What Happens When You Eat?
Objectives:
These activities will show students what organs aid in digestion and how digestion occurs in the
human body. This lesson may be appropriate for middle grades, but is designed for the upper grade
curricula.
Materials Needed:
Activity #1: How Long is the Digestive System?
- yarn (4 different colors)
Assign different color yarns to represent the different organs of the digestive system shown
below. After the yarn has been cut tie the pieces together. Students will be using the same
colored yarns to estimate what they think the length of each is. Once all students have done this,
compare each group’s length to one you have made according to the measurements below
Esophagus
Stomach
Small Intestine
Large Intestine
TOTAL
25 cm
20 cm
700 cm
150 cm
895 cm
Activity #2: Digestion
- sugar cubes
- granulated sugar
- 2 beakers (at least 250ml)
- water
Activity #3: Carbohydrate Digestion
- unsalted soda crackers (2 per student)
Activity #4: Hands on Digestion (Use only if you have these chemicals)
- a small lump of cooked hamburger (meatball size)
- one plastic baggie
- 1M HCl
- Digestive Juice A (pepsin (25 g/$8.70 at Flinn), trypsin and water)
- Digestive Juice B (bile salts (order from Flinn), pancreatin enzyme and water)
Kneading the bag simulates the stomach. After students have kneaded the bag for about 10-15
minutes, the substances inside will have been reduced to mainly liquid and will have a definite odor.
Activity #5: How do Villi aid the Small Intestine in Absorption?
- paper towels (10 per group) (Or change to bar towels vs. towels with pilings)
- four 250 ml beakers
- water
- graduated cylinder
Whole class demonstration:
Activity #6: A Digestive System Simulation
- large thin plastic bag
- newspaper
- paper sacks (2 sizes)
- Zip-lock bags
- M&M's candy
- masking tape
- markers & paper
- sponges
- trash can
- labeled spray bottles of water
Procedure:
Things to make ahead of time:
1. FOOD TUBE:
Lay out two parallel lines of tape on the floor, 3' apart and long enough for
half the class to stand shoulder to shoulder on one side of the parallel lines.
2. FOOD PARTICLE: The food particle consists of M&M's placed in small zip-lock bags. These
are placed in wadded newspapers in small paper sacks. Place the small sacks in larger sacks with
added newspaper. Place all sacks and add newspaper until the large plastic bag is full. This bag is
then taped or tied closed to complete the food particle.
Action:
1. Peristaltic Movement: Put the food particle to be eaten at one end of the food tube and a
large trash can at the other. Have students line up on both sides, facing each other,
squeeze the food particle the length of the food tube.
2. Digestion: Label and/or instruct the players. As the food comes to a student they should
narrate what they are doing and why.
Teeth - tear food apart (break plastic bag)
Saliva - use spray bottles to moisten food particle
Stomach - tear small bags apart
Pancreatic juices - spray food
Small Intestine - absorbs food, find bags of candy and pass to blood
(The teacher can play the role of the blood)
Large Intestine - reabsorbs water, sponge up water on the floor
Rectum/Anus - puts the waste papers in the trash can
Performance Assessment:
Follow the path of a food particle through the digestive system - include the organs and their
functions. Illustrate or draw this in your notebook.
Conclusion:
These six activities will enhance the student's knowledge of what organs aid in digestion and how
digestion occurs in the human body. Students will have a more comprehensive understanding of
what happens in their bodies when they eat.
Station 1 – How long is the digestive system?
As food travels through the digestive system it passes through the
esophagus, stomach, small intestine and large intestine. Using the
indicated color of yarn for each organ, cut a piece that corresponds
to the length you think the organ is. After the yarn has been cut,
label the pieces with masking tape, and tie them together in this
order:
Esophagus
Stomach
Small intestine
Large intestine
 Label the string with your group number and give your string to
your teacher.
Station 2 - Digestion
1. Fill both beakers with 200 ml of water.
2. Place a sugar cube in one beaker and stir until it
dissolves.
3. Place a spoonful of granulated sugar in the other beaker.
Stir until it dissolves.
4. Rinse out beakers.
 What can you conclude must be done to food
before digestion begins?
 What part of your body do you think performs this
task?
Station 3 – Carbohydrate Digestion
1. Chew two unsalted soda crackers for two
minutes without swallowing.
2. Observe what happens to the taste of the
crackers.
The crackers contain carbohydrates
which are long chains of sugars linked
together. What role do you think your
saliva plays in the digestion process?
Station 4 – Hands-on digestion
1. Make observations of the hamburger (sight, smell).
2. Place the hamburger, 3 eyedroppers full of 1M HCl, one tablespoon of
Digestive Juice A and two tablespoons of Digestive Juice B into a plastic
bag.
3. Knead the bag with your hands for about 10-15 minutes,
4. Make observations of the hamburger (sight, smell).
 Mechanical digestion was simulated with your hands kneading the
bag. Chemical digestion was simulated with the Digestive Juices.
What do you think the terms mechanical digestion and chemical
digestion mean?
 What part of the digestive system do you think the plastic bag
and the kneading of your hands represent?
Station 5 – How do villi aid the small intestine in
absorption?
1. Fold 1 paper towel in fourths. Layer 2 paper towels together and fold the stack in
fourths. Layer 3 more paper towels together and fold the stack in fourths. Layer
4 more paper towels together and fold the stack in fourths
2. Fill each of the four beakers with 200 ml of water.
3. Dip the 1 folded paper towel into a beaker of water.
4. Using a graduated cylinder, record the volume of water left in the cup. Repeat
steps 3 and 4 with the other beakers of water and the other stacks of paper
towels.
 Which paper towel had the largest surface area?
 Which cup had the lowest volume of water left?
 The paper towels modeled villi - small projections along the surface of the
small intestine similar to the small loops on a bath towel. What do you
think the purpose of the villi is?