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Experiment to find out how the concentration of caffeine will affect the heart rate of water daphnia.

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As level Biology Experimenting the effects of caffeine on water daphnia Alex Jones Experiment to find out how the concentration of caffeine will affect the heart rate of water daphnia. Hypothesis/prediction I predict that when the water daphnia are given caffeine the higher the concentration the faster the daphnia's heart beat will be. I think this because caffeine is a stimulant that affects your heart rate keeping you awake and making you more alert. I will be counting the daphnia's heartbeat to see if the caffeine has any effect. Information on water daphnia Water daphnia are more commonly known as water fleas or water flies and you can buy them at most local pet shops or fishing shops as they are used to feed goldfish because they eat algae and take in all the nutrients and so are full of them. The chief characteristic of the water fleas is that the main part of the body is enclosed in a kind of shell, with the appearance of two lids, but made of one piece. They are interesting animals for the microscopist. Because you can see through them, you can study for instance the beating of the heart and follow the course of the blood cells round part of the body. Their sizes differ from several hundred microns to more than five millimetres for the larger species. The common water flea, Daphnia pulex can be found in almost all sorts of eutrophic (rich in nutrients) ...read more.


When I did the experiment I did a number of things to keep the water daphnia alive: - * I placed ice under the slide to help keep him cool * I started with the least amount of caffeine first so that he could slowly get used to the caffeine * I tried to use as little as possible of the stronger solutions of caffeine so he wouldn't have a heart attack. * Tried to make the experiment as quick as possible. The experiment I performed needed live specimens otherwise it would not have been possible to measure the effects of caffeine on the heart. So it was necessary to use the water daphnia in this experiment. Producing Reliable and Valid Results The results I produced are very valid, but are not accurate. They aren't very accurate because of the method we used to collect the results. The method of tapping a pencil and someone counting them wasn't very accurate because: - * When the daphnia's heartbeat got really fast you couldn't keep time with the rapid heartbeat. * If you lost count while trying to count the heartbeat and still carried on counting the beats per minute wouldn't be right. Variables There are two main variables for this experiment; the independent variable and the dependant variable. The Independent variable This variable is the concentration of caffeine, which is given to the daphnia. ...read more.


This is because it goes up gradually and you can see it easily. On a pie cart you wouldn't be able to see the patterns because it is in sections and so you can only see the most popular or highest heartbeat. For the axis I have to decided to put the independent and dependant variables because that is what we have been looking at. The two variables are the most important ones so they need to be on the graph somewhere so that I can recognise that they are important. Conclusions Through the results I have collected I can conclude that the more caffeine you give the water daphnia the higher their heart rate will accelerate. I can tell this through the results in the graph. As you go along the concentration of caffeine axis the higher the heart rate goes up. So this is a continuous graph because when you continue along one axis the other axis continues with it. If I were to have any doubts about the results, they would be: - * Me or my partner not counting the daphnia's heart beat properly * Counting over a minute accidentally or under a minute accidentally- incorrect timing. I couldn't put a line of best fit onto my graph. I think this is because we took an average so you can't get results all in line because you have done 3 separate experiments and the different daphnia's heart beats will be at different starting rates and will be effected differently by the caffeine. ...read more.

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