Apparatus:
Daphnia, Caffeine solutions, Distilled water, Microscope, Cavity slide, Pipettes, Wax or Vaseline, Petri dish and Measuring cylinder, Filter paper.
Plan:
The variables in this experiment are:
Caffeine concentration as the independent variable. The heart rate of the daphnia as the dependant variable. The controlled variables are temperature, sample size of the daphnia, volume of caffeine solutions and the stress levels of the daphnia.
A risk assessment has shown that as the caffeine and distilled water are going to be contained in glass beaker they could be dropped and smash, these glass splinters may then cut or pierce the surrounding area including myself and fellow students/ experimenters. To prevent this from occurring the glass should be handled carefully as well as myself and my peers having a distance between us so there is no chance of being bumped and dropping the glass. Also the use of pipettes can a very small but still a risk as if someone squeezes the pipette and the water or caffeine containing a daphnia goes into a peers eye then damage may occur to prevent this goggles should be worn or when the pipette is being used only the person using it should stand in the area.
To make sure I have reliable and valid I will repeat the experiment on each solution 3 times, on different daphnia.
Some errors may occur as the heart will be beating relatively quickly so my counting and recording may not be as accurate as they could possibly be. As well as my measurements of the volume of solutions may not be as accurate as possible as I will be using my eyes to see where the volume is.
Method:
1st step of the experiment is to select the daphnia you want to use in the experiment from the beaker of distilled water they are kept in; selection of daphnia must be that of a relative similar size so the effects of different solutions can be compared accurately. Using the pipette select 3-5 daphnia of the same size and place them in a Petri dish so they are easily accessed later.
2nd step of the experiment is measure out is to measure out volumes of liquids being used, the volume of 1
, volume of 3
and 5
.The volume of distilled water is already measured.
3rd step of the experiment is to rub some wax onto the dip of the cavity slides so when the daphnia is place in it, its movement is restricted, making it easier to observe heart rate.
4th step of the experiment is to place a daphnia that is in distilled water into the cavity in the slide, then place the slide under the microscope and proceed to record the number of beats of the heart for 30 seconds then, double the number for a the amount per minute. Repeat this step 2 more times.
5th step of the is experiment is to place the 1
solution into the cavity of the slide, then using some filter paper separate the water and daphnia. After this place the daphnia into the cavity of the slide, then place the slide under the microscope and proceed to record the number of beats of the heart for 30 seconds then, double the number for a the amount per minute. Repeat this step 2 more times.
6th step of the is experiment is to place the 3
solution into the cavity of the slide, then using some filter paper separate the water and daphnia. After this place the daphnia into the cavity of the slide, then place the slide under the microscope and proceed to record the number of beats of the heart for 30 seconds then, double the number for a the amount per minute. Repeat this step 2 more times.
7th step of the is experiment is to place the 5
solution into the cavity of the slide, then using some filter paper separate the water and daphnia. After this place the daphnia into the cavity of the slide, then place the slide under the microscope and proceed to record the number of beats of the heart for 30 seconds then, double the number for a the amount per minute. Repeat this step 2 more times.
Results:
Number: outlier
Analysis:
As a conclusion I can see that my hypothesis was correct as the results from my table and graphs are in a supporting correlation with it, as the heart rate of the daphnia did increase as the concentration of the caffeine solutions increased, this could be used to show that the amount of neurotransmitters released increased as this is what caffeine has been known to achieve. The results show that a correlation between heart rate and caffeine concentration, as when the daphnia where in the distilled water or 0
group the average result was 118 beats per minute and when you compare this to the 1
group the average result is 307 beats per minute.
Evaluation:
My method and therefore my results could be improved by using apparatus that will lead to more accurate results such as a burette instead of a measuring cylinder to make sure my volumes were absolutely accurate as human involvement which included measuring with my eye and not a continuous measuring scale could lead to large amounts of human error.
Also as I had difficulty in recording the exact number of beats per minute as I kept finishing with outliers in each test group, I had to use the results provided to me by my teacher to create my table and graphs.
Also some ethical issues could be raised with my experiment as I was provided with the daphnia and so do not know what the previous care conditions were for the creatures, also after questioning my teacher I was told that the daphnia will not be returned to their natural habitat after the experiments but will instead be terminated, although this will be as humanly possible.
Sources for pictures:
1.
2. http://chemistry.about.com/od/factsstructures/ig/Chemical-Structures---C/Caffeine-Chemical-Structure.htm