Effect of concentration of caffeine on the heart beat rate of Daphnia

Effect of concentration of caffeine on the heart beat rate of Daphnia
Title:
Effect of concentration of caffeine on the heart beat rate of Daphnia
Objective:
1. To investigate the effect of concentration of caffeine on the heart beat rate of Daphnia
2. To learn the effective experimental techniques in carrying out an experiment
Hypothesis:
The higher the concentration of caffeine solution, the higher the heart beat rate of Daphnia. However, this will reach a limit where the Daphnia is saturated with caffeine and no more caffeine will be taken in from the surrounding solution.Introduction:
Caffeine is a stimulant that can increase the amount of neurotransmitters in the human body. It can increase the heart beat rate. Caffeine blocks a receptor in the heart called A1 adenosine receptor. Caffeine acts as a competitive inhibitor to the receptor, preventing the chemical adenosine from binding with the receptor, which is important for suppressing the neural activity. Increase in consumption of caffeine will lead to restlessness, insomnia, and anxiety. Recent research shows that the drinking of caffeine containing beverages may lead to hallucinations by increase the concentration cortisol in our body. Caffeine is made by plants to get rid of insects. Now caffeine is also used as a flavour enhancer in cola and other soft drinks. It has medicinal uses in aspirin preparations and is found in weight-loss drugs and as a stimulant in normal people in everyday to keep them alert in lessons. An average adult is advised not to have more than 300mg of caffeine per day.
Daphnia live in various aquatic environments ranging from acidic swamps to freshwater lakes, ponds, streams and rivers. The average heart rate is approximately 180 beats per minute under normal conditions. Daphnia suffer no harm when return to water after being observed under the cover slip. Furthermore, the exoskeleton is translucent and the heart beating is easy to see. In addition to that, a wide range of chemicals such as caffeine, nicotine, and adrenaline can be tested with Daphnia. The lifespan of a Daphnia does not exceed one year and is largely temperature dependent. Daphnia are widely used in testing the effect of toxins on an ecosystem. This makes Daphnia an indicator species, particularly useful because of their reproductive capacities and short lifespan.

Figure 1: The image above shows the location of heart in the body of Daphnia
There are no ethical issues in this experiment because small pond animal is used to determine the effect of caffeine on human heart beat rate. We have to take a substitute of human being to investigate the effect of caffeine on their heart beat rate. This result obtain in this experiment will be assumed to be the same as what happened in the human body.
Controlled variable: the volume of the drop of solution, the type and age of Daphnia, temperature of the solution, the concentration of oxygen and other gases in the solution, time taken for the Daphnia to stay in the solution, pH of the solution
Manipulated variable: concentration of caffeine solution
Responding variable: the heart beat rate of Daphnia
Apparatus:
Cavity slides, dropping pipettes, cotton wool, standard glassware, stopclock, microscope
Materials:
Culture of Daphnia, distilled water or pond water, varying caffeine solution (0.1%, 0.2%, 0.3%, 0.4%, 0.5%), paper towels or filter paper
Procedure:
1. Different concentrations of caffeine are prepared.
2. A microscope is set up and the brightness is adjusted to prepare for the observation of Daphnia.
3. A Daphnia is removed from the water by using a dropping pipette.
4. The Daphnia is then quickly transferred to a cavity slide
5. A cotton wool is used to absorb water from the cavity slide
6. A drop of distilled water is placed on the cavity slide.
7. A few strands of cotton wool are placed around the Daphnia to restrict the movement of Daphnia. If some water is accidentally absorbed, then add more water.
8. After the heart of Daphnia is clearly seen, a stop watch is started and the counting of the heart beat is initiated.
9. The number of heart beats is counted for 20 seconds. The trial is repeated by 2 times.
10. After the counting is completed, the water on the slide is quickly adsorbed by using a cotton wool and the nest drop of solution is placed on the cavity by using a dropper.
11. The experiment is repeated by using 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% of caffeine solution.
12. Each of the results is multiplied by 3 to obtain heart beat rate per minute. The results are tabulated and a histogram is drawn to show the distribution.
Risk assessment:
1. The concentration of the solution should not exceed 1% to prevent the organism from dying.
2. The glassware such as cavity slide should be handled carefully so that they do not break.
3. Light bulb should be used carefully to ensure that your hand is not bruised as a result of heat.
4. The Daphnia should be handled carefully to keep the organism from injury and lead to decrease in heart beat rate.
5. Be careful that the water does not spill over and damaging the microscope.
Results:
Concentration of caffeine solution/% The number of heart beats of Daphnia per minute Average number of heart beats of Daphnia per minute
1st reading 2nd reading 3rd reading
0.0 45 51 48 48?2.45
0.1 66 69 60 65?3.74
0.2 75 78 78 77?1.41
0.3 87 90 87 88?1.41
0.4 96 93 96 95?1.41
0.5 102 99 102 101?1.41

