Effect of Caffeine on the Heart Rate of Daphnia

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1. Objective

  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,  , between 0.2 and 5 mm in length. Daphnia are members of the  , and are one of the several small aquatic crustaceans.

                   In most species, the body is covered by a  ( section of the  or shell) and has five or six pairs of legs. The most prominent features are the  and the second . 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  and various sorts of  ,  and yeast. They live in various aquatic environments ranging from   to  lakes, ponds, streams and rivers.

                     Daphnia reproduce  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  using a specialised abdominal , 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 while some organisms live for only 29 days at 28°C. Also, Daphnia has been proven to be very sensitive to poor water conditions. As such, Daphnia may be used to test the effects of  on an . Thus, a number of research and industrial groups use Daphnia to test water quality. In addition to that, Daphnia are also a popular live food for tropical and marine fish keeping.

                    In this experiment, Daphnia is used because they are prone to caffeine intoxication. Small amounts of chemicals will have dramatic effects on them. Thus, they are chosen as subjects for studying the effects of the stimulant on the .  Also, in many species of Daphnia, the carapace is translucent. Thus, they make excellent subjects for the  as the beating heart can be observed. Moreover, they are tolerant of being observed live under a cover slip and appear to suffer no harm when returned to open water. Last but not least, they are inexpensive and are fairly easy to keep.

                   On the other hand, caffeine is a bitter white crystalline  that acts as a   . It is also a mild  which speeds up urine production in humans and other animals. In humans, caffeine is a  (CNS) , which temporarily reduces  and restores alertness. The precise amount of caffeine necessary to produce effects varies from person to person depending on body size and degree of tolerance to caffeine.

                       Caffeine is found in varying quantities in the , , and  of some plants. The world's primary source of caffeine is the coffee "bean" (which is actually the seed of the ), from which  is brewed. It acts as a natural  that  and kills certain  feeding on the plants.  is another common source of caffeine. Although tea contains more caffeine than coffee, a typical serving contains much less, as tea is normally brewed much weaker.

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                     Caffeine can be absorbed rapidly into the bloodstream from the gastro-intestinal tract. It reaches maximum concentration within an hour. The blood distributes it throughout the body. One effect of caffeine is to interfere with adenosine at multiple sites in the brain. Caffeine also acts at other sites in the body to increase heart rate, constrict blood vessels, relax air passages to improve breathing and allow some muscles to contract more easily. Caffeine is also an addictive substance and is associated with many withdrawal symptoms. Typical withdrawal symptoms include headache, fatigue ...

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