Biology Core Practical
Daphnia in Caffeine Experiment
As the caffeine increases, the heart rate of the Daphnia also increases.
There are the following risks in this experiment which are for both the daphnia and the person carrying out the experiment:
• I must make sure not to spill the Daphnia water on the floor as I may slip and hurt myself
• Be careful not to let the Daphnia be exposed to the light for a long period of time as it may cause them to die and also the heat may harm them as they are not used to it
• The caffeine in high concentration may mean that their heart will beat so fast that they will die
• The last risk is that the Daphnia may dry up which may kill it during the experiment
1. Use a pipette to transfer one Daphnia to a cavity slide
2. Add some fine cotton fibres to the slide and place them to a point where the Daphnia will not be able to move
3. Turn the microscope on and locate the Daphnia’s heart beat
4. One person will then have a stopwatch which will count to 30 seconds. This is the time during which the measurement of the heart rate will take place
5. Measure the rate of the heartbeat
6. Repeat these step two more times and double the results to get the number of heart beats per minute. Then average them.
7. Clean the cavity slide of the pond water
8. Use a pipette to transfer some caffeine solution of about 0.1% to the slide
9. Then get a new Daphnia and place it in to the caffeine solution
10. Measure the heart rate of the Daphnia per 30 seconds following the same procedure as before
11. Repeat steps 7-10 but using caffeine solutions of 0.2%, 0.3%, 0.4% and 0.5%
• Experimenting on animals allows scientists to study things that would be unethical on humans. Many people believe using animals is unethical (they can’t give consent and may be subjected to painful procedures
• Some people believe it is more acceptable to perform experiments on invertebrates...