BioEd Online

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 down food 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. Saliva mixes with the food and begins to break it down further. 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 down food.

• 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 4.

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.

Handouts and Downloads