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Introduction

Does Caffeine affect heart rate? Hypothesis I think caffeine will increase the heart rate of the Daphnia. I think this because caffeine is a stimulant that causes more stimulatory neurotransmitters to be released than normal, and so will increase the rate at which the heart muscles works/beats. Apparatus * Culture of Daphnia * Cavity Slides - to place flea on to view under a microscope * Dropping pipettes - to pick up fleas as they are too small to handle * Distilled Water - to act as a control * Ice Water - to cool the Daphnia so the light used when using the microscope does not heat it causing the heart rate to increase causing a systematic error * Caffeine Tablets - crushed and used as the independent variable * Stopclock - to time the length of time (1 minute) the experiment lasts for * Paper Towels - to blot the pond water away off the cavity slide * Microscope - to view the Daphnia to allow a measurement of the heart rate to be taken * Light - used with the microscope to allow the Daphnia to be seen Method 1. Using a dropping pipette drop a Daphnia and some distilled water onto a cavity slide 2. ...read more.

Middle

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. ...read more.

Conclusion

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. ...read more.

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