BioEd Online

Teacher Background

Bones are living tissues that contain blood vessels and nerve cells within a structure composed of collagen (a flexible fibrous material) and minerals (mainly calcium and phosphate). Without calcium (in the form of calcium salts), bone would be flexible and soft, and without collagen fibers, bone would be brittle. The collagen fibers and calcium salts together make bone almost as strong as steel, but much lighter. Unlike steel, bone can repair itself when broken with the help of bone-forming cells (osteoblasts) and bone digesting cells (osteoclasts). The prefix “osteo” means bone.

To provide support and still be easy to move, bones must be both strong and lightweight. These features are most important for the long bones in arms, legs and wings.

Each human long bone is composed of a shaft (diaphysis) with two flared ends (epiphyses). The diaphysis resembles a hollow cylinder. It is made of hard compact bone that is resistant to bending.

The inner cavity of the diaphysis contains yellow marrow that stores fat. The epiphysis is a thin shell of compact bone filled with a lattice or sponge-like structure that is surrounded by red marrow (which makes red blood cells).

Objectives and Standards

Concepts

• Long bones are made of hollow tubes, which give strength with minimal weight.

Science, Health and Math Skills

• Predicting

• Observing

• Comparing

• Weighing

• Gathering data

• Recording data

Materials and Setup

Teacher Materials

• Heavy-weight balance or bathroom scale

• Poultry scissors or small saw

Materials per Group of Students (see Setup below)

• 2 bathroom-sized paper cups

• 6–10 heavy, stackable weight units (bricks, cans, reams of paper or books)

• 1/3 cup dried beans

• 1 long bone from a chicken leg or thigh that has been cooked and cleaned (see Setup)

• Magnifiers

• Sheet of corrugated cardboard

• Copy of student sheets

Setup

1. Obtain and cook enough chicken pieces to provide one or more different bones (any size or shape) to each group of students. You also may have students bring leftover cooked chicken bones from home. OR use the long bones prepared for the activity, "The Skeleton."

2. Remove all meat from the bones (additional boiling may be necessary), and soak the bones in a 1:10 bleach/water solution for five minutes.

3. Allow the bones to dry before using them in class.

4. Place all materials in a central location.

5. Have students work in groups of two or four.

6. Dispose of the bones after the activity.

Safety

Please read “Setup & Management,” and follow all school district and school laboratory safety procedures. It always is a good idea to have students wash hands before and after any lab activity.

Procedure and Extensions

Time: One or two sessions of 45-60 minutes

1. Point to your arm or leg and ask students to think about characteristics that might be important for large arm or leg bones. Stimulate their thinking by asking questions such as, What type of work does my arm/leg do? Does it matter how much the bones in my arm/leg weigh? Does it matter if my arm/leg bones are very strong? Based on students’ answers, make a list of desirable characteristics of long bones.

2. Tell students they will be conducting an investigation that will provide clues about the structure of long bones in humans and other vertebrates. Specifically, they will be comparing the relative abilities of solid and hollow cylinders to support external weights. Ask, Is a hollow cylinder or a solid cylinder able to support more weight, relative to its own weight?

3. Have each group’s Materials Manager and a helper collect two paper cups, beans, cardboard and a set of weights. Using the “Weighing ‘In’” sheet as a guide, have students compare the weights that can be supported by a hollow cylinder (empty cup) and a solid cylinder (cup filled with dried beans). Each group should conclude its explorations by calculating the ratio of weight supported to cylinder weight for each kind of cylinder.

4. Initiate a class discussion of students’ results by asking, Which cylinder was heaviest? (solid), and, Which cylinder held the most weight? (solid). Did either cylinder hold more weight than you expected? Which cylinder had a higher ratio of weight supported? (hollow). Did you expect this result?

5. Ask students to think about which type of cylinder (hollow or solid) might make a better bone. Pass out the “Hollow or Solid?” student sheet. Have students record their predictions about the structure of long bones (hollow or solid).

6. Have the Materials Managers pick up one or more bones for their groups. Have students observe the outsides of the bones with and without a magnifier, and draw an exterior view of a bone in the space provided on their sheets.

7. Using a small saw, hammer or poultry scissors, cut or break open the bone(s) for each group. Students will observe that the bones have hard walls and a central space filled with a soft substance (marrow). Ask students to compare the structure of the bone to the hollow and solid cylinders. Ask, Which cylinder does the bone most resemble? Help students to conclude that the relatively hollow design of real bones allows them to be light, but still strong enough to do their jobs. Relate students’ conclusions to the list of valuable characteristics of bones made earlier.

Extensions

• The thighbone (femur) is the longest bone in the body. Its shaft is round in cross section. The main shinbone (tibia) is the second longest bone in the body. Its shaft is triangular in cross section. Challenge students to investigate the relative strengths of different-shaped columns. Have students use note cards to create columns with different shapes in cross section (round, square, triangular, etc.). Ask them to consider the total amount of material necessary to build each kind of column as they reach their conclusions about relative strength.

• To observe how calcium contributes to the hardness of bones, have students soak cleaned chicken bones in vinegar for about one week. Vinegar, a weak acid, will leach calcium out of the bones, which then will become weaker and softer.

Handouts and Downloads

Download color images from The Science of Muscles and Bones Teacher's Guide.