Content Standard B:
Energy is a property of many substances.

1. Ask students, “What is energy?”

Accept all responses and post them on the board. Energy allows us, or provides us with the ability, to do work. Energy may be stored for later use, or it may be used immediately to do something, such as provide light, heat, or motion. Students may view energy simply as something that lets you do things, such as run, walk, or just stay alive.

Teacher note: Asking this question requires students to call on their prior knowledge and to engage their thinking. At this point, do not critique student responses. Appropriate teacher comments are short and positive, such as “good” and “what else?” Other appropriate teacher responses include, “Why do you believe that?” or “How do you know that?” Questions such as these allow the teacher to assess current student knowledge about the subject and adjust lessons accordingly. They also provide a springboard to “Let’s find out” or “Let’s investigate.” In general, it is time to move forward when the teacher sees that thinking has been engaged.

2. Continue by asking, “Do living things require energy?” Follow this with, “How do living things get their energy?”

It is important to establish that all living things do need energy. This could be a time to reinforce the idea that the continuous use of energy is one of the features that helps distinguish living from nonliving things. This is also a good place to define food as the source of materials and energy needed to support life. Food as a source of energy will be explored in Lessons 2 and 3.

3. After establishing the idea that living things require and use energy, ask students to name things they do that use energy.

List student responses on the board. List enough activities that a wide range of types and intensities is included. Students may respond with activities such as running, walking, riding bicycles, or playing sports. Ask them to consider reading, thinking, sleeping, and growing. Do these activities require energy? Lead students to the idea that humans, like all living things, require energy continuously.

Teacher note: The base level of energy required to maintain basic body function is called the basal metabolic rate, or BMR. Typical teenagers use 60 to 70 percent of their energy to maintain normal body function, or basal metabolism. You may need to define metabolism for students: the sum of all chemical reactions occurring in the body.

4. Referring to the list of activities on the board, ask students if these activities all use the same amount of energy.

Students should recognize that the energy required to perform different activities varies.

5. Ask students what determines how much energy they use in a physical activity.

Energy use is determined by both the intensity and the duration of the activity. Students may not know that energy use is also determined by body size.

6. Give each student one copy of Master 1.1, Physical Activity Diary: School Day, and one copy of Master 1.2, Physical Activity Diary: Weekend Day.

Students will record their physical activities for 24 hours on a school day using their copy of Master 1.1. They will repeat this for a weekend day using Master 1.2.

7. Show students the transparency of Master 1.3, Some Typical Activities, by Intensity Level.

Teacher note: The values listed in the table on Master 1.3 represent average values for middle-school–aged individuals for a range of activities within each category. The values include the calories used for BMR.

8. Refer to the list of activities on the board from Step 3. Ask students to consider the activity category (resting/sleeping, very light, light, moderate, or heavy) into which their typical activities fall.

Students should recognize that activities can be separated and organized based on their intensity. Resting activities use the least energy over a given time, while high-level activities require the most energy over that same time period.

Tip from the field test: Emphasize that the calories listed for the activities in Master 1.3 are calories per hour. This will help students understand why they need to divide the number of minutes they spent at each activity level by 60 on Master 1.5, Total Calories Used Per Day at Various Intensity Levels, in Activity 2, Steps 2 and 3.

9. Show students the transparency of Master 1.4, Sample Physical Activity Diary for a School Day. Explain that each line represents a full one-hour period (60 minutes).

This sample demonstrates that students are to use abbreviated descriptions of their activities in each 60-minute period and estimates of the number of minutes spent in activities at the various intensity levels.

10. Point out that the first time period on the diaries is from 5:00 a.m. to 6:00 a.m. that morning. The last period they will enter is 4:00 a.m. to 5:00 a.m. the next morning.
11. Tell students that they will begin their own physical activity diary for today in class. They first will consider the time from 5:00 a.m. to 6:00 a.m. that morning. Ask students to describe the activity or activities in the column labeled Activity and then enter the minutes spent in activities at each intensity level.

Use the transparency of Master 1.4 to point out that the individual in this example was sleeping during that one-hour period. Students, however, should enter their own activities during that time period. Tell students to estimate the time spent at each type of activity to the nearest five minutes.

Tip from the field test: Emphasize that the total minutes on each line should add to 60. Students are likely to participate in activities at more than one level during most one-hour periods. Tell students that they need to write only one or a few words to remind themselves of activities in which they participated in each time slot. Point to examples on the transparency. For example, within a single hour, students may sit and listen in class, stand up and complete a lab exercise, walk to their lockers and to their next class, and stand in the hall and talk with friends. These students may record “science/walk & talk” in the Activity blank on the diary, and indicate 30 minutes of sitting activity for the time they sat and listened in science class and 30 minutes of light (walking) activity for the time they worked on the lab exercise, walked through the hallways, and stood and talked with friends. This gives a total of 60 minutes.

12. Ask students to enter their activities from 6:00 a.m. to 7:00 a.m. Students should continue until they reach the present time.

