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Effect of Caffeine on the Heart Rate of Daphnia

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1. Objective 1.1 Introduction Daphnia are fresh water animals, commonly called 'water fleas' because of the manner by which they swim - a sort of hopping or jigging in the water, a movement brought about by their swimming appendages. Daphnia are small, planktonic crustaceans, between 0.2 and 5 mm in length. Daphnia are members of the order Cladocera, and are one of the several small aquatic crustaceans. In most species, the body is covered by a carapace (dorsal section of the exoskeleton or shell) and has five or six pairs of legs. The most prominent features are the compound eyes and the second antennae. The heart is situated just behind the head, and the average heart rate is approximately 180 beats per minute under normal conditions. Most daphnia are filter feeders, ingesting mainly unicellular algae and various sorts of protists , bacteria and yeast. They live in various aquatic environments ranging from acidic swamps to freshwater lakes, ponds, streams and rivers. Daphnia reproduce parthenogenetically usually in the spring until the end of the summer. In harsh environmental conditions, production of new female generations stops and parthenogenic males are produced. Males are much smaller in size than the female. During mating, a male grasps a female from behind and prises open her carapace using a specialised abdominal appendage, and thus fertilises the eggs. Sexual reproduction allows greater offspring variation through genetic recombination. The lifespan of a Daphnia does not exceed one year and is largely dependent on temperature. For example, individual organisms can live up to 108 days at 3�C while some organisms live for only 29 days at 28�C. Also, Daphnia has been proven to be very sensitive to poor water conditions. ...read more.


3. The Daphnia is observed using low power magnification (40x). 4. The heart is identified and the heart beat is counted for 15 seconds. The values are multiplied by 4 to obtain the number of heart beats per minute. 5. Step 3 is repeated to obtain another reading. 6. The Daphnia is then removed and placed into a Petri dish filled with pond water. It is left to swim in the pond water for about one minute. 7. One drop of 0.1% caffeine solution is added into the cavity of the slide. The Daphnia is then placed onto the slide lined with muslin cloth. 8. The heart is identified and the heart beat is counted for 15 seconds. The values are multiplied by 4 to obtain the number of heart beats per minute. 9. The measurement is repeated to obtain another reading. 10. The experiment is repeated using 0.2%, 0.3%, 0.4% and 0.5% caffeine solution. 11. The results obtained are recorded. A graph of heart rate against concentration of caffeine solution is drawn to illustrate the relationship between the concentration of caffeine solution and heart rate of Daphnia. 7. Precautions: * The same volume of caffeine solution is used throughout the experiment. * Other factors affecting the heart rate such as the temperature of the solution is kept constant throughout the experiment. * The same Daphnia is used throughout the experiment to minimise errors. * The Daphnia is a very delicate creature. It should be handled with extra care. * Muslin cloth is used to ensure that the Daphnia remains in position in the cavity of the slide. * Excess water on the cavity slide is absorbed using paper towels. ...read more.


There are some organisations that oppose the use of animals in such experiments. This is based on a range of arguments; that it is cruel, poor scientific practice, cannot reliably predict effects in humans, poorly regulated, that the costs outweigh the benefits, or that animals have an intrinsic right not to be used for experimentation. Also, if every biology student uses the Daphnia for this experiment, the population of Daphnia in that particular area would decrease drastically and may cause a major disruption in the food chain of the aquatic habitat. This is only if all the Daphnia are euthanized after the experiment. Thus, the solution to this problem would be to avoid killing these animals and to return all the Daphnia to its original habitat. 10.5 Further investigations 1. This experiment can also be done using nicotine or adrenaline to replace caffeine and observing the effects on the heart rate of Daphnia. 2. Apart from stimulants, a depressant such as alcohol can also be used to replace caffeine in this experiment. Daphnia are prone to alcohol intoxication and make excellent subjects for studying the effects of the depressant on the nervous system. 3. The effect of temperature on heart rate in Daphnia can also be investigated. To carry out the experiment, identical culture solutions at temperatures of 5, 10, 15, 20, 25 and 30 degrees Celsius are used. The Daphnia is then placed into these cultures in turn, allowing 5 minutes to elapse before taking a new heart rate determination. Similarly, a graph of heart rate of Daphnia against temperature can be plotted. 11. Conclusion: - The higher the caffeine concentration, the higher the heart rate of Daphnia. Sources: Books 1. Title: Edexcel Biology for AS Author: C.J.Clegg Publisher: Hodder Education, 2008 Website 1. www.neiljohan.com/projects/biology/enzymes.htm 2. http://en.wikipedia.org/wiki/Caffeine 3. http://www.sciencebuddies.org/mentoring/project_ideas/Pharm_p009.shtml 4. http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/wimsmall/crust.html 5. http://en.wikipedia.org/wiki/Daphnia 6. http://en.wikipedia.org/wiki/Animaltesting ?? ?? ?? ?? ...read more.

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