Biology > Using the Scientific Method to Study Daphnia Magna - lab report
Every organism’s full contraction and dilation of the heart is different. The way organism’s heart rate changes to different chemical solutions and temperature change is very similar. The purpose of this experiment is to study the effect of pond water, acetylcholine, adrenaline, ice and recovery from ice on the Daphnia. Daphnia magna, or water fleas, are small aquatic, transparent organism and they belong to the Phylum Arthrooda and it the Class Crustacea. The Daphnia magna is a perfect organism for this experiment because Daphnia are small and they can easily be placed under the microscope, their exoskeleton body is transparent, therefore the heart can be easily seen, they are very sensitive to their environment, therefore they will quickly react to the stimuli, they are cold blooded and easy to keep them in the laboratory and handle them throughout the experiment. The scientific question is: How will the Daphnia magna react to several different stimuli?
My hypothesis is that the Daphnia’s heart rate won’t be affected in its natural environment, the pond water, but it will be affected by acetylcholine and it will reduce the heart rate, it will be affected by adrenaline and it will increase the heart rate, it will be affected by cold temperature change which will decrease the heart rate and Daphnia will recover in its natural habitat -the pond water- and its heart rate will be normal again. Humans and water fleas have a common ancestor and we both belong to the Animal Kingdom. As a result of this it’s possible that we will react to neurotransmitters and cold temperature change the same way.
I believe my hypothesis is true because both acetylcholine and adrenaline are neurotransmitters and they will control the autonomic nervous system which carries signals to the cardiovascular function of the body. As evidence, it is scientifically proven that acetylcholine in case of vertebrates is going to slow down the heart rate and adrenaline is going to increase the heart rate. Some animals, like bears, skunks, chipmunks and some bats hibernate. When winter comes the animals body temperature drops, and their heartbeat and breathing slow down. Mammals and we, humans also react to cold temperature and slow our heart rate.
Methods
The methods for this laboratory experiment can be found on pp. 31 to 40 of General Biology Laboratory Manual Second Edition by Edith S. Robbins and Stephanie C. Mazur, Outernet Publishing, LLC, 2006. By my partner and me the following changes were made to the protocol:
1. We allowed 2 minutes between treatments, instead of one.
2. We put pond water back on the Daphnia between treatments to equilibrate the heart rate.
3. We left out the baseline measurement in our experiment.
4. We held the slide with the Daphnia on the ice for 2 minutes instead of 30 to 45 seconds.
5. We allowed 3 minutes instead of 2 minutes for the Daphnia to recover from the cooling.
Results
| Condition | Measurement 1 | Measurement 2 |
| Pond Water | 120 | 136 |
| Acetylcholine | 104 | 92 |
| Adrenaline | 188 | 204 |
| Cold | 76 | 84 |
| Recovery from Cold | 108 | 124 |
The results of the experiment can be seen in the table and graph above. The Daphnia’s heart rate was 120-136/minutes in the pond water. After we treated the Daphnia with acetylcholine its heart rate decreased to 104-92/minutes. The Daphnia’s heart rate increased in the adrenaline solution to 188-204/minutes. The Daphnia’s heart rate decreased when we put it on ice to 76-84/minutes. The Daphnia was placed back to pond water and it was given a recovery time; and its heart rate was 108-124/minutes. Compared to the Daphnia’s normal heartbeat in the pond water, which was the control because its heart rate is normal in its habitat, the Daphnia’s heart rate to acetylcholine reacted inhibitory, it slowed down. The Daphnia’s heart rate to adrenaline increased. When we put the water flea on ice its heart rate decreased and when we put back the Daphnia to its habitat its heart rate was normal again.
We didn’t do any repeat measurement because we didn’t get any data that was questionable. We had some problems throughout this experiment. The Daphnia was moving very fast, sometimes we couldn’t find the heart and sometimes the heart was beating faster than we could count. Discussion All our results agreed with our hypothesis which was that the Daphnia’s natural environment; the pond water won’t have any affect on its heart rate, which is its normal habitat and has normal heart rate in it. The Daphnia’s heart rate was affected when we put acetylcholine solution on it and it reduced the heart rate. The water flea’s heart rate was also affected by adrenaline; it increased its heart rate. The Daphnia reacted to cold temperature and it reduced its heart rate. The Daphnia’s heart rate was normal again in its natural habitat after the recovery from cold. Because of humans and water fleas belong to the Animal Kingdom these experiments most likely will have the same affect on humans and any other vertebrates. We didn’t do any repeat measurement because our data was very close to our expectation for each of the stimulation. We had some problems throughout this experience, because the Daphnia was moving very fast, and when we covered it with cotton, it covered the heart or made it even harder to find it and observe it. It was also very hard to count the heart beat when we put the adrenaline solution on the water flea. In 15 seconds we had to count until 51. Although we had some problems, none of them affected our data. It was a pleasure to work with my partner, Peter on this project and to observe the Daphnia magna and its reaction to chemical solutions and to cold temperature. The similarity how our nervous system would react to these changes and observing the beating heart of the Daphnia made us realize that we are indeed all connected with living organisms and we all belong to the Animal Kingdom.
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