Key Variables, Predictions and Abstract,
Key Variables
In order to test out my hypothesis, I am going to look at how different concentrations of caffeine and alcohol affect the heart rate of a single daphnia. In this experiment, the variable that changes is the concentration of the alcohol or caffeine. All of the other variables- for example temperature- remain the same. Also, I will try to use the same daphnia for all of the experiments, because different daphnia will have different natural heart rates, in the same way that humans do. However, it may not be possible to use the same daphnia all the time, because daphnia have a tendency to die when used in experiments. If the daphnia does die, it will be replaced by one of similar size and development.
Predictions
In this experiment, I predict that as the concentration of the stimulant, caffeine, increases, so the heart rate of the daphnia will increase. This is because caffeine, as mentioned above, increases the activity of the central nervous system- in humans, daphnia do not posses a central nervous system- and other body organs. As the concentration increases, so does the affect that the stimulant has on the daphnia.
My second prediction is that as the concentration of the depressant, alcohol, increases, the daphnia’s heart rate will fall. I think this because alcohol suppresses the activity of the central nervous system and bodily organs. As the concentration of the depressant increases, so does the affect that it has on the daphnia.
Introduction
Abstract
The aim of this experiment was to study the effects of alcohol and caffeine on the heart, using a daphnia as the test subject. The hypothesis under investigation was:
Increasing the concentration of caffeine (a stimulant) solution in which a daphnia is immersed will cause its heart rate to increase, whilst increasing the concentration of alcohol (a depressant) solution in which it is immersed will cause its heart rate to decrease.
To test this hypothesis a daphnia was exposed to both alcohol and caffeine and its heartrate recorded by placing it on a microscope slide and counting the number of heart beats. It was found that both alcohol and caffeine had a very significant effect on the heart, with alcohol slowing it down and caffeine speeding it up. At the strongest concentration of alcohol, the heartrate slowed by 54%. The strongest concentration of caffeine resulted in the heartrate increasing by 50%. The c2 statistical test used to analyse the results confirmed that both chemicals had a `very highly significant` effect on the daphnia’s heart. It is my opinion that these chemicals would have a similar effect on the human heart, although greater quantities would be needed to give similar increases in heartrate.
Introduction
It was decided to investigate the effects that alcohol and caffeine have on the human heart. The effects of alcohol and caffeine were of particular interest because they are drugs that are consumed on a large scale in society. However, because it is difficult to perform experiments of this nature on humans and get accurate results, I decided to use a daphnia as a substitute for a human. Although humans and daphnia are very different organisms, alcohol and caffeine should have a similar effect on them, although the effect when both organisms are exposed to the same amounts of alcohol and caffeine will be more pronounced in daphnia as they are much smaller, so the chemicals will travel around the daphnia’s body much more quickly and effect each cell more.
There are a number of reasons why it is more practical to use a daphnia than it is to use a human being as test subject. Firstly, daphnia are much simpler organisms than humans, so there are fewer variables that I have no control over that could effect the heartrate. Secondly, the heart of the daphnia is particularly easy to observe due to their transparent carapace. Thirdly, it is more practical to use a daphnia because the effects of the drug will be observed much more rapidly, in a matter of minutes as opposed to around half an hour in humans. Also, to get useful results, it would be necessary to supply a human subject with reasonably large amounts of alcohol or caffeine, which may not be good for short term health, as well as unethical.
The hypothesis under investigation was developed because depressants, like alcohol tend to decrease the activity of the body’s organs, whilst stimulants like caffeine tend to increase such activity. This belief has been confirmed by previous studies-both my own GCSE investigations and other scientific papers- on the effect of alcohol and caffeine on daphnia. For example it has been found that:
“The addition of a depressant seriously impairs the activity of all of an invertebrate’s normal body functions. ” (Hewson 1996)
Scientists have also found that:
“The stimulant caffeine acts in a similar way to other stimulants like amphetamines and cocaine, in that it results in a heightened state of awareness and general body activity. ” (Evans 1985)
Although this paper was not specifically concerned with the action of drugs on daphnia, it is still applicable to daphnia as the effect of these drugs on humans and daphnia is similar. This is confirmed by the following reference:
“The daphnia is suitable for use in most laboratory experiments involving the action of chemicals because due to its simple nature, chemicals have a similar effect as they do on more complex organisms. ” (Clayton 1979)
Depressants and stimulants usually work by suppressing or exciting the central nervous system (CNS). Although the heart is not controlled by the CNS, it is still influenced by chemicals in the bloodstream. It therefore follows that alcohol and caffeine should have some effect on it. Although daphnia do not have a CNS is still possible to use them to investigate the effects of alcohol and caffeine as I am interested in an area of the body outside the control of the CNS.
