Research also showed that decaffeinated coffee and tea did not provide the same benefits as the caffeinated versions. The well-respected Framingham Heart Study examined all potential links between caffeine intake and cardiovascular disease and found no harmful effects from drinking coffee. There can, however, be exceptions to this. People react differently to caffeine, and some may experience elevations in blood pressure or arrhythmias. The effects on blood pressure are most likely when caffeine is taken in excessive quantities or by people who are highly sensitive to it. People who are hypertensive (have habitual high blood pressure) are advised to avoid caffeinated drinks, and should limit their intake of caffeine to less than 300mg a day.
Hypothesis: Caffeine will cause the heart rate of the Daphnia to increase
Equipment Used:
- Wide-mouthed pipette
- Tally counter
- Small Beaker
- Dimple Slide
- Standard Pipette
- Caffeine solutions
- Cotton Wool
- Microscope
- Daphnia
Method:
- A single Daphnia was removed from a beaker filled with pond water using a wide-mouthed pipette.
- The Daphnia was then placed in the caffeine solution for 3 minutes, and then removed.
- Then, the Daphnia was placed on a dimple slide and surrounded by fibres of cotton wool to prevent movement.
- 3 drops of the same % caffeine solution was added to the dimple slide, covering the Daphnia.
- The heart rate of the daphnia was then taken for 30 seconds, and then doubled to find its BPM (Beats per Minute).
- Steps 1-5 were repeated 3 times for each caffeine solution then recorded in the table of results below.
In this experiment, the caffeine concentration was the independent variable, with the heart rate of the Daphnia being the dependent variable. To ensure the experiment was fair, the size and age of the water fleas, time left in the caffeine solution, and the amount of caffeine solution used were controls, meaning they were kept the same at all times. To further ensure the results were as reliable as possible, the experiment was repeated 3 times and the microscope was turned of between every measurement, ensuring heat wasn’t a factor.
Ethical issues
There is obviously a big ethical issue here because we have used a living creature to conduct an experiment on a living creature. This can be made worse if we waste some of the daphnia as this is just pointlessly killing them. We also used cotton wool which can’t be recycled so is bad for the environment.
Safety risks
One safety risk was the use of glass as it can be very dangerous if it smashed as it is sharp and cannot be seen easily if you are not aware it is there. Some precautions that can be taken are gloves and careful handling.
Fair test
To ensure it was a fair test i tried to pick daphnia that were around the same size although it was difficult to be accurate. Also i made sure that it was the same person counting the heart rate because some people might be quicker than others. In addition to this I made sure that I started counting as soon as the daphnia was on the microscope so that the heat from the microscope light didn’t affect the daphnia. I also made sure that the transfer time from beaker to microscope was always kept roughly the same so the affects of caffeine wouldn’t wear off. This helped to make sure that my results would be as reliable as possible.
Table of Results:
The results gained from the experiment are displayed in the table below:
A table showing the heart rate of Daphnia when place in different concentrations of caffeine solution
A graph displaying these results is located on the page below:
Evaluation:
From my results, I can see that the increase in caffeine concentration caused an increase in the heart rate of the Daphnia, to a certain extent. However, once the concentration reached 0.5% there was a steep decrease in the heart rate, possibly due to the paralysis affect on the Daphnia. Nevertheless, the fact that the increased caffeine concentration did cause an increase in heart rate did agree with my hypothesis. This suggests, as expressed earlier, caffeine does have a stimulatory effect on the heart rate of living organisms. The fact that higher concentrations of caffeine caused the heart rate of the Daphnia to decrease supports the reasoning behind using caffeine as a pesticide.
Although my results did show a trend, they also included a set of anomalous results, or outliers. This occurred at the caffeine concentration of 0.2%. These anomalous results suggest there were certain factors during my experiment that affected the accuracy and trend that the data showed. Furthermore, the error bars on the graph above show a fair range in some of my results, suggesting the results were not of the highest precision. This further suggests that certain sources of error resulted in parts of the experiment being inaccurate. Nevertheless, all necessary precautions and guidelines were followed to ensure the test was as fair as possible.
On the whole, I believe the experiment did work as the results were mainly what were expected. Unfortunately, there were a few difficulties encountered when performing the experiment. Firstly, obtaining a single Daphnia using a wide-mouthed pipette was very difficult as they were very small and moved fast. In addition to this, securing the Daphnia in a fixed position using fibres of cotton wool proved extremely difficult, as it was hard to separate the strands quickly and effectively. Furthermore each daphnia differed so some may have reacted differently to caffeine than others therefore not making the test particularly fair. Finally, measuring the heart rate also proved difficult due to the minute size of the Daphnia. In addition, to the difficulties, there were certain limitations to the experiment. Firstly, time allowance meant only a limited amount of data could be collected. In addition to this, only 5 different concentrations of caffeine solutions were used, restricting the amount of scatter collected.
During the experiment, there were several factors that could have affected the accuracy of the results. Firstly, the different concentrations of caffeine solution could have easily been contaminated if the same pipette was used in extracting the solution. This was eradicated in the experiment as separate pipettes were used. Nevertheless, this was a source that could have posed a potential problem. Secondly, the fact that extracting the Daphnia was extremely difficult could have resulted in the organism being left in the solution. Unfortunately, this form of extraction was the only method available therefore I believe that this is the most likely reason for any anomalous results. Finally, due to the minute size of the Daphnia, a microscope was used to count the heart rate (BPM) of the Daphnia. Sometimes the heart was difficult to see therefore an aspect of human error could have affected the results. Also if you lose count then you have to start again and this is very time consuming and difficult to do as we only had a limited amount of time. To reduce this risk, we could have used a more powerful microscope. However, I believe that this source of error is one of the most likely reasons for anomalies.
Conclusion
In conclusion, my results were fairly mixed in comparison to my hypothesis. I believe that if the factors above could have been reduced or eliminated, my results would have followed my predictions. If I were to carry out this experiment again, I would use a stronger microscope in order to increase the accuracy when counting the heart rate (BPM). In addition to this, I would make sure that all Daphnia used were roughly the same size, as this could have also affected the precision of my results.
To increase the validity of the finding of this experiment, some further tests would need to be carried out. This would involve repeating the test experiment at each concentration at least 5 times. I would also use more concentration of caffeine solution in order to identify a more specific trend in the results.
On the whole I believe the experiment was a success as a trend in the results was identified. Nevertheless if more controls were in place, the reliability and accuracy of the results would have been much improved.
