o investigate the change in a daphnia’s heart rate resulting from a change in its surroundings

... at a rough formula for the calculation of heart rate when a certain concentration of caffeine is introduced is as follows:

h = 450c + 240 where h is the heart rate in b.p.m. and c is the concentration of caffeine (percentage) The second prediction that was made before beginning the experiment would seem, according to these results, to be incorrect. However, one cannot make such a definite conclusion because in this investigation, concentrations above 1.0% where not used so it is feasible that the concentration that is the maximum a daphnia's system can absorb is above 1.0%. Having said that, it is also possible that such a maximum cannot be reached since there will inevitably be a concentration that is too high for the daphnia to survive and the resulting death would make proving this hypothesis difficult if death comes before a noticeable drop in the increase in heart rate. The reason why the heart rate of the daphnia increases when it is given a dose of caffeine is the same reason as for a human's rise in heart rate due to its intake. Caffeine belongs to a group of compounds called methylxanthines and among its effects are two that result in a higher heart rate. Firstly, it blocks a receptor, called an A1 adenosine receptor, on the surface of the heart muscle which produces an enzyme called adenosine. One of the effects of adenosine, and the one that is relevant here, is that it slows down the heart rate. Indeed, in humans ...