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Does caffeine affect heart rate?

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Biology - Does caffeine affect heart rate? Hypothesis The higher the concentration of caffeine, the higher the heart rate of Daphnia. Caffeine: Caffeine can block a receptor on the surface of heart muscle cells called an A1 adenosine receptor, which releases adenosine that has the effect of decreasing heart rate. Also, caffeine has the effect of inhibiting a group of enzymes called cyclic nucleotide phosphodiesterases. This group of enzymes is needed to degrade a stimulatory signal transmitted by excitatory neurotransmitters. Caffeine dissolves in water and alcohol. Daphnia: Daphnia are small, mostly planktonic, crustaceans, between 0.2 and 5 mm in length. The body is covered by a carapace, which is translucent. Daphnia have simple heart with no pacemaker. Summary: Caffeine, being soluble in water, diffuses from the water surrounding the Daphnia into their bodies directly. Caffeine reaches the simple heart and give rise to a series of reactions. Firstly, blockage of the A1 adenosine receptor stops the release of adenosine, so heart rate cannot be slowed down. Secondly, when cyclic nucleotide phosphodiesterases are inhibited by caffeine, nerve signals remain active for a longer time, resulting in higher heart rate. Apparatus/Materials o Culture of Daphnia o 0.5% caffeine o Distilled water o Microscope o Cavity slides o 6 beakers o 2 10cm3 syringes o 7 pipettes o Stopwatch o Cotton wool o Filter paper Procedure 1. ...read more.


Here water acts as a standard environment. Accuracy and validity * Measurements: suitable apparatuses are used to measure independent and dependent variables. It is also important to measure controlled variables, making sure they are constant. A thermometer can be used to measure temperature of water and caffeine before they are transferred onto cavity slides The caffeine solution's temperature is kept constant at room temperature by keeping the microscope's light off whenever I am not viewing the Daphnia and measuring its heart rate. * Each experimentor repeated the measurement of heart rate for 3 times, so that any anamolous results can be spotted easily. Safety precautions When a cavity slide breaks, dispose it into a special bin safely. Results % Caffeine Concentration T: time taken for 20 beats/s Mean 0.00 5.12 5.09 5.44 5.22 0.10 5.16 5.10 5.12 5.13 0.20 4.87 4.69 4.69 4.75 0.30 4.32 4.38 4.25 4.32 0.40 4.06 4.03 4.00 4.03 0.50 3.80 4.00 3.78 3.86 Presenting Data I have decided to plot a line graph. Firstly, it can show the relationship between the 2 data: "caffeine concentration" and "time taken for 20 beats" which is not immediately obvious from the table above. Secondly, both the dependant variables (time taken) and the independent variables (caffeine concentration) are continuous. The dependant variables are put on the y-axis, and the independent variables are put on the x-axis. Graph A: a line graph of time taken for 20 beats(s) ...read more.


When the beating gets very quick, we cannot react and count quickly enough. This leads to inaccurate heart rate. 2. We started the experiment with water, and than the lowest concentration of caffeine(0.1%), and then gradually increased to a maximum(0.5%). We should do blind sampling by covering the concentration. 3. The in-built light of the microscope has a heating effect on the caffeine and the Daphnia. Temperature control was difficult because a light source is necessary when viewing the Daphnia. We could prepare a heat sink by putting some ice water between 2 cavity slides. This heat sink can then be put under the slide with Daphnia to regulate temperature. 4. Caffeine was not completely mixed with water, so the concentration obtained was not what was expected. 5. Pipette was not cleaned and dried thoroughly, so there were impurities in the caffeine solution. 6. I did not add exactly 5 drops of caffeine-water solution onto the cavity slide every time, so the amount of liquid surrounding the Daphnia was not constant. Ethics This experiment involved living organisms; hence it is important to consider ethical issues. All living organisms should have the right to live in a natural system as freely as possible. Some Daphnia might die of heart failure when the concentration of caffeine is too high, or when they are in a stressed state for too long. We cannot obtain consent from the Daphnia before carrying out the experiment. But does this does not necessarily mean that we have absolute power over them. ...read more.

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