How does caffeine affect the heart rate of Daphnia?

Risk Assessment

• We will handle cavity slides and test tubes carefully to prevent breakage
• Be cautious not to touch the lamp with wet hands since it uses electricity
• Be careful not to spill any of the testing solutions on the floor.

There are some ethical issues involved in using these invertebrates. Many people believe that it’s unethical to cause distress or suffering to any living organism - e.g. by subjecting them to extremes of temperature or depriving them of food. I will take this into account whilst doing my experiment by not putting the microscope on a high power. Some people believe it’s more acceptable to perform experiments on invertebrates (like Daphnia) than vertebrates (like dogs and monkeys). This is because they’re considered to be simpler organisms than vertebrates. For example they have a much less sophisticated nervous system, which could mean that they feel less pain (or no pain). After using each Daphnia, I will return them back to the water where I collected them from.

The dependant variable in this experiment is the heart rate of the tested Daphnia’s. The independent variable is the concentration of the caffeine solutions. The following variables will be controlled:

• volume of caffeine/water solution – This will be controlled by using a pipette (applying the same amount of drops)
• Temperature of Caffeine/water solution –Temperature must be controlled because it increases heart rate. This is because the molecules in our bodies bump into each other much more frequently when the temperature goes up, thus increasing the chemical rate of reactions in the body. It is difficult to maintain a constant temperature but I will monitor it with a thermometer.
• Size of Daphnia – Using Daphnia of the similar size for each test will make the results as valid as possible. The culture of Daphnia which are taken from the same environment ensures the same species of Daphnia. 
• Microscope (same light intensity)

To ensure that reliable and valid results are produced I will repeat each measurement and take an average. To determine the heart rate, the beats are counted in pulses under a microscope and recorded using a hand counter. This is accurate; however a margin of systematic error should be accounted for in the results. We will make sure measurements are precise and accurate by making the tests repeatable.

Results

Conclusion –

I stated in my hypothesis that I think that a Daphnia subjected to a caffeine solution will show a rise in heart rate. The results obtained by my group and I indicates that my hypothesis was correct because the more concentrated the caffeine solution was, the higher the heart rate of the daphnia; at 0.1 % caffeine solution the mean heart rate of the Daphnia was 53 beats per minute; with 0.3 % caffeine solution the mean heart rate of the Daphnia was 173 beats per minute.