2) Use a stopwatch to record the number of heartbeats per minute. This is made easier by working in a pair, with one person counting beats while the other person tells them the time period. Tap a pencil on a piece of paper and count up the pencil marks at the end of the time period. Record the heart rate at intervals of 2 minutes over a 10 minute period. It is a good idea to do a ‘blind’ study to avoid bias in the results. The person counting the heartbeats should be unaware as to whether the Daphnia is in water or water with added caffeine.
3) Repeat the procedure using other water fleas from the culture solution and fresh, clean slides. Replace the water with caffeine solution. Repeat the procedure using several different concentrations of caffeine.
4) Record your results in a suitable format and present them in an appropriate graph.
5) Compare the treatments and try to explain the effect of each treatment on the heart rate.
6) Comment on the validity of your study. For example, would it have been better or worse to use the same Daphnia throughout the study?
7) If time permits, look at the effect of other chemicals, e.g. ethanol, on the heart rate.
Equipment:
- Culture of daphnia
- Cavity slides
- Dropping pipettes
- Distilled water
- Caffeine tablets
- Cotton wool
- Beakers
- Measuring cylinders
- Stop clock
- Filter paper
- Microscope
The method-
The variables involved in this experiment are-
The concentration of caffeine= independent variable.
The BPM of daphnia= dependent variable.
When experimenting with these variables, there are factors which can affect these variables, which should be taken into account. The concentration of the caffeine will have to be checked whether it is safe for the daphnia to take in. care should also be taken, so that the concentrations are not altered which could affect the validity of the results. When measuring the BPM, it should be made sure the heart is correctly identified and that it is also measured properly. The variables which we will be keeping the same are the volume of concentration, this is because by having different volumes of caffeine, the concentration level will be altered and this will not give us valid results. The size of the flie will have to be the same, as this can also be a factor affecting the heart rate, if we used different sized daphnia, we would not be directly measuring the affect of ‘caffeine’ on BPM as we would be taking others factors into account. Plus, it would be sensible to have different persons for each trial measuring the BPM; this will give us an idea if the results are valid and reasonable.
Furthermore the temperature conditions, the same equipment (microscope giving off heat), the same volume of distilled water and the same amount of time for measuring the heart beat of the daphnia.
In order to keep the results reliable and valid, we will have to take the above factors into account to help minimise the impact of the control variables. Furthermore the experiment will be repeated three times to get an average, giving us more valid and reliable results. The apparatus will also be analysed and altered so the most accurate results are given and that no systematic or random errors will be made using the equipment.
I will also be doing a control experiment, to highlight that that the caffeine is having a direct affect on the daphnia, and to show that it cannot be any other factors affecting the BPM.
Ethical issues arising from the experiment-
Ethical issues may arise from this experiment as we are testing living things for the use of science. This may be controversial. Using fleas, may be considered cruel and also against animal rights. Furthermore, there is a small risk of killing the fleas. If this experiment is created on a mass scale, then there is a danger disrupting the food chain. Therefore we will analyse aspects of the experiment, which may endanger the daphnia and produce other methods which will be safer and less harmful for the daphnia. To ensure the daphnia is not killed-
- Distilled water placed on the cavity for the flea, so it does not suffocate and instead of tap water because the chlorine may toxicate.
- Strands of cotton wool will be added to restrict movement of the daphnia out of the slide.
- Large sized pipettes will be used so the flies aren’t squashed.
- Distilled water will be added on the slip, so the flea is not poisoned.
- A cover slip will not be used, which can squash the daphnia.
- Excess water on the sides of the cavity slip will be absorbed using filter, giving a sufficient supply of oxygen.
- Generally, at each stage of the experiment, the daphnia will be treated with extreme care to ensure the daphnia is not harmed; by doing so, this will prevent us from using too many daphnia, which is wasteful and unethical.
Perhaps the most dangerous factor would be the high concentration of caffeine which could kill the daphnia; therefore the solutions will be diluted to a safe level. We will keep the microscope within the edge of the table so it does not fall and cause injury.
Furthermore, using daphnia safely for this experiment can be justifiable, as the research can benefit the health of humans at large. Throughout the experiment we will be responsible for treating the daphnia with care.
The table below will look at the suitability, possible risks of the apparatus and changes made to improve accuracy and safety of the daphnia.
Risk assessment-
The results will be presented in a table and graph. The line graph will be suitable in order to illustrate the affect of different levels of caffeine on BPM and to analyse any possible correlations.
The experiment will be suitable to test the hypothesis, because we can see if the heart rate increases by increasing the concentration of caffeine. The heart beat can be seen without operating. We know that by adding caffeine more neurotransmitters are released, therefore we can use this knowledge to see if it works in the experiment.
Results
Affect of different caffeine concentrations on BPM of daphnia-
We can notice from the graph a significant trend. The graph shows that as the caffeine concentration increases, the BPM also increases. The line also shows us a positive correlation. For instance at 0.3%, the BPM was 78 and at 0.6% the BPM was a 100. Also, the control (distilled water) proves to us that caffeine has an affect on the BPM, because there is no change in the BPM under distilled water. The heart rate is higher under caffeince than distilled water.
Furthermore we can see that the hypothesis matches the results of the experiment. As the caffeine concentration increases, the amount of neurotransmitters released would have increased which in effect increased the BPM.
There may have been two random errors as the results from 0.3% and 0.6% which do not match the line. This was probably a human error in counting the number of heart beats, which was quite difficult to count under a microscope. The counting was made as accurate as possible, using the equipment we had. Plus, insteadof using pipette we could have used a burette measuring by one decimal place, this would have made the results much more accurate and the concentration accuracy could have been improved by using caffeine tablets.
However, most aspects of the experiment were done accurately and changes were made to the apparatus, the experiment was repeated three times to give an average and overall is reliable and valid.
The results are significant to us as we can now analyse the effect of caffeine on the heart, this may allow us research about the effect on circulatory system and factors which lead to cardiovascular disease. It implies that our caffeine consumption should be controlled as there could be further possible risks involved. However the results are quite limited in that, we do not know any other effects caffeine has on the heart apart from increasing the heart rate. It can only suggest to us or imply possible effects like causing stress e.t.c.
Also, there were a few limitations in the apparatus, the counting technique was the least accurate part of the experiment, because it is considerably difficult to do, perhaps better equipment in counting would have increased the accuracy of the experiment.
In conclusion we can see that the experiment has tested the hypothesis, and generally the results have been valid, reliable and useful, which reflects the experiment in general.
