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Author(s): Nancy Moreno, PhD, and Barbara Tharp, MS.


Food must be broken down, both physically and chemically, before it can be used by the cells within an organism. The process of breaking food down into usable components is known as digestion. Within the human body, digestion begins in the mouth, where pieces of food are mechanically broken, by chewing, into smaller pieces. In addition saliva mixes with the food and begins to break it down. After food is swallowed, other components of the digestive system—stomach, small intestine, large intestine, liver and pancreas—continue the process of making food available for use by cells in the body.

The stomach serves as a powerful mixing machine in which food is combined with special chemicals (enzymes) that begin to break large food molecules into smaller ones. Food usually stays in the stomach for two to three hours, after which it passes into the small intestine, where it is combined with secretions from the liver and pancreas. These very important organs produces substances (bile from the liver and pancreatic fluid from the pancreas) that help break down fats, proteins and carbohydrates into smaller molecules. The small intestine is responsible for absorbing the nutrients released during digestion. The walls of the small intestine are covered with millions of tiny, finger-like projections called villi. These structures increase the surface area of the small intestine to facilitate the absorption of nutrients into the bloodstream.

Proteins and their building blocks (amino acids) are vital to every cell in the body. Humans are not able to make their own amino acids, so they must include protein (equivalent to 4 ounces of chicken white meat) in their daily diet. During digestion, proteins are broken down into the different amino acids of which they are made. Then the body builds new proteins from the amino acids. You might say that the amino acids are recycled!

This activity will allow students to observe how chemicals in the body begin to break down proteins.

Complete instructions for conducting activities in this slide set, including materials needed, setup instructions, student sheets (in English and in Spanish), answer keys and extensions, can be found in The Science of Food Teacher’s Guide, which is available free-of-charge at

Session 1: Setting Up

1. Let Materials Managers collect 1/2 slice of turkey luncheon meat, a plastic knife and two resealable plastic bags. Have the groups label their bags “1” and “2.” Ask students, What happens to food when you eat it? Do you think that food stays the same inside your body? Discuss students’ ideas about digestion. Mention that they will be able to explore what happens to one kind of food—turkey meat (protein)—when digestion begins.

Funded by the following grant(s)

National Institute of Environmental Health Sciences, NIH

National Institute of Environmental Health Sciences, NIH

My Health My World: National Dissemination
Grant Number: 5R25ES009259
The Environment as a Context for Opportunities in Schools
Grant Number: 5R25ES010698, R25ES06932

Houston Endowment Inc.

Foundations for the Future: Capitalizing on Technology to Promote Equity, Access and Quality in Elementary Science Education