Discussion:
It is known that the chemicals absorbed by the Daphnia will be stayed in the body in half an hour. Therefore, the caffeine solution could be introduced to Daphnia 5 minutes prior before the experiment. Daphnia is suitable for the experiment because it has no selection in absorbing chemical substances from the surrounding environment. Any chemicals will have the physiological effect on the Daphnia immediately. Besides, Daphnia body is translucent which allows the observation of heart beat of Daphnia to be made without cutting them open. The experiment should be made as quickly as possible because Daphnia may not survive in the new environment.
Furthermore, large Daphnia may show different heart rate compared to smaller Daphnia due to the discrepancy in concentration of caffeine in the system between the large and the small Daphnia. Slower heart beat rate may be shown by larger Daphnia. Therefore, it is important to use the same Daphnia throughout the experiment without injured or kill the Daphnia.
The temperature could be easily controlled before the experiment by placing Daphnia in a water bath. The temperature should be controlled because an increase in temperature of 10 degree Celsius will increase the rate of reaction, and thus the heart rate of Daphnia. The amount of water on the slide could be controlled by using a dropper that only allows a drop of water on the slide.
In order to observe Daphnia more effectively, the Daphnia has to be propped up by cotton wool to show the Daphnia?s ventral view. The heart is at the top of the back, just behind the head. At the beginning of the experiment, the Daphnia may struggle in the cavity slide, making the observation of the heart beat rate more difficult. It is important that only a drop of solution is placed on the cavity slide which is smeared thinly with grease in order to secure Daphnia in place. Small pieces of cotton wool may be added to restrict the movement of Daphnia.
The concentration of oxygen and other gases in the solution could be controlled by using an aeration pump that can dissolve the maximum amount of oxygen gas in the solution before the experiment. pH of the solution could be controlled by using a buffer solution. The concentration of caffeine in the solution should be carefully monitored to by measuring out the exact mass of caffeine during the preparation of the standard solution by using a volumetric flask.
During the experiment, a natural light is preferred over the artificial light because artificial light generates more heat than natural light. Alternatively, a cooling system on the slide or a thermostat may be installed.
A video camera may be used to increase the accuracy of the readings. This is because human reflexes is not enough to count the fast beating rate of Daphnia?s heart especially at high concentration of caffeine solution. A video may be taken and the recordings can be played at a slower pace the heart rate to be counted more accurately.
In addition to that, the time for the Daphnia to be stayed in the solution should be constant. If the Daphnia stay longer in the solution, then it may have taken more caffeine and the heart rate may increase. Therefore, it is essential to time exactly how long the Daphnia to be stayed in the solution.
The results of this experiment are fair and reliable. Three readings were repeated during the experiment and the average is taken. A control experiment was set up to compare the heart beat rate of Daphnia before and after the adding of the caffeine solution. The only manipulated variable is the concentration of caffeine and the heart beat rate of Daphnia is the responding variable. The remaining variables are constant.
However, the range of the concentration of caffeine solution used in this experiment is not enough to prove the second statement of the hypothesis-the maximum absorption of Daphnia. Furthermore, the Daphnia may die before the readings are taken when the solution is used. This experiment had tested only one organism. A different range of Daphnia such as different ages and sizes should be tested in order to make the results more comprehensive.
There are some anomalies between the three readings because our group used a light microscope in with artificial light in the experiment. The artificial light from the microscope has caused the temperature of the water in the cavity slide to increase. This may doubles the rate of heart beat of Daphnia for every 10 degrees rise in temperature. The propping of and the struggling of Daphnia may cause some injuries to the Daphnia. This may impair the heart of the Daphnia and decrease the heart beating rate of Daphnia. In addition to that, Daphnia may have taken up different amounts of caffeine from the solution. The longer the Daphnia stayed in the solution, the greater the number of heart beats.
Furthermore, due to human limited abilities, some heart beats may be missed from being taken into account. The heart beats may be too fast to be counted. Some Daphnia may not show regular heart beats. Furthermore, the sensitivity of Daphnia towards caffeine may also need to be taken into consideration. Each Daphnia may take different time to absorb the caffeine. The heart beating rate of the Daphnia being investigated is abnormally low because an old Daphnia may be used in this investigation or the Daphnia is probably injured or ill.

Conclusion:
The result from the histogram has shown that the heart beat rate of Daphnia increases with temperature. The steep increase of heat beat at the beginning of the experiment shows that at low concentration of caffeine, the rate of absorption by Daphnia is the highest. The highest possible heart beat rate is 102 beats per minute while the lowest possible heart beat is 45 beats per minute. The heart beat increases linearly at the beginning of the experiment. The rate of increase of heart beat then reduced starting from 0.3% caffeine solution. The hypothesis is supported by this experiment.

Effect of concentration of caffeine on the heart beat rate of Daphnia 9.6 of 10 on the basis of 2601 Review.