Considering the effect caffeine has on humans, it is likely that the effect will be similar. It stimulates our heart to beat faster, so I predict that the effect on daphnia will most likely be the same if not more prominent in Daphnia die to their large surface area to mass ratio. I can predict that the heart rate will also increase, similar to a human and furthermore, the increase will probably be steeper when shown in a graph due to the miniscule size of a daphnia. Overall, I believe that a daphnia subjected to caffeine will show a rise in heart rate. The more caffeine in the solution should reflect the concentration in heart beat.
To carry out this experiment, I need:
- Daphnia
- 9 cavity slides
- Distilled water
- Pipettes
- Stopwatch
- Microscope
- Caffeine solutions
- Test tubes
- Cotton wool
First of all, to limit the movement of the daphnia, I placed cotton wool onto the 9 cavity slides. In turn, this will make is easier to observe the daphnia under the microscope. Instead of obtaining the daphnia from the large container, I filled up test tubes and acquired them from the test tube. Using pipettes, I placed the 9 daphnia onto the cavity slide and cotton wool. I placed each one under the microscope and due to their high tolerance to light intensity, kept the light of for five minutes slowing the heart rate down before recording their heart beat. Daphnia have been proven to be negatively phototaxic and therefore, it is definitely best to be in an environment without intense exposure to light. When I turned on the light for each, I used a stop watch to time 6 seconds and depicted dots to represent each heart beat. I then multiplied this by ten to calculate how many beats per minutes (bpm) a Daphnia has. I then gave each a drop of solution mixed with the amounts 0.1%, 0.2% and 0.5%. It has been proven that a daphnia given a dosage of 1% is most likely to die. I knew not to exceed this amount so avoided deaths of the daphnia. I left each on the side for another five minutes. I placed each under the microscope for the second time and did the same thing as before. I then put all of Daphnia I had used back into the distilled water. It is quite hard to avoid death in this experiment considering we’re dealing with such small organisms; one could easily crush a daphnia, or it could even die due to stress. I didn’t use one daphnia to record three different solutions, as when I first tried this, it proved difficult and the daphnia died. Instead I used three daphnia for the three solutions and instead of comparing the repeats, I need to measure the rate of increase from 0 and manipulate the average from that.