Assist students as they estimate the intensity levels of their activities and the amount of time they spent doing each activity. Be prepared to hold brief class discussions about activities that are difficult to categorize. Strive to develop a class consensus on how to categorize these activities. For example, a two-hour basketball practice may be composed of 30 minutes of sitting and listening and 90 minutes of running drills and playing the game. Students should enter both types of activity on their sheets (30 minutes of sitting and 30 minutes of heavy activity for the first hour and 60 minutes of heavy activity for the second hour).

13. Ask students to continue to fill in their diary throughout the day. Their final entry should be for the period from 4:00 a.m. to 5:00 a.m. the next morning.

Emphasize that the total minutes for the 24-hour period must add to 1,440 (24 hours × 60 minutes/hour), as indicated in the diary.

14. Ask students to consider activities they are likely to engage in over the weekend that are different from their school-day activities. Resolve issues of how to categorize activities, as described above.

Doing this now will save time later when students enter their results in the database. You may also want to explain to students that they will enter information from their physical activity diary into a database on Monday. Emphasize that they will need a complete (24-hour) diary for both a school day and a weekend day.

1. Ask students to have their completed physical activity diaries available. Ask students to add the total minutes they spent each day at each intensity level if they have not already done so.

Students should do this for the school day and the weekend day. They should check the accuracy of their diaries by adding the total number of minutes allotted to all activity levels. This should equal 1,440 minutes (60 minutes/hour × 24 hours/day).

Content Standard A:
Mathematics is important in all aspects of scientific inquiry.

2. Give each student a copy of Master 1.5, Total Calories Used Per Day at Various Intensity Levels. Ask students to copy the total minutes of activity at each intensity level from the last row of their two diaries (labeled Total Minutes on Masters 1.1 and 1.2) to the first row in the tables (labeled Minutes of Activity) on Master 1.5.
3. Guide students through the instructions at the top of Master 1.5 to allow them to calculate the calories used at each of the five intensity levels and the total calories used for both a school day and a weekend day.

Use a transparency of Master 1.5 to guide students through the calculations.

Tip from the field test: Students who forgot to complete their activity diaries should use data from one of their classmates so that the numbers are real student data rather than fabricated.

Teacher note: The energy values (cal/hour) used in this exercise are age-adjusted, average values that include the BMR. They provide only a rough estimate of each student’s energy expenditure. To be more precise, the values would have to be activity-specific and adjusted for age, gender, and weight. This issue is addressed in Discussion Questions at the end of this lesson.

4. Draw two tables on the board, with the following headings:

Label one table School Day and the other Weekend Day.

5. Ask students to enter their summary data (bottom row of the table) from Master 1.5 into the two tables on the board. Also ask them to put an M in the last column for males and an F for females.

Because individual activity levels may vary widely, the data entry needs to be done with sensitivity. As an alternative, you can collect the diaries and prepare a summary table yourself. Retain a copy of the class data for later reference.

Tip from the field test: Distribute highlighter pens to students and suggest that they highlight the last row of each table on Master 1.5 (the summary data). This will help ensure that students enter the correct data on the board.

6. Ask students to count off using the numbers 1 through 12. Instruct students to calculate the class average for one table column based on their number.

Use the following code: students with numbers 1 to 6, school-day table; 1 = resting calories, 2 = very light calories, and so forth; and students with numbers 7 to 12, weekend-day table; 7 = resting calories, 8 = very light calories, and so forth.

Make sure students have the correct number of entries when they calculate the average values.

Content Standard A:
Use appropriate tools and techniques to gather, analyze, and interpret data.

7. Ask students who have made the same calculation to compare answers and resolve any discrepancies before reporting results to the class.
8. Ask a representative of each student group to write the averages for each column on the board at the bottom of the appropriate column.
9. Tell students that they will make two bar graphs to analyze their results.

Students will construct one bar graph to compare their own physical activity data with the class averages for a school day and another graph for comparison with the weekend-day results.

10. Instruct students to graph calories on the y-axis. The x-axis will contain these categories: resting, very light, light, moderate, heavy, and total calories.

One bar in each category will represent the student’s own results. The other bar represents the average class results. An example graph is presented here. Students can use two different colored pencils to distinguish their results from the average class results, or they can use other means to distinguish one bar from the other.

Graphing results in this way allows students to compare their energy (calories) used (total calories as well as calories in each activity intensity level) with the average results of the whole class. Students construct a similar graph for the weekend-day results.

Assessment:
If you wish, collect and score the graphs for a more formal assessment of students’ graphing skills.

Teacher note: This activity introduces students to data analysis. This topic is addressed in greater detail in Lesson 4, where students explore the value of different types of graphs for analyzing data. Lesson 4 is a good time to discuss why bar graphs, and not line graphs, were appropriate for this activity.

Content Standard A:
Design and conduct a scientific investigation.

11. Ask the class what questions they can ask that can be answered using these data. Can they formulate a hypothesis they can test using the class data?

There are several questions students could ask. For example, students might ask, “Do students have higher activity levels on weekends than on school days?” This question can be transformed into a hypothesis by rewording it as a statement: “Middle school students have higher activity levels on weekend days than on school days.” Students could compare the average calories used for each activity level on the two days to test this hypothesis.

