1. Several days prior to conducting Activity 2, decide which students will be in the group that drinks a caffeinated soft drink and which students will be in the group that drinks a caffeine-free soft drink. Tell students which group they will be a part of if you are asking them to bring a can of soft drink to class. Make sure students understand the need to bring only the specified type of drink.

Approximately half of the class should be assigned to each group. You should have permission letters specifying the type of drink for both of these groups. Any student who does not have parental permission can participate in the activity by drinking water.

Tip from the field test: Knowing which beverage they are consuming may influence students’ results. To avoid this possibility, you can prepare cups of soda in advance. Cups labeled “A” could contain a noncaffeinated soft drink, and cups labeled “B” could contain a caffeinated soft drink. Reveal which cups contain each beverage type only after students have collected their data.

2. Because their heart rates might be elevated from their walk to class, spend several minutes allowing students to rest and talk quietly. Find out what students know about caffeine.

Caffeine is a mild stimulant contained in coffee and some soft drinks. People often report that mild doses of caffeine increase their alertness and their ability to concentrate. Higher doses can cause a person to feel jittery or nervous. High doses can cause sleeplessness.

Related chemicals theophylline (found in tea) and theobromine (found in cocoa and tea) are very mild stimulants also.

3. If you have not already done so, teach students how to find their pulse, count their heartbeats, and calculate their resting heart rate.

A student can find his or her pulse most easily by pressing two fingers against the artery in the neck or on the inside of the wrist. It is easiest to count for 15 seconds and then multiply that number by four to obtain the resting heart rate for one minute. Students should repeat the process several times until they get a consistent resting heart rate.

4. Distribute one copy of Master 3.5, Caffeine: How Does Your Heart Respond?, to each student. On your signal, ask students to measure their heartbeats one more time for 15 seconds, stopping when you call time. Instruct students to calculate their resting heart rate for one minute by multiplying the number they counted by four. Direct them to record it on the data table on the master.
5. Ask students to work in pairs. Distribute cans of the appropriate soft drink, one to each student. Instruct students to follow the directions on the master, and remind them to continue to sit at rest. They can talk to their partner or work on Activity 3 in this lesson, but they should keep their bodies still so that they do not elevate their heart rate with activity.
6. When all the students have filled in their data tables and calculated the difference between their resting heart rate and their heart rate after drinking a soft drink, discuss their findings by asking:

• Did your heart rate go up, down, or stay the same after you drank a caffeinated soft drink?
• If you drank a caffeine-free soft drink, how did your heart rate change?
• What happened if you drank water?

On average, most students should have seen their heart rate go up after drinking the caffeinated soft drink. Drinking a caffeinated soft drink increased the heart rate of students in a field-test class by an average of 15 beats per minute. Drinking either a caffeine-free soft drink or water should not change the heart rate significantly.

Scientists don’t know exactly how caffeine increases heart rate, but it is likely to work in two ways:

• –  It acts on parts of the brain that regulate the heart rate.
• –  It acts directly on the heart.

• Why was it important that some students drink the same amount of a caffeine-free soft drink? Why did some students drink water?

These questions address the need for controls in scientific investigations. Students will recognize that they are interested in determining the effect of caffeine on their heart rate. Because caffeine-free soft drinks generally contain the same ingredients as caffeinated varieties except for the caffeine, the caffeine-free soft drink serves as a control to ensure that the response is due to the caffeine in the soft drink rather than some other ingredient. Water is a second control; it ensures that the effect on the heart rate of drinking a soft drink is not caused by an ingredient other than caffeine or by simply drinking something.

• How long did the effect of caffeine last?

Most students will find that their heart rates are either back to the resting rate or very close to it after one hour.

• Did all the members of the class have exactly the same results when they drank a caffeinated soft drink?

While most members of the class will see their heart rate increase, the amount of increase will vary.

• Why do people respond differently to caffeine?

Students differ from one another in gender, size, frequency of caffeine consumption, metabolic rates, genetic makeup, and so on. This variability makes each student react differently to exposure to caffeine.

• What could your results from the caffeine investigation tell you about how individuals respond to drugs of abuse?

Just as individuals vary in their response to caffeine, individuals will vary in their response to drugs of abuse. The same factors—gender, body size, frequency of use (development of tolerance), genetics, and the individual’s metabolic rate—will influence a person’s response.

7. If you are conducting this activity in several classes, you may wish to pool the data from all classes to have a larger sample size.
8. Discuss the last item on the master that asks students to consider how different doses of caffeine might affect the response. Encourage students to design an experiment to investigate this.

Students likely will propose that drinking a small amount of soft drink will cause only a slight increase, if any, in a person’s heart rate, while drinking a large volume of soft drink will cause a larger increase in heart rate. This leads students to consider the concept of dose.

To investigate the effect of dose on the body’s response to caffeine, students may propose that different groups of students drink different amounts of caffeinated soft drink. For example, students could drink 1 ounce, 2 ounces, 4 ounces, 8 ounces, or 16 ounces of soft drink. The design should include appropriate controls. Caffeine-free soft drink again could serve as the control if it is consumed in equal amounts to the caffeinated variety.

Many soft drinks popular among youth contain caffeine. The accompanying table lists some soft drinks and the amounts of caffeine a 12-ounce size contains.

