Investigating the Vitamin C Content of Fruit Juices

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Investigating the Effect of Caffeine on the Heart Rate of Daphnia Daphnia are extremely small aquatic invertebrates. They are transparent, so you are able to see their internal organs; this means it is easy to monitor their heart rate by observing them through a microscope [1]. Physiological results from caffeine consumption include the stimulation of heart rate, blood pressure, metabolism, body temperature and alertness. [2] In this practical investigation the aim was to determine whether the hypothesis that caffeine increases the heart rate of Daphnia, was true or false or whether caffeine decreased the heart rate of Daphnia. To determine this you need to test this hypothesis practically; in order to do this you have to make up a range of caffeine solutions of different concentrations; this is the independent variable – the thing that you change during the investigation. You also need a control variable, which would be a solution which has no caffeine in at all, to compare the results from the caffeine solutions. In addition to this, you need a dependent variable; this is what you measure in the experiment and what is affected during the experiment, in the case of this investigation it would be the Daphnia’s heart rate which you would measure, and is affected by the independent variable – the concentration of caffeine solution.

In all practical investigations you need to take into account any hazards (situations that pose a level of threat to life, health, property, or environment) [2] that you may encounter: Hazard| Outcome of hazard if it is realised| How to control/reduce hazard| Breakage of cavity slide| Less risk of the cavity slide breaking – less chance of getting cut by glass| Handle slide very carefully, do not squash with microscope lenses| Spillage of water/solutions| Less of a chance of falling over due to spillages| Place water/solutions away from edge of desk, and clear desks of unnecessary things to avoid knocking them over| Glass...
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