
    • Test for Fat: Cut up some brown paper squares. Rub food on the paper and let it dry. If fat is present, light will show through.
    • Test for Starch: Put a drop of iodine tincture on the food. If starch is present, the iodine will turn blue/black.
    • Test for Protein*: Add the food to a solution of potassium or sodium hydroxide. Add a few drops of diluted copper sulfate solution. If protein is present, you will see a pink or bluish color.

*This test requires some chemicals that you may not have. Adult assistance recommended.


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