PREPARATION

Activity 1

If necessary, fill the 3 beakers from Lesson 2 with equal amounts of water. Add 1 drop of the mystery chemical to Beaker #1, 4 drops to Beaker #2, and 16 drops to Beaker #3.

Collect 3 clear containers of different sizes and label them #1, #2, and #3. Fill each container with water, making sure that each container holds obviously different amounts of water, with #1 having the least and #3 having the most.

Make a transparency of Master 4.1, Acetaminophen Dosage Chart.

Activity 2

Decide whether you will use the Web site or print version of this activity. If you choose the Web version, arrange for students to have access to computers.

If you use the print version, conduct the activity with the whole class. Later, let students review the problem using the Web site on their own at a computer center. Make a transparency of Master 4.2, A Poisonous Dose? The Case History. Duplicate Master 4.3, A Poisonous Dose? The Problem, 1 for each student.

Activity 3

At least one week before conducting Activity 3, send home personalized parent letters (Master 4.4, Parent Letter) to inform parents of the investigation and to get permission for the students to consume a caffeinated soft drink during science class. You can use the letter to ask each student to bring in his or her own can of the designated caffeinated soft drink.

Arrange to have enough cans of the same kind of caffeinated soft drink for each student who participates in the investigation. There are several ways to do this:

• purchase all the soft drinks yourself through your school budget,
• ask for parent or business donations to cover the cost, or
• request that each student bring in one can of the same kind of soft drink, labeled with his or her name, for his or her consumption only.

Before the day of Activity 3, have students practice taking a resting heart rate so they are used to finding their pulse, counting the beats for 15 seconds, and multiplying the number they count by four to get a resting heart rate for one minute (see Activity 3).

Duplicate Master 4.5, The Chemical Caffeine: How Do You Respond?, 1 for each student.

Procedure

ACTIVITY 1: DIFFERENT DOSES FOR DIFFERENT PEOPLE

1. Ask students why they think toxicologists look at both whether a chemical has an effect on living things and what happens at different doses. Why do students think it matters to look at doses?

Students may bring up the term overdose, which refers to a situation in which a person receives too much of a particular chemical, usually a drug. Students should realize that the proper dose of a chemical is what makes it beneficial to people and that knowing the dose is useful in determining the appropriate human consumption of that chemical. Some chemicals, such as vitamins and minerals, are beneficial at a particular dose, but human health suffers if the chemicals are present in high or very low doses (you can have too much or not enough). Other chemicals, such as drugs and pesticides, usually are more harmful as the dose increases.

2. Tell students that you are going to demonstrate one reason why paying attention to dose is important in the study of toxicology.

• First, on one side of a desk at the front of the room, place the three large beakers filled with equal amounts of water and different amounts of mystery chemical from the demonstration in Lesson 2. Remind students that this is the demonstration they saw before they began their seed investigation.
  
  
• Then, place three different-sized clear containers on the desk. Fill each container with water, making sure that it is obvious that each container holds a different amount of water (#1 holds the least and #3 holds the most).
  
  
• Using the eyedropper from Lesson 1, place two drops of mystery chemical in each of the containers. Swirl the containers to mix the chemical and the water.

3. Ask students to observe the three new containers and compare them with the setup of the demonstration from Lesson 2. Discuss their observations by asking questions like these:

• Content Standard A: Students think critically and logically to make the relationships between evidence and explanations.

  Is this new demonstration the same as the one I did for you before you began your seed investigation? Why or why not?
  
  Students will recognize that the demonstration is different. Today, you are using different-sized containers (and different amounts of water) and the same amount of chemical; earlier, you used the same-sized containers and different amounts of chemical.
  
  
• What was the variable in the earlier demonstration?
  
  The variable was the amount of chemical you added to each beaker of water. The dose was the variable. The amount of water was the constant.
  
  
• What is the variable I am using today?
  
  Today, the variable is the amount of liquid in each container. The dose of chemical is a constant.
  
  
• How would you describe the concentrations of chemicals in each of the containers in today's demonstration?
  
  The concentration of chemical in each container is different in today's demonstration because the amount of water in each container is different although the amount of chemical is the same. Because concentration is a measurement of the amount of chemical compared with the volume of water, the concentration of chemical in Container #1 is higher than the concentration in #2 or #3.
  
  
• What do you think the containers in today's demonstration are illustrating? Why do you think it matters that the containers are different sizes?
  
  The different-sized containers represent the different variations in size of people who might be exposed to the mystery chemical. In smaller people (Container #1), two drops of chemical result in a higher concentration of chemical in their bodies than do two drops in either of the larger people (Containers #2 and #3). This higher concentration could be beneficial (if it approaches the threshold that creates beneficial results) or it could be harmful (if the higher concentration exceeds the threshold for safe use of the chemical).
  
  
• When might understanding this relationship of dose to size matter?
  
  When people use drugs to treat illness, they are exposing themselves to chemicals. To understand how much of a chemical is needed to get the desired effect, such as lowering fever or reducing pain, you need to understand that the same dose of chemical will have different effects on different-sized people because it results in different concentrations in their bodies.
  
  

  Ask students to write about the two demonstrations and clearly discuss what is different about the two.

