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Does caffeine affect heart rate

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Does caffeine affect heart rate? Aim To determine how caffeine effects the heart rate of Daphnia. Prediction I predict that as the concentration of caffeine is increase, the heart rate of the Daphnia will increase. I predict this because of my knowledge of caffeine - it is a type of chemical called a stimulant. When you drink a caffeinated beverage, the caffeine enters into your blood stream dilating the capillaries and causing blood to flow more quickly. If the blood is flowing more quickly, the heart rate needs to increase to pump more blood through the dilated capillaries. In humans, caffeine acts as a stimulant drug, causing increased amounts of stimulatory neurotransmitters to be realeased. At high levels of consumption, caffeine has been linked to high blood pressure and raised heart rate. From this knowledge, I predict that the caffeine will have this effect on the Daphnia too, thus an increase in their heart rate. Risk Assessment If a stroboscope is being used to show the Daphnia's heart rate in this experiment, and you know that you suffer from photosensitive epilepsy, then you need to make sure you make appropriate precautions. Goggles will be worn to prevent any touching of eyes, which could cause irritation. ...read more.


When calculating the heart rate of the Daphnia, we used the method of tapping a pencil on the table and then counting up the marks made. This method of tapping a pencil and someone counting them wasn't very accurate because: When the daphnia's heartbeat got really fast you couldn't keep time with the rapid heartbeat. If you lost count while trying to count the heartbeat and still carried on counting the beats per minute wouldn't be right. There are two main variables for this experiment; the independent variable and the dependant variable. The independent variable is the concentration of the caffeine, which was given to the Daphnia. As you can see in the result table, the concentration was given in 0% (water), 20, 40, 60, 80 and 100% dosages. We could not go any higher because the amount of caffeine would probably cause the daphnia to have a heart attack and die. The dependent is the effect that the independent variable has on the Daphnia's heart rate. When we put the concentration on the daphnia we tried to make it a drop each time, so that each daphnia would be getting the same amount, making the results more accurate. We couldn't get it exact each time but it was very close. ...read more.


As I said in my findings, this is because the Daphnia are very small, and their heart rate is already quite fast, so when the caffeine increased their heart rate, it was hard to keep count of the beats by purely tapping a pencil on the table. I would also do more trials, because as you can see from the results, I did not complete the table of trials for the reliability of the experiment to be sufficient. Therefore, I had to calculate an average with the data I did have, and create a graph using these averages. Not doing 3 trials makes the experiments results less reliable because it could have been chance that these first results show a positive increase as the concentration of caffeine increases. It would have been much more reliable to do 3 trials for each concentration to get an overall average value for each one. As these results are similar to what you would find in humans, if I were to re do this experiment, I may use alcohol to see whether it has the same effect on Daphnia as it does humans. Alcohol is a depressant and therefore slows down the heart rate, so I would test to see whether the same affect happens to the Daphnia in this experiment. Charlotte Johnson Miss Tate ...read more.

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