Compared with other caffeinated drinks popular with adults, the caffeine content in soft drinks is lower. Coffee can contain between 80 and 175 milligrams of caffeine (per 7 ounces) depending on how it is brewed; espresso has 100 milligrams in just 1.5 to 2.0 ounces. Tea can contain 40–60 milligrams of caffeine (per 7 ounces). Ice tea contains 70 milligrams of caffeine in 12 ounces.

Caffeine in Soft Drinks

Soft Drink	Milligrams in 12 ounces
Red Bull	117 mg
Jolt Cola	72 mg
Code Red	54 mg
Mountain Dew	54 mg
Mellow Yellow	53 mg
Diet Coke	47 mg
Coca-Cola Classic	35 mg
Dr Pepper	41 mg
Pepsi Cola	38 mg
Diet Pepsi	36 mg
Coke Zero	35 mg
Barq’s Root Beer	23 mg
Mug Root Beer	0 mg
Sprite	0 mg
Sierra Mist	0 mg
Source: Center for Science in the Public Interest. Caffeine Content of Food and Drugs.

1. Give students the opportunity to view the segment Pathways to the Brain online, if possible. If not possible, move to Step 2.

Go to the Web site. Select Lesson 3—Drugs Change the Way Neurons Communicate and then Pathways to the Brain.

2. Give each student a copy of Master 3.6, How Do Drugs Get Into the Brain? Students may work in groups of three to analyze the graph and answer the questions.

Note to teachers: The graph shown on Master 3.6 is a generalized representation of the speed and intensity of response to drugs. Very few, if any, drugs are commonly taken by all of the different routes.

Sample Answers to Questions on Master 3.6

Question 1. Four people who abuse drugs each take a drug. One person injects 100 milligrams of a drug into a vein, one person smokes 100 milligrams of the drug, one person snorts 100 milligrams of the drug, and one person swallows or ingests 100 milligrams of the drug. Who will experience the greatest effect of the drug? The individual with the greatest concentration of drug in the brain will have the greatest effect.

The graph indicates that the individuals who inhale the drug or inject the drug into a vein will experience the greatest effect from the drug. These individuals will have a higher concentration of the drug in the brain than the people who snort (absorption through the mucous membranes) or ingest the drug. The concentration of drug in the brain will be slightly lower for inhalation than injection because some of the smoked drug is exhaled in the smoke.

Question 2. Who will experience the quickest effect from the drug?

The person who inhales the drug will experience the quickest effect from the drug (assuming the person inhales the whole 100 mg). The inhaled drug goes through the lungs and into the left side of the heart and then enters the arterial circulation to the brain, while injected drugs enter the venous circulation that returns the blood to the right side of the heart. The drug that enters the venous system takes longer to exert its effect because the blood must go to the lungs and then to the left side of the heart before it is pumped to the brain and the rest of the body.

Question 3. Who will experience the least behavioral effect from the drug?

The person who ingests, or swallows, the drug will experience the least effect.

Question 4. Who will experience the slowest effect from the drug?

The person who ingests, or swallows, the drug will also have the slowest effect.

Question 5. Tobacco smokers can use nicotine patches to help them quit smoking. The nicotine patches help the smoker slowly lower the amount of nicotine that enters the body. How does the nicotine in the patch enter the body?

Nicotine enters the body by absorption through the skin into capillaries.

Question 6. Explain why the different ways of taking drugs cause different behavioral responses.

Taking drugs by inhalation causes a very rapid increase in the level of drug in the brain. Inhaled drugs are absorbed into the arterial bloodstream in the lungs and then pumped to all parts of the body including the brain. Taking drugs by intravenous (IV) injection also causes a rapid increase in the drug level in the brain. It is slightly slower than inhalation because the drug goes first to the right side of the heart, is then pumped to the lungs where the blood is oxygenated, then goes back to the left side of the heart, and finally to the brain and body. Absorption through the skin or mucous membranes would be even slower because the drug has a longer path to travel before being circulated throughout the body. Drug response would be the slowest after ingestion because the drug goes into the digestive tract and then must pass through the walls of the stomach and intestine to enter the blood capillaries.

Assessment:
If students understand that taking drugs into the body by different routes causes different responses, they should be able to explain that the different ways of administering drugs can have advantages and disadvantages. Use this scenario to evaluate students’ understanding.

3. Display a transparency of Master 3.7, What Should the Doctor Do? Discuss the reasons why one action may be more appropriate than others.

On the basis of what you have learned about how drugs act in the body, how should morphine be given to the patient? Should the morphine be given as a pill, a shot, or an inhalant? Consider each alternative and explain why the different methods should or should not be chosen.

The question concerning how morphine should be administered to a patient to relieve pain is designed to assess whether students understand how different ways of getting drugs into the body changes their effects. The doctor’s goal is to relieve the patient’s pain quickly so that the fracture can be set.

On the basis of the graph that students analyzed on Master 3.6, the doctor should elect to give morphine as an inhalant or an injection. In each case, the drug reaches the brain quickly. Inhaled drugs can reach the brain even faster than injected drugs. Perhaps the main disadvantage of giving the morphine as an inhaled drug is the amount of drug that actually enters the bloodstream is more variable. If the drug is injected, all of the drug is delivered into the bloodstream. The doctor knows how much morphine enters the bloodstream. Giving a pill to the patient would be less effective than the other means for pain relief because it would take longer for the drug to act and its concentration in the bloodstream would be lower.