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Does caffeine affect heartrate?

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Does caffeine affect heat rate? I am doing an experiment on daphnia to see the effect of caffeine on their heart rate. Hypothesis I predict that the intake of caffeine by daphnia will increase their heart rate because caffeine is a stimulant drug. Risk Assessment I will not consume the daphnia as they may be carrying bacteria or microbes and I will also make sure I was my hands with soap thoroughly after doing the experiment. Ethical issues Using living organisms in an experiment could go against some people's beliefs. In my experiment I will not use concentrations of caffeine that could harm the daphnia and I will not harm them in the experiment by keeping them in water and putting them back in some clean water afterwards. Plan I will use 15 daphnia in total. There will be 5 different solutions of caffeine used, 0.01, 0.02, 0.03, 0.04 and 0.05%. I will record the daphnia's heart rate in water using a cavity slide and microscope before and then place 3 daphnia in each of the solutions for 5 minutes before replacing them in the cavity slide and measuring their heart rate. I will measure the daphnia's heart rate by looking at them under a microscope as their body is translucent and you can see their heart beat and using a clicker to count the beats to make sure they are ore accurate because if their heart rate is very fast I may lose count. ...read more.


We then put a very thin layer of cotton wool fibres on top of them to secure them in place. We recorded the heart rate of the daphnia for 20 seconds using a counter to count the heart rate as it was quite fast. We measured the heart rate for 20 seconds, three times to ensure my results are consistent and reliable. When the daphnia are placed under the microscope the heart is clearly seen through their transparent bodies so it is easy to measure. We used different daphnia for the different concentrations of caffeine solution and also measured the heart rate of daphnia in pond water as a control. I needed: - 20 daphnia - Caffeine solutions of 0.1% 0.2%, 0.3%, 0.4% and 0.5% - Pond water - A microscope - A pen and paper - A stop watch - A pipette - Cotton wool - A cavity slide Results Caffeine concentration % Number of heart beats in 20 seconds Mean number of heart beats in 20 seconds Mean heart rate / beats per min -� Trial 1 Trial 2 Trial 3 0.0 47 51 57 51.6 154.8 0.1 44 44 47 45 135 0.2 55 61 54 56.6 169.8 0.3 58 63 53 58 174 0.4 75 68 71 71.3 213.9 0.5 25 25 30 26.7 80.1 Analysis My results show that, in general, the daphnia's heart rate did increase when in a caffeine solution and supported my original hypothesis. ...read more.


This meant that some people's results were not as accurate as they could have been if they miscounted the dots. I think it should have been made very clear to everyone in my class what the heart was so that everyone counted the same thing instead of the legs beating. This would have hopefully made my results more accurate and valid. I think that to improve the accuracy of my results drastically, I should have done the whole experiment myself and recorded the heart rate before and during the experiment to obtain a percentage change in heart rate. Also if I didn't it all myself, I would know that my apparatus is reliable and that what I am counting is reliable each time. This would take much more time, but I think it would make my results more valid. Evaluation I used different concentrations of caffeine solutions to measure the heart rate of daphnia when in those concentrations. I found that for most of my results the heart rate increased when in a higher concentration of caffeine, but I had two anomalies. I think the results that I have, excluding the anomalies, are valid, but they would be more accurate and reliable if the percentage change in the heart rate was recorded instead of the new heart rate. ?? ?? ?? ?? Joelle Pike ...read more.

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