One of the many CPACs needed to pass the practical element of SNAB Biology. This is the effect of caffeine on heart rate, we did this with daphnia so this is a fictional set of results and analysis which helped me receive an A in Biology to help with analysing your own results!
CPAC- Effect of caffeine on heart rate in daphnia
Independent variable- caffeine concentration
Dependant variable- heart rate of daphnia (beats per minute)
Control variable How to achieve this Why this is important
Volume of caffeine added Add two drops using a So that the results are valid
pipette each repeat and each concentration is
done consistently
Stress of daphnia Turning off the microscope Ensure validity of results,
light between readings also for ethical reasons
Size/ age of daphnia Choose daphnia that are To ensure repeatability of the
roughly same size and age for experiment
repeats
Time to acclimatise One minute for Ensure repeatability and so
acclimatisation for each that the daphnia do not
daphnia stress
[1]
Why use daphnia?
Daphnia are very common small crustaceans , so by using them in science, there is no
real threat to their survival as a species. They also reproduce asexually, and therefore
are genetic clones, which also helps with the validity of our experiment. They are
inexpensive and also have translucent bodies, which means that we can easily see their
heart beating though a microscope.[2]
Ethical issues of using daphnia-
As the daphnia have not consented to being used for this practical, we have to work
ethically by minimising their suffering. Although we believe they most likely do not have
a nervous system complex enough for them to feel any pain, we still must act
accordingly to reduce any suffering[2]. This is done by:
Storing the daphnia in conditions similar to their natural habitat(pond water)
Working at a suitable pace so that they are not stressed for a long period of time
(this may also increase their hear rate, affecting our results)
Turing the light off between reading(Daphnia are poikilotherms-cold blooded)
Not add too much cotton onto cavity slide to not suffocate them
Not removing too much water with tissue to not suffocate them
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