Each experiment will be repeated ten times every ½ minute (30 seconds), this is because the more times each experiment is done the better and more reliable the results will be, as the results in each experiment will be averaged. If each experiment is repeated ten times, it also shows how the heartrate varies with time. I will use the same daphnia when doing the experiment as daphnia’s heartrate varies between individuals, this will also make it a fair test. If the daphnia dies, the experiment will have to be redone, as it would not be a fair test because each daphnia varies from another.
The water will have to be removed from the cavity slide using a pipette. The water will then be replaced with caffeine and the number of heartbeats will be counted instantly to see how effective the concentration is on the daphnia’s heartrate. Then a cavity slide will be placed under the microscope. The test will be done 10 more times, every 30 seconds for caffeine. The results will be recorded in a table, such as the one shown below.
Two variables will be used-these are caffeine and aspirin, the reason why alcohol is not being used is because caffeine and alcohol will both stimulate the heart rate of daphnia.
The caffeine will be removed using a pipette, ready for the next experiment. Then water will be put onto the daphnia to allow its heartbeat to reach normal rate. This will be done with an interval of 1 minute each time. The next solution will be placed onto the daphnia and the experiment will be repeated using aspirin. Different concentrations of caffeine and aspirin (e.g. 0.01%, 0.1%, 0.05%, 0.75%), will be used. This is to see which amount has the greater effect on the heartbeat.
Results
Conclusion
Higher concentration of caffeine causes higher heartbeat compared to aspirin e.g. 257 was the average heartbeat/minute for caffeine (0.75%) and 253 was the average heartbeat/minute for aspirin (0.75%). The higher the concentration of any variable the more rise in the heartrate e.g. 244 was caffeine (0.05%) average heartbeat/minute whereas 246 was the average heartbeat/minute for caffeine (0.1%). The same thing also happens to the variable aspirin e.g. 236 was aspirin (0.05%) average heartbeat and 240 was aspirin (0.1%) average heartbeat. This also shows that the caffeine concentrations have higher average heartbeats than the aspirin concentration i.e. 240 was aspirin (0.1%) average heartbeat whereas 246 was caffeine (0.1%) average heartbeat.
This agrees with my prediction. Caffeine increased the number of heartbeats per minute, because caffeine increases the blood pressure in humans, which stimulates the central nervous system and stimulates the action of the heart and lungs. Therefore caffeine stimulated the heart and nervous system in daphnia.
During the experiment certain factors would have effected the daphnia’s heartrate. For example the heat of the light bulb could have evaporated the solution. Therefore there is less solution for the daphnia to survive as the daphnia is a waterfly which needs water to survive in. This then causes the heartrate to intentionally increase because there is less solution, harder to survive the heart will have to work harder to help the daphnia to survive.
At each experiment the heartrate was different each time this then makes it an unfair test, as the heartbeats weren’t the same, this therefore makes it difficult to compare the results.
Evaluation
I would expect the caffeine to stimulate the heartrate, the higher the concentration of caffeine the higher the amount of heartbeat/minute. It was difficult to compare the results as I started off with different heartrates for each variable, this therefore means that I will have to compare the averages.
If I was to repeat this experiment again different condition would be used e.g. alcohol, as I would want to see what effect it has on the daphnia’s heartbeat. I would also change the temperature, to see at which temperature the daphnia’s heartrate is stimulated the most and I would use different daphnia’s this is because I would obtain more accurate results.
There are certain factors which could have had an effect on the results e.g. the heat of the light bulb, the effect of the temperature could have also caused the daphnia’s heartrate to stimulate. When placing water with the pipette after each test so that the heartrate could go back to normal, that might not have been very accurate. This therefore means that if the experiment could be repeated I would need some level of accuracy e.g. the same amount of solution would be needed for each solution.
But overall I felt my results were quite accurate as it showed which solution i.e. caffeine or aspirin was more stimulant on the daphnia’s heartbeat. The rate of heartbeat was affected more by caffeine than aspirin.