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INVESTIGTING THE EFFECT OF CAFFEINE CONCENTRATION ON THE HEART RATE OF DAPHNIA Aim - The aim of the investigation is to observe and examine the effect different concentrations of caffeine have on the heart rate of Daphnia. http://www.cals.ncsu.edu/course/zo150/ mozley/fall/Daphnianat.jpg Daphnia are tiny water fleas with an average size of less than 3mm. Daphnia are translucent invertebrates (have no backbone) and their outer body is made up of a hard shell which protects the whole body except for the head. Daphnia's are found in ponds, lakes, and calm streams where the temperature is between 21-24�C (68-71�F). Daphnia reproduce rapidly. Up to 13 billion related offspring can occur within 60 days for one Daphnia. In winter the eggs are thick-shelled and thin shelled in the summer. In warmer temperatures the eggs will hatch female, and in colder temperatures the eggs will be male. Daphnia's will be used to experiment the on as although they are tiny in size their heart beat can be examined through a microscope because of their transparency. Caffeine is a common stimulant drug that is produced by some plants, including coffee beans, kola nut and cacao pod. For the plant caffeine acts as a natural pesticide by paralysing or killing insects that tries to feed on the plants. However when caffeine is purified it is a very bitter, odourless white powder, which humans then use a flavour enhancer by adding it to products such as coffee, and soft drinks and chocolates. Caffeine is also used in medicines such as aspirins. Caffeine is a nitrogenous organic molecule that has a pharmacological effect on humans and animals. If small amounts of caffeine are used by humans it acts as a stimulant and increases circulation. However large doses cause nervousness excitement and hallucination. Also because of being addictive withdrawal of caffeine can cause headaches, lower blood pressure and raised stress. In the brain we have Adenosine receptors which work by slowing the never cells so that the body can prepare itself for sleep. ...read more.


The Petri-dish will then be placed on to the microscope and observed through the lens to record the heartbeat of The Daphnia every 10 seconds. Whilst looking the microscope hands must be kept on the stop clock so that the clock can be started/ stopped when needed without having to look away, (makes ticking noise per second)as this would slow down the reaction time and maybe heartbeats could be miscounted and therefore alter the results. After the experiment the results will be needed to be multiplied by the value by 6 to get the average beats for a minute. This procedure will be used as looking for too long could waver the concentration and consequently beats could be miscounted. Carry out each concentration three times so that an average from the results can be obtained and that the precision and accuracy of the result can be evaluated. However carry out all the different concentrations once and then repeat the procedure, in case there is not enough time to repeat it. This same procedure must be followed for all the different concentrations. The results obtained from the investigation will be firstly presented in a table so that the values can be systematically looked at and an average from the three trials can be worked out at the end, so that any tends/pattern or anomalies will be more easily distinguished. However a graph will then be produced as it will allow the result to be visualised better. Fair testing- To ensure that the experiment is fair and reliable results are obtained the only variable that will be changed is the concentration of caffeine as this will be constantly getting higher (Independent variable)and have an effect on the heart rate. Distilled water with no concentration of caffeine will be used as a control. All other variables that could affect the results will need to be controlled to ensure that the results are reliable and that it is a fair test. ...read more.


Whilst observing the Daphnia under a microscope light was not used to aid the visibility and therefore the view could have been slightly obscured and eyesight could have contributed to some inaccuracy, a lamp could have been used to aid visibility. Also personal interpretation of the Daphnia's heartbeats could not be 100% accurate. To overcome this problem of interpretation a video microscope could be used so that the beats could have been slowed down and counted more accurate, or a devise such as and ECG sensor would provide most accurate results. Also through personal bias a systematic error could have been created. Because the effect of Caffeine on the heart rate was already known this could cause an expectation of higher results. The best way to avoid personal bias is to conduct a blind test. Further more whilst start/stopping the clock the reaction time is bound to have been slightly slower than intended. Although equipment was checked for cleanliness the microscope was not taken into account and could have also caused systematic error errors-(values differing from the true value by the same amount) as the lens, eyepiece and stage were not checked for cleanliness. Also the stage had not been illuminated and the sub-stage condenser was not adjusted. To improve the reliability-large replicates of the results should be made using the same procedure will be used and results that vary considerably should be discounted or repeated. As it would allow seeing the degree of error as greater the variation of replicates the greater the degree of error Further work The heart rate was measured against a specific time scale, alternatively it could have been measured by calculating the time for a specific number of heart beats, or also calculated the heart beat against how many times the Daphnia moved its leg. The experiment could have been carried out with more concentration of caffeine; to see what effect it had on the heart rate. Also different stimulants cold have been used to see if they all followed the same pattern as the results. ...read more.

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