RESULTS
Table of results:
Results in bold: anomalous results identified.
TRENDS AND PATTERNS
Looking at the graph, it can be seen that as the concentration of caffeine was increased the heart rate also increased.
Between 0.0-2.5 mg dm , there is a significantly fast increase in the heart rate
Between 2.5-5.0 mg dm , there was a very steep increase in the heart rate
Between 5.0-7.5 mg dm , there was only a slight increase in the heart rate
Between 7.5-10.0 mg dm , there was a sudden decrease in the heart rate
There were 2 anomalous results for the 10.0 mg dm concentration and this may have caused the heart rate to drop, as the results (252 and 246) did not fit in with the trend for this concentration.
CONCLUSION
According to the results and graph, my hypothesis was proved correct (that the heart rate increased as the caffeine concentration was increased). Although the last point in the graph does not follow this. I think this is mainly due to the fact that there were two anomalous results and this affected the calculation of the mean heart rate.
DISCUSSION
A daphnia’s heart will beat faster when it receives a dose of caffeine. Caffeine belongs to a class of compounds called methylxanthines and can block a receptor on the surface of heart muscle cells for adenosine. In fact, it is caffeine's blockade of the A1 adenosine receptor in the heart that causes the heart to pound after a significant caffeine dose. Caffeine and similar compounds also inhibit a class of enzymes known as cyclic nucleotide
phosphodiesterases. These enzymes are, in part responsible for degrading a
stimulatory signal produced when excitatory neurotransmitters activate
different neurons in the central nervous system (CNS). Thus, when they are
inhibited by caffeine, the stimulatory signal remains active for a longer period
of time resulting in a greater sense of alertness (a CNS effect) but also a
higher heart rate, blood pressure and respiratory rate.
This can clearly be seen in the results, that the daphnia’s heart rate increased as the concentration of the caffeine was increased. I also think that the 10.0 concentration of caffeine was too much for the daphnia as the heart rate decreased from the 7.5 concentration of caffeine, (except for 2 anomalous results). I think the high concentration of caffeine denatured any enzymes, therefore decreasing the heart rate of daphnia.
EVALUATION
Errors:
- The daphnia will not all be the same. Some may be healthier than others, this will have an effect on the results as health is directly linked to heart rate and this is what was being measured.
- The concentration of caffeine, which was measured and diluted down with distilled water, will not be accurate. There will be a significantly small error in the results.
- The amount of caffeine added on the daphnia will vary even though it was added using a dropping pipette. This could account for the anomalous results at the 7.5 and 10.0 mg dm concentration of caffeine.
Limitations:
- The whole experiment should be repeated atleast twice to make the results more reliable
- A stethoscope could be used for accuracy of results, but this is not safe to use.
- If the caffeine was added in smaller doses, i.e. the concentration did not increase so rapidly, e.g. if we increased the concentration by 0.5 mg dm then we could have seen a clearer pattern relating the concentration of caffeine and its effect on heart rate.
RISK ASSESSMENT
Care had to be taken in the duration of this experiment. This was because the concentration of caffeine could have a big impact on the daphnia. Too much caffeine could kill the daphnia and too much water could fill the daphnia’s lungs up and also kill them. These factors had to be taken into consideration when doing the experiment.
This experiment was fairly accurate in terms of ethical considerations. The only errors may have come from human errors, which are unavoidable.
