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Overview

Many effects of regular exercise are obvious, such as well-defined muscles, weight loss, and less huffing and puffing through workouts. But few people consider the cellular changes underlying noticeable physical results. Improved endurance is one aspect of exercise training that has been studied at the cellular level. In this lesson, students will analyze pictures of magnified muscle cells from a hypothetical experiment to determine the effects of exercise and performance-enhancing drugs.

Objectives

Students will be able to:

• describe the function of mitochondria
• describe cellular changes caused by exercise
• analyze a cause-and-effect relationship between behavior and physiology
• make predictions based on data
• explain the importance of a control group in an experiment
• debate the pros and cons of performance-enhancing substances

Grade Level: 9–12

Suggested Time

• One class period

Media Resources

• NOVA scienceNOW: Marathon Mouse Video (12:27)
• HHMI: The Fate of Fat Video
• Where Do You Get Your Energy? Flash Interactive
• HHMI: Marathon Mouse Lecture Demonstration Video
• How the Body Responds to Exercise QuickTime Video
• HHMI: PPAR-delta Activation in the Muscle Cell Video (optional)

Materials

• Marathon Mouse Student Handout PDF Document
• Marathon Mouse Teacher Blackline Master PDF Document
• Envelopes, one per student pair

Before the Lesson

• Make copies of the Student Handout (one per student)
• Make copies of the Teacher Blackline Master, cut out the images, and place the images from two different mice in each envelope. If you plan to reuse the materials, consider laminating the images.
• If possible, provide computer access for each pair of students. Alternatively, as a class, watch the two videos mentioned in the student handout.
• Read the Teacher Notes—Marathon Mouse PDF Document for background information and assessment tools
• Bookmark the Web sites for the media resources

The Lesson

1. As a class, watch the NOVA scienceNOW: Marathon Mouse Video (12:27 minutes). Discuss any questions students have about the video.

2. Ask students where people get their energy. Then, to illustrate how food is digested and distributed to various tissues for storage or energy, show the class HHMI: The Fate of Fat Video.

3. Discuss the video and tell students that the fat entering muscle cells will be broken down and used by the mitochondria. Remind them that mitochondria convert food molecules into usable energy and that a simplified reaction for aerobic respiration is:

4. Tell students that they will analyze data from a hypothetical experiment similar to the ones presented in the NOVA scienceNOW: Marathon Mouse video. Divide the class into pairs, and give each pair a copy of the Marathon Mouse Student Handout PDF Document. Also give each pair an envelope containing data from two of the four experimental mice. Tell students that the darker areas in the images are the mitochondria-rich muscle cells.

5. Have each pair read the handout's opening statement and complete the procedure for analyzing their cell samples, including viewing Where Do You Get Your Energy? Flash Interactive and How the Body Responds to Exercise QuickTime Video.

6. Write a chart on the board to organize the class data. Once pairs have completed step 3 of the handout, have them fill in their responses on the class chart. Here is an example: (Note: The numbers in the chart are hypothetical numbers.)

7. Ask students to look at the class data and predict which mouse received which treatment. Then, reveal the answers.

8. Ask students to compare the effects of each treatment. For example, both Drug X and Exercise created more mitochondria. On the other hand, "no treatment" led to no change in the number of mitochondria-rich cells, just like the ineffective Drug Y. Ask students to explain any incorrect predictions. For example, did they know which drugs were effective in this hypothetical experiment before all the available information was compared?

9. Optional Extension Activities:

1. Examine and discuss the differences between light and dark meat in chicken. Dark meat contains more fat, has a richer blood supply, and is composed primarily of slow-twitch muscle fibers, which are full of cells rich in mitochondria. This muscle is well adapted to low-intensity, long-duration activities. Ask students to consider why dark meat is concentrated in specific locations in the chicken. They should move toward the understanding that it is full of mitochondria-rich cells and is found in muscles used in activities requiring endurance, such as flying and walking. Then, ssk students to hypothesize where dark meat might be found in other animals, such as those that travel long distances (e.g., ducks, caribou, and certain turtles and fish).

2. For advanced students, show the HHMI: PPAR-delta Activation in the Muscle Cell Video. It illustrates how the PPAR-delta receptor activates certain genes in a muscle cell, resulting in the burning of fat. Show the video several times and have students summarize what is happening: PPAR-delta is a type of receptor related to the metabolism and storing of fat. It activates certain genes that signal the muscle cell to burn fat for energy. Also, relate this video to the NOVA scienceNOW: Marathon Mouse video, in which the mouse was genetically engineered to have PPAR-delta in overdrive, allowing it to run significantly longer distances than regular mice could.

Check for Understanding

Have students debate the pros and cons of a pill that simulates exercise. For example, such a pill could benefit the elderly, hospital patients, and people with muscular conditions. On the other hand, a pill that simulates exercise could be abused in sports and might have adverse side effects. Also, remind students that, currently, the only guaranteed way for people to increase their fitness is to exercise.

You can also use the answer key and rubric in the Teacher Notes—Marathon Mouse PDF Document to assess each student's work on the handout.