  Tip from the field test: This is a simple demonstration that, when coupled with students' understanding of the earlier demonstration, moves students to use the language of toxicology: dose, response, concentration.

4. Keep the containers of water on the desk while you display the transparency of Master 4.1, Acetaminophen Dosage Chart. Ask questions such as these to discuss the concept of dose with respect to body size:

• What is acetaminophen?
  
  Students might need you to tell them that acetaminophen is the active ingredient in Tylenol® products. It is a chemical that, when taken into the human body, elevates the pain threshold and reduces fever.
  
  
• For all people, what is the response they want to get from exposure to a dose of acetaminophen?
  
  They want to reduce their fever or pain.
  
  
• What does the dosage chart tell you about the relationship between dose and body size?
  
  The dose increases as the body size of the individual increases. Students can see from the chart that each tablet of Children's Chewable Acetaminophen provides a dose of 80 milligrams of acetaminophen. As a child grows, the amount of acetaminophen needed to reduce fever and pain increases. For example, a child weighing 40 pounds needs a dose of three tablets at 80 milligrams of acetaminophen per tablet, or 240 milligrams of medicine. A child weighing 80 pounds needs six tablets at 80 milligrams each, or a dose of 480 milligrams of acetaminophen.
  
  Tip from the field test: Use this time to teach students how to read a dosage chart. Show them where to find information about the number of milligrams of acetaminophen each measurement contains (for example, one tablet contains 80 milligrams of acetaminophen). Impress upon them the importance of knowing a person's size (weight) to determine correct dosage. Familiarity with dosage charts makes it easier for students to work the problem in Activity 2.

D

• Look again at today's demonstration. Which size child from the chart might each container in today's demonstration represent?
  
  Container #1 represents the smallest child, #2 a medium-sized child, and #3 the largest child.
  
  
• If the 2-drop dose the smallest child received in Container #1 was correct for the child's size, what can you say about the dose the other two children received?
  
  The concentration of chemical in the larger children's bodies would be lower and might not be enough to provide the desired effect.
  
  
• If the 2-drop dose in Container #3 resulted in a toxic response for the largest child, what can you say about the dose for the two smaller children?
  
  The dose for the two smaller children would almost certainly be toxic because the concentration of chemical in their bodies is higher.

Content Standard F: Students should develop understanding of personal health.

5. Tell the students that size is one difference in people that can effect how susceptible they are to chemicals. Ask students what other factors about an individual might make the individual more or less susceptible to chemicals such as acetaminophen. List the factors on the board.

Start the list with size (weight). Other factors that can affect susceptibility to chemicals are age, lifestyle or behavior (such as being an alcoholic), gender, genetics, and general health.

6. Tell students that toxicologists know that these variable factors determine an individual's susceptibility to the effects of environmental toxicants. Write individual susceptibility as the title of the list you made on the board in Step 5. Tell students that, because of their understanding of individual susceptibility, toxicologists expect that individuals may respond differently to the same dose of a chemical.

Photos: Corel

7. Ask students to apply the concept of individual susceptibility to their observations of the seeds in their investigation. If students need help, prompt them with questions such as these:

• Did all of the seeds in each of your bags respond to their dose of chemical in the same way?
  
  Answers will vary, but most likely students will have had bags in which not all of the seeds reached the same stage of germination by Day 3.
  
  
• What factors in the seeds might account for the differences in germination among them?
  
  Seeds are processed from many different plants, so the genetic makeup might not be exactly the same among 10 seeds. Age might be a factor, because some seeds might be older than other seeds. General health of the seeds could be a factor, because some seeds might be less healthy than other seeds.
  
  
• Why did you use 10 seeds to test each of the concentrations of chemical?
  
  By using 10 seeds, you can compensate for possible responses due only to individual susceptibility by observing the response in the majority of the seeds. If you tested only one seed, you wouldn't know if the response you observed was due only to the dose of the chemical or was a reflection of the seed's individual susceptibility to the chemical.

ACTIVITY 2: A POISONOUS DOSE?

The following procedures describe how to conduct the Web version of this activity, which is the preferred method of instruction. Instructions for the print version follow.

Use a computer lab where you can set up multiple computers. Open the Web site in your browser (see instructions for using the Web site). From the main page, click on Web Portion of Student Activities, then select Lesson 4—Individual Responses Can Be Different. Start the activity by watching the video. Encourage students to work in pairs to solve the problem.

Print Version

If your students do not have access to computers equipped with the Internet or you would like an opportunity to assess students individually on their understanding of a toxicology problem involving humans, use the following print version of Activity 2.

1. Display the first page of the transparency you made from Master 4.2, A Poisonous Dose? The Case History. Read the transparency with the students.

2. Distribute copies of the first page of Master 4.3, A Poisonous Dose? The Problem. Ask students to work in teams of three to complete Part I. Circulate around the room to help students read the dosage chart, understand the math, and draw some conclusions.

Students should select letter e: Both b and d are correct. Andy received 1 teaspoon four times a day, or 4 teaspoons in all. Because there are 6.25 dropperfuls of acetaminophen in each teaspoon and 80 milligrams of acetaminophen in each dropper, the calculation of the amount of acetaminophen Andy received from his aunt should read:

 

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