Activity from NSTA's Guide to the Nervous System (www.nsta.org/Nerves/)
The environment challenges each living thing to react. It includes the air, the water, heat and light, and the chemicals which enter our bodies. Some chemicals look much like neurotransmitters to our bodies; we react to them in ways that can help or harm us.
You can explore the effects of some chemicals using a simple organism called a Daphnia.
In this exercise you'll explore National Science Education Content Standard C: Life Science - Structure and function
Multicellular animals have nervous systems that generate behavior. Nervous systems are formed from specialized cells that conduct signals rapidly through the long cell extensions that make up nerves. The nerve cells communicate with each other by secreting specific excitatory and inhibitory molecules. In sense organs, specialized cells detect light, sound, and specific chemicals and enable animals to monitor what is going on in the world about them.
What You'll Need:
Also Good to Have:
Your teacher will give your group only 5 drops of each liquid. They are toxic (poisonous). In your room, your teacher should also have a special report on the dangers of each chemical, called an MSDS sheet. Never taste any chemicals in the lab. Wash your hands after touching the Daphnia culture.
A Daphnia is a tiny crustacean (in the group with shrimp) that has a clear outside skeleton and jointed legs. Like other arthropods, its heart is on its back.
Put one Daphnia into the well of a cover slip. Give the critter a little water, but not much, or it will swim too quickly for you to observe it. (You may have to experiment a bit.) If your microscope has an electric light source, make sure it does not cause the water to evaporate or the Daphnia will die. Put a cover slip over the depression, and look carefully at your organism. Can you see the tiny, beating heart? Hint: It's on its back. Count the number of beats per minute. Then have each of your lab partners count the heart rate and average the results. Record the average in the table.
Next add one drop of caffeine solution to your Daphnia culture. Wait 30 seconds, then count the heartbeat three times. Finally, add a drop of alcohol solution. Repeat your counts.
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