PBS - Scientific American Frontier:Changing Your Mind


	Feeling Pressured

	Memory Matters

	Getting the Minerals Out

Bone is a tissue that is made up of both living cells and mineral deposits. The bone cells form what is called the protein matrix - a type of framework that defines the shape of every bone. Although the matrix is firm, it is not hard. The hardness and strength of a bone arise from minerals that are deposited alongside the living cells. Without these minerals, bone would be soft and flexible.

Throughout your life, your bones are constantly being reshaped by specialized bone cells. Some of these cells take away regions of old bone. Other cells direct the formation of new bone material. The remodeling of a bone reflects how the structure is being used (or under-used). Bones in our body that are frequently used may become thicker and stronger. Bones with minimal usage may diminish in size.

In order for a bone to decrease in size, it must lose both protein and minerals such as calcium. The protein framework is taken apart by special enzymes. But since minerals are not made of protein, they are unaffected by these destructive chemicals. In order to dislodge these harder mineral deposits, your body releases citric acid and lactic acid through a process called decalcification.

As you saw in "I Was a Spaceman," during extended weightless periods, astronauts like Jerry Linenger lose bone mass because their bodies don't need as much structural support from their skeletal system. Bone decalcification can also occur in the classroom. In this activity, you'll test several liquids to find out which ones best dissolve the minerals in bones.

OBJECTIVE
This activity page will offer:

background in bone composition and physiology
an opportunity to compare and contrast the decalcifying properties of several liquids

MATERIALS:

old chicken bones (boiled with all meat removed)

vinegar (0.4% acetic acid)

dilute hydrochloric acid solution (0.2%) *see teacher note

window washing solution (ammonia based)

alcohol (methanol or ethanol)

distilled water

safety goggles

protective apron

5 jars with lids

forceps

PROCEDURE

PART 1 - Dissolving Minerals

Work with a partner.

Obtain five chicken bones that have been stripped of all meat.

Put on your safety goggles and protective apron

Label five jars: water, alcohol, HCl, window cleaner, and vinegar. What do you know about each of these liquids? Which ones are acids? Which ones are bases? Which ones are neutral?

Fill these jars halfway with the identified liquids.
NOTE: The jars must contain enough liquid so that the entire bone sample will be immersed.

Examine each of your five bone samples. Describe their physical appearance and properties.
Are the bones hard or soft?
Do the bones bend and twist easily or are they too rigid to flex?

Use forceps to place one bone into each solution.

Cover each jar with a lid. Place it in a secure area identified by your instructor.

Make a guess.
Which of these solutions will affect the hardness and rigidity of the bone? Record your prediction.

Several days later collect the jars. Put on safety goggles and a protective apron. Use your forceps to remove the bones from the liquid.

Rinse the bones thoroughly in water. Let them soak in a water bath for several minutes. Rinse them again.

When your instructor has given the approval, you may test the bones for any changes. Try twisting and bending the bones. Can any of these bones be tied into a knot? How did your predictions compare with the results you obtained?

Share your results with other teams.
Did all the groups obtain the same results?
Explain any observed differences in bone changes.

QUESTIONS

Which solutions softened the bones?

Why did these solutions affect the property of the bone material?

How were the bone-weakening solutions similar?

What was the purpose of putting one of the bones in water?

APPLY WHAT YOU'VE DONE

How can this laboratory experience be applied to the challenges of extended space flight?

EXTENSIONS

1) Like bone, marble statues are made of a calcium compound. Using your equipment from the previous experiment, design and carry out an experiment to determine the effects of acids and other solutions on marble chips. Don't forget to use a control such as water that will not react with the marble.

2) Think of some other reasons why people might experience bone decalcification. What can this experiment teach you about osteoporosis in older people, or the importance of good nutrition in children?

WEB CONNECTION

Laboratory of Cell Growth
This is a rich site on cell growth, osteoporosis, and bones in space.

Space Medicine
The medical challenges awaiting the Mars journey.

Musculoskeletal Experiments
NASA site on the musculoskeletal concerns of shuttle missions.

ANSWERS

"Memory Matters" and "Getting the Minerals Out" were contributed by Michael Dispezio, a Massachusetts-based science writer and author of "Critical Thinking Puzzles" and "Awesome Experiments in Light & Sound" (Sterling Publishing Co., NY).