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# Daphnia Write-Up

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Introduction

Daphnia Write Up In this experiment we investigated the effects of caffeine on the heart rate of living organisms. We chose to use daphnia in this experiment, a kind of small organism found in water, similar to a prawn or insect, which has completely transparent skin, making it easy to see the heart, and thus count the rate of its heart beat. My prediction was that the caffeine would increase the heat rate of the daphnia. Procedure The procedure was not too complicated, but there was a lot to keep in mind, and to be careful about. Since we were working with living organisms, we had to be extremely careful with there lives, and take care not to harm and stress them. 1. We set up a microscope, and got a ball of cotton wool ready. ...read more.

Middle

We then observed the daphnia under the microscope, and found the heart. Once we had found the heart, we used a counter to count how many times the daphnia's heart beat in 15 seconds. At the end of the investigation we multiplied this number by four to get the heart rate per minute. 7. We repeated steps 5 & 6 for each concentration, and finished of by putting the daphnia back in the main tank. Unfortunately, our results show no correlation, probably due to the daphnia getting stressed. Here is a table of our results. Concetration Of Caffeine Average BPM 0 240 0.125 208 0.25 244 0.5 228 And here is a graph showing the correlation. However, the graph is useful at all since there was no correlation. Ethical issues Any experiment that involves living organisms may be controversial. ...read more.

Conclusion

Variables Independent: The concentration of the caffeine solution. Dependant: The heart rate of the daphnia Variables which may affect the result: o The concentration of the caffeine solution. o How long the daphnia was left in the solution. o The age of the daphnia. o The gender of the daphnia. o The genetic makeup of the daphnia. Controlled Variables: o Concentration of caffeine o Daphnia (same daphnia on all trials) o Distilled water (no caffeine) o Time daphnia is given a rest Improvements To improve the experiment, I think instead of clicking the number of heart beats for 15 seconds. It would be more accurate if the view of the microscope was recorded to a computer, so it can be slowed down and counted more accurately. In addition to that I think that the daphnia should not be immediately tested on after the last testing. It should be given time for it to relax such as 10 minutes. Otherwise the effects of the previous test will still be apparent. ...read more.

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A good plan but errors in the presentation of results and at time a lack of attention to detail reduce the quality.

Marked by teacher Adam Roberts 26/06/2013

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