Teaching Tips

Teaching Tips:The Water Flea Experiment

Synopsis:
In this module students use a simulation to investigate the effects of drug type, dosage, gender, and recent meal status on the heart rate of a water flea. Students count the heart rate of a magnified water flea while adding a variety of drugs and dosages.

Big Ideas:
a. Drugs impact heart rates.
b. Stimulants increase heart rates.
c. Depressants decrease heart rates.
d. Drugs do not affect different genders in the same manner.
e. Recent meal status affects a drug’s impact.

Misconceptions Addressed:
a. Drugs affect all individuals in the same way.
b. Drugs always affect a given individual to the same extent.
c. The amount of a drug taken does not impact its effect.

NSES Grades 5 – 8 Content Standards Addressed:
a. Life Science
i. Structure and function in living systems
ii. Regulation and behavior
b. Science in Personal and Social Perspectives
i. Personal health
ii. Natural hazards
iii. Risks and benefits

Here are explanations that you may find useful as class discussion topics:

Why are they called Water Fleas?

Water fleas move through the water making short jerky movements. Because of this "hopping" movement, they are called fleas. Daphnia live in freshwater all over the world, and are crustaceans. There are many species of water fleas, and they are the major food source for many freshwater fish. The size of Dapnia varies greatly, and some are too large to be eaten by small fish. Dapnia have both sexual and asexual phases, and a female may produce up to 100 eggs at a time. Females can reproduce after about four days, and every three days after that. On average, the females lay between 4 and 22 eggs. Dapnia can live in water with very low dissolved oxygen content (the topic of the The Fish Experiment PSI Sim). Even though Daphnia are tolerant of low dissolved oxygen, they can be killed by the addition of salts, bleaches, detergents, and pesticides in the water.

Teaching about stimulants and depressants

If you ask most teachers how to teach the difference between stimulants and depressants, they usually talk about providing definitions and examples. The Water Flea Experiment takes a different approach. The student experiments with the simulator and learns that different drugs affect the water flea in different ways. Although they might not know the definition of stimulant and depressant, they understand the effect. It is then up to the teacher to apply the definitions and generalize the concept. The effects of the drugs are mitigated by amount of food consumed and gender. So, the experiment offers a good model to allow the student to manipulate variables and study the effects.

Doing the "real" experiment

Water fleas can be ordered from scientific supply stores and sometimes pet stores, so a "real" classroom experiment may be used as well. If you choose to do this, we suggest that you use the PSI Sim experiment first, so that the virtual experiment can help the student with the procedural aspects of the experiment.

Doing the virtual experiment

The Water Flea Experiment includes a counter to help students count the heartbeat of the water flea. The counter is not automatic, and students will have to click start, "get in sync" with the heartbeat and then start clicking the mouse along with the heartbeat. When they are finished, they click the stop button. The time between clicking start and first clicking along with the heartbeat is not counted. This is done so that they can get in sync with the heartbeat before clicking along with it. After they stop clicking along with the heartbeat they can take their time clicking stop.

Classroom Discussion

Once students have viewed the effects of drugs on the water flea, they may be motivated to discuss the effects on the human body. This can lead in a plethoa of directions, but some of the following points may help you direct the discussion:

Stimulants work in a part of the brain stem called the reticular activating system, or RAS. They increase alertness and heighten awareness by sending signals to the cerebral cortex which controls thought processes. Stimulants trigger the release of noradrenailine by the cells in the brain, which increases RAS activity.
The best known stimulant is caffeine.
The rate at which doctors are prescribing stimulants to preschoolers is rising rapidly.
Many stimulants have been banned because of side effects, particularly those used to control diet.
Stimulants can be used to treat narcolepsy and hyperactivity (see the assessment section).
Depressants work by decreasing brain activity. Some, like stimulants, work on the RAS, while others work in different areas of the brain.
Personal decision making is affected by many factors including peer pressure, advertising, role-models, media influences (movies), and legality.