BioEd Online

Teacher Background

Living things that cannot harness solar energy through photosynthesis must eat other organisms or the products of other organisms as food. Consumers, which include members of the animal and fungus Kingdoms, frequently use a variety of food sources to meet their energy and nutritional needs.

The amount of energy stored in food usually is measured in calories. One calorie is defined as the amount of energy it takes to raise the temperature of one gram of pure water (equivalent to one milliliter of water) one degree Celsius. The calories shown on most food labels are written with an uppercase “C” and represent one kilocalorie or 1,000 calories.

Carbohydrates, fats and proteins are the primary sources of energy in foods. Sugars, starches (such as those in bread, pasta and potatoes) and fiber (such as in many vegetables, whole fruits and whole grains) are the main forms of carbohydrates. Foods rich in fats include animal and vegetable oils, lard, butter and cream. Proteins, the building blocks of muscles and molecules within cells, are present in meats, eggs, and animal products, as well as in plant materials, like nuts and beans.

Each of these classes of nutrients provides a different amount of energy as food. Fats and oils provide about nine Calories (Cal) per gram. Carbohydrates and proteins each provide four Cal per gram. The amount of energy provided by each of these kinds of foods is independent of the source and presence of other nutrients. In other words, olive oil and peanut oil both provide about nine Cal per gram.

This activity introduces students to the concept of “calorie” and allows them to compare the relative amounts of energy in similar-sized portions of a carbohydrate-based food and a food rich in oils.

Objectives and Standards

Life Science

• All animals, including humans, are consumers, which obtain food by eating other organisms.

Physical Science

• Energy is a property of many substances and is associated with heat, light, electricity, mechanical motion, and the nature of chemicals. Energy is transferred in many ways.

Science in Personal and Social Perspectives

• Food provides energy and nutrients for growth and development. Nutrition requirements vary with body weight, age, sex, activity, and body functioning.

Science, Health and Math Skills

• Observing

• Comparing

• Predicting

Materials and Setup

Teacher Materials (see Setup)

• Single-hole punch

Materials per Group of Students

• Prepared soft drink can (see Setup)

• Pencil (to be used as a holder for can)

• Graduated cylinder or beaker

• 6-in. thermometer (°C)

• 2 pieces of round unsweetened oat cereal (“Cheerios^®”)

• 1/2 pecan (without shell)

• Large paper clips

• 2-cm piece of clay

• Matches or birthday candles

• Safety goggles (one pair per student)

• Water

• Copy of student sheet (see Lesson pdf)

Setup

1. Each student group will need one prepared soft drink can (or you may choose to conduct this activity as a class demonstration). Each class will need a new set of prepared cans.

2. Cut the top one third off of a soft drink can using scissors. Discard top half. Smooth the edges by cutting around again or by covering the edges with masking tape.

3. Use a single-hole punch to make a pencil sized hole on each side of the open end of the can, so that a pencil may be inserted as a holder.

4. Have students work in teams of four.

5. Set out all materials for each group of students to collect.

Safety

• Students should wear goggles and conduct the activity on a nonflammable, flat surface.

Procedure and Extensions

1. Remind students of the "Energy for Life," activity, in which they cultivated yeast in sugar water. Ask, What happened to the temperature or appearance of the water in which the yeast cells were growing? Students should be able to report that water became warmer or that the yeast used sugar as food. Follow by asking, What do you think would happen if we tried to release all of the energy in the sugar as heat? Use students’ answers to guide them into a discussion of energy stored in food. Ask, Do all kinds of food provide the same amount of energy?

2. Challenge students to predict which provides more energy: the same portion of a carbohydrate-rich food or an oil-rich food.

3. Have the Materials Managers collect the materials for their groups from a central area in the classroom.

4. Each group will need to make a holder for the food they will be investigating. They should bend a paper clip so that it looks like the image on the student page, and anchor the base using clay.

5. Have students follow the instructions on their activity sheets to complete the investigation. They will pour 50 mL of water into the prepared soft drink can and measure the temperature of the water. Next, they will hang two oat cereal pieces on the paper clip and light them from below. They should hold the can by the pencil support with the bottom of the can about one inch above the flame. If necessary, they should relight the cereal pieces until they will no longer burn. They should record the final water temperature.

6. Have students repeat the investigation using a piece of pecan approximately the same size as two pieces of cereal together (place on top of holder).

7. Have students follow the instructions on the student page to calculate (approximately) the number of calories released by the similar volume of different foods.

8. Discuss results with students. Ask, Which food released more heat when burned? Which volume of food had more calories? Help students understand that fats and oils are more energy-rich than carbohydrates, because of the nature of the chemicals involved.

Extensions

• Have students conduct the investigation again using similar masses of cereal and pecan. Have students weigh the pieces in advance and make adjustments so that similar masses of cereal and pecan are compared.

• The diets of some ethnic groups living in extremely cold climates are very high in fats. Have students investigate why such diets might be necessary.

Handouts and Downloads

Download color images from The Science of Food and Fitness Teacher's Guide.