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# Does Caffeine affect heart rate?

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Introduction

Does Caffeine affect heart rate? Aim: To investigate the effect of caffeine on the heart rate of Daphnia Introduction: I will be measuring the heart rate of a Daphnia once I have exposed it to different concentrations of caffeine to see if caffeine affects heart rate. I have done a preliminary experiment so that I know which concentrations to use, how long to measure the Daphnia's heart rate for and so that I have practised counting the Daphnia's heart beat. This means that I will harm the Daphnia the smallest amount possible, will know how long the experiment will take me and will be fully prepared. My hypothesis is: when the concentration of caffeine increases, the heart rate of the Daphnia will also increase. I think this because caffeine is a stimulant of the central nervous system, cardiac muscle, and respiratory system. This means that it increases your body actions, such as heart rate, blood pressure and metabolism. I believe that it will have the same effect on Daphnia so that their heart rate increases as the concentraion of caffeine increases. Variables: My independent variable is the concentration of caffeine, whilst my dependent variable is the heart rate of the Daphnia. ...read more.

Middle

This means my partner will make up each solution and give them to me in a random order so that I do not know which solution is which concentration. Therefore I will not be thinking that the heart rate should be higher or lower than the solution before, so will not sub-consciously change the rate at which I am counting. Apparatus: ?2 cavity slides-To put the Daphnia on so they are in a smaller space so that it is easier for me to measure their heart rate. ?2 Daphnia-To measure the effect of caffeine on. ?2 measuring cylinders-To accurately measure out the solutions. ?10 beakers-To mix the solutions together in to create the right concentration. ?0.5% Caffeine solution-To put the Daphnia in. ?Distilled water-To change the concentration of the caffeine. ?10 Pipettes-To transfer the solutions from the beakers to the cavity slides. ?Microscope-To magnify the Daphnia so that I can see its heart and will be able to count the number of times it beats. ?Heat Sink-To place over the lamp below the microscope to stop convection occurring. ?Stopwatch-To measure the amount of time I count the heart rate of the Daphnia. ...read more.

Conclusion

Likewise Daphnia number two had a mean heart rate of 240 beats per minute in Distilled water, and a mean heart rate of 754 beats per minute in 0.5% Caffeine. I have no anomalies from either set of results. My graph shows me that the two sets of results are very similar and follow exactly the same pattern. My results back up my hypothesis that when the concentration of caffeine increases, the heart rate of the Daphnia also increases. Evaluation: My results are accurate and reliable because my results are very close together. In order to improve my results I would take five readings for each concentration rather than three and I would also test five Daphnia rather than two. This way I would get a wider range of readings and they would be even more accurate than they already are. If I was do the experiment again then I would count the Daphnia's heart beats for 15 seconds rather than 10 seconds, because then I would only have to multiply the result by four so I think the results would be slightly more accurate. Apart from this I think the procedure I used worked very well. ...read more.

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