Digesting Digestion: An Educational Laboratory to Teach Students about Enzymes and the Gastrointestinal Tract

Digestion is a fundamentally important process for an individual’s life. However, the physical process of digestion is hidden inside the body, making it challenging to understand and a particularly difficult topic for students to learn in the classroom. Traditional approaches to teaching body processes include a mixture of textbook teaching and visual learning. However, digestion is not particularly visual. This activity is designed to engage students using a combination of visual, inquiry-based, and experiential learning approaches and introduces the scientific method to students in secondary school. The laboratory simulates digestion, creating a “stomach” inside of a clear vial. Students fill the vials with a protease solution and visually observe the digestion of food. By making predictions about the types of biomolecules that will be digested, students begin to learn and understand basic biochemistry in a relatable context, while simultaneously understanding anatomical and physiological concepts. We trialled this activity at two schools, where we received positive feedback from teachers and students, indicating that the practical enhanced student understanding of the digestion process. We see this lab as a valuable learning activity that can be extended broadly across multiple classrooms around the world.


Objectives:
Students will learn about digestion in the human body, the function and structure of enzymes, and the process by which enzymes break down food. They will weigh out and produce enzymatic digestion solutions and apply these solutions to a variety of foods representing different food groups. The students will record observations as these foods are digested by the enzymes, while learning about the chemistry behind enzymatic digestion. They will study the association between enzymatic digestion in a laboratory setting versus in the human body.

Students Will:
 Learn the basics of digestion in the human body  Review the anatomy of the gastrointestinal tract and associate different organs with different digestive process  Study the process of enzymatic digestion, learn about different enzymes and the chemistry by which they work  Mix enzymatic digestion solutions  Take observations of the digestion of different food groups  Learn the chemistry that is occurring in this experiment and make predictions as to which foods will digest most  Demonstrate their findings in writing o In Celiac Disease the immune system is triggered by gluten, protein found within some carbohydrates. The lining of the small intestine is degraded which leads to flattened and/or damaged microvilli (see images below and worksheet). Symptoms include malnourishment, diarrhea, cramps, weakened immune system and in children stunted growth. Effects can be reversed by adopting a strict gluten free diet.

Intestinal microvilli in healthy and diseased conditions (beyondceliac.org)
 Gut microbiome o Digestive dysfunction can have a great impact on the mood and psychological well being. This area of research, termed the gut-brain-axis (see image below), has received a lot of interest in the scientific community in recent years.
o Interestingly, 95% of the chemical serotonin (5HT), which is naturally made in our bodies, responsible for feelings of pleasure and wellbeing and used to treat depression, is actually found in our gut!

Gut-Brain-Axis connections (adapted from Saurman, V., Margolis, K.G. & Luna, R.A. Autism Spectrum Disorder as a Brain-Gut-Microbiome Axis Disorder. Dig Dis
Sci 65, 818-828 (2020). DOI:10.1007/s10620-020-06133-5) o Aside from the chemicals produced in our gut, many microorganisms thrive and 'feed' on carbohydrate/fibrous rich foods and release nutrients into our gut through an anaerobic process called fermentation. o The microorganisms living in our gut are individual to each person, like a finger print, and collectively are called the gut microbiome. o During fermentation these microorganisms release gas, which is why after eating a fibrous meal you may feel bloated!  Fermentation in the food industry o Bacteria and yeast are also used outside of our bodies to produce fermented foods and beverages such as sourdough bread, dairy and alcohol. o The fermentation process has been used for thousands of years in many cultures to help purify and preserve food. o It is now known that fermented foods also improve the nutritional content of meals and feed the 'good' bacteria in our guts.
o Set out materials for each group. Each group will need:  >6g of each food type (bread, sweets, spinach, banana, egg [optional -hard-  The products of digestion are used to build new carbohydrates, lipids and proteins.
Some glucose is used in respiration. Bile is made in the liver and stored in the gallbladder. It is alkaline to neutralize hydrochloric acid from the stomach. It also emulsifies fat to form small droplets which increases the surface area. The alkaline conditions and large surface area increase the rate of fat breakdown by lipase.
 (Higher tier GSCE only) The digestion of proteins from the diet results in excess amino acids which need to be excreted safely. In the liver these amino acids are deaminated to form ammonia. Ammonia is toxic and so it is immediately converted to urea for safe excretion.

NGSS:
 HS-LS1-2: Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.
 HS-LS1-6: Construct and revise an explanation based on evidence for how carbon, hydrogen, and oxygen from sugar molecules may combine with other elements to form amino acids and/or other large carbon-based molecules.
 HS-LS1-7: Use a model to illustrate that cellular respiration is a chemical process whereby the bonds of food molecules and oxygen molecules are broken and the bonds in new compounds are formed resulting in a net transfer of energy.

Resources:
Digestion