Daphnia Experiment Report 1. Introduction Caffeine is found in many plant species, where it acts as a natural pesticide. It is found most commonly in cocoa, tea and coffee, but is also artificially added to some soft drinks such as cola to act as a flavour enhancer. When consumed by humans, caffeine works as a stimulant causing amounts of released neurotransmitters to be increased. High use of caffeine has been related with raised blood pressure, restlessness, insomnia and anxiety which, in the long term, can lead to heart and circulation problems.
The aim of this experiment is to observe whether caffeine has any significant effect on heart rate. To test this, daphnia will be placed in water and then caffeine solution, so the difference in heart rates can be compared. Daphnia are small invertebrates that are found in aquatic environments, more commonly known as ‘water fleas’. They are approximately 3mm in length and have simple internal structures. They have transparent skin that allows you to view their internal organs, making them ideal subjects for scientific experiments. 2.
Hypothesis It is expected that the daphnia’s heart rate will be greater in the caffeine solution than in the water. This prediction can be justified with the fact that caffeine is a stimulant drug that affects the central nervous system, speeding up your metabolism and increasing alertness. 3. Method The independent variable in this experiment is the use of caffeine. The dependent variable in this experiment is the heart rate of the daphnia. Equipment: * Pipette | * Cotton wool| * Concaved microscope slide| * Water (20cm? )| Microscope slide cover| * Caffeine Solution (20cm? )| * Microscope| * 1 daphnia| * Thermometer| * Stopwatch/timer| * Petri dish * Two experimenters | * Pen * Paper| 1. A concaved microscope slide is placed in a lidless Petri dish. 2. A tiny strand of cotton wool is placed in the concave of the microscope slide. 3. A pipette is used to pick out a single daphnia from a beaker of water. 4. The daphnia is then placed on the cotton wool on microscope slide. 5. A microscope slide cover is then put over the concaved slide. . The Petri dish is topped up with 20cm? of water (20°C). 7. The Petri dish is placed on the microscope platform. 8. The microscope is adjusted so that the daphnia can be observed. 9. Experimenter 1 counts the daphnia’s heart rate for 20 seconds, dotting on a piece of paper with each beat whilst experimenter 2 keeps track of time with the stopwatch. This is repeated four times and then an average is calculated. 10. The microscope slide is removed. 11. The Petri dish is emptied of water. 12. The slide is placed back in the Petri dish. 13.
The Petri dish is topped up with 20cm? of caffeine solution (20°C). 14. The Petri dish is placed on the microscope platform. 15. Experimenter 1 counts the daphnia’s heart rate for 20 seconds, dotting on a piece of paper with each beat whilst experimenter 2 keeps track of time with the stopwatch. This is repeated four times and then an average is calculated. Controlled Variable| Reason| Same Daphnia| The same daphnia must be used for both parts of the experiment as every individual daphnia’s metabolism works at different speeds. | Same volume of liquid (20cm? | The same volume of both water and caffeine solution must be used in both parts of the experiment as the temperatures two different volumes of water would be dissimilar. | Water temperature| Daphnia do not thermoregulate as they are cold-blooded animals, meaning they will be at the same temperature as the water they are placed in. As the temperature of the water is increased, so is the metabolism of the daphnia, consequently causing it’s heart rate to increase. So, to ensure a balanced experiment the temperature of the water and the caffeine solution must be about the same so that temperature cannot be a consequential factor. Microscope Light Intensity | The microscope light has the potential to heat up the liquid in the Petri dish and temperature can be a changing factor of the daphnia’s heart rate (see above). | 4. Ethics Daphnia have been used in this experiment as they have suitable characteristics that make them simple to examine in an ethical way. Daphnia are invertebrates which means no consent is needed for heart rate experiments; they have been used in testing other drugs such as pain killers and aspirin. Because they are invertebrates, they are ideal to examine because their bodies are a lot less complex than that of a mammal.
They have a simple internal structure made up of antennae, eyes, abdominal organs, a heart and limbs. A daphnia under a microscope. The heart can be seen above the cluster of eggs on the left. A daphnia under a microscope. The heart can be seen above the cluster of eggs on the left. The process of observing the daphnia’s heart rate is not invasive as it’s body is transparent meaning we are able to monitor the heart rate without making any incisions. Also, the experiment is made quicker by recording the heart rate for just 20 seconds at a time so that daphnia can be placed back in their natural habitat as promptly as possible. . Results The following table shows the results of the experiment – four records of the daphnia’s heart rate in water and four records of the daphnia’s heart rate in caffeine solution. The average heart rate in each is shown in red. Water| Caffeine Solution| 210| 255| 219| 246| 276| 234| 252| 225| 239| 240| The following graph plots the average heart rate of the daphnia in water and caffeine solution. The error bars display the range of the recorded heart rates. 6. Precision, Reliability and Validity The experiment was designed to produce reliable results to some extent.
For example: * Controlled variables were put in place so that the daphnia’s heart rate could not be effected by any other factor than caffeine content and; * Four heart rates were recorded in both water and caffeine solution so that an average could be produced. However, the experiment could have been conducted in further detail to produce a more accurate set of results. Firstly, the fact that only one daphnia was tested in the experiment minimizes the results accuracy greatly. If the experiment had been carried out on more daphnia, an average of averages could have been calculated for in water and in caffeine solution.
Also, only four heart rates (BPM) were recorded for each liquid, which were used to produce an average. Four records to produce an average is probably insufficient; a reasonable amount to produce an average is about ten records. Another factor that may decrease the validity of the results is that the heart rate was only counted for 20 seconds at a time and then multiplied by 3 to calculate beats per minute. This was done for ethical reasons – so that the daphnia could be placed back in it’s natural habitat as quickly as possible.
This could have devaluated the results slightly as the heart rate may have varied more in a whole minute compared to in just 20 seconds. For a more reliable set of results, multiple daphnia could be tested in the same way but with additional heart rate records so that the average would be more precise and an average of averages could be produced. Also, the heart rates should be counted for a minimum of 30 seconds for a more accurate beats per minute calculation. 7. Conclusions Conclusively, the averages of the heart rates of the daphnia show that the heart rate was in fact 1 BPM faster when the daphnia was placed in the caffeine solution.
The bar graph shows that the heart rate of the daphnia in the water ranges between 210 and 276 and the heart rate of the daphnia in the caffeine solution ranges between 225 and 255. The error bars show that the heart rates in water had a much wider result scale than that of the heart rates in caffeine solution. One significant point to mention is that the highest heart rate value in the results is from when the daphnia was placed in water, not in the caffeine. One possible reason for this could be that the change in water temperature from the beaker to the new water in the Petri dish could have affected the daphnia’s heart rate.
Although the results have shown that the hypothesis was correct, the results do not show such a significant range that could be used to prove that caffeine does increase heart rate as the heart rate only went up by approximately 0. 4%. Although the close averages could just be a result of an insufficient amount of records, I still believe that for better evidence that caffeine does increase heart rate; the experiment should be carried out in further detail – with more daphnia and a minimum of ten heart rate recordings per liquid.