Daphnia Experiment

Daphnia, also known as the water flea are planktonic crustaceans that are found in lakes, ponds, and streams. They received “their common name from their jerky movement through the water” (Clare). They are also “very small, usually 2-5mm long, with an overall shape similar to a kidney bean” (Elenbaas). Daphnia play an important role in the freshwater food chains and serve as food for other freshwater organisms such as fish. They are also commonly used to test for chemical toxicity in water. Since Daphnia have transparent body, it is easier to observe their heart rates, and other visceral organ systems. Its small heart rate is easily visible when viewed under a microscope. A change in its heart rate plays a crucial role in determining whether
In this laboratory experiment, our control was the Daphnia that gets spring water, whereas the drugs were the independent variable and the heart rate was the dependable variable. The first step our group did was to place the Daphnia into a clean depression slide. Next, we added a small drop of the spring water and put a cover slip over the slide. Then, we waited for one minute prior to placing the slide on the microscope in order to allow time for either solution or the drug to take its effect. After we put the slide on the microscope, we located the heart of Daphnia and counted its heartbeats while the other member kept time for each three 10-second trials. We recorded our data and calculated the average heart rates of three trials we found during the experiment. Afterwards, we calculated the average 60-second heart rates by multiplying the averages of our 10-second heart rates by 6. These procedures were repeated with the rest of solutions as well, including caffeine, aspirin, alcohol, sleep-aid, and
According to our experiment, only caffeine and aspirin increased the heart rate of Daphnia; whereas the rest of the drugs decreased its heart rate. Initially, we expected that aspirin would not have any effect but it had an increasing effect, which was a bit surprising. During the experiment, we encountered some counting errors that we had to repeat the procedure and do the calculations again. For example, when we tested our control--spring water, we had a suspicious result; thus, we asked other groups to make sure if our trial results were close to theirs. Furthermore, it was important to switch the microscope light off and wait at least 30 seconds before starting the next trial because the microscope lights heat up the Daphnia and increase their heart rates if left on for long. This could potentially harm and result in death of Daphnia, which suggest that we should be ethical while doing the experiment. Lastly, we also observed that different daphnia gave different