Richmond upon Thames College AS SNAB Biology Name : Core practical 1.23 Research Question : Does caffeine affect heart rate? Purpose To investigate the effect of caffeine on the heart rate of Daphnia (water Daphnia (water fleas). To introduce practical skills
Caffeine Plants produce caffeine as an insecticide. insecticide. Cocoa in South America, coffee in Africa and tea t ea in Asia have all been used for hundreds of years to produce ‘pick me up’ drinks containing caffeine. These days, caffeine is also used as a flavour enhancer in a wide range of cola and other soft drinks. In addition, it has medicinal uses in aspirin preparations, and is found in weight-loss drugs and as a stimulant in students’ exam-time exam-time favourites like Pro-plus and Red Bull. In humans, caffeine acts as a stimulant drug, causing increased amounts of stimulatory neurotransmitters to be released. At high levels of consumption caffeine has been linked to restlessness, insomnia and anxiety, resulting in stress and raised blood pressure which can lead to heart and circulation problems.
Making a hypothesis What do you think will be the effect of different concentrations concentrations of caffeine on the heart rate of water fleas? Write down your ideas and support your prediction (or, hypothesis) with biological knowledge. knowledge. You now have an idea (prediction /hypothesis) to test. Hypothesis: I hypothesise that the higher the concentration of caffeine the higher the heart rate of the daphnia will be .
Scientific Reasoning: Caffeine is found to effect the central nervous system and speed up the rate of nerve pulses being sent and received in humans. Caffeine is a drug that is known to be a stimulant, this explains explains its effect on the t he central nervous system and heart rate in humans
Analysis of Variables: Independent variable The independent variable in this experiment was the concentration of the caffeine solution that the daphnia was placed in., this is a continuous variable This was measured in percentage of caffeine in the solution. It ranged from 0.0% to 0.5% in intervals of 0.1.
Dependent variable The dependant variable in this experiment is the heart rate of daphnia that was measured in beats per minute, also a continuous variable. variable . We measured this by counting how many times the daphnia’s heart beat within the space of a minute by looking through a microscope at the daphnia.
Controlled variables There were some variables that we kept the same to increase the validity of our results, we had to control the temperature as the daphnia’s heart rate is temperature t emperature sensitive. sensitive. We also had to ensure the daphnia weren’t stressed as this can raise the heart rate.
Control Procedure: We turned off the light between counting to help prevent a raise in the temperature of the water and we used pond water to ensure the daphnia are in a similar physical environment.
Procedure The beating heart of a water flea can be seen through its translucent body, by placing the flea in a few drops of water in a cavity slide. A few strands of cotton wool will help to reduce the movements of the water flea. A cover slip helps stop the water evaporating.
The following equipment will be available: Standard glassware (beakers, • Culture of Daphnia (water fleas) measuring cylinders, etc.) • Cavity slides Stopclock • Dropping pipettes (blunt-ended) Paper towels or filter paper • Distilled water Microscope • Caffeine solutions of different Marker concentrations • Cotton wool
Work in pairs (you might collect results as a group). 1. Set up a range of labelled test tubes each containing about 10cm 3 Of a caffeine solution, and one tube containing pond water only. 2. using a wide ‘mouthed’ dropper pipette place two or three Daphnia Into each tube. Leave in the solution for about 5 minutes. 3. Prepare labelled cavity microscope slides with a few strands of cotton wool and a few drops of caffeine solution or pond water. 4. Transfer a water flea to the microscope slide, and place a cover slip over the top. 5. View under the microscope and count the heart rate for 30 seconds. 6. Record heart rate into the results table. 7. Return water flea to labelled beaker, so that they can be returned to the college pond. 8. Repeat measures at each concentration of caffeine and the control – or, the class will pool collected data.
Results table to show the effect of different concentrations of caffeine solution on the heart rate of Daphnia . Concentration of caffeine solution / % 1
2
Daphnia Heart rate / beats per minute Standard 3 4 5 Mean Deviation
0.0
136
195
169
169
139
162
24
0.1
264
268
254
262
276
265
8
0.2
152
174
256
252
250
217
50
0.3
284
288
296
282
288
288
5
0.4
218
260
258
272
276
257
23
0.5
221
264
230
224
223
232
18
Analyse your results:
Line Graph to Show Average BPM of Daphnia When In Caffeine Solution 350 300
a i n h 250 p a 200 D f 150 o M100 P B
50 0
0.0
0.1
0.2
0.3
0.4
0.5
Percentage of Caffeine In Solution
Conclusions: These results don’t support my hypothesis, the results don’t show a trend and you cannot say that caffeine has an effect on the heart rate as the results do not support this. There is significant difference between the intervals 0.0 and 0.1 but apart from that none of the results show a significant difference making it difficult to find a trend in these results. I believe this lack of a trend is due to many factors of our experiment. If the daphnia died and we replaced it, it was sometimes slightly bigger or smaller than the previous daphnia. The cotton we used to restrict the movement of the daphnia may have caused anxiety, this being an extraneous variable that could greatly affect the heartbeat of the daphnia and therefore this could have aff ected the results. There may have been human error in the counting that caused miscalculations in the data. The standard deviation appears to be very high in places this shows that the repeats of the experiments have produced very varied results supporting my view that it may be other extraneous variables or human error causing the lack of a trend in these results. Evaluation Did you identify any errors creeping into your results? Systematic/Human errors There is little chance of a systematic error as the only equipment used is pipettes to measure the caffeine solution and the microscope. But human error can cause many problems in this experiment; there could of been error in measurement using the pipette, or counting of the heartbeats. Random errors Random errors that may affect the results are things such as daphnia becoming stressed and their heart rates increasing, the waters temperature increasing, the daphnia dying and having to be replaced and the biological differences between each daphnia. Making improvements by choosing alternative apparatus. We could have used a microscope without a light to stop the effect of light on the temperature of the water. Can you ever justify the use of animals in experimentation? I believe that it is justifiable for animals to be used in experimentation if it is for medicinal purposes or in research of diseases and other such things that research would improve the health and well-being of other animals or humans.
