Daphnia Investigation.

rule states that a 10¦C increase in temperature will double the rate of reaction). 1.) A glass dish was prepared containing water with the relevant concentration of caffeine using a pipette. 2.) A single daphnia was obtained using a different pipette from the beaker containing the daphnia available for the investigation. 3.) This daphnia was then placed into the glass dish. 4.) Steps 1 to 3 were repeated for an additional two concentrations. 5.) One daphnia was removed from its glass dish and placed on to the glass slide. 6.) The glass slide was then placed under the microscope and the microscope adjusted appropriately to allow the daphniaÆs heart to be visible through the viewfinder. 7.) A ticker timer was then used to time the number of heartbeats in ten seconds, which was timed using the stop-clock. This number was then recorded. 8.) Steps 5 to 7 were then repeated for the two additional daphnia. 9.) Steps 1 to 8 were then repeated until results were recorded for all concentrations planned. 10.) Steps 1 to 9 were then repeated an additional three times in their entirety, in order to ensure accurate results by calculating an average heart rate for each concentration. It was decided to obtain results for the following concentrations of caffeine: 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% and 1.0%. Results Concentration(%) Heart Rate (beats per minute) Test 1 Test 2 Test 3 Test 4 Average 0.1 258.0 264.0 276.0 288.0 271.5 0.2 282.0 312.0 330.0 336.0 315.0 0.3 360.0 360.0 348.0 372.0 360.0 0.4 408.0 444.0 444.0 468.0 441.0 0.5 480.0 504.0 504.0 480.0 492.0 0.6 480.0 516.0 504.0 522.0 505.5 0.7 528.0 576.0 564.0 564.0 558.0 0.8 612.0 606.0 594.0 624.0 609.0 0.9 648.0 624.0 660.0 630.0 640.5 1.0 672.0 636.0 714.0 696.0 679.5 Analysis The following conclusions were made on completion of the experiments: À The results form an unfaltering line of best fit as seen on the graph which clearly shows that the higher the concentration the higher the heart rate. This proves the original prediction. As was mentioned before, the reason for this is most likely be due to the fact that caffeine is a stimulant and as a result one of its effects is an increased rate of reaction and thus a higher heart rate. The daphnia is unique in that it absorbs the chemicals that are present in the water surrounding it without selection. Therefore, with low concentrations such as those used in these experiments, it is likely that the daphnia will absorb most, if not all, of the caffeine present in the surrounding water. This results in a relatively steep line of best fit. À Using the averages in the results table above the increases in heart rate can be calculated to be the following: 0.1% Ó 0.2% = 43.5 b.p.m. 0.2% Ó 0.3% = 45 b.p.m. 0.3% Ó 0.4% = 81 b.p.m. 0.4% Ó 0.5% = 51 b.p.m. 0.5% Ó 0.6% = 13.5 b.p.m. 0.6% Ó 0.7% = 52.5 b.p.m. 0.7% Ó 0.8% = 51 b.p.m. 0.9% Ó 1.0% = 39 b.p.m. Whilst these may not appear to be relatively useful, using the line of best fit, the increase in heart rate can be calculated to be around 45 b.p.m. Therefore, we can come to the conclusion that 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) À 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 daphniaÆs 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. À 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 humanÆs 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, adenosine results in sleepyness, one of the causes being a slower heart rate. Therefore, if this receptor, which regulates the heart rate by controlling the level of adenosine, is blocked and thus the level of this enzyme is lowered then the heart rate rises. Secondly, caffeine and similar compounds have the effect of inhibiting a group of enzymes called cyclic nucleotide phosphodiesterases. These enzymes are partly responsible for degrading the nerve signals that are sent by excitatory neurotransmitters. To use a human example, a sense of fear would trigger an excitatory response. Thus when these enzymes are inhibited, the nerve signals remain active for a longer period of time. The effect of this is, among other things, a higher heart rate. À One of the important reasons why such a noticable change in heart rate takes place due to an increased concentration of chemicals surrounding the daphnia, is its physical makeup. As was mentioned previously, the daphnia is unique in that it absorbs any chemicals in the water surrounding it straight into its body. Therefore any chemical that has a physiological effect affects the daphnia almost instantaneously. For this reason, the daphnia is actually used as an indicator for toxicity of chemicals. Its heart rate is measured to find out how toxic a liquid is. Evaluation Improvements From the graph it is clear that the results fit neatly together to show a clear line of best fit but there are some anomalous results which could have altered the findings slightly. The most notable ones are the heart rates recorded for concentrations of 0.4% and 0.5%, which are significantly above the line of best fit. Having said that, they are not dramatically so. The reasons for such anomalies and their possible solutions are detailed below: À The most obvious reason lies with the method used to measure the daphniaÆs heart rate. A daphniaÆs heart rate can rise to a very high rate, especially when using a stimulant such as caffeine, and thus it can be very difficult to measure using a ticker timer or even dotting on a paper. This is due to the restraints of the human reflexes û they are simply not fast enough in some cases. A possible solution would be to use a video camera to film the daphnia under the microscope for a set amount of time. The film can then be played back in slow motion allowing the daphniaÆs heart rate to be measured considerably more accurately. À Secondly, it is feasible that a larger daphnia would not be as greatly affected by a certain concentration of caffeine as a smaller daphnia. This is because a larger daphnia would have a more diluted level of caffeine within its system. À Another obvious reason for anomalies such as these is the unfortunate side effect of using a lamp as a light source û heat. It is known that temperature has a strong effect on a daphniaÆs rate of reaction, and thus its heart rate, and if one experiment results in the daphnia spending more time under the microscope, and thus heated to a further degree, then its heart rate is likely to be slightly higher. A possible solution to this problem would be to use natural light as a light source for the microscope or to otherwise cool the platform upon which the daphniaÆs slide sits. À An additional reason is that the concentrations of caffeine were not properly prepared, although this is unlikely since there is a very small margin of error in such a procedure. The only solution to this problem, if it does exist, is to be more careful when measuring out the concentrations. À Lastly, if a daphnia is left to stand longer in its solution then it is feasible that it will have had longer to absorb the caffeine and thus will contain a higher concentration in its body that it would have otherwise had. The obvious solution to this is to time exactly how long the daphnia stand in their solutions and ensure it is the same time for each. Extensions À It was mentioned previously that the original hypothesis, that there is a maximum concentration before the daphniaÆs system becomes concentrated, was not proved by these results. Therefore, a possible extension of this investigation could be to repeat the procedure with higher concentrations to prove or disprove that hypothesis. This would also allow the maximum concentration before expiration to be investigated.