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The Effect of Caffeine on the Heart Rate of Daphnia.

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The Effect of Caffeine on the Heart Rate of Daphnia Introduction Caffeine is widely known as a stimulant. Stimulants cause an increase in the metabolism of the human body resulting in an increase in the rate of the heart and lungs. In small doses they wake you up and give you a high by exciting the central nervous system. In high doses they can make you anxious, irritable and even psychotic. Caffeine perks you up by stimulating the heart and suppressing the effect of adenosine, one of the brains inhibitory chemicals. Caffeine also increases blood pressure and promotes urine formation. I will only be investigating the effect of caffeine on the heart rate. Daphnia are typically freshwater creatures but are capable of surviving in slightly salty water. There is a big difference in the size of a Daphniidae, depending on the species. Newly hatched Moina are slightly larger than newly hatched brine shrimps and twice as large as average adult rotifers. Most daphnia populations consist entirely of females that reproduce asexually. A female can produce 100 eggs per brood and can have a brood every 3 days. The female will begin reproducing at about 4 days old. When there is a low food supply, low temperature or lack of oxygen, males are produced and sexual reproduction occurs. Daphnia need oxygen for respiration to occur but they can survive in water with a very low oxygen concentration. This is largely due to their ability to produce haemoglobin. ...read more.


The caffeine solution will be constructed using distilled water and caffeine mixed to give a total volume of 10cm3. The daphnia will then be immersed in the solution for a set period. The heart rate will then be monitored under a microscope for a minute whilst using a clicker timer to keep count. Following my preliminary work I found it difficult to distinguish between separate heartbeats. I decreased the temperature of the water using an ice bath to decrease the heart rate of the daphnia and make it easier to count. It worked and so for my final experiments the water will be 5?C. Variable Setting Temperature of water 5?C Salinity Negligible-that of water pH Negligible-that of water Time immersed in caffeine 1 minute Time heart rate monitored for 1 minute (20 seconds x 3) Time between immersion and microscope 30 seconds Amount of readings 5 per caffeine concentration Daphnia Small Safety The only safety concern is that of the caffeine. I will not be using particularly concentrate caffeine because the school is forbidden to allow me. However, the 0.01-mol solution I am using is still quite dangerous. Goggles will be worn to prevent any touching my eyes, which can cause blindness. If any caffeine does touch skin or eyes it must be cleaned with copious amounts of water for at least 15 minutes. Contaminated clothing must be removed. Do not inhale caffeine, if done inadvertently get fresh air and seek medical advice. ...read more.


Mole of Caffeine Heart Rate (BPM) Increase 0.000 218.33 0.001 230 11.67 0.002 237.33 7.33 0.003 254 16.7 0.004 253 -1 0.005 256.33 3.33 0.006 275.33 19 0.007 287.33 12 0.008 298.67 11.34 0.009 304.67 6 0.01 307.33 2.66 The heart rate always increased positively (except one occasion) but the extent at which it increased ranged from 2.66 to 16.7. I have included a graph to show the extent of variation. The reasons that could be to blame for the wide range of increase include variety in the individual daphnia. Certain daphnia might have been more stressed than others, which would have caused an increase in heart rate. Other Daphnia might have been of a differing age meaning a lower or higher resting heart rate to begin with. Another cause may have been the inaccuracy of my counting. Despite using a clicker counter to keep count and cooling the water with ice to lower the resting heart rate it was still a very fast and difficult to count heart rate. This meant that there was great variety in the results. This was almost definitely the cause for the anomalous negative heart rate increase. All three attempts were relatively low and the relatively high results of the previous concentration meant that the average heart rate of the higher concentration was actually lower than the average heart rate of the lower concentration. If these problems could feasibly be precisely controlled the graph should actually be a horizontal line as opposed to a graph that shows no correlation what so ever. Ross Cook 1 ...read more.

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