Caffeine is a stimulant drug, which causes increased amounts of stimulatory neurotransmitters to be released. At high levels of consumption caffeine has been linked to restlessness, insomnia and anxiety, causing raised stress and blood pressure. This can lead to heart and circulatory problems.

The daphnia’s heart will beat faster when it receives a dose of caffeine. Caffeine belongs to a class of compounds called methylxanthines and can block a receptor on the surface of heart muscle cells for adenosine. It is caffeine's blockage of the A1 adenosine receptor in the heart that causes the heart to pound after a significant caffeine dose. Caffeine also inhibits a class of enzymes known as cyclic nucleotide phosphodiesterases. These enzymes are, in part responsible for degrading a stimulatory signal produced when excitatory neurotransmitt

· A ‘blind’ study was carried out in order to prevent any bias in the results. The person counting the heartbeats was unaware of the concentrations used.

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Hypothesis Caffeine, Validity Experiment, Justification Method, Beats Minute, Caffeine Concentration, , distilled water, heart rate, dose caffeine, beats minute, Concentration Caffeine, affect heart rate, water flea, blood pressure, affect heart, human error, concentration caffeine, results obtained, average beats minute,