Reliability: To make this experiment a fair test the same daphnia should be used for all of the different caffeine concentrations. Also I will repeat the experiment to accurate results, and do blind counting; which is when the person counting the beats should not know which concentration of caffeine has been used so that it will not be biased.
Ethical issues: to ensure that the daphnia is not harmed we need to cut off the end of the pipette so that it will nor be harmed when it is squeezed in. also that water flea should be returned back in to its natural habitat when you finish using it and you should only add 0-0.5% of caffeine concentration as more than 0.5% could harm or kill the daphnia.
Safety issues: you must take care with the pond water as it might carry bacteria and viruses. Also to make sure that water does not get into any electrical appliances.
Detailed method:
1) Then take out a daphnia from the pond water by using a cut off pipette on its end so that it will be easier for the daphnia to be squeezed through with no harm.
2) Then place the daphnia on to a cavity slide and removing some of the pond water using filter paper.
3) Then pull out a few strands of cotton wool and place it on the daphnia. This will ensure you that the daphnia will stay on one place so that it makes it clear to see the heart beat.
4) Put the slide underneath the microscope making sure you use the clip in the microscope and focus the lens to the heart.
5) Next choose one of the four different types of caffeine concentration and put two drops on the cavity slide where the daphnia is placed.
6) Leave it for 2 minutes in order for it to climatise, then start counting the heart beat (you must make sure that you do not get mixed up with the heart and legs) for 30 seconds.
7) You must put in mind that the person that is counting the beats does not know which concentration it is so that the experiment will not be bias; this is called blind counting.
8) Repeat the procedure for all different types of concentration a few times so that it will be accurate.
Actual method: a modified method was used by all class members so that the results could be compared
1) Place a few strands of cotton wool on to a cavity slide; this restrict the movement of the water flea. Using a pipette, transfer one large water flea to the slide. Remove the water from around the water flea using filter paper, then add one drop of test solution. Use as much water as you can and do not use a cover slip as this will increase the amount of oxygen concentration which will kill the water flea. Leave for 2 minutes to climatise.
2) View the water flea under low power. Focus on its heart which can be seen through its translucent body. At the end of the 2 minutes use the stop watch to record the number of heart beat in 30 seconds. This is made easier by working on a pair, with one person counting the beats while the other person tells them the time period.
3) Repeat the procedure for 5 daphnia at each concentration of caffeine.
4) Record your results on a table in a situation format and present them in a suitable graph for interpretation and evaluation.
Conclusion: the data tells me that as you increase the amount of caffeine concentration the heart rate of the water flea increases. The graph also shows a positive correlation, which means that the data that I have collected supports my hypothesis; ‘the higher the concentration of caffeine the higher the heart rate (B.P.M)'. My hypothesis also supports my biological information on caffeine.
Evaluation: in my experiment there could be a few anomalies that may have effected my results which means that my results could be unreliable. For example the volume of caffeine was not precise as it has been measured by drops. Another anomaly could be caused by contamination from the previous caffeine concentration on the slide to the next. This can effect the heart rate of the daphnia. There is also some times where the lamp from the microscope had been left on, this might have effected my result as the light may have raised the daphnia’s temperature which might have increased its heart rate. Another reason could be that when a higher concentration of caffeine was added to the daphnia its heart rate could be faster than the previous one so it made it harder to count the heart beats because the beats were too fast or we might have put the dots one the same place while we are focusing our eyes on the microscope so we couldn’t look at the dots that we were making. But even though there were a few anomalies my graph proves my hypothesis which shows that the anomalies did not have an affect on my results. The results are close together and so are the repeats making them precise, this means the experiment was successful. The errors that we made were random error which means that my results were precise but not accurate. In the experiment there were a few errors which we could have taken in a account. So in order to make the experiment more reliable we need:
1. To collect more data, i.e. we need to look in to the experiment in more depth. For example more caffeine concentration; 0.1%, 0.2%, 0.3%, 0.4%. 2. To also try to keep the temperature of the daphnia constant, this could be turning the lamp off every time you are not using it and also the temperature of the daphnia should be checked regularly by using thermometer.
3. To measure the pH of the solution making sure that it is neutral and not an acid or an alkali.
4. Finally check that the daphnia is not pregnant or else it would not be a fair test.
Summary: My aim in doing this experiment was to find out whether caffeine concentration affected the heart rate of the daphnia. My hypothesis was 'the higher the concentration of caffeine the higher the heart rate (BPM) of the daphnia'. To get accurate results in my experiment I have followed a method where I had to take out a daphnia from the pond water by using a cut off pipette, then the daphnia was places in a cavity slide where it is put underneath the microscope and then clipped to ensure that it stays in one place and focus the lens in the daphnia’s heart , then I had to add two drops of caffeine concentration and leave it for 2 minutes to acclimatise so you can start counting its heart beats for 30 seconds, this procedure must be carried out for all the different concentrations. After doing my experiment I have looked back at my hypothesis and I have found out that my results supports my hypothesis. There were a few anomalies that I could have avoided but the errors were minor so it did not have a large effect on my results. I have then drawn an appropriate graph of my results in order to interpret it. I identified that my errors were random.
References:
Biological information
1) published on 13/07/1999 Author: Terry Herbet
2) Published on year 2000/01 Author: Tiera G
Table of results