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Effect of caffeine on heart rate in Daphnia
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Full write up for CPAC 1 Biology Edexcel new spec, passed core practical aspect of course
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Hiba Majid 12EQUESTION TO BE INVESTIGATED: DOES CAFFEINE AFFECT THE HEART RATE OF DAPHNIA?
SCIENTIFIC RESEARCH (REFERENCED):
Possible ethical issues:
Daphnia are most likely not complex enough to suffer physical and mental stress. Nevertheless,
there is still debate over whether or not animals should possess rights as humans do. Due to a lack of
consent from the Daphnia, we can instead try to minimise the amount of suffering by considering
animal welfare. The purpose of the investigation can be justified if the daphnia do not suffer as
much. We can minimise the suffering by:
● Returning the Daphnia to their natural habitat after use
● Storing the Daphnia in conditions that replicate their natural environment
● Working at a good pace to minimise time Daphnia are under any possible stress
● Turning off the microscope lamp when not in use, as Daphnia are poikilotherms (cold-
blooded)
● Not using an excessive amount/concentration of caffeine (Isa, 2021) [1]
What is caffeine and its effects?
Caffeine is a central nervous system (CNS) stimulant, it reversibly blocks the action of adenosine on
its receptors and consequently prevents the onset of drowsiness induced by adenosine. Caffeine also
stimulates certain portions of the autonomic nervous system. Caffeine in high doses raises your
blood level of epinephrine (adrenaline), which can increase blood pressure, increase the contractility
or force of the heart, and mildly increase the heart rate.(14 Jul 2016)
HYPOTHESIS: The higher the concentration of caffeine, the higher the heart rate of Daphnia
METHOD:
Piece of apparatus Purpose of piece of Comment on how piece of equipment Appendix
apparatus was used 5c
accurately/appropriately/safely technique
Culture of Daphnia Daphnia will be used to For the safety of those doing the
observe the circulatory experiment, they should wash their
system’s reaction to hands thoroughly after handling the
caffeine daphnia (low risk)
Microscope Used to observe the To ensure it is used safely, it should be
Daphnia under kept away from the edge of the table
so that it does not fall over and should
be kept in the middle. For accuracy,
the correct resolution and objective
lens should be used. (Medium risk)
, Hiba Majid 12E
Cavity slide Used to put the Daphnia Should be handled carefully as it is
on in water made of glass and may break (Medium
to high risk (if broken))
Stopwatch Used to time one minute Communication between person
to calculate beats per counting and person starting the timer
minute is important to ensure accuracy. The
person counting may also have to use
a pencil and paper and make dots in
an S shape to make it more accurate
(low risk)
Pipette Used to pick up the Use a small amount of pressure to
Daphnia from their ensure only one Daphnia is picked up
container (Low risk)
Cotton wool Strands used to inhibit To use a small amount so as not to
movement of Daphnia disturb vision. This improves reliability
(Low risk)
Tissue Used to dry up excess It should dry up the water around it
water around the and not on it as to not get rid of the
daphnia Daphnia's supply of oxygen and kill it
(No risk)
(CPAC a2a, 2b, 2d, 3a, 3b)
Procedures, Difficulties faced, any changes that were made (diagram as necessary)
Preliminary method:
1. Obtain a watch glass, where daphnia will be placed
2. Place a small amount of cotton, to prevent movement of the daphnia so that they can be
observed more easily
3. Use a pipette to remove a Daphnia, and some of the water it’s in, from its jar and place it on
the cotton, while ensuring Daphnia is covered by water
4. Remove the water from around the water flea using tissue, then add 2 drops of distilled
water or pond water. Do not use a coverslip. There should be a 2 minute acclimatisation
period to allow the daphnia to settle
5. View the water flea under low power. Focus on its heart, which can be seen through its
translucent body. The location of the heart is shown in Figure 1.
6. Use a stopwatch to record the number of heartbeats per minute. To count, you may tap a
pencil on a piece of paper in an S shape and count up the pencil marks at the end of the time
period. It is a good idea to do a ‘blind’ study to avoid bias in the results.
7. 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.
8. Record your results in a suitable format and present them in an appropriate graph.
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