How does Caffeine affect the heart rate of a Daphnia?

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  • Created by: Beth
  • Created on: 20-08-14 16:10

Daphnia and Caffeine

‘How does Caffeine affect the heart rate of a Daphnia?’

Caffeine is popular in human society and also important for our survival. However, it has been said that large amounts of caffeine can have negative problems to health. It is possible to use Daphnia to test how different amounts of caffeine could change a heart rate, and therefore challenge a person’s health. In this experiment I will be measuring to see whether adding Caffeine to the environment that a Daphnia is in will affect their heart rate in comparison to their normal heart rate without caffeine.  

Caffeine is a crystalline compound that is found in tea and coffee plants and is a stimulant of the central nervous system. Caffeine is going to be the independent variable in this investigation.
Daphnia, a kind of crustacean, is an invertebrate, has no bones in its body, and has a hard shell protecting all of its body except its head. It has three main parts to its body, the head, the thorax, and abdomen. The daphnia is commonly known as the water flea. Other kinds of common crustaceans are the brine shrimp, crabs, and lobsters. The Daphnia is going to be the dependent variable in this investigation. There may also be other variables that could affect the result of this experiment. One of these variables could be the light from the microscope that could heat up the Daphnia.

I predict that when caffeine is added to the concave slide that the daphnia will be placed on, the Daphnia’s heart rate will increase. I predict this outcome due to previous scientific knowledge that Caffeine is a stimulant. Caffeine takes about 45 minutes to be absorbed into the bloodstream. Once there, caffeine can make its way to the heart, where it acts as a stimulant by binding, or attaching itself to, specific receptors on the heart tissues causing the heart rate to increase.


Equipment needed includes:

·         Daphnia – Daphnia are important for this investigation as a variable to test the caffeine effects on. They are useful to use as their hearts can be easily seen as they are semi-transparent creatures.

·         Microscope – A microscope is needed to enlarge the Daphnia. This will make measuring the Daphnia’s heart rate a lot easier to measure.

·         Caffeine – Caffeine is important as it is the main variable of this investigation. This investigation will determine whether or not this variable increases heart rate.

·         Concave slide – This slide is important in order to ensure that the daphnia is kept in a pool of water whilst the experiment is taking place.

·         Small clear elastic bands – These are important when trying to hold the Daphnia in place during the experiment.

·          Pipette – The pipette is important when transferring the Daphnia from their


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