Ms Isaac Kevin Pereira

The Effect Of Caffeine On The Heart Rate of Daphnia.

Plants produce caffeine as an insecticide. Cocoa in South America, coffee in Africa and tea in Asia have all been used for hundreds of years to produce ‘pick me up’ drinks containing Caffeine. These days, caffeine is also used as a flavour enhancer in a wide range of cola and other soft drinks. In addition, it has medicinal uses in aspirin preparations, and is found in weight-loss drugs and as a stimulant. In humans, caffeine acts as a stimulant drug, causing increased amounts of stimulatory neurotransmitters to be released. This also causes it to have an effect on the heart. In this experiment we aim to see how Caffeine concentration affects the heart rate of Daphnia. Daphnia are 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. This is one of the main reasons we use Daphnia in this experiment. It is also much easier and cheaper to obtain results from them compared to doing the experiment on humans for results, though they might not be as accurate. We decided to carry out this experiment as a double blind test, to make the results more accurate and less biased. We used two solutions, one with normal coffee and the other with de-caffeinated coffee. Both were put in unlabeled beakers, so that nobody knew which solution was in which beaker. Normal coffee would act as a stimulant drug and increase the heart rate of the Daphnia, we assumed de-caffeinated coffee would not affect the heart rate of the Daphnia since most of the caffeine is removed, but after further research we realized that de-caffeinated coffee is also a stimulant drug and would increase the heart rate of the Daphnia as well.

Aim: To determine the effect of Caffeine on the heart rate of Daphnia.

Hypothesis: The heart rate of the Daphnia will increase when it is exposed to Caffeine and will keep increasing with exposure to higher concentrations of Caffeine.

Substances and Equipment Needed: Culture Of DaphniaDistilled WaterCaffeine Solution De-caffeinated Coffee SolutionPaper TowelsDroppersLight Microscope

Ms Isaac Kevin Pereira

Glass/Cavity SlidesCounterStopwatchCalculator50ml beakerMeasuring cylinder

Variables in this experiment:Manipulated Variable: Presence of CaffeineDependent Variable: The heart rate of the DaphniaIndependent Variable: Surrounding temperature and light intensity

The surrounding temperature and light intensity should be kept constant because any changes could result in an inaccurate heart rate, for example, high light intensity could stress the Daphnia out and cause their heart rate to increase and give inaccurate results.

Plan:

1. Take a small piece of cotton wool and keep reducing its size until it is just a few fibres.

2. Place the fibres on a glass slide.3. Add the Daphnia and some water until the Daphnia is just covered by

it.4. Put the slide under a light microscope and adjust the magnification so

that the organs of the Daphnia can be seen clearly.5. Identify the heart of the Daphnia through the light microscope.6. Add a few drops of ethanol to slow down the heart rate of the

Daphnia if it is too fast to count.7. Start a stopwatch and record the number of heartbeats with a

counter for 20 seconds.8. Repeat step 7 at least 3 times and record it in a table along with the

calculated mean.9. Repeat steps 1-6 again with another Daphnia of similar size to the

one used previously.10. Add 5 drops of one of the unmarked solutions and repeat steps

7 and 8.11. Repeat steps 1-6 again with a third Daphnia of similar size.12. Add 5 drops of the second unmarked solution and repeat steps

7 and 8

Ms Isaac Kevin Pereira

Risk Assessment: The test tubes and beakers should be handled with care, to avoid damaging or breaking them and harming the people using them and the people around them. The light microscope should also be used with caution because they are expensive pieces of equipment and are quite heavy, they should be placed on proper tables so that they do not drop on anybody and cause injuries. If precautions are taken to ensure that these accidents don’t happen, there should be no incidents, because apart from these pieces of equipment there isn’t anything else that could cause harm. No hazardous chemicals were used during this experiment so goggles and lab coats did not need to be worn. The temperature and light intensity should also be monitored carefully as there is a chance for the daphnia to die when they are exposed to light and heat which they aren’t used to. There were a few ethical issues in this experiment as the Daphnia are living organisms and died by the end of the experiment. This could raise some ethical issues as they were killed for the experiment, but it does not really make a big difference because they have short life spans and are plentiful in nature.

Ms Isaac Kevin Pereira

Ms Isaac Kevin Pereira

Analysis: By looking at the bar chart we can see that the mean of the heart rate of the Daphnia with exposure to Caffeine (assumed to be caffeinated solution) was only slightly more than the heart rate without Caffeine(assumed to be decaffeinated solution). The chart shows the mean of the heartbeats of the Daphnia with exposure to the different solutions, which is good because it shows the results more clearly, in the table some values are much lower than others and some values are higher in the control than in the caffeine graph, which make the results seem inaccurate. The bar chart is likely to look like this as decaffeinated also contains stimulants in it and still contains a small amount of Caffeine, this would’ve meant that the heart rates of the Daphnia would still increase even without the Caffeine solution. This could also be due to different sizes of Daphnia used and also Daphnia that are of different ages. For example, younger Daphnia could have faster heart rates than Daphnia that might be nearing the end of their lifespan. The bar chart could also be slightly inaccurate because alcohol was added at the start to decrease the heart rate to make it easier to count. Different amounts of alcohol given to the different Daphnia could have caused some heart rates do decrease more than the others and thus show a lower heart rate in the Caffeine graph. Another reason that the lines might not be accurate is the amount of Caffeine added could have varied slightly as it wasn’t measure in definite amounts, rather in drops and some drops could have been greater than others and thus affect the heart rate.

Improvements: 1. Use another control solution as well that contains no stimulants, such

as water.2. Use Daphnia that are all roughly the same size or the same mass.3. Add equal amounts of alcohol and solution (caffeinated or

decaffeinated) to each Daphnia slide.

Conclusion: The heart rate of the Daphnia does increase with Caffeine as seen in the bar chart, even though it is just slightly as Caffeine is a stimulant and affects the nervous system. I have also concluded that de-caffeinated coffee does increase the heart rate even though 97% of the caffeine concentration is reduced as caffeine is not the only stimulant in coffee and there are other factors that affect the nervous system and increase the heart rate in coffee as well.