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The effect of Caffeine on the heart rate Aim: To investigate the effect of caffeine on the heart rate of Daphnia (water fleas). Background Knowledge: 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 produced by plants as an insecticide. Cocoa in South America, coffee in Africa and tea in Asia has all been used for hundreds of years to produce "pick me up" drinks containing caffeine. These days, caffeine is used as a flavour enhancer in a wide range of cola and other soft drinks. In addition, it has medicinal uses in aspirin preparation, and is found in weight-loss drugs and as a stimulant in students' exam-time favourites like Pro-plus and Red Bull. In humans, caffeine acts as a stimulant drug, causing increased amounts of stimulatory neurotransmitters to be released.
Also, the Daphnia should not be left without water longer than a few seconds as lack of water could kill them. After the experiment is finished particular care must be taken in determining whether the Daphnia is dead or alive. Therefore, using the Daphnia for this experiment is morally and ethically acceptable. Independent variables * The concentration of caffeine in the solution Dependant variable * The size of the water flea * Amount of solution covering the water flea on the cavity slide The independent variable will be controlled by measuring out the amount of distilled water and caffeine needed. In a solution of 10ml, it is possible to measure out exact concentrations of both distilled water and caffeine. For 100% distilled water, 10ml of distilled water is poured into a test tube. For a solution with a 10% concentration of caffeine, pour 9ml of distilled water and 1ml of caffeine into the test tube. For a solution with a 30% concentration of caffeine, pour 7ml of distilled water and 3ml of caffeine into the test tube. For a solution with a 50% concentration of caffeine, pour 5ml of distilled water and 5ml of caffeine into the test tube. For a solution with a 70% concentration of caffeine, pour 3ml of distilled water and 7ml of caffeine into the test tube. The size of the water fleas cannot realistically be measured, but because they are between 0.2 and 0.5 mm in length they do not pose a serious change in results.
This is not very accurate as some solution may have remained in the pipette and could have transferred some solution from one beaker to another. Also with dropping pipettes it was difficult to control the drops and sometimes several drops will come out. Also many times the end of the pipette was taken out of the solution before the bulb was released so a little air had got drawn into the pipette. 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 an 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. Furthermore, whilst starting or 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 errors values differing from the true value by the same amount as the lens, eyepiece and stage were not checked for cleanliness. To improve the reliability, the experiment should be repeated a number of times. Results that vary considerably should be discounted or repeated. This would allow us to see the degree of error, because the greater the variation of results the greater the possibility of error.
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