An alternative hypothesis, “Middle school students have higher activity levels on school days than on weekend days,” is equally acceptable. A hypothesis is a statement that predicts a result. The statement is tentative because empirical evidence has not yet been obtained to support or contradict it. However, the statement is reasonable, because it is based on prior knowledge about the phenomenon. For example, some students may know that they spend more time doing outdoor chores and running around with friends on weekend days than on school days. For these students, the first hypothesis is reasonable. Other students may know that they spend more time watching TV and playing computer games on weekend days than on school days. For these students, the second hypothesis is reasonable.

The validity of either hypothesis is tested using data. The data will either support or not support the hypothesis. Many students think that a good hypothesis is one that the data support. In fact, neither hypothesis (one that the data support or one that the data do not support) is better. The important result is that students will have engaged in authentic scientific activity: they will have formulated a hypothesis and used data to determine whether their hypothesis is supported or not supported. Using empirical evidence to draw conclusions about phenomena is a key feature of science.

Assessment:
If you want to use this activity as a more formal opportunity to evaluate students' science skills (writing hypotheses, analyzing data, and drawing conclusions), collect and review the student reports. The reports should include a statement of the hypothesis, a statement indicating what reports were generated, data from the reports, interpretation of the data, and a discussion of how the results support or do not support the hypothesis.

12. As a written assignment, ask students to formulate another hypothesis and then test their hypothesis using the data available.

Students may need to be reminded that their research questions need not deal only with total calories for all five activity-intensity levels. They might ask about changes in the distribution of activity intensity levels between the two days. Or, they might compare high-intensity activities with resting activities on the two days. Many different questions can be asked. Reports should contain a statement of the hypothesis, the data collected to test the hypothesis, and an evaluation and interpretation of the data. Students should indicate whether the data supported or did not support their hypothesis.

Teacher note: Information in the tables on the board allows students to compare results between males and females. To do this, students pool male and female results separately and calculate average values for each of these two groups.

Teacher note: Students may be tempted to say a hypothesis has been proved or not proved. However, better terms are supported and not supported. In this activity, students draw conclusions on the basis of limited data collected for only two days. The results would be more reliable if data had been taken for a longer period of time. Scientists are hesitant to use the word proven. It indicates a very high degree of certainty. The key point to look for in the discussions is the evidence students use to support their conclusions.

13. Ask the class what other questions they believe would be interesting to ask, even if they do not have the information to produce an answer. What additional information would they need to answer the question?

This allows students to use their imaginations. You might need to make some suggestions to get them going. For instance, students might want to know whether time of year has an effect on activity level. To answer this question, they would need information about the time of year the activity diary was kept. As an extension of this question, students might speculate about, or even investigate, the combined effects of geographical location and time of year.

1. Tables that list energy used for different activities (in calories per hour) usually include a statement similar to the following: “These values (calories/hour) are for an adult male who weighs 150 pounds.” The values take into account a person’s BMR. What might this statement tell you about BMR in different people?

The statement correctly indicates that BMR values vary from person to person, and that BMR depends on the age, gender, and weight of the individual.

2. The total energy expenditures calculated by students are rough estimates of their actual energy expenditures. What would they need to do to make their estimates more accurate?

They may respond that they should be more precise in determining how long they spend in each activity and that they should have better information available to determine the energy expended for specific activities. More importantly, they should recognize that they would need to take into account their age, gender, and weight in calculating energy expenditures.

Teacher note: The BMR value is comparable to the energy used by a person who sleeps all day. Students may be interested in seeing how much of their total daily energy expenditure is due to BMR. If students would like to estimate their BMR, we recommend using a formula that accounts for differences due to age, gender, and weight.
For males 10 to 18 years old, BMR = (17.5 × weight in kilograms) + 651
For females 10 to 18 years old, BMR = (12.2 × weight in kilograms) + 746

Pounds may be converted to kilograms by dividing weight in pounds by 2.2. For example a student who weighs 110 pounds would weigh about 46 kilograms (that is, 100 pounds ÷ 2.2 pounds per kilogram = 45.45 kilograms).

To simplify the arithmetic, the formulas are
For males 10 to 18 years old, BMR = (7.95 × weight in pounds) + 651
For females 10 to 18 years old, BMR = (5.55 × weight in pounds) + 746

One factor that is not accounted for in this equation is overall activity level. People who are more active have a slightly higher BMR than less active people. The BMR also decreases in starvation conditions. This is one reason why radical dieting is not recommended and is not as effective as gradual changes in diet and exercise.

3. Ask students to examine their physical activity diaries and look for patterns. Do they use more energy on weekend days or school days? What would happen to their energy consumption if they got two more hours of sleep every day? What would be the effect of watching TV for one hour less and doing one hour more of light or moderate activity?

This is a time for students to talk about choices they make. Which of their daily activities can they choose? Can they choose how active they are in school? What about how active they are after school? Be prepared for comments about homework being a Very Light Activity and taking time during which they could be more active. Suggest that students look at the amount of time they choose to watch television or play computer games.