Learning Scenario - Bone Density Model (AgentSheets)

Basic Model:

Description

Loss of bone density is dependent on many variables, such as age, gender, and calcium intake. This model simulates a person's bone loss based on these factors. Bone density decreases at a specific rate based on the values the user assigns to the variables. The time that it takes for the bone to completely lose its density can be long or short, based on the initial parameters. Independent variables may be changed in order to determine their effect on the degradation time. The Bone Density model is a real-world simulation that students will be able to take and understand in a non-classroom context.

Background Information

Many people are affected by bone density loss in their later years. In fact, 1 in 3 women over 50 will suffer a broken bone as a result of osteoporosis . Osteoporosis can be the result of many factors, including not having enough calcium intake, gender, or age. People who feel like they might be at risk for osteoporosis may have their bones tested for density. Calcium levels and other important bone characteristics are recorded and analyzed. The Bone Density model simulates this process over time and allows students to understand the factors that play into osteoporosis. This model will allow students to manipulate variables in order to understand the affect that each has on bone density over time.

Science/Math

The fundamental principle behind this model is HAVE = HAD + CHANGE. For each time tick, the following things happen:

1. The bone cells' average calcium amount decreases based on the age, gender, and intake variables set by the user.
2. The total calcium in bone amount decreases based on the age, gender, and intake variables set by the user.

As the steps above suggest, the model is focused on the CHANGE in the simulation properties to produce a different result in the degradation of the bone. Age, gender, and calcium intake will play a part in how quickly the bone will lose density. In general, women lose bone density quicker than men, those at a higher age will lose bone density quicker than those who are young, and those with less calcium intake will lose bone density quicker than those with more.

Teaching Strategies

An effective way of introducing this model is to ask students to think about the effects that they believe the different variables of this simulation would have on bone density. Have them come up with hypotheses intuitively and test them when the simulation is run.

1. What would happen to the density of your bones if you suddenly could not absorb any calcium? Why?
2. Do you know any elderly people who have broken a bone? How did they get hurt? Would you have gotten hurt if you had the same thing happen? Why or why not?
3. Who do you think would have less dense bones, males or females? Why?
4. How does drinking milk help your bones? Explain.

Implementation:

How to use the model

This model has a few parameters that can be changed to produce faster or slower bone density loss:

1. The age of the bone's hypothetical person
2. The gender, where 1.0 corresponds to male and 2.0 corresponds to female
3. The calcium intake percentage by typing in a percentage without the percent symbol (i.e. 75.0)

All of these parameters may be changed by editing the "Simulation Properties" located within the gray dropdown arrow on the right hand side of the page and clicking "Save." The other fields should not be changed but are to be studied. To run the simulation, click the green triangle in the bottom left hand of the worksheet. The speed of the simulation may be changed using the slider under the worksheet, and the simulation may be reset by clicking the "Reset" button in the bottom right hand corner of the same window. Use the operator hand tool and click on the timekeeper above the bone to reset the time and generate new, random bone cells. For more information about Agentsheets reference the Agentsheets tutorial at: http://shodor.org/tutorials/agentSheets/Introduction.

Learning Objectives

1. Understand the effects of age, gender, and calcium intake on bone density
2. Determine the best strategy for maintaining a good bone density

Objective 1

For this objective, students will be able to manipulate the variables of the simulation to study the effects that each variable has on the bone density loss (or perhaps gain). Ask the following questions to guide the students to an understanding of the topic:

1. Set a younger age and a high calcium intake and graph the AvCalcium variable. Run the simulation and compare the graph to the graph of an older age and a low calcium intake. How do the graphs compare? Why would one be different from another?
2. Compare the graphs of a male and female with the same age and calcium intake. Which one had the quickest loss of bone density? Is this a sex-linked trait?
3. How much calcium intake would a 75 year old need to maintain if he wanted to have about the same bone density as a 55 year old with a 50% intake?
4. How does age affect the average calcium level and its rate of decline?

Have students compare their findings with their initial hypotheses.

Objective 2

In order to find the best strategy for maintaining bone density, students will have to use what they learned in the previous objective coupled with their problem solving abilities. The goal is to achieve a bone that maintains dense bone cells (represented by white pixels) for the longest time possible. Allow the students to try and find the best solution for different ages and ask the following questions:

1. Set the parameters to a 60 year old male. Adjust the calcium intake level until the bone density loss is negligible. Is this result realistic? If so, explain. If not, find another solution with minimal bone loss that is realistic.
2. Would you expect the calcium intake required for a female to maintain proper bone density to be higher or lower than that for a male? Does that change with age?
3. Change the age and gender to your own. What is the intake that you need in order to maintain proper bone density? How does this compare to the 60 year old you calculated in the previous question?
4. What is the best plan for maintaining bone density if you were to try and keep healthy bones starting now? Compare with other members of the class.

Extensions and Related Models:

1. Understand real-life bone density tests and connect them to the model
2. Learn how calcium helps bone health and find the recommended daily values

Extension 1

Those who think they might be at risk for osteoporosis undergo bone density tests. An X-ray is taken of a person's bones and the grams of calcium and important bone materials are calculated. Have students research bone density tests and find how the model attempts to simulate them over time.

1. What is the process for evaluating bone density? What specifically is counted or calculated in the process?
2. Can the Bone Density model that you just worked with act as a sort of bone density scanner for a hypothetical patient? Explain.

Extension 2

Calcium is important for both young and old to include in their diets. As one's bones are growing in early youth, enough calcium is needed to allow for proper calcium storage within the bones. When he or she grows older, though, proper dietary calcium is necessary to maintain bone density. There is a recommended amount of calcium that each age should obtain every day. Ask students to research the daily value for themselves and study intake trends for increasing age categories. Ask the following questions:

1. What is the general trend for the recommended amount of calcium intake as age increases? Is this consistent with the Bone Density model? Explain any differences.
2. What is the recommended daily intake for someone who is your age and gender? What could happen if you do not get the right amount of calcium?
3. Are there any exceptions to the recommended daily amounts of calcium? What are they and why would a person need more? Explain.

Related Models

Dominant Recessive Sampling

The Dominant Recessive Sampling Model will allow students to understand genetics. Osteoporosis could potentially be an inherited condition. This model will provide students with an understanding of how scientists would determine the genetic linkage through experimentation. In genetics, if the recessive allele has a certain frequency, one can attempt to find this number by counting the number of individuals with the recessive alleles in a given population. As the number increases, the actual allelic frequency will begin to appear.

Supplemental Materials:

• Dominant Recessive Sampling tutorial and background information

Pseudo Random Numbers

This model will present a way for students to understand flaws in the model in relation to its simulation of a real world, random event. The Bone Density model provides a bone based off random numbers, and the loss of density is somewhat based off of random numbers. Since the model is on the computer, though, there is some hidden bias involved, since programs cannot generate random numbers on their own. The Pseudo Random Numbers model explores this idea and shows how random chance is presented in the model through multipliers and shifts. Ask students how pseudo random numbers are related to the computer simulations, and specifically how they affect the results of the gas model.