As has been said before, daphnia are effected significantly by even small amounts of chemicals in their environment. Although this investigation is mainly concerned with the effects of alcohol and caffeine, the ramifications of the effect of chemicals on daphnia and other freshwater creations should be considered. It has been found that:
“Domestic waste [including alcohol and caffeine] that ultimately ends up in waterways has a deleterious effect on the immediate wildlife. Small invertebrate organisms are the first to succumb but as these are eaten by larger organisms the food web is effected and many organisms die directly or indirectly. ” (Hasler 1977)
Method
Method
In the experiment, 1% solutions of alcohol and caffeine were taken and diluted to the required concentrations. The dilutions used in the experiment are recorded in the table below.
Firstly, 10ml of 1% alcohol solution was taken and placed in a test tube. A single daphnia was taken and placed in the test tube with the 1% alcohol solution and left to acclimatise for five minutes. The same daphnia was used in all of the experiments conducted. After the daphnia had been in the solution for five minutes it was removed using a teat pipette and placed in a microscope cavity slide. The daphnia was observed under low power and the position of the heart identified. When the heart had been identified, the stopwatch was started and the number of heartbeats in fifteen seconds was recorded. This number was then multiplied by four to get the daphnia’s heartrate in beats per minute. The experiment was repeated twice more, with a break of one minute between each reading.
After three readings had been taken using 1% alcohol solution the next solution was prepared and the daphnia was immersed in it for five minutes. The same procedure as detailed above was used at this and every other required solution. Once the daphnia had been tested at every concentration of alcohol, 1% caffeine solution was taken and the daphnia immersed in it. The procedure detailed above was then repeated until all the required concentrations had been tested. After both caffeine and alcohol had been used, a control experiment was conducted using distilled water instead of solutions of either caffeine or alcohol. Distilled water was chosen as the control because it is pure and so free from chemicals that could effect the daphnia’s heart so the daphnia’s `natural` heartrate could be observed and the results obtained from alcohol and caffeine could be compared with it.
Once all the results had been obtained, the three results obtained where averaged out to calculate the average heartrate of the daphnia. The results were then analysed using the c2 test to determine whether they were significant or came about purely by chance. The c2 test was used because in the experiment observed frequencies were being compared to expected frequencies (i.e. that heartbeat remains the same in each solution).
Results and Observations
Results
This section contains the raw data that I obtained in the tables below. After the tables, the results are presented graphically and are then analysed using the c2 statistical test. This section also contains the observations that were noted whilst the experiment was being conducted.
Results tables
Observations
Whilst the experiments were being carried out, various observations were noted about the behaviour of the daphnia. When the daphnia was immersed in distilled water, it swam around quite a lot, and at a relatively high speed. However, once the daphnia had been in the 1% alcohol solution for a few minutes, its movements slowed down and eventually stopped, so that it appeared that the daphnia was dead. The only way to confirm that it was still living was to observe its heart under the microscope. As the daphnia was immersed in progressively weaker solutions of alcohol, the level of movement increased, but was still nowhere near the amount that was present in distilled water. Once the daphnia was returned to distilled water its normal level of movement soon returned. There was no repeat of a noticeable change in the level of movement observed when the daphnia was in any of the caffeine solutions.
Conclusions and discussions
Discussion
As can be seen from both the graph of my results and the statistical analysis of my results, alcohol and caffeine both effect the heartrate of my test daphnia. The overall effect of alcohol and caffeine was, as expected, to decrease or increase respectively, the heartrate of the daphnia.
