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A stroboscopic method is a method used to investigate the effect of caffeine on daphnia heart rate. This experiment gives a clear and visible response on this experiment; the good visibility of daphnia’s heart and the rapid ability to absorb the solutions makes it easy to investigate. The daphnia heart is fairly easily seen but counting the number of heart beats is considerably hard. Therefore, it was easier to count per 15 seconds and multiply by 4. From the experiment carried, varying results were obtained. Different caffeine concentrations on different products like coffee, coke, green tea, black tea and espresso have different results on different specimens. A control experiment was carried out to first record the results of the heart rate of the daphnia when it is under normal conditions. Various experiments were carried out with the same solution testing 4 specimens of daphnia magna and the various results recorded.

Various experiment materials were used to carry out the experiment and a defined method of carrying out the experiment followed. The results were recorded in charts, graphs and a scatter diagram was drawn to represent the data. The hypothesis being tested indicates that that caffeine increases the heart rate of daphnia magna. Each specimen was put under different concentrations of each type of caffeine to observe whether the heart rate increase or decreases with each concentration level.

This experiment was used to show the practical application of how stimulants affect animals; this was explained that the effect is different depending on the level of caffeine concentration. From the experiment, it was evident that daphnia magna was influenced by caffeine; this highly depended on the caffeine concentration. Fitzgerald, 2003 states that the ectothermic nature and transparency of daphnia made it very easy to observe the effects of environmental changes.

Daphnia, otherwise known as water fleas usually have a circulatory system that is similar to those of mammals; they have a chambered heart whose heart beat can be observed under a microscope. In this project, Daphnia magna, which is a transparent fresh water crustacean, will be used to study the effects of caffeine on their heart rate. Clare, 2002 illustrates that the goal of this is to test whether caffeine has an effect on the heart rate of Daphnia magna as an experimental model. The body diameter of adult females is about 3-5mm. LaFave, 2003 states that caffeine being a stimulant will work causing the nervous system to work faster than usual; this in turn causes the blood vessels to constrict. These two effects will work together to increase Daphnia’s heart rate. Campbell, 2005 states that usually the heart rate increases when caffeine is added to a solution that has Daphnia; but at some point high concentrations of caffeine can cause the heart to stop beating. From the experiment it is observed that the heart of the Daphnia is dorsal to the backbone; which is just behind the heart. The average Daphnia has a heart rate of about 180 beats per minute under normal conditions; the experiment therefore seeks to establish the effect of caffeine on ectothermic animal.

The hypothesis is that the heart rate of Daphnia magna will increase as higher as higher concentrations of the caffeine solution are introduced to the system. Using pond water/ Daphnia culture solution is recommended for both the control experiment and to dissolve the caffeine as this may give more valid results and might be less stressful to the Daphnia. If put in distilled water; the heart rate may rise due to lack of oxygen.

Material and methods

Culture of Daphnia, cotton wool, dropping pipettes, different concentrations of caffeine solution, Petri dishes, Vaseline, and tooth picks. Live daphnia were obtained form a pond that they were store in and put in jars; they were put in the laboratory in tanks with normal room temperature. Helms, 1998 indicates that the caffeine dose was calculated on the basis of feasible mass to mass ratio using advised dose on human specimen.

The students cut the plastic pipette that they had initially cut of the top to so that the Daphnia magna would fit into the pipette. The student teams obtained the depression slides and put some cotton wool on it. The teams used their pipettes to get Daphnia magna out of the tin and put it on the petroleum jelly. Wipes were used to remove the excess water from the slide; a small amount of each solution was dropped on the Daphnia magna to avoid drying it out. The stroboscope was placed parallel to the microscope so that both the normal illumination and the stroboscopic light were visible when looking at the microscope. The slides were then located on a microscope for dissection and the heart seen under the microscope and with the help of the lab technician. Foster 2005 explains that adjustment of the position of the stroboscope and the microscope condenser was made according to the preference prior to recording. When the Daphnia was calm, the heart rate was recorded; the reading was taken for 15 seconds and multiplied by 4 to get the heart rate per minute. After that, the students placed a Petri dish on the stage of the microscope, on which the Daphnia was placed on top. The Daphnia was given enough time to adapt to a different environment before taking the second heart rate reading. A similar process was repeated several times using different solutions with different caffeine concentration; the solutions include coffee, coke, black tea, and Espresso. The heart beat for the specimen was recorded after each of the solution was used; when the final experiment was taken, all the solution was drawn from the specimen and the Daphnia was taken back to it culture solution.

Results

Effect of Caffeine Solutions of Heart Rate of Daphnia magna

Table 2 shows the mean beats per minute of the daphnia magna when pit in different solutions of caffeine. The experiment used 4 specimens of daphnia on each solution and the heart rare readings were recorded. Each specimen was put under different concentrations of each type of caffeine to observe whether the heart rate increase or decreases with each concentration level. The results were as follows Green tea 343, black tea 207, coke 230, Espresso 159, coffee 336.

Discussion

The table shows the trend of Daphnia Magna’s heart rate when put under different concentrations of caffeine, based on the data provided above; it can be conclude that Daphnia heart rate is altered by different caffeine levels; the caffeine levels tend to increase their heart rate. The more caffeine concentration the more the heart rates kept increasing up to a level that thee daphnia couldn’t survive. With the above data that was recorded, green tea increased the heart rate more than any other solution while black tea records the lowest heart rate. The control experiment shows that the mean heart rate Daphnia is around 336 beats per minute; this heart rate was recorded under the normal culture of daphnia magna without any caffeine.

The results in table 1 show that only green tea causes the heart rate of daphnia magna to increase compared to the control experiment. The other caffeine concentrations actually cause the heart rate to decrease; this is especially in Espresso that records 166, 116, 240, and 120 for specimen 1 to specimen 4 respectively. This shows that the heart rate lowers to as low as 168 beats per minute which is relatively low compared to the same specimen 1 that records a heart rate of 332 during the control experiment. This is contrary to the hypothesis that states that caffeine increases the heart rate of daphnia magna. Coke also records a low mean of 230 heart beats per minute; this is lower than the control mean of 336. Black tea consequently records 207 which are also lower than the control experiment that recorded 236 heart beats per minute.

The green tea experiment records the highest heart rates when daphnia magna is put into the solution; the results were 352, 384, 344, and 292 for specimen 1 to specimen 4 respectively. This gives the highest mean recorded of 343 which is higher than the control experiment that records 336. The green tea solution therefore holds shows a positive hypothesis that states caffeine increases the heart rate of daphnia magna. Form the scatter diagram that is drawn on the Cartesian plane, there is a significant relationship between the heart rate of daphnia magna and caffeine. In the diagram, the dependent variable is the heart rate while the independent variable heart caffeine. From then scatter diagram, there is a correlation between the independent variable and the dependent variable tough it is minimal. This is because when the line of best fit is drawn; most of the variables are outside the line and are on the left side. This shows that the correlation is significantly less. From the diagram, when the caffeine level increases from 0 to 0.3 the heart rate increases from 200 to 250; but this rate is not as high as the control experiment that records a high level of heart rate.

Foster 2005 states that this experiment can be used to show the practical application of how stimulants affect animals; this can be explained that the effect is different depending on the level of caffeine concentration. From the experiment, it is evident that daphnia magna is influenced by caffeine; this highly depends on the caffeine concentration. The ectothermic nature and transparency of daphnia made it very easy to observe the effects of environmental changes.

Code: Sample20

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