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Digestion

Digestion

Green papaya fruit is rich in papain, used for in powdered meat tenderizers.
Courtesy of Hardyplants.

  • Grades:
  • 3-5
  • Length: 30 Minutes

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Overview

Life Science

Students learn about digestion and proteins by observing the action of meat tenderizer on luncheon meat. Student sheets are provided in English and in Spanish.

This activity is from The Science of Food Teacher's Guide. Although it is most appropriate for use with students in grades 3-5, the lessons are easily adaptable for other grade levels. The guide also is available in print format.


Teacher Background

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.

Objectives and Standards

Concepts

  • Food must be broken down into smaller units before it can be used by the body.

  • Digestion is the process of breaking food down.

  • Special chemicals in the body break food molecules into smaller units.

  • Proteins—found in all meats, dairy products and vegetables (especially peas and beans)—are important for muscles and cell growth and repair.


Science, Health and Math Skills

  • Predicting

  • Making qualitative observations

  • Drawing conclusions

Materials and Setup

Materials per Student Group

  • 2 clear, resealable plastic bags, sandwich size

  • 1/2 slice of turkey luncheon meat

  • 1/2 tsp of meat tenderizer, or papaya enzymes (available at health food stores)

  • Plastic, serrated knife


Setup

  1. Purchase meat tenderizer, located in the spice section at the grocery store, and a piece of sliced turkey luncheon meat for each group.

  2. Have students conduct this activity in groups of four.


Safety

Have students wash hands before and after the activity. Clean work areas with disinfectant.

Procedure and Extensions

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.

  2. Have the students in each group cut the piece of turkey in half and place one section in the bag labeled “1.” Direct them to place the other section in bag “2” and to add 1/2 teaspoon of meat tenderizer to that bag. Have them seal the bag and shake the turkey slice within the bag so that it is well coated with the tenderizer.

  3. Have the students place the bags to one side of the classroom for about an hour. (If students will be making observations the following day, refrigerate the bags to prevent spoilage.) Have students write, in their journals or on a sheet of paper, what they predict will happen to the slices of turkey.


Session 2: Making observations

  1. Have students observe the texture and color of the meat samples without removing them from the plastic bags. Ask, Is there anything different about the turkey that was combined with the meat tenderizer? What do you think happened?

  2. Ask students to think about the changes they observed in the meat with tenderizer. Mention that the substance they added was a chemical that helps soften the muscle fibers in meat by beginning to break them down into smaller pieces.

  3. Help students understand that similar substances work within their stomachs and small intestines to break down the food they eat. Have students draw or write about their observations.

  4. Mention that turkey meat is a muscle. Help students understand that protein is the building block for muscles and that it is used inside each muscle cell. Protein that we eat must be broken into smaller components before it can be used by our bodies. You may want to mention that the chemical meat tenderizer also is a kind of protein. It provides another example of the variety of roles that proteins play inside plants and animals.


Extension

Students can investigate the importance of chewing by repeating the experiment using a finely chopped piece of luncheon meat and comparing the outcomes.

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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

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