Procedure
- Using 6 beakers, label and set up the following solutions using the correct volumes: -
- Set up the microscope.
- Fill a petri dish with water. This will be placed underneath the cavity slide, to absorb the heat from the lamp. If this is not done the daphnia will overheat, causing it to die.
- Use a tiny piece of cotton wool; put it onto the curve of the cavity slide, this will prevent the daphnia from moving, making it easier to count the heartbeats.
- Using a pipette, transfer a daphnia into the 0ml caffeine solution.
- Leave them to accumulate for 2 minutes.
- Use the pipette to take out the daphnia out of the water pond solution, and onto the curve into the cavity slide, also adding a drop of the pond water.
- Put the cavity slide on top of the petri dish.
- Using the stop clock, count the number of heartbeats, for a minute. An easier way to do this is to, use a pen and paper and dot the paper with each heartbeat. Then afterwards count the dots.
- Record the result.
- Then, using the pipette transfer all the daphnia into the 5ml caffeine solution beaker.
- Repeat steps 6-10, with the remaining caffeine solutions.
Planning
The independent variable in this experiment is the different amounts of caffeine solution present in each beaker. The dependent variable is the rate of the daphnia’s heartbeat. The controlled variables used in this experiment are the same species of daphnia, the same water temperature and the same microscope. The age of the daphnia being used cannot be controlled.
In this experiment it will be appropriate to use a 10ml pipette to measure volumes than it would be to use a 1ml pipette. For this experiment the pipette measurement is the correct degree of accuracy being used.
The systematic errors in this experiment could be reading volumes in pipettes could cause faulty measurements. Personal bias of the person taking the measurements can also introduce systematic errors. For example, expecting higher results with caffeine when investigating the effect of caffeine on the heart rate of daphnia could lead to higher results when caffeine is in the solution. This is best avoided by using a blind testing method where the investigator recording the results does not know which treatment contains the caffeine solution and which is the control.
The random errors may be reading the volumes, or not precisely measuring out the volumes. Carelessness can produce random errors, like not concentrating on using exactly the same procedure each time. Also, giving the daphnia an equal amount of time in the caffeine solutions, before testing.
In every experiment, only the reliable and accurate results are useful. The more trials that are done, the average will be a fairly good result and more reliable. This way the data is not displaced by any anomalous results. To make the results more reliable the class results are going to be and an average is going to be taken.
Ethics
In this experiment because real life creatures are being used, ethical issues has to be taken into consideration. The chlorine in tap water may kill daphnia, so the daphnia is going to be kept in its culture water. As soon as the trials are finished, the daphnia should be taken out of the caffeine solution and transferred back into the 0ml caffeine solution. A limited amount of daphnia should be given to each pair, a way to look at this is if each individual were to adhere to their own experiment, there would be a decrease in the amount of daphnia and this would cause a major disruption in the food chain, and could have some deadly effects. The ethical issues will be mainly brought up when we use a higher concentration that will kill the daphnia this is why we have to make the solution dilute first.
Risk Assessment
- Carelessness could cause glass apparatus to break, which can cause an injury.
- Ensure all glass apparatus are kept in the middle of the worktop.
- Wash hands after handling the daphnia and pond water.
- Be careful of the lamp in the microscope it will get very hot.
Table of results
Analysis of results
Group 1 and group 5’s data were the most unreliable because there were peaks that were off the average points. Group 5 had miscounted data at 159. Moreover Group 1 had 2 sets of data that seemed anomalous, which were 381 and 211.
The most reliable data, which can be seen from the graph, were from Group 4. The points steadily rise until it reaches its peak.
Conclusion
When looking at the results that I have obtained I can see that when adding more caffeine concentration to the water flea, the heart will also increase and there fore the prediction that it will be directly proportional is correct. This change in heart rate is due to caffeine being a drug that stimulates the body, and increases the amount of stimulatory neurotransmitters released. With high levels of caffeine, restlessness, anxiety, and insomnia can arise, causing an increase in the heart rate.
If I were to conduct this experiment again I would try and have a more accurate way to measure the heartbeats, a larger sample size of daphnia, and run more trials. I would also have a wider range of caffeine levels to test.
