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Does Caffeine Affect the Heart Rate of Daphnia

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Essay title: Does Caffeine Affect the Heart Rate of Daphnia

Does caffeine affect the heart rate of Daphnia?


In this experiment I aim to find out if caffeine has an affect on heart rate. Instead of using human subject, whom may already have a high tolerance to caffeine or could have ingested caffeine that day making the tests unfair, I will use Daphnia, a crustacean. They have on contact with caffeine making it fair. It will be easier to observe as it has a translucent body, making it able to see the heart beating under a microscope. It will be a “blind study” to avoid bias results, so everyone will be unaware what the solution consists of.


The purpose of my experiment was to determine how caffeine affected the heart rate of Daphnia.


I believe that a Daphnia subjected to a caffeine solution will show a rise in heart rate, this rise in heart rate should reflect the concentration of caffeine in a given solution. My theory can be backed up well, as caffeine is a stimulant that speeds up the body affecting the nervous system and rate in which the nerve pulses are sent and received in humans.


• Daphnia

• 6 Cavity slides

• Dropping pipette

• Distilled water

• Caffeine solutions

• Cotton wool

• Pipettes

• Test tubes

• Stop clock

• Paper towels or filter paper

• Microscope


• Place a few strand of cotton wool onto the cavity slide, this will help restrict the movement of the Daphnia making it easier to see under the microscope. Using a pipette place a daphnia on the cotton wool. The microscope should not be on a high power and will be centred on the heart. The first test on the heart rate will be done with just the pond water in which they live, so we have a set of results that can compare to when they are intoxicated by the caffeine. The heart rate will be recorded at intervals of 2 minutes over a 10-minute period, give five sets of results that can be averaged.

• Using a stop watch the number of heart beats will be recorded, we shall perform this in a pair, as it will be easier for one person to count whilst the over person keeps an eye on the time.

• This procedure will be repeated using different Daphnia and clean slides when we use a different solution.

• These results will be put into a suitable table and then presented in a graph that will show the solution to the heart rate.


Heart rate

2 mins 2 mins 2 mins 2 mins 2 mins Average over the 2 mins Average bpm

Pond water 260 271 253 258 286 266 133

Solution 1 258 256 279 306 377 295 148

Solution 2 380 390 390 380 370 382 191

Solution 3 389 398 404 410 50 400 200

Solution 4 267 440 410 440 420 428 214

Solution 5 436 419 443 450 425 435 218

These are the results collected from the experiment; each solution will have a different concentration of caffeine. The cells in the table that have been highlighted seem to be anomalies thus to keep the experiment fair I did not take these two results into account when producing my average heart rate over the two minutes and the average bpm. Including these two results in the averages and graph would unbalance the whole experiment and probably have a significant affect on the way the graph should really look.

Using these results my Hypothesis would argue that solution 5 should have the highest

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