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Daphnia experiment - Does caffeine affect heart rate?

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DOES CAFFEINE AFFECT HEART RATE? PLAN The aim of the following experiment is to determine whether the amount of caffeine concentration affects heart rate in Daphnia. Hypothesis When caffeine is added to water containing Daphnia, its heart will be observed to be beating faster. SCIENTIFIC BACKGROUND Daphnia Daphnia, popularly known as water fleas, are small crustaceans that live in fresh water such as ponds, lakes, and streams. They serve as an important source of food for fish and other aquatic organisms. Daphnia are excellent organisms to use in bioassays because they are sensitive to changes in water chemistry and are simple and inexpensive to rise in an aquarium. Daphnia hearts a fairly easily seen but counting the number of beats can be difficult. Counting is easier if each heart beat is recorded by tapping a pencil on a piece of paper and counting up the pencil marks after the specified time. In addition, cooling the daphnia before the experiment may help slow their heart rate: heart rate is highly temperature dependant. An I Cam above the eye-piece of the microscope to project an image of the slide onto a large screen may also help with counting. ...read more.


A cover slip helps stop the water evaporating. 2. Place a few strands of cotton wool on a cavity slide; this will help restrict the movement of the water flea. 3. Uusing a pipette, transfer one large water flea to a cavity slide. Remove the water from around the water flea using filter paper, then add one or two drops of distilled water. 4. Use as much water as you can and do not use a cover slip. 5. Together these precautions will help maintain sufficient oxygen supply to the flea. A cavity slide filled with iced water and placed under the slide will act as a heat sink. 6. View the water flea under low power. Focus on its heart which can be seen through it translucent body. 7. Use a stop watch to record the number of heart beats per minute. 8. Tap a pencil on a piece of paper and count up the pencil marks at the end of the time period. 9. Record the heart rate at intervals of two minutes over a 10 minute period. It is a good idea to do a 'blind' study to avoid bias in the results. ...read more.


This may not be the case when we get errors from places and so to get an even better result we should look at the results and take out some of the anomalous results. An example of an anomalous result is that I had got a lower heart beat rate when using a 0.00001% concentration of caffeine and if my prediction is to be right this cannot be. I then have to blame this on systematic errors. As I have mentioned before we may have to see different daphnia for different concentration this by itself will produce a very high % error as we can only assume that the heart beat for every daphnia will be the same but in reality it is not. This can also be put down to just clumsy result taking. As we had left this one till last it is clear that we could not really be bothered to be as accurate as we had been with the other ones. Another example is that the room may have been at different temperatures at different times and therefore this is an error as we know that the temperature will also make a difference to the heart beat. ...read more.

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Here's what a teacher thought of this essay

3 star(s)

This write up has some good background information but marks would be lost due to a lack of precise scientific language and the method described might well produce unreliable results.

Marked by teacher Adam Roberts 11/04/2013

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