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An experiment to see if caffeine affects heart rate

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An experiment to see if caffeine affects heart rate Hypothesis To test if caffeine affects the heart of daphnia Prediction I think that the higher the concentration of the caffeine solution the faster the heart rate will be. Caffeine is also known as trimerhylaxanthine and the chemical formula is C8H10N4O2. The caffeine will be absorbed into the blood where it travels into the brain. The caffeine molecule is the same size as the adenosine. Adenosine is a chemical in the blood that attaches to the nerve cells and slows it down therefore making a person tired. As caffeine is the same shape as adenosine the caffeine molecules attach to the nerve cell instead meaning, the adenosine molecule cannot get into the nerve cell. As the caffeine is a stimulant it then stimulates the nerve cell and this makes a person feel more awake and speeding up the heart rate. Caffeine also stimulates the pituitary gland to release cortiocostreiods, which then travel to the adrenal gland triggering the release of adrenaline. Adrenaline is a hormone, which helps to stimulate the body therefore making the heart beat faster. Variables The independent variable is the variable that we change. In this experiment the thing we are measuring in the concentration of caffeine that the daphnia is put into. The dependent variable is the variable in the experiment that we measure. In this experiment it is the heart rate of the daphnia. ...read more.


Once the daphnia have been used in the experiment it needs to be considered what will happen to them after this. It is best to place the, back into their natural environment, so they adjust back to this, but this may again cause them more stress as they are being moved from one place to another. Concentration The 0.5% of caffeine must be made up to do this the following equation is used: Volume of stock solution to be diluted = Final volume of diluted solution x concentration of diluted solution Concentration of stock solution 10cm3 = 10cm3 x 0.5 molar 0.5% 8cm3 = 10cm3 x 0.4 molar 0.5% 6cm3 = 10cm3 x 0.3 molar 0.5% 4cm3 = 10cm3 x 0.2 molar 0.5% 2cm3 = 10cm3 x 0.1 molar 0.5% 0cm3 = 10cm3 x 0.0 molar 0.5 Apparatus: * Culture of daphnia * Cavity slides * Dropping pipettes * Distilled water * 05% solution of caffeine * Cotton wool * Measuring cylinder * 7 beakers * Stopclock * Filter paper * Microscope * Pen * Paper Method: * Make up the caffeine solutions and place in beakers. Label each beaker * Get a daphnia out of the pond culture with a pipette * Place daphnia on a cavity slide and place under a microscope. This is a control * If the daphnia move to much use cotton wool to restrict their movement * Start stop clock * Record heart beat every 2 minutes for 15 seconds * Do this for 6 minutes * To ...read more.


The daphnia were also moving around in the cavity slide this also meant that the heart rate was difficult to record; we had to restrict the daphnia's movement so we could see them under the microscope, by using cotton wool, but this soaked up all the solution out of the cavity slide and may have caused discomfort for the daphnia raising ethical issues. All the daphnia had very different heart rates even when in the control solution, if I were to do this experiment again I would use daphnia which had similar heart rates when in the control, so the results when added to caffeine could have been seem a lot easier. The experiment also needed to be repeated more three times, because if there were a problem with one the daphnia's heart, for example it was stressed and this increased the heart rate it would be impossible to tell which daphnia had a unreliable heart rate if we were to do only two experiments. Doing three or more experiments means that if one of the sets of results were invalid it means we can easily see this and analyse the results on the other two sets of results. Evaluation If I were to repeat this experiment I would use daphnia with the same speed heart beat for each test as there are many varying degrees of heart beat even when in the control. Looking at the results the daphnia with the fastest heart rate in the control all seemed to be placed in the lower concentration of caffeine. This meant our results look as though caffeine slows down the heart rate. ...read more.

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