Although research has been done on the subject, no-one is sure how or why alcohol and caffeine effect the heart. Normally these chemicals act on body systems under the control of the CNS. It is thought that alcohol works by inhibiting the action of the neurotransmitters that transmit nerve impulses across a synapse. Caffeine is known to inhibit the action of the enzyme phosphodiesterase, resulting in an increased intracellular concentration of cyclic AMP. This can result in the release of increased amounts of excitatory transmitter substances in the brain, which has a stimulatory effect. However, the heart in humans is outside the control of the CNS, while daphnia have no CNS present. In both organisms The rate of heartbeat is controlled by the autonomic nervous system, being accelerated by the sympathetic system and depressed by the parasympathetic system. The heartrate is also influenced by the hormone adrenaline, which has a similar effect as the sympathetic nervous system in that it causes the heart to beat faster. This is the so-called `fight or flight` reflex. It is possible that alcohol and caffeine work in a similar way to adrenaline. All three chemicals are transported in the blood, so it is possible that their action on the heart is similar. However, as nothing has ever been proven, this is just speculation.
It is important that the effects of alcohol and caffeine on humans are known because their use is so widespread. For many people with conditions such as heart disease, fluctuations in the chemicals that control the heart could prove fatal. It is not just alcohol and caffeine that effect the heart, but many `harder` drugs, such as cocaine and amphetamines. These drugs, which although illegal, are still used in society and so it is important that their effects are known.
Although the overall effect of the alcohol and caffeine was as expected, when lower concentrations of the chemicals were added the heartrate moved in the opposite direction to the one which would be expected; that is, low concentrations of alcohol increased the heartrate while low concentrations of caffeine resulted in the heartrate falling. As the concentrations of the chemicals increases, this trend is reversed and the pattern follows that which was expected. The abnormality in the alcohol result could be caused by the fact that when humans consume a small amount of alcohol- up to around 40mg of alcohol per 100ml of blood- they become more active than usual. This increase in activity results in an increase in heartrate. I am less sure why low concentrations of caffeine decrease instead of increase the heartrate.
Limitations of the experiment
As with any experiment carried out in the school laboratory, there are limitations with my experiment. These limitations are considered below.
- Firstly, although it is accepted that alcohol and caffeine effect humans and daphnia in similar ways, they are still different organisms so will be effected in slightly different ways. Although the general effects- increasing and decreasing heartrate- should be the same, the amount of variation will almost certainly be different. As discussed in the introduction, because humans are much larger than daphnia, a much larger quantity of alcohol or caffeine would be required to produce the same degree of change in the heartrate. To get results that are completely accurate for humans, a large scale medical study would have to be undertaken.
- It is known from previous investigations that increasing the temperature of the solution in which the daphnia is kept will increase the heartrate of the daphnia. When the daphnia is being observed under the microscope it is in close proximity to the lamp, which gives out heat. Because the quantity of water in which the daphnia is immersed in when it is under the microscope is very small, only a small amount of heat is required to raise the temperature. Because the daphnia was under the microscope for just under five minutes, it is likely that the temperature increased by several degrees, possibly increasing the daphnia’s heart rate. This is a problem that is very difficult to remove. However, because the increase in temperature should be roughly similar for all of the experiments performed, the overall effect should not be too significant.
- Thirdly, living creatures tend to behave in a very unpredictable way. Although the same daphnia was used in all the experiments, the problem of unpredictability is still significant. For example, the experiments were carried out over a period of three days, so it is likely that the daphnia’s behaviour will vary from day to day. Also, the conditions in the laboratory may have varied over the course of the three days. For example, changes in room temperature could produce subtle variations in the behaviour of the daphnia. The only way to solve this problem would be to conduct the experiment as detailed above, but testing hundreds or even thousands of daphnia and taking an overall average result. However, for obvious reasons this was not possible in this investigation.
- Finally, it could at times be difficult to accurately count the daphnia’s heartbeat. This was because the daphnia moved around a little whilst under the microscope and also because the heart at times beat very quickly indeed and it was not always possible to keep up with it.
Conclusion
From the results obtained in the experiments, it can be confidently stated that the heart of a daphnia, and so the heart of a human, is effected by both alcohol and caffeine. Alcohol causes the heartrate to decrease significantly, whilst caffeine significantly increases the heartrate. These conclusions are supported by the statistical analysis performed which showed that they are `very highly significant`. The results allow the original hypothesis to be accepted.