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AS Edexcel Biology - Aim: To investigate the effect of caffeine on the heart rate of Daphnia (water fleas).

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The effect of caffeine on heart rate. Aim: To investigate the effect of caffeine on the heart rate of Daphnia (water fleas). Background Information: Plants produce caffeine as an insecticide. Cocoa in South America, coffee in Africa and tea in Asia has all been used as 'pick-me-up' drinks containing caffeine. These days caffeine is used in a wide variety of soft drinks such as cola to enhance flavours. In addition to this, stimulant drinks such as Red Bull and Boost also carry high levels of caffeine as well as some weight-losing drugs and medicines such as Aspirin. IN humans, caffeine acts as a stimulant drug, causing increased amounts of stimulatory neurotransmitters to be released. At high levels of consumption caffeine has been linked to restlessness, insomnia and anxiety, causing raised stress and blood pressure. This can lead to heart and circulation problems. Hypothesis: I think that the Daphnia's heart rate will rapidly increase when the caffeine solution is added. ...read more.


2. Stopwatch - So I measure the heart rate of each Daphnia with caffeine solutions for the same period of time (1 minute) 3. Cavity Slide - So I can hold the Daphnia in a small area so it cant move away from me when trying to measure the heart rate. 4. Strands of Cotton Wool - So I can prevent the Daphnia from moving fully when it reacts with the caffeine solution. 5. Pipette - So I can accurate collect one Daphnia needed and the correct levels of water and caffeine. 6. Glass Beakers - This is so I can have the correct measurements of water and caffeine concentration. Results: Beats per minute. Concentration of Caffeine Test 1 Test 2 Test 3 Average beats per minute Control (no caffeine) 128 131 132 130.3 0.1 122 120 140 127.3 0.2 132 134 144 136 0.3 148 152 160 153.3 0.4 169 152 160 160.3 0.5 162 172 168 167.3 Table showing all the results obtained during the experiment plus the averages of beats of the Daphnia per minute for each concentration of caffeine. ...read more.


This has allowed me to gather more data than many of my fellow experimenters and so I am therefore able to have a more detailed conclusion with more evidence to back it up. Because of this reason alone I am pleased with how the experiment went. Furthermore I am able to say that there are no anomalies. This is good because it means all of my results are reliable and therefore my conclusions that I've drawn are valid. The one improvement I would make next time is to only time the heart rate for 30 seconds and then double the heart rate after that time to make it one minute. This is because I found it hard to constantly focus for a minute on the heart rate and could sometimes lose count and need to start over again. For an extended project of this practical experiment I believe it would be interesting to find out if substitutes for caffeine and similar products have the same effect as caffeine on the heart rate of Daphnia. ?? ?? ?? ?? Sam Lingwood Biology Practical Investigation ...read more.

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Here's what a teacher thought of this essay

3 star(s)

Quite a good overall account of the investigation but analysis of the results could have been more critical, and plotting of wrong graph is a major error.

Marked by teacher Adam Roberts 11/04/2013

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