The effect of caffeine on the heart rate of Daphnia

AIM:
In this experiment I am going to investigate the effect of different concentrations of caffeine on the heart rate of Daphnia. My hypothesis is that the higher the concentration of caffeine, the higher the heart rate. Also, I think that there would be a concentration of caffeine where the daphnia would not be able to live.
INTRODUCTION:
Daphnia are tiny crustaceans which are about 0.2 to 5 mm that live mainly in fresh water; lakes, rivers and ponds. They are perfect to be used in experiments to needs observation of organs as Daphnia are transparent animals. The lifespan of a Daphnia doesn’t exceed 365 days and is mainly temperature-dependent. For example, some individuals can live up to 108 days at 3°C, while others live for only 29 days at 28°C. A clear exclusion to this trend is during the winter, when harsh conditions limit the population. Under these conditions, females have been noted to live for over six months; they normally cultivate at a slower rate, but are bigger than those under normal environment (“Why Daphnia?” 2009 ).

(http://www.sciencebuddies.org/science-fair-projects/project_ideas/Zoo_p048.shtml#background)
Caffeine is a stimulant in humans with the chemical formula of C8H10N4O2. Stimulants induce short-term improvements in either mental or physical function or both. These kinds of effects may include enhanced wakefulness, quicker and clearer surge of thought, improved focus, and enhanced general body coordination (“Caffeine” 17/10/12). But the U.S. is far from the lead when it comes to national caffeine consumption. According to a 2010 report by commodities analysts for Business week, Scandinavian nations such as Finland consume more caffeine per capita -- mostly in coffee -- than any other country. The report noted other surprising trends, like a move in Brazil to offer coffee drinks as part of primary school lunches. (Brain, Marshall et al, 2001).
I have studied two report papers on this experiment. The first report was done by a university where not only caffeine was a factor being investigated. Also, they were investigating on the effect on alcohol and temperature. This gave a wide variety of conclusions on different effects of different substances. For the caffeine solution, they came to a conclusion that the higher concentration of caffeine solution the higher the heartbeat per minute. This was proved by the results recorded and also showed that the Daphnia with 10% caffeine concentration died. For the alcohol, the heart rate decreased which showed a similar trend on the human heart. The effect of temperature was that the colder the environment, the lower the heart rate. The second report paper was less detailed and at a lower standard than the first one. This was done by a secondary student. It was basic and only focused on the effect of caffeine. Both papers came to the same conclusion that caffeine increases the heart rate.