Purpose: To investigate the effect of caffeine on the heart rate of Daphnia (water fleas).

Authors Avatar

Does caffeine affect heart rate?        


        To investigate the effect of caffeine on the heart rate of Daphnia (water fleas).


Caffeine is a drug that is naturally produced in the leaves and seeds of many plants. It is also produced artificially and added to certain foods. These days, caffeine is also used as flavour enhancer in wide range of cola and other soft drinks. In addition, it has medicinal use in aspirin preparations and is found in weight-loss drugs and as a stimulant in Red Bull.

In humans, caffeine acts a stimulant drug, causing increased amount of stimulatory neurotransmitters to be relaxed. At high levels of caffeine consumption can lead to restlessness, insomnia and anxiety, causing raised stress level and high blood pressure. This can lead to heart and circulatory problems.


  1. Handle glassware with care.
  2.  Wear a lab coat to prevent spill on fabrics.
  3. The microscope is fragile and the light bulbs can get hot so handle with care.
Join now!


  1. Culture of Daphnia (water fleas)
  2. Cavity slides
  3. Dropping pipettes
  4. Distilled water
  5. Cotton wool
  6. Standard glassware (beakers, measuring cylinders, etc.)
  7. Stopwatch
  8. Filter paper
  9. Microscope


        I believe that the Daphnia subjected to caffeine solution will show a rise in heart rate, this rise in heart rate will depend on the concentration of caffeine in the solution. My theory can be justified, because caffeine is a stimulant and speeds up the body affecting the nervous system and rate in which nerve impulses sent and received in mammals.


        The beating heart of a Daphnia water flea ...

This is a preview of the whole essay

Here's what a star student thought of this essay


Punctuation, grammar and spelling are all to a high level and the layout of the experiment is done well and clearly.

The hypothesis is clearly defined and well researched. The method is clearly explained with images that aid the candidates explanations. The flea may have had a fast heart beat being such as small animal so it is dubious as to whether the candidate could get accurate results from this experiment so should maybe have used a larger organism. The candidate did not identify enough errors and improvements with the experiment but considered possible ethical issues with using live organisms thoroughly.

The purpose of the experiment and the introduction are well done. The effects of caffeine are defined and this leads to what the candidate would expect to happen in the experiment. The main body of text is well presented but the conclusion is not well portrayed as it does not take into account external factors which may have affected the experiment.