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The effect of caffeine concentration on the heart rate of Daphnia.

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The effect of caffeine concentration on the heart rate of Daphnia Aim To conduct an experiment into the relationship between the heart rate of a Daphnia and its exposure to various concentrations of caffeine. Method For this experiment we had: Culture of Daphnia in various concentrations (%) of caffeine (0.0, 0.0025, 0.005, 0.025, 0.05, 0.25, 0.5) Two cavity slides A pipette Stop watch Microscope Ice water Firstly, a job was designated to each member of the group and each had a counter, a recorder and a controller. The controller always set up each slide to ensure that the other members of the group were unaware of the concentration of caffeine that the Daphnia were exposed to, thereby eradicating bias, and also controlled the time. The counter would count the number of heart beats in ten second intervals by stabbing at a piece of paper with a pen, in an 'S' shape. This allowed for easy counting and a control on human error. The recorder counted the dots on the paper to ensure that an extra heart beat was not added here and there in order to make the results match their prediction. A microscope was then set up and the x10 lens was used to ensure that the Daphnia's heart could be seen clearly. The slide was then set up. Some ice water was then placed on one cavity and the second cavity slide placed on top of the first. ...read more.


Discussion The chemical formula for caffeine is C8H10N4O2 and is known medically as trimethylxanthine. Caffeine also belongs to a class of compounds called methylxanthines. When in its pure form, caffeine is a white crystalline powder with a very bitter taste. Medically, caffeine is useful as a cardiac stimulant and also as a mild diuretic. Recreationally, it is used to provide a "boost of energy" or a feeling of heightened alertness. Among its many actions, caffeine operates using the same mechanisms that amphetamines, cocaine and heroin use to stimulate the brain. On a spectrum, caffeine's effects are more mild than amphetamines, cocaine and heroin, but it is manipulating the same channels. Adenosine is one of these chemicals. Adenosine is a relatively simple, nitrogen-containing compound used widely by the body. It forms the core of adenosine triphosphate, or ATP, the energy-storage molecule that powers most of the biochemical reactions inside cells. In the brain, adenosine secretion by cells such as neurons often reflects how busy the cells are. Areas that are active generate adenosine; areas that aren't active tend not to. As adenosine is created in the brain, it binds to adenosine receptors. The binding of adenosine causes drowsiness by slowing down nerve cell activity. In the brain, adenosine binding also causes blood vessels to dilate to allow more oxygen perfusion to the body during sleep. ...read more.


Apart from sources of error, other considerations must be taken when conducting an experiment. Firstly safety. There were not many safety issues which arose from this experiment. The experimenters were aware of what to do in the instance of a slide breaking exposing them to sharp glass. They were to dispose of it cleanly and safely in a designated bin. If the liquid being used had been hazardous they would, of course, have taken the necessary procedure to protect themselves; for instance wearing protective clothing. One safety issue that may arise if a stroboscope were to be used would be the effect on people who may suffer from epilepsy. The second consideration is that of ethics. Living organisms were used in this experiment, and inevitably some suffered as a direct cause of the experiment. Many exposed to the higher concentrations died. This meant there was a need to weigh up the costs and benefits of using these organisms for this particular experiment. The cost of the experiment was the poisoning of the Daphnia and as a result their death. On the other side of the argument, the next generation of doctors and scientists may be being trained through this experiment. As a result of this weighing up, it was decided that it was ethically justified to use these Daphnia in this experiment, especially as they were bred as fish food and would have died anyway; and they were a valid method of measuring heart rate. Anjali Lockett 1 05/05/2007 ...read more.

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