SOURCE Lesson Plans Detail

Delving into Digestion

Topic The Digestive System
Program Brown Science Prep
Developed by Joseph Botros, Priya Patel
Developer Type High school students

Overview / Purpose / Essential Questions

How do we process the nutrients we absorb during eating?

Performance / Lesson Objective(s)

Learn about the pathway of digestion and the organs that assist in this process.

Lesson Materials

Benedict's solution

Tennis balls



Tight ziploc bags

Orange juice


Lesson Motivation

To illustrate the mechanisms of digestion that occur in our bodies.

Lesson Activities

Benedict Solution experiment- Put crushed crackers into 2 vials and have one student spit into one of them, put water into the other. Place a drop of Benedicts solution in each one, observe a precipitate in vial containing saliva.
Peristalsis upside down- Hold oneself upside down or horizontally and eat a cracker, thus proving that gravity must not be the only force involved in swallowing food.
Ball and Stocking esophagus demo- Shove a tennis ball into a stocking to show the bolus going down the esophagus.
Making a stomach model

First break the crackers into pieces and drop them into the bag. Your hands will be acting like the mouth that breaks the food into little pieces.
Second, pour a little orange juice into the bag to act as the "digestive juices" in your stomach.
Observe what happen to the crackers. Are they getting soft?
Now squeeze the bag for one minute. Your hands are now acting like the stomach walls that squeeze the food you eat.
What happens to the crackers? Are they liquid now? That means that the stomach's job has finished and the food is ready to be sent to the intestines where the water and nutrients will be absorbed

Emulsification game- Half the kids are designated enzymes and half are designated fats. First the fat is in one big glob and the kids try and get at it. The fat in the middle is untouched by the enzymes and digestion is incomplete. Next, with the introduction of bile from the liver, the fat glob is emulsified into many smaller fat globs and the enzymes have a much easier time at digesting them.
Yarn Demo- Show 20 ft of yarn. to illustrate the length of the intestine

Final Activity-
Have everyone come into the auditorium. There are pictures with people on them, and a list of symptoms under each person, as well as an envelope. Each group has several cards (each group is a different color) with a disease, and a description of what goes wrong in that disease. In their groups, they are to try and match the disease with the symptom and put that card in the envelope. At the end, we will reveal the correct answer and then talk about why a disease would cause certain symptoms.


Overview- The food you eat must be converted into small molecules that your body can use for fuel and building material. This is the job of the digestive system
Mouth: Foodstuffs are broken down mechanically by chewing and saliva is added as a lubricant

- Talk about how Amylase breaks starches down into simple sugars.

- Four types of teeth to mechanically break down different food types.

Incisor- biting large pieces of food

Canine- tearing off large chunks of meat


Molar- grinding food into very small pieces.

- Once chewed and mixed in with saliva, the ball of soggy food is called “bolus”

Pharynx: This is an opening for food to go through before it reaches the esophagus.

-A thin flap of tissue called the “epiglottis” closes off the respiratory tract during swallowing to prevent food from going down the trachea

-When laughing or speaking, the epiglottis remains open, so chances of choking increase if you are doing those things

Esophagus: A simple conduit between the mouth and stomach.

– Ask kids whether food falls down esophagus by gravity or if it goes down by another method.

*Peristalsis Demo

*Ball and stocking model to illustrate peristalsis and food bolus (a tennis ball squeezed down a stocking)

Stomach: Where food becomes liquid.

chemical digestion of proteins initiated and foodstuffs reduced to liquid form.

Enzymes—Enzymes are biological molecules that speed up the rate of a reaction. (In this case, the reaction would be the breakdown of food, so enzymes in the digestive system make the breakdown of food faster)

-HCl is an acid in your stomach that converts an inactive enzyme, pepsinogen, into its active form, pepsin

-pepsin breaks proteins up into smaller chains of amino acids

-The stomach has three layers of muscle coated by a layer of mucus.

The muscle helps with the mechanical digestion of food while the mucus layer protects the stomach from its own digestive juices-otherwise, the stomach would digest itself

*Make a Model of the Stomach- (Demo or Experiment)

Duodenum- Upper part of the small intestine where a lot of the chemical digestion takes place (of proteins and fats especially).

-Also controls when the stomach empties into the small intestine using a sphincter

-sphincter is a ring of muscle that contracts or relaxes in order to let things pass through openings.

-at this point, the bolus is now liquid, and called “chyme”

• Liver: The center of metabolic activity in the body

- its major role in the digestive process is to provide bile salts to the small intestine, which are critical for digestion and absorption of fats.

-Nested in the liver is the gallbladder

-The gallbladder stores and concentrates bile salts, and passes them through the bile duct into the small intestine where they can digest

*Emulsification demo:
Pancreas: provides a potent mixture of digestive enzymes to the small intestine which are critical for digestion of fats, carbohydrates and protein.

-Also insulin, which is a hormone that lets cells take sugar out of the blood.

• Small Intestine: The most exciting place to be in the entire digestive system - this is where the final stages of chemical digestion occur and where almost all nutrients are absorbed.

*Hold up 20 ft of yarn. 0:53-1:35 Show video of villi and microvilli.

Large Intestine: Major differences among species in extent and importance - in all animals water is absorbed, bacterial fermentation takes place and feces are formed.

-In carnivores, that's about the extent of it, but in herbivores like the horse, the large intestine is huge and of critical importance for digesting fiber

-Humans cannot use fiber for energy. For humans, fiber serves as sort of “roughage” to help clear out the large intestine.

Undigested food continues down the digestive tract to the rectum and anus. (which are both sphincters) and into the toilet. Potty training is learning to detect the signal of the involuntary sphincter (rectum) and control the voluntary one (anus).

Wrap up / Conclusion


1. Esophageal Motility Disorder-- A disease of the esophagus which causes spasm type pain of the esophagus and trouble performing peristalsis
(Symptoms: Throat pain, trouble swallowing)

2. Peptic Ulcers- A mucosal erosion- i.e. when a significantly large area (.5 cm or larger) of the stomach no longer has a mucous lining. Can be caused by a variety of things, including bacteria, certain drugs like aspirin, and even tumors. (Symptoms: Vomiting of blood, pain in the abdomen, nausea)

3. Whipple's disease -- a rare condition that prevents the small intestines from properly absorbing nutrients. This is called malabsorption
(Symptoms: Rapid weight loss, abdominal pain)

4. Obstructive Jaundice- when gallstones block the bile duct and do not let bile to the digestive system (Symptoms: Pale feces due to excess fat)

5. Lactose intolerance- Lack of the lactase enzyme (the enzyme that digests the sugar, lactose, found in milk) (Symptoms: Gas, bloating, diarrhea when milk or milk products are eaten)

6. Schatzki’s Ring- When a ring of tissue forms in the esophagus. If it becomes large enough, can block part of the esophagus (Symptoms: A sticking feeling in the chest; difficulty swallowing saliva).

Students will match the disease with the associated symptoms.

Pre Assessment Plan

Provide an image of the digestive system and ask students to try to label as many organs as possible.

Post Assessment Plan

Repeat the pre assessment but allow students to work together to remember all of the organ names.

Alignment Info

Audience(s) High school students
STEM Area(s) Biology
Life Sciences (RI GSE) LS1.9-11.1a
Students demonstrate understanding of structure and function-survival requirements by… explaining the relationships between and amongst the specialized structures of the cell and their functions (e.g. transport of materials, energy transfer, protein building, waste disposal, information feedback, and even movement).
Activity Type(s) Lecture
Grade Level(s) High School
Version 1
Created 11/11/2012 12:54 PM
Updated 12/20/2018 11:38 AM