Daphnia (water flea)
Daphnia are small crustaceans. Daphnia are one of a number of small aquatic crustaceans commonly called water fleas because of their saltatory swimming style. They live in a variety of aquatic environments, ranging from acidic swamps to freshwater lakes, ponds, streams and rivers.
Hypothesis
I consider that a Daphnia subjected to a caffeine solution will show a raise in the average heart rate, this rise in heart rate should correspond with the concentration of caffeine in a given solution. My theory can be backed up well, because caffeine is a stimulant that speeds up the body affecting the nervous system and pace in which the nerve pulses are sent and received in humans.
Equipment
- Culture of Daphnia
- 3 cavity slides
- 3 dropping pipettes
- Distilled water
- Caffeine solution ranging from 1% to 5%
- Cotton wool
- Pipettes
- Test tubes
- Stopwatch
- Paper towels or filter paper
- Microscope
Procedure
- To start with I must obtain a daphnia; to do this I will use a pipette and a cavity slide to put it on. When I have one daphnia I will place in on the cavity slide but before hand I must put down a strand of cotton wool this will restrict the movement of the daphnia making it easier to see under the microscope. I will then remove the excess water using the filter paper, and then I will add a few drops of either pond or distilled water. I must be careful not to have too little water otherwise the daphnia will be limited of oxygen.
- I will use a stopwatch to record the heart-rate of the daphnia, as I will be working in a pair I will get one of us to count the beats and the other to time. I will record the heart rate at interval of 2 minutes over a 10 minute period; the first result will be our control. As I am doing a blind study, the one of us who is counting the heart-rate will be unaware of whether the water is plain or contains caffeine.
- I will repeat the procedure using other daphnia from the culture solution and clean cavity slides. Instead of using water I will now replace it with the 1% caffeine solution. I will now repeat this process using the different concentrations of caffeine.
- I will record my results in a sensible table and use a graph to compare the results with the control.
From these results I can clearly see an increase in the heart-rate of the daphnia with the addition of stronger caffeine content. From the control, the average has increased by over 50% to the 5% solution of caffeine this is a vast increase for such a simple organism, however I was careful not to keep them exposed to caffeine for too long otherwise this would bring up an issue of ethics. These results prove my theory about caffeine increasing the heart-rate in the daphnia.
You can clearly see here an increase in the heart-rate of the daphnia; it increases more after the 1% dose of caffeine than the 4% and 5% solution, them being apart by only 8 beats. This shows that the daphnia responds similarly to both the 4% and the 5% dose of caffeine.
It is important for me to control this experiment as a simple mistake can lead to wrong and misleading results. A way to make sure I didn’t go wrong was to measure the exact amount of caffeine used for each daphnia, also measuring the heart rate of a daphnia precisely, each minute. Finally recording or making a note of the change in the daphnia when adding caffeine e.g. did they struggle to move or try to move faster.
Validity of study
It would have been a bad idea to use the same daphnia throughout the experiment for obvious reasons, a daphnia can only possibly take so much caffeine, increasing its consumption of a stimulant it may never have consumed will cause serious damage. Also the results would not have been accurate or reliable because the daphnia would not have had enough time to shake off the previous dose of caffeine. To make the results valid, i needed to trial various daphnia to ensure I had varying results and no outliers.
Conclusion
My hypothesis was that as the caffeine increases, the heart rate of the daphnia will also. The results I obtained indicate that my theory was accurate this is because as the different types of caffeine solutions are added the heart rate increased. Although the results of this experiment are accurate, I speculate whether the temperature of the surroundings played a part in the daphnia’s heart rate, as daphnia are dependable on temperature to survive. I also consider that alcohol, a depressant, could possible lower their heart rate. If I were to conduct this investigation again I would like to use a larger range of caffeine solutions, as I believe this would give precise results. Also I would like to use a thermometer to measure whether temperature does have an effect on the daphnia.