BONE COMPARISON

Research How does a bird's bone differ from a mammal's bone?
Goals
1. Learn the structure and parts of a bone
2. Compare the bone structures of two animals of different classes
3. Learn how bone structure can result in better adaptation of an animal to its environment
4. Observe differing bone structures
5. Practice making scientific drawings
Materials and Equipment
Magnifying glass
Ruler (from dissection kit)
Toothpicks
Materials Not Included
Raw beef leg bone with the bone cut in half
as a cross section
Raw chicken leg with the bone cut in half as
a cross section
Introduction
There is a reason why elephants do not fly. One of many reasons is the skeleton of a land animal is not suited for flight. Birds, on the other hand, have perfect bone structure for flight; many of their bones are hollow, making them light weight for flight. In the
"trade off" for lighter, hollow bones, birds sacrifice a certain amount of bone strength.

Although birds bones are hollow, they are strengthened by cross-struts. Not all the bones in a bird are hollow, but gliding and soaring birds tend to have a higher percentage of hollow bones than other birds.
Mammals, on the other hand, do not need lightweight bones for flight but need stronger bones to carry their weight as they run on land. It only makes sense that mammals that do not need to fly should have heavy, dense bones.
In this activity, you will compare the bones of a bird with that of a land animal.
You will be examining the dense, outer part of the bone called compact bone and the blood vessel rich bone marrow which is housed in the interior, spongy looking part of the bone. Take special note of the amount of heavy bone material in companson to the amount of the spongy marrow section afforded to each type of bone.
Procedure

1. Get a chicken leg bone and a piece of beef leg bone (soup bone) at a grocery store or butcher shop. Ask the butcher to cut both in half as a cross section. Note: If the beef leg bone is in a package of frozen soup bones, defrost the bone before doing this activity.
2. Using a magnifying glass, look at the cross section of each bone.
3. Draw a picture of the cut end of each bone in the circles provided in the Questions section of this Lab.
4. Label the compact bone section and the marrow section of the bone.
5. To find the width of the compact bone portion of the bone in relation to the marrow portion of the bone, use your ruler to measure the width in centimeters of the cross section of bone. Record it in Table 1.
6. Use a toothpick and scrape around the edge of the marrow section making a visible line where the marrow meets the compact bone.
7. Then, measure the width, in centimeters, of only the marrow section of the bone and record it in Table 1.
8. Subtract the marrow measurement from the width of the whole cross section of the bone. This gives you the thickness of the compact bone.
9. Divide the difference calculated in step 8 by the width of the whole cross section. Multiply that number by 100. This is the percentage of the bone that is compact bone.
10. Repeat for the other bone.
11. Notice the difference between the two bones.
12. Using a toothpick scoop a small portion of marrow from the chicken leg. Describe its texture in the Questions section.
13. Repeat Procedure 12 for the beef leg bone.

Questions for Bone Comparison
1. Draw the cross section of the leg bones in the circles provided.
* BIRD (CHICKEN) BONE
* MAMMAL (COW) BONE

Portion of bone
Width of the whole cross section
Width of the marrow section
Width of the compact bone section
Chicken leg
1.0 cm
0.8 cm
0.2 cm
% of bone cross section that is compact bone
20%
Beef leg
4.5 cm
2.7 cm
1.8 cm
40%

3. What effect does the higher percentage of the compact bone portion have upon the weight of the bone?

4. Describe the texture of the marrow from the chicken bone.

5. Describe the texture of the marrow from the beef bone.

6. Which marrow was denser (had more mass in the given volume)? What impact would that have on the overall density of the bone?

7. In a short paragraph, relate the density of the bone to the activities and environment of each animal, both bird and cattle.