The aim of this experiment is to research on the effect caffeine has on Daphnia heart rate.

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 The aim of this experiment is to research on the effect caffeine has on Daphnia heart rate. To enable this, a certain percentage of caffeine solution was tested on Daphnia (water fleas) as it will be a lot easier to monitor their heart rate due to their translucent body. This practical will help develop data representation and improve key practical skills.


         Caffeine is an odourless, slightly bitter alkaloid found in coffee, kola nuts and small amounts of cocoa. In humans, Caffeine acts as a stimulant on the central nervous system preventing drowsiness temporarily in order to keep the brain ‘alert’. Caffeine is one of the world’s most popularly used drugs and acts a mild diuretic in humans and animals. It will be unethical to carry out this experiment on humans as they have a high level tolerance to caffeine as it was proven in a recent experiment that higher concentrations of caffeine solution causes the heart to beat abnormal fast so an alternative source.  Daphnia will be used to carry out this investigation as their resting heart rate is very high and this will air to provide rapid results.

1.1. Diagram of a typical Daphnia

    Daphnia are small water crustaceans which share a slight resemblance to water fleas and are mostly found in lakes and ponds. Food sources and beverages containing caffeine such as: soft drinks, energy drinks, chocolate and tea enjoy great popularity as caffeine is one of the most wildly consumed substance. Although caffeine is a psychoactive drug, and unlike any other drug it is legal and although a lot of consumers claim caffeine isn’t a drug like ‘alcohol’ or ‘nicotine’ it has been proven to have the same effect.


 The effects of caffeine may vary from person to person however; excess intake of caffeine can result in: Insomnia, irritability and headaches. It can also cause prolonged depression, panic attacks and irregular heartbeats. However, these symptoms are only common in regular consumers. Caffeine addiction can be cured by reducing the daily intake and switching to de-caffeinated coffee/tea. Once these are regularly consumed, the caffeine ‘boost’ goes away although heavy consumers may suffer headaches and minor mood swings.

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It is predicted that the heart rate of the Daphnia will slowly increase when differing amounts of caffeine solution is administered to it. If it is tested on humans or animals, it may be proven to be unethical. However, if a greater amount of the caffeine solution (1%) is added to Daphnia it may cause paralysis.


  • Cotton
  • Caffeine solution (0.1%, 0.2%,0.3%, 0.5%, )
  • Daphnia
  • Pond water
  • Wide mouth pipette
  • Tally counters/ stop watch
  • Dropping pipettes
  • Microscope
  • Cavity slide
  • Beakers
  • Petri dishes


  A microscope with microscope light is set ...

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