1. Focus student attention on the three pairs of materials on the front table. Begin with the paper and skin. Ask students, “What do these two items have in common?”

Allow only two to three minutes to develop this list. Student responses will vary. They may indicate that both skin and paper are flat and flexible. In addition to observable characteristics, try to focus students on functions. Both items can be used as coverings to contain things or as a protective layer for items beneath them.

Note to teachers: 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 you 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 you see that thinking has been engaged.

2. Ask students, “How are paper and skin different?”

Once again, allow only two to three minutes to develop this list. Student responses again will vary. Although they probably will lack details, they may indicate that paper and skin are made of different things. Try to get students to elaborate on this response. They may also indicate that both came from sources that were alive at one time.

3. Repeat the questions in Steps 1 and 2 for chalk and bone and for the rubber band and meat.

Developing lists of similarities and dissimilarities for these two pairs should proceed quickly. For each pair, try to have students come up with at least one response relating to what each item is composed of. Note that it is possible that students may not know that meat is animal muscle. If necessary, tell them that meat is muscle tissue.

4. Break both the chalk and the bone. Cut both the rubber band and the piece of meat. Cut both the paper and the chicken skin. Ask students, “Can these items repair themselves? Why or why not?”

Students will realize that the chalk, rubber band, and paper cannot repair themselves. They also should realize that the bone, meat, and skin cannot repair themselves. Some students, however, may make the leap to bone, muscle, and skin in an intact organism, such as a human, and indicate that these three systems can indeed repair themselves.

5. Ask students to raise their hands if they have ever broken a bone, injured a muscle, or cut their skin.

6. Ask students to lower their hands if their injuries healed.

All students should lower their hands unless their injury is very recent or they have a condition that prevents normal healing. Some students may indicate that healing occurred, but it took a long time. All student responses are appropriate for discussions later in this lesson and in subsequent lessons.

Note to teachers: Some students may raise the issue of scars forming at the site of a previous skin injury. Rather than allow this topic to change the focus of class discussion, simply indicate that scar formation is an indication that the tissue has healed.

7. Ask students, “Why could the bone, muscle, and skin of your body heal while the broken chicken bone, cut piece of meat, and cut chicken skin could not repair themselves?”

While students may understand that there are basic differences between muscle in their body and meat on the table, for instance, they may have trouble expressing what those differences are and why the two function differently. You may have to guide the discussion by asking additional questions:

• “Can the chicken bone, meat, and skin ‘feel’ pain or respond to a stimulus, like a pinprick, as bone, muscle, and skin in the body would?”
• “If your skin were cut, it would bleed—why didn’t the chicken skin bleed when cut?”
• “Can the chicken bone, meat, and skin grow as bone, muscle, and skin in the body do?”

Try to guide this brief discussion so that students view the bone, muscle, and skin of their bodies as active, changing, and responsive systems that are connected to other body systems, such as nerves and blood vessels.

8. Divide the class into teams of three or four. Ask each team to make a list of characteristics of living systems.

Give teams just five minutes for this task. If students need help getting started, suggest that they think about finishing sentences that begin, “Living systems are made of …” or “Living systems are able to ….”

9. Ask teams to share the items on their list with the class.

Write the responses on the board. Try to summarize the responses like this: living systems

• are composed of one or more cells;
• function according to a genetic blueprint (the cells contain DNA);
• obtain and make energy; and
• interact with their environment.

If students respond that living systems can move, for instance, you might indicate that this characteristic is the result of obtaining and making energy and interacting with the environment.

Note to teachers: The ability to reproduce is a commonly listed characteristic of living systems. In this lesson, that characteristic is not listed separately because bone, although it is a living system, does not reproduce itself. Rather, the cells of bone reproduce and carry out those activities (such as making protein and depositing mineral) that allow bone to grow, repair, and remodel itself. If students mention reproduction as a characteristic of living systems, list this response under “function according to a genetic blueprint (the cells contain DNA).”

10. Provide each student with one copy of Master 1.1, It’s Alive! Or Is It? Ask students to fill in the first column, Characteristics of Living Systems, with the summary items you’ve created from Step 9.

11. Ask students to consider the class discussion and complete the table. For instance, if the first item in the characteristics column is “Living systems are made of cells,” students should check the “Yes” column if they agree with this statement or the “No” column if they disagree with this statement. They do this for each system—bone, muscle, and skin—for each characteristic of a living system.

12. Ask students if they believe that bone, muscle, and skin are living systems. Ask for a show of hands.

13. Ask several students to share their thoughts and reasoning with the class.

14. Ask students to write an answer to the question at the bottom of Master 1.1, It’s Alive! Or Is It?, Why do you believe bone, muscle, and skin have been grouped together for study in this module?

15. Ask several students to share their thoughts with the class.

Why bone, muscle, and skin have been grouped for this module may not be obvious to students. Answering this question provides an opportunity for students to reflect on prior knowledge, and it sets the stage for the investigations to follow. Over the course of this module, students will develop the understanding that these systems all have structural functions and they protect the body. Also, these systems simultaneously allow flexibility and strength.

16. Explain to students that they are about to begin their study of bone, muscle, and skin. As they investigate these three systems, they can reflect on their understanding of bone, muscle, and skin as living systems by comparing their new insights with their responses in this lesson.