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Does Caffeine affect Heart Rate?

             The aim of the activity was to investigate the effect of caffeine on the heart rate of Daphnia.
             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 neurotransmitters activate different neurons in the central nervous system (CNS). Therefore, when they are inhibited by caffeine, the stimulatory signal remains active for a longer period of time resulting in a greater sense of alertness (a CNS effect) but also a higher heart rate, blood pressure and respiratory rate.
             The independent variable used in this experiment is the concentration and the dependant variable is the rate.
             Justification of Method.
             · Cotton wool was used to restrict the movement of the water flea. .
             · One large water flea was transferred to the cavity slide so it is easier to view the heart, therefore the percentage of human error can be decreased.
             · A cover slip was not used and the distilled water was used to maintain sufficient oxygen supply to the flea. Distilled water was used in preference to tap water so that we can be sure that any changes noted was the cause of the caffeine only not by any impurities in the water.
             · A ‘blind’ study was carried out in order to prevent any bias in the results.