The experiment is to find out the effect that caffeine has on the heart rate of Daphnia. My hypothesis is that the higher the percentage caffeine solution the faster the Daphnia heart rate. The independent variable is the percentage of caffeine concentration the Daphnia are submerged into for 2 minutes. The dependant variable in the Daphnia heart rate.
Method
1. place cotton wall on a cavity slide. This helps to restrict the movement of Daphnia
2. Using a pipette transfer a Daphnia to a cavity slide
3. Remove water from around Daphnia using filter paper
4. Add a couple of drops of distilled/pond water to the Daphnia
5. Focus on either the Daphnia's heart or their moving legs to be able to count their heart beat
6. Use a stop watch to record the number of heart beats during 30 seconds (advisable to work in pairs so that one person can count and one person can time)
7. Tap a pencil on a piece of paper to represent the heart beats and then count the number of heart beats at the end of 30 seconds
8. Repeat the procedure 5 times using different Daphnia for each concentration of caffeine solution
9. Record your findings in suitable table to give you the results of your experiment
Risks
1. Use goggles to prevent water entering your eyes
2. Take care with the cavity side and if broken take great care in cleaning it up
3. Do not shine microscope light directly into eyes
There are ethical issues with the experiment. This is because the experiment has to be done using live Daphnia. In order to reduce ethical issues and look after the welfare of the Daphnia precautions are taken: the Daphnia are kept in water constantly to provide a supply of oxygen. When looking at the Daphnia they are kept under the light for the shortest possible time (30 seconds) this avoids distress and great change in temperature. After Daphnia have been used place them in a clean tank with food. The greatest care is taken whilst handing the Daphnia to minimise stress to them.
My results showed a positive correlation between the concentration percentage of caffeine and the heart rate of the Daphnia. The causation of this is the caffeine percentage increase. My result at 0.2% is slightly out of the line of best fit however still indicating a positive correlation.
In order to increase internal validity and test the reliability of my results I repeated my experiment five times for each caffeine concentration. I then took an average for accuracy and plotted my data. In future I would make sure that the Daphnia I used were about the same size. I would also control their environment before the experiment.
I found that counting the heart rate of Daphnia was tricky which left room for error. Dotting on a piece of paper also allowed room for error when trying to count the dots. This problem would be solved by using electronic technology to count the Daphnia heart rate or using a tap counter in order to count the heartbeat. You should always make sure you do not use the same Daphnia twice. This is because they will end up with high amounts of caffeine in the Daphnia effecting the results. You can ensure not to use the same Daphnia twice by putting them in a separate container when you have finished with them.
I have concluded that the percentage of caffeine concentration does increase the heart rate of Daphnia.