- Wait 5 minutes and repeat the experiment (steps 1-10) again using the same Daphnia until I have concordant results and I can conclude they are reliable
Risks and Ethics
There is a risk with using a microscope that with improper use the glass could smash or shatter and so cause injury. I will always make sure the door is locked when the microscope is inside and be careful to use it properly and to follow guidelines. I will also take care when handling the cavity slides as they are made of thin glass and would be easy to break. I will wear goggles throughout the experiment incase any of the caffeine solution or any smashed glass splashes into my eyes.
I will try not to kill the Daphnia by being careful not to place the flea in too much caffeine. I will also watch it carefully as if it seems to be having a reaction to the caffeine I will stop the experiment and use a different flea.
Variables
The dependant variable in my experiment is the heart rate of the daphnia. The independent variable is the concentration of caffeine in the solution I gave them. There are other variables I can control such as the temperature (replacing the ice water before each experiment and turning the light off when not using the microscope) and if the Daphnia is pregnant or not (as this may increase the caffeine intake of the flea). The size of the Daphnia is uncontrollable if I repeat using a different flea therefore I will avoid this, as well as this reason using a different flea may mean a faster or slower intake rate.
Reliability
To ensure my results are reliable I will repeat them and exclude any anomalies therefore I will not use a method that cannot be repeated and I have chosen equipment that I am familiar with using to increase precision (My familiarity with how the equipment works will reduce errors). Also I will repeat my experiment until I have concordant results.
Errors
To prevent any systematic errors I will prepare and apply the solutions but then ask a friend to count the heart beats without telling them which solution is on the daphnia. By doing a blind test like this it prevents personal bias. I will also make sure that the microscope’s lenses are correctly in place before starting. To prevent random errors I will use the same daphnia for all repeats and always use the same amount of drops of solution. I will also always take care when conducting the experiment to reduce random errors; but random errors cannot be eliminated as distractions from other people will always happen.
Results (using the same Daphnia)
Graph
The bars on my graph are showing that there is an increase in the heart rate of a Daphnia as the amount of caffeine in the solution also increased. This supports my hypothesis.
Anomalies and errors
After repeating the experiment 3 times I noticed that my results were not concordant and so I concluded they were not reliable. Therefore I decided to repeat the experiment until I got at least a set of three concordant results. My next three sets of data were concordant with each other. I then took an average of all 6 sets of results and made the average results into a graph. In my results graph experiments 4-6 support my hypothesis; but with experiments 1-3 I cannot see any other obvious trends or patterns and because of my non-concordant results I can assume that it was errors in my method that led to anomalous results. The major anomalies are highlighted in red. Any reasons I identify for these anomalies would be guesses as I used the same method throughout the experiment and for all repeats and so the error was probably a random error. The only guess I could make as to why there were so many errors with my experiment would be that as using the method we did to count the heart beats is not a very reliable way of counting them, this would be a systematic error. Without using very sophisticated computer-linked equipment I do not know how else we would measure the dependant variable. And so using the apparatus available to us in school it would be the best way of measuring the heart rate of the Daphnia.
Conclusion
I cannot draw very valid conclusions about my results when there are errors with my method and I have anomalous results, but based on experiments 4-6 and my graph I can recognise a trend that did support my hypothesis. It shows that as the number of caffeine tablets in the solution increased so did the heart rate of the Daphnia: the results for experiment 4 for example are a positive example that supports my hypothesis; the value for my control was 198bpm, and Caffeine 3 was 320bpm; with all other values lying between these numbers. This happened because the amount of caffeine was increased and so the heart rate increased. This is because in humans caffeine is a stimulant drug. It increases the amount of stimulatory neurotransmitters that are released. Neurotransmitters are chemicals that are released by the brain which allow an impulse from one neurone to pass to another neurone. The increased amount would mean that impulses travel from each neurone at an increased rate meaning that muscles are stimulated to work at a quicker pace therefore the heart rate increases.
