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The heart rate of a Daphnia (water flea)

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The heart rate of a Daphnia (water flea) Aims & Objectives To observe and test how the heart rate of a Daphnia water flea changes when the temperature of the surrounding water varies. I will count the heart rate of the Daphnia by observing it through a microscope. Background information The Daphnia water flea is a cold-blooded organism. This means it has absolutely no control over its own body temperature. Therefore it is cold in cold water and warm in warm water. It has a massively large heart rate. This is a labelled picture of a Daphnia. The area and information highlighted is relevant to this particular investigation. I have highlighted the gut on the diagram because that is where many of the enzymes in the Daphnia are. Enzymes as in all other living organisms control a Daphnia's metabolic rate. I will keep this in mind when investigating the heart rate. Enzymes are biological catalysts in all organisms that make certain reactions occur. They allow these reactions to occur without the high temperatures that would usually be required. These temperatures are so high that if enzymes were not present it would lead to the break down of most of the organic matter in the area. ...read more.


After this point it will drop until the temperature of the water becomes to great for the Daphnia to remain alive in. The reason that I think the heart rate will do this is to do with enzymes. Enzymes control the metabolic rate of any living organism, therefore as the temperature rises, so to does the energy of each enzyme and it carries out its job more effectively. When the temperature gets too hot the enzymes' active site begins to disfigure and the enzyme becomes useless. As a result the organism will slowly die. When the organism becomes too cold the enzymes will cease to function correctly without energy. If I were to sketch a graph of the heart rate I predict it would look like this. It is easier for something like this to happen to a Daphnia than a human because a Daphnia has no control over its body temperature, therefore it is much more easily affected by the surrounding water than a human would be in air. When a human is dying, their heart rate slows down, therefore when it is too cold or too hot, the Daphnia begins to die too. Results and analysis These are the results that I obtained during my experiment: Looking at the graph (overleaf); it can be seen that the Daphnia has a slower heart rate at lower temperatures and the graph peaks out at 25oC where it has the highest heart rate. ...read more.


This meant that the same Daphnia could not be used for a long time, thus meaning that we could not conduct a fair test due to the Daphnia differing Heart rates. The volume of water we used was not sufficient for the Daphnia to breathe as normally. This in turn could effect the heart rate of the Daphnia, but if we added any more water the Daphnia would have too much room to move, and this would make it nearly impossible to count the heart rate of the Daphnia. It would have been very useful to repeat the experiment many more times. We could have gone up 1oC every time to give a greater degree of accuracy. We could also have used a narrower temperature range. E.g. 1oC, 2oC, 3oC. I could also have allowed the Daphnia to acclimatise in a thermostatically controlled water bath. Lastly I could have done the experiment in bright daylight, thus eliminating the need of a lamp. This in turn would eliminate any extra heat coming from there. The fact that I timed my experiment each time for 15 seconds meant that to obtain the results for a full minute I would have to multiply the results by 4. This would compound the accuracy of the results obtained. Biology Daphnia Matthew Young 11JSM2 Page 1 of 6 11B3 ...read more.

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