Daphnia: Null Hypothesis and Heart Rate

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Effect of caffeine on Daphnia (Water fleas)


In this study I am going to investigate the effect of caffeine on Daphnia (water fleas) heart rate. I shall use daphnia as they would never have been exposed to caffeine before, unlike a human, who may have already developed a high tolerance to it. Another reason is that Daphnia have a very translucent body; therefore, it is relatively easy to see their heart under a microscope, which makes it easier to count the number of heartbeats, thus, making my results more accurate.


Their will be a positive correlation between the concentration of caffeine given to the Daphnia and its heart rate.

My reason behind this hypothesis is based on the fact that caffeine affects the heart rate of humans, as it is a stimulant. From this, I can assume that it also affects the heart rate of Daphnia and that the rise in heart rate should reflect the concentration of caffeine. Many scientific studies within the last few years have proven this, for example,

Null hypothesis-

Their will be no correlation between the concentration of caffeine given to the Daphnia and its heart rate.

Using a pipette with a wide opening, carefully remove a Daphnia from the bag and put in a watch glass. •Collect some extra water and put it in the glass to enable the Daphnia to be able to move around and not dry out. •Place the Daphnia on a cavity slide with not too much water and place a circle of thin cotton wool around it to stop it from moving too much. •Use filter paper to remove any excess water and then add 3 drops, with the dropping pipette vertical so they are even, of a caffeine solution. •Allow the Daphnia to rest in the caffeine for 30 seconds. •Place the cavity slide under the microscope and focus so you can see the Daphnia’s heart clearly. •Set up a stop clock and assign someone to start and stop it when appropriate. •Then, using a pen and paper, watch the Daphnia’s...
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