DOES CAFFEINE EFFECT
HEART RATE?
HYPOTHESIS
I predict that caffeine will increase the heart rate of the daphnia compared to the control (distilled water in my
investigation). Caffeine is a stimulant which in some respects acts very similar to the way that adrenalin
works in our bodies, caffeine increases heart rate is through the action of what is known as a 'transduction
component', in this case it is a chemical made in the cell known as cyclic adenosine monophosphate
(cAMP). Transduction is the process that follows the action of a drug, hormone or neurotransmitter at a
receptor. Caffeine increases the amount of cAMP in the sinoatrial node. Then cAMP levels increase and this
increases the electrical activity of the sinoatrial node, making it beat faster and thus, increasing the heart
rate. It is also important to mention that daphnia have no brain, this therefore means that the results may be
slightly varied to our initial thoughts.
PLAN
1. Add one daphnia to the 0.5% caffeine solution for 5 minutes, you can measure this using a
stopwatch, we allow the daphnia to acclimatise for 5 minutes (controlled variable) because a
sudden change in environment may cause an irregular heartbeat of the daphnia which could
effect our results by giving an anomalous result, we also allow the daphnia to acclimatise to get
used to its environment because if not, the daphnia could become stressed and its heart beat
could become so high that it may die and this is an ethical issue.
2. Once the daphnia has been removed from the caffeine solution, place a few strands of cotton
wool onto a cavity slide to restrict the movement of the daphnia, then place a single daphnia
with plenty of the solution surrounding it onto the slide.
3. You can then turn the microscope onto the lowest light intensity thats possible to clearly view
the daphnia and prepare to count its heart beat.
4. Use a pen and a piece of paper and a stop clock to record the daphnia’s heart...