31.2: Exercise
Getting Started
- Use a pipette to place one Daphnia on a concave microscope slide. Do not put a cover slip over your live specimen.
- Look at your specimen under the microscope. Keep the light low and turn off when not looking at your specimen (this keeps the live Daphnia more comfortable).
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Find the major body parts under the microscope
- Head with eyes and antenna
- Legs
- Intestine
- Heart
- Ovary, brood pouch, embryos (if gravid female)
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Locate the heart, practice counting heart beats
- Heart rate = beats per minute
- Count the number of heart beats in 15 seconds, multiply by 4
The Effects of Caffeine on Heart Rate
Think about what effect caffeine might have on heart rate. You may want to do some research in an online database in order to come up with your hypothesis.
1. Detail your hypothesis in your lab notebook
2. Place one Daphnia in the control solution (freshwater), wait 2 minutes for it to acclimate with the light off, then record its heart rate in beats per minute.
3. Place the Daphnia in .1 mg/L caffeine solution, wait 2 minutes for it to acclimate with the light off, then record its heart rate in beats per minute.
4. Place the Daphnia in 1 mg/L caffeine solution, wait 2 minutes for it to acclimate with the light off, then record its heart rate in beats per minute.
5. Place the Daphnia in 10 mg/L caffeine solution, wait 2 minutes for it to acclimate with the light off, then record its heart rate in beats per minute.
6. If time permits, repeat this experiment with a second Daphnia .
Design Your Own Experiment
Now that you've seen the effects of caffeine on heart rate, what else do you think might affect heart rate? Can you think of factors that might affect cardiac physiology? Further database research or observations may give you some ideas.